Switched capacitor amplifier for dynamic vision sensor chip based on pseudo-resistance switch

Abstract

The present invention proposes a dynamic vision sensor chip switched capacitor amplifier based on a pseudo-resistance switch, which is used in the fields of machine vision, unmanned driving, etc., and includes an input capacitor, a feedback capacitor, an operational amplifier, and a pseudo-resistance switch. The pseudo-resistance switch includes a reset switch P-type metal oxide semiconductor (PMOS) tube and one or more parallel N-type metal oxide semiconductor (NMOS) tube groups, or includes a reset switch NMOS tube and one or more parallel PMOS tube groups, and a MOS tube group includes two MOS tubes connected in series and using a diode connection. The pseudo-resistance switch of the present invention can provide a current that is equal in magnitude and opposite in direction to the leakage current of the reset switch, and exhibits a large equivalent impedance between the negative input terminal and the output terminal of the switched capacitor amplifier, and reduces the equivalent inductance of the output terminal of the switched capacitor amplifier, effectively improving the reliability and accuracy of the output data of the dynamic vision sensor chip.

Description

Technical Field

[0001] The present invention belongs to the field of electronic circuit technology and relates to a switched capacitor amplifier, specifically to a dynamic vision sensor chip switched capacitor amplifier based on pseudo-resistance switching in the field of microelectronics technology, which can be used in machine vision, unmanned driving and other fields. Background Art

[0002] Dynamic vision sensor chips simulate the information processing mechanism of biological retinas. When external lighting conditions change, the pixel circuits in the dynamic vision sensor chip asynchronously generate pulse events, which are then transmitted through the address-event representation communication protocol, and finally output the address information corresponding to the pulse events. However, because the dynamic vision sensor chip outputs pixel address information that recognizes changes in lighting conditions, there is no output when the light intensity information does not change. Unlike complementary metal oxide semiconductor (CMOS) image sensors, which globally output grayscale value information at fixed time intervals, dynamic vision sensor chips have the characteristics of small data volume, low power consumption, and fast response. They have broad application prospects in high-speed moving target detection fields such as machine vision and unmanned driving.

[0003] The dynamic vision sensor chip includes pixel circuit, line OR circuit, arbitration circuit, encoding circuit and handshake circuit. The pixel circuit determines the data reliability and imaging quality of the dynamic vision sensor chip. Its structure is as follows: Figure 1 As shown, the device includes a photodiode, an IV conversion circuit, a voltage follower, a switched capacitor amplifier, and a logic circuit connected in sequence. A high-threshold comparator and a low-threshold comparator arranged in parallel are provided between the switched capacitor amplifier and the logic circuit, and the reset signal output terminal RST of the logic circuit is connected to the reset signal control terminal of the switched capacitor amplifier. When the pixel circuit is operating, the photodiode receives ambient light to generate photocurrent, which is output through the IV conversion circuit and outputs a photovoltage. The photovoltage is transmitted to the input terminal of the switched capacitor amplifier through a voltage follower. The switched capacitor amplifier amplifies the photovoltage and compares it with a preset threshold value through a high-threshold comparator and a low-threshold comparator. If the value is greater than the high threshold, the pixel circuit outputs an ON event, and the reset switch MOS transistor resets the pixel circuit. If the value is less than the low threshold, the pixel circuit outputs an OFF event, and the reset switch MOS transistor resets the pixel circuit. Otherwise, the pixel circuit does not output a valid event.

