JP2012090330A - A/d conversion device and method of the same, solid state imaging device and method for driving the same, and camera system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an A/D conversion device and a method of the A/D conversion device, a solid state imaging device and a method for driving the solid state imaging device, and a camera system in which a P-phase variation amount and a vertical line amount, in an intermittent column operation, can be reduced, resulting in an improvement in image quality.SOLUTION: An ADC group 150 includes: plural comparators 151 which are respectively arranged corresponding to columns of pixels and which each compares and determines a read-out signal potential and a reference voltage and outputs the determination signal; and plural counters 152 whose operations are controlled by outputs of the comparators 151 and which respectively count comparison time units of the corresponding comparators 151. A comparator 200 (151) includes cascade-connected first and second amplifiers, and, by independently controlling, in parallel, by a basic unit of a horizontal intermittent operation, an initialization signal to be applied to a switch (AZ switch) for initialization (AZ) for determining an operation point for each column at an operation start point, fixes only the AZ switch of a non-operative comparator to be off at a non-operation start time.

Description

  The present invention relates to a solid-state imaging device represented by a CMOS image sensor and a camera system.

In recent years, CMOS image sensors have attracted attention as solid-state imaging devices (image sensors) that replace CCDs.
This requires a dedicated process for manufacturing the CCD pixel, requires a plurality of power supply voltages for its operation, and further requires a combination of a plurality of peripheral ICs to operate, resulting in a very complicated system. This is because the CMOS image sensor overcomes various problems such as.

  The CMOS image sensor can be manufactured by using a manufacturing process similar to that of a general CMOS integrated circuit, can be driven by a single power source, and further, an analog circuit or a logic circuit using the CMOS process. Can be mixed in the same chip, so that it has a plurality of great merits such as reducing the number of peripheral ICs.

The output circuit of a CCD is mainly a 1-channel (ch) output using an FD amplifier having a floating diffusion layer (FD).
In contrast, a CMOS image sensor has an FD amplifier for each pixel, and its output is a column parallel output type in which one row in the pixel array is selected and read out in the column direction at the same time. Mainstream.
This is because it is difficult to obtain a sufficient driving capability with an FD amplifier arranged in a pixel, and therefore it is necessary to lower the data rate, and parallel processing is advantageous.

  Various signal output circuits of this column parallel output type CMOS image sensor have been proposed.

As a technique used for pixel signal readout of a CMOS image sensor, a signal charge, which is an optical signal generated by a photoelectric conversion element such as a photodiode, is temporarily sampled in a capacitor ahead through a MOS switch arranged in the vicinity thereof. There is a method of reading out.
In the sampling circuit, noise having an inverse correlation with the normal sampling capacitance value is carried. In the pixel, when the signal charge is transferred to the sampling capacitor, the potential gradient is used to completely transfer the signal charge. Therefore, no noise is generated in this sampling process, but the voltage level of the previous capacitor is set to a certain reference value. Noise appears when resetting.

As a general method for removing this, there is correlated double sampling (CDS). This is a method of removing noise by reading and storing signal charges in a state (reset level) immediately before sampling once, then reading the signal level after sampling and subtracting it.
There are various specific methods of CDS.

  A general CMOS image sensor will be described below.

  FIG. 1 is a diagram illustrating an example of a pixel of a CMOS image sensor including four transistors.

  This pixel 10 has, for example, a photodiode 11 as a photoelectric conversion element. For this one photodiode 11, four transistors of a transfer transistor 12, an amplification transistor 13, a selection transistor 14, and a reset transistor 15 are active elements. Have as.

The photodiode 11 photoelectrically converts incident light into charges (here, electrons) of an amount corresponding to the amount of light.
The transfer transistor 12 is connected between the photodiode 11 and the floating diffusion FD, and a drive signal is given to the gate (transfer gate) through the transfer control line LTx, so that the electrons photoelectrically converted by the photodiode 11 are floated. Transfer to diffusion FD.

The gate of the amplification transistor 13 is connected to the floating diffusion FD. The amplification transistor 13 is connected to the signal line LSGN via the selection transistor 14, and constitutes a constant current source 16 and a source follower outside the pixel portion.
When the address signal is applied to the gate of the selection transistor 14 through the selection control line LSEL and the selection transistor 14 is turned on, the amplification transistor 13 amplifies the potential of the floating diffusion FD and outputs a voltage corresponding to the potential (vertical). Output to the signal line LSGN. The signal voltage output from each pixel through the signal line LSGN is output to the pixel signal readout circuit.

  The reset transistor 15 is connected between the power supply line LVDD and the floating diffusion FD, and resets the potential of the floating diffusion FD to the potential of the power supply line LVDD by applying a reset signal to the gate through the reset control line LRST.

More specifically, when resetting a pixel, the transfer transistor 12 is turned on, the charge accumulated in the photoelectric conversion element 11 is removed, and then the transfer transistor 12 is turned off, so that the photoelectric conversion element 11 receives an optical signal. Convert to charge and accumulate.
At the time of reading, the reset transistor 15 is turned on to reset the floating diffusion FD, the reset transistor 15 is turned off, and the voltage of the floating diffusion FD at that time is output through the amplification transistor 13 and the selection transistor 14. The output at this time is defined as a P-phase output.
Next, the transfer transistor 12 is turned on to transfer the charge accumulated in the photoelectric conversion element 11 to the floating diffusion FD, and the voltage of the floating diffusion FD at that time is output by the amplification transistor 13. The output at this time is defined as a D-phase output.
By using the difference between the D-phase output and the P-phase output as the image signal, not only the variation in the DC component of the output for each pixel but also the FD reset noise of the floating diffusion can be removed from the image signal.
These operations are performed simultaneously for each pixel for one row because, for example, the gates of the transfer transistor 12, the selection transistor 14, and the reset transistor 15 are connected in units of rows.

  Various pixel signal readout (output) circuits for column parallel output type CMOS image sensors have been proposed, and one of the most advanced forms is an analog-to-digital converter (hereinafter referred to as ADC) for each column. (Abbreviated as “Analog digital converter”), which extracts pixel signals as digital signals.

  A CMOS image sensor equipped with such a column parallel ADC is disclosed in Non-Patent Document 1 and Patent Document 1, for example.

