GB2577353A

GB2577353A - A pixel unit, image sensor and camera

Info

Publication number: GB2577353A
Application number: GB1901466.1A
Authority: GB
Inventors: Ma Jianguo; Zhou Shaohua; Gao Zhiyuan
Original assignee: Guangdong University of Technology
Current assignee: Guangdong University of Technology
Priority date: 2018-09-19
Filing date: 2019-02-04
Publication date: 2020-03-25
Anticipated expiration: 2039-02-04
Also published as: CN109005329A; GB2577353B; GB201901466D0; CN109005329B

Abstract

The present invention discloses a pixel unit, comprising: a sampling circuit, an exposure circuit and a threshold determination circuit wherein the sampling circuit is configured to acquire an analog voltage corresponding to a collected optical signal of a dynamic target, the exposure circuit is configured to acquire a difference value between an analog voltage of a Kth frame and an analog voltage of a (K-1)th frame of the dynamic target and the threshold determination circuit is configured to compare the difference value with a preset voltage threshold, so as to determine, according to the comparison result, whether the optical signal collected by the pixel unit in the Kth frame changes relative to the optical signal of the (K-1)th frame and encode a dynamic event signal of the pixel unit in the Kth frame by using a preset number of bits of data less than eight. The pixel unit provided by the present invention reduces the amount of data of the output result and reduces the occupation of data transmission resources and processing resources in the image processing. The sampling circuit may comprise a photoelectric converter, an operational amplifier and a capacitor. The threshold determination circuit may comprise a comparator and an analog multiplexer possibly with a digital buffer to shape and buffer the comparison result. The present invention also provides an image sensor and a camera having the above-described advantageous effects.

Description

A PIXEL UNIT, IMAGE SENSOR AND CAMERA

Technical field

The present invention relates to the field of image processing technologies, and in particular, to a pixel unit, an image sensor, and a camera.

Technical background

An image sensor is a sensor that records the intensity of light. At present, the most commonly used CMOS image sensor converts an optical signal into an electrical signal through a pixel, and outputs and stores it in a digital form, that is, photographs are taken. At present, almost all image sensors perform image acquisition in a frame-by-frame manner, and subsequent image processing also processes and analyzes data frame by frame. In a dynamic target capture application, the image sensor needs to quickly capture at a high frame rate, and the captured data is sent to a processor for data processing. In order to capture dynamic targets quickly while avoiding blurring caused during the movement of a moving target, the image sensor has a high frame rate. The high frame rate also brings a high data volume and the pressure on transmission and processing increases accordingly. In applications such as miniaturization and low power consumption, the shooting rate and processing speed will be severely limited, so that fast target capture cannot be achieved.

In the traditional imaging schemes of image sensors, 8 bits -12 bits is generally used to represent an output result of one pixel, and these data will be greatly reduced in image processing. Such an operation wastes data transmission bandwidth resources and processing resources, resulting in a target acquisition speed that cannot reach a high frame rate.

In summary, it can be seen that how to reduce the number of bits occupied by the output result of one pixel unit in the image sensor is currently a problem to be solved.

Summary of the Invention

An object of the present invention is to provide a pixel unit, an image sensor, and a camera to solve the problem of imaging schemes of image sensors in the prior art that a large amount of data is generated when a dynamic target image is acquired, to by using 8 bits -12 bits to represent the output result of one pixel, resulting in waste of data transmission bandwidth resources and processing resources.

To solve the above technical problem, the present invention provides a pixel unit, comprising: Is a sampling circuit, an exposure circuit, and a threshold determination circuit; wherein the sampling circuit is configured to acquire an analog voltage corresponding to a collected optical signal of a dynamic target; the exposure circuit is configured to acquire a difference value between an analog voltage of a Kth frame and an analog voltage of a (K-1)th frame of the dynamic 20 target; the threshold determination circuit is configured to compare the difference value with a preset voltage threshold, so as to determine, according to the comparison result, whether the optical signal collected by the pixel unit in the Kth frame changes relative to the optical signal of the (K-1)th frame, and encode a dynamic event signal of the pixel unit in the Kth frame by using a preset number of bits of data; wherein the preset number of bits is less than eight bits.

