JP2008259228A - A/d converting method and a/d converting apparatus, and semiconductor device and electronic instrument for physical quantity distribution detection - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To keep continuity of count values when switching count modes in an asynchronous counter circuit capable of switching count modes. <P>SOLUTION: In an A/D converting method, between flip-flops 410, three-input and one-output type three-value switching sections 420 (422, 424, 426) are provided, each of which switches three values of non-inverted output Q, inverted output NQ and power supply (Vdd) level of each flip-flop 410. The three-value switching section 420 switches three input signals in accordance with two-bit control signals SW1, SW2 and inputs one selected signal to a clock terminal CK of the post-state flip-flop 410. In accordance with the control signals SW1, SW2, when switching count mode, a count value just before mode switching is initially set and then count processing after mode switching can be started. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an AD (analog-digital) conversion method and AD converter for converting an analog signal into digital data, and a semiconductor device and electronic apparatus for physical quantity distribution detection in which a plurality of unit components are arranged.

  More specifically, for example, a plurality of unit components that are sensitive to electromagnetic waves input from the outside such as light and radiation are arranged, and the physical quantity distribution converted into an electric signal by the unit components is addressed. The present invention relates to an AD conversion process suitable for use in a semiconductor device for physical quantity distribution detection such as a solid-state imaging device and other electronic devices, which can be arbitrarily selected by control and read out as an electric signal.

  2. Description of the Related Art Physical quantity distribution detection semiconductor devices in which a plurality of unit components (for example, pixels) that are sensitive to electromagnetic waves input from the outside such as light and radiation are arranged in a line or matrix form are used in various fields. ing.

  For example, in the field of video equipment, CCD (Charge Coupled Device) type, MOS (Metal Oxide Semiconductor) type or CMOS (Complementary Metal-oxide Semiconductor) type solid-state imaging devices that detect light (an example of electromagnetic waves) in physical quantities are used. It is used. These read out, as an electrical signal, a physical quantity distribution converted into an electrical signal by a unit component (a pixel in a solid-state imaging device).

  Further, in some solid-state imaging devices, an amplifying solid-state imaging device (APS; Active Pixel Sensor) that has a driving transistor for amplification in a pixel signal generation unit that generates a pixel signal corresponding to the signal charge generated in the charge generation unit. There is an amplification type solid-state imaging device including a pixel having a configuration (also called a gain cell). For example, many CMOS solid-state imaging devices have such a configuration.

  In such an amplification type solid-state imaging device, in order to read out a pixel signal to the outside, address control is performed on a pixel unit in which a plurality of unit pixels are arranged, and signals from individual unit pixels are arbitrarily selected. I am trying to read it out. That is, the amplification type solid-state imaging device is an example of an address control type solid-state imaging device.

  For example, an amplification type solid-state imaging device which is a kind of XY address type solid-state imaging device in which unit pixels are arranged in a matrix form an active element (MOS transistor) such as a MOS structure in order to give the pixel itself an amplification function. ) To form a pixel. That is, signal charges (photoelectrons) accumulated in a photodiode which is a photoelectric conversion element are amplified by the active element and read out as image information.

  In this type of XY address type solid-state imaging device, for example, a plurality of pixel transistors are arranged in a two-dimensional matrix to form a pixel unit, and a signal charge corresponding to incident light for each line (row) or each pixel. Accumulation is started, and a current or voltage signal based on the accumulated signal charge is sequentially read out from each pixel by addressing. Here, in the MOS (including CMOS) type, as an example of address control, a system in which one row is accessed simultaneously and a pixel signal is read from the pixel unit in units of rows is often used.

  The analog pixel signal read from the pixel unit is converted into digital data by an analog-digital converter (AD converter; Analog Digital Converter) as necessary. Here, since the pixel signal is output in a form in which the signal component is added to the reset component, a true effective signal can be obtained by taking the difference between the signal voltage corresponding to the reset component and the signal voltage corresponding to the signal component. It is necessary to take out the ingredients.

  The same applies to the case where an analog pixel signal is converted into digital data. Finally, the difference signal component between the signal voltage corresponding to the reset component and the signal voltage corresponding to the signal component needs to be converted to digital data. For this reason, various AD conversion mechanisms have been proposed (see, for example, Non-Patent Documents 1 to 5 and Patent Document 1).

W. Yang et. Al., “An Integrated 800x600 CMOS ImageSystem,” ISSCC Digest of Technical Papers, pp. 304-305, Feb., 1999) Kazuya Yonemoto, “Basics and Applications of CCD / CMOS Image Sensors”, CQ Publisher, August 10, 2003, first edition, p201-203 Toshifumi Imamura and Miko Yamamoto, “3. Research on high-speed and functional CMOS image sensors”, [online], [March 15, 2004 search], Internet <URL: http://www.sankaken.gr.jp/ project / iwataPJ / report / h12 / h12index.html> Toshifumi Imamura, Miko Yamamoto, Naoya Hasegawa, “3. Research on high-speed and functional CMOS image sensors”, [online], [Search on March 15, 2004], Internet <URL: http://www.sankaken.gr .jp / project / iwataPJ / report / h14 / h14index.html> Oh-Bong Kwon et. Al., “A Novel Double Slope Analog-to-Digital Converter for a High-Quality 640x480 CMOS Imaging System”, VL3-03 1999 IEEE p335-338 Japanese Patent Laid-Open No. 11-331883

  Here, the AD conversion mechanism described in Non-Patent Documents 1 to 5 and Patent Document 1 performs AD conversion processing using a counter circuit, and the counter circuit used here is usually a counter clock. A synchronous counter that obtains a count value at the output of the flip-flop (basic element of the counter) is used in synchronization with.

  However, in the case of a synchronous counter, since the operation of all flip-flops is limited by the count clock, there is a problem when a higher frequency operation is required.

  On the other hand, as a counter circuit, it is conceivable to use an asynchronous counter as in Non-Patent Documents 4 and 5. The asynchronous counter is suitable for high-speed operation because its operation limiting frequency is determined only by the limiting frequency of the first flip-flop. Therefore, when higher frequency operation is required, it is preferable to use an asynchronous counter as the counter circuit.

  For example, FIG. 18 is a diagram illustrating a conventional example of an asynchronous counter capable of mode switching. The counter circuit 900 can constitute a 4-bit asynchronous counter. For example, in the counter circuit 900, a plurality of negative edge type and D type flip-flops 912, 914, 916, and 918 (collectively referred to as 910) are cascade-connected. Each flip-flop 910 receives an inverted output NQ (indicated by a horizontal bar “-” above Q in the figure) input to its D input terminal. The count clock CK0 is input to the clock terminal CK of the first flip-flop 910.

  In addition, the counter circuit 900 is a two-input / one-output type switch 922, 924, 926 (collectively 920) that switches between two values of the non-inverted output Q and the inverted output NQ of each flip-flop 910 between the flip-flops 910. Say). Each switch 920 switches between two input signals in accordance with a control signal SW from a control unit (not shown), and inputs the selected one signal to the clock terminal CK of the subsequent flip-flop 910.

  The control signal SW is for switching the counting operation of the counter circuit 900 to either up-counting or down-counting, and selects and outputs the non-inverted output Q when the control signal SW is at a high (H) level. Thus, the counter circuit 900 enters the up-count mode. On the other hand, when the control signal SW is at the low (L) level, the counter circuit 900 enters the down-count mode by selecting and outputting the inverted output NQ.

  However, since the conventional asynchronous counter as shown in FIG. 18 uses the up / down counter in common regardless of the operation mode and switches the processing mode to perform the counting process, the circuit can be made compact. However, for example, after counting up to a predetermined value and then counting down from this value, the continuity of the count value is not maintained at the time of switching the count mode, and it is not suitable for applications in which a continuous count operation is performed while switching the count mode. There is a problem (called the first problem). Hereinafter, this point will be described.

  FIG. 19 is a timing chart for explaining the operation of the counter circuit 900 shown in FIG.

  In this example, a non-inverted output Q and an inverted output NQ are switched by a control signal SW by a 4-bit asynchronous counter, and then up-counting and then down-counting. However, when switching from up-counting to down-counting, the count value changes from 6 to 10, and a continuous pulse train with a high frequency is continuously counted while maintaining the count value before and after switching the count mode. Cannot up and down.

  One method for solving such a problem has been proposed in Patent Document 2, for example. As shown in FIG. 20, the mechanism described in Patent Document 2 includes means for inverting the state of each flip-flop and means for initializing all flip-flops for each even number of pulse trains. .

JP-A-6-216762

  The counting method in the mechanism described in Patent Document 2 is as follows. Assume that the asynchronous counter can count up to a maximum number n, the first pulse train contains i pulses, and the second pulse train contains j pulses.

  The counter is reset in advance and counts from 0 to i during the first pulse train. The state of the flip-flop of the counter is then inverted, thereby obtaining a complement relationship of the value i to n, and this counter having the value n-1.

  During the second pulse train, the counter counts from ni to ni-j. Since the desired difference is i−j, it is the complement of n−i + j obtained by reinverting the state of the flip-flop with respect to n. As a result, an asynchronous counter structure for counting up and counting down high-frequency continuous pulse trains can be realized.

  However, the mechanism described in Patent Document 2 has a disadvantage that is not straightforward because the up / down count is calculated by a calculation including a complement (referred to as a second problem).

  In addition, the AD conversion mechanism described in Non-Patent Documents 1 to 5 and Patent Document 1 includes the circuit scale, the circuit area, the power consumption, the number of interface wirings with other functional units, and the noise and noise caused by these wirings. There are difficulties in terms of current consumption. Hereinafter, this point will also be described.

<Configuration of conventional solid-state imaging device>
FIG. 21 is a schematic configuration diagram of a conventional CMOS solid-state imaging device (CMOS image sensor) in which an AD conversion device is mounted on the same semiconductor substrate as a pixel portion. As shown in FIG. 21, the solid-state imaging device 1 includes a pixel unit (imaging unit) 10 in which a plurality of unit pixels 3 are arranged in rows and columns, and a drive control unit 7 provided outside the pixel unit 10. , A counter unit (CNT) 24, a column processing unit 26 having a column AD circuit 25 arranged for each vertical column, and a DAC (Digital) for supplying a reference voltage for AD conversion to the column AD circuit 25 of the column processing unit 26 A reference signal generation unit 27 configured to include an analog converter, and an output circuit configured to include a subtraction circuit 29.

  The drive controller 7 includes a horizontal scanning circuit (column scanning circuit) 12 that controls column addresses and column scanning, a vertical scanning circuit (row scanning circuit) 14 that controls row addresses and row scanning, and a master via a terminal 5a. It includes a timing control unit 21 that receives the clock CLK0, generates various internal clocks, and controls the horizontal scanning circuit 12, the vertical scanning circuit 14, and the like.

  Each unit pixel 3 is connected to a row control line 15 controlled by the vertical scanning circuit 14 and a vertical signal line 19 that transmits a pixel signal to the column processing unit 26.

  The column AD circuit 25 passes through the reference signal RAMP generated by the reference signal generator 27 and the vertical signal line 19 (V0, V1,...) From the unit pixel 3 for each row control line 15 (H0, H1,...). The voltage comparison unit 252 that compares the obtained analog pixel signal, and data as a memory device that holds the result of counting the time until the voltage comparison unit 252 completes the comparison process using the counter unit 24 And a storage unit (latch) 255, and has an n-bit AD conversion function. The data storage unit 255 includes an n-bit latch 1 and a latch 2 as independent storage areas.

  One input terminal RAMP of the voltage comparison unit 252 receives the step-like reference signal RAMP generated by the reference signal generation unit 27 in common with the input terminal RAMP of the other voltage comparison unit 252, and inputs to the other input terminal. Are connected to the vertical signal lines 19 of the corresponding vertical columns, and the pixel signal voltages from the pixel unit 10 are individually inputted. The output signal of the voltage comparison unit 252 is supplied to the data storage unit 255. The reference signal RAMP counts based on a count clock CK0 (for example, both clock frequencies are equal) corresponding to the master clock CLK0 supplied from the outside to the solid-state imaging device 1, and converts the count value into an analog signal. Generate digitally.

  The counter unit 24 performs a count process based on a count clock CK0 (for example, both clock frequencies are equal) corresponding to the master clock CLK0, and outputs the count outputs CK1, CK2,... CKn together with the count clock CK0 to the column processing unit 26. Are commonly supplied to the column AD circuits 25.

  That is, the column AD circuit 25 of each vertical column can be arranged by routing the wiring of the count outputs CK1, CK2,..., CKn from the counter unit 24 to each latch of the data storage unit 255 arranged for each vertical column. One counter unit 24 is used in common.

  The output side of each column AD circuit 25 is connected to the horizontal signal line 18. The horizontal signal line 18 has a signal line having a width of 2n bits, and is connected to the subtraction circuit 29 of the output circuit 28 via 2n sense circuits corresponding to the respective output lines (not shown).

  The timing control unit 21 instructs the horizontal scanning circuit 12 to read out pixel data via the control line 12c. In response to this, the horizontal scanning circuit 12 sequentially shifts the horizontal selection signal CH (i) to sequentially send the pixel data held in the latches 1 and 2 to the subtraction circuit 29 of the output circuit 28. That is, readout scanning in the horizontal (row) direction is performed.

  Here, the horizontal scanning circuit 12 receives a horizontal selection signal CH (i) for performing readout scanning in the horizontal (row) direction, similarly to the count clock CK0, a master clock CLK0 supplied to the solid-state imaging device 1 from the outside. Generate based on

  FIG. 22 is a timing chart for explaining the operation of the conventional solid-state imaging device 1 shown in FIG.

  For example, for the first reading, the count value of the counter unit 254 is first reset to the initial value “0”. Then, after the first reading from the unit pixel 3 in an arbitrary row Hx to the vertical signal lines 19 (V0, V1,...) Is stabilized, the reference signal generation unit 27 makes a substantially sawtooth (ramp; RAMP) shape. A reference signal RAMP that is time-changed in a stepwise manner is input to the voltage comparison unit 252 for comparison with a pixel signal voltage of an arbitrary vertical signal line 19 (column number Vx).

  At this time, in order to measure the comparison time in the voltage comparison unit 252 using the counter unit 24 simultaneously with the input of the reference signal RAMP to one input terminal RAMP of the voltage comparison unit 252, the reference signal generation unit 27 In synchronization with the generated ramp waveform voltage (t10), the counter unit 24 starts down-counting from the initial value “0” as the first count operation.

  The voltage comparison unit 252 compares the ramp-shaped reference signal RAMP from the reference signal generation unit 27 with the pixel signal voltage Vx input via the vertical signal line 19, and when both voltages become the same, The comparator output is inverted from H level to L level (t12).

  In response to this result, the data storage unit 255 synchronizes the count outputs CK1, CK2,..., CKn from the counter unit 24 corresponding to the comparison period in synchronization with the count clock CK0 almost simultaneously with the inversion of the comparator output. The first AD conversion is completed by latching (holding and storing) in the latch 1 of 255 (t12).

