High-dynamic-range pixel circuit based on spatial difference, and chip and imaging system

Abstract

Provided in the present application are a high-dynamic-range pixel circuit based on spatial difference, and a chip and an imaging system. The pixel circuit comprises a photocurrent signal acquisition unit and a current domain calculation unit, wherein the photocurrent signal acquisition unit acquires photocurrent signals of a plurality of spatial-difference pixel units by means of linear or non-linear photocurrent acquisition, the current domain calculation unit directly performs spatial difference or contrast calculation in a current domain on the photocurrent signals of the plurality of spatial-difference pixel units, so as to obtain a high-dynamic-range current domain calculation result, and then quantization is performed on the basis of the high-dynamic-range current domain calculation result, so that the dynamic range of a vision sensor can be greatly widened.

Description

High dynamic range pixel circuit, chip and imaging system based on spatial difference

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 2024103670028, filed on March 28, 2024, entitled “Pixel circuit, chip and imaging system with high dynamic range based on spatial difference”, which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the field of visual sensing technology, and in particular to a pixel circuit, chip and imaging system with a high dynamic range based on spatial differentiation. Background Art

[0004] A visual sensor refers to an instrument that uses optical elements and imaging devices to obtain image information of the external environment. Visual sensors in the prior art generally include: APS (Active Pixel Sensor) and DVS (Dynamic Vision Sensor). Among them, APS is usually an image sensor based on the frame sampling principle, which is widely used in the camera unit of mobile phones or cameras. This type of image sensor has the advantages of high color reproduction and image quality. However, the dynamic range of the image signal it obtains is small, and the shooting speed is slow. The characteristic of DVS is that it can perceive changes in dynamic scenes in the form of a sparse event stream. Due to the fast shooting speed and the large dynamic range of the image signal obtained, the logarithmic response pixel has characteristics such as high noise and nonlinearity, resulting in its actual dynamic range being lower than the nominal value and poor imaging quality.

[0005] Summary of the Invention

[0006] This application provides a high dynamic range pixel circuit, chip, and imaging system based on spatial differentiation. This approach addresses the existing shortcomings of DVS logarithmic response pixels, which suffer from high noise and nonlinearity, resulting in actual dynamic range lower than the nominal value and poor imaging quality. By performing spatial differentiation or contrast calculation directly in the pixel current domain—the most advanced circuitry—this approach can significantly improve the dynamic range of visual sensors.

[0007] The present application provides a pixel circuit based on spatial differential high dynamic range, including: a photocurrent signal acquisition unit, used to obtain photocurrent signals of multiple spatial differential pixel units using a linear or nonlinear photocurrent acquisition method; a current domain calculation unit, used to perform spatial differentiation or contrast calculation on the photocurrent signals of multiple spatial differential pixel units directly in the current domain to obtain a current domain calculation result with a high dynamic range, and then quantize according to the current domain calculation result with the high dynamic range.

[0008] According to a pixel circuit based on spatial differential high dynamic range provided by the present application, the photocurrent signal acquisition unit includes a first photodiode, a first switching tube, a first amplifier, a first capacitor, a second capacitor, a second amplifier and a switching element; the anode of the first photodiode is grounded, the cathode of the first photodiode is respectively connected to the first end of the first switching tube and the first end of the first amplifier, the second end of the first switching tube is connected to the positive power supply end, the control end of the first switching tube is respectively connected to the second end of the first amplifier and the first end of the first capacitor, the second end of the first capacitor is respectively connected to the first end of the second capacitor, the first end of the second amplifier and the first end of the switching element, and the second end of the second capacitor is respectively connected to the second end of the second amplifier and the second end of the switching element.

[0009] According to a pixel circuit based on spatial differential high dynamic range provided by the present application, the current domain calculation unit includes a first subtractor and a second subtractor; the positive input terminal of the first subtractor is respectively connected to the second terminal of the first amplifier, the first terminal of the first capacitor and the positive input terminal of the second subtractor.

