CN109005374B - Working method of image sensor pixel circuit - Google Patents

Working method of image sensor pixel circuit Download PDF

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CN109005374B
CN109005374B CN201811066988.6A CN201811066988A CN109005374B CN 109005374 B CN109005374 B CN 109005374B CN 201811066988 A CN201811066988 A CN 201811066988A CN 109005374 B CN109005374 B CN 109005374B
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comparison
transistor
image data
signal
level value
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CN109005374A (en
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任张强
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Rockchip Electronics Co Ltd
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Rockchip Electronics Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
    • H04N25/70—SSIS architectures; Circuits associated therewith
    • H04N25/71—Charge-coupled device [CCD] sensors; Charge-transfer registers specially adapted for CCD sensors
    • H04N25/75—Circuitry for providing, modifying or processing image signals from the pixel array

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  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Transforming Light Signals Into Electric Signals (AREA)

Abstract

An image sensor pixel circuit and a method of operating the same, the image sensor pixel circuit comprising: a pixel unit including: a column readout line; a detection unit, the detection unit comprising: a capacitor having opposing first and second capacitor terminals, the first capacitor terminal being connected to the column sense line; the comparator is provided with a first comparison input end, a second comparison input end and a comparison output end, the second comparison input end is connected with the second capacitor end, and the first comparison input end is suitable for inputting a comparison time sequence signal; and the switch is respectively connected with the second comparison input end and the comparison output end. The performance of the image sensor pixel circuit is improved.

Description

Working method of image sensor pixel circuit
Technical Field
The invention relates to the field of semiconductor detection, in particular to an image sensor pixel circuit and a working method thereof.
Background
An image sensor is a semiconductor device that converts an optical signal into an electrical signal.
Image sensors are classified into Complementary Metal Oxide (CMOS) image sensors and Charge Coupled Device (CCD) image sensors. The CMOS image sensor has the advantages of simple process, easiness in integration of other devices, small size, light weight, low power consumption, low cost and the like. Therefore, with the development of image sensing technology, CMOS image sensors are increasingly used in various electronic products instead of CCD image sensors. At present, CMOS image sensors have been widely used in still digital cameras, digital video cameras, medical imaging devices, vehicle imaging devices, and the like.
However, the performance of the existing image sensor is to be improved.
Disclosure of Invention
The invention provides an image sensor pixel circuit and a forming method thereof, which are used for improving the performance of the image sensor pixel circuit.
To solve the above problem, the present invention provides an image sensor pixel circuit, comprising: a pixel unit including: a column readout line; a detection unit, the detection unit comprising: a capacitor having opposing first and second capacitor terminals, the first capacitor terminal being connected to the column sense line; the comparator is provided with a first comparison input end, a second comparison input end and a comparison output end, the second comparison input end is connected with the second capacitor end, and the first comparison input end is suitable for inputting a comparison time sequence signal; and the switch is respectively connected with the second comparison input end and the comparison output end.
Optionally, the column readout line has opposite first and second readout terminals; the pixel unit further includes: a photodiode; a transfer transistor, a source of the transfer transistor being connected to the photodiode; a floating diffusion point connected to a drain of the transfer transistor; the source electrode of the reset transistor is connected with the floating diffusion point, and the drain electrode of the reset transistor is connected with a power line; the grid electrode of the amplifying transistor is connected with the floating diffusion point, and the drain electrode of the amplifying transistor is connected with a power line; a selection transistor, a drain of which is connected to a source of the amplification transistor; the first readout terminal is connected to the source of the selection transistor, and the second readout terminal is connected to the first capacitor terminal.
Optionally, the method further includes: the analog-to-digital conversion module is provided with a first image data input end, a second image data input end and an image data output end, the first image data input end is connected with the column readout line, the second image data input end is connected with the comparison output end, the image data output end is suitable for outputting a digital image signal, and the digital image signal is suitable for being acquired according to data input by the first image data input end and data input by the second image data input end.
Optionally, the method further includes: and the image processing module is connected with the image data output end and is suitable for carrying out noise reduction processing on the digital image signal.