Preferably, the sampling circuit comprises: a photoelectric converter, an operational amplifier and a capacitor; an output terminal of the photoelectric converter is connected to a left plate of the capacitor, and a right plate of the capacitor is connected to a negative input terminal of the operational amplifier; the operational amplifier is configured to sample the analog voltage of the (K-1)th frame output by the photoelectric converter on the left plate of the capacitor.

Preferably, the exposure circuit comprises: the photoelectric converter and the capacitor; the right plate of the capacitor is in a floating state, the photoelectric converter is configured to output a voltage value after reset, and the voltage value rises to a maximum voltage and then decreases with an exposure time of the Kth frame; the right plate of the capacitor is configured to obtain a difference value between an analog voltage outputted by the Kth frame and an analog voltage outputted by the (K-1)th frame.

Preferably, the threshold determination circuit comprises: a comparator and an analog multiplexer; an output terminal of the analog multiplexer is connected to a positive input terminal of the comparator; a negative input terminal of the comparator is configured to input a difference value 20 between the analog voltage outputted by the Kth frame and the analog voltage outputted by the (K-1)th frame; the analog multiplexer is configured to input the preset voltage threshold to a positive input terminal of the comparator; an output terminal of the comparator is configured to output a comparison result of the difference value with the preset voltage threshold.

Preferably, the threshold determination circuit further comprises a digital buffer for shaping and buffering the comparison result.

Preferably, the operational amplifier and the comparator are the same operational amplifier Al; an operational amplifier sampling switch is connected between a negative input terminal and an output terminal of the operational amplifier Al; the operational amplifier Al operates as an operational amplifier when the operational amplifier sampling switch is turned on; the operational amplifier Al operates as a comparator when the operational amplifier sampling switch is turned off.

Preferably, the threshold determination circuit comprises an ON readout circuit and an OFF readout circuit when the preset number of bits is two bits; wherein the ON readout circuit is configured to compare the difference value with a preset ON threshold, and if the difference value is less than the preset ON threshold, it is determined that the light intensity of the optical signal collected by the pixel unit in the Kth frame increases relative to the optical signal of the (K-1)th frame, and output 11 is used as the dynamic event signal of the pixel unit in the Kth frame; the OFF readout circuit is configured to determine whether the difference value is less than a preset OFF threshold when the difference value is greater than the preset ON threshold; if the difference value is less than the preset OFF threshold, it is determined that the light intensity of the optical signal collected by the pixel unit in the Kth frame does not change relative to the optical signal of the (K-1)th frame, and 01 is outputted as the dynamic event signal of the pixel unit in the Kth frame; if the difference value is larger than the preset OFF threshold, it is determined that the light intensity of the optical signal collected by the pixel unit in the Kth frame decreases relative to the optical signal of the (K-1)th frame, and 00 is outputted as the dynamic event signal of the pixel unit in the Kth frame.

The present invention also provides an image sensor comprising: a pixel array, a chip control circuit and a readout circuit; wherein the pixel array includes MxN pixel units described above; the pixel array is configured to convert an optical signal of a dynamic target in a Kth frame into a dynamic event signal of the Kth frame; the readout circuit is configured to read the dynamic event signal output by the pixel array to obtain a target image of the dynamic target in the Kth frame; the chip control circuit is configured to control operations of the respective pixel units and the readout circuit.

Preferably, the readout circuit comprises N data buses; each column of pixel units in the pixel array shares one data bus; each pixel unit in one column is connected to a data bus respectively through one gate switch.

The present invention also provides a camera comprising the image sensor described above.

