JP2005322996A - Image sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image sensor to which a storage time automatic control function is attached in order to avoid saturation of storage electric charges for each pixel. <P>SOLUTION: The image sensor includes: a plurality of pixel configuration sections arranged in a form of an array including electric charge generating sections PD0, PD1, ... for generating electric charges in response to a light receiving amount, and electric charge storage sections C0, C1, ... for storing the produced electric charges; global shutters TR20, TR21, ... for controlling start and stop of storing electric charges in response to the light receiving amount in a plurality of the pixel configuration sections almost at the same time for all the pixel configuration sections; a plurality of comparators CMP0, CMP1, ... for individually comparing a value equivalent to the stored electric charges of all or part of a plurality of the pixel configuration sections with a common reference value; and storage time control circuits AND1, INV1 for controlling the global shutters to execute stopping the storage of the electric charges in each of the pixel configuration sections when at least one of outputs of a plurality of the comparators indicates that the value of the stored electric charges is greater than the reference value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image sensor to which an automatic control function of charge accumulation time is added in order to avoid saturation of each pixel.

  In an optical displacement meter that measures the displacement of an object using an image sensor (also called a solid-state image sensor) and an optical reader such as a barcode reader that reads an image pattern, it is important to adjust the charge accumulation time appropriately. It is. The charge accumulation time (sometimes simply the accumulation time) corresponds to the exposure time (shutter time). If this is not appropriate, the image of the object will be too dark or conversely too bright, and the object will be displaced. It becomes difficult to accurately perform measurement and image pattern recognition. In addition, since the amount of light received by the image sensor varies depending on the intensity of illumination light and the reflectance of an object, it is necessary to set an appropriate charge accumulation time according to them.

  In general, the greater the maximum amount of light received, the more fully the dynamic range of the image sensor can be utilized, so the accuracy of displacement measurement and image pattern recognition is improved. However, if the maximum amount of received light is set large, saturation of the amount of received light for each pixel (saturated accumulated charge) is likely to occur. When saturation occurs, for example, in the case of an optical displacement meter using the principle of triangulation, the peak position of the light distribution waveform obtained from the linear image sensor becomes unclear, and the displacement of the object can be detected correctly. Disappear. Similarly, in an optical reader, there is a risk of erroneous recognition of an image pattern due to saturation.

As a conventional method for avoiding the saturation of the accumulated charge as described above, for example, in the optical displacement meter described in Patent Document 1, the light emission amount of the laser diode based on the light reception amount data obtained from the linear image sensor. Control is performed. That is, saturation is prevented by controlling the peak output or light emission time (pulse width) of the laser diode based on digital data obtained by AD conversion of the output signal of the linear image sensor. Alternatively, saturation is prevented by controlling the accumulation time (exposure time or shutter time).
JP-A-10-267648

  Control of the light emission amount or accumulation time for avoiding saturation in the conventional optical displacement meter as described above is performed based on the received light waveform obtained from the linear image sensor. The received light waveform, which is a one-dimensional received light amount distribution, is obtained by calculating the received light amount data obtained from the linear image sensor. After reading this received light waveform for one frame, it is determined whether or not it is saturated after the next frame, and the light emission amount or the accumulation time is controlled based on the determination result. Delay occurs. Specifically, when transfer and waveform calculation are performed simultaneously, a delay of 2 frames may be sufficient, but when transfer and waveform calculation are not simultaneous, a delay of 3 frames or more is required.

  Due to this delay in feedback control, if the sampling period is shortened (high-speed sampling), saturation may not be avoided accurately. For example, when the control for reducing the light emission amount or the accumulation time is executed based on the data when the light reception amount is sufficiently large (light reception waveform), the actual light reception amount has already greatly decreased due to the change in the reflectance of the object. There may be. On the contrary, when the control for increasing the light emission amount or the accumulation time is executed based on the data (light reception waveform) when the light reception amount is small, the actual light reception amount greatly increases due to the change in the reflectance of the object. May have. In this case, saturation occurs and correct measurement values cannot be obtained.

  Further, the peak position cannot be determined from the received light waveform when saturation occurs, and it is also difficult to determine the degree of saturation. For this reason, when the control for decreasing the light emission amount or the accumulation time is executed step by step, the saturation state may continue for several frames.

