Image pickup device and electronic device

The present technology relates to an image pickup device and an electronic device that enables a reduction in influence exerted by a dark current. The image pickup device and the electronic device include a sample and hold unit configured to perform sampling and holding of a pixel signal, an analog digital (AD) conversion unit configured to perform AD conversion of the pixel signal that includes a digit after a decimal point, a digital gain processing unit configured to apply a predetermined gain to a digital signal from the AD conversion unit, and a gain setting unit configured to set an analog gain of a column unit including the sample and hold unit and the AD conversion unit. The gain setting unit sets the analog gain in accordance with a measured dark current amount. The present technology can be applied, for example, to a CMOS image sensor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Phase of International Patent Application No. PCT/JP2019/006222 filed on Feb. 20, 2019, which claims priority benefit of Japanese Patent Application No. JP 2018-038235 filed in the Japan Patent Office on Mar. 5, 2018. Each of the above-referenced applications is hereby incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present technology relates to an image pickup device and an electronic device, and for example, relates to an image pickup device and an electronic device that can suppress noise.

BACKGROUND ART

In an electronic device such as a digital still camera or a digital video camera that includes an image capturing function, an image pickup device such as a charge coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor, for example, has been conventionally used.

An image pickup device includes a pixel formed by combining a photodiode (PD) that performs photoelectric conversion and a plurality of transistors. An image is formed on the basis of pixel signals output from a plurality of planarly-arranged pixels. In addition, the pixel signals output from the pixels are output after being concurrently AD-converted by a plurality of analog to digital (AD) converters arranged for each column of pixels, for example.

Patent Document 1 proposes clamping a dark current by detecting a dark current amount as a digital value and feeding back the detected value to a digital analog converter (DAC). In addition, Patent Document 2 proposes clamping a dark current by enhancing the accuracy of AD conversion.

CITATION LIST

Patent Document

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

It is demanded to more accurately reduce influence exerted by a dark current, without upsizing a circuit scale due to a configuration for reducing the influence exerted by a dark current, and without complicating a circuit configuration.

The present technology has been devised in view of such a situation, and enables a reduction in influence exerted by a dark current.

Solutions to Problems

An image pickup device according to an aspect of the present technology includes a sample and hold unit configured to perform sampling and holding of a pixel signal, an analog digital (AD) conversion unit configured to perform AD conversion of the pixel signal that includes a digit after a decimal point, a digital gain processing unit configured to apply a predetermined gain to a digital signal from the AD conversion unit, and a gain setting unit configured to set an analog gain of a column unit including the sample and hold unit and the AD conversion unit.

An electronic device according to an aspect of the present technology includes an image pickup device, and a signal processing unit configured to process a signal output from the image pickup device, in which the image pickup device includes a sample and hold unit configured to perform sampling and holding of a pixel signal, an analog digital (AD) conversion unit configured to perform AD conversion of the pixel signal that includes a digit after a decimal point, a digital gain processing unit configured to apply a predetermined gain to a digital signal from the AD conversion unit, and a gain setting unit configured to set an analog gain of a column unit including the sample and hold unit and the AD conversion unit.

In the image pickup device according to an aspect of the present technology, sampling and holding of the pixel signal are performed, AD conversion of the pixel signal that includes a digit after a decimal point is performed, the predetermined gain is applied to the digital signal, and an analog gain of the column unit is set.

In the electronic device according to an aspect of the present technology, the image pickup device is included.

Note that an image pickup device may be an independent device or may be an internal block constituting one device.

Effects of the Invention

According to an aspect of the present technology, influence exerted by a dark current can be reduced.

Note that in this connection, the effects described here are not necessarily limited, and may be any of the effects described in the present disclosure.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a mode for implementing the present technology (hereinafter referred to as an embodiment) will be described.

Because the present technology can be applied to an imaging device, the description will now be given using an example case where the present technology is applied to an imaging device. Note that the description will now be given using an imaging device as an example, but the application of the present technology is not limited to the application to an imaging device. The present technology can be applied to any electronic device that uses an imaging device as an image capturing unit (photoelectric conversion unit). Examples of such an electronic device include an imaging device such as a digital still camera and a video camera, a mobile terminal device including an image capturing function such as a mobile phone, a copying machine that uses an imaging device as an image reading unit, and the like. Note that a modular configuration mounted on an electronic device, that is to say, a camera module is regarded as an imaging device in some cases.

FIG. 1is a block diagram illustrating a configuration example of an imaging device serving as an example of an electronic device according to the present disclosure. As illustrated inFIG. 1, an imaging device10includes an optical system including a lens group11or the like, an image pickup device12, a DSP circuit13serving as a camera signal processing unit, a frame memory14, a display unit15, a recording unit16, an operation system17, a power system18, and the like.

In addition, the DSP circuit13, the frame memory14, the display unit15, the recording unit16, the operation system17, and the power system18are connected to one another via a bus line19. A CPU20controls each component in the imaging device10.