The pixel unit provided by the present invention comprises a sampling circuit, an exposure circuit, and a threshold determination circuit. The sampling circuit is configured to acquire an analog voltage corresponding to a collected optical signal of a dynamic target. The exposure circuit is configured to acquire a difference value between an analog voltage in a Kth frame and an analog voltage in a (K-1)th frame of the dynamic target. The difference value is compared with the preset voltage threshold, and the light intensity of the optical signal collected by the pixel unit in the Kth frame in relation to the optical signal collected in the (K-1)th frame is determined according to the comparison result, and a dynamic event signal of the pixel unit in the Kth frame is encoded by using a preset number of bits of data. Moreover, the pixel unit provided by the present invention integrates an interframe moving determination mechanism to compare the exposure signals of previous and subsequent frames in the pixels, determines whether the contents of corresponding target scenes from the (K-1)th frame to the Kth frame in the pixel unit has changed, and uses the dynamic event signal to characterizes this change. Since the dynamic event signal is encoded with less than eight bits of data, in the pixel unit provided by the present invention, the collected optical signal of the dynamic target is converted into a dynamic event signal. As compared with the prior art where the optical signal of the dynamic target is converted into a digital signal of 8 bits to 12 bits, the data amount of the output result of the pixel unit is reduced, the rate of data transmission is increased, the efficiency of subsequent data processing is improved, and the occupation of the data transmission resource and processing resource in the image processing is reduced.

Brief description of the drawings

In order to more clearly illustrate the technical solutions in embodiments of the present invention or the prior art, the accompanying drawings needed to be used in to the description of the embodiments or the prior art will be briefly described below.

Obviously, the accompanying drawings in the following description are only some embodiments of the present invention, and other accompanying drawings can be obtained by ordinary persons skilled in the art from these without any inventive efforts.

Fig. 1 is a structural block diagram of a first specific embodiment of a pixel unit provided by the present invention; Fig. 2 is a structural block diagram of a second specific embodiment of a pixel unit provided by the present invention; Fig. 3 is a timing chart of operation of a pixel unit provided by the present invention; Fig. 4 is a structural block diagram of an image sensor provided by an embodiment of the present invention; Fig. 5 is a timing chart of operation of an image sensor provided by the present invention.

Detailed Description of the Embodiment

The core of the invention is to provide a pixel unit which reduces the amount of data of the output result, thereby improving the efficiency of data processing and the rate of data transmission. The present invention also provides an image sensor and a camera having the above-described advantageous effects.

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, in order to make those skilled in the art better understand the solution of the present invention. It is apparent that the described embodiments are only a part of the embodiments of the invention, and not all of them. All other embodiments obtained by ordinary persons skilled in the art based on the embodiments of the present invention without creative efforts are within the scope of the present invention.

Refer to Fig. 1, which is a structural block diagram of a first specific embodiment of a pixel unit provided by the present invention. The pixel unit provided in this embodiment comprises: a sampling circuit 11, an exposure circuit 12, and a threshold determination circuit 13; and the sampling circuit 11 is configured to acquire an analog voltage corresponding to the collected optical signal of the dynamic target. The exposure circuit 12 is configured to acquire a difference value between an analog voltage of a Kth frame and an analog voltage of a (K-1)th frame of the dynamic target. The threshold determination circuit 13 is configured to compare the difference value with a preset voltage threshold, so as to determine, according to the comparison result, whether the optical signal collected by the pixel unit in the Kth frame changes relative to the optical signal of the (K-1)th frame, and encode a dynamic event signal of the pixel unit in the Kth frame by using a preset number of bits of data; wherein the preset number of bits is less than eight bits.

In this embodiment, the sampling circuit 11 may comprises: a photoelectric converter, an operational amplifier and a capacitor; an output terminal of the photoelectric converter is connected to a left plate of the capacitor, and a right plate of the capacitor is connected to a negative input terminal of the operational amplifier; the operational amplifier is configured to sample the analog voltage of the (K-1)th frame output by the photoelectric converter on the left plate of the capacitor.

In this embodiment, the photoelectric converter may be a photodiode or other photoelectric elements.

In the exposure circuit, the acquisition of the (K-1)th frame analog voltage and the Kth frame analog voltage is performed using the photoelectric converter and the capacitor in the sampling circuit. In the exposure circuit, the right plate of the capacitor is in a floating state. After the photoelectric converter inputs the analog voltage of the (K-1)th frame to the left plate of the capacitor, it is reset firstly. The voltage value outputted by the photoelectric converter decreases with the exposure time of the Kth frame after rising to the highest voltage value, so that the difference value of the analog voltage of the Kth frame and the analog voltage of the (K-1)th frame, i.e. the exposure signal of the Kth frame, is acquired on the right plate of the capacitor.