  In addition, when controlling the light emission amount by the light emission time (pulse width) of the laser diode, since the pulse width is normally controlled in units of clocks, saturation cannot be avoided even if the light emission amount is reduced to the minimum pulse width. is there. For example, such a situation is likely to occur when the surface of the object is a highly reflective mirror surface.

  The above-described problems become particularly noticeable when a CMOS image sensor is used as the image sensor. The CMOS image sensor has an advantage that it can be systematized by adding an on-chip function, but the dynamic range is narrower than that of the CCD and saturation is likely to occur. Further, the above-described problem relating to saturation is a problem common to various optical electronic devices such as an optical reading device and an imaging device, as well as an optical displacement meter.

  An object of the present invention is to provide an image sensor to which an accumulation time automatic control function for avoiding saturation of accumulated charges for each pixel is added in view of the conventional problems as described above.

  A first configuration of an image sensor according to the present invention includes a plurality of pixel configuration units arranged in an array having a charge generation unit that generates a charge according to the amount of received light and a charge storage unit that stores the generated charge. The shutter means for controlling the start and stop of charge accumulation according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components, and corresponds to all or part of the accumulated charges of the plurality of pixel components. When at least one of the plurality of comparators individually comparing the value with the common reference value and the output of the plurality of comparators indicates that the accumulated charge is greater than the reference value, the shutter means is controlled. And an accumulation time control circuit for stopping charge accumulation in each pixel component.

  According to such a configuration, by setting the reference value to a value immediately before saturation, the charge accumulation in each pixel component can be stopped immediately before the accumulated charge in any pixel component is saturated. Therefore, saturation can be avoided while fully utilizing the dynamic range of the image sensor. Note that “all or a part of the plurality of pixel components” is not common to the pixel components in the entire pixel range of the image sensor, for example, but common to the pixel components in the effective pixel range excluding the peripheral part. This is intended to consider the case where a plurality of comparators for individually comparing with a reference value are provided. Furthermore, even within the effective pixel range, for example, a plurality of comparators that select a plurality of pixel components instead of all pixel components and compare them individually with a common reference value are provided. It is also intended to include.

  According to a second configuration of the image sensor of the present invention, in the first configuration, the accumulation time control circuit controls each of the pixel configurations by controlling the shutter means when the elapsed time from the start of accumulation has passed a predetermined upper limit time. The charge storage is stopped in the unit.

  According to such a configuration, if for some reason the amount of received light is small and the elapsed time from the start of accumulation becomes abnormally long, the charge accumulation is forcibly stopped in each pixel component, so the charge accumulation is completed There is no need to wait for a long time for reading. Note that whether or not the elapsed time has exceeded a predetermined upper limit time may be determined by counting clocks from the start of accumulation, or may be determined using a time constant circuit.

  A third configuration of the image sensor according to the present invention is characterized in that, in the first or second configuration, a reference value given to a plurality of comparators can be selected from a plurality of values. Thereby, not only the value immediately before the saturation but also a value having a lower margin can be selected and set as the reference value. For example, when the surface of the object partially has a mirror surface, it is preferable to set a value having a margin lower than a value immediately before saturation as a reference value in order to avoid saturation. According to this configuration, it is possible to select an appropriate reference value according to the object and other conditions.

  A fourth configuration of the image sensor according to the present invention is characterized in that, in any of the above configurations, a terminal for outputting a logical sum signal of the output signals of the plurality of comparators is provided. According to such a configuration, at least one of the outputs of the plurality of comparators outputs a signal indicating that the accumulated charge is larger than the reference value to the outside of the image sensor. Therefore, a control unit outside the image sensor can control, for example, the light emission amount using the signal. The circuit configuration for obtaining the logical sum signal of the outputs of the plurality of comparators includes a wired OR circuit that is the simplest circuit configuration.

  A fifth configuration of the image sensor according to the present invention includes a plurality of pixel configuration units arranged in an array having a charge generation unit that generates charges according to the amount of received light and a charge storage unit that stores the generated charges. The shutter means for controlling the start and stop of charge accumulation according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components, and corresponds to all or part of the accumulated charges of the plurality of pixel components. A plurality of comparators for individually comparing values with a common reference value are incorporated, and a control input terminal for the shutter means and a terminal for outputting a logical sum signal of the output signals of the plurality of comparators are provided. It is characterized by that.

  According to such a configuration, a portion (control unit) corresponding to the storage time control circuit in the first configuration can be configured by an external circuit. The sixth configuration of the image sensor according to the present invention is characterized in that, in the fifth configuration, the reference value given to the plurality of comparators can be selected from the plurality of values. According to this configuration, the same effect as the third configuration can be obtained.

