Solid-state imaging device and imaging device

Abstract

The objective of the present invention is to reduce power consumption in a solid-state image capturing element which amplifies a voltage for each column.　This solid-state image capturing element is provided with a pixel circuit, an input transistor, a reference side current source, and a feedback circuit. The pixel circuit generates an input voltage by means of photoelectric conversion. The input transistor outputs, from the drain thereof, an output voltage corresponding to the voltage between the source, into which the input voltage is input, and the gate. The reference side current source is connected to a reference node at a prescribed reference voltage, and supplies a prescribed current. The feedback circuit feeds back a portion of the current to the gate of the input transistor.

Description

[Technical field]

[0001] The present technology relates to a solid-state imaging element, and more particularly to a solid-state imaging element that converts an analog signal into a digital signal for each column, and an imaging device. [Background technology]

[0002] Conventionally, in solid-state imaging devices and the like, various ADCs (Analog to Digital Converters), such as single-slope type, have been used to convert analog signals into digital signals. When this ADC is arranged for each column, a current source is generally connected to a node on the ground side of a vertical signal line wired along the column, and an analog signal from the node is input to the ADC. For example, a solid-state imaging device has been proposed in which an amplifier is inserted between the ADC and a node between the vertical signal line and the current source for the purpose of amplifying the voltage (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-5054 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the above-mentioned conventional technology, the voltage of the analog signal is amplified by inserting an amplifier. However, in order to drive the amplifier, a current source must be provided on the power supply side of the amplifier in addition to the current source on the ground side of the vertical signal line. The addition of this current source on the power supply side may increase power consumption compared to when the voltage is not amplified.

[0005] The present technology was developed in light of these circumstances, and aims to reduce power consumption in solid-state imaging devices that amplify voltage for each column. [Means for solving the problem]

[0006] The present technology has been made to solve the above-mentioned problems, and a first aspect of the present technology is a solid-state imaging device including a pixel circuit that generates an input voltage by photoelectric conversion, an input transistor that outputs an output voltage from a drain according to a voltage between a source and a gate to which the input voltage is input, a reference-side current source that is connected to a reference node of a predetermined reference voltage and supplies a predetermined current, and a feedback circuit that feeds back a part of the current to the gate of the input transistor. This brings about an effect that the input voltage is amplified only by the current of the reference-side current source.

[0007] In addition, in the first aspect, the feedback circuit may include a feedback capacitance inserted between the gate and an output node at which the output voltage is output, a reference side capacitance inserted between the gate and a reference node of the reference voltage, and an input side auto-zero switch that opens and closes a path between the gate and the output node, thereby providing an effect of obtaining a closed loop gain determined by the respective values ​​of the feedback capacitance and the reference side capacitance.

[0008] In addition, in the first aspect, the input transistor may further include a cascode transistor inserted between the reference current source and the drain, and a cascode capacitance inserted between the source of the input transistor and the gate of the cascode transistor, and the output node may be a node between the cascode transistor and the reference current source, thereby improving linearity.

[0009] In addition, in the first aspect, the input / output circuit may further include a power supply side current source connected to a power supply node of a predetermined power supply voltage, and a pair of cascode transistors inserted between the power supply side current source and the reference side current source, and the output node may be a node between the pair of cascode transistors, thereby providing an effect of expanding the output range.

[0010] In addition, in the first aspect, the amplifier may further include an intermediate switch that opens and closes a path between the feedback capacitance and the output node, and a reference switch that opens and closes a path between the feedback capacitance and a node of a predetermined reference voltage, thereby providing an effect that the output range is expanded according to the reference voltage.

[0011] In addition, in the first aspect, the input / output amplifier may further include a cascode capacitance connected to a power supply node of the power supply voltage, an output side auto-zero switch that opens and closes a path between the cascode capacitance and the output node, and an intermediate switch, the reference side current source includes a first reference side current source transistor and a second reference side current source transistor, the first reference side current source transistor is inserted between the input transistor and the reference node, the second reference side current source transistor is inserted between one of the pair of cascode transistors and a reference node of the reference voltage, and the intermediate switch opens and closes a path between the node between the input transistor and the first reference side current source transistor and a node between one of the pair of cascode transistors and the second reference side current source transistor. This provides an effect of expanding the output range.

[0012] In addition, in the first aspect, the power supply may further include a boost-side current source connected to a power supply node of a predetermined power supply voltage, a boost transistor inserted between the boost-side current source and a reference node of the reference voltage and having a gate connected to an output node from which the output voltage is output, and a boost-side capacitance inserted between the source and a node between the boost-side current source and the boost transistor, thereby providing an effect of shortening the time required for settling.

[0013] A second aspect of the present technology is an imaging device including a pixel circuit that generates an input voltage by photoelectric conversion, an input transistor that outputs an output voltage from a drain according to a voltage between a source and a gate to which the input voltage is input, a reference-side current source that is connected to a node of a predetermined reference voltage and supplies a predetermined current, a feedback circuit that feeds back a part of the current to the gate of the input transistor, and an analog-to-digital converter that converts the output voltage into a digital signal. This provides the effect that the input voltage is amplified only by the current of the reference-side current source, and the amplified output voltage is converted into a digital signal. [Brief description of the drawings]

[0014] [Figure 1] 1 is a block diagram showing an example of a configuration of an imaging device according to a first embodiment of the present technology. [Diagram 2] 1 is a diagram showing an example of a layered structure of a solid-state imaging element according to a first embodiment of the present technology. [Diagram 3] 1 is a block diagram showing a configuration example of a solid-state imaging element according to a first embodiment of the present technology. [Figure 4] 1 is a circuit diagram showing a configuration example of a pixel circuit according to a first embodiment of the present technology. [Diagram 5] 2 is a block diagram showing a configuration example of a constant current source unit according to the first embodiment of the present technology; FIG. [Figure 6] 2 is a circuit diagram showing a configuration example of a column amplifier according to a first embodiment of the present technology. [Figure 7] 2 is a block diagram showing a configuration example of an analog-to-digital conversion unit according to the first embodiment of the present technology. FIG. [Figure 8] FIG. 11 is a block diagram showing another example of an ADC according to the first embodiment of the present technology. [Figure 9] 4 is a timing chart showing an example of an operation of the column amplifier according to the first embodiment of the present technology. [Figure 10] FIG. 11 is a circuit diagram illustrating a configuration example of a column amplifier in a comparative example. [Figure 11]1 is a circuit diagram showing a configuration example of a current reuse column amplifier according to a first embodiment of the present technology. [Figure 12] 4 is a graph showing an example of an input-referred noise frequency distribution in the first embodiment of the present technology and a comparative example. [Figure 13] 4A to 4C are diagrams illustrating an example of noise components in the first embodiment of the present technology and a comparative example. [Figure 14] 4 is a graph showing an example of input / output voltage waveforms in the first embodiment of the present technology. [Figure 15] 1 is a graph showing an example of an output voltage settling waveform in the first embodiment of the present technology and a comparative example. [Figure 16] 4 is a graph showing an example of an error for each output voltage in the first embodiment of the present technology. [Figure 17] 11 is a circuit diagram showing a configuration example of a current reuse column amplifier according to a second embodiment of the present technology. FIG. [Figure 18] 11 is a graph showing an example of an error for each output voltage in the first and second embodiments of the present technology. [Figure 19] FIG. 13 is a circuit diagram showing a configuration example of a current reuse column amplifier according to a third embodiment of the present technology. [Figure 20] FIG. 13 is a circuit diagram showing a configuration example of a current reuse column amplifier in a modified example of the third embodiment of the present technology. [Figure 21] FIG. 13 is a circuit diagram showing a configuration example of a current reuse column amplifier according to a fourth embodiment of the present technology. [Figure 22] 13 is a timing chart showing an example of an operation of a column amplifier according to a fourth embodiment of the present technology. [Diagram 23] FIG. 13 is a circuit diagram showing a configuration example of a column amplifier according to a fifth embodiment of the present technology. [Figure 24] 13 is a graph showing an example of waveforms of input / output voltages in the fifth embodiment of the present technology. [Diagram 25] FIG. 13 is a circuit diagram showing another example of a column amplifier according to the fifth embodiment of the present technology. [Figure 26] FIG. 11 is a diagram showing an example of an output range in a comparative example and the first to fifth embodiments of the present technology. [Figure 27] FIG. 11 is a diagram showing an example of an input range in a comparative example and in the first to fifth embodiments of the present technology. [Figure 28] FIG. 11 is a diagram showing an example of noise characteristics in a comparative example and the first to fifth embodiments of the present technology. [Figure 29] 1 is a block diagram showing a schematic configuration example of a vehicle control system; [Diagram 30] FIG. 4 is an explanatory diagram showing an example of an installation position of an imaging unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, modes for carrying out the present technology (hereinafter, referred to as embodiments) will be described. The description will be made in the following order. 1. First embodiment (example in which an input transistor and a feedback circuit are provided) 2. Second embodiment (example in which a cascode transistor, an input transistor, and a feedback circuit are provided) 3. Third embodiment (example in which an input transistor and a feedback circuit are provided and a folded stage is added) 4. Fourth embodiment (an example in which an input transistor, a feedback circuit, and a folded stage are provided and initialized separately) 5. Fifth embodiment (example in which an input transistor and a feedback circuit are provided and a boost circuit is added) 6. Mobile application examples