The threshold determination circuit 13 comprises a comparator and an analog multiplexer. An output terminal of the analog multiplexer is connected to a positive input terminal of the comparator; a negative input terminal of the comparator is connected to a right plate of the capacitor in the exposure circuit, for inputting the difference value of the analog voltage outputted by the Kth frame and the analog voltage outputted by the (K-1)th frame.

The analog multiplexer is configured to input the preset voltage threshold to a positive input terminal of the comparator; thereby comparing the difference value with the preset voltage threshold, and determining, according to the result, whether there are changes from the target scene in the Kth frame to the target scene in the (K-1)th frame in the pixel unit. An output terminal of the comparator is configured to output a comparison result of the difference value with the preset voltage threshold. After the result is encoded using a preset number of bits less than eight bits, the dynamic event signal is output.

The threshold determination circuit may further comprise a data buffer for shaping and buffering the comparison result.

The pixel unit provided in this embodiment integrates elements such as a photoelectric converter, a comparator, an operational amplifier, and a capacitor, determines the difference value between the integrated signals of the (K-1)th frame and the Kth frame, and outputs the determination result in a form of less than eight bits of data, as the dynamic event signal of the pixel unit. The data amount of the output result of the pixel unit is reduced, so that the rate of data transmission is increased, the efficiency of subsequent data processing is improved, and the occupation of the data transmission resource and processing resource in the image processing is reduced.

Based on the above embodiment, in this embodiment, the operational amplifier and the comparator are both implemented by the same operational amplifier Al, and the negative input terminal of the operational amplifier Al and the output terminal of the operational amplifier Al are connected with one operational amplifier sampling switch. When the operational amplifier sampling switch is turned on, the operational amplifier Al operates as an operational amplifier; when the operational amplifier sampling switch is turned off, the operational amplifier Al operates as a comparator Refer to Fig. 2, which is a structural diagram of a second specific embodiment of a pixel unit provided by the present invention.

The pixel unit provided in this embodiment comprises: a pixel photodiode, a capacitor Cs, an operational amplifier Al, an operational amplifier sampling switch SWs, a digital buffer B1, an analog multiplexer MUX (1-out-of-3), and a gate switch SWsel. The photoelectric converter inputs an optical signal of a dynamic target; an analog voltage output from the photoelectric converter is connected to an upper plate of the capacitor Cs, and a lower plate of the capacitor Cs is connected to a negative input terminal of the operational amplifier Al. The operational amplifier sampling switch SWs is connected across the negative input terminal and the output terminal of the operational amplifier Al. The three inputs of the analog multiplexer MUX are Vref, Vref on, and Vref_off, respectively, and are output to a positive input terminal of the operational amplifier Al according to the operation demand. An output terminal of the operational amplifier Al is connected to an input terminal of the digital buffer B1. The gate switch Swsel is connected to the output terminal of B1 and a data readout bus of the image sensor.

In this embodiment, it is determined by the preset ON threshold Vref_on whether the light intensity of the optical signal collected by the optical unit in the Kth frame reduces relative to the optical signal in the (K-1)th frame. It is determined by the preset OFF threshold whether the light intensity of the optical signal collected by the optical unit in the Kth frame increases relative to the optical signal in the (K-1)th frame.

The dynamic event information is encoded by using 2 bits of data. At this time, a low level 0 indicates that the difference value is large than the preset ON threshold/OFF threshold; a high level 1 indicates that the difference value is less than the preset ON threshold/OFF threshold. When the dynamic event signal of the pixel unit shown in the 2Bit data table is utilized, the threshold determination circuit 13 includes an ON readout circuit and an OFF readout circuit.

The ON readout circuit is configured to compare the difference value with the preset ON threshold, and if the difference value is less than the preset ON threshold, it is determined that the light intensity of the optical signal collected by the pixel unit in the Kth frame increases relative to the optical signal of the (K-1)th frame, and output 11 is used as the dynamic event signal of the pixel unit in the Kth frame.

