A pixel self-biasing structure and method applied to a light-receiving stage circuit of a dynamic vision sensor

Abstract

The application discloses a pixel self-biasing structure and method applied to a light receiving stage circuit of a dynamic vision sensor, and can realize adaptive biasing of single pixels and multiple pixels. The pixel self-biasing structure comprises a photodiode PD, a feedback tube Mfb, a biasing tube Mpr, an amplification tube Mn and a mirror tube Mb. A photoelectric current Iph is generated by the photodiode PD. The photoelectric current Iph is established as a mirror reference at the mirror tube Mb. A biasing current Ipr is obtained by copying through a current mirror structure composed of the mirror tube Mb and the biasing tube Mpr. The biasing current Ipr is applied to the amplification tube Mn to serve as a non-inverting amplifier biasing, so that the biasing is adaptively adjusted according to the photoelectric current Iph and the light receiving stage gain is improved.

Description

Technical Field

[0001] This invention relates to the field of dynamic vision sensors, and in particular to a pixel self-biasing structure and method for use in the light receiving stage circuit of a dynamic vision sensor. Background Technology

[0002] Driven by the continuous iteration and interdisciplinary integration of optical sensing technology, image sensors have deeply penetrated diverse scenarios such as industrial automation, smart terminals, medical imaging, and environmental monitoring, becoming a core medium for machines to perceive the physical world. Essentially, they convert light signals from the external environment into quantifiable and analyzable electrical signals through the synergistic action of photosensitive element arrays and optical systems, thereby constructing a digital visual information representation system. Dynamic Vision Sensors (DVS), as a breakthrough technology in the field of biomimetic vision, overturn the traditional image sensor model that relies on fixed frame rate sampling. They simulate the asynchronous response mechanism of the biological retina to dynamic information—generating an event stream composed of pixel coordinates, timestamps, and the polarity of brightness changes in real time only for local areas of light intensity change in a scene. This biomimetic logic naturally gives them three advantages: millisecond-level real-time response, efficient filtering of redundant data, and extremely low power consumption. It can avoid invalid information load in static scenes and accurately capture dynamic details under high-speed motion or extreme lighting conditions, providing a perception paradigm closer to biological instincts for scenarios such as real-time decision-making in autonomous driving, high-speed sorting by industrial robots, and obstacle avoidance in complex environments for drones.

[0003] Compared to traditional image sensors, DVS outputs data as digital pulse events based on continuous time variations. The current generated by the photodiode is amplified and then compared by a comparator to generate ON / OFF events. The gain of the amplification section plays a crucial role in improving its sensitivity.

[0004] like Figure 1 As shown, in traditional DVS inverting amplifiers, the gate voltage bias of the bias MOSFET Mpr is usually externally controlled, requiring manual adjustment of the bias current. Furthermore, the gain improvement of traditional optical receiver stages is generally achieved by adding a preamplifier. While adding a preamplifier can effectively improve gain and the bias current can be manually adjusted by externally biasing the current at Mpr, it may significantly increase the number of MOSFETs, leading to increased area and power consumption. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a pixel self-biasing structure and method for use in the light receiver stage circuit of a dynamic vision sensor. This invention achieves adaptive biasing while increasing the gain of the light receiver stage by modifying the pixel structure within the light receiver stage circuit, and automatically adjusts the current of the light receiver stage by tracking light intensity.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A pixel self-biasing structure for use in the light receiving stage circuit of a dynamic vision sensor, for adaptive biasing of a single pixel, the pixel self-biasing structure includes a photodiode PD, a feedback transistor Mfb, a bias transistor Mpr, an amplifying transistor Mn, and a mirror transistor Mb.

[0008] The source of the mirror transistor Mb is connected to the power supply, the drain of the mirror transistor Mb is connected to the drain of the feedback transistor Mfb, the source of the feedback transistor Mfb is connected to the negative terminal of the photodiode PD, and the positive terminal of the photodiode is grounded.

[0009] The source of the bias transistor Mpr is connected to the power supply, the drain of the bias transistor Mpr is connected to the drain of the amplifier transistor Mn, and the source of the amplifier transistor Mn is grounded.

[0010] The drain of the mirror transistor Mb and the drain of the feedback transistor Mfb are connected to the gate of the bias transistor Mpr, and the gate of the mirror transistor Mb is connected to the gate of the bias transistor Mpr. The mirror transistor Mb and the bias transistor Mpr form a current mirror structure. The drain of the bias transistor Mpr and the drain of the amplifying transistor Mn are also connected to the gate of the feedback transistor Mfb to form a node of the output voltage Vpr.