[0016] <1. First embodiment> [Example of imaging device configuration] 1 is a block diagram showing an example of a configuration of an imaging device 100 according to a first embodiment of the present technology. The imaging device 100 is a device for capturing image data (frames), and includes an optical unit 110, a solid-state imaging element 200, and a DSP (Digital Signal Processing) circuit 120. The imaging device 100 further includes a display unit 130, an operation unit 140, a bus 150, a frame memory 160, a storage unit 170, and a power supply unit 180. As the imaging device 100, for example, in addition to a digital camera such as a digital still camera, a smartphone or personal computer having an imaging function, an in-vehicle camera, and the like are assumed.

[0017] The optical unit 110 collects light from a subject and guides it to the solid-state imaging element 200. The solid-state imaging element 200 generates frames by photoelectric conversion in synchronization with a vertical synchronization signal. Here, the vertical synchronization signal is a periodic signal of a predetermined frequency that indicates the timing of imaging. The solid-state imaging element 200 supplies the generated image data to the DSP circuit 120 via a signal line 209.

[0018] The DSP circuit 120 executes a predetermined signal processing on the frames from the solid-state imaging device 200. The DSP circuit 120 outputs the processed frames via a bus 150 to a frame memory 160 or the like.

[0019] The display unit 130 displays a frame. For example, a liquid crystal panel or an organic EL (Electro Luminescence) panel is assumed as the display unit 130. The operation unit 140 generates an operation signal in accordance with a user's operation.

[0020] The bus 150 is a common path for the optical unit 110, the solid-state imaging device 200, the DSP circuit 120, the display unit 130, the operation unit 140, the frame memory 160, the storage unit 170 and the power supply unit 180 to exchange data with one another.

[0021] The frame memory 160 holds image data. The storage unit 170 stores various data such as frames. The power supply unit 180 supplies power to the solid-state imaging device 200, the DSP circuit 120, the display unit 130, and the like.

[0022] [Example of the configuration of a solid-state imaging element] 2 is a diagram showing an example of a stacked structure of a solid-state imaging element 200 according to the first embodiment of the present technology. The solid-state imaging element 200 includes a circuit chip 202 and a pixel chip 201 stacked on the circuit chip 202. These chips are electrically connected through a connection portion such as a via. Note that, other than the via, the chips can also be connected by Cu-Cu bonding or bumps.

[0023] 3 is a block diagram showing an example of a configuration of a solid-state imaging element 200 according to the first embodiment of the present technology. The solid-state imaging element 200 includes a row selection section 210, a digital to analog converter (DAC) 220, and a timing control circuit 230. The solid-state imaging element 200 further includes a pixel array section 240, a constant current source section 300, an analog-to-digital conversion section 260, a horizontal transfer scanning section 270, and an image processing section 280.

[0024] Furthermore, a plurality of pixel circuits 250 are arranged in a two-dimensional lattice in the pixel array section 240. Hereinafter, a set of pixel circuits 250 arranged in a predetermined horizontal direction will be referred to as a "row", and a set of pixel circuits 250 arranged in a direction perpendicular to the horizontal direction will be referred to as a "column".

[0025] The timing control circuit 230 controls the operation timing of each of the row selection section 210, the DAC 220, the constant current source section 300, the analog-to-digital conversion section 260, and the horizontal transfer scanning section 270 in synchronization with the vertical synchronization signal Vsync.

[0026] The row selection section 210 sequentially selects and drives the rows, and outputs analog pixel signals to the analog-to-digital conversion section 260 via the constant current source section 300 .

[0027] The pixel circuits 250 generate analog pixel signals by photoelectric conversion under the control of the row selection unit 210. Each of the pixel circuits 250 outputs the pixel signal to the constant current source unit 300 via a vertical signal line 259.

[0028] A constant current is supplied to each column in the constant current source unit 300. Also, a column amplifier that amplifies a pixel signal is provided for each column.

[0029] The DAC 220 generates a reference signal by DA (Digital to Analog) conversion and supplies the reference signal to the analog-to-digital conversion unit 260. As the reference signal, for example, a sawtooth ramp signal is used.

[0030] The analog-to-digital converter 260 converts the analog input signal into a digital signal for each column using a reference signal. The analog-to-digital converter 260 supplies the digital signal to the image processor 280 under the control of the horizontal transfer scanner 270.

[0031] The horizontal transfer scanning section 270 controls the analog-to-digital conversion section 260 to output digital signals in sequence.

[0032] The image processing unit 280 performs predetermined image processing on the frames in which the digital signals are arranged. The image processing unit 280 supplies the processed frames to the DSP circuit 120.

[0033] Moreover, the above-mentioned circuits in the solid-state imaging element 200 are distributed and disposed on the pixel chip 201 and the circuit chip 202. For example, the pixel array unit 240 is provided on the pixel chip 201, and circuits other than the pixel array unit 240 (such as the analog-to-digital conversion unit 260) are disposed on the circuit chip 202. Note that the circuits disposed on the pixel chip 201 and the circuit chip 202 are not limited to this combination. For example, it is also possible to dispose the pixel array unit 240, the constant current source unit 300, and the comparator in the analog-to-digital conversion unit 260 on the pixel chip 201, and dispose the other circuits on the circuit chip 202.

[0034] [Pixel circuit configuration example] 4 is a circuit diagram showing an example of a configuration of a pixel circuit 250 according to the first embodiment of the present technology. The pixel circuit 250 includes a photoelectric conversion element 251, a transfer transistor 252, a reset transistor 253, a floating diffusion layer 254, an amplification transistor 255, and a selection transistor 256.

[0035] The photoelectric conversion element 251 converts incident light into an electric charge and generates an electric charge. The transfer transistor 252 transfers an electric charge from the photoelectric conversion element 251 to the floating diffusion layer 254 in accordance with a transfer signal TRG from the row selection unit 210. The reset transistor 253 initializes the amount of electric charge in the floating diffusion layer 254 in accordance with a reset signal RST from the row selection unit 210.

[0036] The floating diffusion layer 254 accumulates electric charges and generates a voltage according to the amount of electric charges. The amplification transistor 255 amplifies the voltage of the floating diffusion layer 254. The selection transistor 256 outputs the amplified voltage signal as a pixel signal SIG in accordance with a selection signal SEL from the row selection unit 210. Assuming that the number of columns is N (N is an integer), the pixel signal of the nth column (n is an integer from 1 to N) is transmitted to the constant current source unit 300 via a vertical signal line 259-n.

[0037] The circuitry of the pixel circuit 250 is not limited to the one illustrated in the figure, as long as it is capable of generating a pixel signal by photoelectric conversion.

[0038] [Constant current source configuration example] 5 is a block diagram showing an example of a configuration of the constant current source unit 300 according to the first embodiment of the present technology. A column amplifier 310 is arranged for each column in the constant current source unit 300. If the number of columns is N, N column amplifiers 310 are arranged.

[0039] A pixel signal of a corresponding column is input to the n-th column amplifier 310 via a vertical signal line 259-n. The column amplifier 310 amplifies the voltage of the pixel signal and outputs it to the analog-to-digital conversion unit 260 via a signal line 309-n. Hereinafter, the voltage of the pixel signal before amplification is referred to as the "input voltage Vin", and the voltage after amplification is referred to as the "output voltage Vout". In addition, the column amplifier 310 is initialized by an auto-zero signal AZ from the timing control circuit 230.

[0040] [Column amplifier configuration example] 6 is a circuit diagram showing a configuration example of a column amplifier 310 according to the first embodiment of the present technology. The column amplifier 310 is provided with a current reuse column amplifier 320. Hereinafter, the current reuse column amplifier 320 is referred to as a "CRCA (Current Reuse Column Amp)". The CRCA includes an input transistor 322, a feedback circuit 323, and a reference-side current source transistor 327. The feedback circuit 323 includes an input-side auto-zero switch 324, a feedback capacitance 325, and a reference-side capacitance 326. In addition, in the figure, a VSL capacitance 400 connected to the vertical signal line 259-n indicates a wiring capacitance between the vertical signal line 259-n and a reference voltage (such as a ground voltage).