  FIG. 2 is a block diagram illustrating a configuration example of a solid-state imaging device (CMOS image sensor) equipped with column parallel ADCs.

  As shown in FIG. 2, the solid-state imaging device 20 includes a pixel unit 21 as an imaging unit, a vertical scanning circuit 22, a horizontal transfer scanning circuit 23, a timing control circuit 24, an ADC group 25, a digital-analog conversion device (hereinafter, referred to as a “digital-analog converter”) DAC (Digital-Analog Converter) 26, amplifier circuit (S / A) 27, and signal processing circuit 28.

The pixel unit 21 includes a photodiode and an in-pixel amplifier, and for example, pixels as shown in FIG. 1 are arranged in a matrix (matrix).
In the solid-state imaging device 20, as a control circuit for sequentially reading out signals from the pixel unit 21, a timing control circuit 24 that generates an internal clock, a vertical scanning circuit 22 that controls row address and row scanning, and a column address and A horizontal transfer scanning circuit 23 for controlling the column scanning is arranged.

The ADC group 25 compares the reference voltage Vslop, which is a ramp waveform (RAMP) obtained by changing the reference voltage generated by the DAC 26 in a stepped manner, with an analog signal obtained from a pixel via a vertical signal line for each row line. A plurality of ADCs including a comparator (comparator) 25-1, a counter 25-2 that counts the comparison time, and a latch 25-3 that holds the count result are arranged.
The ADC group 25 has an n-bit digital signal conversion function and is arranged for each vertical signal line (column line) to constitute a column parallel ADC block.
The output of each latch 25-3 is connected to a horizontal transfer line 29 having a width of 2n bits, for example.
Then, 2n amplifier circuits 27 and signal processing circuits 28 corresponding to the horizontal transfer lines 29 are arranged.

In the ADC group 25, the analog signal (potential Vsl) read out to the vertical signal line is changed linearly with a reference voltage Vslop (a certain slope) by a comparator (comparator) 25-1 arranged for each column. Compared to the slope waveform).
At this time, as with the comparator 25-1, the counter 25-2 arranged for each column is operating, and the vertical signal is obtained by changing the potential Vslop having a ramp waveform and the counter value in a one-to-one correspondence. The line potential (analog signal) Vsl is converted into a digital signal.
The change in the reference voltage Vslop is to convert the change in voltage into a change in time, and is converted into a digital value by counting the time in a certain period (clock).
When the analog electrical signal Vsl and the reference voltage Vslop intersect, the output of the comparator 25-1 is inverted, the input clock of the counter 25-2 is stopped, and AD conversion is completed.
After the above AD conversion period, the data held in the latch 25-3 by the horizontal transfer scanning circuit 23 is input to the signal processing circuit 28 via the horizontal transfer line 29 and the amplifier circuit 27, and a two-dimensional image is generated. The
In this way, column parallel output processing is performed.

W. Yang et al. (W. Yang et. Al., “An Integrated 800x600 CMOS Image System,” ISSCC Digest of Technical Papers, pp. 304-305, Feb., 1999)

JP-A-2005-278135

  As described above, in a column parallel ADC-mounted CMOS image sensor (column AD type CMOS image sensor), the comparator compares the RAMP wave from the DAC with the pixel signal, and performs AD conversion by performing digital CDS with the counter at the subsequent stage. I do.

When the frame rate is increased in the preview or draft mode, it is effective to reduce the current consumption, so that the column comparator needs to be intermittently operated.
However, when only the control for turning off the current source of the comparator is performed, the operation time until each node of the non-operation comparator is determined is two p-channel MOS (PMOS) transistors or n-channel MOS (NMOS) transistors. It is determined by the time constant determined by on-resistance and parasitic capacitance.
For this reason, the initialization operation of the non-operation comparator is slower than the operation time of one row, and the comparator in operation is initialized immediately after the start of the row operation (hereinafter referred to as AZ), reset signal sampling, AD conversion (hereinafter referred to as AD conversion) When performing P phase), pixel signal sampling, and AD conversion (hereinafter referred to as D phase), the non-operation comparator initialization failure causes feed-through amount and charge injection amount at the end of AZ in the non-operation comparator unit. Therefore, the AC coupling to the RAMP wave increases, and the P-phase variation amount and the fixed vertical stripe amount increase in the intermittent operation of the column comparator, which affects the image quality.

  It is an object of the present invention to provide a solid-state imaging device and a camera system that can reduce the amount of P-phase variation and the amount of vertical streak during intermittent column operation and can improve the image quality.

  A first aspect of the present invention is a solid-state imaging device capable of intermittent operation, a pixel unit in which a plurality of pixels that perform photoelectric conversion are arranged in a matrix, and a pixel signal from the pixel unit in units of a plurality of pixels A pixel signal readout circuit that performs readout for each column, and the pixel signal readout circuit is arranged corresponding to the column arrangement of the pixels, compares and determines the readout signal potential and the reference voltage, and determines the determination signal. And a plurality of counters whose operations are controlled by the outputs of the comparators and that count the comparison time of the corresponding comparators. There is an initialization switch for determining the operating point for each column, and the initialization signal applied to the initialization switch is independently controlled in parallel for the basic unit of intermittent operation in the horizontal direction, and does not operate To start line For initialization switch is held in the off state.

  Preferably, each of the comparators receives the reference voltage at the gate of one transistor and the read signal at the gate of the other transistor, and performs a comparison operation between the reference voltage and the read signal potential. A first amplifier including a dynamic transistor; and a second amplifier that increases the output of the first amplifier and outputs the first amplifier. The first amplifier includes a control terminal of one of the differential transistors and the control terminal. A first capacitor connected between the reference voltage input lines; and a second capacitor connected between the control terminal of the other transistor of the differential transistor and the input line of the read signal. The switch for switching is connected between the connection node between the gate of the one transistor and the first capacitor and between the drain of the one transistor. To a connection node between the gate and the second capacitor of the other transistor are respectively disposed between the drain of the other transistor.

  Preferably, between the one initialization switch on the one transistor side, a connection node between the gate of the one transistor and the first capacitor, and the other initialization on the other transistor side. And at least one of the initialization switch, the gate of the one transistor, and the first capacitor among the connection nodes of the switch for switching, the gate of the other transistor, and the first capacitor. Further, an additional initialization switch is arranged between the node and the additional initialization switch is held in the OFF state when the target comparator starts a non-operation row.