[0011] The current mirror structure allows the photocurrent Iph generated by the photodiode PD to be replicated to the bias transistor Mpr via the mirror transistor Mb as the bias current Ipr, thereby enabling the output voltage Vpr to be adaptively adjusted according to the change of the photocurrent Iph.

[0012] Furthermore, Ipr = kIph, where k is the current mirror replication factor, which is obtained by comparing the width-to-length ratio of the bias transistor Mpr with that of the mirror transistor Mb.

[0013] Furthermore, the mirror transistor Mb and the bias transistor Mpr are both P-type MOS transistors; the feedback transistor Mfb and the amplification transistor Mn are both N-type MOS transistors.

[0014] Furthermore, the gain was increased. times, κ n is the back gate coefficient of the feedback transistor Mfb.

[0015] Furthermore, the pixel self-biasing structures are arranged in an array of several, and a bias current generation circuit is also provided for the adaptive biasing of multiple pixels. The bias current generation circuit sums the photocurrents Iph of several pixel self-biasing structures as needed and copies them to a global mirror bias transistor Mmp, so as to simultaneously provide bias current Ipr to the bias transistors Mpr of all pixel self-biasing structures in the array.

[0016] Furthermore, the bias current generation circuit includes a global current mirror structure, a global mirror bias transistor Mmp, and several replica transistors. Within each pixel's self-biasing structure, the mirror transistor Mb and each replica transistor form a current mirror structure to replicate each photocurrent Iph. These replicas are then summed to form a total photocurrent Iph_total. The global current mirror structure then replicates the total photocurrent Iph_total to the global mirror bias transistor Mmp according to a set ratio, generating a stable global bias voltage Vmirror. The global bias voltage Vmirror is returned to each pixel's self-biasing structure via the bias transistor Mpr within each pixel's self-biasing structure to generate a bias current Ipr, thus achieving adaptive bias and gain adjustment for multiple pixels.

[0017] Preferably, the present invention also provides a dynamic visual sensor pixel array or device based on the above-described pixel self-biasing structure.

[0018] Preferably, the present invention also provides an adaptive adjustment method for the photocurrent of a dynamic visual sensor, based on the above-described pixel self-biasing structure, comprising:

[0019] A photocurrent Iph is generated by a photodiode PD; the photocurrent Iph is established as a mirror reference at the mirror tube Mb; the bias current Ipr is obtained by replicating the current mirror structure composed of the mirror tube Mb and the bias tube Mpr; the bias current Ipr is applied to the amplifier tube Mn as the bias of the inverting amplifier, so as to realize the adaptive adjustment of the bias with the photocurrent Iph and improve the gain of the optical receiver stage.

[0020] Preferably, the present invention also provides a non-transitory computer-readable medium storing computer-executable instructions for causing an electronic device to perform the above-described adaptive adjustment method.

[0021] Compared with the prior art, the beneficial effects of the technical solution of the present invention are:

[0022] 1. A current mirror structure is introduced inside the pixel self-biasing structure, so that the photocurrent of the photodiode is mirrored at the bias transistor Mpr using the mirror transistor Mb as a reference. The current mirror structure maps the amplitude of the photogenerated current to the bias circuit, and changing the bias current directly affects the gain. This enables automatic adjustment of the bias current with the photocurrent, achieving adaptive biasing within the pixel without the need for external manual adjustment. In low-light or slightly changing light scenarios, the operating point of the inverting amplifier is optimized with light intensity, improving the gain and sensitivity of the light receiver stage. This solves the problem that external fixed bias is difficult to adjust in real time with changes in light intensity; and in traditional structures, increasing gain significantly increases power consumption. The technical solution of this invention can reduce the number of MOS transistors, significantly reducing power consumption.

[0023] 2. The mirror transistor Mb and the bias transistor Mpr constitute a current mirror structure. The current mirror replication factor is obtained by comparing the width-to-length ratio of the bias transistor Mpr with that of the mirror transistor Mb. The predetermined replication ratio is achieved by clearly setting the device geometry, thereby allowing for engineered control of the gain boost and bias margin; providing quantifiable design parameters.

[0024] 3. Several pixel self-biasing structures can be configured. Adaptive biasing of multiple pixels can be achieved through a single current generation circuit. Multi-pixel convergence further reduces the size requirements of individual devices and generates a more stable bias source. Current summation smooths out random fluctuations between pixels, making the bias source more stable. Converging multiple pixel currents can achieve a larger bias current without significantly increasing the area of ​​a single transistor, improving matching and noise performance, and enhancing gain support under low-light conditions. This solves the problem of traditional structures significantly increasing area to improve gain, and compared to single-pixel adaptive biasing, it can reduce the aspect ratio of the Mb transistor. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the pixel structure within a traditional dynamic vision sensor.