The lens group11takes in incident light (image light) from a subject and forms an image on an imaging plane of the image pickup device12. The image pickup device12converts a light amount of the incident light formed as the image on the imaging plane by the lens group11, into an electrical signal for each pixel, and outputs the electrical signal as a pixel signal. An image pickup device (image sensor) including pixels to be described below can be used as the image pickup device12.

The display unit15includes a panel display unit such as a liquid crystal display unit or an organic electro luminescence (EL) display unit, and displays a moving image or a still image that has been captured by the image pickup device12. The recording unit16records a moving image or a still image that has been captured by the image pickup device12, onto a recording medium such as a video tape or a digital versatile disk (DVD).

In accordance with an operation performed by a user, the operation system17issues operation commands for executing various functions included in the imaging device. The power system18appropriately supplies the DSP circuit13, the frame memory14, the display unit15, the recording unit16, and the operation system17with various types of power for operating these components.

<Configuration of Image Pickup Device>

FIG. 2is a block diagram illustrating a configuration example of the image pickup device12. A complementary metal oxide semiconductor (CMOS) image sensor can be used as the image pickup device12. The image pickup device12includes a pixel array unit51, a row selection unit52serving as a pixel driving unit, and a reading unit53.

In the pixel array unit51, a plurality of pixels50(FIG. 3) is two-dimensionally arrayed in an M-by-N matrix including M rows and N columns. Control lines54wired to the pixel array unit51include a transfer line, a reset line, and a row selection line as one set, and each set is wired to a corresponding one of the rows of the pixel array. M transfer lines, M reset lines, and M row selection lines are provided as control lines. These transfer lines, reset lines, and row selection lines are driven by the row selection unit52.

The row selection unit52controls an operation of pixels arranged on an arbitrary row in the pixel array unit51. The row selection unit52controls a pixel portion through the control lines54. The reading unit53receives data of a pixel row of which readout is controlled by the row selection unit52, via vertical signal lines55, and transfers the data to a subsequent signal processing unit. A constant current unit and the reading unit53are connected to the vertical signal lines55.

FIG. 3is a circuit diagram of the pixel50arranged in the pixel array unit51(FIG. 2).

The pixel50includes a photodiode (PD)71, a transfer transistor72, a floating diffusion (FD)73, a reset transistor74, an amplification transistor75, and a selection transistor76.

The PD71functions as a photoelectric conversion element that generates and accumulates electric charges (signal charges) corresponding to a received light amount. An anode terminal of the PD71is grounded and a cathode terminal of the PD71is connected to the FD73via the transfer transistor72.

When the transfer transistor72is turned on in accordance with a transfer signal TR, the transfer transistor72reads out the electric charges generated by the PD71, and transfers the electric charges to the FD73. The FD73holds the electric charges read out from the PD71. When the reset transistor74is turned on in accordance with a reset signal RST, the reset transistor74resets an electric potential of the FD73by the electric charges accumulated in the FD73being discharged to a drain (constant voltage source Vdd).

The amplification transistor75outputs a pixel signal corresponding to the electric potential of the FD73. In other words, the amplification transistor75forms a source follower circuit with a load MOS (not illustrated) serving as a constant current source that is connected via the vertical signal line55. A pixel signal indicating a level corresponding to the electric charges accumulated in the FD73is output from the amplification transistor75to the reading unit53(FIG. 2) via the selection transistor76and the vertical signal line55.

The selection transistor76is turned on when the pixel50is selected in accordance with a selection signal SEL, and outputs a pixel signal of the pixel50to the reading unit53via the vertical signal line55. Signal lines to which the transfer signal TR, the selection signal SEL, and the reset signal RST are transmitted correspond to the control lines54illustrated inFIG. 2.

The pixel50can have the above-described configuration, but the configuration of the pixel50is not limited to this configuration and another configuration can also be employed.

<Configuration of Reading Unit>

FIG. 4is a diagram illustrating a configuration example of the reading unit53. The reading unit53has a configuration including a sample and hold unit (S/H unit)111, an analog digital converter (ADC)112, a digital processing unit113, and a conversion and transmission unit114.

The S/H unit111, the ADC112, and the digital processing unit113are provided for each of the vertical signal lines55(FIG. 3). The S/H unit111includes a function of sampling a photoelectric conversion amount of the pixel50as a sample and holding the photoelectric conversion amount. A signal held by the S/H unit111is supplied to the ADC112. The signal supplied to the ADC112is an analog signal, and the ADC112converts the supplied analog signal into a digital signal.

The signal converted into the digital signal by the ADC112is supplied to the digital processing unit113. The digital processing unit113generates final digital data by further clamping and rounding data converted by the ADC112into digital data, and supplies the final digital data to the conversion and transmission unit114. The conversion and transmission unit114includes a function of converting parallel data into serial data and transmitting the converted data to a subsequent signal processing unit (not illustrated). Because pixel values are respectively supplied from a plurality of ADCs112to the conversion and transmission unit114, the conversion and transmission unit114converts the plurality of pixel values into serial data and outputs the converted data.