The OFF readout circuit is configured to determine whether the difference value is less than a preset OFF threshold when the difference value is greater than the preset ON threshold; if the difference value is less than the preset OFF threshold, it is determined that the light intensity of the optical signal collected by the pixel unit in the Kth frame does not change relative to the optical signal of the (K-1)th frame, and 01 is outputted as the dynamic event signal of the pixel unit in the Kth frame; if the difference value is larger than the preset OFF threshold, it is determined that the light intensity of the optical signal collected by the pixel unit in the Kth frame decreases relative to the optical signal of the (K-1)th frame, and 00 is outputted as the dynamic event signal of the pixel unit in the Kth frame. The preset ON threshold is less than the preset OFF threshold. The first preset threshold is greater than the preset ON threshold and is less than the preset OFF threshold.

In this embodiment, the working principle of the illustrated pixel unit is explained by taking the dynamic event signal information of the Kth frame of the pixel unit as an example. One working cycle of the pixel unit includes four phases: a sampling 15 phase, an exposure phase, an ON readout phase, and an OFF readout phase.

In the sampling phase of the (K-1)th frame, the MUX outputs a first preset threshold voltage Vref, the operational amplifier sampling switch SWs is turned on, the analog voltage (Vph_sig_k-1) of the (K-1)th frame outputted by the pixel photodiode under the action of the operational amplifier Al is sampled on the left plate of the capacitor Cs, the right plate of the capacitor Cs is the Vref voltage, and B1 outputs a default low level.

In the exposure phase of the kth frame, the MUX outputs Vref, the sampling switch SWs of the operational amplifier is turned off, the pixel photodiode is reset firstly, the output voltage value Vph rises to a higher voltage Vph_rst, and after reset the voltage value Vph decreases with the exposure time, the magnitude of the voltage value Vph decreases in proportion to the light intensity. In this mode, the operational amplifier Al operates as a comparator since the operational amplifier sampling switch SWs is turned off. Also, after Vph drops from Vph_rst to (Vph_sig_k-1), the comparator is inverted.

In the ON readout phase of the kth frame, the operational amplifier sampling switch SWs remains off, and the MUX outputs the preset ON threshold Vref on. The voltage Vref on is lower than Vref by Vthon, so the determination threshold of the comparator also changes by Vthon. Therefore, after Vph changes to (Vph_sig_k-1)-Vthon, the comparator will be inverted, that is, the ON data output is only generated when the optical signal intensity of the (K-1)th frame is greater than the optical intensity of the Kth frame by a certain extent. In the OFF readout phase of the kth frame, the operational amplifier sampling switch SWs remains off, the MUX outputs the preset OFF threshold Vref_off, and the Vref_off voltage is higher than Vref by Vthoff, so the determination threshold of the comparator also changes by Vthoff. Therefore, the comparator will be inverted after Vph changes to (Vph_sig_k-1) + Vthoff. Then, if both the ON readout and the OFF readout phases are inverted, that is, the light intensity is significantly increased, it is considered that the ON event is triggered, and 11 is outputted as the dynamic event signal of the pixel unit in the (K-1)th frame. If the ON readout phase is not inverted, the OFF readout phase is inverted, that is, the light intensity variation range is not large, no event is triggered, and 01 is used as the dynamic event signal of the pixel unit in the (K-1)th frame. If both the ON readout phase and the OFF readout phase are inverted, the light intensity is significantly reduced, an OFF event is triggered, and 00 is output as a dynamic event signal of the pixel unit in the (K-1)th frame.

In the sampling phase of the kth frame, the MUX outputs Vref, the operational amplifier sampling switch SWs is turned on, and under the action of the operational amplifier A1, the output analog voltage (Vph_sig_k) of the pixel photodiode is sampled on the left plate of the capacitor Cs, the right plate of Cs is the Vref voltage, and B1 outputs a default low level. The pixel unit provided in this embodiment operates according to the above working sequence, as shown in Fig. 3.