[0041] Furthermore, for example, a pMOS (p-channel Metal Oxide Semiconductor) transistor is used as the input transistor 322. For example, an nMOS (n-channel MOS) transistor is used as the reference side current source transistor 327.

[0042] The source of the input transistor 322 is connected to the vertical signal line 259-n, and the drain is connected to the drain of the reference side current source transistor 327. In addition, the pixel circuit 250 generates a pixel signal by photoelectric conversion, and inputs the voltage of the pixel signal as an input voltage Vin to the source of the input transistor 322 via the vertical signal line 259-n.

[0043] The source of the reference-side current source transistor 327 is connected to a reference node of a predetermined reference voltage (such as a ground voltage). A predetermined bias voltage nbias is applied to the gate of the reference-side current source transistor 327, and the reference-side current source transistor 327 supplies a constant bias current according to the bias voltage nbias. The reference-side current source transistor 327 is an example of a reference-side current source as defined in the claims.

[0044] Furthermore, an output voltage Vout is output from an output node 328 between the input transistor 322 and the reference side current source transistor 327 to the analog-to-digital conversion section 260 via a signal line 309-n.

[0045] In the feedback circuit 323, a feedback capacitance 325 is inserted between an output node 328 and the gate of the input transistor 322. Also, a reference-side capacitance 326 is inserted between the gate of the input transistor 322 and a reference node of a reference voltage. The input-side auto-zero switch 324 opens and closes a path between the output node 328 and the gate of the input transistor 322 in accordance with an auto-zero signal AZ.

[0046] With the above-described configuration, the gate-source voltage V GSfluctuates, causing a change in the drain current of the input transistor 322. An output voltage Vout corresponding to this drain current is output from the drain of the input transistor 322 (i.e., output node 328). In this way, an output voltage corresponding to the gate-source voltage of the input transistor 322 is output from the drain. In addition, a portion of the constant bias current supplied by the reference side current source transistor 327 is fed back to the gate of the input transistor 322 by the feedback circuit 323.

[0047] [Example of analog-to-digital conversion section configuration] 7 is a block diagram showing an example of a configuration of the analog-to-digital conversion unit 260 according to the first embodiment of the present technology. In this analog-to-digital conversion unit 260, an ADC 261 and a latch circuit 266 are arranged for each column. If the number of columns is N, N ADCs 261 and N latch circuits 264 are arranged.

[0048] The ADC 261 converts an analog pixel signal into a digital signal. The ADC 261 includes capacitors 262 and 263, a comparator 264, and a counter 265. The ADC 261 also performs a correlated double sampling (CDS) process.

[0049] The comparator 264 compares the reference signal from the DAC 220 with the pixel signal of the corresponding column. The comparator 264 is provided with a pair of input terminals, one of which receives the reference signal via a capacitor 262, and the other of which receives the pixel signal via a capacitor 263. The comparator 264 supplies the comparison result to a counter 265.

[0050] The counter 265 counts the count value over a period until the comparison result is inverted under the control of the timing control circuit 230. The counter 265 outputs a signal indicating the count value to the latch circuit 266 as a digital signal.

[0051] The latch circuit 266 holds the digital signal and outputs the digital signal to the image processing unit 280 in synchronization with a synchronizing signal from the horizontal transfer scanning unit 270.

[0052] 8, in the ADC 261, the capacitors 262 and 263 can be connected in parallel to one of the input terminals (such as the inverting input terminal) of the comparator 264. This allows the voltage of the comparator 264 to be reduced compared to that in FIG.

[0053] [Column amplifier operation example] 9 is a timing chart showing an example of the operation of the column amplifier 310 according to the first embodiment of the present technology. At timing T0 when the voltage of the vertical signal line 259-n is initialized, the timing control circuit 230 controls the input side auto-zero switch 324 to a closed state by the auto-zero signal AZ. This determines the initial voltages stored in the feedback capacitance 325 and the reference side capacitance 326.

[0054] Then, at timing T1 when a predetermined pulse period has elapsed, the timing control circuit 230 controls the input side auto-zero switch 324 to an open state by the auto-zero signal AZ. When the voltage of the floating diffusion layer generated by photoelectric conversion lowers the gate voltage of the amplification transistor 255, the amount of current supplied to the vertical signal line 259-n decreases, and the voltage of the vertical signal line 259-n (i.e., the input voltage Vin) also decreases. Due to the decrease in the input voltage Vin, the gate-source voltage V of the input transistor 322 GS decreases, and the current is further restricted. Here, since the reference side current source transistor 327 continues to draw a constant current, the reduced current from the vertical signal line 259-n is drawn from the output side. Also, the change in the output voltage Vout is negatively fed back to the input transistor 322 by the feedback capacitance 325 and the reference side capacitance 326. The closed loop gain g obtained in this way is expressed by the following equation. g = (C F +C S ) / C F In the above formula, CF indicates the capacitance value of the feedback capacitance 325, and C S indicates the capacitance value of the reference side capacitor 326.

[0055] The current reuse column amplifier 320 uses the relatively large current of the vertical signal line 259-n as a bias to amplify, so it can perform amplification efficiently, leading to power reduction. In addition, it can reduce the capacitance used compared to the comparative example of an inverting amplification type described later, which also has the effect of reducing the circuit area.

[0056] 10 is a circuit diagram showing a configuration example of a column amplifier 500 in a comparative example. In this comparative example column amplifier 500, a current source 501 and an input transistor 505 are connected in series to a power supply, and an output voltage Vout is output from a node between them. The gate of the input transistor 505 is connected to a vertical signal line 259-n via a capacitance 503, and a feedback capacitance 504 is inserted between the source and gate. In addition, an auto-zero switch 502 opens and closes a path between the source and gate of the input transistor 505. Note that a load capacitance 401 connected to the output terminal indicates the capacitance of a circuit (such as an ADC) in the subsequent stage of the column amplifier 500.

[0057] The column amplifier 500 plays a role of accurately amplifying the signal of the vertical signal line 259-n and transmitting it to the next stage ADC. When the signal of the vertical signal line 259-n is small, the noise requirement of the ADC can be relaxed by amplifying the signal. When the signal is large, the amplification rate can be suppressed by switching the size of the capacitance. In this way, a wide range of signals can be handled by an ADC with a low specification. Although an amplifier such as the column amplifier 500 suppresses noise in the subsequent stage, it is necessary to note that the amplifier itself generates noise. In the same figure, a general single-ended inverting amplifier is adopted as the column amplifier 500, but in order to suppress noise, it is necessary to ensure the mutual conductance Gm of the input transistor 505 by flowing a sufficient current. For example, if a current of the same level as the current of the reference side current source transistor 327 (hereinafter referred to as "load MOS") flows, the mutual conductance Gm of the input transistor 505 becomes equal to or greater than that of the load MOS, and the column amplifier becomes a sufficiently low-noise column amplifier.

[0058] 11 is a circuit diagram showing a configuration example of the current reuse column amplifier 320 in the first embodiment of the present technology. In the column amplifier 500 of the comparative example, a current about the same as the current of the load MOS (i.e., the reference side current source transistor 327) is consumed in order to obtain a large mutual conductance Gm. In contrast, in the current reuse column amplifier 320, the column amplifier can be made only with the current of the load MOS, so that the power can be reduced by half in principle compared to the column amplifier 500 of the comparative example.

[0059] In order to compare the CRCA shown in the figure with a case in which there is no column amplifier and only load MOS, test circuits for each were created and the characteristics were examined by simulation. The test circuit conditions are as follows: Transconductance of the amplifier transistor 255: 25 microsiemens (μS) Bias current: 4 microamps (μA) VSL capacitance: 2 picofarads (pF) Reference capacitance value: 1.05 picofarads (pF) Feedback capacitance value: 150 femtofarads (fF) Load capacitance value: 300 femtofarads (fF) Input transistor size: 32u / 1u (LVT: Low Threshold Voltage)

[0060] FIG. 12 shows the frequency distribution of input-referred noise. The vertical axis in the figure shows the input-referred noise, and the horizontal axis shows the frequency. The dashed line shows the frequency distribution of only the load MOS, and the solid line shows the frequency distribution of the CRCA. The input-referred noise is the converted noise at the input of the pixel amplifier (i.e., the gate of the amplifying transistor 255), and the noise of the pixel amplifier is not taken into consideration. In a solid-state image sensor, low-frequency flicker noise is canceled by CDS processing, and high-frequency noise is band-limited in the subsequent stage, so attention is focused on the floor noise in the mid-range (500 kilohertz: kHz). The converted noise of the CRCA at this 500 kilohertz (kHz) is almost double that of only the load MOS. This is due to the increase in noise of the added pMOS (input transistor 322) and the increase in the input-referred noise of the load MOS. From this result alone, it appears that the noise has simply worsened, but the noise of the subsequent stage (comparator) is reduced to 1 / 8 by obtaining gain. 2 The noise in the subsequent stages can be suppressed to a minimum, and the total noise can be reduced depending on the noise in the subsequent stages. In this case, if the noise in the subsequent stages is sufficiently greater than the difference between the noise in the load MOS and the CRCA, the noise in the CRCA can be made lower. The comparator in the subsequent stage tends to reduce the current more than the pixel amplifier to reduce power consumption, which increases noise, so this condition can be expected to be met in most cases.