A gain setting unit115determines a dark current amount using data from the ADC112, and sets a gain for suppressing a dark current. The gain setting unit115controls the S/H unit111and the digital processing unit113using the set gain.

First Embodiment

FIG. 5is a diagram illustrating the details of the reading unit53illustrated inFIG. 4. Here, the reading unit53that expands a circuit range and reduces noise by adjusting a resistance value of variable resistance will be described as the first embodiment.

A part including the S/H unit111and the ADC112will be referred to as a column unit116. The column unit116includes two S/H units111. In this example, the two S/H units111will be referred to as a S/H unit111P and a S/H unit111D. The S/H unit111P performs sampling and holding in readout of a P-phase, and the S/H unit111D performs sampling and holding in readout of a D-phase. In addition, here, the readout of the P-phase means the readout of a pixel reset signal, and the readout of the D-phase means the readout of a pixel data signal.

Because the S/H unit111P and the S/H unit111D have similar configurations, in a case where there is no need to make a distinction between the S/H unit111P and the S/H unit111D, the S/H unit111P and the S/H unit111D will be simply described as the S/H unit111.

The S/H unit111has a configuration including an operational amplifier131, a switch SW1, a switch PH1, a switch PH2, and a capacitor C1. A S/H circuit includes the capacitor C1having one end connected to an inverting input terminal IN (“-” in the drawing) of the operational amplifier131.

The electric potential of one end of the capacitor C1can be set to an electric potential V of an output terminal Vout of the operational amplifier131by turning on (closing) the switch PH1. When the switch SW1is turned on in a state in which the switch PH1is turned, and another end of the capacitor C1is connected to an input terminal VIN (“Vpix” in the drawing) of a sampling voltage, electric charges corresponding to an input electric potential to Vin are charged in the capacitor C1.

When the switch PH1and the switch SW1are turned off at a sampling time ts, the capacitor C1holds the charged electric charges, and the electric potential of the other end of the capacitor C1is held at an input electric potential VH at the time ts. The electric potential VH of the other end of the capacitor C1is taken out as an output value of the output Vout by turning on the switch PH2.

One end of the switch PH2of the S/H unit111P is connected to a signal line141and a source of a transistor143. An output end of the operational amplifier131of the S/H unit111P is connected to a gate of the transistor143.

One end of the switch PH2of the S/H unit111D is connected to the signal line141and a source of a transistor144. An output end of the operational amplifier131of the S/H unit111D is connected to a gate of the transistor144.

A current source142is connected to one end of the signal line141and a current with a constant current value flows in the signal line141. The ADC112is connected to another end of the signal line141, and the ADC112converts a current that has flowed to the ADC112via the signal line141, into a digital value. The ADC112is a current input type analog digital converter.

A variable resistance145is connected to the middle of the signal line141. The variable resistance145is provided between a point to which an output of the S/H unit111P is connected, and a point to which an output of the S/H unit111D is connected. The variable resistance145functions as an analog gain in the column unit116.

A current corresponding to a difference between a voltage value held by the S/H unit111P and a voltage value held by the S/H unit111D flows in the signal line141. The voltage value held by the S/H unit111P corresponds to a pixel signal of a reset level, and the voltage value held by the S/H unit111D corresponds to a pixel signal of a signal level. Thus, the difference between the voltage value held by the S/H unit111P and the voltage value held by the S/H unit111D becomes a value obtainable when the pixel signal of the reset level is subtracted from the pixel signal of the signal level, and becomes a pixel value from which reset noise has been removed.

The ADC112converts such a pixel value into digital data, and supplies the converted data to the digital processing unit113and the gain setting unit115. In this manner, the column unit116acquires a pixel value from which reset noise has been removed, on the basis of the pixel signals respectively held by the S/H unit111P and the S/H unit111D, converts the pixel value into a digital signal by the ADC112, and supplies the digital signal to the digital processing unit113and the gain setting unit115.

The digital processing unit113has a configuration including a digital clamp unit151, a digital gain processing unit152, and a rounding processing unit153. The digital clamp unit151clamps a digital signal from the ADC112, and supplies the digital signal to the digital gain processing unit152.

The digital gain processing unit152applies a gain to a digital signal using a gain set by the gain setting unit115, and supplies the resultant digital signal to the rounding processing unit153. The rounding processing unit153executes rounding processing. The ADC112performs AD conversion including digits after the decimal point, and the rounding processing unit153performs processing of rounding a value to an integer value. An output from the digital processing unit113is supplied to the conversion and transmission unit114, converted into serial data together with other types of data, and supplied to a subsequent processing unit (not illustrated).

Among outputs from the ADC112, an output at dark current detection is supplied to the gain setting unit115. The description about dark current detection will be added. The dark current detection is performed using a pixel value of a predetermined line of the pixel array unit51as illustrated inFIG. 6.