The invention also provides a working method of the pixel circuit of the image sensor, which comprises the following steps: providing the image sensor pixel circuit; the detection unit carries out reference sampling on the voltage of the column readout line, and the switch is in a conducting state in the process of carrying out the reference sampling; after the reference sampling is carried out, the switch is switched off; after the switch is disconnected, reducing the magnitude of the comparison time sequence signal to a first level value; after the magnitude of the comparison time sequence signal is reduced, a comparison sampling step is carried out; the step of comparing samples comprises: sampling the signal of the column readout line and coupling to a second comparison input terminal, so that the second comparison input terminal has a second level value; and the comparator outputs a detection signal after comparing the second level value with the first level value.
Optionally, the column readout line has opposite first and second readout terminals; the pixel unit further includes: a photodiode; a transfer transistor, a source of the transfer transistor being connected to the photodiode; a floating diffusion point connected to a drain of the transfer transistor; the source electrode of the reset transistor is connected with the floating diffusion point, and the drain electrode of the reset transistor is connected with a power line; the grid electrode of the amplifying transistor is connected with the floating diffusion point, and the drain electrode of the amplifying transistor is connected with a power line; a selection transistor, a drain of which is connected to a source of the amplification transistor; the first reading end is connected with the source electrode of the selection transistor, and the second reading end is connected with the first capacitor end; the working method of the image sensor pixel circuit further comprises the following steps: performing a reset operation before the detection unit performs reference sampling on the voltage of the column readout line; during the reset operation, the selection transistor is in an on state, the transfer transistor is in an off state, the reset transistor is in an on state, the switch is in an on state, the comparison timing signal has an initial level value, and the initial level value is greater than the first level value; in the reference sampling step, the selection transistor is in a conducting state, the transmission transistor is in a disconnecting state, the reset transistor is in a disconnecting state, and the switch is in a conducting state; the comparison timing signal has an initial level value.
Optionally, a difference between the initial level value and the first level value is equal to a comparison threshold, and the comparison threshold is 90 mv to 110 mv.
Optionally, after the reference sampling and before the comparison sampling step, the selection transistor is in a conducting state, the transmission transistor is in a disconnecting state, the reset transistor is in a disconnecting state, and the switch is in a disconnecting state.
Optionally, in the comparing and sampling step, when the second level value is greater than the first level value, the detection signal is "0"; in the comparing and sampling step, when the second level value is less than the first level value, the detection signal is "1".
Optionally, the image sensor pixel circuit further includes: an analog-to-digital conversion module having a first image data input terminal, a second image data input terminal, and an image data output terminal, the first image data input terminal being connected to the column readout line, the second image data input terminal being connected to the comparison output terminal, the image data output terminal being adapted to output a digital image signal, the digital image signal being obtained from data input by the first image data input terminal and data input by the second image data input terminal; if the detection signal is '0', the signal output by the image data output end is obtained by directly converting the signal input by the first image data input end; and if the detection signal is '1', setting the signal output by the image data output end to full-scale data of the analog-to-digital conversion module.
Compared with the prior art, the technical scheme of the invention has the following advantages:
in the operating method of the pixel circuit of the image sensor provided by the technical scheme of the invention, in the process of reference sampling, the switch is in a conducting state, so that the potential of the second comparison input end is equal to the potential of the first comparison input end, and the capacitor stores the difference between the potential of the column readout line and the potential of the second comparison input end. After the reference sampling is carried out, the switch is switched off, so that the potential of the second comparison input end is not influenced by the potential of the first comparison input end; after the switch is disconnected, reducing the magnitude of the comparison time sequence signal to a first level value; then, a comparison sampling step is performed, in which the signals of the column readout lines are sampled and capacitively coupled to the second comparison input terminal, so that the second comparison input terminal has a second level value. Since the capacitance stores the difference between the potential of the column readout line and the potential of the second comparison input terminal, the magnitude of the change in the potential on the column readout line and the magnitude of the change in the potential of the second comparison input terminal coincide. The comparator compares the second level value with the first level value and outputs a detection signal, so that the magnitude of the detection signal represents the variation amplitude of the second comparison input end potential, and the variation amplitude of the second comparison input end potential is consistent with the variation amplitude of the potential on the column readout line, and therefore the magnitude of the detection signal also indirectly represents the variation amplitude of the potential on the column readout line. Therefore, the detection signal is not influenced by the threshold deviation of each transistor in the pixel circuit and the fluctuation of the pixel power supply voltage, and the accuracy of the detection result of the pixel blooming is improved. Therefore, the performance of the pixel circuit of the image sensor is improved.