  Preferably, between the one initialization switch on the one transistor side, a connection node between the gate of the one transistor and the first capacitor, and the other initialization on the other transistor side. And at least one of the initialization switch, the gate of the one transistor, and the first capacitor among the connection nodes of the switch for switching, the gate of the other transistor, and the first capacitor. Further, an additional initialization switch is arranged between the nodes and the additional initialization switch is held in the on state regardless of the operation state.

  Preferably, one of the initialization switches on the one transistor side, a connection node between the gate of the one transistor and the first capacitor, and the other initialization switch on the other transistor side Of the connection nodes between the gate of the other transistor and the first capacitor, at least the connection node between the initialization switch, the gate of the one transistor, and the first capacitor is subject to comparison. Set to a fixed potential at the start of the non-operating row of the device.

  A camera system according to a second aspect of the present invention includes a solid-state imaging device capable of intermittent operation and an optical system that forms a subject image on the imaging device, and the solid-state imaging device performs photoelectric conversion. A pixel unit in which a plurality of pixels are arranged in a matrix; and a pixel signal readout circuit that reads out a pixel signal from the pixel unit in units of a plurality of pixels for each column. A plurality of comparators that are arranged in correspondence with the column arrangement, compare and determine the read signal potential and the reference voltage, and output the determination signal, and the operation is controlled by the output of the comparator, and the corresponding comparator Each of the comparators has an initialization switch for determining an operating point for each column at the start of the row operation, and applies to the initialization switch. The initialization signal is Are independently controlled in parallel by the basic unit of the intermittent operation in the horizontal direction, the initializing switch is held in the OFF state to start non-operating lines.

According to the present invention, the initialization switch for determining the operating point for each column at the start of the row operation in the comparator is independently controlled in parallel by the basic unit of the intermittent operation in the horizontal direction by the initialization signal. Is done.
In the pixel signal readout circuit, the readout signal potential and the reference voltage are compared and determined, and the determination signal is output. The operation of the counter is controlled by the output of the comparator, and the comparison time of the corresponding comparator is counted.

  According to the present invention, it is possible to reduce the amount of P-phase variation and the amount of vertical streak during intermittent column operation, thereby improving the image quality.

It is a figure which shows an example of the pixel of the CMOS image sensor comprised by four transistors. It is a block diagram which shows the structural example of a column parallel ADC mounting solid-state image sensor (CMOS image sensor). It is a block diagram which shows the structural example of the solid-state image sensor (CMOS image sensor) mounted with column parallel ADC which concerns on embodiment of this invention. It is a block diagram which shows more specifically the ADC group in the column parallel ADC mounting solid-state image sensor (CMOS image sensor) of FIG. It is a circuit diagram which shows the 1st structural example of the comparator which concerns on this embodiment. 6 is a timing chart when all the pixels of the comparator according to the present embodiment are operating. It is a timing chart of the 1st example at the time of 1 / 4H column intermittent operation of the comparator concerning this embodiment. It is a timing chart of the 2nd example at the time of 1 / 4H column intermittent operation of the comparator concerning this embodiment. It is a figure which shows the example which put together the comparator of the 1st structural example for 4 columns, and made it 1 group of control object. It is a circuit diagram which shows the 2nd structural example of the comparator which concerns on this embodiment. It is a figure which shows the example which put together the comparator of the 2nd structural example for 4 columns, and made it 1 group of a control object. It is a circuit diagram which shows the 3rd structural example of the comparator which concerns on this embodiment. It is a figure which shows the example which put together the comparator of the 3rd and 4th structural example for 4 columns, and made it 1 group of control object. It is a circuit diagram which shows the 4th structural example of the comparator which concerns on this embodiment. It is a figure which shows an example of a structure of the camera system with which the solid-state image sensor which concerns on embodiment of this invention is applied.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 is a block diagram illustrating a configuration example of a solid-state imaging device (CMOS image sensor) with column-parallel ADCs according to an embodiment of the present invention.
FIG. 4 is a block diagram showing more specifically an ADC group in the column-parallel ADC-mounted solid-state imaging device (CMOS image sensor) of FIG.

3 and 4, the solid-state imaging device 100 includes a pixel unit 110 as an imaging unit, a vertical scanning circuit 120, a horizontal transfer scanning circuit 130, a timing control circuit 140, and an ADC group 150 as a pixel signal readout circuit. , A DAC and bias circuit 160 including a DAC (digital-analog converter) 161, an amplifier circuit (S / A) 170, a signal processing circuit 180, and a line memory 190.
Among these components, the pixel unit 110, the vertical scanning circuit 120, the horizontal transfer scanning circuit 130, the ADC group 150, the DAC and bias circuit 160, and the amplifier circuit (S / A) 170 are configured by analog circuits.
The timing control circuit 140, the signal processing circuit 180, and the line memory 190 are configured by digital circuits.

The pixel unit 110 includes, for example, pixels as shown in FIG. 1 including a photodiode and an in-pixel amplifier arranged in a matrix (matrix).
In the solid-state imaging device 100, as a control circuit for sequentially reading out signals from the pixel unit 110, a timing control circuit 140 that generates an internal clock, a vertical scanning circuit 120 that controls row address and row scanning, and a column address and A horizontal transfer scanning circuit 130 for controlling the column scanning is arranged.
The timing control circuit 140 performs signal processing of the pixel unit 110, the vertical scanning circuit 120, the horizontal transfer scanning circuit 130, the ADC group (column ADC circuit) 150, the DAC and bias circuit 160, the signal processing circuit 180, and the line memory 190. Generate the necessary timing signals.

The pixel unit 110 photoelectrically converts an image and a screen image for each pixel row by photon accumulation and discharge using a line shutter, and outputs an analog signal VSL to the ADC group.
In the ADC group 150, the ADC block (each column unit) performs an APGA-compatible integral ADC using the ramp signal RAMP from the DAC 161 and digital CDS on the analog output of the pixel unit 110, and outputs a digital signal of several bits. To do.