[0061] Also, looking at the solid line (CRCA) in the figure, it appears that noise increases at high frequencies, but this is because the amplifier gain attenuates at high frequencies. Since input-referred noise is the output noise divided by the gain, it appears to increase dramatically in frequency bands where the gain is small. However, frequency ranges where such signals are cut off are not important in the first place, so they are not used in estimating noise.

[0062] Figure 13 shows the breakdown of input-referred noise at 500 kilohertz (kHz). Here, we consider why the input-referred noise of the load MOS increases. Let us consider the transconductance of the input transistor and the pixel amplifier as gm p , gm x Then, the effective resistance value for converting the current noise of the pixel amplifier transistor into an input-referred voltage can be expressed by the following formula: (1 / gm p )+(1 / gm x )...Equation 1

[0063] From the simulation, gm p is 93.5 microsiemens (μS), and gm x If we take the resistance to be 25 microsiemens (μS), then the first term in Equation 1 is approximately 40 kilohms (kΩ) and the second term is 10.75 kilohms (kΩ). In the case of only the load MOS, the second term is 0 ohms (Ω), so the resistance of the CRCA is approximately 1.27 times that of the case of only the load MOS. This results in a noise (power) contribution of 1.61 times. Looking at the figure, the thermal noise of the load MOS is 1.67 times, which is roughly in line with our prediction.

[0064] 14 shows the waveform of the output voltage when the input voltage amplitude is swept in CRCA. In the figure, the vertical axis indicates voltage, and the horizontal axis indicates time. The dashed line indicates the waveform of the voltage of the vertical signal line (i.e., the input voltage), and the solid line indicates the waveform of the output voltage. One cycle begins with an auto-zero period of 1 microsecond (μs), followed by output of a P-phase voltage for 2 microseconds (μs), and finally ends with output of a D-phase voltage for 2 microseconds (μs). Here, the P-phase voltage is the voltage when the floating diffusion layer in the pixel circuit 250 is initialized, and the D-phase voltage is the voltage when charge is transferred to the floating diffusion layer.

[0065] Also, the input voltage (PD) is assumed to be swept in the range from 0 millivolts (mV) to 100 millivolts (mV) in steps of 10 millivolts (mV). Since the auto-zero signal AZ shorts the gate-drain of the input transistor 322 and sets the output voltage to zero voltage, the output voltage is lower than the voltage of the vertical signal line by the gate-source voltage V GS The test circuit uses LVT transistors, but they drop 335 millivolts (mV), limiting the output range.

[0066] Figure 15 shows the settling of the output voltage when the voltage (input voltage) of the vertical signal line is changed by 100 millivolts (mV). In the figure, the vertical axis indicates the output voltage of the column amplifier, and the horizontal axis indicates time. The dashed and dotted line indicates the trajectory of the output voltage of the load MOS only, and the solid line indicates the trajectory of the output voltage of the CRCA with a gain of 8 times. When the time constant for the time to reach 63% of the final voltage is measured, it is 100 nanoseconds (ns) for the load MOS only, while it is 256 nanoseconds (ns) for the CRCA, which is a significant increase in the settling time. Since the gain of the CRCA is 8 times, the charge required to charge the capacitance attached to the output is also 8 times as much. This increases the effective load capacitance seen by the pixel amplifier, worsening the settling. In the test circuit, the load capacitance (300 fF) and C F / / C S Since the sum of the VSL capacitance (131 fF) is multiplied by 8, it appears that a capacitance of 3.45 picofarads (pF) has been added to the vertical signal line. In the case of only the load MOS, the sum of the VSL capacitance and the load capacitance is 2.3 picofarads (pF). On the other hand, the load capacitance (300 fF) and C F / / C S Eight times the sum of (131fF) is 5.45 picofarads (pF). Thus, the total capacitance of the CRCA is increased by a factor of 2.37, which matches well with the simulation results.

[0067] FIG. 16 shows the error from the regression line of the output voltage after settling when the input voltage is swept, which is so-called linearity. The vertical axis in the figure shows the error, and the horizontal axis shows the output voltage. CRCA tries to suppress the error by using negative feedback, but the open gain is originally low, and the feedback ratio is small due to voltage division, so it is not possible to obtain sufficient loop gain. As a result, the linearity is about 0.3 percent (%) as shown in the figure. In the case of 11 bits (i.e., 2048 gradations), this is about 6 LSB (Least Significant Bit), which is not small. Methods for improving this linearity will be described later.

[0068] As described above, according to the first embodiment of the present technology, the input transistor 322 having an input voltage input to its source and the feedback circuit 323 that feeds back a part of the current of the current source to the gate of the input transistor 322 are provided, so that amplification can be performed using only the current of the current source. This makes it possible to reduce power consumption compared to a comparative example in which an input voltage is input to the gate of the input transistor and a current source is added to its source.

[0069] <2. Second embodiment> In the first embodiment described above, negative feedback is formed by the feedback circuit 323, but in this configuration, the feedback ratio is small, so a sufficient loop gain cannot be obtained, and there is a risk of linearity deteriorating. The current reuse column amplifier 320 of the second embodiment differs from the first embodiment in that linearity is improved by adding a cascode transistor.

[0070] 17 is a circuit diagram showing a configuration example of a current reuse column amplifier 320 according to a second embodiment of the present technology. The current reuse column amplifier 320 according to the second embodiment differs from the first embodiment in that it further includes a cascode capacitance 331, a cascode transistor 332, and a cascode-side auto-zero switch 333. As the cascode transistor 332, for example, a pMOS transistor is used.

[0071] The cascode transistor 332 is inserted between the drain of the input transistor 322 and the drain of the reference side current source transistor 327 (load MOS). In addition, the cascode capacitance 331 is inserted between the source of the input transistor 322 (i.e., the vertical signal line 259-n) and the gate of the cascode transistor 332.

[0072] The cascode-side auto-zero switch 333 opens and closes the path between the gate of the cascode transistor 332 and its drain in accordance with an auto-zero signal AZ.

[0073] In a normal analog circuit, the gate voltage of the cascode transistor is biased at a constant voltage, but in a CRCA, the source voltage of the input transistor 322 (i.e., the input voltage) fluctuates, so it is necessary to bias it at a voltage that follows it. Therefore, as shown in the figure, a cascode capacitance 331 is connected between the vertical signal line 259-n and the gate of the cascode transistor 332, and the cascode side auto-zero switch 333 is closed during auto-zero. This makes it possible to link the gate voltage of the cascode transistor to the vertical signal line 259-n. The current reuse column amplifier 320 shown in the figure is hereinafter referred to as "C (Cascode)-CRCA."

[0074] 18 is a graph showing an example of an error for each output voltage in the first and second embodiments of the present technology. The vertical axis in the figure shows the error, and the horizontal axis shows the output voltage. The dashed line in the figure shows the linearity of the CRCA of the first embodiment in which the cascode transistor 332 and the like are not provided, and the solid line shows the linearity of the C-CRCA of the second embodiment. As shown in the figure, in the second embodiment, the linearity is significantly improved by adding the cascode transistor 332, and the linearity is 0.06 percent (%).

[0075] As described above, according to the second embodiment of the present technology, the cascode transistor 332 having a gate to which a voltage corresponding to an input voltage is applied is inserted, so that the linearity of the output voltage with respect to the input voltage can be improved.

[0076] <3. Third embodiment> In the above-mentioned second embodiment, the cascode transistor 332 is inserted between the drain of the input transistor 322 and the reference side current source transistor 327 (load MOS). However, in this C-CRCA, the output range becomes narrow, which is a problem. The current reuse column amplifier 320 of the third embodiment differs from the second embodiment in that the output range is expanded by a folded stage.