[0010] According to a pixel circuit based on spatial differential high dynamic range provided by the present application, the photocurrent signal acquisition unit includes a second photodiode, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a third photodiode; the anode of the second photodiode is grounded, and the cathode of the second photodiode is respectively connected to the first end of the second switch tube, the control end of the second switch tube and the control end of the third switch tube, the second end of the second switch tube, the first end of the third switch tube, the first end of the fourth switch tube and the first end of the fifth switch tube are all connected to the positive power supply end, the control ends of the four switch tubes are respectively connected to the control end of the fifth switch tube, the second end of the fifth switch tube and the cathode of the third photodiode, and the anode of the third photodiode is grounded.

[0011] According to a pixel circuit based on spatial differential high dynamic range provided by the present application, the current domain calculation unit includes a sixth switch tube, a third capacitor, a seventh switch tube and an eighth switch tube; the first end of the sixth switch tube is respectively connected to the first end of the third capacitor, the second end of the third switch tube and the first end of the seventh switch tube, the second end of the third capacitor is grounded, the second end of the seventh switch tube and the first end of the eighth switch tube are both grounded, and the control end of the seventh switch tube is respectively connected to the control end of the eighth switch tube, the second end of the eighth switch tube and the second end of the fourth switch tube.

[0012] According to a pixel circuit based on spatial differential high dynamic range provided by the present application, the photocurrent signal acquisition unit includes a third photodiode, a ninth switch tube, a tenth switch tube and a comparator; the anode of the third photodiode is grounded, the cathode of the third photodiode is connected to the first end of the ninth switch tube, the second end of the ninth switch tube is respectively connected to the first end of the tenth switch tube and the positive input end of the comparator, and the second end of the tenth switch tube is connected to the positive power supply end.

[0013] According to a pixel circuit based on spatial differential high dynamic range provided by the present application, the current domain calculation unit includes a third subtractor and a fourth subtractor; the positive input terminal of the third subtractor is respectively connected to the second end of the ninth switch tube, the first end of the tenth switch tube, the positive input terminal of the comparator and the positive input terminal of the fourth subtractor.

[0014] The present application also provides a visual sensor chip based on spatial differential high dynamic range, including the above-mentioned pixel circuit based on spatial differential high dynamic range.

[0015] The present application also provides an imaging system, comprising the above-mentioned visual sensor chip based on spatial differential high dynamic range.

[0016] The present application provides a high dynamic range pixel circuit, chip, and imaging system based on spatial differentiation. The pixel circuit includes a photocurrent signal acquisition unit and a current domain calculation unit. The photocurrent signal acquisition unit uses a linear or nonlinear photocurrent acquisition method to obtain the photocurrent signals of multiple spatially differential pixel units. The current domain calculation unit directly performs spatial differentiation or contrast calculation on the photocurrent signals of multiple spatially differential pixel units in the current domain to obtain a high dynamic range current domain calculation result. The current domain calculation result is then quantified based on the high dynamic range current domain calculation result, which can significantly improve the dynamic range of the visual sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the present application or the prior art, a brief introduction will be given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0018] FIG1 is a schematic structural diagram of a high dynamic range pixel circuit based on spatial differentiation provided in an embodiment of the present application;

[0019] FIG2 is a schematic diagram of a high dynamic range pixel circuit based on spatial differentiation according to an embodiment of the present application;

[0020] FIG3 is a second schematic diagram of a principle of a high dynamic range pixel circuit based on spatial differentiation provided in an embodiment of the present application;

[0021] FIG4 is a third schematic diagram of a principle of a high dynamic range pixel circuit based on spatial difference provided in an embodiment of the present application. DETAILED DESCRIPTION

[0022] To make the objectives, technical solutions, and advantages of this application more clear, the technical solutions of this application are described clearly and completely below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of this application, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0023] The basic principle of current mainstream image sensors is frame-based shooting and recording, achieved through an active pixel (APS) array. APS sensors can only process color images arranged in pixel matrix image frames. They offer advantages such as high color reproduction, high resolution, and high image quality. However, the dynamic range of the image signals they acquire is limited, and the capture speed is slow.