The ADC group 150 includes a reference voltage Vslop, which is a ramp waveform (RAMP) obtained by changing the reference voltage generated by the DAC 161 in a staircase pattern, and an analog signal (potential VSL) obtained from a pixel via a vertical signal line for each row line. ), A counter 152 for counting the comparison time, and a latch 153 for holding the count result are arranged in a plurality of columns.
The ADC group 150 has an n-bit digital signal conversion function and is arranged for each vertical signal line (column line) to constitute a column parallel ADC block.
The output of each latch 153 is connected to a horizontal transfer line LTRF having a width of 2n bits, for example.
Then, 2n amplifier circuits 170 and signal processing circuits 180 corresponding to the horizontal transfer lines LTRF are arranged.
The specific configuration and function of the comparator 151 will be described in detail later.

In the ADC group 150, an analog signal (potential VSL) read out to a vertical signal line is a reference waveform Vslop (a slope waveform that changes linearly with a certain slope) in a comparator 151 arranged for each column (each column). Is compared with the ramp signal RAMP).
At this time, the counters 152 arranged for each column are operating similarly to the comparator 151, and the ramp signal RAMP (potential Vslop) having a ramp waveform and the counter value change while taking a one-to-one correspondence to each other. The potential (analog signal) VSL of the signal line is converted into a digital signal.
The change in the reference voltage Vslop (ramp signal RAMP) is to convert the change in voltage into a change in time, and the time is counted in a certain period (clock) and converted into a digital value.
When the analog signal VSL and the ramp signal RAMP (reference voltage Vslop) intersect, the output of the comparator 151 is inverted, the input clock of the counter 152 is stopped, or the clock whose input has been stopped is input to the counter 152. Then, AD conversion is completed.

  After the end of the above AD conversion period, the data held in the latch 153 is transferred to the horizontal transfer line LTRF by the horizontal transfer scanning circuit 130, input to the signal processing circuit 180 through the amplifier 170, and 2 by the predetermined signal processing. A dimensional image is generated.

The horizontal transfer scanning circuit 130 performs simultaneous parallel transfer of several channels in order to ensure the transfer speed.
In the timing control circuit 140, timing necessary for signal processing in each block such as the pixel unit 110 and the ADC group 150 is created.
In the subsequent signal processing circuit 180, vertical line defects and point defects are corrected from the signals stored in the line memory 190, the signals are clamped, parallel-serial conversion, compression, encoding, addition, averaging, and intermittent operation. Digital signal processing is performed.
The line memory 190 stores a digital signal transmitted for each pixel row.
In the solid-state imaging device 100 of the present embodiment, the digital output of the signal processing circuit 180 is transmitted as an input of an ISP or a baseband LSI.

  In the ADC group (pixel signal readout circuit) 150 according to the present embodiment, the non-operating comparator section has a poor initialization, so that the feed-through amount and the charge injection amount at the end of AZ in the non-operating comparator unit are small. It is possible to suppress the increase, suppress the increase of AC coupling to the RAMP wave, reduce the amount of P-phase variation and the amount of fixed vertical stripes in the intermittent operation of the column comparator, and improve the image quality. The comparator 151 is configured as in first to fourth configuration examples shown below.

Each comparator 151 arranged for each column has a first amplifier and a second amplifier connected in cascade as a first configuration example, and initialization for determining an operating point for each column at the start of row operation Only the AZ switch of the non-operation comparator is turned off at the start of non-operation lines by performing parallel independent control of the initialization signal applied to the switch for auto-zero (AZ) (hereinafter referred to as AZ switch) for the basic unit of horizontal intermittent operation. To be fixed.
The first amplifier is configured to perform a low-speed signal comparison operation in the first stage to narrow the operating band, and the second amplifier in the next stage is configured to increase the gain.

In each comparator of the second configuration example, an additional AZ switch is provided so that two AZ switches are connected in series. At the start of the non-operating row of the target comparator, at least a switch transistor on the capacitive coupling side with the RAMP wave is provided. Turn off.
In each comparator of the third configuration example, an additional AZ switch is provided to connect two AZ switches in series, and at least a switch transistor on the capacitive coupling side with the RAMP wave is always turned on.
In each comparator of the fourth configuration example, at least the capacitive coupling end of the AZ switch with the RAMP wave is pulled up at the start of the non-operating row of the target comparator.

Hereinafter, the configuration, function, and control of the comparator 151 of the ADC group (pixel signal readout circuit) 150 having the characteristic configuration of the present embodiment will be described in detail.
The following comparator will be described with reference numeral 200.

  FIG. 5 is a circuit diagram showing a first configuration example of the comparator according to the present embodiment.

As shown in FIG. 5, the comparator 200 includes a first amplifier 210 having a function of performing a low-speed signal comparison operation in the first stage and narrowing an operation band, and a second amplifier having a function of increasing the output of the first amplifier 210. 220 are connected in cascade.
The comparator 200 outputs a first AZ (initialization) signal PSEL for the first amplifier 210 to be applied to the AZ switch for determining the operating point for each column at the start of the row operation in the horizontal direction (comparator). In this case, only the AZ switch of the non-operation comparator is fixed to OFF at the start of the non-operation row.

  The first amplifier 210 includes p-channel MOS (PMOS) transistors PT211 to PT215, n-channel MOS (NMOS) transistors MT211 to NT214, and a first capacitor C211 and a capacitor C212 which are AZ level sampling capacitors.

The source of the PMOS transistor PT211 and the source of the PMOS transistor PT212 are connected to the power supply potential VDD.
The drain of the PMOS transistor PT211 is connected to the drain of the NMOS transistor NT211 and a node ND211 is formed by the connection point. Further, the drain and gate of the PMOS transistor PT211 are connected, and the connection point is connected to the gate of the PMOS transistor 212.
The drain of the PMOS transistor PT212 is connected to the drain of the NMOS transistor NT212, and an output node ND212 of the first amplifier 210 is formed by the connection point.
The sources of the NMOS transistor NT211 and the NMOS transistor NT212 are connected to each other, the connection point is connected to the drain of the NMOS transistor NT214, and the source of the NMOS transistor NT214 is connected to the drain of the NMOS transistor NT213. The source of the NMOS transistor NT213 is connected to the ground potential GND.