Referring toFIG. 6, the pixels50are arranged in an array in the pixel array unit51. In the pixel array unit51, a plurality of pixels is arranged on one line, and a plurality of lines each including a plurality of pixels arranged in this manner is provided. A predetermined line of the pixel array unit51such as a first line positioned on the top inFIG. 6, that is to say, a line that is to be initially read out in the readout is shielded and is configured not to receive light. A dark current is detected using pixel values corresponding to the one line, and a gain corresponding to the dark current is set by the gain setting unit115.

Note that the description will now be given of an example case where processing is performed using pixel values corresponding to one line, but processing can also be performed using pixel values corresponding to two or more lines, for example.

In addition, the description will now be continued using an example in which processing is performed using the top one line of the pixel array unit51as illustrated inFIG. 6, but the position of this line is not limited to the top one line, and a bottom one line may be used. In addition, for example, in a case where a dark current is detected using two lines, shielded lines may be used as the top one line and the bottom one line of the pixel array unit51, for example, and processing may be performed using the two lines.

The description will return to the description of the configuration of the reading unit53that is illustrated inFIG. 5. In the column unit116, an output from the column unit116that is obtained when a signal from the pixel50arranged on a line of a pixel array unit22that is provided for dark current detection is processed is supplied to the gain setting unit115. The gain setting unit115detects a dark current, and sets a gain in the column unit116and a gain of the digital gain processing unit152in the digital processing unit113in accordance with a dark current amount.

In the reading unit53according to the first embodiment that is illustrated inFIG. 5, a case where a gain in the column unit116that is set by the gain setting unit115is a resistance value of the variable resistance145is illustrated. In a case where the gain setting unit115decreases a gain in the column unit116, for example, the gain setting unit115increases a gain of the digital gain processing unit152. The gain of the column unit116and the gain of the digital gain processing unit152are set in such a manner that a constant value is obtained when one gain is multiplied by the other gain, for example. In other words, the gains are set in such a manner that, when one gain is decreased, the other gain is increased.

By performing such a setting of gains, a gain in the reading unit53can be set to a constant value, and processing can be performed using the gain with the constant value. The first embodiment corresponds to a case where a resistance value of the variable resistance145is adjusted for adjusting a gain of the column unit116. In a case where the gain of the column unit116is to be decreased, the resistance value of the variable resistance145is set to a higher value. In a case where the gain of the column unit116is to be increased, the resistance value of the variable resistance145is set to a lower value.

Processing of the reading unit53illustrated inFIG. 5will be described with reference to a flowchart illustrated inFIG. 7.

In step S11, a dark current is detected. As described above with reference toFIG. 6, by processing an output from a pixel on a shielded line of the pixel array unit51, a dark current is detected. Because a dark current depends on a usage environment and can possibly fluctuate in accordance with a heat change, for example, a dark current is detected at predetermined intervals or at a predetermined timing such as every time image capturing is performed or a time when power is turned on.

In step S12, it is determined whether or not the dark current is equal to or larger than a threshold value. A pixel value read out from the shielded pixel50essentially becomes zero, but the pixel value does not become zero due to various factors. A current detected in a state in which a pixel value essentially becomes zero is referred to as a dark current.

When a pixel value read out from a shielded line and supplied from the ADC112is input, that is to say, a digital signal indicating a dark current in this case is input, the gain setting unit115determines whether or not the dark current indicated by the digital signal is equal to or larger than a threshold value.

In a case where it is determined in step S12that the dark current is not equal to or larger than the threshold value, the processing proceeds to step S13. In step S13, the gain setting unit115sets a gain of the column unit116to “×1”. In this case, an analog gain of the column unit116is adjusted to “×1” by adjusting a resistance value of the variable resistance145.

When an analog gain of the column unit116is set in this manner, in step S14, a digital gain is set to “×1” as a digital gain corresponding to the analog gain. In other words, the gain setting unit115sets a gain of the digital gain processing unit152to “×1”.

When a gain of the column unit116and a gain of the digital gain processing unit152are set in this manner, image capturing processing using the set gains is performed. Referring again to the pixel array unit51illustrated inFIG. 6, lines excluding the top one line of the pixel array unit51are regarded as an opening portion and are configured to receive light. Processing of acquiring pixel values from the pixels50arranged in this opening portion is performed.

In step S15, the ADC112executes processing of converting a signal obtained from the pixel50. In other words, the ADC112executes processing of converting a current value being an analog signal of a current flowing in the signal line141, into a current value of a digital signal. In this manner, the ADC112is a current input type analog digital converter. In addition, the ADC112converts an analog signal into a digital signal including digits after the decimal point. For example, an analog signal is converted into a digital signal including 2 bits after the decimal point.

An output from the ADC112is subjected to multiplication processing of a digital gain that is performed by the digital gain processing unit152provided subsequent to the ADC112. For suppressing a deterioration in image information that is caused by the digital gain, the ADC112preliminarily converts an analog signal into a digital signal including bits after the decimal point with low accuracy, and uses the converted signal as random numbers.

For example, in a case where a digital gain is set to “×2”, carry-up occurs, and if digital data from the ADC112has the accuracy up to an integer value, data in the lower first digit becomes meaningless data. In other words, by multiplying a digital gain, image information can possibly deteriorate.