[0077] 19 is a circuit diagram showing a configuration example of a current reuse column amplifier 320 according to the third embodiment of the present technology. The current reuse column amplifier 320 according to the third embodiment includes an input stage 321 and a folded stage 340. The input stage 321 includes an input transistor 322, an input auto-zero switch 324, a feedback capacitance 325, a reference side capacitance 326, and a reference side current source transistor 327. The connection configuration of the input transistor 322, the reference side capacitance 326, and the reference side current source transistor 327 is the same as that of the first embodiment.

[0078] Also, in the folded stage, there are arranged a power supply side current source transistor 342 and cascode transistors 343 and 345. As the power supply side current source transistor 342 and the cascode transistor 343, a pMOS transistor is used, and as the cascode transistor 345, an nMOS transistor is used.

[0079] The power supply side current source transistor 342 and the cascode transistor 343 are connected in series to a power supply node. A bias voltage pbias is applied to the gate of the power supply side current source transistor 342, and a bias voltage pcas is applied to the gate of the cascode transistor 343. The power supply side current source transistor 342 is an example of a power supply side current source as defined in the claims.

[0080] The cascode transistor 345 is inserted between the cascode transistor 343 and the reference side current source transistor 327. A predetermined bias voltage ncas is applied to the gate of the cascode transistor 345.

[0081] In addition, a node between the cascode transistors 343 and 345 is used as an output node 328. An input-side auto-zero switch 324 opens and closes a path between the input transistor 322 and the output node 328, and a feedback capacitor 325 is inserted between the input transistor 322 and the output node 328.

[0082] The current reuse column amplifier 320 illustrated in the figure is hereinafter referred to as "FC (Folded Cascode)-CRCA." In this FC-CRCA, an additional current flows through the folded stage 340, but this current can be reduced compared to the current of the input stage 321. It is better to reduce the current because the input-equivalent noise of the power supply side current source transistor 342 also becomes smaller when the current is reduced. In the FC-CRCA of the third embodiment, the current is 1V lower than that of the C-CRCA of the second embodiment. GS The output range can be expanded.

[0083] As described above, according to the third embodiment of the present technology, since the cascode transistors 343 and 345 are added, the output range can be expanded compared to the second embodiment in which only the cascode transistor 332 is provided.

[0084] [Variations] In the above-described third embodiment, the cascode transistors 343 and 345 are added, but this configuration may cause the output range to be insufficient. The current reuse column amplifier 320 of the modified third embodiment differs from the first embodiment in that a reference voltage is applied to the feedback capacitance 325 during auto-zero to widen the output range.

[0085] 20 is a circuit diagram showing a configuration example of a current reuse column amplifier 320 in a modification of the third embodiment of the present technology. The current reuse column amplifier 320 in the modification of the third embodiment differs from the third embodiment in that it further includes an intermediate switch 330 and a reference switch 330-1. In addition, one end of the feedback capacitance 325 is connected to a node between the intermediate switch 330 and the reference switch 330-1, rather than the output node 328.

[0086] The intermediate switch 330 opens and closes the path between the output node 328 and one end of the feedback capacitance 325 in accordance with an inverted signal xAZ. Here, the inverted signal xAZ is an inverted signal of the auto-zero signal AZ. The reference switch 330-1 connects one end of the feedback capacitance 325 to a predetermined reference voltage V R This opens and closes the path between the node A and the node B in accordance with the auto-zero signal AZ.

[0087] With the configuration illustrated in the figure, the timing control circuit 230 closes the input side auto-zero switch 324 and the reference switch 330-1 during auto-zero and opens the middle switch 330. This allows the zero voltage, which is the output voltage during auto-zero, to be determined independently of the vertical signal line. R is set to a high voltage so that the power supply side current source transistor 342 and the cascode transistor 343 do not enter the linear region. This makes it possible to make maximum use of the output range.

[0088] In this way, according to the modified example of the third embodiment of the present technology, the reference voltage V RSince we have added a reference switch 330-1 that connects the nodes, the zero voltage is connected to the reference voltage V R This allows the output range to be expanded by adjusting the voltage according to the input voltage.

[0089] <4. Fourth embodiment> In the third embodiment described above, the input-side auto-zero switch 324 opens and closes the path between the input transistor 322 and the output node 328. In this configuration, during auto-zero, the zero voltage of the output is 1V from the vertical signal line. GS The current reuse column amplifier 320 of the fourth embodiment differs from the third embodiment in that auto-zero is performed separately for the input stage 321 and the folded stage 340, and a switch is inserted between them to suppress the drop in the zero voltage.

[0090] 21 is a circuit diagram showing a configuration example of a current reuse column amplifier 320 in a fourth embodiment of the present technology. The current reuse column amplifier 320 of the fourth embodiment is different from the third embodiment in that it further includes a cascode capacitance 341, an output side auto-zero switch 344, an intermediate switch 346, and a reference side current source transistor 347. An nMOS transistor is used as the reference side current source transistor 347. Also, the connection configuration of each element in the input stage 321 of the fourth embodiment is the same as that of the first embodiment.

[0091] In addition, the cascode capacitance 341 is inserted between a power supply node of a predetermined power supply voltage and the output-side auto-zero switch 344. The gate of the power supply-side current source transistor 342 is connected to the node between the cascode capacitance 341 and the output-side auto-zero switch 344.

[0092] Furthermore, the reference side current source transistor 347 is inserted between the cascode transistor 345 and the reference node. The same bias voltage nbias as that of the reference side current source transistor 327 is applied to the gate of the reference side current source transistor 347. Note that the reference side current source transistor 327 is an example of a first reference side current source transistor as set forth in the claims, and the reference side current source transistor 347 is an example of a second reference side current source transistor as set forth in the claims.

[0093] The intermediate switch 346 opens and closes a path between a node between the input transistor 322 and the reference side current source transistor 327 and a node between the cascode transistor 345 and the reference side current source transistor 347 in accordance with an inverted signal xAZ.

[0094] Moreover, the output side auto-zero switch 344 opens and closes the path between the cascode capacitor 341 and the output node 328 in accordance with the auto-zero signal AZ.

[0095] The current reuse column amplifier 320 illustrated in the figure will be referred to as a "Modified Folded Cascode (MFC)-CRCA" hereinafter.

[0096] With the configuration illustrated in the figure, the input stage 321 and the folded stage 340 are separated by the intermediate switch 346 during auto-zero, and auto-zero can be performed separately. In the input stage 321, the input-side auto-zero switch 324 performs auto-zero using the intermediate node. Meanwhile, in the folded stage 340, the output-side auto-zero switch 344 shorts the gate of the power supply-side current source transistor 342 and the output node 328. In this way, the zero voltage of the output is 1V from the power supply of the folded stage 340. GSThe voltage drops, and a voltage higher than that of the FC-CRCA of the third embodiment can be made zero voltage. This widens the output range. Since the current source, which was one in the third embodiment, is divided into two in the fourth embodiment (reference side current source transistors 327 and 347), it is necessary to note that the effect of auto-zero is weakened and an offset occurs. In particular, the drain voltage of the input transistor 322 drops during normal operation compared to during auto-zero, so an offset occurs in the direction of increasing the output voltage. This offset becomes particularly large when the current of the folded stage 340 is reduced compared to the input stage 321.

[0097] Also, although the output range is greatly expanded, the maximum value of the input range is smaller by the saturation voltage of the input transistor 322 compared to the case of only the load MOS. When used with a gain of 1, the input range is narrower than that of only the load MOS, and noise also increases. There is a risk that the noise suppression effect in the subsequent stages will be lost.

[0098] 22 is a timing chart showing an example of the operation of the column amplifier 310 in the fourth embodiment of the present technology. At timing T0 when the voltage of the vertical signal line 259-n is initialized, the timing control circuit 230 controls the input side auto-zero switch 324 and the output side auto-zero switch 344 to the closed state by the auto-zero signal AZ. In addition, the timing control circuit 230 controls the middle switch 346 to the open state by the inverted signal xAZ.

[0099] Then, at timing T1 when a predetermined pulse period has elapsed, the timing control circuit 230 controls the input side auto-zero switch 324 and the output side auto-zero switch 344 to an open state using the auto-zero signal AZ. The timing control circuit 230 also controls the middle switch 346 to a closed state using the inverted signal xAZ.

[0100] When the voltage of the floating diffusion layer generated by photoelectric conversion lowers the gate voltage of the amplification transistor 255, the amount of current supplied to the vertical signal line 259-n decreases, and the voltage of the vertical signal line 259-n (input voltage Vin) also drops. GS decreases, and the current is further restricted. Here, the reference side current source transistors 327 and 347 continue to draw a constant current, so the reduced current from the vertical signal line 259-n is drawn from the output side. The output node 328 has high impedance due to the cascode transistors 343 and 345, causing a large voltage drop. Also, the change in the output voltage Vout is negatively fed back to the input transistor 322 by the feedback capacitance 325 and the reference side capacitance 326.