The gate of the NMOS transistor NT211 is connected to the first electrode of the capacitor C211 and a node ND213 is formed by the connection point. The second electrode of the capacitor C211 is connected to the input terminal TRAMP for the ramp signal RAMP.
The gate of the NMOS transistor NT212 is connected to the first electrode of the capacitor C212, and a node ND214 is formed by the connection point. The second electrode of the capacitor C212 is connected to the input terminal TVSL for the analog signal VSL.
The gate of the NMOS transistor NT213 is connected to the input terminal TBIAS for the bias signal BIAS.
The gate of the NMOS transistor NT214 is connected to the input terminal TMABK for the control signal MABK.
The drain of the PMOS transistor PT213 is connected to the node ND211 and the source is connected to the node ND213. The drain of the PMOS transistor PT214 is connected to the node ND212, and the source is connected to the node ND214.
The gates of the PMOS transistors PT213 and PT214 are commonly connected to the input terminal TPSEL of the first AZ signal PSEL which is active at a low level.
The source of the PMOS transistor PT215 is connected to the power supply potential VDD, the drain is connected to the output node ND212, and the gate is connected to the input terminal TMABK of the control signal MABK.

In the first amplifier 210 having such a configuration, a current mirror circuit is configured by the PMOS transistors PT211 and PT212, and a differential comparison unit using the NMOS transistor NT213 as a current source is configured by the NMOS transistors NT211 and NT212.
The PMOS transistors PT213 and PT214 function as AZ switches, and the capacitors C211 and C212 function as AZ level sampling capacitors.
The output signal 1stcomp of the first amplifier 210 is output from the output node ND212 to the second amplifier 220.
Further, the NMOS transistor NT214 has a function of turning off the first amplifier 210 when the control signal MABK is at a low level and putting the first amplifier 210 into an operating state when the control signal MABK is at a high level. Have.
The PMOS transistor PT215 is turned on when the control signal MABK is at a low level to fix the output line connected to the output node ND212 when the control circuit MABK is in the non-operating state to the power supply potential VDD. It has a function of reliably cutting off the gate input transistor of the amplifier 220. The PMOS transistor PT215 has a function of turning off and transmitting the output 1stcomp of the first amplifier 210 to the second amplifier 220 when the control signal MABK is at a high level.

  The second amplifier 220 includes a PMOS transistor PT221, NMOS transistors NT221 and NT222, and an AZ level sampling capacitor C221.

The source of the PMOS transistor PT211 is connected to the power supply potential VDD, and the gate is connected to the output node ND212 of the first amplifier 210.
The drain of the PMOS transistor PT211 is connected to the drain of the NMOS transistor NT211, and an output node ND221 is formed by the connection point.
The source of the NMOS transistor NT221 is connected to the ground potential GND, the gate is connected to the first electrode of the capacitor C221, and a node ND222 is formed by the connection point. A second electrode of the capacitor C221 is connected to the ground potential GND.
The drain of the NMOS transistor NT222 is connected to the node ND221, and the source is connected to the node ND222.
The gate of the NMOS transistor PT222 is commonly connected to the input terminal TNSEL of the second AZ signal NSEL which is active at a high level.
The second AZ signal NSEL takes a level complementary to the first AZ signal PSEL supplied to the first amplifier 210.

In the second amplifier 220 having such a configuration, an input and a current source circuit are configured by the PMOS transistor PT221.
The NMOS transistor NT222 functions as an AZ switch, and the capacitor C221 functions as an AZ level sampling capacitor.
The output node ND221 of the second amplifier 220 is connected to the output terminal TOUT of the comparator 200.

  Next, the operation of the comparator 200 according to the present embodiment will be described with reference to FIGS.

FIG. 6 is a timing chart during the operation of all the pixels of the comparator according to the present embodiment.
FIG. 7 is a timing chart of the first example during the 1 / 4H column intermittent operation of the comparator according to the present embodiment.
FIG. 8 is a timing chart of the second example during the 1 / 4H column intermittent operation of the comparator according to the present embodiment.
FIG. 9 is a diagram illustrating an example in which the comparators of the first configuration example are grouped into four columns to form one group to be controlled. One group of four columns in FIG. 9 is an example of a basic unit of intermittent operation in the horizontal direction.

In the comparator 200, in the AZ period, the first AZ signal PSEL is supplied at the low level and the second AZ signal NSEL is supplied at the high level in order to determine the operating point for each column at the start of the row operation. As a result, the PMOS transistors PT213 and PT214 as the AZ switch of the first amplifier 210 are turned on. Similarly, the NMOS transistor NT222 as the AZ switch of the second amplifier 220 is turned on.
As described above, in the ADC group 150, the comparator 200 (151) is used to sample the DAC offset level, the pixel reset level, and the AZ level for each column, and the capacitors C211, C212, which are AZ level sampling capacitors. Charge is stored in C221.

  That is, as shown in the timing chart during normal operation in FIG. 6, immediately after the row operation is started, the first AZ signal PSEL is set to the low level (L) and the second AZ signal NSEL is set to the high level (H). However, AZ is performed during this pulse period.

Next, P-phase operation is performed. The analog signal VSL changes in response to the pixel reset signal RST, and AD conversion is performed for each column by comparing with the ramp signal RAMP from the DAC 161.
The AD conversion is in a high impedance (HiZ) state after AZ of the comparator 200 (151), and the ramp signal RAMP to the nodes ND213 and ND214 of the first amplifier 210 and the time when the coupled signals of the analog signal VSL intersect. Thus, the counter operation of the subsequent stage is controlled by changing the output of the comparator 200 (151).
The P-phase period in FIG. 6 is the operation timing. It can be seen from the timing chart of FIG. 6 that the output signal compout once changes to low level immediately after the start of the P-phase period, and changes to high level when the RAMP wave and the analog signal VSL intersect.

Next, the D-phase operation is performed. Although AD conversion is performed along the same path as the P phase, since the amount of signal photoelectrically converted by the pixel is larger in the D phase than in the P phase, the dynamic range of AD conversion is generally widened.
Therefore, when AD conversion is performed at the same gradation as the P-phase RAMP wave in FIG. 6, the D-phase period is longer than the P-phase period. The AD conversion operation is coupled to the ramp signal RAMP and the analog signal VSL to the nodes ND213 and ND214 of the first amplifier 210, which are in the high impedance (HiZ) after AZ of the comparator 200 (151), as in the P phase. The counter operation of the subsequent stage is controlled by changing the output of the comparator 200 (151) at the time when each signal crosses.
The D phase period in FIG. 6 is the operation timing. In the timing chart of FIG. 6, it can be seen that the output signal compout changes to the low level again immediately after the end of the P-phase period, but changes to the high level when the RAMP wave and the analog signal VSL intersect in the D-phase period.
As described above, the AZ, P-phase, and D-phase operations for each column are performed twice by the same path in each row operation, so that the inherent variation for each column, kTC noise, and the like are removed by the analog CDS.