[0024] An event camera, also known as a dynamic visual sensor (DVS), is a new type of imaging system. Unlike traditional cameras, which use a shutter to control the frame rate and record light intensity on a per-frame basis for all pixels, an event camera is sensitive to the rate of change of light intensity. Each pixel independently records the change in the logarithm of the light intensity at that pixel, generating a positive or negative pulse when the change exceeds a threshold. The asynchronous nature of event cameras allows them to be unrestricted by shutter speeds and achieve extremely high temporal resolution (frame rates of approximately 1,000,000 fps, compared to the approximately 100 fps of traditional cameras). This, combined with their sensitivity to change, makes them naturally suitable for tasks such as motion monitoring.

[0025] Due to its logarithmic pixel response, DVS has a high dynamic range per pixel. However, logarithmic pixel response has high noise and nonlinearity, resulting in its actual dynamic range being lower than the nominal value and poor image quality.

[0026] Please refer to FIG1 , which is a schematic structural diagram of a high dynamic range pixel circuit based on spatial differentiation provided in an embodiment of the present application.

[0027] In order to solve the technical problems existing in the prior art, the present application provides a pixel circuit based on spatial differential high dynamic range, including: a photocurrent signal acquisition unit 1, used to obtain the photocurrent signals of multiple spatial differential pixel units using a linear or nonlinear photocurrent acquisition method; a current domain calculation unit 2, used to perform spatial differentiation or contrast calculation on the photocurrent signals of multiple spatial differential pixel units directly in the current domain to obtain a current domain calculation result with a high dynamic range, and then quantize according to the current domain calculation result with a high dynamic range.

[0028] The human visual system can perceive both temporal and spatial variations, and is more sensitive and robust to the outside world. Inspired by human vision, this application proposes a pixel architecture for current domain spatial difference and contrast. By performing differential or contrast calculations directly in the current domain, this application can extract the difference / contrast between the photocurrents of pixels in dark light (weak pixel photocurrent) and strong light (pixel photocurrent is close to saturation), thereby achieving a high dynamic range imaging effect.

[0029] Based on the above embodiment:

[0030] Please refer to FIG. 2 , which is one of the principle schematic diagrams of a high dynamic range pixel circuit based on spatial differentiation provided in an embodiment of the present application.

[0031] As a preferred embodiment, the photocurrent signal acquisition unit 1 includes a first photodiode, a first switching tube, a first amplifier, a first capacitor, a second capacitor, a second amplifier and a switching element; the anode of the first photodiode is grounded, the cathode of the first photodiode is respectively connected to the first end of the first switching tube and the first end of the first amplifier, the second end of the first switching tube is connected to the positive power supply end, the control end of the first switching tube is respectively connected to the second end of the first amplifier and the first end of the first capacitor, the second end of the first capacitor is respectively connected to the first end of the second capacitor, the first end of the second amplifier and the first end of the switching element, and the second end of the second capacitor is respectively connected to the second end of the second amplifier and the second end of the switching element.

[0032] As a preferred embodiment, the current domain calculation unit 2 includes a first subtractor and a second subtractor; the positive input terminal of the first subtractor is respectively connected to the second terminal of the first amplifier, the first terminal of the first capacitor and the positive input terminal of the second subtractor.

[0033] In this embodiment, the photocurrent of the photocurrent signal acquisition unit 1 is first converted into a voltage with a logarithmic response. Then, the current domain calculation unit 2 calculates the voltage difference of multiple pixel units (eg, adjacent pixel units), and the output is a spatial difference with a high dynamic range.

[0034] Please refer to FIG3 , which is a second schematic diagram of the principle of a high dynamic range pixel circuit based on spatial differentiation provided in an embodiment of the present application.