Nevertheless, if digital data from the ADC112includes data including a numerical value after the decimal point, the numerical value after the decimal point is carried up, and data in the first digit after an integer part can be made into meaningful data. Thus, even if a digital gain is multiplied, a deterioration in image information can be prevented.

The description will now be continued using an example case where the ADC112converts an analog signal into a digital signal including bits after the decimal point, and the number of bits after the decimal point is two, but the number of bits after the decimal point may be the number of bits other than two.

In step S16, the digital clamp unit151performs digital clamp processing on the digital signal including 2 bits after the decimal point that has been supplied from the ADC112, and supplies the resultant digital signal to the digital gain processing unit152. Because a gain of the digital gain processing unit152is set to “×1” in the above-described processing, the digital gain processing unit152executes processing of dividing the supplied digital signal by the gain of “×1”, and supplies the resultant digital signal to the rounding processing unit153.

The processing described so far is performed using data including 2 bits after the decimal point. Then, in step S17, data is converted into an integer value by the rounding processing unit153rounding out or rounding down the data including 2 bits after the decimal point.

On the other hand, in a case where it is determined in step S12that the dark current is equal to or larger than the threshold value, in processing in step S19and subsequent steps, the resetting of a user gain is performed. The user gain is a gain obtained by multiplying a gain of the column unit116by a gain of the digital processing unit113. The user gain is set to be a constant gain. That is to say, the user gain is set to be 1.

In step S19, the gain setting unit115sets an analog gain of the column unit116to “×(1/Y)”. In this case, an analog gain of the column unit116is adjusted to an analog gain of “×(1/Y)” by adjusting a resistance value of the variable resistance145. The gain (1/Y) can be set to a value corresponding to the magnitude of a dark current. That is to say, as a value of (1/Y), a plurality of values can be set instead of presetting one value, and a value corresponding to the magnitude of a dark current can be set.

When an analog gain of the column unit116is set in this manner, in step S20, a digital gain is set to “×Y” as a digital gain corresponding to the analog gain. In other words, the gain setting unit115sets a gain of the digital gain processing unit152to “×Y”. In this case, because an analog gain is “1/Y” and a digital gain is “Y”, a value obtained by multiplying the analog gain by the digital gain becomes 1 (=(1/Y)×Y).

When an analog gain of the column unit116and a digital gain of the digital gain processing unit152are set in this manner, image capturing processing using the set gains is performed. Because processing in step S22and a subsequent step is performed basically similarly to the processing in step S15and subsequent steps, the description thereof will be omitted here.

In this manner, a user gain (=analog gain×digital gain) is set in accordance with the magnitude of a dark current and image capturing with a suppressed dark current can be performed using the set user gain. In addition, generally, if an analog gain is changed by decreasing the analog gain, for example, a noise characteristic can possibly deteriorate. Nevertheless, by applying such circuit noise to a region dominated by a dark current, the circuit noise can be processed by burying the circuit noise into noise attributed to the dark current.

In addition, for preventing a deterioration in image information that is caused by a digital gain, the ADC112preliminarily converts analog data into digital data including bits after the decimal point with low accuracy, and the converted data is used as random numbers. Thus, deterioration in image information that is caused by a digital gain can be prevented.

Second Embodiment

Next, a reading unit53according to the second embodiment will be described.FIG. 8is a diagram illustrating a configuration example of the reading unit53according to the second embodiment. In the second embodiment, the reading unit53that expands a circuit range and reduces noise by adjusting the capacitance of a capacitor will be described.

The configuration of the reading unit53(hereinafter, will be referred to as a reading unit53b) illustrated inFIG. 8is a configuration similar to the configuration of the reading unit53(hereinafter, will be referred to as a the reading unit53a) according to the first embodiment that is illustrated inFIG. 5, but differs from the reading unit53ain a part controlled by the gain setting unit115. Because the other parts are similar, the description of similar parts will be omitted.

A gain setting unit115bof the reading unit53billustrated inFIG. 8adjusts an analog gain of the column unit116by adjusting capacitance values of the capacitor C1included in the S/H unit111P in the column unit116, and the capacitor C1included in the S/H unit111D in the column unit116. Because capacitance values of the capacitor C1included in the S/H unit111P and the capacitor C1included in the S/H unit111D are adjusted, the capacitors C1are variable capacitance type capacitors.

In a case where the gain setting unit115bchanges an analog gain in such a manner that a user gain becomes a constant value, similarly to the first embodiment, the gain setting unit115bchanges a digital gain. The gain setting unit115balso sets a gain of the digital gain processing unit152of the digital processing unit113.

Because a resistance value of a resistance145of the column unit116is not changed unlike the first embodiment, the resistance145is a resistance having a fixed resistance value.