  A seventh configuration of the image sensor according to the present invention is characterized in that, in any of the above configurations, the image sensor is a CMOS image sensor. As described above, since the CMOS image sensor has a narrow dynamic range and is likely to be saturated, the effect of the configuration of the present invention as described above is enhanced.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating the measurement principle of an optical displacement meter that is an example of an optical electronic device in which the image sensor of the present invention is used. This optical displacement meter is also called a laser displacement meter, and is used to measure the displacement of a measurement object in a non-contact manner using the principle of triangulation. Laser light emitted from the laser diode 12 under the control of the LD driver 11 passes through the light projecting lens 13 and irradiates the measurement object WK. Part of the laser light reflected by the measurement object WK passes through the light receiving lens 14 and is received by the linear image sensor 15.

  When the measurement object WK is displaced as indicated by a broken line in FIG. 1, the optical path of the laser light that is reflected by the measurement object WK and reaches the linear image sensor 15 changes as indicated by the broken line. As a result, the position of the light receiving spot on the light receiving surface of the linear image sensor 15 moves.

  The linear image sensor 15 has a structure in which a plurality of pixel configuration units are arranged in a line, and each pixel configuration unit generates a charge according to the amount of received light and a charge storage unit that stores the generated charge. And have. Accumulated charges corresponding to the amount of received light in each pixel component of the linear image sensor 15 are read out by the readout circuit 16 and a received light waveform that is a one-dimensional received light amount distribution is obtained by signal processing. The displacement of the measurement object WK is obtained from the peak position of the received light waveform.

  2A and 2B show the appearance of the optical displacement meter, FIG. 2A is a plan view, and FIG. 2B is a side view. The optical displacement meter includes a sensor head unit 21 and a controller unit 22. The sensor head unit 21 incorporates the LD driver 11, the laser diode 12, the light projecting lens 13, the light receiving lens 14, the linear image sensor 15, and the readout circuit 16. The controller unit 22 includes a microprocessor (control unit), controls the output (light emission amount) of the laser diode 12 via the LD driver of the sensor head unit 21, and uses signals read from the linear image sensor 15. A process for obtaining the displacement of the measuring object WK is executed.

  The sensor head unit 21 and the controller unit 22 are connected by an electric cable 23 to exchange electric signals with each other, and a power supply voltage is supplied from the controller unit 22 to the sensor head unit 21. The sensor head unit 21 is fixed to a predetermined mounting base 25 using two bolts 24. Two mounting holes through which the bolts 24 are inserted are provided along the reference surface 26 of the sensor head portion 21. The reference surface 26 is a surface on which the laser beam for measurement is emitted and the reflected light from the measurement object WK is incident.

  FIG. 3 is a block diagram showing a main circuit configuration of the optical displacement meter. The sensor head unit 21 includes a laser diode 12 and its drive circuit (LD driver) 11, a linear image sensor 15 and its readout circuit 16, a light projecting lens 13 and a light receiving lens 14. The controller unit 22 includes a low-pass filter (LPF) 41, a peak hold circuit 42, AD converters (A / D) 43 and 47, a microprocessor (MPU) 44, a DA converter (D / A) 45, and an AGC (automatic gain control) amplifier. 46 and a reset / control circuit 48.

  The laser light emitted from the laser diode 12 passes through the light projection lens 13 and irradiates the measurement object WK. Part of the laser light reflected by the measurement object WK passes through the light receiving lens 14 and enters the linear image sensor 15. The charge accumulated in each pixel component of the linear image sensor 15 is read out by the readout circuit 16. The readout circuit 16 obtains a time-series voltage signal corresponding to a one-dimensional received light amount distribution by applying a pixel selection signal that is a readout pulse signal to the linear image sensor 15 and sequentially scanning each pixel component. For example, when the linear image sensor 15 is composed of 256 pixels and the transfer rate for each pixel is 1 microsecond, the accumulated charge of all the pixel components is read out in 256 microseconds, and the time series voltage is read from the readout circuit 16. Output as a signal. The time required to read the accumulated charges of all the pixels is the sampling period. The output signal of the readout circuit 16 is passed to the controller unit 22, and the high frequency component is first removed by the low pass filter 41. This high frequency component includes the frequency component of the pixel selection signal given to the linear image sensor 15.