[0101] As described above, according to the fourth embodiment of the present technology, the intermediate switch 346 separates the input stage 321 and the folded stage 340 during auto-zero and performs auto-zero individually, so that the zero voltage can be made higher and the output range can be made wider compared to the case where they are not separated.

[0102] <5. Fifth embodiment> In the first embodiment described above, since the gain is higher than that of only the load MOS, the effective load capacitance seen from the pixel amplifier increases, and the settling deteriorates. The column amplifier 310 of the fifth embodiment differs from the first embodiment in that the load capacitance is reduced by adding a boost circuit 350.

[0103] 23 is a circuit diagram showing a configuration example of a column amplifier 310 according to a fifth embodiment of the present technology. The column amplifier 310 according to the fifth embodiment differs from the first embodiment in that it further includes a boost circuit 350 in addition to the current reuse column amplifier 320. The boost circuit 350 includes a boost side capacitance 351, a boost side current source transistor 352, a cascode transistor 353, and a boost transistor 354. pMOS transistors are used as the boost side current source transistor 352, the cascode transistor 353, and the boost transistor 354.

[0104] The boost side current source transistor 352, the cascode transistor 353, and the boost transistor 354 are inserted in series between a power supply node and a reference node. A predetermined bias voltage pbias is applied to the gate of the boost side current source transistor 352, and a predetermined bias voltage pcas is applied to the gate of the cascode transistor 353. The gate of the boost transistor 354 is connected to the output node 328. The boost side current source transistor 352 and the cascode transistor 353 are an example of a boost side current source as defined in the claims.

[0105] In addition, the boost-side capacitance 351 is inserted between the vertical signal line 259 - n and the node between the cascode transistor 353 and the boost transistor 354 .

[0106] With the configuration shown in the figure, the output voltage Vout can be buffered using the source follower of the boost transistor 354 and capacitively coupled to the vertical signal line 259-n. For example, when the gain is 8 times, the voltage drop of the output voltage Vout is 8 times the voltage drop of the vertical signal line 259-n, and a voltage fluctuation of 7 times the difference between them occurs in the boost side capacitance 351. Then, a current for charging the boost side capacitance 351 is drawn from the vertical signal line 259-n, which helps settling. This operation can be regarded as if a negative capacitance to earth that is 7 times the size of the vertical signal line 259-n is attached to the vertical signal line 259-n, and has the effect of effectively reducing the load capacitance.

[0107] Here, the load capacitance on the output side is expressed by the following formula: C L +C S / / C F ...Formula 2

[0108] If the capacitance value of the boost side capacitance 351 is set to about the same as in Equation 2, it is expected that the virtual capacitance that increases with gain can be completely canceled. However, it should be noted that when the gain is 1, the voltage of the boost side capacitance 351 does not change and it does no work at all.

[0109] In the fifth embodiment, an additional branch current to the boost circuit 350 is required, but this current can be relatively small. When there is gain, the gate-source voltage V of the boost transistor 354 GS This allows a large current to flow to the reference node, and the noise of the additional boost circuit 350 does not appear at the output because it is filtered by the VSL capacitance 400.

[0110] 24 is a graph showing an example of input / output voltage waveforms in the fifth embodiment of the present technology. In the figure, the vertical axis indicates voltage, and the horizontal axis indicates time. The dashed line indicates the input voltage waveform, and the solid line indicates the output voltage waveform when the boost circuit 350 is added. The dotted line indicates the output voltage waveform when the boost circuit 350 is not added.

[0111] The size of the boost transistor 354 is 8u / 1u, the current is 1 microampere (μA), and the capacitance value of the boost side capacitance 351 is 431 femtofarads (fF). In this case, the waveform shown in the figure is obtained. The time constant, which was 256 nanoseconds (ns) with only the CRCA, is improved to 167 nanoseconds (ns) by adding the boost circuit 350.

[0112] Although the boost circuit 350 is added to the CRCA of the first embodiment, the boost circuit 350 can also be added to the second to fourth embodiments. For example, as shown in FIG. 25, the boost circuit 350 can also be added to the MFC-CRCA of the fourth embodiment.

[0113] In this way, according to the fifth embodiment of the present technology, the load capacitance is reduced by adding the boost circuit 350, so that the time required for settling can be shortened.

[0114] Next, a comparison example with only a load MOS is compared with the first to fifth embodiments. Fig. 26 shows an example of an output range in the comparison example with only a load MOS and the first to fifth embodiments. Fig. 27 shows an example of an input range in the comparison example with only a load MOS and the first to fifth embodiments.

[0115] The zero voltage of the input signal is set to 2 volts (V), the voltage width that can be lowered from that is set as the input range, and the voltage width that can be output at any gain is set as the output range. First, in the case of only the load MOS of the comparative example, only 300 millivolts (mV) is required in terms of the circuit for the reference side current source to saturate. However, if 900 millivolts (mV) is secured as a margin to absorb variations and IR drop, the remaining 800 millivolts (mV) after subtracting this from 2 volts (V) becomes the net output range.

[0116] Next, in the CRCA of the first embodiment, the auto-zero operation of the input transistor 322 causes a voltage drop of 335 millivolts (mV), reducing the output range by that amount. Furthermore, in the C-CRCA of the second embodiment, the auto-zero voltage drop is doubled, and the output range is only 130 millivolts (mV). Note that the input and output ranges are the same for the comparative example with only load MOS, the CRCA, and the C-CRCA.

[0117] In the FC-CRCA of the third embodiment, the auto-zero voltage drop is sufficient for one stage, but since the nMOS cascode transistor 345 is added, it is necessary to ensure a saturation voltage of about 100 millivolts (mV).

[0118] In the MFC-CRCA of the fourth embodiment, the subtraction can be started from the power supply voltage (here, 2.8 volts) instead of the input signal of 2 volts (V) due to the difference in the auto-zero method. The voltage drop during auto-zero is 600 millivolts (mV). Even if the saturation voltage of the nMOS cascode transistor 345, 100 millivolts (mV), is subtracted, the output range is 900 millivolts (mV), which is larger than any other method. As for the input range, the voltage drop due to auto-zero is eliminated, but only the saturation voltage of the input transistor 322, 100 millivolts (mV), is required, so the input range is 700 millivolts (mV), which is slightly less than the case of only load MOS.

[0119] Next, Figure 28 shows the predicted input-equivalent noise and SNR (Signal-Noise Ratio) when taking into account the noise of the subsequent comparator. Comparator A is a type of comparator that operates at a lower voltage than comparator B. Comparator A consumes less power than comparator B, but has a larger noise.

[0120] CRCA is particularly effective when used with comparators that have a lot of noise, such as comparator A. For this reason, we predicted the noise when combining A with the CRCA of the first embodiment and the MFC-CRCA of the fourth embodiment. When CRCA is combined with comparator A, the input-equivalent noise is suppressed to about 1 / 3 compared to comparator A at a gain of 8x. However, because the input / output range is reduced, the SNR does not improve much. When the gain is 1x, the SNR deteriorates significantly.

[0121] When MFC-CRCA is combined with comparator A, the input / output range is not reduced. As a result, when the gain is 8 times, the SNR improves by more than 3 decibels (dB), and when the gain is 1 time, there is no deterioration in the SNR. Compared to comparator B, when the gain is 8 times, the SNR is the same, but when it is 1 time, it is no match. There is a difference of several times in the power consumption of comparators A and B, but when the gain is 8 times, if MFC-CRCA is used for comparator A, it is possible to obtain the same noise performance as comparator B with a small amount of power.

[0122] <6. Application examples for mobile devices> The technology according to the present disclosure (the present technology) can be applied to various products. For example, the technology according to the present disclosure may be realized as a device mounted on any type of moving body such as an automobile, an electric vehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personal mobility device, an airplane, a drone, a ship, a robot, etc.

[0123] FIG. 29 is a block diagram showing a schematic configuration example of a vehicle control system, which is an example of a moving object control system to which the technology according to the present disclosure can be applied.

[0124] The vehicle control system 12000 includes a plurality of electronic control units connected via a communication network 12001. In the example shown in Fig. 29, the vehicle control system 12000 includes a drive system control unit 12010, a body system control unit 12020, an outside-vehicle information detection unit 12030, an inside-vehicle information detection unit 12040, and an integrated control unit 12050. Also, as functional configurations of the integrated control unit 12050, a microcomputer 12051, an audio / video output unit 12052, and an in-vehicle network I / F (interface) 12053 are illustrated.