[0026] Figure 2 This is a schematic diagram of a pixel self-biasing structure that achieves single-pixel bias.

[0027] Figure 3 This is a schematic diagram of a pixel self-biasing structure that implements multi-pixel bias.

[0028] Figure 4 This is a diagram illustrating the different MOSFET models involved in this invention.

[0029] Figure 5a and Figure 5b The diagrams show the gains resulting from the traditional pixel structure and the pixel self-biasing structure of this invention, respectively. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0031] like Figure 1 As shown, the pixel structure in the light receiver stage circuit of a traditional dynamic vision sensor consists of a photodiode PD, a feedback transistor Mfb, a bias transistor Mpr, and an amplifier transistor Mn. Mpr is the bias MOS transistor of the inverting amplifier, and Vbias is the external bias voltage of Mpr. The function of Mfb is to provide negative feedback to the inverting amplifier, thereby stabilizing Vpd. By adjusting the bias of the amplifier transistor Mn, the bias current of the inverting amplifier can be adjusted.

[0032] The gain derivation of a traditional optical receiver stage is as follows:

[0033] ; (1)

[0034] Where I 0,log κ is the characteristic current of the feedback transistor Mfb. n V is the back-gate coefficient of the feedback transistor Mfb. G,log and V S,log These are the gate and source voltages of the feedback transistor Mfb, respectively, U T Thermoelectric voltage, For output voltage, Let Vpd be the photocurrent. According to formula (1), Vpd can be derived as follows:

[0035] ; (2)

[0036] Then the optical receiver gain ΔV pr It can be represented as

[0037] ;(3)。

[0038] Figure 2 This embodiment presents a modified pixel self-biasing structure capable of achieving single-pixel adaptive biasing. A mirror transistor Mb is added to the traditional photodetector stage. The photocurrent is replicated through a current mirror structure formed by the mirror transistor Mb and the bias transistor Mpr. The photocurrent flows through the mirror transistor Mb, while the replicated current, kIph, flows through the bias transistor Mpr, where k is the current mirror replication factor, determined by comparing the aspect ratio of the bias transistor Mpr with that of the mirror transistor Mb. This achieves adaptive biasing of the amplifying transistor Mn. Specifically:

[0039] The source of the mirror transistor Mb is connected to the power supply, the drain of the mirror transistor Mb is connected to the drain of the feedback transistor Mfb, the source of the feedback transistor Mfb is connected to the negative terminal of the photodiode PD, and the positive terminal of the photodiode is grounded.

[0040] The source of the bias transistor Mpr is connected to the power supply, the drain of the bias transistor Mpr is connected to the drain of the amplifier transistor Mn, and the source of the amplifier transistor Mn is grounded.

[0041] The drain of the mirror transistor Mb and the drain of the feedback transistor Mfb are connected to the gate of the bias transistor Mpr, and the gate of the mirror transistor Mb is connected to the gate of the bias transistor Mpr. The mirror transistor Mb and the bias transistor Mpr form a current mirror structure. The drain of the bias transistor Mpr and the drain of the amplifying transistor Mn are also connected to the gate of the feedback transistor Mfb to form a node of the output voltage Vpr.

[0042] The current mirror structure allows the photocurrent Iph generated by the photodiode PD to be replicated to the bias transistor Mpr via the mirror transistor Mb as the bias current Ipr, thereby enabling the output voltage Vpr to be adaptively adjusted according to the change of the photocurrent Iph.

[0043] Specifically, in this embodiment, both the mirror transistor Mb and the bias transistor Mpr are P-type MOS transistors; both the feedback transistor Mfb and the amplification transistor Mn are N-type MOS transistors, see [link to documentation]. Figure 4 .

[0044] The gain derivation of the modified optical receiver stage circuit is as follows:

[0045] (4)

[0046] (5)

[0047] If this structure is adopted, then After substituting, we get

[0048] (6)

[0049] (7)

[0050] (8)

[0051] Compared with Equation 1.3, the modified structure shows that the gain is improved compared to the traditional structure. The gain is times that of the current mirror. Furthermore, its gain is independent of the replication ratio k of the current mirror.

[0052] The sensitivity TC of a DVS is defined as the smallest logarithmic change in photocurrent that it can sense.

[0053] (9)

[0054] For the same amount of photocurrent change, the improved structure has a higher amplification factor. Therefore, for a given ON / OFF threshold, the structure provided in this embodiment can sense a smaller minimum logarithmic photocurrent change, thus resulting in higher sensitivity.