Further, the image sensor pixel circuit further includes: and an analog-to-digital conversion module. If the detection signal is '0', the signal output by the image data output end is consistent with the signal input by the first image data input end; if the detection signal is '1', the detection signal is obtained by directly converting the signal input by the first image data input end; and if the detection signal is '1', setting the signal output by the image data output end to full-scale data of the analog-to-digital conversion module. Therefore, the analog-digital conversion module outputs digital image signals according to the detection signals and the signals of the column reading lines, and the digital image signals modulate the signals of the column reading lines to a certain degree, so that the phenomenon of 'sun black spots' is avoided.
Drawings
FIG. 1 is a schematic diagram of an image sensor pixel circuit;
FIG. 2 is a schematic diagram of a solar black spot in an image sensor pixel circuit;
FIG. 3 is a schematic diagram of an image sensor pixel circuit according to an embodiment of the invention;
FIG. 4 is a flow chart of the operation of an image sensor pixel circuit according to another embodiment of the present invention;
fig. 5 is a timing diagram of an image sensor pixel circuit of the present invention.
Detailed Description
As described in the background, the prior art forms image sensor pixel circuits with poor performance.
An image sensor pixel circuit, please refer to fig. 1, comprising: a photodiode; a transfer transistor TG having a source connected to the photodiode; a floating diffusion point FD node connected to a drain of the transfer transistor TG; reset transistor PGRSTThe reset transistor PGRSTIs connected to the floating diffusion point FD node, the reset transistor PGRSTThe drain of the second transistor is connected with a power supply line VDDPIX; selection transistor PGSFSaid selection transistor PGSFIs connected to a floating diffusion point FD node, the select transistor PGSFThe drain of the second transistor is connected with a power supply line VDDPIX; amplifying transistor PGRSELSaid amplifying transistor PGRSELAnd the selection transistor PGSFA source level connection of; a column readout line BL, the column readout line BL and the amplifying transistor PGRSELIs connected to the source.
When the pixel circuit of the image sensor works under strong illumination, excessive photo-generated charges can be generated, and photoelectrons can overflow from the corresponding pixel to the floating diffusion point FD node. When overflowing to the floating diffusion point FD node, the reset voltage of the pixel is lowered. When the photoelectrons overflow to a large extent, the reset voltage is lowered much or even to 0 level, resulting in a "0" signal output from the pixel.
The overflow point should be a very bright overexposed point, and the electron overflow turns into a black point instead, which is called "solar black spot" (see fig. 2). Due to the occurrence of the above-mentioned "solar black spot", the quality of the image is severely degraded, resulting in poor performance of the pixel circuit of the image sensor. Therefore, whether the image sensor pixel circuit generates the blooming phenomenon causing the sun black spot needs to be accurately detected.
Setting a comparison voltage value, directly reading a voltage signal of a column read-out line BL, comparing the read voltage signal of the BL with the comparison voltage value, if the read voltage signal of the BL is greater than the comparison voltage value, judging that no blooming occurs, and if the read voltage signal of the BL is less than the comparison voltage value, judging that the blooming occurs.
The above method for detecting blooming phenomenon has the following disadvantages: due to the influence of threshold deviation of each transistor in the pixel circuit and fluctuation of the pixel power supply voltage, the voltage signals of the BL corresponding to the same photoelectron overflow degree are different for different pixel units, and different detection results may be obtained when comparing the comparison voltage value with the voltage signal of the BL. Thus resulting in poor accuracy of the blooming detection.