  The timing control unit 21 stops supplying the control data to the voltage comparison unit 252 and the supply of the count clock CK0 to the counter unit 254 when a predetermined down-count period has elapsed (t14). As a result, the voltage comparison unit 252 stops generating the ramp-shaped reference signal RAMP.

  At the time of the first reading, the reset component ΔV of the unit pixel 3 is read, and noise that varies for each unit pixel 3 is included as an offset in the reset component ΔV. However, since the variation of the reset component ΔV is generally small and the reset level is common to all pixels, the output of an arbitrary vertical signal line 19 (Vx) is approximately known.

  Therefore, when the reset component ΔV is read for the first time, the comparison period can be shortened by adjusting the reference signal RAMP. In this conventional example, the reset component ΔV is obtained in a count period (128 clocks) of 7 bits. Comparison of

  In the second reading, in addition to the reset component ΔV, the signal component Vsig corresponding to the amount of incident light for each unit pixel 3 is read, and the same operation as the first reading is performed.

  That is, for the second reading, first, the count value of the counter unit 254 is reset to the initial value “0”. Then, after the second reading from the unit pixel 3 of the arbitrary row Hx to the vertical signal lines 19 (V0, V1,...) Is stabilized, the reference signal generator 27 performs a time stepwise so as to be substantially ramp-shaped. The changed reference signal RAMP is input, and the voltage comparison unit 252 performs comparison with the pixel signal voltage of an arbitrary vertical signal line 19 (column number Vx).

  At this time, in order to measure the comparison time in the voltage comparison unit 252 using the counter unit 24 simultaneously with the input of the reference signal RAMP to one input terminal RAMP of the voltage comparison unit 252, the reference signal generation unit 27 In synchronization with the generated ramp waveform voltage (t20), the counter unit 24 starts down-counting from the initial value “0” as the second counting operation.

  The voltage comparison unit 252 compares the ramp-shaped reference signal RAMP from the reference signal generation unit 27 with the pixel signal voltage Vx input via the vertical signal line 19, and when both voltages become the same, The comparator output is inverted from H level to L level (t22).

  In response to this result, the data storage unit 255 synchronizes the count outputs CK1, CK2,..., CKn from the counter unit 24 corresponding to the comparison period in synchronization with the count clock CK0 almost simultaneously with the inversion of the comparator output. The second AD conversion is completed by latching (holding / storing) to 255 (t22).

  At this time, the data storage unit 255 holds the first count value and the second count value in different locations in the data storage unit 255, specifically, in the latch 2. At the time of the second reading, the combined amount of the reset component ΔV and the signal component Vsig of the unit pixel 3 is read.

  The timing control unit 21 stops supplying control data to the voltage comparison unit 252 and supply of the count clock CK0 to the counter unit 254 when a predetermined down-count period has elapsed (t24). As a result, the voltage comparison unit 252 stops generating the ramp-shaped reference signal RAMP.

  At a predetermined timing after the second count process is completed (t28), the timing control unit 21 instructs the horizontal scanning circuit 12 to read out pixel data. In response to this, the horizontal scanning circuit 12 sequentially shifts the horizontal selection signal CH (i) supplied to the data storage unit 255 via the control line 12c.

  In this way, the count value stored and held in the data storage unit 255, that is, the first and second n-bit pixel data represented by n-bit digital data, respectively, is n (total of 2n). The signals are sequentially swept out of the column processing unit 26 via the horizontal signal line 18 and input to the subtraction circuit 29 of the output circuit 28.

  The n-bit subtracting circuit 29 corresponds to the pixel position corresponding to the first pixel data indicating the reset component ΔV of the unit pixel 3 from the second pixel data indicating the composite of the reset component ΔV and the signal component Vsig of the unit pixel 3. By subtracting every time, the signal component Vsig of the unit pixel 3 is obtained.

  Thereafter, the same operation is sequentially repeated for each row, whereby an image signal representing a two-dimensional image is obtained in the output circuit 28.

  However, in the configuration shown in FIG. 21, the column AD circuit 25 in each vertical column uses one counter unit 24 in common, and the first and second counts are stored in the data storage unit 255 as a memory device. It is necessary to hold the result, and for an n-bit signal, two sets of n-bit latches (2n latches for each bit) are required, which increases the circuit area (referred to as a third problem).

  Further, wiring for inputting the count clock CK0 and the n count outputs CK1, CK2,..., CKn from the counter unit 24 to the data storage unit 255 is necessary, and there is a concern about an increase in noise and an increase in power consumption ( This is called the fourth problem).

  Furthermore, in order to hold the first count value and the second count value at different locations in the data storage unit 255, 2n for transmitting the first and second count results to the data storage unit 255. Signal lines are required, and the accompanying increase in current occurs (referred to as the fifth problem).

  In addition, before external output, in order to subtract the first count value and the second count value in the output circuit 28, 2n leads each count value to the n-bit subtraction circuit 29 provided in the output circuit 28. Therefore, there is a concern about noise for data transfer and an increase in power consumption (referred to as a sixth problem).

  That is, a memory device that holds the first read result and a memory device that holds the second read result must be prepared separately (that is, prepared for two systems) separately from the counter unit. A signal line for transmitting the n-bit count value from the counter unit is required, and 2n bits (ie, twice) of n bits are transferred to transfer the first and second count values to the subtractor. A signal line is required, which increases the circuit scale and circuit area, and causes problems of increased noise, increased current consumption and power consumption.

  In order to perform a pipeline operation in which AD conversion processing and reading processing are performed in parallel, a memory device that holds AD converted data is required separately from a memory device that holds a count result. Similarly to the third problem, since two memory devices are required for this purpose, the circuit area increases (referred to as the seventh problem).

  As a technique for solving the third problem, for example, a counter unit commonly used for vertical columns, a CDS (Correlated Double Sampling) processing function unit for each vertical column, and a counter unit are provided. A column AD conversion circuit that realizes a CDS processing function and an AD conversion function by arranging a latch that holds a count value in series has been proposed (see, for example, Non-Patent Document 2).

  As a technique for solving the second problem, for example, a mechanism for realizing an AD conversion function by providing a counter unit for each vertical column in the column processing unit 26 has been proposed (for example, Non-Patent Document 3, 4).

  The column AD conversion circuit described in Non-Patent Document 2 uses a counter unit that performs parallel processing for each vertical signal line (vertical column) and an AD conversion circuit that uses a latch to obtain a difference between a reset component and a signal component. Since it is converted into a digital signal while suppressing fixed pattern noise, a subtraction process is not required and only one count process is required. Further, a memory device that holds AD-converted data can be realized with a latch, which increases the circuit area. It can be prevented, that is, the third, fifth, sixth and seventh problems can be solved.

  However, a wiring for inputting the count clock CK0 and n count outputs from the counter unit to the latch is necessary, and the fourth problem cannot be solved.

  In addition, the mechanism described in Non-Patent Documents 3 and 4 outputs current from a plurality of pixels that detect light to the output bus at the same time, and performs addition / subtraction with current on the output bus. Is converted to a pulse width signal having a large size, and AD conversion is performed by counting the number of clocks of the pulse width of the pulse width signal by a counter circuit provided in parallel with the column. In other words, the fourth problem can be solved.

  However, the handling of the reset component and the signal component is not described, and the above third, fifth, sixth, and seventh problems are not necessarily solved. The non-patent documents 1 and 5 also have no description about the handling of the reset component and the signal component.

  On the other hand, Patent Document 1 describes the handling of reset components and signal components. In order to extract voltage data of only a pure image from the reset component and the signal component, such as correlated double sampling, a subtraction process for subtracting the digital data of the reset component from the digital data of the signal component is performed for each vertical column. Therefore, the sixth problem can be avoided.

  However, in the mechanism described in Patent Document 1, a count signal is generated in the external system interface unit to generate a count signal, and the count value at the time when the voltage of the reset component or signal component matches the reference voltage of the comparison processing Are stored in a set of buffers provided for each vertical column, and the AD conversion processing mechanism is configured such that each vertical column uses one counter in common. It is the same as that of description. Therefore, the third to fifth and seventh problems cannot be avoided.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a new mechanism capable of solving at least one of the third to seventh problems. More preferably, an object is to provide a new mechanism capable of solving the first and second problems.

  An AD conversion method according to the present invention is a method of converting a difference signal component between a reference component and a signal component in an analog processing target signal including a reference component and a signal component into digital data, Compares the signal corresponding to each component and the signal component with the reference signal for conversion to digital data, and performs the count process in either the down-count mode or the up-count mode in parallel with this comparison process. And the count value when the comparison process is completed is held. At this time, the count processing mode is switched depending on which of the reference component and the signal component is being compared.

  Here, as the counter circuit used for the count process, an asynchronous counter circuit configured to selectively operate the count process in the up-count mode and the count process in the down-count mode is used. More preferably, when the count mode is switched, an initial value setting processing unit is used that initializes the count value immediately before the mode switching and starts the count processing after the mode switching.

  As the configuration of the initial value setting processing unit, for example, in a counter circuit in which a plurality of flip-flops that are basic elements of the counter are arranged in cascade, either the non-inverted output or the inverted output of the preceding flip-flop is counted as a counter. A switching process for selecting the clock and supplying it to the clock terminal of the subsequent flip-flop, and for switching the count value immediately before the mode switching to the initial flip-flop. The section may be provided between flip-flops arranged in cascade.

  Alternatively, an asynchronous counter having a configuration capable of loading an arbitrary initial value is used, and the count terminal before the mode change is controlled by controlling the load terminal of the counter circuit before starting the count process after switching the count mode. The acquired count value immediately before the mode change may be set in the counter circuit as an initial value.

  In addition, as a mode switching process of the count process, as a first process, either one of a reference component and a signal component having different physical properties in one processing target signal output from the same unit element such as a pixel is used. And a reference signal for conversion to digital data are compared, and in parallel with this comparison process, the count process is performed in one of the down-count mode and the up-count mode. Holds the count value when the processing is completed.

  Thereafter, as the second processing, the reference signal is compared with the other of the reference component and the signal component, and the count processing is performed in the other mode of the down-count mode and the up-count mode in parallel with the comparison processing. And the count value at the time when the comparison process is completed is held. By doing so, the count value held after the second process becomes a difference from the first count value. That is, by performing the count process twice while switching the count mode, a digital value corresponding to the difference between the reference component and the signal component is obtained as the count value of the second count process.

  It should be noted that the signal component to be processed in the second processing only needs to indicate at least the true signal component in the processing target signal, and does not mean only the true signal component. May include a noise component, a reset component, and the like.

  In addition, the reference component and the signal component are relative, and the difference signal component between the reference component and the signal component is, in short, the physical property of one processing target signal output from the same unit element such as a pixel. Any difference component between two different signal components may be used.

  When comparing the reference component and the signal component, the signal corresponding to the reference component or the signal component is compared with the reference signal that changes at a predetermined slope, and the signal corresponding to the reference component or the signal component is referred to. It is better to look for a point where the signal matches. The predetermined gradient is not limited to a constant gradient, and the dynamic range may be expanded by setting a plurality of gradients stepwise so that the gradient increases as the signal component increases, for example. .

  In addition, when performing the counting process, a count clock is used to count (count) from the generation time of the reference signal used in the comparison process to the time when the signal corresponding to the reference component or the signal component matches the reference signal. It is preferable to obtain count values corresponding to the sizes of the reference component and the signal component.

  When performing count processing in the down count mode or the up count mode, it is preferable to switch the processing mode while using a common up / down counter. By doing so, the counter circuit used for the counting process can be made compact. In addition, by performing the counting process by switching between the two modes, the subtraction process between the reference component and the signal component can be performed directly, and a special subtractor for taking the difference between the reference component and the signal component is not necessary.

  The count process in the second process is preferably started from the count value held in the first process. For this purpose, when the count mode is switched, an initial value setting processing unit is provided which is configured to start the count process after the mode switching after initial setting of the count value immediately before the mode switching. It is preferable to use an asynchronous counter circuit. By doing so, the count value held after the second processing becomes a digital value of the difference between the reference component and the signal component itself.

  Here, if the comparison process and the count process are performed for the reference component as the first process and the comparison process and the count process are performed for the signal component as the second process, the count held after the second process is performed. The value is a digital value obtained by subtracting the reference component side from the signal component side.

  In addition, when the signal to be processed of a unit component such as a pixel is a signal component that appears after the reference component as a time series, the second processing is processing for a signal obtained by adding the signal component to the reference component, The count value held after the second process represents the signal component of the unit component.

  In addition, if the processing for the reference component is performed in the down-count mode and the processing for the signal component is performed in the up-count mode, the count value retained after the two processings is determined from the signal component side. A digital value obtained by subtracting the component side is obtained as a positive value.

  By combining these two, the comparison process and the down-count process are performed for the reference component as the first process, and the comparison process and the up-count process are performed for the signal component as the second process. The count value retained after processing is obtained as a positive value obtained by subtracting the reference component side from the signal component side. When the signal to be processed of the unit component is a signal component that appears after the reference component as a time series, digital data representing the effective signal component of the unit component is obtained as a positive value.

  When comparing the reference component with the signal component, the reference component is generally constant and the amount of signal is small, whereas the signal component is detected by detecting electromagnetic waves such as light by unit components such as pixels. This is a fluctuation component obtained, and the maximum value of the signal amount increases. Therefore, the longest period of comparison processing of both the reference component and the signal component, that is, the maximum value of the AD conversion period is not made the same, but the longest period of comparison processing for the reference component is set to be longer than the longest period of comparison processing for the signal component. It is preferable to shorten the AD conversion period twice.

  In addition, the count value held in the second process for the previous process target signal is further stored in another data storage unit, and the first process and the second process are performed for the current process target signal. When performing, it is preferable to perform the reading process of the count value from the data storage unit in parallel.

  The above-described AD conversion processing includes in a unit component a charge generation unit that generates a charge corresponding to an incident electromagnetic wave, and a unit signal generation unit that generates a unit signal according to the charge generated by the charge generation unit, Processing for converting analog unit signals generated by the unit signal generation unit and output in the column direction into digital data as processing target signals in a semiconductor device for physical quantity distribution detection in which the unit components are arranged in a matrix Can be used.

  In this way, when the unit components are arranged in a two-dimensional matrix, the analog unit signal generated by the unit signal generation unit and output in the column direction is accessed and fetched in units of rows (in column parallel) ( (Vertical) Scan reading is performed, and it is preferable to speed up reading of unit signals and AD conversion processing by performing the first process and the second process for each unit component in this line unit. .

  An AD conversion apparatus according to the present invention is an apparatus suitable for carrying out the AD conversion method according to the present invention, and compares a signal corresponding to each of a reference component and a signal component with a reference signal for AD conversion. In parallel with the comparison process in the comparison unit and the comparison process in the comparison unit, the count process is performed in one of the down-count mode and the up-count mode, and the asynchronous count value is held when the comparison process in the comparison unit is completed And a counter part of the mold.

  Preferably, a reference signal generation unit that generates a reference signal for conversion into digital data and supplies the reference signal to the comparison unit, or a counter unit according to which of the reference component and the signal component the comparison unit is performing comparison processing on It is further preferable that a timing control unit for switching the count processing mode is provided.