Here, in a case where an amount of electric charges that can be accumulated in the capacitor C1is denoted by Q, a capacitance of the capacitor C1is denoted by C, and a voltage applied to the capacitor C1is denoted by V, a relational expression represented as Q=CV is satisfied. In a case where electric charges with the same amount are to be accumulated (the electric charge amount Q is set to a constant value), in a case where the capacitance C is changed to a larger value, the voltage V becomes a smaller value. Thus, an output voltage from the S/H unit111also becomes a smaller value. In this manner, by adjusting the capacitance C of the capacitor C1, an output voltage from the S/H unit111can be changed, and a gain in the column unit116can be adjusted.

In this manner, by adjusting the capacitance of the capacitor C1in the S/H unit111, a circuit range can be expanded and noise caused by a dark current or the like can be reduced. An operation of the reading unit53baccording to the second embodiment is an operation basically similar to that of the reading unit53aaccording to the first embodiment, and is performed on the basis of the processing in the flowchart illustrated inFIG. 7flowchart. Thus, the description thereof will be omitted here.

Nevertheless, the setting of an analog gain is set to a capacitance value of the capacitor C1that realizes an analog gain desired to be set, and a digital gain corresponding to the analog gain is set in the digital gain processing unit152.

Also in the reading unit53bin the second embodiment, a user gain (=analog gain×digital gain) is set in accordance with the magnitude of a dark current and image capturing with a suppressed dark current can be performed using the set user gain. In addition, if an analog gain is changed, for example, a noise characteristic can possibly deteriorate. Nevertheless, by applying such circuit noise to a region dominated by a dark current, the circuit noise can be processed by burying the circuit noise into noise attributed to the dark current.

In addition, for preventing a deterioration in image information that is caused by a digital gain, the ADC112preliminarily converts analog data into digital data including bits after the decimal point with low accuracy, and the converted data is used as random numbers. Thus, deterioration in image information that is caused by a digital gain can be prevented.

Third Embodiment

Next, a reading unit53according to the third embodiment will be described.FIG. 9is a diagram illustrating a configuration example of the reading unit53according to the third embodiment. In the third embodiment, the reading unit53that expands a circuit range and reduces noise by adjusting a current that flows in the signal line141will be described.

The configuration of the reading unit53(hereinafter, will be referred to as a reading unit53c) illustrated inFIG. 9is a configuration similar to the configuration of the reading unit53according to the first embodiment that is illustrated inFIG. 5, but differs from the reading unit53ain a part controlled by the gain setting unit115. Because the other parts are similar, the description of similar parts will be omitted.

A gain setting unit115cof the reading unit53cillustrated inFIG. 9adjusts an analog gain of the column unit116by adjusting the magnitude of a current flowed by a current source112in the column unit116and the magnitude of a current in the ADC112. Because the magnitude of a current flowed by the current source112in the column unit116is adjusted, the current source112is a variable current type current source.

Note that the current source112in the first and second embodiments is a constant current source that flows a constant current. Because a resistance value of a resistance145of the column unit116is not changed unlike the first embodiment, the resistance145is a resistance having a fixed resistance value.

In a case where the gain setting unit115cchanges an analog gain in such a manner that a user gain becomes a constant value, similarly to the first embodiment, the gain setting unit115cchanges a digital gain. The gain setting unit115calso sets a gain of the digital gain processing unit152of the digital processing unit113.

In a case where the magnitude of a current flowed by the current source142is a current value A, the ADC112measures the magnitude of an input current at a scale set in a case where the magnitude is the current value A. A case where the ADC112performs AD conversion of the same pixel value (will be referred to as a pixel value B) will be assumed.

In a case where the magnitude of a current flowed by the current source142is the current value A, the ADC112measures the magnitude of an input current at a scale set in a case where the magnitude is the current value A, and outputs the pixel value B as a result. For example, when the current of the current source142is changed, if AD conversion is performed without changing the scale of the ADC112, a value of the pixel value B can possibly become a wrong value.

Thus, in a case where a current value of the current source142is changed, a scale of the ADC112needs to be changed to a scale corresponding to the changed current value. For example, in a case where a double gain is desired to be obtained, a scale of the ADC112is halved (×½) with the current of the current source142remaining unchanged (×1). In addition, for example, in a case where the scale of the ADC112is doubled, because a ½ gain is applied, the current of the current source142is doubled. In this manner, a current value of the current source142and the size of a scale of the ADC112are adjusted in such a manner that a desired gain is to be obtained.

In a case where the ADC112is configured to perform AD conversion in accordance with an input current value and an output from a digital analog converter (DAC), the scale of the ADC112can be adjusted by changing a current value of the DAC. For example, in a case where a current value of the ADC112is changed to a smaller value (a current value of the DAC in the ADC112is changed to a smaller value), an ADC result becomes larger. By utilizing such a relationship, a scale of the ADC112can be adjusted.

In this manner, by adjusting a current value of the current source142and a scale of the ADC112, a circuit range can be expanded and noise caused by a dark current or the like can be reduced. An operation of the reading unit53caccording to the third embodiment is an operation basically similar to that of the reading unit53aaccording to the first embodiment, and is performed on the basis of the processing in the flowchart illustrated inFIG. 7flowchart. Thus, the description thereof will be omitted here.