[0055] Specifically, in traditional structures, the bias of the bias transistor Mpr is determined by a specified voltage bias from external circuitry of the pixel structure. In this embodiment, the pixel self-biasing structure can self-bias based on Iph. All pixel self-biasing structures are on-chip, while VDD and GND power supplies are externally supplied and introduced onto the chip via wires.

[0056] Specifically, in a particular experiment, the current mirror replication factor was 9. The gain effect diagrams of the conventional structure and the DVS optical receiver circuit using the pixel self-biasing structure of this invention are shown below. Figure 5a and Figure 5b When the photocurrent Iph changes, the gain of Vpr in the modified structure is improved compared to the gain of the traditional structure. times.

[0057] Table 1 shows a comparison of relevant parameters between the traditional structure and the structure presented in this paper.

[0058] Table 1 (at Ipr=9 Iph)

[0059]

[0060] Example 2

[0061] This embodiment is based on several such Figure 2 The pixel self-biasing structure involved in Example 1 realizes adaptive biasing of multiple pixels; the pixel self-biasing structure is arranged in an array of several, and a bias current generation circuit is also provided. The bias current generation circuit sums the photocurrents Iph of several pixel self-biasing structures as needed and copies them to a global mirror bias transistor Mmp, so as to simultaneously provide bias current Ipr to the bias transistors Mpr of all pixel self-biasing structures in the array.

[0062] Specifically, if the light intensity in the application scenario does not change significantly, the following can be adopted: Figure 3 The structure, Each pixel is a group, and n can be 1, 4, etc., depending on the requirements. The square root can be taken to obtain the integer value, that is, n can be a perfect square.

[0063] The current generation circuit includes a global current mirror structure, a global mirror bias transistor Mmp, and several replica transistors Mp1, Mp2…Mpn. The global current mirror structure is composed of MOS transistors Mnn1 and Mnn2. The mirror transistor Mb in each pixel self-biasing structure, together with each replica transistor Mp1, Mp2…Mpn, forms a current mirror structure to replicate each photocurrent Iph. For example, replica transistor Mp1 is responsible for replicating the photocurrent of pixel self-biasing structure 1 to obtain kIph1, replica transistor Mp1 is responsible for replicating the photocurrent of pixel self-biasing structure 1 to obtain kIph1, and replica transistor Mpn is responsible for replicating the photocurrent of pixel self-biasing structure n to obtain kIphn, where k is the replication factor of the corresponding current mirror structure.

[0064] Then, these photocurrents are summed to obtain the total photocurrent Iph_total. The total photocurrent Iph_total is then copied to the global mirror bias transistor Mmp according to the required ratio through a global current mirror structure. A voltage Vmirror is generated at the gate of the global mirror bias transistor Mmp. Vmirror is connected to the gate of the bias transistor Mpr of each pixel self-biasing structure 1-n, thereby biasing the amplifying transistor Mn of each pixel self-biasing structure 1-n.

[0065] Specifically, the width-to-length ratio (W / L) of the bias MOSFETs (Mmn1, Mmn2, Mmp, Mpn, Mb, Mpr, etc.) can be set according to the required multiple of the replication current. If the W / L of all bias MOSFETs is set to be the same, then k=1, and the final replicated Ipr is equal to n×Iph. This achieves adaptive bias and gain adjustment for multiple pixels.

[0066] Specifically, in traditional structures, the bias of the bias transistor Mpr is determined by a specified voltage bias from external circuitry of the pixel structure. In this embodiment, the pixel self-biasing structure can self-bias based on Iph. All pixel self-biasing structures are on-chip, while VDD and GND power supplies are externally supplied and introduced onto the chip via wires.

[0067] Example 3

[0068] This embodiment provides an adaptive adjustment method for the photocurrent of a dynamic visual sensor, based on the aforementioned pixel self-biasing structure, including:

[0069] A photocurrent Iph is generated by a photodiode PD; the photocurrent Iph is established as a mirror reference at the mirror tube Mb; the bias current Ipr is obtained by replicating the current mirror structure composed of the mirror tube Mb and the bias tube Mpr; the bias current Ipr is applied to the amplifier tube Mn as the bias of the inverting amplifier, so as to realize the adaptive adjustment of the bias with the photocurrent Iph and improve the gain of the optical receiver stage.

[0070] In one embodiment, a non-transitory computer-readable medium storing computer-executable instructions is provided, the instructions being used to cause an electronic device to perform the above-described adaptive adjustment method for the photocurrent of a dynamic visual sensor.

[0071] In one embodiment, a dynamic visual sensor pixel array or device based on the pixel self-biasing structure described above is provided.