  The counter unit is preferably configured by a common counter circuit and configured to be switchable between an up-count mode and a down-count mode. In this case, when the count mode is switched, the asynchronous type according to the present invention is provided with an initial value setting processing unit that starts the count processing after the mode switching after initial setting of the count value immediately before the mode switching. It is preferable to use a counter circuit.

  The semiconductor device and electronic apparatus according to the present invention are apparatuses to which the AD conversion method according to the present invention is applied, and have the same configuration as the AD conversion apparatus according to the present invention.

  In the semiconductor device according to the present invention, it is preferable that a plurality of AD conversion units including a comparison unit and a counter unit are provided in the row direction, which is the arrangement direction of the unit component columns.

  The comparison unit captures the analog unit signal generated by the unit signal generation unit and output in the column direction in units of rows, and the comparison unit and the counter unit are in charge of each unit component in units of rows. It is better to perform the process. Further, the unit signal generation unit preferably has a semiconductor element for amplification.

  Here, if the charge generation unit has a photoelectric conversion element that receives light as electromagnetic waves and generates charge corresponding to the received light, the semiconductor device is configured as a solid-state imaging device. be able to.

  According to the AD conversion method, the AD conversion apparatus, the semiconductor device, and the electronic apparatus according to the present invention, the reference signal for AD conversion is compared with the signal to be processed that includes the reference component and the signal component. In parallel with the processing, the asynchronous counter circuit is used to count in either the down-count mode or the up-count mode, and when the count value at the time when the comparison processing is completed, The count processing mode is switched depending on which of the component and the signal component is being compared.

  By using the asynchronous counter, the operation limit frequency is determined only by the limit frequency of the first flip-flop, so that high-speed operation is possible. Even when the difference signal component between the reference component and the signal component is converted into digital data by performing AD conversion twice, the total AD conversion processing can be operated at high speed, and the AD conversion period can be increased. Can be shortened.

  In addition, since the AD conversion processing for the reference component and the signal component is performed while switching between the down-count mode and the up-count mode, the digital data representing the difference between the reference component and the signal component is converted into the down-count mode and the up-count mode. This can be obtained as a result of counting in two modes of the count mode.

  As a result, a memory device that holds the count results of the reference component and the signal component can be realized by a latch function provided in the counter unit, and it is necessary to prepare a dedicated memory device that holds AD converted data separately from the counter. Therefore, the problem of increase in circuit scale and circuit area can be solved.

  In addition, since the AD conversion unit is configured by the comparison unit and the counter unit, the count process can be controlled by one count clock for operating the counter unit and a control line for switching the count mode regardless of the number of bits. A signal line leading to the memory device is not necessary, and an increase in noise and an increase in power consumption can be eliminated.

  In addition, by using an asynchronous counter circuit including an initial value setting processing unit, it is possible to perform a continuous counting operation while maintaining continuity of count values before and after switching when the count mode is switched. Thereby, it is possible to continuously subtract values from each other by performing up-to-down or down-to-up. The subtraction process between the reference component and the signal component can be performed directly, and a special subtracter for taking the difference between the reference component and the signal component is not required. In addition, data transfer to the subtracter becomes unnecessary, and an increase in noise and an increase in current or power consumption can be eliminated.

  In addition, since the AD conversion unit is configured by pairing the comparison unit and the counter unit, when a unit signal output from a semiconductor device in which unit component elements are arranged in a matrix is used as a processing target signal, the unit component element Even in the case where a plurality of AD conversion units are arranged in the row direction, which is the column arrangement direction, it is possible to provide each with a counter unit, and as in the conventional example shown in FIG. 21, the count output from the counter unit There is no need to route the wiring to the latch, and there is no problem of increase in noise or power consumption due to the wiring.

  Also, when the pipeline operation is performed in which the AD conversion process and the read process are performed in parallel, it is sufficient that the memory device holding the AD converted data has only one system for each AD conversion unit. The increase in circuit area can be minimized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, an asynchronous counter circuit according to the present invention will be described, and then an example in which the asynchronous counter circuit is applied to an electronic device or a semiconductor device will be described.

<Configuration of Counter Circuit; First Embodiment>
FIG. 1 is a circuit block diagram showing a basic configuration of a first embodiment of an asynchronous counter circuit according to the present invention. FIG. 2 is a circuit block diagram further embodying the basic configuration of the first embodiment.

  As shown in FIG. 1, in the counter circuit 400 of the first embodiment, first, a plurality of negative edge type and D type flip-flops 412, 414, 416, and 418 (also collectively referred to as 410) are cascade-connected. It has become. Each flip-flop 410 is configured such that an inverted output NQ (indicated by a horizontal bar “−” on Q in the figure) is input to its D input terminal. As a result, the counter circuit 400 can constitute a 4-bit asynchronous counter. In the figure, the flip-flops 412, 414, 416, and 418 are arranged in ascending order in a four-stage configuration (for 4 bits), but in actuality, the number is provided by the number of bits.

  In addition, the counter circuit 400 is a three-input / one-output type as a switching processing unit that switches between the non-inverted output Q, the inverted output NQ, and the power supply (Vdd) level of each flip-flop 410 between the flip-flops 410. Three-value switching units 422, 424, and 426 (collectively referred to as 420) are provided. Each ternary switching unit 420 switches three input signals in accordance with 2-bit control signals SW1 and SW2 from a control unit (not shown), and inputs the selected one signal to the clock terminal CK of the flip-flop 410 at the subsequent stage. It is like that.

  Here, each of the three-input / one-output type ternary switching units 420 initializes the count value immediately before the mode switching at the time of switching the count mode and starts the count process after the mode switching. Has the function of a value setting processing unit.

  That is, in a state where a plurality of flip-flops that are the basic elements of the counter are arranged in cascade, the ternary switching unit 420 is arranged between the flip-flops 410 arranged in cascade. By selecting either the non-inverted output NQ or the inverted output Q as a counter clock and supplying it to the clock terminal CK of the subsequent flip-flop 410, the count mode can be switched, and the previous stage just before the mode switching can be switched. Switching is performed to initialize the count value of the flip-flop 410 to the flip-flop 410 at the subsequent stage.

  Specifically, as shown in FIG. 2, the ternary switching unit 420 includes a pair of binary switching units 432 and 433 having a two-stage configuration and a binary switching unit 434 and 435 respectively. A pair and a pair of binary switching units 436 and 437 can be configured. Each pair is collectively referred to as a binary switching unit 430.

  In this case, the respective binary switching units 430 are switched by switching control signals SL and FL issued at different timings as 2-bit switching control signals SW1 and SW2 from a control unit (not shown).

  The binary switching units 432, 434, and 436 on the upstream side switch the non-inverted output Q and the inverted output NQ of the corresponding flip-flops 410 according to the switching control signal SL, and the corresponding binary switching unit 433 on the subsequent stage side. 435 and 437 to one input terminal. The binary switching units 433, 435, and 437 on the subsequent stage convert the data passed from the binary switching units 432, 434, and 436 on the previous stage and the power level input to the other input terminal into the switching control signal FL. And switch to the clock terminal CK of the subsequent flip-flop 410.

  For example, the binary switching unit 430 (432, 434, 436) on the previous stage side selects either the non-inverted output NQ or the inverted output Q of the previous flip-flop 410 based on the switching control signal SL, This is supplied to one input terminal of the binary switching unit 430 (433, 435, 437) on the rear stage side. The switching control signal SL is for switching the counting operation of the counter circuit 400 to either up-counting or down-counting by controlling the binary switching unit 430 (432, 434, 436) on the preceding stage side. .

  The rear-stage binary switching unit 430 (433, 435, 435) outputs the output of the front-stage flip-flop 410 output from the front-stage binary switching section 430 (432, 434, 436) (inverted with the non-inverted output NQ). The supply to the clock terminal CK of the subsequent flip-flop 410 is adjusted under the control of the switching control signal FL.

  The switching control signal FL controls the binary switching unit 430 (433, 435, 435) on the rear stage side, and outputs the output (one of the non-inverted output NQ and the inverted output Q) of the preceding flip-flop 410. The supply to the clock terminal CK of the subsequent flip-flop 410 is stopped for a predetermined period after the switching of the count mode, and the clock of the subsequent flip-flop 410 is resumed when the supply of either the non-inverted output NQ or the inverted output Q is resumed. A signal corresponding to a clock is supplied to the terminal CK. In this way, the continuity of the count value is maintained when the count mode of up-counting and down-counting is switched. Details of the function of the switching control signal FL will be described later.

  “Maintaining continuity of count value” means that the count value is broken by switching the count mode, but it returns to the final count value in the previous mode before the count is started after the mode is switched. This means that the count operation after switching is started from the final count value in the previous mode.

  FIG. 3 is a diagram illustrating a circuit configuration example of the binary switching unit 430. For example, FIG. 3A illustrates a case where each switch is configured by a transfer gate. All circuit elements are constructed using CMOS technology.

  Transfer gates 442 and 443 are provided corresponding to the binary switching units 432, 434, and 436 on the preceding stage side. Also, transfer gates 446 and 447 are provided corresponding to the binary switching units 433, 435, and 437 on the rear stage side. Hereinafter, it is also collectively referred to as a transfer gate 440.

  The inverted output NQ of the preceding flip-flop 410 is input to the input of the transfer gate 442, the non-inverted output Q of the preceding flip-flop 410 is input to the input of the transfer gate 443, and the outputs of the transfer gates 442 and 443 are common. Are connected to the input of the transfer gate 446. The input of the transfer gate 447 is connected to the power supply level, and the outputs of the transfer gates 446 and 447 are commonly connected to the clock terminal CK of the subsequent flip-flop 410.

  Each transfer gate 440 includes a CMOS switch including an Nch (ch) channel n1 and a Pch transistor p1. The gates (control input terminals) of the transistors n1 and p1 correspond to the input terminals of the switching control signals SL and FL or their inverted signals NSL and NFL. The inversion signal NSL is generated by an inverter 444 that inverts the switching control signal SL, and the inversion signal NFL is generated by an inverter 448 that inverts the switching control signal FL.

  The CMOS switch including the transistors n1 and p1 is turned on when the gate of the transistor n1 is high and the gate of the transistor n1 is low, thereby selecting the non-inverted output Q or the inverted output NQ of the flip-flop 410 in the previous stage. Output. This CMOS switch may be a switch composed of only one of the transistors n1 and p1, or an Nch type MOS transistor or a Pch type MOS transistor. In this case, however, there is a problem of the threshold voltage Vth. A CMOS switch using both of these was adopted.

  FIG. 3B illustrates a case where each switch is configured with a logic gate. Three two-input NAND gates 452, 453, and 454 are provided corresponding to the binary switching units 432, 434, and 436 on the preceding stage side. Further, an OR gate including a 2-input NOR gate 456 and an inverter 457 is provided corresponding to the binary switching units 433, 435, and 437 on the rear stage side.

  An inverted signal NSL obtained by inverting the switching control signal SL by the inverter 455 is input to one input of the NAND gate 452, and the switching control signal SL is input to one input of the NAND gate 453. The other input of the NAND gate 452 receives the inverted output NQ of the preceding flip-flop 410, the other input of the NAND gate 453 receives the non-inverted output Q of the preceding flip-flop 410, and the NAND gates 452 and 453. Are connected to the input of a NAND gate 454.

  In the NOR gate 456, the output signal of the NAND gate 454 is input to one input terminal, and the switching control signal is input to the other input terminal. The output signal of the NOR gate 456 is inverted by the inverter 457 and then connected to the clock terminal CK of the subsequent flip-flop 410.

  In both FIG. 3A and FIG. 3B, the binary switching units 432, 434, and 436 on the previous stage side select and output the non-inverted output Q when the switching control signal SL is at high level, When the switching control signal SL is at a low level, the inverted output NQ is selected and output.

  Further, when the switching control signal FL is at a low level, the binary switching units 433, 435, and 437 on the subsequent stage side select and output the outputs of the corresponding binary switching units 432, 434, and 436 on the upstream side, When the switching control signal FL is at a high level, the power supply level (high level) is selected and output.

<Operation of Counter Circuit; First Embodiment>
FIG. 4 is a timing chart for explaining the operation of the counter circuit 400 of the first embodiment shown in FIG. FIGS. 5A and 5B are diagrams for explaining output changes of the flip-flop 410 in the configuration of the first embodiment.

  As described above, when the switching control signal SL is at the high level and the switching control signal FL is at the low level, the binary switching units 432, 434, and 436 on the front stage side select and output the non-inverted output Q, and further on the rear stage side. The binary switching units 433, 435, and 437 select and output the outputs of the binary switching units 432, 434, and 436 on the preceding stage side. Accordingly, the non-inverted output Q of the preceding flip-flop 410 is input to the clock terminal CK of the succeeding flip-flop 410 between the flip-flops 410.

  In this state, when the clock CK0 is input to the clock terminal CK of the first flip-flop 410, a state transition occurs between the flip-flops 410 for each negative edge of the non-inverted output Q. As a result, the counter circuit 400 performs an up-count operation. (Count period 0 to 6).

  After up-counting for an arbitrary period, when the clock CK0 is stopped and the switching control signal SL is inverted from high level to low level (t30), the counter circuit 400 switches from the up-count mode to the down-count mode and restarts the clock CK0. Start down-counting. For example, in this example, after up-counting from 0 to 6, the switching control signal SL is switched from the high level to the low level.

  By switching the count mode by the switching control signal SL at time t30, the binary switching unit 430 of the pair configuration selects the inverted output NQ of the previous flip-flop 410 and applies it to the clock terminal CK of the next flip-flop 410. input.

  At this time, if the non-inverted output Q of the flip-flop 410 in the previous stage is at a high level, that is, the inverted output NQ is at a low level, the switching control signal SL is switched to cause a negative edge ( Since (H → L) is applied, the output of the flip-flop 410 at the next stage is inverted (t30 +).

  In FIG. 5A, the output of the second-stage flip-flop 410 is inverted from the low level to the high level, and the output of the third-stage flip-flop 410 is also inverted (t30 +). In FIG. 5B, the output of the flip-flop 410 at the second stage is inverted from the high level to the low level (t30 +).

  That is, the count value starts to be destroyed only on the rear stage side of the flip-flop 410 in which the non-inverted output Q of the flip-flop 410 at the time of the count mode switching is at the high level, that is, the inverted output NQ is at the low level.

  Further, when the output of the flip-flop 410 at the next stage is inverted, when the inverted output NQ is inverted from the low level to the high level, the clock terminal CK of the subsequent flip-flop 410 becomes the high level. Inversion of the output does not occur (t30 ++; see the third stage in FIG. 5A).

  On the other hand, when the inverted output NQ is inverted from the high level to the low level, the negative flip-flop 410 is applied to the clock terminal CK in the subsequent flip-flop 410. The output of 410 is inverted (t30 ++; see the third stage in FIG. 5B).

  Similarly, the influence of the data inversion (H → L) of the inverted output NQ is continued until the flip-flop 410 where the inverted output NQ is inverted from the low level to the high level. In this example, as shown in FIG. 4, the count value changes from “6” to “10”.

  In other words, when switching from up-counting to down-counting, the count value is destroyed and the continuity of the count value cannot be maintained, and the count value is kept up and down continuously before and after switching. Cannot be counted.