In this embodiment, basically, the first AZ (initialization) signal PSEL which is the AZ input of the comparator 200 (151) is compared with the comparator 200 (151) by the basic unit of the intermittent operation in the horizontal direction. ) In parallel independent control, only the AZ switch of the non-operation comparator is fixed off at the start of the non-operation row.
As an example, FIG. 9 shows a block diagram in which the comparators of FIG. 5 are combined for four columns, and FIG. 7 shows a timing chart of 1 / 4H column intermittent operation.
The analog signal VSL, the first AZ signal PSEL, and the control signal MABK are provided for each column, and the ramp signal RAMP and the bias signal BIAS are input to each column in parallel.
The control signal MABK is a signal for setting the comparator 200 (151) in FIG. 5 to be in a standby state when not operating, and is supplied to the gate of the NMOS transistor NT214. The bias signal BIAS is supplied from the NMOS transistor NT213 as a constant current source of the first amplifier 210. It is a DC (direct current) analog signal supplied to the gate.

In order to control the horizontal intermittent operation in an analog manner, the non-operating column comparator 200 (151) needs to be in a standby state at the start of the row operation. For example, in order to deactivate only 0 to 2 columns, The control signal MABK <2: 0> is fixed to the low level (L), and only the control signal MABK <3> is fixed to the high level (H).
In the first configuration example, in the case of the above example, not only the control signal MABK but also the first AZ signal PSEL <2: 0> is fixed to the high level (H) at the start of the row operation, and the AZ of the non-operation comparator is set. Control is performed so as not to perform the switch operation.
At this time, in order to turn on the AZ switch of the comparator in the operation column, the first AZ signal PSEL <3> is set to the low level as usual.
As shown in FIG. 7, the comparator in the third column performs AZ, P-phase, and D-phase operations, but in the 0th to second columns, each node of the comparator is in a standby state, and no current flows. The output is fixed at a low level (L). At the same time, feedthrough and charge injection generated when the PMOS transistors PT213 and PT214 which are AZ switches are turned on and off are not transmitted to the RAMP wave through the capacitive coupling. For this reason, in the intermittent operation of the column comparator, it is possible to reduce the amount of P-phase variation and the amount of fixed vertical stripes in the operation column.

FIG. 10 is a circuit diagram illustrating a second configuration example of the comparator according to the present embodiment.
FIG. 11 is a diagram illustrating an example in which the comparators of the second configuration example are grouped into four columns to form one group to be controlled. One group of four columns in FIG. 11 is an example of a basic unit of intermittent operation in the horizontal direction.

  The comparator 200A of the second configuration example is different from the comparator 200 of the first configuration example in that two additional AZ switches are provided in series on the node ND213 and ND214 side of the AZ switch of the first amplifier 210A. At the start of the non-operating row of the target comparator, at least the switch transistor on the capacitive coupling side with the RAMP wave is turned off.

Specifically, in the first amplifier 210A, the source and drain of the PMOS transistor PT216 as an AZ switch are connected between the node ND213 and the source of the PMOS transistor PT213. Similarly, the source and drain of a PMOS transistor PT217 as an AZ switch are connected between the node ND214 and the source of the PMOS transistor PT214.
The gates of the PMOS transistors PT213 and PT214 are commonly connected to the input terminal TXMABK of the inverted signal XMABK of the control signal MABK.

As an example, FIG. 11 shows a block diagram in which the comparators of FIG. 10 are combined for four columns, and FIG. 8 shows a timing chart of 1 / 4H column intermittent operation in the second configuration example.
The difference between FIG. 10 and FIG. 9 used in the first configuration example is that the first AZ signal PSEL is input to all the columns in parallel, and each inverted signal XMABK of the control signal MABK <3: 0>. <3: 0> is used as a control signal and is input to the gates of the PMOS transistors PT216 and PT217 of the added capacitance AZ switch.

In order to control the horizontal intermittent operation in an analog manner, the comparator of the non-operating column needs to be in a standby state at the start of the row operation. For example, in order to deactivate only 0 to 2 columns, the control signal MABK < 2: 0> is fixed to the low level (L), and only the control signal MABK <3> is fixed to the high level (H).
At this time, as shown in FIGS. 8 and 11, the first AZ signal PSEL is inputted to the gates of the PMOS transistors PT213 and PT214 as the AZ switches of the first amplifiers 210A of all the columns.
For this reason, the AZ switch operation is performed for all the columns, but in the 0th to 2nd columns, each node of the comparator is in a standby state, the current stops flowing, and the comparator output is fixed to the low level (L). The comparator in the third column performs AZ, P phase, and D phase operations.
Also, feedthrough and charge injection that occur when the PMOS transistors PT213 and PT214, which are AZ switches of the non-operation comparator, are turned on and off are controlled at the start of the row by the PMOS transistors PT216 and PT217 as another AZ switch added to the capacitor side. Since it is turned off by the inverted signal XMABK <2: 0> of the signal MABK, it is not transmitted to the RAMP wave through the capacitive coupling, and the P-phase variation amount of the operating column and the fixed amount are not transmitted in the intermittent operation of the column comparator. It is possible to reduce the amount of vertical stripes.
Note that all column operations are shown in a timing chart in which the first AZ signal PSEL is not known for each column in the timing chart shown in FIG.

FIG. 12 is a circuit diagram showing a third configuration example of the comparator according to the present embodiment.
FIG. 13 is a diagram illustrating an example in which the comparators of the third and fourth configuration examples are grouped for four columns to form one group to be controlled. One group of four columns in FIG. 13 is an example of a basic unit of intermittent operation in the horizontal direction.

  The difference between the comparator 300B of the third configuration example and the comparator 220A of the second configuration example is that two AZs of the first amplifier 210A are connected in series, and the RAMP wave is generated at the start of the non-operating row of the target comparator. The gates of PMOS transistors PT216 and PT217, which are AZ switches on the capacitive coupling side, are connected to the fixed potential VSS and are always turned on.