Refer to Fig. 4, which is a structural block diagram of an image sensor provided by an embodiment of the present invention. The image sensor provided in this embodiment comprises: a pixel array, a chip control circuit and a readout circuit; wherein the pixel array includes Mxf\I pixel units as described above; the pixel array is configured to convert an optical signal of a dynamic target in a Kth frame into a dynamic event signal of the Kth frame; the readout circuit is configured to read the dynamic event signal output by the pixel array to obtain a target image of the dynamic target in the Kth frame; the chip control circuit is configured to control operations of the respective pixel units and the readout circuit.

In the image sensor provided in this embodiment, each column of pixel units shares one data bus, and there is a total of N data buses. The rest signals for the photoelectric conversion, MUX selection, switch control and the like are all row-level shared, and there is a total of M sets of control signals. The readout circuit collects the data on the N data buses, and then performs parallel high-speed serial output of the data through parallel-to-serial conversion, thereby obtaining an image of the dynamic target. The chip control circuit is specifically configured to control the global operation of the chip, and provides M sets of timing signals for pixel exposure, readout, reset, readout, and readout circuits and data outputs.

As shown in Fig. 5, the chip control circuit controls the pixel array to perform readout of the array signal by using a drum type readout mode. In the readout period of the pixel unit, the ON readout phase and the OFF readout phase are collectively referred to as a readout phase, and the sampling and exposure phases are collectively referred to as a sampling and exposure phase. Then, for one pixel unit, the readout phase occupies the data bus, and the pixel array uses the column-level parallel bus. That is, one row of pixel units is simultaneously read. After the readout of this row is completed, the bus is unoccupied, and the next row of pixels is read out again. The specific workflow is as follows: when the (K-1)th row of pixels is in the readout phase, the column bus is occupied by the (K-1)th row of pixels, and the ON data and the OFF data are sequentially outputted. The output of the pixels of the (K-1)th row ends, and the sampling and exposure phase is entered. At this time, the pixels of the kth row enter the readout stage, and the column bus is occupied by the pixels of the (K-1)th row, and the ON data and the OFF data of the kth row are sequentially outputted. The output of the pixels of all the rows is sequentially performed in this timing. The ON data and the OFF data in each row are read out in the readout circuit, and after parallel-serial conversion, the pixels of the row are sequentially outputted to outside of the chip in a high-speed serial manner.

The image sensor provided in this embodiment compares the information of two adjacent frames captured by the traditional sensor in the pixel, and when the light intensity becomes larger or smaller to a certain extent, the ON/OFF event of the pixel is triggered, so that the image information of a moving target is obtained in a smaller amount of data, avoiding a large amount of data transmission and processing load.

The image sensor provided in this embodiment has a lower data amount of the output image than the image sensor in the prior art. The output signal of each pixel unit in the image sensor provided in this embodiment may be 2 bits of data, 1 bit of ON data, and 1 bit of OFF data, which is reduced by 70%-90% with comparison to the output data amount of traditional image sensors. Moreover, the data output by the image sensor itself provided in the embodiment is inter-frame dynamically processed data, which is equivalent to having completed the primary dynamic target capturing operation, and the subsequent processing based on the data can be faster. The reduction in the amount of data transmitted and processed by the image sensor provided in this embodiment effectively reduces the hardware performance requirements of the overall system, and can realize system integration of miniaturization and low power consumption.

A specific embodiment of the present invention further provides a camera, comprising: the image sensor described above.

The various embodiments in the specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same or similar parts between various embodiments may be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant part can be referred to the method part.

The pixel unit, image sensor and camera provided by the present invention are described in detail above. The principles and embodiments of the present invention have been described herein with reference to specific examples, and the description of the above embodiments is only to assist in understanding the method of the present invention and its core idea. It should be noted that some improvements and modifications to the present invention can be made for those skilled in the art without departing from the principle of the present invention. These improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