[0035] As a preferred embodiment, the photocurrent signal acquisition unit 1 includes a second photodiode, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a third photodiode; the anode of the second photodiode is grounded, the cathode of the second photodiode is respectively connected to the first end of the second switch tube, the control end of the second switch tube and the control end of the third switch tube, the second end of the second switch tube, the first end of the third switch tube, the first end of the fourth switch tube and the first end of the fifth switch tube are all connected to the positive power supply end, the control ends of the four switch tubes are respectively connected to the control end of the fifth switch tube, the second end of the fifth switch tube and the cathode of the third photodiode, and the anode of the third photodiode is grounded.

[0036] As a preferred embodiment, the current domain calculation unit 2 includes a sixth switch tube, a third capacitor, a seventh switch tube and an eighth switch tube; the first end of the sixth switch tube is respectively connected to the first end of the third capacitor, the second end of the third switch tube and the first end of the seventh switch tube, the second end of the third capacitor is grounded, the second end of the seventh switch tube and the first end of the eighth switch tube are both grounded, and the control end of the seventh switch tube is respectively connected to the control end of the eighth switch tube, the second end of the eighth switch tube and the second end of the fourth switch tube.

[0037] In this embodiment, the photocurrents of adjacent pixels are copied to the pixel itself using a current mirror or other means, and the current difference is integrated, ultimately integrating the charge onto the intermediate capacitor. The core idea behind saturation clamping is that, although strong photocurrents can quickly saturate one pixel in strong light, immediately halting differential sensing, recording only the current difference between the two pixels significantly mitigates the saturation issue.

[0038] The differential calculation circuit can be converted into a contrast calculation circuit (ie, a division calculation circuit) to implement division calculation.

[0039] Please refer to FIG4 , which is a third schematic diagram of a principle of a high dynamic range pixel circuit based on spatial difference provided in an embodiment of the present application.

[0040] As a preferred embodiment, the photocurrent signal acquisition unit 1 includes a third photodiode, a ninth switching tube, a tenth switching tube and a comparator; the anode of the third photodiode is grounded, the cathode of the third photodiode is connected to the first end of the ninth switching tube, the second end of the ninth switching tube is respectively connected to the first end of the tenth switching tube and the positive input end of the comparator, and the second end of the tenth switching tube is connected to the positive power supply end.

[0041] As a preferred embodiment, the current domain calculation unit 2 includes a third subtractor and a fourth subtractor; the positive input terminal of the third subtractor is respectively connected to the second terminal of the ninth switch tube, the first terminal of the tenth switch tube, the positive input terminal of the comparator and the positive input terminal of the fourth subtractor.

[0042] In this embodiment, Time-mode can also be used to implement it, and it can also be pulse width or frequency modulation. Each pixel unit is connected to two pixel units, and the photodiode will produce a linear integral response to light. This signal will be used to perform differential calculation of the analog circuit with the signal generated at the same position of the two connected pixel units. When the value of this pixel reaches a certain threshold, it may reflect that it has been saturated, and a self-feedback comparator will turn off the current pixel so that its spatial differential will not be saturated. Among them, the differential calculation circuit can be converted into a contrast (i.e., a division calculation circuit) to implement the division calculation.

[0043] The following describes the visual sensor chip based on spatial differential high dynamic range provided by the present application. The visual sensor chip based on spatial differential high dynamic range described below and the pixel circuit based on spatial differential high dynamic range described above can refer to each other.

[0044] The present application also provides a visual sensor chip based on spatial differential high dynamic range, including the above-mentioned pixel circuit based on spatial differential high dynamic range.

[0045] The imaging system provided by the present application is described below. The imaging system described below and the pixel circuit based on spatial differential high dynamic range described above can refer to each other.