As an example, FIG. 13 is a block diagram in which the comparators of FIG. 12 are combined for four columns, and FIG. 8 is a timing chart of 1 / 4H column intermittent operation.
FIG. 13 is different from FIG. 11 used in the second configuration example in that each inverted signal XMABK <3: 0> of the control signal MABK <3: 0> is not used, and the input of the added capacitor side AZ switch is used. Is fixed at the reference potential VSS, and is always on during all column operation and intermittent column operation.
In order to control the horizontal intermittent operation in an analog manner, the comparator of the non-operating column needs to be in a standby state at the start of the row operation. For example, in order to deactivate only 0 to 2 columns, the control signal MABK < 2: 0> is fixed to the low level (L), and only the control signal MABK <3> is fixed to the high level (H).
At this time, as shown in FIGS. 8 and 13, the first AZ signal PSEL is input to the gates of the PMOS transistors PT213 and PT214 as the AZ switches of the first amplifiers 200B of all the columns.
For this reason, the AZ switch operation is performed for all the columns, but in the 0th to 2nd columns, each node of the comparator is in a standby state, the current stops flowing, and the comparator output is fixed to the low level (L). The comparator in the third column performs AZ, P phase, and D phase operations.
Also, feedthrough and charge injection that occur when the PMOS transistors PT213 and PT214, which are AZ switches of the non-operational comparator, are turned on and off, cause the on-resistance and source of the PMOS transistors PT216 and PT217 as another AZ switch added to the capacitor side. Filter out high frequency components with / drain-substrate capacitance, gate-source / drain capacitance, and other wiring parasitic capacitance.
For this reason, the components of the AZ switching noise transmitted to the RAMP wave through the capacitive coupling are low frequency and low amplitude, and in the intermittent operation of the column comparator, the amount of variation in the P phase and the amount of fixed vertical stripes of the operating column can be reduced. Is possible.
Note that all column operations are shown in a timing chart in which the first AZ signal PSEL is not known for each column in the timing chart shown in FIG.

  FIG. 14 is a circuit diagram showing a fourth configuration example of the comparator according to the present embodiment.

The comparator 200C of the fourth configuration example is different from the comparator 200A of the second configuration example in that the capacitive coupling ends with the RAMP wave of the AZ switch of the first amplifier 201C, that is, the nodes ND213 and ND214 are connected to the target comparator. The point is to pull up at the start of non-operating lines.
Specifically, the PMOS transistor PT218 as a switch having a drain connected to the node ND213 and the source connected to the power supply potential VDD, and a switch having a drain connected to the node ND214 and a source connected to the power supply potential VDD. The PMOS transistor PT219 is provided, and the gates of the PMOS transistors PT218 and PT219 are connected to the input terminal TMABK of the control signal MABK.

As an example, FIG. 13 is a block diagram in which the comparators of FIG. 14 are combined for four columns, and FIG. 8 is a timing chart of 1 / 4H column intermittent operation.
The comparator 200C of FIG. 14 differs from the comparators 200A and 200B of the second and third configuration examples in that a PMOS transistor PT218 that pulls up the nodes ND213 and ND214 in parallel with the PMOS transistors PT213 and PT214 as AZ switches, PT219r is connected and the control signal MABK <3: 0> is used as its input.
In order to control the horizontal intermittent operation in an analog manner, the comparator of the non-operating column needs to be in a standby state at the start of the row operation. For example, in order to deactivate only 0 to 2 columns, the control signal MABK < 2: 0> is fixed to the low level (L), and only the control signal MABK <3> is fixed to the high level (H).
At this time, as shown in FIGS. 8 and 14, the first AZ signal PSEL is input to the gates of the PMOS transistors PT213 and PT214 as the AZ switches of the first amplifiers 200B of all the columns.
For this reason, the AZ switch operation is performed for all the columns, but in the 0th to 2nd columns, each node of the comparator is in a standby state, the current stops flowing, and the comparator output is fixed to the low level (L). The comparator in the third column performs AZ, P phase, and D phase operations.
Further, the nodes ND213 and ND214 of the first amplifier 210C of the non-operation comparator are pulled up to the analog power supply by fixing the control signal MABK <2: 0> to the low level (L) at the start of the row operation. During the AZ period, feedthrough and charge injection generated when the PMOS transistors PT213 and PT214 as AZ switches are turned on and off can be released to the analog power supply via the PMOS transistors PT218 and PT219 for pull-up.
In addition, it is not transmitted to the RAMP wave via the capacitive coupling, and it is possible to reduce the amount of variation in the P phase and the amount of fixed vertical stripes in the operation column in the intermittent operation of the column comparator.
Note that all column operations are shown in a timing chart in which the first AZ signal PSEL is not known for each column in the timing chart shown in FIG.

  As described above, according to this embodiment, the pixel unit 110 in which a plurality of pixels that perform photoelectric conversion are arranged in a matrix, and the pixel signal readout circuit (ADC) that reads data from the pixel unit 110 in units of rows. The ADC group (pixel signal readout circuit) 150 is arranged corresponding to the column arrangement of the pixels, compares and determines the readout signal potential and the reference voltage, and outputs a judgment signal. Comparator 151 and a plurality of counters 152 whose operations are controlled by the output of the comparator and count the comparison time of the corresponding comparator. The comparator 151 includes a first amplifier connected in cascade. A basic unit of intermittent operation in the horizontal direction having a second amplifier and applying an initialization signal applied to an initialization (AZ) switch (AZ switch) for determining an operating point for each column at the start of row operation Only the AZ switch of the non-operation comparator is fixed to OFF at the start of the non-operation line, or two additional AZ switches are provided in series so that the target comparator does not operate. At the start of the row, at least the switch transistor on the capacitive coupling side with the RAMP wave is turned off, or two AZ switches are provided in series by providing an additional AZ switch, and at least the capacitive coupling side switch transistor with the RAMP wave is always connected. Since it is configured to turn on or pull up at least the capacitive coupling end of the AZ switch with the RAMP wave at the start of the non-operating row of the target comparator, the following effects can be obtained.

  In other words, the amount of vertical streak and P phase variation during intermittent column operation are reduced by feedthrough to the high impedance (HiZ) node of the non-operation comparator, reduction of charge injection, high frequency noise component filtering, or pull-up. As a result, the image quality can be improved.