Claims 1. A pixel unit, characterized in that it comprises: a sampling circuit, an exposure circuit, and a threshold determination circuit; wherein said sampling circuit is configured to acquire an analog voltage corresponding to a collected optical signal of a dynamic target; said exposure circuit is configured to acquire a difference value between an analog voltage of a Kth frame and an analog voltage of a (K-1)th frame of said dynamic target; said threshold determination circuit is configured to compare said difference value with a preset voltage threshold, so as to determine, according to the comparison result, whether the optical signal collected by the pixel unit in the Kth frame changes relative to the optical signal of the (K-1)th frame, and encode a dynamic event signal of the pixel unit in the Kth frame by using a preset number of bits of data; wherein said preset number of bits is less than eight bits.
2. The pixel unit of claim 1, characterized in that said sampling circuit 20 comprises: a photoelectric converter, an operational amplifier and a capacitor; an output terminal of said photoelectric converter is connected to a left plate of said capacitor, and a right plate of said capacitor is connected to a negative input terminal of said operational amplifier; said operational amplifier is configured to sample the analog voltage of said (K-1)th frame output by said photoelectric converter on the left plate of said capacitor.
3. The pixel unit of claim 2, characterized in that said exposure circuit 30 comprises: said photoelectric converter and said capacitor; the right plate of said capacitor is in a floating state, said photoelectric converter is configured to output a voltage value after reset, and said voltage value rises to a maximum voltage and then decreases with an exposure time of the Kth frame; the right plate of said capacitor is configured to obtain a difference value between an analog voltage outputted by said Kth frame and an analog voltage outputted by said (K-1)th frame.
4. The pixel unit of claim 3, characterized in that said threshold determination circuit comprises: a comparator and an analog multiplexer; an output terminal of said analog multiplexer is connected to a positive input terminal of said comparator; a negative input terminal of said comparator is configured to input a difference 15 value between the analog voltage outputted by the Kth frame and the analog voltage outputted by the (K-1)th frame; said analog multiplexer is configured to input said preset voltage threshold to a positive input terminal of said comparator; an output terminal of said comparator is configured to output a comparison result of said difference value with the preset voltage threshold.
5. The pixel unit of claim 4, characterized in that said threshold determination circuit further comprises a digital buffer for shaping and buffering said comparison result.
6. The pixel unit according to claim 4, characterized in that said operational amplifier and said comparator are the same operational amplifier Al; an operational amplifier sampling switch is connected between a negative input terminal and an output terminal of said operational amplifier Al; said operational amplifier Al operates as an operational amplifier when said operational amplifier sampling switch is turned on; said operational amplifier Al operates as a comparator when said operational amplifier sampling switch is turned off.
7. The pixel unit according to claim 1, characterized in that the threshold determination circuit comprises an ON readout circuit and an OFF readout circuit when the preset number of bits is two bits; wherein said ON readout circuit is configured to compare said difference value with a preset ON threshold, and if said difference value is less than said preset ON threshold, it is determined that the light intensity of the optical signal collected by the pixel unit in the Kth frame increases relative to the optical signal of the (K-1)th frame, and output 11 is used as the dynamic event signal of said pixel unit in the Kth frame; said OFF readout circuit is configured to determine whether said difference value is less than a preset OFF threshold when said difference value is greater than said preset ON threshold; if said difference value is less than said preset OFF threshold, it is determined that the light intensity of the optical signal collected by the pixel unit in the Kth frame does not change relative to the optical signal of the (K-1)th frame, and 01 is outputted as the dynamic event signal of said pixel unit in the Kth frame; if said difference value is larger than said preset OFF threshold, it is determined that the light intensity of the optical signal collected by the pixel unit in the Kth frame decreases relative to the optical signal of the (K-1)th frame, and 00 is outputted as the dynamic event signal of said pixel unit in the Kth frame.
8. An image sensor, characterized in that it comprises: a pixel array, a chip control circuit, and a readout circuit; wherein said pixel array includes MXN pixel units according to any one of claims 1-7; said pixel array is configured to convert an optical signal of a dynamic target in a Kth frame into a dynamic event signal of the Kth frame; said readout circuit is configured to read the dynamic event signal output by said pixel array to obtain a target image of said dynamic target in the Kth frame; said chip control circuit is configured to control operations of the respective pixel units and said readout circuit.
9. The image sensor of claim 8, characterized in that said readout circuit comprises N data buses; each column of pixel units in said pixel array shares one data bus; each pixel unit in one column is connected to a data bus respectively through one gate switch.
10. A camera, characterized in that it comprises the image sensor according to any one of claims 8-9.