  FIG. 4 is a diagram schematically illustrating how the voltage signal output from the readout circuit 16 changes via the low-pass filter 41 and the peak hold circuit 42. As shown in FIG. 4, the output signal 31 of the readout circuit 16 is a continuous rectangular wave, and the frequency of this rectangular wave corresponds to the frequency of the pixel selection signal. When the output signal 31 passes through the low pass filter 41, the high frequency component corresponding to the frequency of the pixel selection signal is removed, and the voltage signal 32 includes only the low frequency component corresponding to the envelope. The voltage signal 32 includes information on the distribution of the amount of received light related to the pixel position in the linear image sensor 15. The higher the voltage value, the greater the amount of light received at that pixel position. Therefore, the peak position of the voltage signal 32 corresponds to the pixel position having the largest amount of received light that changes according to the displacement of the measurement object WK.

  The voltage signal 32 output from the low pass filter 41 is given to the peak hold circuit 42. The peak hold circuit 42 holds the peak value Vp of the voltage signal 32 and outputs it to the first AD converter 43. The AD converter 43 converts the peak value Vp into a digital value and gives it to the microprocessor 44. As shown in FIG. 3, the voltage signal 32 output from the low-pass filter 41 is also supplied to the AGC amplifier 46. The voltage signal amplified by the AGC amplifier 46 is converted into a digital value by the second AD converter 47, and the digital value is sequentially given to the microprocessor 44. The gain of the AGC amplifier 46 is automatically controlled so that the amplified voltage value falls within a predetermined range.

  The microprocessor 44 determines the position of the barycentric value of the amount of received light based on the peak data input through the first AD converter 43 and the sequential data input through the second AD converter 47. When the position of the barycentric value of the amount of received light is obtained, the distance or displacement to the measurement object WK is obtained from the principle of triangulation described above. The distance or displacement to the measurement object WK determined in this way is given from the microprocessor 44 to the DA converter 45, converted into an analog voltage and output.

  In FIG. 3, the intensity (light emission amount) of the laser light emitted from the laser diode 12 is controlled by the microprocessor 44 via the LD driver 11. If the intensity of the laser beam changes, the amount of light (the amount of received light) reflected by the measurement object WK and incident on the linear image sensor 15 also changes. Therefore, by adjusting the intensity of the laser light emitted from the laser diode 12 according to the light reflectance (brightness) of the measurement object WK, the dynamic range of the received light amount of the linear image sensor 15 can be fully utilized. I have to. Specifically, the intensity of the laser beam is adjusted by changing the pulse width or duty ratio of a pulse for driving the laser diode 12. Of course, the intensity of the laser beam may be adjusted by changing the pulse voltage (peak value).

  Next, an automatic accumulation time control function provided in the linear image sensor 15 used in the optical displacement meter of the present embodiment will be described. In this embodiment, a CMOS image sensor is used as the linear image sensor 15. The CMOS image sensor has an advantage that it can be systemized by adding an on-chip function, but has a disadvantage that the dynamic range is narrower than that of the CCD and the stored charge is likely to be saturated. When saturation occurs, the peak position (or centroid position) of the received light amount obtained from the linear image sensor becomes unclear, and the displacement of the object cannot be detected correctly.

  The linear image sensor of this embodiment uses a global shutter (shutter means) that controls the start and stop of charge accumulation according to the amount of received light in each pixel configuration unit for all pixel configuration units at the same time. In this configuration, the dynamic range can be fully utilized while avoiding the saturation of accumulated charges in the unit.

  FIG. 5 is a circuit diagram showing a first embodiment of the image sensor according to the present invention. In this linear image sensor, photodiodes PD0, PD1,... That are charges generating units that generate charges according to the amount of received light, and capacitors C0, C1,. A plurality of pixel constituent parts having the above are arranged in a line. Although only two pixel components are illustrated in FIG. 5, the actual linear image sensor has as many pixel components as the number of pixels (for example, 256).

  Charges generated by the photodiodes PD0, PD1,... According to the amount of light received are accumulated in the capacitors C0, C1,. The transistors TR20, 21,... Are simultaneously turned on / off by a common global shutter signal GS. This realizes a global shutter function that controls the start and stop of charge accumulation in accordance with the amount of received light in a plurality of pixel components substantially simultaneously for all the pixel components.