Nevertheless, the setting of an analog gain is set to a combination of the current value of the current source142and the scale of the ADC112that realize an analog gain desired to be set, and a digital gain corresponding to the analog gain is set in the digital gain processing unit152.

Also in the reading unit53cin the third embodiment, a user gain (=analog gain×digital gain) is set in accordance with the magnitude of a dark current and image capturing with a suppressed dark current can be performed using the set user gain. In addition, if an analog gain is changed, for example, a noise characteristic can possibly deteriorate. Nevertheless, by applying such circuit noise to a region dominated by a dark current, the circuit noise can be processed by burying the circuit noise into noise attributed to the dark current.

In addition, for preventing a deterioration in image information that is caused by a digital gain, the ADC112preliminarily converts analog data into digital data including bits after the decimal point with low accuracy, and the converted data is used as random numbers. Thus, deterioration in image information that is caused by a digital gain can be prevented.

In the above-described embodiments, the description has been given of an example case where the gain setting unit115suppresses a dark current by setting a resistance value, a capacitance value, or a current value. As described above, these embodiments can be individually implemented, or these embodiments can also be implemented in combination. For example, the gain setting unit115may set a resistance value and a capacitance value, and suppress a dark current using a combination of the resistance value and the capacitance value.

<Configuration Example of Laminated Imaging Device to which Technology According to Present Disclosure can be Applied>

FIGS. 10A, 10B, and 10Cis a are views illustrating outline of a configuration example of a laminated solid-state imaging device to which the technology according to the present disclosure can be applied.

FIG. 10Aillustrates a schematic configuration example of a non-laminated solid-state imaging device. As illustrated inFIG. 10A, a solid-state imaging device510has one die (semiconductor substrate)511. On this die511, a pixel region512in which pixels are arranged in an array, a control circuit513which performs various kinds of control including driving of pixels, and a logic circuit514for performing signal processing are mounted.

The column unit116, the gain setting unit115, the digital processing unit113or the like according to the above-described embodiments can be mounted in the region in where the control circuit513and the logic circuit514are mounted.

FIGS. 10B and 10Cillustrate a schematic configuration example of a laminated solid-state imaging device. As illustrated inFIGS. 10B and 10C, in the solid-state imaging device520, two dies of a sensor die521and a logic die524are laminated and electrically connected to be constituted as one semiconductor chip.

InFIG. 10B, the pixel region512and the control circuit513are mounted on the sensor die521, and the logic circuit514including a signal processing circuit which performs signal processing is mounted on the logic die524.

InFIG. 10C, the pixel region512is mounted on the sensor die521, and the control circuit513and the logic circuit514are mounted on the logic die524.

<Application Example to Endoscopic Surgery System>

A technology (present technology) according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may be applied to an endoscopic surgery system.

FIG. 11is a view depicting an example of a schematic configuration of an endoscopic surgery system to which the technology according to the present disclosure (present technology) can be applied.

An optical system and an image pickup device are provided in the inside of the camera head11102such that reflected light (observation light) from the observation target is condensed on the image pickup device by the optical system. The observation light is photo-electrically converted by the image pickup device to generate an electric signal corresponding to the observation light, namely, an image signal corresponding to an observation image. The image signal is transmitted as RAW data to a camera control unit (CCU)11201.

The light source apparatus11203includes a light source such as, for example, a light emitting diode (LED) and supplies irradiation light upon imaging of a surgical region and the like to the endoscope11100.

It is to be noted that the light source apparatus11203which supplies irradiation light when a surgical region is to be imaged to the endoscope11100may include a white light source which includes, for example, an LED, a laser light source or a combination of them. Where a white light source includes a combination of red, green, and blue (RGB) laser light sources, since the output intensity and the output timing can be controlled with a high degree of accuracy for each color (each wavelength), adjustment of the white balance of a picked up image can be performed by the light source apparatus11203. Further, in this case, if laser beams from the respective RGB laser light sources are irradiated time-divisionally on an observation target and driving of the image pickup devices of the camera head11102are controlled in synchronism with the irradiation timings, it is also possible to time-divisionally capture images corresponding to respective R, G and B. According to the method just described, a color image can be obtained even if a color filter is not provided for the image pickup device.

FIG. 12is a block diagram depicting an example of a functional configuration of the camera head11102and the CCU11201depicted inFIG. 11.

The number of image pickup devices which is included by the imaging unit11402may be one (so-called single-plate type) or a plural number (so-called multi-plate type). Where the imaging unit11402is configured as that of the multi-plate type, for example, image signals corresponding to respective R, G and B are generated by the image pickup devices, and the image signals may be synthesized to obtain a color image. The imaging unit11402may also be configured so as to have a pair of image pickup devices for acquiring respective image signals for the right eye and the left eye ready for three dimensional (3D) display. If 3D display is performed, then the depth of a living body tissue in a surgical region can be comprehended more accurately by the surgeon11131. It is to be noted that, in a case where the imaging unit11402is configured as that of multi-plate type, a plurality of systems of lens units11401is provided corresponding to the individual image pickup devices.