[0004] A switched capacitor amplifier (SCA) consists of an input capacitor, a feedback capacitor, an operational amplifier, and a reset switch MOSFET. Its function is to detect changes in ambient light. When ambient light increases, the SCA's input voltage gradually increases, and the SCA's output voltage increases accordingly. When ambient light decreases, the SCA's input voltage gradually decreases, and the SCA's output voltage decreases accordingly. Leakage current from the SCA's reset switch MOSFET and the switching transient pulse can trigger the subsequent threshold comparator, generating false events and reducing the reliability of the dynamic vision sensor chip's output data. The reason why the SCA's leakage current affects the reliability of the SCA's output data is that a current path exists between the MOSFET's substrate and source terminals. When ambient light intensity remains constant, the SCA is in its refractory period, and the MOSFET's gate voltage is high, turning it off. At this point, charge leaks through the MOSFET's substrate-source path to the power supply voltage, generating a leakage current. This causes the SCA's output voltage to gradually decrease until it falls below the threshold voltage of the low-threshold comparator, causing the system to reset the MOSFET, generating a false OFF event. The reason switching transients affect the reliability of the dynamic vision sensor chip's output data is that when the reset switch MOSFET turns on or off, a switching transient pulse is generated at the output of the switched capacitor amplifier. If the pulse amplitude is greater than the preset high threshold of the subsequent high-threshold comparator, an ON error occurs; if the pulse amplitude is less than the preset low threshold of the subsequent low-threshold comparator, an OFF error occurs. Furthermore, because the equivalent impedance between the switched capacitor amplifier's negative input terminal (Vx) and output terminal (Vdiff) is finite, its closed-loop gain is less than the ratio of the capacitances of C1 and C2, resulting in poor closed-loop gain accuracy, affecting the accuracy of the dynamic vision sensor chip's output data. This severely impacts the reliability of the dynamic vision sensor chip's output data.

[0005] How to eliminate the false events caused by the leakage current of the MOS tube of the reset switch of the switched capacitor amplifier, and reduce the probability of false events caused by the threshold comparator triggered by the instantaneous switching pulse, so as to improve the reliability of the output data of the dynamic vision sensor chip, is the focus and difficulty of the study of switched capacitor amplifiers. For example, in 2022, Xia Cancan of Xidian University disclosed a switched capacitor amplifier based on the gate-induced barrier lowering effect GIDL suppression switch in his master's thesis "High-performance dynamic vision sensor chip design". Its structure is as follows Figure 2As shown, it includes an input capacitor C1, a feedback capacitor C2, an operational amplifier AMP and a GIDL inhibition switch unit; the positive input terminal Vref of the AMP is connected to an external reference voltage source, the negative input terminal Vx of the AMP is connected to the output terminal Vlog of the voltage follower of the previous stage, and the output terminal Vdiff of the AMP is connected to the positive input terminal of the high threshold comparator and the negative input terminal of the low threshold comparator of the subsequent stage; C1 is loaded between Vlog and Vx; the GIDL inhibition switch is loaded between Vx and Vdiff, and includes a first P-type metal oxide semiconductor (PMOS) transistor M1, a second PMOS transistor M2, a third PMOS transistor M4 and an N-type metal oxide semiconductor (NMOS) transistor M3. The drain of the first PMOS transistor M1 is connected to the negative input terminal Vx of the AMP, its source is connected to the drain of M2 and the drain of M3, its gate is connected to the gate of M2, the source of M3, and the source of M4, and its substrate is connected to the power supply VDD. The source of the second PMOS transistor M2 is connected to the output terminal Vdiff of the AMP, and its substrate is connected to VDD. The drain of the third PMOS transistor M4 is connected to ground, its gate is connected to the gate of M3 and the logic circuit reset signal output terminal RST, and its substrate is connected to VDD. The substrate of the NMOS transistor M3 is connected to ground GND. When the switched capacitor amplifier is reset, the reset voltage is sampled at the node Vnet between M1 and M2. During normal operation after reset, the source follower formed by M3 and M4 biases the sampled reset voltage to the gate nodes of M1 and M2. As a result, the gate-source voltage difference between M1 and M2 is almost zero, suppressing the leakage current of the reset switch MOS transistor to a negligible level, eliminating false events caused by the reset switch MOS transistor leakage current. However, due to the large equivalent inductance at the output, this invention generates large switching transient pulses, increasing the probability of false triggering of the threshold comparator. This results in low reliability of the dynamic vision sensor chip's output data. Furthermore, the GIDL suppression switch does not increase the equivalent impedance between the switched capacitor amplifier's negative input terminal, Vx, and output terminal, Vdiff. Its closed-loop gain is less than the ratio of the capacitances of C1 and C2, resulting in poor closed-loop gain accuracy, which affects the accuracy of the dynamic vision sensor chip's data. Summary of the Invention