  Therefore, in the present embodiment, after the switching control signal SL for switching the count mode is switched, before the negative edge of the down-counting clock CK0 is input to the first flip-flop 410, the binary switching units 433, 435 on the rear stage side. An active H one-shot pulse is applied to 437 as a switching control signal FL (t32 to t34).

  By doing so, the power supply level (high level) is input to the clock terminals CK of all the negative edge flip-flops 410. However, before and after the one-shot pulse input of the switching control signal FL, the output of the negative edge flip-flop 410 does not change.

  Thereafter, when the one-shot pulse period elapses (t34), the inverted output NQ of the preceding flip-flop 410 is input to the clock terminal CK again. At this time, if the inverted output NQ of the previous flip-flop 410 is at a low level, the negative flip-flop 410 is applied to the clock terminal CK in the next flip-flop 410, and therefore the output of the next flip-flop 410 is output. Is reversed.

  In FIG. 5A, the output of the flip-flop 410 at the second stage is inverted from the high level to the low level (t34 +). In FIG. 5B, the output of the second-stage flip-flop 410 is inverted from the low level to the high level, and the output of the third-stage flip-flop 410 is also inverted (t34 +).

  Further, when the output of the flip-flop 410 is inverted, when the inverted output NQ is inverted from the low level to the high level, the clock terminal CK of the subsequent flip-flop 410 becomes the high level. It does not occur (t34 ++; see the third stage in FIG. 5B).

  On the other hand, when the inverted output NQ is inverted from the high level to the low level, the negative flip-flop 410 is applied to the clock terminal CK in the subsequent flip-flop 410. The output of 410 is inverted (t34 ++; see the third stage in FIG. 5A). Similarly, the influence of the data inversion (H → L) of the inverted output NQ is continued until the flip-flop 410 where the inverted output NQ is inverted from the low level to the high level.

  As a result, in any flip-flop 410 whose output is inverted when the count mode is switched by the switching control signal SL, the output is inverted again. As a result, the count value is restored.

  After the above operation, when the clock CK0 is input again, this time, a state transition occurs between the flip-flops 410 every negative edge of the inverted output NQ, that is, every positive edge of the non-inverted output Q. As a result, the counter circuit 400 Then, a down-count operation is performed (period of count value 6 to 1).

  As described above, according to the counter circuit 400 of the first embodiment, the count value changed at the time of switching from the up-count to the down-count is used as the switching control signal FL, and the active H one-shot pulse is added to the flip-flop 410. The clock terminal is forcibly set to high level and then returned to the state after mode switching. If the inverted output NQ of the preceding flip-flop 410 is at a low level when returning to the state after the mode switching, the output of the succeeding flip-flop 410 is inverted and returned to the original count value.

  By doing so, the count value before switching the count mode can be substantially held, and therefore, after the up-counting, the down-count can be continuously performed while maintaining the continuity of the count value.

  The counter value of the down count is counted in a negative direction with respect to the counter value of the up count. Therefore, after i up-counting and j down-counting continuously, the subtraction result of i−j is obtained as the count result of the counter circuit 400. The count value obtained by switching the up / down mode does not include a complement, and the subtraction result is obtained directly, which is convenient.

  By using such an asynchronous counter circuit 400, it is possible to perform direct continuous up / down counting with an asynchronous counter, which has been difficult in the past, only by adding a simple switching means (switch). Even when switching up / down counts, the value before switching is maintained, so it is possible to continuously subtract the count value at the time of up and the count value at the time of down by going up from down or up from down. .

  In the first embodiment, an example of switching from up-counting to down-counting is shown, but even when switching from down-counting to up-counting, the continuity of the counter value can be maintained by simply switching the count mode. In the same way as described above, the switching control signal FL is used to forcibly set the clock terminal of the flip-flop 410 to the high level and then return to the state after the mode switching to restore the original count value. In this case, the count value before switching the count mode can be substantially held, so that after the down-count, the up-count can be continuously performed while maintaining the continuity of the count value. it can.

  Furthermore, even when up-counting and down-counting are performed in any combination, it is possible to control to return to the original count value at the time of mode switching.

  However, in the first embodiment, the count overflow is not detected. For example, an overflow surplus bit is added, or a carry or carry bit is used. By using a known technique such as, it is possible to easily cope with the overflow.

<Configuration of Counter Circuit; Second Embodiment>
FIG. 6 is a circuit block diagram showing the configuration of the second embodiment of the asynchronous counter circuit according to the present invention, and corresponds to the embodied circuit block diagram shown in FIG. 2 of the first embodiment.

  In the second embodiment, three input signals are switched between each flip-flop 510 in accordance with 2-bit control signals SW1 and SW2 from a control unit (not shown), and the selected one signal is used as a clock for the subsequent flip-flop 510. This is shared with the first embodiment in that it includes three-input / one-output ternary switching units 522, 524, and 526 (also collectively referred to as 520) that are input to the terminal CK.

  Each of the three-input / one-output ternary switching units 520 initializes the count value immediately before the mode switching when the count mode is switched, and then starts the count process after the mode switching. Have the function of the department.

  On the other hand, as each flip-flop 510, a positive edge type is used, and a ternary switching unit 520 provided between the flip-flops 510 is provided so as to correspond to the reversal of the edge operation associated with the positive edge type. , Except that the corresponding three values of the non-inverted output Q, the inverted output NQ, and the ground (GND) level of the corresponding flip-flop 510 are switched.

  Specifically, as shown in FIG. 6, the counter circuit 500 according to the second embodiment is different from the three-input / one-output type ternary switching unit 520 in the two-stage / two-input / one-output type. The pair of binary switching units 532 and 533, the pair of binary switching units 534 and 535, and the pair of binary switching units 536 and 537 are configured. Each pair is collectively referred to as a binary switching unit 530.

  The binary switching units 532, 534, and 536 on the preceding stage are similar to the binary switching units 432, 434, and 436 on the preceding stage in the first embodiment, and the non-inverted output Q and the inverted output NQ of the corresponding flip-flops 510, respectively. Are switched in accordance with the switching control signal SL and passed to one input terminal of the corresponding binary switching unit 533, 535, 537 on the subsequent stage side.

  On the other hand, the binary switching units 533, 535, and 537 on the rear stage side switch control between the data passed from the binary switching units 532, 534, and 536 on the previous stage side and the ground level input to the other input terminal. The signal is switched according to the signal FL and input to the clock terminal CK of the subsequent flip-flop 510. That is, it differs from the first embodiment in that one input of the binary switching unit on the rear stage side in the ternary switching unit 520 is changed from the power supply to the ground level.

  The binary switching units 532, 534, and 536 on the front stage side select and output the non-inverted output Q when the switching control signal SL is high level, and select and output the inverted output NQ when the switching control signal SL is low level. To do. Further, when the switching control signal FL is at a low level, the binary switching units 533, 535, and 537 on the subsequent stage side select and output the outputs of the corresponding binary switching units 532, 534, and 536 on the upstream side, while switching When the control signal FL is at high level, the ground level (low level) is selected and output.

<Operation of Counter Circuit; Second Embodiment>
FIG. 7 is a timing chart for explaining the operation of the counter circuit 500 of the second embodiment shown in FIG. FIGS. 8A and 8B are diagrams for explaining the output change of the flip-flop 510 in the second embodiment.

  In the second embodiment, the first embodiment that counts up or counts down for each negative edge may be modified to count up or count down for each positive edge. It is the same as the form, and the obtained effect does not change.

  For example, when the switching control signal SL is at a low level and the switching control signal FL is at a low level, the binary switching units 532, 534, 536 on the front stage side select and output the inverted output NQ, and further the binary switching on the rear stage side Units 533, 535, and 537 select and output the outputs of binary switching units 532, 534, and 536 on the preceding stage side. Therefore, between each flip-flop 510, the inverted output NQ of the previous flip-flop 510 is input to the clock terminal CK of the next flip-flop 510.

  In this state, when the clock CK0 is input to the clock terminal CK of the first flip-flop 510, a state transition occurs between the flip-flops 510 at every negative edge of the non-inverted output Q, that is, every positive edge of the inverted output NQ. Counter circuit 500 performs an up-count operation (period of count values 0 to 6).

  After counting up for an arbitrary period, when the clock CK0 is stopped and the switching control signal SL is inverted from the low level to the high level (t40), the counter circuit 500 switches from the upcount mode to the downcount mode and restarts the clock CK0. Start down-counting. For example, in this example, after up-counting from 0 to 6, the switching control signal SL is switched from the low level to the high level.

  By switching the count mode by the switching control signal SL at time t40, the binary switching unit 530 of the pair configuration selects the non-inverted output Q of the previous flip-flop 510 and the clock terminal CK of the next flip-flop 510. To enter.

  At this time, if the inverted output NQ of the flip-flop 510 in the previous stage is at a low level, that is, the non-inverted output Q is at a high level, the positive flip-flop (510) Since L → H) is applied, the output of the flip-flop 510 at the next stage is inverted (t40 +).

  In FIG. 8A, the output of the second-stage flip-flop 410 is inverted from the low level to the high level, and the output of the third-stage flip-flop 410 is also inverted (t30 +). In FIG. 8B, the output of the flip-flop 410 at the second stage is inverted from the high level to the low level (t30 +).

  That is, the count value starts to be destroyed only on the rear stage side of the flip-flop 410 in which the inverted output NQ of the flip-flop 510 at the time of the count mode switching is at the low level, that is, the non-inverted output Q is at the high level.

  When the output of the flip-flop 510 at the next stage is inverted, when the non-inverted output Q is inverted from the high level to the low level, the clock terminal CK of the flip-flop 510 at the subsequent stage goes to the low level. Output inversion does not occur (t40 ++; see the third stage in FIG. 8A).

  On the other hand, when the non-inverted output Q is inverted from the low level to the high level, in the subsequent flip-flop 510, a positive edge is applied to the clock terminal CK. The output of the group 510 is inverted (t40 ++; see the third stage in FIG. 8B).

  Similarly, the influence of the data inversion (L → H) of the non-inverted output Q is continued until the flip-flop 510 in which the non-inverted output Q is inverted from the high level to the low level. In this example, as shown in FIG. 7, the count value changes from “6” to “10”.

  In other words, as described in the first embodiment, when switching from up-counting to down-counting, the count value is destroyed and the continuity of the count value cannot be maintained, and the count is not changed before and after switching. It is impossible to count up / down continuously while keeping the value.

  Therefore, in the second embodiment, after the switching control signal SL for switching the count mode is switched, before the positive edge of the down-counting clock CK0 is input to the first flip-flop 510, the binary switching unit 533 on the rear stage side. , 535, 537, an active H one-shot pulse is applied as the switching control signal FL (t42 to t44).

  As a result, the ground level (low level) is input to the clock terminals CK of all the positive edge flip-flops 510. However, the output of the positive edge flip-flop 510 does not change before and after the one-shot pulse input of the switching control signal FL.

  Thereafter, when the one-shot pulse period elapses (t44), the non-inverted output Q of the preceding flip-flop 510 is input again to the clock terminal CK. At this time, if the non-inverted output Q of the previous flip-flop 510 is at a high level, the positive flip-flop 510 is applied to the clock terminal CK in the next flip-flop 510, so The output is inverted.

  In FIG. 8A, the output of the flip-flop 510 at the second stage is inverted from the low level to the high level (t44 +). In FIG. 8B, the output of the second-stage flip-flop 510 is inverted from the high level to the low level, and the output of the third-stage flip-flop 510 is also inverted (t44 +).

  Further, when the output of the flip-flop 510 is inverted, when the inverted output NQ is inverted from the high level to the low level, the clock terminal CK of the subsequent flip-flop 510 is changed to the low level. It does not occur (t44 ++; see the third stage in FIG. 8B).

  On the other hand, when the inverted output NQ is inverted from the low level to the high level, the positive flip-flop is applied to the clock terminal CK in the subsequent flip-flop 510. The output of 510 is inverted (t44 ++; see the third stage in FIG. 8A). Similarly, the influence of the data inversion (L → H) of the non-inverted output Q is continued until the flip-flop 510 in which the non-inverted output Q is inverted from the high level to the low level.

  As a result, even in the configuration of the first embodiment, the output is inverted again in any flip-flop 510 whose output is inverted when the count mode is switched by the switching control signal SL. The value is restored.

  When the clock CK0 is input again after the above operation, a state transition occurs between the flip-flops 510 every negative edge of the inverted output NQ, that is, every positive edge of the non-inverted output Q. As a result, the counter circuit 500 Down count operation is performed (period of count value 6 to 0).

  As described above, according to the counter circuit 500 of the second embodiment, the count value changed at the time of switching from the up-count to the down-count is used as the switching control signal FL, and the one-shot pulse of active H is added to the flip-flop 410. The clock terminal is forcibly set to low level and then returned to the state after mode switching. If the non-inverted output Q of the preceding flip-flop 410 is at a high level when returning to the state after the mode switching, the output of the succeeding flip-flop 410 is inverted and returned to the original count value.

  By doing so, the count value before switching the count mode can be substantially held, and therefore, after the up-counting, the down-count can be continuously performed while maintaining the continuity of the count value.

  The counter value of the down count is counted in a negative direction with respect to the counter value of the up count. Therefore, after i up-counting and j down-counting continuously, the subtraction result of i−j is obtained as the count result of the counter circuit 500.

  Also in the second embodiment, an example of switching from up-counting to down-counting has been shown, but even when switching from down-counting to up-counting, continuity of the counter value cannot be maintained by simply switching the count mode. However, in the same manner as described above, the switching control signal FL is used to forcibly set the clock terminal of the flip-flop 410 to a low level and then return to the state after the mode switching to restore the original count value. Since the count value before the switching of the count mode can be substantially held by returning the count value, the up-count can be continuously performed after the down-count while maintaining the continuity of the count value. .

  Furthermore, even when up-counting and down-counting are performed in any combination, it is possible to control to return to the original count value at the time of mode switching.

  However, the second embodiment is not configured to detect the overflow of the count. For example, an extra bit for overflow is added, or a carry or carry (borrow) bit is used. By using a known technique such as, it is possible to easily cope with the overflow.

<Configuration of Counter Circuit; Third Embodiment>
FIG. 9 is a circuit block diagram showing the configuration of the third embodiment of the asynchronous counter circuit according to the present invention, and corresponds to the embodied circuit block diagram shown in FIG. 2 of the first embodiment.

  The counter circuit 400 according to the third embodiment has a configuration in which a clock signal input to the clock terminal CK of the first stage flip-flop 412 in the counter circuit 400 according to the first embodiment shown in FIG. 2 is added. Has characteristics. Further, as a whole of the counter circuit 400, the clock CK0 itself is the least significant bit Q0, and the count output of the flip-flop 410, which is the other bits Qx (Q1 to Q4 in this example), is 1 bit compared to the first embodiment. It is characterized in that it is shifted to the upper bits one by one.

  Specifically, the 400 of the third embodiment selects either the inverter 462 that inverts the clock CK0, or the clock CK0 and the inverted clock NCK0 that is inverted by the inverter 462, and the clock terminal CK of the flip-flop 412 at the first stage is selected. A 2-input / 1-output type binary switching unit 464 that inputs, that is, switches between non-inversion and inversion of the clock CK0.