On this basis, the invention provides an image sensor pixel circuit, comprising: a pixel unit including: a column readout line; a detection unit, the detection unit comprising: a capacitor having opposing first and second capacitor terminals, the first capacitor terminal being connected to the column sense line; the comparator is provided with a first comparison input end, a second comparison input end and a comparison output end, the second comparison input end is connected with the second capacitor end, and the first comparison input end is suitable for inputting a comparison time sequence signal; and the switch is respectively connected with the second comparison input end and the comparison output end. The method improves the performance of the pixel circuit of the image sensor.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
The present embodiment provides an image sensor pixel circuit, please refer to fig. 2, which includes:
a pixel cell 10, the pixel cell 10 comprising: a column readout line BL;
a detection unit 20, the detection unit 20 comprising: a capacitor C having opposite first and second capacitor ends, the first capacitor end being connected to the column readout line BL; the comparator 201 is provided with a first comparison input end VREF _ BL, a second comparison input end VN node and a comparison output end, the second comparison input end VN node is connected with the second capacitor end, and the first comparison input end VREF _ BL is suitable for inputting comparison timing signals; switch CMPRSTThe switch CMPRSTRespectively connected with the second comparison input end VN node and the comparison output end.
The switch CMPRSTAdapted to electrically connect or disconnect the second comparison input VN node to the comparison output. In particular, when the switch CMPRSTIn the on state, the switch CMPRSTElectrically connecting a second comparison input terminal VN node with the comparison output terminal; when the switch CMPRSTIn the off state, the switch CMPRSTThe second comparison input VNnode is electrically disconnected from the comparison output.
The switch CMPRSTThe second comparison input VN node is electrically connected to the comparison output so that the potential of the second comparison input VN node is equal to the potential of the first comparison input VREF _ BL.
The switch CMPRSTThe second comparison input terminal VN node is electrically disconnected from the comparison output terminal, so that the potential of the first comparison input terminal VREF _ BL is not affected by the potential of the first comparison input terminal VREF _ BL, which is obtained by coupling the potential on the column readout line BL to the first comparison input terminal VREF _ BL through the capacitor C.
The column readout line BL has opposite first and second readout terminals.
The pixel cell 10 further includes: a photodiode 101; a transfer transistor TG having a source connected to the photodiode 101;a floating diffusion point FD node connected to a drain of the transfer transistor TG; reset transistor PGRSTThe reset transistor PGRSTIs connected to the floating diffusion point FDnode, the reset transistor PGRSTThe drain of the second transistor is connected with a power supply line VDDPIX; amplifying transistor PGSFSaid amplifying transistor PGSFIs connected to a floating diffusion point FD node, the amplifying transistor PGSFThe drain of the second transistor is connected with a power supply line VDDPIX; selection transistor PGRSELSaid selection transistor PGRSELAnd the amplifying transistor PGSFA source level connection of; the first readout terminal and the selection transistor PGRSELAnd the second sensing terminal is connected to the first capacitor terminal.
The image sensor pixel circuit further comprises: an analog-to-digital conversion module 30(ADC module), where the analog-to-digital conversion module 30 has a first image data input end, a second image data input end, and an image data output end, the first image data input end is connected to the column readout line BL, the second image data input end is connected to the comparison output end, the image data output end is adapted to output a digital image signal, and the digital image signal is adapted to be obtained according to data input by the first image data input end and data input by the second image data input end.
The analog-to-digital conversion module 30 includes: the image processing device comprises an analog-to-digital converter and a logic unit, wherein a first image data input end is an input end of the analog-to-digital converter, the logic unit is provided with a first logic input end, a second logic input end and a logic output end, the first logic input end is a second image data input end, the second logic input end is connected with an output end of the analog-to-digital converter, and the logic output end is an image data output end.
The logic unit is an OR gate and is suitable for carrying out OR logic processing on signals input by the first logic input end and the second logic input end. The analog-to-digital converter is adapted to convert an analog signal to a digital signal.