  The charges accumulated in the capacitors C0, C1,... Pass through the buffers BF20, 21,... And the transistors TR30, TR31, etc., and are read as the output voltage Vout through the common output buffer BF3. The pixel selection signals Add0, Add1,..., Which are readout pulse signals, are sequentially applied, so that the transistors TR30, TR31,... Are sequentially turned on, and the capacitors C0, C1,. The charge is read out as a time-series voltage signal Vout.

  The outputs of the buffers BF20, 21,... Are connected to comparators CMP0, CMP1,... Via transistors TR40, TR41,.・ Is connected. In the process of accumulating charges in the capacitors C0, C1,..., The transistors TR40, TR41,... Are turned on by a common comparator switching input (CMP switching input) signal. A common reference voltage Vref is input to the other input of each of the comparators CMP0, CMP1,. Each of the comparators CMP0, CMP1,... Is an open drain output, and is connected in common to form a wired OR output (WOR) line. A pull-up resistor Rup is connected to the wired OR output line WOR. The signal of the wired OR output line WOR is input to the negative logic input NOR gate (AND gate) AND1 via the inverter INV1. A reset signal (RESET input) is input to the other input of the gate AND1. The output of the gate AND1 becomes the above-described global shutter signal GS.

  With the circuit configuration as described above, when at least one of the outputs of the plurality of comparators indicates that the accumulated charge is larger than the reference value, the global shutter is controlled to stop accumulating the charge in each pixel component. Is realized. In other words, an accumulation time automatic control function that prevents saturation of the accumulated charge of each pixel is realized by an accumulation time control circuit including transistors TR40, TR41,..., Comparators CMP0, CMP1,. Yes.

  Hereinafter, the operation of the circuit of FIG. 5 will be described in order. Note that the reset input (RESET), pixel selection signal input (Add0, Add1,...) And comparator switching (CMP switching) input in FIG. 5 are reset and controlled by the microprocessor 44 of the controller unit 22 shown in FIG. It is included in a signal given to the sensor head unit 21 via the circuit 48.

  First, the comparator switching (CMP switching) input is set to L level, and the transistors TR40, TR41,... Are turned on. Also, the pixel selection signal inputs (Add0, Add1,...) Are all set to the H level, and the transistors TR30, TR31,. When the reset input signal is set to L level in this state, the global shutter signal GS is set to L level and the transistors TR20, 21,... Are simultaneously turned on, so that the capacitors C0, C1,. At this time, charges corresponding to the power supply voltage Vcc are accumulated. As a result, the outputs of all the comparators CMP0, CMP1,...

  When the reset input signal is set to H level (the reset state is released), the transistors TR10, 11,... Are turned on, and the photodiodes PD0, PD1,. The generation of the corresponding charge is started. At this time, since the outputs of all the comparators CMP0, CMP1,... Are at the H level, the global shutter signal GS is maintained at the L level, and the transistors TR20, 21,. Therefore, charge accumulation in the capacitors C0, C1,.

  As the charge accumulation in each capacitor C0, C1,... Progresses, the input voltage of each comparator CMP0, CMP1,. Eventually, when the accumulated charge of the capacitor of any of the pixel components having the largest amount of received light becomes larger than the reference value, the input voltage of the comparator becomes larger than the reference voltage Vref, and the output of the comparator is inverted to the L level. . As a result, the wired OR output line WOR becomes L level and the global shutter signal GS is inverted to H level, so that the transistors TR20, 21,. That is, the accumulation of charge in each capacitor C0, C1,... Is stopped, and the accumulated charge in each pixel component at that time is stored in the capacitors C0, C1,.

  Subsequently, the accumulated charge in each pixel component is read out. First, the comparator switching input is set to H level, and the transistors TR40, TR41,. Then, by sequentially scanning the pixel selection signal inputs (Add 0, Add 1,...) To the L level, the accumulated charges of the capacitors C 0, C 1,. Is read as After the accumulated charges of all the capacitors C0, C1,... Are read, the comparator switching input is again set to the L level, and the pixel selection signal inputs (Add0, Add1,. return.

  With the operation as described above, in the linear image sensor of the present embodiment, the charge accumulation in all the pixel components stops when the accumulated charge in any pixel component exceeds the reference value, and the accumulated charge at that time Is saved. Therefore, by setting the reference value (reference voltage Vref) to a value immediately before saturation, the charge accumulation in each pixel component can be stopped immediately before the accumulated charge in any pixel component is saturated. In this way, saturation can be avoided while fully utilizing the dynamic range of the image sensor.