  A solid-state imaging device having such an effect can be applied as an imaging device for a digital camera or a video camera.

  FIG. 15 is a diagram illustrating an example of a configuration of a camera system to which the solid-state imaging device according to the embodiment of the present invention is applied.

  As shown in FIG. 15, the camera system 300 guides incident light to a pixel region of the imaging device 310 to which the solid-state imaging device 100 according to the present embodiment is applicable and forms a subject image. ) Optical system, for example, a lens 320 that forms an incident light (image light) on the imaging surface, a drive circuit (DRV) 330 that drives the imaging device 310, and a signal processing circuit that processes an output signal of the imaging device 310 ( PRC) 340.

  The drive circuit 330 includes a timing generator (not shown) that generates various timing signals including a start pulse and a clock pulse that drive a circuit in the imaging device 310, and drives the imaging device 310 with a predetermined timing signal. .

Further, the signal processing circuit 340 performs predetermined signal processing on the output signal of the imaging device 310.
The image signal processed by the signal processing circuit 340 is recorded on a recording medium such as a memory. The image information recorded on the recording medium is hard copied by a printer or the like. The image signal processed by the signal processing circuit 340 is displayed as a moving image on a monitor including a liquid crystal display.

  As described above, a high-precision camera can be realized by mounting the above-described solid-state imaging device 100 as the imaging device 310 in an imaging apparatus such as a digital still camera.

  DESCRIPTION OF SYMBOLS 100 ... Solid-state image sensor, 120 ... Pixel part, 130 ... Vertical scanning circuit, 130 ... Horizontal transfer scanning circuit, 140 ... Timing control circuit, 150 ... ADC group, 151 ... Comparator, 152 ... Counter, 153 ... Latch, 160 ... DAC, 170 ... Amplifier circuit, 180 ... Signal processing circuit, 190 ... Line memory, LTRF ... Horizontal transfer Line 200, Comparator 210 ... First amplifier 220 ... Second amplifier 300 ... Camera system 310 ... Imaging device 320 ... Drive circuit 330 ... Lens, 340... Signal processing circuit.

The present invention relates to an AD conversion apparatus and method, a solid-state imaging device represented by a CMOS image sensor, a driving method thereof, and a camera system.

The present invention provides an AD conversion apparatus and method thereof, a solid-state imaging device and a driving method thereof, and a camera system that can reduce the amount of P-phase variation and the amount of vertical streak during intermittent column operation, thereby improving the image quality. It is to provide.

Claims (6)

A solid-state image sensor capable of intermittent operation,
A pixel unit in which a plurality of pixels that perform photoelectric conversion are arranged in a matrix;
A pixel signal readout circuit that reads out a pixel signal from the pixel unit in units of a plurality of pixels for each column;
The pixel signal readout circuit is
A plurality of comparators that are arranged corresponding to the column arrangement of pixels, compare and determine a read signal potential and a reference voltage, and output a determination signal;
A plurality of counters whose operations are controlled by the outputs of the comparators and which count the comparison time of the corresponding comparators,
Each of the above comparators
There is an initialization switch for determining the operating point for each column at the start of row operation, and the initialization signal applied to the initialization switch is independently and in parallel for the basic unit of intermittent operation in the horizontal direction. A solid-state imaging device that is controlled and the initialization switch is held off at the start of a non-operating row. Each of the above comparators
A first amplifier including a differential transistor that receives the reference voltage at the gate of one transistor and receives the read signal at the gate of the other transistor and performs a comparison operation between the reference voltage and the read signal potential;
A second amplifier for gaining up the output of the first amplifier and outputting it,
The first amplifier is
A first capacitor connected between a control terminal of one of the differential transistors and an input line of the reference voltage;
A second capacitor connected between a control terminal of the other transistor of the differential transistor and an input line of the read signal;
The initialization switch
A connection node between the gate of the one transistor and the first capacitor, a drain node of the one transistor, a connection node between the gate of the other transistor and the second capacitor, and the other transistor The solid-state image sensor of Claim 1. Between the one initialization switch on the one transistor side and a connection node between the gate of the one transistor and the first capacitor, and on the other initialization switch and the other on the other transistor side Between at least one of the initialization switch and the connection node between the gate of the one transistor and the first capacitor among the connection node between the gate of the other transistor and the first capacitor. An additional initialization switch is placed in the
The solid-state imaging device according to claim 2, wherein the additional initialization switch is held in an off state at the start of a non-operating row of the target comparator. Between the one initialization switch on the one transistor side and a connection node between the gate of the one transistor and the first capacitor, and on the other initialization switch and the other on the other transistor side Between at least one of the initialization switch and the connection node between the gate of the one transistor and the first capacitor among the connection node between the gate of the other transistor and the first capacitor. An additional initialization switch is placed in the
The solid-state imaging device according to claim 2, wherein the additional initialization switch is held in an on state regardless of an operating state. One initialization switch on the one transistor side, a connection node between the gate of the one transistor and the first capacitor, and the other initialization switch and the other transistor on the other transistor side Among the connection nodes between the gate of the first capacitor and the first capacitor, at least one of the initialization switch, the connection node between the gate of the one transistor and the first capacitor is a non-operation of the target comparator. The solid-state imaging device according to claim 2, wherein the solid-state imaging device is set to a fixed potential at the start of the line. A solid-state imaging device capable of intermittent operation;
An optical system for forming a subject image on the image sensor,
The solid-state imaging device is
A pixel unit in which a plurality of pixels that perform photoelectric conversion are arranged in a matrix;
A pixel signal readout circuit that reads out a pixel signal from the pixel unit in units of a plurality of pixels for each column;
The pixel signal readout circuit is
A plurality of comparators that are arranged corresponding to the column arrangement of pixels, compare and determine a read signal potential and a reference voltage, and output a determination signal;
A plurality of counters whose operations are controlled by the outputs of the comparators and which count the comparison time of the corresponding comparators,
Each of the above comparators
There is an initialization switch for determining the operating point for each column at the start of row operation, and the initialization signal applied to the initialization switch is independently and in parallel for the basic unit of intermittent operation in the horizontal direction. A camera system that is controlled and the initialization switch is held off at the start of a non-operating line.

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