The image sensor pixel circuit further comprises: an image processing module 40, wherein the image processing module 40 is connected to the image data output end, and the image processing module 40 is adapted to perform noise reduction processing on the digital image signal.
Accordingly, the present embodiment further provides a working method of the pixel circuit of the image sensor, referring to fig. 4, including the following steps:
s01: providing the image sensor pixel circuit;
s02: the detection unit 20 performs reference sampling on the voltage of the column readout line BL, and the switch CMP performs the reference samplingRSTIn a conducting state;
s03: after the reference sampling is performed, the switch CMP is turned offRST；
S04: opening the switch CMPRSTThen, reducing the magnitude of the comparison time sequence signal to a first level value;
s05: after the magnitude of the comparison time sequence signal is reduced, a comparison sampling step is carried out; the step of comparing samples comprises: sampling the signal of the column readout line BL and coupling to a second comparison input terminal VN node so that the second comparison input terminal VN node has a second level value; the comparator 201 compares the second level value with the first level value and outputs a detection signal.
Fig. 5 is a timing diagram of an image sensor pixel circuit of the present invention. V (PG)RSEL) Is the selection transistor PGRSELWhen the timing signal of the gate is V (PG)RSEL) When high, the selection transistor PGRSELIs turned on when V (PG)RSEL) When low, the selection transistor PGRSELAnd (5) disconnecting.
V(PGRST) Is the reset transistor PGRSTWhen the timing signal of the gate is V (PG)RST) At high level, the reset transistor PGRSTIs turned on when V (PG)RST) At low level, the reset transistor PGRSTAnd (5) disconnecting.
V(CMPRST) Is the switch CMPRSTTiming signal of (2), when V (CMP)RST) At high levelThe switch CMPRSTOn when V (CMP)RST) At low level, the switch CMPRSTAnd (5) disconnecting.
V (TG) is a timing signal of the gate of the transfer transistor TG, and when v (TG) is high, the transfer transistor TG is on, and when v (TG) is low, the transfer transistor TG is off.
V (ADC _ SMP) is a timing signal of the analog-to-digital conversion module 30, when V (ADC _ SMP) is at a high level, the analog-to-digital conversion module 30 operates, and both the analog-to-digital converter and the logic unit operate, and when V (ADC _ SMP) is at a low level, the analog-to-digital conversion module 30 does not operate, and both the analog-to-digital converter and the logic unit suspend operation.
V (VN node) is the timing signal of the second comparison input terminal VN node, where L1 represents the timing signal of the second comparison input terminal VN node when no blooming occurs, and L2 represents the timing signal of the second comparison input terminal VN node when blooming occurs.
V (VREF _ BL) is a timing signal of the first comparison input VREF _ BL.
The working method of the image sensor pixel circuit further comprises the following steps: before the detection unit 20 performs reference sampling on the voltage of the column readout line BL, a reset operation is performed.
During the reset operation, the selection transistor PGRSELIn an on state, the transfer transistor TG is in an off state, and the reset transistor PG isRSTIn the on state, the switch CMPRSTIn an on state, the comparison timing signal has an initial level value, which is greater than the first level value.
During the reset operation, the potential of the floating diffusion point FD node is set to the potential VDD of the power supply line VDDPIX, and the potential of the column readout line at this time is VDD-Vm, and Vm is the selection transistor PGRSELAnd an amplifying transistor PGSFThe equivalent resistance of the capacitor.
In the reference sampling step, the selection transistor PGRSELIn an on state, the transfer transistor TG is in an off state, the resetBit transistor PGRSTIn an off state, the switch CMPRSTIn a conducting state; the comparison timing signal has an initial level value.
The starting time of the reset operation is T0, and the ending time of the reset operation is T01. The starting time of the reference sampling step is T01, and the ending time of the reference sampling step is T1.
In the reference sampling process, the switch CMPRSTIn the on state, so that the potential of the second comparison input terminal VNnode is equal to the potential of the first comparison input terminal VREF _ BL, i.e., equal to the initial level value. In the reference sampling process, the capacitor C stores the difference between the potential on the column readout line BL and the potential of the second comparison input terminal VN node, and the potential difference between the two ends of the capacitor C is the difference between (VDD-Vm) and the initial level value.