[0072] This invention is not limited to the embodiments described above. The above description of specific embodiments is intended to illustrate and explain the technical solutions of this invention. The specific embodiments described above are merely illustrative and not restrictive. Without departing from the spirit and scope of the claims, those skilled in the art can make many specific modifications based on the teachings of this invention, and these modifications all fall within the scope of protection of this invention.

Claims

1. A pixel self-biasing structure applied to the light-receiving stage circuit of a dynamic vision sensor, characterized in that, For adaptive biasing of a single pixel, the pixel self-biasing structure includes a photodiode PD, a feedback transistor Mfb, a bias transistor Mpr, an amplifying transistor Mn, and a mirror transistor Mb. The source of the mirror transistor Mb is connected to the power supply, the drain of the mirror transistor Mb is connected to the drain of the feedback transistor Mfb, the source of the feedback transistor Mfb is connected to the negative terminal of the photodiode PD, and the positive terminal of the photodiode is grounded. The source of the bias transistor Mpr is connected to the power supply, the drain of the bias transistor Mpr is connected to the drain of the amplifier transistor Mn, and the source of the amplifier transistor Mn is grounded. The drain of the mirror transistor Mb and the drain of the feedback transistor Mfb are connected to the gate of the bias transistor Mpr, and the gate of the mirror transistor Mb is connected to the gate of the bias transistor Mpr. The mirror transistor Mb and the bias transistor Mpr form a current mirror structure. The drain of the bias transistor Mpr and the drain of the amplifying transistor Mn are also connected to the gate of the feedback transistor Mfb to form a node of the output voltage Vpr. The current mirror structure allows the photocurrent Iph generated by the photodiode PD to be replicated to the bias transistor Mpr via the mirror transistor Mb as the bias current Ipr, thereby enabling the output voltage Vpr to be adaptively adjusted according to the change of the photocurrent Iph.

2. The pixel self-biasing structure according to claim 1, characterized in that, Ipr = kIph, where k is the current mirror replication factor, which is obtained by comparing the width-to-length ratio of the bias transistor Mpr with that of the mirror transistor Mb.

3. The pixel self-biasing structure according to claim 1, characterized in that, The mirror transistor Mb and the bias transistor Mpr are both P-type MOS transistors; the feedback transistor Mfb and the amplification transistor Mn are both N-type MOS transistors.

4. The pixel self-biasing structure according to claim 1, characterized in that, The gain has been increased times, κ n is the back gate coefficient of the feedback transistor Mfb.

5. The pixel self-biasing structure according to claim 1, characterized in that, The pixel self-biasing structures are arranged in an array of several, and a bias current generation circuit is also provided for the adaptive biasing of multiple pixels. The bias current generation circuit sums the photocurrents Iph of several pixel self-biasing structures as needed and copies them to a global mirror bias transistor Mmp, so as to simultaneously provide bias current Ipr to the bias transistors Mpr of all pixel self-biasing structures in the array.

6. The pixel self-biasing structure according to claim 5, characterized in that, The bias current generation circuit includes a global current mirror structure, a global mirror bias transistor Mmp, and several replication transistors. In each pixel self-bias structure, the mirror transistor Mb and each replication transistor form a current mirror structure to replicate each photocurrent Iph. These photocurrents are then summed to form a total photocurrent Iph_total. The global current mirror structure then replicates the total photocurrent Iph_total to the global mirror bias transistor Mmp according to a set ratio and generates a stable global bias voltage Vmirror. The global bias voltage Vmirror is returned to each pixel self-bias structure through the bias transistor Mpr in each pixel self-bias structure to generate a bias current Ipr. Achieve adaptive bias and gain adjustment for multiple pixels.

7. A dynamic visual sensor pixel array or device based on the pixel self-biasing structure according to any one of claims 1 to 6.

8. An adaptive adjustment method for the photocurrent of a dynamic visual sensor, based on the pixel self-biasing structure according to any one of claims 1-6, characterized in that, include: The photocurrent Iph is generated by the photodiode PD; The photocurrent Iph is established as a mirror reference at the mirror tube Mb. The bias current Ipr is obtained by replicating the current mirror structure consisting of a mirror transistor Mb and a bias transistor Mpr. A bias current Ipr is applied to the amplifier tube Mn as a bias for the inverting amplifier, so that the bias can be adaptively adjusted with the photocurrent Iph and the gain of the optical receiver stage can be improved.

9. A non-transitory computer-readable medium storing computer-executable instructions, characterized in that, The instructions are used to cause the electronic device to perform the adaptive adjustment method of claim 8.

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