[0006] The purpose of the present invention is to address the deficiencies of the above-mentioned existing technologies and propose a dynamic vision sensor chip switched capacitor amplifier based on pseudo-resistance switching to solve the technical problems of poor data reliability and data accuracy in the existing technologies.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A dynamic vision sensor chip switched capacitor amplifier based on a pseudo-resistance switch includes an input capacitor C1, a feedback capacitor C2, an operational amplifier AMP, and a pseudo-resistance switch; the AMP's positive input terminal Vref, negative input terminal Vx, and output terminal Vdiff are respectively connected to an external reference voltage source, the output terminal Vlog of a voltage follower at the preceding stage, the positive input terminal of a high-threshold comparator at the following stage, and the negative input terminal of a low-threshold comparator; C1 is loaded between Vlog and Vx; C2 is loaded between Vx and Vdiff; the pseudo-resistance switch includes a reset switch P-type complementary metal oxide semiconductor (PMO) An S transistor M1 and one or more parallel-connected N-type complementary metal oxide semiconductor (NMOS) transistor groups, each NMOS transistor group including a first NMOS transistor M2 and a second NMOS transistor M3; the reset switch PMOS transistor M1, having a gate terminal connected to an external logic circuit reset signal output terminal RST, a substrate connected to a power supply VDD, a source terminal connected to Vdiff, and a drain terminal connected to Vx; the first NMOS transistor M2, having a drain terminal and a gate terminal connected to Vx, and a substrate connected to ground GND; the second NMOS transistor M3, having a drain terminal and a gate terminal connected to Vdiff, a substrate connected to GND, and a source terminal connected to the source terminal of M2.

[0009] A dynamic vision sensor chip switched capacitor amplifier based on a pseudo-resistance switch includes an input capacitor C1, a feedback capacitor C2, and an operational amplifier AMP; the AMP's positive input terminal Vref, negative input terminal Vx, and output terminal Vdiff are respectively connected to an external reference voltage source, the output terminal Vlog of a preceding voltage follower, the positive input terminal of a subsequent high-threshold comparator, and the negative input terminal of a subsequent low-threshold comparator; C1 is loaded between Vlog and Vx; C2 is loaded between Vx and Vdiff; the pseudo-resistance switch includes a reset switch NMOS transistor M 4 and one or more parallel PMOS transistor groups, each PMOS transistor group includes a first PMOS transistor M5 and a second PMOS transistor M6; the reset switch NMOS transistor M4 has a gate terminal connected to the external logic circuit reset signal output terminal RST, a substrate connected to GND, a source terminal connected to Vx, and a drain terminal connected to Vdiff; the drain terminal and gate terminal of the first PMOS transistor M5 are connected to Vx, and the substrate is connected to the power supply VDD; the drain terminal and gate terminal of the second PMOS transistor M6 are connected to Vdiff, the substrate is connected to VDD, and the source terminal is connected to the source terminal of M5.

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] First, the present invention uses a MOS tube in a pseudo-resistance switch connected to the output end of the switched capacitor amplifier in a diode connection manner to reduce the equivalent inductance of the output end of the switched capacitor amplifier, thereby reducing the switching transient pulse at the output end of the switched capacitor amplifier when it is reset. Under the premise of ensuring that the reliability of the output data of the dynamic vision sensor chip is not reduced due to leakage current, the reliability of the output data of the dynamic vision sensor chip is effectively improved.

[0012] Secondly, since the MOS tube group in the pseudo-resistance switch of the present invention has two MOS tubes connected in a diode connection manner, a larger equivalent impedance is presented between the negative input terminal and the output terminal of the switched capacitor amplifier, making the closed-loop gain of the switched capacitor amplifier closer to the ratio of the capacitance values ​​of C1 and C2, thereby improving the accuracy of the output data of the dynamic vision sensor chip. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is a schematic diagram of the structure of the pixel circuit of an existing dynamic vision sensor chip;

[0014] Figure 2 Schematic diagram of the structure of a conventional switched capacitor amplifier based on a GIDL suppression switch;

[0015] Figure 3 It is a structural diagram of the first embodiment of the present invention;

[0016] Figure 4 FIG. 4 is a schematic structural diagram of a pseudo-resistance switch according to a first embodiment of the present invention.

[0017] Figure 5 2 is a schematic structural diagram of a second embodiment of the present invention;

[0018] Figure 6 FIG. 4 is a schematic structural diagram of a pseudo-resistance switch according to a second embodiment of the present invention. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] The first embodiment includes two parallel-connected N-type complementary metal oxide semiconductor (NMOS) transistor groups.