After the reference sampling is performed, the switch CMP is turned offRSTThe switch CMP is turned off so that the potential of the second comparison input VN node is not affected by the potential of the first comparison input VREF _ BLRSTIs completed during the time period T1 to T2.
Opening the switch CMPRSTThen, the magnitude of the comparison timing signal is reduced to a first level value. The step of reducing the magnitude of the comparison timing signal to the first level value is completed in a period of T2 to T23.
A difference of the initial level value and the first level value is equal to the comparison threshold.
The comparison threshold is 90 mv to 110 mv, for example, 100 mv, if the comparison threshold is too large, the detection sensitivity is low, and if the comparison threshold is too small, the highlight overflow phenomenon may be misjudged.
The compare sampling step is completed during the time period T23 to T3.
After the reference sampling and before the comparison sampling step, the selection transistor PGRSELIn a conducting state, the pass transistor PGRSELIn an off state, the reset transistor PGRSTIn an off state, the switch CMPRSTIn the off state.
In the comparison sampling step, the signal of the column readout line BL is sampled and coupled to the second comparison input terminal VN node through the capacitor C so that the second comparison input terminal VN node has the second level value. Since the capacitance C stores the difference between the potential of the column readout line BL and the potential of the second comparison input terminal VN node, the magnitude of the change in the potential on the column readout line BL and the magnitude of the change in the potential of the second comparison input terminal VN node coincide. The comparator 201 compares the second level value with the first level value and outputs a detection signal, so that the magnitude of the detection signal represents the variation range of the potential of the second comparison input terminal VNnode, and the variation range of the potential of the second comparison input terminal VN node is identical to the variation range of the potential on the column readout line BL, and therefore the magnitude of the detection signal also indirectly represents the variation range of the potential on the column readout line BL. Therefore, the detection signal is not influenced by the threshold deviation of each transistor in the pixel circuit and the fluctuation of the pixel power supply voltage, and the accuracy of the detection result of the pixel blooming is improved. Therefore, the performance of the pixel circuit of the image sensor is improved.
In the step of comparing and sampling, when the second level value is greater than the first level value, the detection signal is '0', which indicates that no blooming occurs; in the comparing and sampling step, when the second level value is smaller than the first level value, the detection signal is "1", which indicates that blooming occurs.
If the detection signal is "0", the signal output by the image data output end is obtained by directly converting the signal input by the first image data input end, that is, the signal output by the image data output end is obtained by directly converting the signal on the column readout line BL from an analog signal to a digital signal; and if the detection signal is '1', setting the signal output by the image data output end to full-scale data of the analog-to-digital conversion module.
When the signal output by the image data output end is set to the full-scale data of the analog-to-digital conversion module, the image corresponding to the signal output by the image data output end is displayed as bright color.
As can be seen from fig. 5, the analog-to-digital conversion module 30 performs two digital image signal acquisition steps before and after the transmission transistor TG is turned on, and the difference between the digital image signal acquired for the second time and the digital image signal acquired for the first time is the effective digital image signal of the corresponding pixel.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (9)

1. A method of operating an image sensor pixel circuit,
providing an image sensor pixel circuit, the image sensor pixel circuit comprising: a pixel unit including: a column readout line; a detection unit, the detection unit comprising: a capacitor having opposing first and second capacitor terminals, the first capacitor terminal being connected to the column sense line; the comparator is provided with a first comparison input end, a second comparison input end and a comparison output end, the second comparison input end is connected with the second capacitor end, and the first comparison input end is suitable for inputting a comparison time sequence signal; the switch is respectively connected with the second comparison input end and the comparison output end;
the detection unit carries out reference sampling on the voltage of the column readout line, and the switch is in a conducting state in the process of carrying out the reference sampling;
after the reference sampling is carried out, the switch is switched off;
after the switch is disconnected, reducing the magnitude of the comparison time sequence signal to a first level value;
after the magnitude of the comparison time sequence signal is reduced, a comparison sampling step is carried out;
the step of comparing samples comprises: sampling the signal of the column readout line and coupling to a second comparison input terminal, so that the second comparison input terminal has a second level value; the comparator compares the second level value with the first level value and outputs a detection signal;
wherein the comparison timing signal has an initial level value, a difference value of the initial level value and the first level value being equal to a comparison threshold value.