Further, the imaging unit11402may not necessarily be provided on the camera head11102. For example, the imaging unit11402may be provided immediately behind the objective lens in the inside of the lens barrel11101.

In addition, the communication unit11404receives a control signal for controlling driving of the camera head11102from the CCU11201and supplies the control signal to the camera head controlling unit11405. The control signal includes information relating to imaging conditions such as, for example, information by which a frame rate of a picked up image is designated, information by which an exposure value upon image picking up is designated and/or information by which a magnification and a focal point of a picked up image are designated.

<Application Example to Mobile Object>

A technology (present technology) according to the present disclosure can be applied to various products. For example, the technology according to the present disclosure may also be realized as a device mounted in a mobile object of any type such as automobile, electric vehicle, hybrid electric vehicle, motorcycle, bicycle, personal mobility, airplane, drone, ship, or robot.

FIG. 13is a block diagram depicting an example of schematic configuration of a vehicle control system as an example of a mobile object control system to which the technology according to the present disclosure can be applied.

The imaging unit12031is an optical sensor that receives light, and which outputs an electric signal corresponding to a received light amount of the light. The imaging unit12031can output the electric signal as an image, or can output the electric signal as information about a measured distance. In addition, the light received by the imaging unit12031may be visible light, or may be invisible light such as infrared rays or the like.

The sound/image output section12052transmits an output signal of at least one of a sound or an image to an output device capable of visually or auditorily notifying an occupant of the vehicle or the outside of the vehicle of information. In the example ofFIG. 13, an audio speaker12061, a display unit12062, and an instrument panel12063are illustrated as the output device. The display unit12062may, for example, include at least one of an on-board display or a head-up display.

FIG. 14is a diagram depicting an example of the installation position of the imaging unit12031.

Incidentally,FIG. 14depicts an example of imaging ranges of the imaging units12101to12104. An imaging range12111represents the imaging range of the imaging unit12101provided to the front nose. Imaging ranges12112and12113respectively represent the imaging ranges of the imaging units12102and12103provided to the sideview mirrors. An imaging range12114represents the imaging range of the imaging unit12104provided to the rear bumper or the back door. A bird's-eye image of the vehicle12100as viewed from above is obtained by superimposing image data imaged by the imaging units12101to12104, for example.

At least one of the imaging units12101to12104may have a function of obtaining distance information. For example, at least one of the imaging units12101to12104may be a stereo camera constituted of a plurality of image pickup devices, or may be an image pickup device having pixels for phase difference detection.

Further, the advantageous effects described in the present specification are merely exemplary and are not limiting, and additional advantageous may be obtained.

Note that the embodiments of the present technology are not limited to the above-described embodiments, and various changes can be made within a scope not deviating from the gist of the present technology.

An image pickup device including:

a sample and hold unit configured to perform sampling and holding of a pixel signal;

an analog digital (AD) conversion unit configured to perform AD conversion of the pixel signal that includes a digit after a decimal point;

a digital gain processing unit configured to apply a predetermined gain to a digital signal from the AD conversion unit; and

a gain setting unit configured to set an analog gain of a column unit including the sample and hold unit and the AD conversion unit.

The image pickup device according to (1),

in which the gain setting unit sets the analog gain in accordance with a measured dark current amount.

The image pickup device according to (1) or (2),

in which the gain setting unit sets the analog gain and the digital gain in such a manner that a value obtained by multiplying the analog gain by the digital gain becomes a constant value.

The image pickup device according to any one of (1) to (3),

in which the column unit includes a variable resistance, and

the gain setting unit sets a resistance value of the variable resistance at which a set analog gain is obtained.

The image pickup device according to (4),

in which the variable resistance is provided between a first sample and hold unit configured to hold a pixel reset signal, and a second sample and hold unit configured to hold a pixel data signal.

The image pickup device according to any one of (1) to (5),

in which the sample and hold unit includes a capacitor, and

the gain setting unit sets a capacitance value of the capacitor at which a set analog gain is obtained.

The image pickup device according to any one of (1) to (6), further including

a current source configured to flow a predetermined current to a signal line connected to the AD conversion unit,

in which the gain setting unit sets a current value of the current source at which a set analog gain is obtained.

The image pickup device according to (7),

in which, in a case where a current value of the current source is changed, the gain setting unit sets a current value of the AD conversion unit to a value corresponding to the current value of the current source.

An electronic device including:

an image pickup device; and

a signal processing unit configured to process a signal output from the image pickup device,

in which the image pickup device includes

a sample and hold unit configured to perform sampling and holding of a pixel signal,

an analog digital (AD) conversion unit configured to perform AD conversion of the pixel signal that includes a digit after a decimal point,

a digital gain processing unit configured to apply a predetermined gain to a digital signal from the AD conversion unit, and

a gain setting unit configured to set an analog gain of a column unit including the sample and hold unit and the AD conversion unit.

REFERENCE SIGNS LIST