  The binary switching unit 464 selects and outputs the clock CK0 when the switching control signal SL is at a high level, and selects and outputs the inverted clock NCK0 when the switching control signal SL is at a low level.

<Operation of Counter Circuit; Third Embodiment>
FIG. 10 is a timing chart for explaining the operation of the counter circuit 400 of the third embodiment shown in FIG.

  In the third embodiment, the clock CK0 itself is the least significant bit Q0 compared to the first embodiment that counts up or counts down for each negative edge. FIG. 5 (A) and FIG. Although description using corresponding figures is omitted, the basic idea is the same as that of the first embodiment, and the same effect as that of the first embodiment can be obtained.

  In addition, by setting the clock CK0 itself to the least significant bit Q0, the number of count bits is increased by one bit, that is, doubled compared to the first embodiment. Since the high level and low level of the clock CK0 also contribute to the count value, the count operation is performed at both edges of the clock CK0, and the count operation is doubled.

  Similar to the application of the second embodiment to the first embodiment, in the third embodiment as well, the negative edge flip-flop 410 is replaced with a positive edge type so as to count up or count down for each positive edge. The flip-flop 510 can be modified to be replaced, and even in this case, the same effect as that of the third embodiment can be obtained.

<< Application example of asynchronous counter >>
Next, an example in which the asynchronous counter circuit according to the present invention is applied to an electronic device or a semiconductor device will be described. In the following, a case where a CMOS image sensor, which is an example of an XY address type solid-state imaging device, is used as a device will be described as an example. The CMOS image sensor will be described on the assumption that all pixels are made of NMOS.

  However, this is merely an example, and the target device is not limited to a MOS imaging device. All the semiconductor device for physical quantity distribution detection in which a plurality of unit components that are sensitive to electromagnetic waves input from outside such as light and radiation are arranged in a line or matrix form, and all implementations described later. Forms are applicable as well.

<Configuration of Solid-State Imaging Device; First Embodiment>
FIG. 11 is a schematic configuration diagram of a CMOS solid-state imaging device (CMOS image sensor) which is the first embodiment of the semiconductor device according to the present invention. This CMOS solid-state imaging device is also an aspect of an electronic apparatus according to the present invention.

  The solid-state imaging device 1 has a pixel unit in which a plurality of pixels including a light receiving element (an example of a charge generation unit) that outputs a signal corresponding to an incident light amount is arranged in rows and columns (that is, in a two-dimensional matrix form). The signal output from each pixel is a voltage signal, and a CDS (Correlated Double Sampling) processing function unit, a digital conversion unit (ADC), etc. are provided in parallel in a column. It is.

  “The CDS processing function unit and the digital conversion unit are provided in parallel with the column” means that a plurality of CDS processing function units and digital conversion units are provided substantially in parallel with the vertical signal line 19 in the vertical column. Means that Each of the plurality of functional units is arranged only on one end side in the column direction with respect to the pixel unit 10 (output side arranged on the lower side of the drawing) when the device is viewed in plan view. Or one end side in the column direction (output side arranged on the lower side in the figure) and the other end side (the upper side in the figure) opposite to the pixel unit 10. The thing of the form distributed separately may be sufficient. In the latter case, it is preferable that the horizontal scanning unit that performs readout scanning (horizontal scanning) in the row direction is also arranged separately on each edge side so that each can operate independently.

  For example, as a typical example in which a CDS processing function unit and a digital conversion unit are provided in parallel in a column, a CDS processing function unit and a digital conversion unit are arranged for each vertical column in a portion called a column area provided on the output side of the imaging unit. And is a column type that sequentially reads out to the output side. In addition to the column type, a configuration in which one CDS processing function unit or digital conversion unit is assigned to a plurality of adjacent (for example, two) vertical signal lines 19 (vertical columns), or every N (N is It is also possible to adopt a form in which one CDS processing function unit or digital conversion unit is assigned to N vertical signal lines 19 (vertical columns) of a positive integer (with N−1 lines in between).

  Except for the column type, in any form, since a plurality of vertical signal lines 19 (vertical columns) commonly use one CDS processing function unit and digital conversion unit, they are supplied from the pixel unit 10 side. A switching circuit (switch) that supplies pixel signals for a plurality of columns to one CDS processing function unit or digital conversion unit is provided. Depending on the subsequent processing, it is necessary to take measures such as providing a memory for holding the output signal.

  In any case, the signal processing of each pixel signal is read out in units of pixel columns by adopting a form in which one CDS processing function unit or digital conversion unit is assigned to a plurality of vertical signal lines 19 (vertical columns). By performing the processing later, the configuration in each unit pixel can be simplified and the number of pixels of the image sensor can be reduced, the size can be reduced, and the cost can be reduced as compared with the case where the same signal processing is performed in each unit pixel.

  In addition, since a plurality of signal processing units arranged in parallel in a column can simultaneously process pixel signals for one row, one CDS processing function unit or digital conversion unit is provided on the output circuit side or outside the device. Therefore, the signal processing unit can be operated at a low speed as compared with the case where processing is performed, which is advantageous in terms of power consumption, bandwidth performance, noise, and the like. In other words, when the power consumption and bandwidth performance are the same, the entire sensor can be operated at high speed.

  In the case of a column type configuration, it can be operated at a low speed, which is advantageous in terms of power consumption, bandwidth performance, noise, and the like, and has an advantage that a switching circuit (switch) is unnecessary. In the following embodiments, this column type will be described unless otherwise specified.

  As shown in FIG. 11, the solid-state imaging device 1 according to the first embodiment includes a pixel unit (imaging unit) 10 in which a plurality of unit pixels 3 are arranged in rows and columns, and a drive provided outside the pixel unit 10. A control unit 7, a column processing unit 26, a reference signal generation unit 27 that supplies a reference voltage for AD conversion to the column processing unit 26, and an output circuit 28 are provided.

  In addition, an AGC (Auto Gain Control) circuit having a signal amplification function or the like can be provided in the same semiconductor region as the column processing unit 26 as needed before or after the column processing unit 26. When AGC is performed before the column processing unit 26, analog amplification is performed. When AGC is performed after the column processing unit 26, digital amplification is performed. If the n-bit digital data is simply amplified, the gradation may be lost. Therefore, it is preferable to perform digital conversion after amplification by analog.

  The drive control unit 7 has a control circuit function for sequentially reading signals from the pixel unit 10. For example, the drive control unit 7 includes a horizontal scanning circuit (column scanning circuit) 12 that controls column addresses and column scanning, a vertical scanning circuit (row scanning circuit) 14 that controls row addresses and row scanning, and an internal clock. And a communication / timing control unit 20 having a function such as generation.

  In the drawing, as shown by a dotted line in the vicinity of the communication / timing control unit 20, the clock conversion unit 23 is an example of a high-speed clock generation unit that generates a pulse having a clock frequency higher than the input clock frequency. May be provided. The communication / timing control unit 20 generates an internal clock based on the input lock (master clock) CLK0 input via the terminal 5a or the high-speed clock generated by the clock conversion unit 23.

  By using a signal derived from the high-speed clock generated by the clock converter 23, AD conversion processing and the like can be operated at high speed. Also, motion extraction and compression processing requiring high-speed calculation can be performed using a high-speed clock. Also, the parallel data output from the column processing unit 26 can be converted into serial data and the video data D1 can be output outside the device. By doing so, it is possible to adopt a configuration in which high-speed operation output is performed with a smaller number of terminals than the number of bits of digital data after AD conversion.

  The clock converter 23 includes a multiplier circuit that generates a pulse having a clock frequency faster than the input clock frequency. The clock conversion unit 23 receives the low-speed clock CLK2 from the communication / timing control unit 20, and generates a clock having a frequency twice or more higher based on the low-speed clock CLK2. As a multiplication circuit of the clock converter 23, a k1 multiplication circuit may be provided when k1 is a multiple of the frequency of the low-speed clock CLK2, and various known circuits can be used.

  In FIG. 11, some of the rows and columns are omitted for the sake of simplicity, but in reality, tens to thousands of unit pixels 3 are arranged in each row and each column. The unit pixel 3 is typically composed of a photodiode as a light receiving element (charge generation unit) and an in-pixel amplifier having an amplifying semiconductor element (for example, a transistor).

  As the intra-pixel amplifier, for example, a floating diffusion amplifier configuration is used. As an example, with respect to the charge generation unit, a read selection transistor that is an example of a charge readout unit (transfer gate unit / read gate unit), a reset transistor that is an example of a reset gate unit, a vertical selection transistor, and a floating diffusion As a CMOS sensor having a source follower-amplifying transistor, which is an example of a detection element for detecting a change in potential, a sensor composed of four general-purpose transistors can be used.

  Alternatively, as described in Japanese Patent No. 2708455, an amplifying transistor connected to a drain line (DRN) for amplifying a signal voltage corresponding to the signal charge generated by the charge generating unit, and the charge generating unit It is also possible to use a transistor composed of three transistors, each having a reset transistor for resetting and a read selection transistor (transfer gate portion) scanned from a vertical shift register via a transfer wiring (TRF). .

  Further, as other components of the drive control unit 7, a horizontal scanning circuit 12, a vertical scanning circuit 14, and a communication / timing control unit 20 are provided. The horizontal scanning circuit 12 has a function of a reading scanning unit that reads a count value from the column processing unit 26. Each element of these drive control units 7 is formed integrally with a pixel unit 10 in a semiconductor region such as single crystal silicon using a technique similar to a semiconductor integrated circuit manufacturing technique, and is a solid-state imaging which is an example of a semiconductor system It is configured as an element (imaging device).

  The unit pixel 3 includes a column processing unit 26 in which a vertical scanning circuit 14 is provided via a row control line 15 for row selection, and a column AD circuit 25 is provided for each vertical column via a vertical signal line 19; Each is connected. Here, the row control line 15 indicates the entire wiring that enters the pixel from the vertical scanning circuit 14.

  The horizontal scanning circuit 12 and the vertical scanning circuit 14 include a decoder as will be described later, and start a shift operation (scanning) in response to control signals CN1 and CN2 given from the communication / timing control unit 20. It has become. Therefore, the row control line 15 includes various pulse signals (for example, a reset pulse RST, a transfer pulse TRF, a DRN control pulse DRN, etc.) for driving the unit pixel 3.

  Although not shown, the communication / timing control unit 20 is a master via a functional block of a timing generator TG (an example of a read address control device) that supplies a clock signal necessary for the operation of each unit and a pulse signal of a predetermined timing, and a terminal 5a. A communication interface functional block that receives the clock CLK0, receives data DATA for instructing an operation mode and the like via the terminal 5b, and outputs data including information of the solid-state imaging device 1;

  For example, the horizontal address signal is output to the horizontal decoder 12a and the vertical address signal is output to the vertical decoder 14a, and each decoder 12a, 14a receives it and selects a corresponding row or column.

  At this time, since the unit pixels 3 are arranged in a two-dimensional matrix, analog pixel signals generated by the pixel signal generation unit 5 and output in the column direction via the vertical signal lines 19 are arranged in a row unit (column parallel). (In) Scan (access) to read (vertical) scan, and then access the row direction, which is the arrangement direction of vertical columns, and read out pixel signals (in this example, digitized pixel data) to the output side (horizontal) scan By performing reading, it is preferable to speed up reading of pixel signals and pixel data. Of course, not only scanning reading but also random access for reading out only the information of the necessary unit pixel 3 is possible by directly addressing the unit pixel 3 to be read out.

  Further, in the communication / timing control unit 20 of the first embodiment, the clock CLK1 having the same frequency as the master clock (master clock) CLK0 input via the terminal 5a, or a clock obtained by dividing the clock CLK1 by two or more is divided. A low-speed clock is supplied to each part in the device, for example, the horizontal scanning circuit 12, the vertical scanning circuit 14, and the column processing unit 26. Hereinafter, the clocks divided by two and the clocks having a frequency lower than that are collectively referred to as a low-speed clock CLK2.

  The vertical scanning circuit 14 selects a row of the pixel unit 10 and supplies a necessary pulse to the row. For example, a vertical decoder 14a that defines a readout row in the vertical direction (selects a row of the pixel unit 10), and a row control line 15 for the unit pixel 3 on the readout address (in the row direction) defined by the vertical decoder 14a. And a vertical drive circuit 14b for driving by supplying a pulse. Note that the vertical decoder 14a selects a row for electronic shutter, in addition to a row from which a signal is read.

  The horizontal scanning circuit 12 sequentially selects the column AD circuit 25 of the column processing unit 26 in synchronization with the low-speed clock CLK2, and guides the signal to a horizontal signal line (horizontal output line) 18. For example, a horizontal decoder 12a that defines a horizontal readout column (selects each column AD circuit 25 in the column processor 26), and each of the column processors 26 according to a read address defined by the horizontal decoder 12a. A horizontal drive circuit 12b for guiding a signal to the horizontal signal line 18. For example, if the number of horizontal signal lines 18 is n (n is a positive integer) handled by the column AD circuit 25, for example, 10 (= n) bits, 10 horizontal signal lines 18 are arranged corresponding to the number of bits. .

  In the solid-state imaging device 1 having such a configuration, the pixel signal output from the unit pixel 3 is supplied to the column AD circuit 25 of the column processing unit 26 via the vertical signal line 19 for each vertical column.

  Each column AD circuit 25 of the column processing unit 26 receives a pixel signal for one column and processes the signal. For example, each column AD circuit 25 has an ADC (Analog Digital Converter) circuit that converts an analog signal into, for example, 10-bit digital data using, for example, a low-speed clock CLK2.

  Although the details of the configuration of the ADC circuit will be described later, the ramp-like reference signal (reference voltage) RAMP is supplied to the comparator (voltage comparator), and at the same time, counting with the clock signal is started. A / D conversion is performed by counting until the pulse signal is obtained by comparing the analog pixel signal input via the reference signal RAMP.

  At this time, by devising the circuit configuration, the signal level (noise level) immediately after the pixel reset and true (for the voltage mode pixel signal input via the vertical signal line 19 as well as AD conversion) are true ( It is possible to perform processing for obtaining a difference from the signal level Vsig (in accordance with the amount of received light). Thereby, it is possible to remove a noise signal component called fixed pattern noise (FPN) or reset noise.

  The pixel data digitized by the column AD circuit 25 is transmitted to the horizontal signal line 18 through a horizontal selection switch (not shown) driven by a horizontal selection signal from the horizontal scanning circuit 12, and further input to the output circuit 28. The Note that 10 bits is an example, and other bit numbers such as less than 10 bits (for example, 8 bits) and more than 10 bits (for example, 14 bits) may be used.

  With such a configuration, pixel signals are sequentially output for each vertical column for each row from the pixel unit 10 in which light receiving elements as charge generation units are arranged in a matrix. Then, one image corresponding to the pixel unit 10 in which the light receiving elements are arranged in a matrix, that is, a frame image, is shown as a set of pixel signals of the entire pixel unit 10.