2. The method of claim 1, wherein the column readout line has first and second opposite readout terminals; the pixel unit further includes: a photodiode; a transfer transistor, a source of the transfer transistor being connected to the photodiode; a floating diffusion point connected to a drain of the transfer transistor; the source electrode of the reset transistor is connected with the floating diffusion point, and the drain electrode of the reset transistor is connected with a power line; the grid electrode of the amplifying transistor is connected with the floating diffusion point, and the drain electrode of the amplifying transistor is connected with a power line; a selection transistor, a drain of which is connected to a source of the amplification transistor; the first reading end is connected with the source electrode of the selection transistor, and the second reading end is connected with the first capacitor end;
the working method of the image sensor pixel circuit further comprises the following steps: performing a reset operation before the detection unit performs reference sampling on the voltage of the column readout line; during the reset operation, the selection transistor is in an on state, the transfer transistor is in an off state, the reset transistor is in an on state, the switch is in an on state, the comparison timing signal has an initial level value, and the initial level value is greater than the first level value;
in the reference sampling step, the selection transistor is in a conducting state, the transfer transistor is in an off state, the reset transistor is in an off state, and the switch is in a conducting state.
3. The method of claim 2 wherein the comparison threshold is between 90 millivolts and 110 millivolts.
4. The method of claim 2, wherein after the reference sampling and before the comparing step, the select transistor is in an on state, the transfer transistor is in an off state, the reset transistor is in an off state, and the switch is in an off state.
5. The method of claim 1, wherein in the step of comparing and sampling, when the second level value is greater than the first level value, the detection signal is "0"; in the comparing and sampling step, when the second level value is less than the first level value, the detection signal is "1".
6. The method of claim 5, wherein the image sensor pixel circuit further comprises: an analog-to-digital conversion module having a first image data input terminal, a second image data input terminal, and an image data output terminal, the first image data input terminal being connected to the column readout line, the second image data input terminal being connected to the comparison output terminal, the image data output terminal being adapted to output a digital image signal, the digital image signal being obtained from data input by the first image data input terminal and data input by the second image data input terminal;
if the detection signal is '0', the signal output by the image data output end is obtained by directly converting the signal input by the first image data input end; and if the detection signal is '1', setting the signal output by the image data output end to full-scale data of the analog-to-digital conversion module.
7. The method of claim 1, wherein the column readout line has first and second opposite readout terminals;
the pixel unit further includes: a photodiode; a transfer transistor, a source of the transfer transistor being connected to the photodiode; a floating diffusion point connected to a drain of the transfer transistor; the source electrode of the reset transistor is connected with the floating diffusion point, and the drain electrode of the reset transistor is connected with a power line; the grid electrode of the amplifying transistor is connected with the floating diffusion point, and the drain electrode of the amplifying transistor is connected with a power line; a selection transistor, a drain of which is connected to a source of the amplification transistor; the first readout terminal is connected to the source of the selection transistor, and the second readout terminal is connected to the first capacitor terminal.
8. The method of operating an image sensor pixel circuit of claim 1, further comprising: the analog-to-digital conversion module is provided with a first image data input end, a second image data input end and an image data output end, the first image data input end is connected with the column readout line, the second image data input end is connected with the comparison output end, the image data output end is suitable for outputting a digital image signal, and the digital image signal is suitable for being acquired according to data input by the first image data input end and data input by the second image data input end.
9. The method of operating an image sensor pixel circuit of claim 8, further comprising: and the image processing module is connected with the image data output end and is suitable for carrying out noise reduction processing on the digital image signal.
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