[0046] The present application also provides an imaging system, comprising the above-mentioned visual sensor chip based on spatial differential high dynamic range.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A pixel circuit based on spatial differential high dynamic range, comprising: A photocurrent signal acquisition unit, configured to acquire photocurrent signals of a plurality of spatially differential pixel units using a linear or nonlinear photocurrent acquisition method; The current domain calculation unit is used to perform spatial difference or contrast calculation on the photocurrent signals of the plurality of spatial differential pixel units directly in the current domain to obtain a current domain calculation result with a high dynamic range, and then perform quantization based on the current domain calculation result with a high dynamic range.

2. The pixel circuit based on spatial differential high dynamic range according to claim 1, wherein: The photocurrent signal acquisition unit includes a first photodiode, a first switching tube, a first amplifier, a first capacitor, a second capacitor, a second amplifier and a switching element; The anode of the first photodiode is grounded, the cathode of the first photodiode is respectively connected to the first end of the first switching tube and the first end of the first amplifier, the second end of the first switching tube is connected to the positive power supply end, the control end of the first switching tube is respectively connected to the second end of the first amplifier and the first end of the first capacitor, the second end of the first capacitor is respectively connected to the first end of the second capacitor, the first end of the second amplifier and the first end of the switching element, and the second end of the second capacitor is respectively connected to the second end of the second amplifier and the second end of the switching element.

3. The pixel circuit based on spatial differential high dynamic range according to claim 2, wherein: The current domain calculation unit includes a first subtractor and a second subtractor; The positive input terminal of the first subtractor is connected to the second terminal of the first amplifier, the first terminal of the first capacitor and the positive input terminal of the second subtractor respectively.

4. The pixel circuit based on spatial differential high dynamic range according to claim 1, wherein: The photocurrent signal acquisition unit includes a second photodiode, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube and a third photodiode; The anode of the second photodiode is grounded, the cathode of the second photodiode is connected to the first end of the second switch tube, the control end of the second switch tube and the control end of the third switch tube respectively, the second end of the second switch tube and the first end of the third switch tube are connected to the first end of the second switch tube and the control end of the third switch tube respectively. The first end of the fourth switch tube and the first end of the fifth switch tube are all connected to the positive power supply end, the control ends of the four switch tubes are respectively connected to the control end of the fifth switch tube, the second end of the fifth switch tube and the cathode of the third photodiode, and the anode of the third photodiode is grounded.

5. The pixel circuit based on spatial differential high dynamic range according to claim 4, wherein: The current domain calculation unit includes a sixth switch tube, a third capacitor, a seventh switch tube and an eighth switch tube; The first end of the sixth switching tube is respectively connected to the first end of the third capacitor, the second end of the third switching tube, and the first end of the seventh switching tube. The second end of the third capacitor is grounded. The second end of the seventh switching tube and the first end of the eighth switching tube are both grounded. The control end of the seventh switching tube is respectively connected to the control end of the eighth switching tube, the second end of the eighth switching tube, and the second end of the fourth switching tube.

6. The pixel circuit based on spatial differential high dynamic range according to claim 1, wherein: The photocurrent signal acquisition unit includes a third photodiode, a ninth switching tube, a tenth switching tube and a comparator; The anode of the third photodiode is grounded, the cathode of the third photodiode is connected to the first end of the ninth switch tube, the second end of the ninth switch tube is respectively connected to the first end of the tenth switch tube and the positive input end of the comparator, and the second end of the tenth switch tube is connected to the positive power supply end.

7. The pixel circuit based on spatial differential high dynamic range according to claim 6, wherein: The current domain calculation unit includes a third subtractor and a fourth subtractor; The positive input terminal of the third subtractor is respectively connected to the second terminal of the ninth switch tube, the first terminal of the tenth switch tube, the positive input terminal of the comparator, and the positive input terminal of the fourth subtractor.

8. A visual sensor chip based on spatial differential high dynamic range, comprising the pixel circuit based on spatial differential high dynamic range according to any one of claims 1 to 7.

9. An imaging system comprising the spatial differential high dynamic range based visual sensor chip according to claim 8.

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