<Details of reference signal generator and column AD circuit>
The reference signal generation unit 27 includes a DA converter circuit (DAC: Digital Analog Converter) 27a, and is stepped in synchronization with the count clock CK0 based on the control data CN4 from the communication / timing control unit 20. A sawtooth wave (ramp waveform) is generated, and the generated sawtooth wave is supplied to each column AD circuit 25 of the column processing unit 26 as a reference voltage (ADC standard signal) for AD conversion. It has become. Although illustration is omitted, a filter for preventing noise may be provided.

  This step-like sawtooth wave is generated based on a high-speed clock from the clock conversion unit 23, for example, a multiplication clock generated by a multiplication circuit, and thus based on the master clock CLK0 input via the terminal 5a. It can be changed faster than it generates.

  The control data CN4 supplied from the communication / timing controller 20 to the DA converter circuit 27a of the reference signal generator 27 has a digital data change rate with respect to time so that the ramp voltage for each comparison process has the same slope (change rate). To be the same. Specifically, the count value is preferably changed by 1 every unit time.

  The column AD circuit 25 includes the reference signal RAMP generated by the DA conversion circuit 27a of the reference signal generation unit 27 and the vertical signal line 19 (V0, V1) from the unit pixel 3 for each row control line 15 (H0, H1,...). ,...), And a counter unit 254 that counts the time until the voltage comparison unit 252 completes the comparison process and holds the result. And has an n-bit AD conversion function.

  The communication / timing control unit 20 functions as a control unit that switches the count processing mode in the counter unit 254 according to which of the reset component ΔV and the signal component Vsig of the pixel signal the voltage comparison unit 252 is performing comparison processing. have.

  Switching control for instructing the counter unit 254 of each column AD circuit 25 from the communication / timing control unit 20 in addition to the clock CK0, whether the counter unit 254 operates in the down-count mode or the up-count mode. A signal SL and a switching control signal FL for maintaining the continuity of the count value when the count mode of up-counting and down-counting is switched are input.

  One input terminal RAMP of the voltage comparison unit 252 receives the step-like reference signal RAMP generated by the reference signal generation unit 27 in common with the input terminal RAMP of the other voltage comparison unit 252, and inputs to the other input terminal. Are connected to the vertical signal lines 19 of the corresponding vertical columns, and the pixel signal voltages from the pixel unit 10 are individually inputted. The output signal of the voltage comparison unit 252 is supplied to the counter unit 254.

  The count clock CK0 from the communication / timing control unit 20 is input to the clock terminal CK of the counter unit 254 in common with the clock terminals CK of the other counter units 254.

  The counter unit 254 is not shown in its configuration, but can be realized by changing the wiring form of the data storage unit 255 configured by the latch shown in FIG. An internal count is performed by inputting CK0. Similarly to the stepped voltage waveform, the count clock CK0 is generated based on a high-speed clock (for example, a multiplied clock) from the clock conversion unit 23, so that the count clock CK0 is faster than the master clock CLK0 input through the terminal 5a. be able to.

  An n-bit counter unit 254 can be realized by a combination of n latches, which is halved with respect to the circuit scale of the data storage unit 255 configured by n latches of two systems shown in FIG. In addition, since the counter unit 24 is not required, the overall configuration is significantly more compact than the configuration shown in FIG.

  Here, the counter unit 254 of the first embodiment switches between a down-count operation and an up-count operation using a common up-down counter (U / D CNT) regardless of the count mode, as will be described in detail later. It is characterized in that it is configured to be able to perform a counting process (specifically alternately).

  The counter unit 254 of the first embodiment uses an asynchronous counter whose count output value is output asynchronously to the count clock CK0. Specifically, a circuit having the counter circuit 400 of the first embodiment described in FIGS. 1 to 4 as a basic element is used.

  In the case of a synchronous counter, the operation of all flip-flops (basic elements of the counter) is limited by the count clock CK0, whereas in the asynchronous counter, the operation limiting frequency of the first flip-flop (basic element of the counter) is limited. Suitable for high-speed operation because it is determined only by the limit frequency. Therefore, when higher frequency operation is required, it is preferable to use an asynchronous counter as the counter unit 254.

  A control pulse is input to the counter unit 254 from the horizontal scanning circuit 12 through the control line 12c. The counter unit 254 has a latch function for holding the count result, and holds the counter output value until an instruction by a control pulse through the control line 12c is given.

  As described above, the column AD circuit 25 having such a configuration is arranged for each vertical signal line 19 (V0, V1,...), And a column processing unit 26 that is an ADC block having a column parallel configuration is configured. The

  The output side of each column AD circuit 25 is connected to the horizontal signal line 18. As described above, the horizontal signal line 18 has a signal line corresponding to the n-bit width which is the bit width of the column AD circuit 25, and passes through n sense circuits corresponding to the respective output lines (not shown). Then, the output circuit 28 is connected.

  In such a configuration, the column AD circuit 25 performs a count operation in the pixel signal readout period and outputs a count result at a predetermined timing. That is, first, the voltage comparison unit 252 compares the ramp waveform voltage from the reference signal generation unit 27 with the pixel signal voltage input via the vertical signal line 19, and if both voltages are the same, the voltage comparison The comparator output of the unit 252 is inverted (in this example, transition from H level to L level).

  The counter unit 254 starts the count operation in the down-count mode or the up-count mode in synchronization with the ramp waveform voltage generated from the reference signal generation unit 27, and the counter unit 254 is notified of the inverted information of the comparator output. Then, the count operation is stopped and the AD conversion is completed by latching (holding / storing) the count value at that time as pixel data.

  Thereafter, the counter unit 254 sequentially stores the stored and held pixel data based on the shift operation by the horizontal selection signal CH (i) input from the horizontal scanning circuit 12 via the control line 12c at a predetermined timing. The data is output from the output terminal 5 c to the outside of the column processing unit 26 and the chip having the pixel unit 10.

  Although not specifically illustrated because it is not directly related to the description of the present embodiment, other various signal processing circuits may be included in the components of the solid-state imaging device 1.

<Configuration Example of Counter Unit; First Example>
FIG. 12 is a circuit block diagram illustrating a first configuration example of the counter unit 254. In this first example, the basic configuration of the asynchronous counter is the same as that of the counter circuit 400 of the first embodiment described with reference to FIGS. 1 to 4, but the counter circuit 400 of the first embodiment shown in FIG. 1 is characterized in that a gate circuit for controlling the input of the clock signal to the clock terminal CK of the first stage flip-flop 412 based on the comparison result of the voltage comparator 252 is added.

  Specifically, the counter unit 254 of the first example includes a 2-input type AND (logical product) gate 472, and its output is connected to the clock terminal of the flip-flop 412 in the first stage. The comparison result of the voltage comparator 252 is input to one input terminal of the AND gate 472, and the counter clock CK 0 is input from the communication / timing controller 20 to the other input terminal.

  With such a configuration, the input clock to the clock terminal of the flip-flop 412 in the first stage becomes a logical product (AND) of the output of the voltage comparison unit 252 and the counter clock CK0, and thus, in the comparison period by the voltage comparison unit 252. It is possible to count accordingly.

  That is, the communication / timing control unit 20 supplies the control data CN4 and the count clock CK0 to the reference signal generation unit 27 in order to activate the generation of the reference signal RAMP by the reference signal generation unit 27. The reference signal generation unit 27 starts a count operation in synchronization with the count clock CK0 from an initial value corresponding to the control data CN4, and generates a stepped ramp waveform by decreasing the voltage at a predetermined stage for each clock. This is supplied to the voltage comparator 252 as a reference signal RAMP.

  The voltage comparison unit 252 searches for a point where the ramp-shaped reference signal RAMP and the voltage of each of the reference component and the signal component in the pixel signal from the unit pixel 3 match, and if they match, sets the comparison output to a low level. .

  The counter unit 254 is commonly supplied with the counter clock CK0 supplied to the reference signal generation unit 27. The AND gate 262 gates the counter clock CK0 with the comparison output supplied from the voltage comparison unit 252.

  In this way, when the reference signal RAMP used for the comparison becomes smaller than the voltage corresponding to the reference component or signal component in the pixel signal, the count clock supplied to the first flip-flop 412 of the asynchronous counter circuit 400 is Since it is stopped, no further counting operation is performed. Therefore, the value finally written in each flip-flop 410 is a value obtained by converting the voltage corresponding to the reference component or signal component in the pixel signal into a digital value.

  In other words, the counter unit 254 starts from the generation time of the ramp waveform reference signal RAMP used in the comparison process in the voltage comparison unit 252 until the signal corresponding to the reference component or the signal component in the pixel signal matches the reference signal RAMP. Is counted with the count clock CK0, so that digital data corresponding to the size of the reference component and the signal component can be obtained.

<Configuration Example of Counter Unit; Second Example>
FIG. 13 is a circuit block diagram (FIG. 13A) showing a second configuration example of the counter unit 254 and a timing chart (FIG. 13B) for explaining the operation thereof. In the second example, the basic configuration of the asynchronous counter is the same as that of the counter circuit 400 of the first embodiment shown in FIG. 2 as in the first example, but the asynchronous counter is connected to the clock terminal CK of the flip-flop 412 in the first stage. A positive edge type D flip-flop 474 and a delay circuit 476 are added before the AND gate 472 for controlling the input of the clock signal.

  The delay circuit 476 may be any circuit that can delay the counter clock CK0 from the communication / timing control unit 20 by a predetermined period (for example, within a range of one clock) as shown in FIG. Various known circuit configurations such as gate delay can be used.

  The comparison result of the voltage comparison unit 252 is input to the D input terminal of the D flip-flop 474, the counter clock CK 0 is input from the communication / timing control unit 20 to the clock terminal CK, and the non-inverted output Q is the AND gate 472. The signal is input to one input terminal. As a result, as shown in FIG. 13B, the output of the D-type flip-flop 474 is output in synchronization with the rising edge of the counter clock CK0.

  The counter clock CK 0 is input from the communication / timing control unit 20 to the other input terminal of the AND gate 472 via the delay circuit 476. The output of the AND gate 472 is connected to the clock terminal of the first stage flip-flop 412.

  In the configuration of the first example, the AND gate 472 is used as a functional element for controlling the input of the clock signal to the clock terminal CK of the flip-flop 412 at the first stage, but such a simple logical product (AND) is used. In such a case, there is a possibility that a glitch or other noise may be caused by a timing shift.

  On the other hand, as in the configuration of the second example, the comparator output is synchronized with the edge of the counter clock CK0 (rising edge in this example), and the logical product (AND) is taken to obtain the voltage comparator 252. This comparison result can be taken into the clock terminal of the first flip-flop 412 in synchronization with the counter clock CK0, and the risk of the influence of glitches and the like is reduced, which is more preferable.

  The counter unit 254 shown in FIGS. 12 and 13 uses the counter circuit 400 of the first embodiment shown in FIG. 2 as the basic configuration of the asynchronous counter, but the counter of the second and third embodiments. Even when the circuits 400 and 500 are used, a similar asynchronous up / down counter can be easily configured based on the same concept.

<Operation of Solid-State Imaging Device; First Embodiment>
FIG. 14 is a timing chart for explaining the operation in the column AD circuit 25 of the solid-state imaging device 1 of the first embodiment shown in FIG. As a mechanism for converting an analog pixel signal sensed by each unit pixel 3 of the pixel unit 10 into a digital signal, for example, a ramp-wave reference signal RAMP descending with a predetermined inclination and a pixel signal from the unit pixel 3 are used. Search for a point where the voltages of the reference component and signal component match, and from the time when the reference signal RAMP used in this comparison processing is generated to the time when the signal corresponding to the reference component or signal component in the pixel signal matches the reference signal Is counted with a count clock to obtain a count value corresponding to each size of the reference component and the signal component.

  Here, the pixel signal output from the vertical signal line 19 is such that the signal component Vsig appears after the reset component ΔV including the noise of the pixel signal as a reference component as a time series. When the first process is performed on the reference component (reset component ΔV), the second process is performed on a signal obtained by adding the signal component Vsig to the reference component (reset component ΔV). This will be specifically described below.

  For the first reading, the communication / timing control unit 20 first resets the count value of the counter unit 254 to the initial value “0” and sets the switching control signal SL to low level to put the counter unit 254 in the down-count mode. Set. Then, after the first reading from the unit pixel 3 in any row Hx to the vertical signal lines 19 (V0, V1,...) Is stabilized, the communication / timing control unit 20 is directed toward the reference signal generation unit 27. The control data CN4 for generating the reference signal RAMP is supplied.

  In response to this, the reference signal generation unit 27 forms a stepped waveform (RAMP waveform) that is time-varying in a sawtooth shape (RAMP shape) as a whole as a comparison voltage to one input terminal RAMP of the voltage comparison unit 252. input. The voltage comparison unit 252 compares the RAMP waveform comparison voltage with the pixel signal voltage of an arbitrary vertical signal line 19 (Vx) supplied from the pixel unit 10.

  Simultaneously with the input of the reference signal RAMP to the input terminal RAMP of the voltage comparator 252, the reference signal generator 27 emits the comparison time in the voltage comparator 252 to be measured by the counter unit 254 arranged for each row. In synchronization with the ramp waveform voltage (t10), the count clock CK0 is input from the communication / timing control unit 20 to the clock terminal of the counter unit 254, and down-counting is started from the initial value “0” as the first count operation. . That is, the count process is started in the negative direction.

  The voltage comparison unit 252 compares the ramp-shaped reference signal RAMP from the reference signal generation unit 27 with the pixel signal voltage Vx input via the vertical signal line 19, and when both voltages become the same, The comparator output is inverted from H level to L level (t12). That is, the voltage signal corresponding to the reset component Vrst is compared with the reference signal RAMP, and an active-low (L) pulse signal is generated after a time corresponding to the magnitude of the reset component Vrst and supplied to the counter unit 254. To do.

  In response to this result, the counter unit 254 stops the counting operation almost simultaneously with the inversion of the comparator output, and latches (holds / stores) the count value at that time as pixel data, thereby completing the AD conversion (t12). . In other words, down-counting is started with the generation of the ramp-shaped reference signal RAMP supplied to the voltage comparison unit 252, and counting (counting) with the clock CK0 until an active-low (L) pulse signal is obtained by the comparison process, A count value corresponding to the magnitude of the reset component Vrst is obtained.

  When a predetermined down-count period has elapsed (t14), the communication / timing control unit 20 stops supplying control data to the voltage comparison unit 252 and supply of the count clock CK0 to the counter unit 254. As a result, the voltage comparison unit 252 stops generating the ramp-shaped reference signal RAMP.

  In the first reading, the reset level Vrst in the pixel signal voltage Vx is detected by the voltage comparison unit 252 and the count operation is performed. Therefore, the reset component ΔV of the unit pixel 3 is read.

  The reset component ΔV includes noise that varies for each unit pixel 3 as an offset. However, since the variation of the reset component ΔV is generally small and the reset level Vrst is generally common to all pixels, the output value of the reset component ΔV in the pixel signal voltage Vx of the arbitrary vertical signal line 19 is approximately known.