[0021] Reference Figure 3A switched capacitor amplifier (SCA) for a dynamic vision sensor chip based on a pseudo-resistance switch includes an input capacitor C1, a feedback capacitor C2, an operational amplifier (AMP), and a pseudo-resistance switch. C1 samples the voltage change at the output terminal Vlog of the previous voltage follower. C2 provides a negative feedback path for the SCA and generates charge transfer with C1. The AMP, with its high open-loop gain, serves as the core operational amplifier. The pseudo-resistance switch controls the SCA's operating state.

[0022] The AMP's positive input terminal Vref, negative input terminal Vx, and output terminal Vdiff are connected to an external reference voltage source, the output terminal Vlog of the preceding voltage follower, and the positive input terminal and negative input terminal of the subsequent high-threshold comparator and low-threshold comparator, respectively. C1 is connected between Vlog and Vx, and C2 is connected between Vx and Vdiff. The closed-loop gain of the switched capacitor amplifier is approximately the ratio of the capacitances of C1 and C2.

[0023] The pseudo-resistance switch includes a reset P-type complementary metal oxide semiconductor (PMOS) switch transistor M1 and one or more parallel N-type complementary metal oxide semiconductor (NMOS) transistor groups, each of which includes a first NMOS transistor M2 and a second NMOS transistor M3. The reset switch PMOS transistor M1 has a gate terminal connected to an external logic circuit reset signal output terminal RST, a substrate connected to a power supply VDD, a source terminal connected to Vdiff, and a drain terminal connected to Vx. The on and off of M1 is controlled by an external logic circuit reset signal. When the external logic circuit reset signal is at a low level, M1 is turned on; when the external logic circuit reset signal is at a high level, M1 is turned off.

[0024] The drain and gate terminals of the first NMOS transistor M2 are connected to Vx, and the substrate is connected to ground GND. The drain and gate terminals of the second NMOS transistor M3 are connected to Vdiff, the substrate is connected to GND, and the source terminal is connected to the source terminal of M2. M2 and M3 are both connected in series using a diode connection, creating an equivalent large impedance between Vx and Vdiff. This makes the closed-loop gain of the switched capacitor amplifier closer to the ratio of the capacitances of C1 and C2, improving the closed-loop gain accuracy of the switched capacitor amplifier and thus the accuracy of the output data of the dynamic vision sensor chip. The gate and drain terminals of M3 are connected to the output terminal Vdiff of the switched capacitor amplifier, reducing the equivalent inductance of Vdiff and minimizing the switching transient pulses of the switched capacitor amplifier.

[0025] When the pseudo-resistance switch is turned on, the switched capacitor amplifier operates in a reset state; when the pseudo-resistance switch is turned off, the switched capacitor amplifier operates in a sampling state.

[0026] Refer to the attached Figure 4The pseudo-resistance switch of the first embodiment of the present invention includes a reset switch PMOS transistor and two NMOS transistor groups. The reset switch PMOS transistor M1 has four terminals: drain, source, gate, and substrate. The source and drain terminals of M1 are interchangeable. The NMOS transistor group includes a first NMOS transistor M2 and a second NMOS transistor M3. Both M2 and M3 have four terminals: drain, source, gate, and substrate.

[0027] The working principle of this embodiment is that when the ambient light changes, the voltage value Vlog at the output end of the previous voltage follower changes, causing charge transfer between the input capacitor C1 and the feedback capacitor C2. The reference voltage source loaded on Vref makes the voltage value of Vx equal to the reference voltage; the dynamic visual sensor chip switch capacitor amplifier based on the pseudo-resistance switch amplifies the voltage change across C1 according to the ratio of the capacitance values ​​of C1 to C2, adds it to the voltage value of Vx, and outputs it to Vdiff. It is then input to the negative input end of the high threshold comparator and the positive input end of the low threshold comparator, and compared with the set high threshold and low threshold, respectively; if the voltage value of Vdiff is greater than the high threshold, the pixel circuit outputs a low-active ON event; if the voltage value of Vdiff is less than the low threshold, the pixel circuit outputs a low-active OFF event; otherwise, the pixel circuit does not output a valid event.