[0125] The drivetrain control unit 12010 controls the operation of devices related to the drivetrain of the vehicle in accordance with various programs. For example, the drivetrain control unit 12010 functions as a control device for a drive force generating device for generating a drive force of the vehicle, such as an internal combustion engine or a drive motor, a drive force transmission mechanism for transmitting the drive force to the wheels, a steering mechanism for adjusting the steering angle of the vehicle, and a braking device for generating a braking force of the vehicle.

[0126] The body system control unit 12020 controls the operation of various devices mounted on the vehicle body according to various programs. For example, the body system control unit 12020 functions as a control device for a keyless entry system, a smart key system, a power window device, or various lamps such as head lamps, back lamps, brake lamps, turn signals, and fog lamps. In this case, radio waves or signals of various switches transmitted from a portable device that replaces a key may be input to the body system control unit 12020. The body system control unit 12020 receives the input of these radio waves or signals and controls the door lock device, power window device, lamps, and the like of the vehicle.

[0127] The outside-vehicle information detection unit 12030 detects information outside the vehicle equipped with the vehicle control system 12000. For example, an imaging unit 12031 is connected to the outside-vehicle information detection unit 12030. The outside-vehicle information detection unit 12030 causes the imaging unit 12031 to capture an image outside the vehicle and receives the captured image. The outside-vehicle information detection unit 12030 may perform object detection processing or distance detection processing for a person, a car, an obstacle, a sign, or characters on a road surface, based on the received image.

[0128] The imaging unit 12031 is an optical sensor that receives light and outputs an electrical signal according to the amount of light received. The imaging unit 12031 can output the electrical signal as an image, or as distance measurement information. The light received by the imaging unit 12031 may be visible light or invisible light such as infrared light.

[0129] The in-vehicle information detection unit 12040 detects information inside the vehicle. For example, a driver state detection unit 12041 that detects the state of the driver is connected to the in-vehicle information detection unit 12040. The driver state detection unit 12041 includes, for example, a camera that captures an image of the driver, and the in-vehicle information detection unit 12040 may calculate the degree of fatigue or concentration of the driver based on the detection information input from the driver state detection unit 12041, or may determine whether the driver is dozing.

[0130] The microcomputer 12051 can calculate control target values ​​for the driving force generating device, the steering mechanism, or the braking device based on the information inside and outside the vehicle acquired by the outside-of-vehicle information detection unit 12030 or the inside-vehicle information detection unit 12040, and output a control command to the drive system control unit 12010. For example, the microcomputer 12051 can perform cooperative control aimed at realizing the functions of an ADAS (Advanced Driver Assistance System), including vehicle collision avoidance or impact mitigation, following driving based on the inter-vehicle distance, vehicle speed maintenance driving, vehicle collision warning, vehicle lane departure warning, etc.

[0131] In addition, the microcomputer 12051 can perform cooperative control for the purpose of autonomous driving, which allows the vehicle to travel autonomously without relying on the driver's operation, by controlling the driving force generating device, steering mechanism, braking device, etc. based on information about the surroundings of the vehicle acquired by the outside vehicle information detection unit 12030 or the inside vehicle information detection unit 12040.

[0132] Furthermore, the microcomputer 12051 can output a control command to the body system control unit 12020 based on the information outside the vehicle acquired by the outside-vehicle information detection unit 12030. For example, the microcomputer 12051 can control the headlamps according to the position of a preceding vehicle or an oncoming vehicle detected by the outside-vehicle information detection unit 12030, and perform cooperative control for the purpose of preventing glare, such as switching from high beams to low beams.

[0133] The audio / video output unit 12052 transmits at least one output signal of audio and video to an output device capable of visually or audibly notifying information to passengers in the vehicle or the outside of the vehicle. In the example of Fig. 29, an audio speaker 12061, a display unit 12062, and an instrument panel 12063 are exemplified as the output device. The display unit 12062 may include at least one of an on-board display and a head-up display, for example.

[0134] FIG. 30 is a diagram showing an example of the installation position of the imaging unit 12031.

[0135] In FIG. 30, the imaging unit 12031 includes imaging units 12101, 12102, 12103, 12104, and 12105.

[0136] The imaging units 12101, 12102, 12103, 12104, and 12105 are provided at positions such as the front nose, side mirrors, rear bumper, back door, and the upper part of the windshield inside the vehicle cabin of the vehicle 12100. The imaging unit 12101 provided at the front nose and the imaging unit 12105 provided at the upper part of the windshield inside the vehicle cabin mainly acquire images of the front of the vehicle 12100. The imaging units 12102 and 12103 provided at the side mirrors mainly acquire images of the sides of the vehicle 12100. The imaging unit 12104 provided at the rear bumper or back door mainly acquires images of the rear of the vehicle 12100. The imaging unit 12105 provided at the upper part of the windshield inside the vehicle cabin is mainly used to detect a preceding vehicle, a pedestrian, an obstacle, a traffic light, a traffic sign, a lane, or the like.

[0137] 30 shows an example of the imaging ranges of the imaging units 12101 to 12104. Imaging range 12111 indicates the imaging range of the imaging unit 12101 provided on the front nose, imaging ranges 12112 and 12113 indicate the imaging ranges of the imaging units 12102 and 12103 provided on the side mirrors, respectively, and imaging range 12114 indicates the imaging range of the imaging unit 12104 provided on the rear bumper or back door. For example, an overhead image of the vehicle 12100 viewed from above is obtained by superimposing the image data captured by the imaging units 12101 to 12104.

[0138] At least one of the imaging units 12101 to 12104 may have a function of acquiring distance information. For example, at least one of the imaging units 12101 to 12104 may be a stereo camera made up of a plurality of imaging elements, or may be an imaging element having pixels for detecting a phase difference.

[0139] For example, the microcomputer 12051 can extract, as a preceding vehicle, a three-dimensional object that is the closest three-dimensional object on the travel path of the vehicle 12100 and travels at a predetermined speed (for example, 0 km / h or more) in approximately the same direction as the vehicle 12100, by calculating the distance to each three-dimensional object in the imaging ranges 12111 to 12114 and the change over time of this distance (relative speed with respect to the vehicle 12100) based on the distance information obtained from the imaging units 12101 to 12104. Furthermore, the microcomputer 12051 can set a vehicle distance to be secured in advance in front of the preceding vehicle, and perform automatic brake control (including follow-up stop control) and automatic acceleration control (including follow-up start control). In this way, cooperative control can be performed for the purpose of automatic driving that travels autonomously without relying on the driver's operation.

[0140] For example, the microcomputer 12051 classifies and extracts three-dimensional object data on three-dimensional objects into two-wheeled vehicles, ordinary vehicles, large vehicles, pedestrians, utility poles, and other three-dimensional objects based on distance information obtained from the imaging units 12101 to 12104, and can use the data for automatic obstacle avoidance. For example, the microcomputer 12051 distinguishes obstacles around the vehicle 12100 into obstacles that are visible to the driver of the vehicle 12100 and obstacles that are difficult to see. Then, the microcomputer 12051 determines a collision risk indicating the risk of collision with each obstacle, and when the collision risk is equal to or greater than a set value and a collision is possible, the microcomputer 12051 can provide driving assistance for collision avoidance by outputting an alarm to the driver via the audio speaker 12061 or the display unit 12062, or by performing forced deceleration or avoidance steering via the drive system control unit 12010.

[0141] At least one of the imaging units 12101 to 12104 may be an infrared camera that detects infrared rays. For example, the microcomputer 12051 can recognize a pedestrian by determining whether or not a pedestrian is present in the captured images of the imaging units 12101 to 12104. The recognition of such a pedestrian is performed, for example, by a procedure of extracting feature points in the captured images of the imaging units 12101 to 12104 as infrared cameras, and a procedure of performing pattern matching processing on a series of feature points that indicate the contour of an object to determine whether or not the object is a pedestrian. When the microcomputer 12051 determines that a pedestrian is present in the captured images of the imaging units 12101 to 12104 and recognizes the pedestrian, the audio / image output unit 12052 controls the display unit 12062 to superimpose a rectangular contour line for emphasis on the recognized pedestrian. The audio / image output unit 12052 may also control the display unit 12062 to display an icon or the like indicating a pedestrian at a desired position.

[0142] An example of a vehicle control system to which the technology according to the present disclosure can be applied has been described above. The technology according to the present disclosure can be applied to, for example, the imaging unit 12031 among the configurations described above. Specifically, the imaging device 100 in FIG. 1 can be applied to the imaging unit 12031. By applying the technology according to the present disclosure to the imaging unit 12031, the power consumption of the column amplifier can be suppressed, and therefore the power consumption of the entire vehicle system can be reduced.