  Therefore, at the time of reading the reset component ΔV for the first time, it is possible to shorten the down-count period (t10 to t14; comparison period) by adjusting the RAMP voltage. In this embodiment, the comparison of the reset component ΔV is performed by setting the longest period of the comparison process for the reset component ΔV to a count period (128 clocks) of 7 bits.

  In the subsequent second reading, in addition to the reset component ΔV, the signal component Vsig corresponding to the amount of incident light for each unit pixel 3 is read, and the same operation as the first reading is performed. That is, first, the communication / timing control unit 20 sets the switching control signal SL to a high level and sets the counter unit 254 to the up-count mode (t16).

  Here, as described above, when switching from the down count mode to the up count mode, the count value is destroyed and the continuity of the count value cannot be maintained, and the count mode is switched. It is impossible to count down / up continuously while maintaining the count value before and after.

  Therefore, prior to the supply of the count clock CK0 for starting the comparison process and the count operation in the up-count mode, an active H one-shot pulse is supplied to the counter unit 254 as the switching control signal FL (t17 to t18). . As a result, the clock terminal of the flip-flop 410 constituting the counter unit 254 that is an asynchronous counter is once forcedly set to the high level and then returned to the state after the mode switching. As a result, as described above, the count value changed at the time of switching from the down count to the up count returns to the original count value.

  Then, after the second reading from the unit pixel 3 of the arbitrary row Hx to the vertical signal line 19 (V0, V1,...) Is stabilized, the communication / timing control unit 20 moves toward the reference signal generation unit 27. Control data CN4 for generating the reference signal RAMP is supplied together with the clock CK0.

  In response to this, the reference signal generation unit 27 forms a stepped waveform (RAMP waveform) that is time-varying in a sawtooth shape (RAMP shape) as a whole as a comparison voltage to one input terminal RAMP of the voltage comparison unit 252. input. The voltage comparison unit 252 compares the RAMP waveform comparison voltage (reference signal RAMP) with the pixel signal voltage of an arbitrary vertical signal line 19 (Vx) supplied from the pixel unit 10.

  Simultaneously with the input of the reference signal RAMP to the input terminal RAMP of the voltage comparator 252, the reference signal generator 27 emits the comparison time in the voltage comparator 252 to be measured by the counter unit 254 arranged for each row. In synchronization with the ramp waveform voltage (t20), the count clock CK0 is input from the communication / timing control unit 20 to the clock terminal of the counter unit 254, and the unit pixel 3 acquired at the time of the first reading is obtained as the second counting operation. In contrast to the first time, up-counting is started from the count value corresponding to the reset component ΔV. That is, the count process starts in the positive direction.

  The voltage comparison unit 252 compares the ramp-shaped reference signal RAMP from the reference signal generation unit 27 with the pixel signal voltage Vx input via the vertical signal line 19, and when both voltages become the same, The comparator output is inverted from H level to L level (t22). That is, the voltage signal corresponding to the signal component Vsig is compared with the reference signal RAMP, and an active low (L) pulse signal is generated after a time corresponding to the magnitude of the signal component Vsig, and supplied to the counter unit 254. To do.

  In response to this result, the counter unit 254 stops the counting operation almost simultaneously with the inversion of the comparator output, and latches (holds / stores) the count value at that time as pixel data, thereby completing the AD conversion (t22). . In other words, down-counting is started with the generation of the ramp-shaped reference signal RAMP supplied to the voltage comparison unit 252, and counting (counting) with the clock CK0 until an active-low (L) pulse signal is obtained by the comparison process, A count value corresponding to the magnitude of the signal component Vsig is obtained.

  When the predetermined down-count period has elapsed (t24), the communication / timing control unit 20 stops the supply of control data to the voltage comparison unit 252 and the supply of the count clock CK0 to the counter unit 254. As a result, the voltage comparison unit 252 stops generating the ramp-shaped reference signal RAMP.

  At the time of the second reading, the signal component Vsig in the pixel signal voltage Vx is detected by the voltage comparison unit 252 and the counting operation is performed. Therefore, the signal component Vsig of the unit pixel 3 is read out.

  Here, in the present embodiment, the counting operation in the counter unit 254 is down-counting at the first reading, and up-counting at the second reading, and therefore, automatically in the counter unit 254, using equation (1) The count value corresponding to the subtraction result is held in the counter unit 254.

  Here, equation (1) can be transformed into equation (2). As a result, the count value held in the counter unit 254 is in accordance with the signal component Vsig.

  That is, as described above, each unit pixel 3 is subtracted in the counter unit 254 by two readings and counting processes, such as down-counting at the first reading and up-counting at the second reading. The reset component ΔV including variation and the offset component for each column AD circuit 25 can be removed, and only the signal component Vsig corresponding to the amount of incident light for each unit pixel 3 can be extracted with a simple configuration. At this time, there is an advantage that reset noise can also be removed.

  Therefore, the column AD circuit 25 of the present embodiment operates not only as a digital conversion unit that converts an analog pixel signal into digital pixel data but also as a CDS (Correlated Double Sampling) processing function unit. It will be.

  In addition, since the pixel data indicated by the count value obtained by Expression (2) indicates a positive signal voltage, a complement calculation or the like is unnecessary, and the compatibility with existing systems is high.

  Here, at the time of the second reading, the signal component Vsig corresponding to the amount of incident light is read out. Therefore, in order to determine the amount of light in a wide range, a wide up-count period (t20 to t24; comparison period) is taken, and the voltage It is necessary to change the lamp voltage supplied to the comparison unit 252 greatly.

  Therefore, in the present embodiment, the comparison of the signal component Vsig is performed by setting the longest comparison period for the signal component Vsig to a count period of 10 bits (1024 clocks). That is, the longest period of the comparison process for the reset component ΔV (reference component) is made shorter than the longest period of the comparison process for the signal component Vsig. The longest period of comparison processing of both the reset component ΔV (reference component) and the signal component Vsig, that is, the maximum value of the AD conversion period is not made the same, but the longest period of comparison processing for the reset component ΔV (reference component) is signaled. By making it shorter than the longest period of the comparison process for the component Vsig, the total AD conversion period of two times is devised.

  In this case, although the number of comparison bits is different between the first time and the second time, control data is supplied from the communication / timing control unit 20 to the reference signal generation unit 27, and the reference signal generation unit 27 based on the control data By generating the ramp voltage, the slope of the ramp voltage, that is, the rate of change of the reference signal RAMP is made the same for the first time and the second time. Since the ramp voltage is generated by digital control, it is easy to make the slope of the ramp voltage the same at the first time and the second time. As a result, the precision of AD conversion can be made equal, so that the subtraction result represented by the expression (1) by the up / down counter can be obtained correctly.

  At a predetermined timing after the second count process is completed (t28), the communication / timing control unit 20 instructs the horizontal scanning circuit 12 to read out pixel data. In response, the horizontal scanning circuit 12 sequentially shifts the horizontal selection signal CH (i) supplied to the counter unit 254 via the control line 12c.

  In this way, the count value represented by the expression (2) stored and held in the counter unit 254, that is, the pixel data represented by n-bit digital data is sequentially transferred via the n horizontal signal lines 18. Video data D1 representing a two-dimensional image is obtained by outputting from the output terminal 5c to the outside of the column processing unit 26 or the chip having the pixel unit 10 and then repeating the same operation for each row.

  As described above, according to the solid-state imaging device of the first embodiment, the count process is performed twice by switching the processing mode while using the asynchronous up / down counter. Further, in the configuration in which the unit pixels 3 are arranged in a matrix, the column AD circuit 25 is configured by a column parallel column AD circuit provided for each vertical column.

  By using the asynchronous counter, the operation limit frequency is determined only by the limit frequency of the first flip-flop, so that high-speed operation is possible. Even if the difference signal component between the reference component and the signal component is converted into digital data by performing AD conversion twice, the total AD conversion processing can be operated at high speed, and the AD conversion period is shortened. can do.

  In addition, a subtraction process between the reference component (reset component) and the signal component can be directly obtained for each vertical column as the second count result, and a memory device that holds the respective count results of the reference component and the signal component is provided. This can be realized by a latch function provided in the counter unit, and it is not necessary to prepare a dedicated memory device for holding AD converted data separately from the counter.

  Furthermore, a special subtracter for taking the difference between the reference component and the signal component is not necessary. Therefore, the circuit scale and circuit area can be reduced as compared with the conventional configuration, and in addition, an increase in noise and an increase in current or power consumption can be eliminated.

  In addition, since the column AD circuit (AD conversion unit) is configured by the comparison unit and the counter unit, the count process can be controlled by one count clock for operating the counter unit and a control line for switching the count mode regardless of the number of bits. A signal line for guiding the count value of the counter unit required in the conventional configuration to the memory device becomes unnecessary, and an increase in noise and an increase in power consumption can be solved.

  That is, in the solid-state imaging device 1 in which the AD conversion device is mounted on the same chip, the voltage comparison unit 252 and the counter unit 254 are paired to configure the column AD circuit 25 as an AD conversion unit, and the operation of the counter unit 254 By using a combination of down-counting and up-counting as a digital data, the difference between the basic component of the signal to be processed (the reset component in this embodiment) and the signal component is converted into digital data. Alternatively, problems such as the number of interface wirings with other functional units, noise and current consumption due to the wirings can be solved.

<Configuration of Solid-State Imaging Device; Second Embodiment>
FIG. 15 is a schematic configuration diagram of a CMOS solid-state imaging device (CMOS image sensor) according to the second embodiment of the present invention. In the solid-state imaging device 1 of the second embodiment, the configuration of the column AD circuit 25 is modified with respect to the solid-state imaging device 1 of the first embodiment.

  That is, the column AD circuit 25 according to the second embodiment includes a data storage unit 256 as an n-bit memory device that holds a count result held by the counter unit 254, a counter unit 254, and data after the counter unit 254 A switch 258 disposed between the storage unit 256 and the storage unit 256.

  A memory transfer instruction pulse CN8 as a control pulse is supplied to the switch 258 from the communication / timing control unit 20 at a predetermined timing in common with the switches 258 in the other vertical columns. When the memory transfer instruction pulse CN8 is supplied, the switch 258 transfers the count value of the corresponding counter unit 254 to the data storage unit 256. The data storage unit 256 holds and stores the transferred count value.

  Note that the mechanism for holding the count value of the counter unit 254 in the data storage unit 256 at a predetermined timing is not limited to the configuration in which the switch 258 is disposed between them, and for example, the counter unit 254 and the data storage unit 256 are directly connected. While being connected, the output enable of the counter unit 254 can be realized by controlling the memory transfer instruction pulse CN8, or the memory transfer instruction pulse CN8 is used as a latch clock for determining the data take-in timing of the data storage unit 256. But it can be realized.

  A control pulse is input to the data storage unit 256 from the horizontal scanning circuit 12 through the control line 12c. The data storage unit 256 holds the count value fetched from the counter unit 254 until there is an instruction by a control pulse through the control line 12c.

  The horizontal scanning circuit 12 reads the count value held by each data storage unit 256 in parallel with the voltage comparison unit 252 and the counter unit 254 of the column processing unit 26 performing the processing that they are responsible for. It has the function of a readout scanning unit.

  According to the configuration of the second embodiment, since the count result held by the counter unit 254 can be transferred to the data storage unit 256, the count operation of the counter unit 254, that is, AD conversion processing, and the count result The reading operation to the horizontal signal line 18 can be controlled independently, and a pipeline operation in which AD conversion processing and signal reading operation to the outside are performed in parallel can be realized.

<Operation of Solid-State Imaging Device; Second Embodiment>
FIG. 16 is a timing chart for explaining the operation in the column AD circuit 25 of the solid-state imaging device 1 of the second embodiment shown in FIG. The AD conversion processing in the column AD circuit 25 is the same as that in the first embodiment. The detailed explanation is omitted here.

  In the second embodiment, a data storage unit 256 is added to the configuration of the first embodiment, and the basic operation including AD conversion processing is the same as that of the first embodiment. Before the operation of 254 (t30), based on the memory transfer instruction pulse CN8 from the communication / timing control unit 20, the count result of the preceding row Hx-1 is transferred to the data storage unit 256.

  In the first embodiment, since the pixel data can be output outside the column processing unit 26 only after the second reading process, that is, the AD conversion process is completed, the reading process is limited. In the configuration of the second embodiment, the count value indicating the result of the previous subtraction process is transferred to the data storage unit 256 prior to the first read process (AD conversion process). Absent.

  By doing so, the signal output operation from the data storage unit 256 to the outside through the horizontal signal line 18 and the output circuit 28 can be performed in parallel with the reading of the current Hx and the counting operation of the counter unit 254. Efficient signal output is possible.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such changes or improvements are added are also included in the technical scope of the present invention.

  Further, the above embodiments do not limit the invention according to the claims (claims), and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, as long as an effect is obtained, a configuration from which these some constituent requirements are deleted can be extracted as an invention.

  For example, in the above embodiment, as a mechanism for returning the count value changed at the time of switching the count mode to the original count value, the clock terminal of the flip-flop (latch), which is a basic element of the counter, is forcibly set to a high level (negative edge type). ) Or low level (positive edge type) and then returned to the state after mode switching, but the mechanism for returning the count value changed at the time of count mode switching back to the original count value is not necessarily like this It is not limited to anything.

  For example, FIG. 17 is a diagram illustrating another configuration example of a mechanism for restoring the count value destroyed when the count mode is switched. First, as a basic configuration of the asynchronous counter, a counter circuit 600 having a configuration in which an arbitrary initial value can be loaded using a known technique is used.

  For example, it is assumed that the counter circuit 600 includes a flip-flop group 610 having a flip-flop (latch) (not shown) and a latch 620 therein. In the figure, an example corresponding to 4 bits is shown.

  Each inverted output NQn of the flip-flop (latch) group 610 constituting the counter circuit 600 which is an asynchronous counter is inputted to the D terminal (D0 to D3) of its own flip-flop (not shown) constituting the flip-flop group 610. Further, each non-inverted output Qn of the flip-flop group 610 constituting the asynchronous counter is input to the D terminal (D0 to D3) of the latch 620 (four-stage configuration in the figure). Each non-inverted output of the latch 620 is input to the corresponding data setting terminals Din0 to Din3 of the flip-flop group 610.

  Each non-inverted output Qn of the flip-flop (latch) group 610 constituting the asynchronous counter is latched by the corresponding clock CKx by the latch 620 (four-stage configuration in the figure), thereby maintaining the state one clock before. Here, the corresponding clock CKx means a clock input to a clock terminal of each flip-flop (latch) (not shown) constituting the flip-flop group 610. Depending on the count mode, either the non-inverted output or the inverted output of the preceding flip-flop is selected.

  After the count mode is switched by the switching control signal SL, the switching control signal FL is input to the load terminal LD of the flip-flop group 610, whereby the data held in the latch 620 is written to the flip-flop group 610, that is, initial Set the value. By doing so, the count value immediately before the count value changed when the count mode is switched is set in the flip-flop group 610. That is, it returns to the count value immediately before switching the count mode, which is the state before the count value is changed. Thus, since the count value before the count mode switching can be held, the count can be continuously performed after the mode switching while maintaining the continuity of the count value.