  The configuration having the automatic accumulation time control function as described above is not limited to a linear image sensor (one-dimensional image sensor) in which each pixel configuration unit is arranged in a row, but an area in which each pixel configuration unit is arranged in a matrix. It can also be applied to image sensors (two-dimensional image sensors). Such an image sensor is not limited to an optical displacement meter, and can be applied to various optical electronic devices such as an optical reading device and an imaging device.

  Further, it is not always necessary to provide a transistor and a comparator for individually comparing a value corresponding to the accumulated charge with a common reference value in all the pixel components. For example, a comparator or the like may be provided only in the pixel configuration part within the effective pixel range excluding the peripheral part of the image sensor. Further, instead of all the pixel components in the effective pixel range, for example, a plurality of pixel components may be selected every other pixel component, and a comparator or the like may be provided.

  As shown by a broken line in FIG. 5, a terminal for outputting a signal of the wired OR output line WOR to the outside (a terminal for outputting a logical sum signal of output signals of a plurality of comparators, WOR output) may be provided. Good. The output signal of the wired OR output line WOR can be used for controlling the intensity (light emission amount) of the laser beam performed by the microprocessor 44, for example. This control will be described later.

  FIG. 6 is a circuit diagram showing a second embodiment of the image sensor according to the present invention. This embodiment is different from the first embodiment of FIG. 5 in that a common reference voltage Vref (reference value) input to each of the comparators CMP0, CMP1,... Can be selected from a plurality of values. The voltage selection circuit 51 is provided. In this embodiment, the reference voltage Vref selected by the reference voltage selection circuit 51 in response to a voltage selection input (Vsel) signal from the outside (microprocessor 44) is applied to each of the comparators CMP0, CMP1,. This makes it possible to select and set not only the reference voltage immediately before saturation but also a reference voltage having a lower margin. For example, when the surface of the measuring object WK partially has a mirror surface, it is preferable to set a reference voltage having a margin lower than the reference voltage immediately before saturation in order to avoid saturation. According to the configuration of the present embodiment, it is possible to select an appropriate reference voltage Vref according to the measurement object WK and other conditions.

  FIG. 7 is a circuit diagram showing a third embodiment of the image sensor according to the present invention. This embodiment differs from the first embodiment of FIG. 5 in that instead of incorporating an accumulation time control circuit including an inverter INV1 and a gate AND1 that generate a global shutter signal GS from a signal of the wired OR output line WOR, An external output terminal (WOR output) of the output line WOR and an external input terminal (GS input) of the global shutter signal GS are provided.

  In the optical displacement meter using the linear image sensor of this embodiment, the microprocessor 44 (control unit) of the controller unit 22 shown in FIG. 3 accumulates charges in each pixel configuration unit of the linear image sensor based on the WOR output signal. By outputting a global shutter signal that stops the operation, an automatic accumulation time control function similar to that of the first embodiment can be realized. However, from the viewpoint of shortening the delay time of the feedback control as much as possible, the first embodiment is superior to the present embodiment. Further, the microprocessor 44 performs control to reduce the output (light emission amount) of the laser diode 12 via the LD driver 11 before saturation occurs in any of the pixel components based on the WOR output signal. It may be.

  Further, the microprocessor 44 may control to output a global shutter signal for stopping the accumulation of electric charges in each pixel component when the elapsed time from the accumulation start exceeds a predetermined upper limit time. If for some reason the amount of received light is small and the elapsed time from the start of accumulation becomes abnormally long, it is possible to shift to charge accumulation completion and readout by forcibly stopping charge accumulation in each pixel component. it can. In the first embodiment, a similar function can be realized by adding a timer circuit or the like to the storage time control circuit.

  In the configuration of the third embodiment, the microprocessor 44 outputs the laser diode 12 output (light emission amount) when the time from the start of charge accumulation to the stop of accumulation in each pixel component of the image sensor is shorter than a predetermined lower limit time. You may make it perform control which reduces this. As a result of the automatic accumulation time control by the global shutter signal, if the time from the accumulation start to the accumulation stop is shorter than the lower limit time, it is considered that the light emission amount is too large, so the microprocessor 44 performs control to reduce the light emission amount This can contribute to reduction of power consumption.