[0143] The above-mentioned embodiment shows an example for realizing the present technology, and the matters in the embodiment and the matters specified in the claims correspond to each other. Similarly, the matters specified in the claims and the matters in the embodiment of the present technology having the same name correspond to each other. However, the present technology is not limited to the embodiment, and can be realized by applying various modifications to the embodiment within the scope of the gist of the technology.

[0144] It should be noted that the effects described in this specification are merely examples and are not limiting, and other effects may also be obtained.

[0145] The present technology can also be configured as follows. (1) a pixel circuit that generates an input voltage by photoelectric conversion; an input transistor that outputs an output voltage from a drain according to a voltage between a source and a gate to which the input voltage is input; a reference-side current source connected to a reference node of a predetermined reference voltage to supply a predetermined current; a feedback circuit that feeds back a portion of the current to the gate of the input transistor; A solid-state imaging device comprising: (2) The feedback circuit comprises: a feedback capacitance inserted between the gate and an output node to which the output voltage is output; a reference side capacitance inserted between the gate and a reference node of the reference voltage; an input-side auto-zero switch that opens and closes a path between the gate and the output node; Equipped The solid-state imaging device according to (1) above. (3) a cascode transistor inserted between the reference side current source and the drain; a cascode capacitance inserted between the source of the input transistor and the gate of the cascode transistor; Further comprising: The output node is a node between the cascode transistor and the reference side current source. The solid-state imaging device according to (2) above. (4) a power supply side current source connected to a power supply node of a predetermined power supply voltage; a pair of cascode transistors inserted between the power supply side current source and the reference side current source; Further comprising: The output node is a node between the pair of cascode transistors. The solid-state imaging device according to (2) above. (5) an intermediate switch that opens and closes a path between the feedback capacitance and the output node; a reference switch that opens and closes a path between the feedback capacitance and a node of a predetermined reference voltage; Further comprising The solid-state imaging device according to (4) above. (6) a cascode capacitance connected to a power supply node of the power supply voltage; an output side auto-zero switch that opens and closes a path between the cascode capacitance and the output node; Intermediate switch and Further comprising: the reference side current source includes a first reference side current source transistor and a second reference side current source transistor; the first reference side current source transistor is inserted between the input transistor and the reference node; the second reference side current source transistor is inserted between one of the pair of cascode transistors and a reference node of the reference voltage; The intermediate switch opens and closes a path between a node between the input transistor and the first reference side current source transistor and a node between one of the pair of cascode transistors and the second reference side current source transistor. The solid-state imaging device according to (4) above. (7) a boost-side current source connected to a power supply node of a predetermined power supply voltage; a boost transistor that is inserted between the boost-side current source and a reference node of the reference voltage and has a gate connected to an output node at which the output voltage is output; a boost-side capacitance inserted between a node between the boost-side current source and the boost transistor and the source; Further comprising The solid-state imaging device according to any one of (1) to (6). (8) a pixel circuit that generates an input voltage by photoelectric conversion; an input transistor that outputs an output voltage from a drain according to a voltage between a source and a gate to which the input voltage is input; a reference-side current source connected to a node of a predetermined reference voltage to supply a predetermined current; a feedback circuit for feeding back a portion of the current to the gate of the input transistor; an analog-to-digital converter for converting the output voltage into a digital signal; An imaging device comprising: [Explanation of symbols]

[0146] 100 Imaging device 110 Optics Department 120 DSP circuits 130 Display section 140 Operation section 150 Bus 160 Frame Memory 170 Storage section 180 Power supply section 200 Solid-state image sensor 201 Pixel Chip 202 Circuit Chip 210 Line Selection 220DAC 230 Timing control circuit 240 Pixel array section 250 pixel circuit 251 Photoelectric conversion element 252 Transfer transistor 253 Reset Transistor 254 Floating Diffusion Layer 255 Amplifying Transistor 256 Select Transistor 260 Analog-to-digital conversion section 261 ADC 262, 263, 503 capacity 264 Comparator 265 Counter 266 Latch Circuit 270 Horizontal transfer scanning section 280 Image Processing Unit 300 Constant current source section 310, 500 Column Amplifier 320 Power Reuse Column Amplifier 321 Input Stage 322, 505 Input transistor 323 Feedback Circuit 324 Input side auto-zero switch 325, 504 Feedback capacitance 326 Reference side capacitance 327, 347 Reference side current source transistor 330, 346 Intermediate switch 330-1 Reference Switch 331, 341 Cascode Capacitance 332, 343, 345, 353 Cascode transistors 333 Cascode side auto-zero switch 340 Folded Stage 342 Power supply side current source transistor 344 Output auto-zero switch 350 Boost Circuit 351 Boost side capacity 352 Boost side current source transistor 354 Boost Transistor 400 VSL capacity 401 Load capacity 501 Current source 502 Auto Zero Switch 12031 Imaging unit

Claims

1. A pixel circuit that generates an input voltage by photoelectric conversion; an input transistor that outputs an output voltage from a drain according to a voltage between a source and a gate to which the input voltage is input; a reference-side current source that is inserted between the drain and a reference node of a predetermined reference voltage to supply a predetermined current; a feedback circuit that feeds back a portion of the current to the gate of the input transistor; A solid-state imaging device comprising:

2. The feedback circuit includes: a feedback capacitance inserted between the gate and an output node to which the output voltage is output; a reference side capacitance inserted between the gate and a reference node of the reference voltage; an input-side auto-zero switch that opens and closes a path between the gate and the output node; Equipped 2. The solid-state imaging device according to claim 1.

3. A pixel circuit that generates an input voltage by photoelectric conversion; an input transistor that outputs from a drain a voltage corresponding to a voltage between a source and a gate to which the input voltage is input; a reference-side current source that is inserted between the output node and a reference node of a predetermined reference voltage to supply a predetermined current; a feedback circuit for feeding back a portion of the current to the gate of the input transistor; a cascode transistor inserted between the reference side current source and the drain; a cascode capacitance inserted between the source of the input transistor and the gate of the cascode transistor; Equipped with The output node is a node between the cascode transistor and the reference side current source. Solid-state imaging element.

4. A pixel circuit that generates an input voltage by photoelectric conversion; an input transistor that outputs from a drain a voltage corresponding to a voltage between a source and a gate to which the input voltage is input; a reference-side current source that is inserted between the drain and a reference node of a predetermined reference voltage to supply a predetermined current; a feedback circuit for feeding back a portion of the current to the gate of the input transistor; A power supply side current source connected to a power supply node of a predetermined power supply voltage; a pair of cascode transistors inserted between the power supply side current source and the reference side current source; Equipped with The feedback circuit includes: A feedback capacitance is inserted between the gate and an output node at which an output voltage is output; a reference side capacitance inserted between the gate and a reference node of the reference voltage; an input-side auto-zero switch that opens and closes a path between the gate and the output node; Equipped with The output node is a node between the pair of cascode transistors. Solid-state imaging element.

5. an intermediate switch that opens and closes a path between the feedback capacitance and the output node; a reference switch that opens and closes a path between the feedback capacitance and a node of a predetermined reference voltage; Further comprising 5. The solid-state imaging device according to claim 4.

6. a cascode capacitance connected to a power supply node of the power supply voltage; an output side auto-zero switch that opens and closes a path between the cascode capacitance and the output node; Intermediate switch and Further comprising: the reference side current source includes a first reference side current source transistor and a second reference side current source transistor; the first reference side current source transistor is inserted between the input transistor and the reference node; the second reference side current source transistor is inserted between one of the pair of cascode transistors and a reference node of the reference voltage; The intermediate switch opens and closes a path between a node between the input transistor and the first reference side current source transistor and a node between one of the pair of cascode transistors and the second reference side current source transistor.

5. The solid-state imaging device according to claim 4.

7. A boost-side current source connected to a power supply node of a predetermined power supply voltage; a boost transistor that is inserted between the boost-side current source and a reference node of the reference voltage and has a gate connected to an output node from which the output voltage is output; a boost-side capacitance inserted between a node between the boost-side current source and the boost transistor and the source; Further comprising 2. The solid-state imaging device according to claim 1.

8. A pixel circuit that generates an input voltage by photoelectric conversion; an input transistor that outputs an output voltage from a drain according to a voltage between a source and a gate to which the input voltage is input; a reference-side current source that is inserted between the drain and a node of a predetermined reference voltage and supplies a predetermined current; a feedback circuit for feeding back a portion of the current to the gate of the input transistor; an analog-to-digital converter for converting the output voltage into a digital signal; An imaging device comprising:

Images