  In this way, the subtraction process between the reference component and the signal component can be performed directly, and a special adder circuit for taking the difference between the reference component and the signal component becomes unnecessary. In addition, data transfer to the subtracter becomes unnecessary, and an increase in noise and an increase in current or power consumption can be eliminated.

  In the above embodiment, the edge trigger type flip-flop is used as the basic element of the counter. However, a level trigger type flip-flop may be used.

  In the above-described embodiment, the column AD circuit 25 including the voltage comparison unit 252 and the counter unit 254 is provided for each vertical column and is converted into digital data for each vertical column. By providing all the switching circuits, one column AD circuit 25 may be arranged for a plurality of vertical columns.

  In the above-described embodiment, the AD conversion function unit is provided in the column region located on the reading side of the pixel unit 10. However, the AD conversion function unit may be provided in other locations. For example, a configuration may be adopted in which pixel signals are output in analog up to the horizontal signal line 18, and then AD conversion is performed and passed to the output circuit 28.

  Even in this case, the AD conversion reference signal, the reference component, and the signal to be processed including the signal component are compared, and in parallel with this comparison processing, either the down count mode or the up count mode is selected. When the count processing is performed in this mode and the count value at the time when the comparison processing is completed is held, the count processing mode is switched according to which of the reference component and the signal component is compared, thereby Digital data representing the difference between the component and the signal component can be obtained as a result of the count processing in the two modes of the down count mode and the up count mode.

  As a result, a memory device that holds the count results of the reference component and the signal component can be realized by a latch function provided in the counter unit, and it is necessary to prepare a dedicated memory device that holds AD converted data separately from the counter. Absent. One AD conversion function unit may be provided for all vertical columns, and although a high-speed conversion process is required, the circuit scale is smaller than that in the above embodiment.

  In the above-described embodiment, the pixel signal has a signal component Vsig after the reset component ΔV (reference component) for the same pixel as a time series, and the processing unit in the subsequent stage has a positive polarity (a larger signal level indicates a positive value). Corresponding to the signal to be processed, the comparison process and the down-count process are performed for the reset component ΔV (reference component) as the first process, and the comparison process for the signal component Vsig is performed as the second process. Although the up-count process is performed, the combination and processing order of the target signal component and the count mode are arbitrary regardless of the time series in which the reference component and the signal component appear. Depending on the processing procedure, the digital data obtained in the second processing may become a negative value. In such a case, a countermeasure such as a correction operation may be taken.

  Of course, as the device architecture of the pixel unit 10, the reset component ΔV (reference component) must be read after the signal component Vsig, and when the subsequent processing unit processes positive signals, the first time It is efficient to perform the comparison process and the down-count process for the signal component Vsig as the above process, and the comparison process and the up-count process for the reset component ΔV (reference component) as the second process.

  In the above-described embodiment, the sensor composed of unit pixels composed of NMOS has been described as an example. However, the present invention is not limited to this, and the potential relationship is also inverted (the positive / negative of the potential is reversed) for a pixel composed of PMOS. By conversely, it is possible to enjoy the same operations and effects as described in the above embodiment.

  In the above-described embodiment, as an example of a solid-state imaging device that can arbitrarily read signals from individual unit pixels by address control, a CMOS sensor including a pixel unit that generates signal charges by receiving light However, the generation of signal charges is not limited to light, and can be applied to electromagnetic waves such as infrared rays, ultraviolet rays, or X-rays in general, and outputs an analog signal corresponding to the amount of the received electromagnetic waves. The matters described in the above embodiments can be applied to a semiconductor device including unit constituent elements in which a large number of elements are arranged.

  Further, in the above embodiment, a comparison unit that compares a signal corresponding to each of the reference component and the signal component with a reference signal for AD conversion, and down-counting using an asynchronous counter in parallel with the comparison processing in the comparison unit AD converter circuit (AD converter; column in the previous example) that includes a counter unit that performs count processing in either one of the mode and the up-count mode, and that holds a count value at the time when the comparison processing in the comparison unit is completed Although the example of applying the AD circuit) to the solid-state imaging device has been described, the mechanism of the AD conversion circuit described in the above embodiment is not limited to the solid-state imaging device, and converts the difference signal component of two signal components into digital data. Therefore, the present invention can be applied to any electronic device that uses the AD conversion mechanism.

  For example, a true signal is obtained by performing AD conversion using the comparator and the counter described in the above embodiment on the basis of an analog pixel signal captured from the solid-state imaging device 1 outside the solid-state imaging device 1. It is also possible to configure an electronic device that acquires component digital data (pixel data) and performs desired digital signal processing based on the pixel data.

  In addition, the AD conversion circuit (AD conversion device) described in the above embodiment is not limited to be provided by being incorporated in a solid-state imaging device or other electronic devices, but may be, for example, an IC (Integrated Circuit) or AD conversion. It may be provided as a single device, such as a module.

  In this case, it may be provided by an AD conversion device including a comparison unit and an asynchronous counter unit, but a reference signal generation unit that generates a reference signal for AD conversion and supplies the reference signal to the comparison unit or The control unit that switches the count processing mode in the counter unit depending on whether the component or signal component is being compared is also a combination of an IC (integrated circuit) or individual chips arranged on the same semiconductor substrate. It may be provided in a module.

  By incorporating and providing these, it is possible to collectively handle the functional units necessary for controlling the operations of the comparison unit and the asynchronous counter unit, and the handling and management of the members are simplified. In addition, since elements necessary for AD conversion processing are integrated (integrated) as an IC or a module, it becomes easy to manufacture a finished product of a solid-state imaging device or other electronic devices.

1 is a circuit block diagram showing a basic configuration of a first embodiment of an asynchronous counter circuit according to the present invention. It is a circuit block diagram which materialized the basic composition of a 1st embodiment more. It is a figure which shows the circuit structural example of a binary switching part. FIG. 3 is a timing chart for explaining the operation of the counter circuit of the first embodiment shown in FIG. 2. It is a figure explaining the output change of the flip-flop in the structure of 1st Embodiment. It is a circuit block diagram which shows the structure of 2nd Embodiment of the asynchronous counter circuit based on this invention. It is a timing chart for demonstrating operation | movement of the counter circuit of 2nd Embodiment shown in FIG. It is a figure explaining the output change of the flip-flop in 2nd Embodiment. It is a circuit block diagram which shows the structure of 3rd Embodiment of the asynchronous counter circuit based on this invention. It is a timing chart for demonstrating operation | movement of the counter circuit of 3rd Embodiment shown in FIG. 1 is a schematic configuration diagram of a CMOS solid-state imaging device according to a first embodiment of the present invention. It is a circuit block diagram which shows the 1st structural example of a counter part. FIG. 6 is a circuit block diagram (A) showing a second configuration example of the counter unit and a timing chart ((B)) for explaining the operation thereof. 12 is a timing chart for explaining an operation in the column AD circuit of the solid-state imaging device according to the first embodiment shown in FIG. 11; It is a schematic block diagram of the CMOS solid-state imaging device which concerns on 2nd Embodiment of this invention. 16 is a timing chart for explaining the operation in the column AD circuit of the solid-state imaging device of the second embodiment shown in FIG. 15. It is a figure which shows the other structural example of the mechanism which returns a count value at the time of switching of count mode. It is a figure which shows the prior art example of the asynchronous counter which can switch modes. FIG. 19 is a timing chart for explaining the operation of the counter circuit shown in FIG. 18. It is a figure which shows the mechanism proposed by patent document 2. FIG. It is a schematic block diagram of the CMOS solid-state imaging device of the prior art example which mounted AD converter on the same semiconductor substrate as a pixel part. It is a timing chart for demonstrating operation | movement of the solid-state imaging device of the prior art example shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Solid-state imaging device, 3 ... Unit pixel, 7 ... Drive control part, 10 ... Pixel part, 12 ... Horizontal scanning circuit, 14 ... Vertical scanning circuit, 15 ... Row control line, 18 ... Horizontal signal line, 19 ... Vertical signal Line 20, communication / timing control unit 21, timing control unit 23, clock conversion unit, 24, counter unit, 25, column AD circuit, 26, column processing unit, 27, reference signal generation unit, 27 a, DA conversion Circuit, 28 ... Output circuit, 252 ... Voltage comparison unit, 254 ... Counter unit, 256 ... Data storage unit, 258 ... Switch, 400, 500 ... Counter circuit, 410-418, 510-518 ... Flip-flop, 420-426 520 to 526... Three-value switching unit (initial value setting processing unit), 430 to 437, 464, 530 to 537... Binary switching unit, 462.

Claims (25)

An AD conversion method for converting a difference signal component between the reference component and the signal component of an analog processing target signal represented including a reference component and a signal component into digital data,
While using an asynchronous counter circuit configured to selectively operate the count process in the up-count mode and the count process in the down-count mode,
As a first process, a signal corresponding to one of the reference component and the signal component is compared with a reference signal for conversion into the digital data, and in parallel with the comparison process, a counter Based on the clock, the count process is performed in one of the down-count mode and the up-count mode, and the count value at the time when the comparison process is completed is held.
Thereafter, as the second process, the reference component is compared with the other of the reference component and the signal component, and in parallel with the comparison process, the down-count mode and the up-count mode are compared. An AD conversion method characterized in that the count process is performed in the other mode and the count value at the time when the comparison process is completed is held. 2. The AD conversion method according to claim 1, wherein each count process in the down-count mode and the up-count mode is performed by switching the process mode while commonly using an up-down counter. The AD conversion method according to claim 1, wherein the count process in the second process is started from the count value held in the first process. The AD conversion method according to claim 1, wherein the change characteristics of the reference signal are the same for each of the first process and the second process. For the previous signal to be processed, the count value held in the second process is held in another data storage unit,
The processing for reading out the count value from the data storage unit is performed in parallel when performing the first processing and the second processing for the current signal to be processed. 5. The AD conversion method according to any one of 4. The signal to be processed includes, in a unit component, a charge generation unit that generates a charge corresponding to an incident electromagnetic wave and a unit signal generation unit that generates a unit signal according to the charge generated by the charge generation unit, 2. The analog unit signal generated by the unit signal generation unit and output in the column direction in a semiconductor device for physical quantity distribution detection in which the unit constituent elements are arranged in a matrix. The AD conversion method as described in any one of -5. The analog unit signal generated by the unit signal generation unit and output in the column direction is taken in row units,
The AD conversion method according to claim 6, wherein the first process and the second process are performed for each of the unit components in units of rows. An AD conversion device that converts a difference signal component between the reference component and the signal component of an analog processing target signal represented by including a reference component and a signal component into digital data,
A comparison unit that compares a signal corresponding to each of the reference component and the signal component with a reference signal for conversion to the digital data;
In parallel with the comparison process in the comparison unit, the count process is performed in one of the down-count mode and the up-count mode based on the counter clock, and the count value when the comparison process in the comparison unit is completed is calculated. An A / D conversion apparatus comprising: an asynchronous counter unit for holding. The AD converter according to claim 8, wherein the counter unit includes a gate circuit that controls input of the count clock based on a comparison output supplied from the comparison unit. The AD conversion apparatus according to claim 8, further comprising a reference signal generation unit that generates a reference signal for conversion into the digital data and supplies the reference signal to the comparison unit. The timing control unit which switches the mode of the counting process in the counter unit according to which of the reference component and the signal component the comparison unit is performing the comparison process. The AD conversion apparatus as described in any one of 8-10. The counter section is configured by a common counter circuit, and is configured to be switchable between the up-count mode and the down-count mode. The AD converter described. The counter unit has an initial value setting processing unit for starting a count process after mode switching after initial setting of a count value immediately before mode switching at the time of switching the count mode,
The said timing control part controls the said initial value setting process part, The said count process in a 2nd process is started from the count value hold | maintained in the 1st process. 11. The AD conversion apparatus according to 11. The AD converter according to claim 10, wherein the reference signal generation unit makes the change characteristics of the reference signal the same for each of the first process and the second process. A data storage unit that holds the count value held by the counter unit for the previous processing target signal;
For the current signal to be processed, the comparison unit and the counter unit further include a reading scanning unit that reads the count value from the data storage unit in parallel with performing the processing each of them is in charge of. The AD conversion apparatus according to claim 8, wherein the AD conversion apparatus is characterized in that A unit for generating an analog unit signal that includes a reference component and a signal component according to the charge generated by the charge generation unit that generates a charge corresponding to the incident electromagnetic wave and the charge generated by the charge generation unit Is a semiconductor device for detecting a physical quantity distribution in which a unit component is included in a unit component and the unit component is arranged in a matrix,
A comparison unit that compares a reference signal for generating digital data of the signal component and a signal corresponding to each of the reference component and the signal component;
In parallel with the comparison process in the comparison unit, the count process is performed in one of the down-count mode and the up-count mode based on the counter clock, and the count value when the comparison process in the comparison unit is completed is calculated. A semiconductor device comprising: an asynchronous counter unit for holding. The semiconductor device according to claim 16, further comprising: a reference signal generation unit that generates a reference signal for conversion into the digital data and supplies the reference signal to the comparison unit. The timing control unit which switches the mode of the counting process in the counter unit according to which of the reference component and the signal component the comparison unit is performing the comparison process. The semiconductor device according to 16 or 17. The counter section includes a common counter circuit, and is configured to be able to switch between the up-count mode and the down-count mode. The semiconductor device described. The counter unit has an initial value setting processing unit for starting a count process after mode switching after initial setting of a count value immediately before mode switching at the time of switching the count mode,
The said timing control part controls the said initial value setting process part, The said count process in a 2nd process is started from the count value hold | maintained in the 1st process. 18. The semiconductor device according to 18. 21. A plurality of AD conversion units configured to include the comparison unit and the counter unit are provided in a row direction, which is a column arrangement direction of the unit component elements. The semiconductor device according to any one of the above. A data storage unit that holds the count value held by the counter unit for the previous unit signal;
For the current unit signal, the comparison unit and the counter unit further include a readout scanning unit that reads out the count value from the data storage unit in parallel with the processing each of which is in charge of. The semiconductor device according to any one of claims 16 to 21. A reference signal generation unit that generates a reference signal for converting a difference signal component between the reference component and the signal component of an analog processing target signal represented by including a reference component and a signal component into digital data;
A comparison unit that compares a signal corresponding to each of the reference component and the signal component with a reference signal generated by the reference signal generation unit;
In parallel with the comparison process in the comparison unit, the asynchronous type performs the count process in one of the down-count mode and the up-count mode, and holds the count value when the comparison process in the comparison unit is completed Counter section of
An electronic device comprising: a timing control unit that switches a mode of the counting process in the counter unit according to which of the reference component and the signal component the comparison unit is performing the comparison process on . The counter unit has an initial value setting processing unit for starting a count process after mode switching after initial setting of a count value immediately before mode switching at the time of switching the count mode,
The said timing control part controls the said initial value setting process part, The said count process in a 2nd process is started from the count value hold | maintained in the 1st process. 23. The electronic device according to 23. A data storage unit that holds the count value held by the counter unit for the previous processing target signal;
For the current unit signal, the comparison unit and the counter unit further include a readout scanning unit that reads out the count value from the data storage unit in parallel with the processing each of which is in charge of. The electronic device according to claim 23 or 24.

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