  FIG. 8 is a circuit diagram showing a fourth embodiment of the image sensor according to the present invention. In this circuit diagram, some components in the embodiment shown in FIG. 5 are simplified and drawn as blocks. For example, the photodiodes PD0, PD1,... Of each pixel configuration part are drawn as blocks of the charge generation part, and the transistors TR20, 21,... Are drawn as switches SW10, SW11,. In this embodiment as well, as in the embodiment shown in FIG. 5, a comparator (comparator) CMP0 that individually compares the voltage corresponding to the accumulated charge of the capacitors C0, C1,... Of each pixel component with the reference voltage Vref. , CMP1,... Are provided. The wired OR signal WOR of these comparators CMP0, CMP1,... Becomes the global shutter signal GS as it is (the storage time control circuit is simplified).

  Further, the transistors (TR30, TR31,... In FIG. 5) for reading out the accumulated charges of the capacitors C0, C1,... Of each pixel component are depicted by switches SW20, SW21,. ing. .. Are connected between the capacitors C0, C1,... And the switches SW20, SW21,. A CDS (Collected Double Sampling) circuit is a circuit that compensates for variations in residual charges (voltage) when accumulated charges of capacitors C0, C1,. The CDS circuit can be omitted.

  FIG. 9 is a diagram showing an example of a circuit embodying the embodiment shown in FIG. This circuit diagram is also simplified compared to the circuit diagram of the embodiment shown in FIG. For example, the wired OR signal WOR of each comparator CMP0, CMP1,... Becomes the global shutter signal GS as it is, and the transistors TR20, TR21,.

  Note that the specific circuits shown in FIGS. 5 to 9 are merely configuration examples. The specific circuit configuration can be changed or reconfigured as appropriate. The present invention is not limited to the above embodiment, and can be implemented in various forms.

It is a figure which shows the measurement principle of the optical displacement meter which is an example of the optical electronic device in which the image sensor of this invention is used. It is a figure which shows the external appearance of an optical displacement meter. It is a block diagram which shows the main circuit structures of an optical displacement meter. It is the figure which drawn typically a mode that the voltage signal output from the read-out circuit changed through a low-pass filter and a peak hold circuit. 1 is a circuit diagram showing a first embodiment of an image sensor according to the present invention. FIG. 6 is a circuit diagram illustrating a second embodiment of the image sensor according to the present invention. FIG. 6 is a circuit diagram showing a third embodiment of the image sensor according to the present invention. FIG. 6 is a circuit diagram showing a fourth embodiment of the image sensor according to the present invention. It is a figure which shows the example of the circuit which actualized the Example shown in FIG.

Explanation of symbols

12 Laser diode (light emitting element)
15 Image sensor 44 Microprocessor (control unit)
AND1, INV1 storage time control circuit C0, C1,... Capacitors (charge storage unit)
CMP0, CMP1, ... Comparator (comparator)
PD0, PD1, ... Photodiode (charge generation unit)
TR20, TR21, ... Transistors (shutter means)

Claims (7)

A plurality of pixel components arranged in an array having a charge generation unit that generates a charge according to the amount of received light and a charge storage unit that stores the generated charge;
Shutter means for controlling the start and stop of charge accumulation according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components;
A plurality of comparators for individually comparing values corresponding to all or a part of the accumulated charges of the plurality of pixel components with a common reference value;
Accumulation for controlling the shutter means to stop accumulating charges in each pixel component when at least one of the outputs of the plurality of comparators indicates that the accumulated charge is greater than the reference value An image sensor comprising: a time control circuit. The accumulation time control circuit is configured to execute the charge accumulation stop in each pixel component by controlling the shutter unit when an elapsed time from the accumulation start exceeds a predetermined upper limit time. The image sensor according to claim 1. The image sensor according to claim 1, wherein a reference value given to the plurality of comparators can be selected from a plurality of values.   4. The image sensor according to claim 1, further comprising a terminal for outputting a logical sum signal of output signals of the plurality of comparators. A plurality of pixel components arranged in an array having a charge generation unit that generates a charge according to the amount of received light and a charge storage unit that stores the generated charge;
Shutter means for controlling the start and stop of charge accumulation according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components;
A plurality of comparators for individually comparing the values corresponding to all or a part of the accumulated charges of the plurality of pixel components with a common reference value;
An image sensor comprising: a control input terminal of the shutter means; and a terminal for outputting a logical sum signal of output signals of the plurality of comparators. The image sensor according to claim 5, wherein a reference value given to the plurality of comparators can be selected from a plurality of values. The image sensor according to claim 1, wherein the image sensor is a CMOS image sensor.

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