[0028] When the ambient light remains unchanged or changes very slightly for a long time, the gate voltage of M1 is high, M1 is in the off state, and the switched capacitor amplifier based on the pseudo-resistance switch operates in the sampling state. The voltage of Vdiff begins to decrease due to the leakage current caused by a current path between the substrate and the source end of M1. At this point, M2 and M3 begin to provide a current of equal magnitude and opposite direction to M1's leakage current to compensate for it, raising Vdiff to near Vref and maintaining this current, thus achieving the leakage current suppression function of existing switched capacitor amplifiers based on the GIDL suppression switch. Simultaneously, the gate and drain of M3 are connected to the output terminal Vdiff of the switched capacitor amplifier, reducing the equivalent inductance of Vdiff. This reduces the switching transient pulse of the switched capacitor amplifier based on the pseudo-resistance switch, lowering the probability of false triggering of the high-threshold and low-threshold comparators in the subsequent stages, and improving data reliability. Due to the limited open-loop gain of the operational amplifier AMP, the closed-loop gain of existing switched capacitor amplifiers based on the GIDL suppression switch is less than the ratio of the capacitances of C1 and C2. However, the series connection of M2 and M3 using a diode creates an equivalent large impedance between Vx and Vdiff, making the closed-loop gain of the switched capacitor amplifier closer to the ratio of the capacitances of C1 and C2. This improves the closed-loop gain accuracy of the switched capacitor amplifier, thereby improving the accuracy of the output data of the dynamic vision sensor chip.

[0029] Second embodiment: The basic structure of this embodiment is the same as that of the first embodiment, except that the number and connection relationship of the NMOS transistors and PMOS transistors included in the pseudo-resistance switch are adjusted.

[0030] Reference Figure 5 , a dynamic vision sensor chip switched capacitor amplifier based on pseudo-resistance switch, wherein the pseudo-resistance switch structure is as follows Figure 6 As shown, the system comprises a reset N-type complementary metal oxide semiconductor (NMOS) switch transistor M4 and one or more parallel P-type complementary metal oxide semiconductor (PMOS) transistor groups, each of which includes a first PMOS transistor M5 and a second PMOS transistor M6. The reset switch NMOS transistor M4 has a gate connected to an external logic circuit reset signal output terminal RST, a substrate connected to ground GND, a source connected to Vdiff, and a drain connected to Vx. The first PMOS transistor M5 has a drain and gate connected to Vx, and a substrate connected to a power supply VDD. The second PMOS transistor M6 has a drain and gate connected to Vdiff, a substrate connected to VDD, and a source connected to the source of M5.

[0031] The working principle of this embodiment is that when the ambient light changes, the voltage value Vlog at the output end of the previous voltage follower changes, causing charge transfer between the input capacitor C1 and the feedback capacitor C2. The reference voltage source loaded on Vref makes the voltage value of Vx equal to the reference voltage; the dynamic visual sensor chip switch capacitor amplifier based on the pseudo-resistance switch amplifies the voltage change across C1 according to the ratio of the capacitance values ​​of C1 to C2, adds it to the voltage value of Vx, and outputs it to Vdiff. It is then input to the negative input end of the high threshold comparator and the positive input end of the low threshold comparator, and compared with the set high threshold and low threshold, respectively; if the voltage value of Vdiff is greater than the high threshold, the pixel circuit outputs a low-active ON event; if the voltage value of Vdiff is less than the low threshold, the pixel circuit outputs a low-active OFF event; otherwise, the pixel circuit does not output a valid event.

[0032] When the ambient light remains unchanged or changes very slightly for a long time, the gate voltage of M4 is low, M4 is in the off state, and the switched capacitor amplifier based on the pseudo-resistance switch operates in the sampling state. The voltage of Vdiff begins to decrease due to the leakage current caused by a current path between the substrate and the source of M4. At this point, M5 and M6 begin to provide a current of equal magnitude and opposite direction to the leakage current of M4 to compensate for it, raising Vdiff to near Vref and maintaining this current, thus achieving the leakage current suppression function of existing switched capacitor amplifiers based on the GIDL suppression switch. Simultaneously, the gate and drain of M6 are connected to the output terminal Vdiff of the switched capacitor amplifier, reducing the equivalent inductance of Vdiff. This reduces the switching transient pulse of the switched capacitor amplifier based on the pseudo-resistance switch, lowering the probability of false triggering of the high-threshold and low-threshold comparators in the subsequent stages, and improving data reliability. Due to the limited open-loop gain of the operational amplifier AMP, the closed-loop gain of existing switched capacitor amplifiers based on the GIDL suppression switch is less than the ratio of the capacitances of C1 and C2. However, the series connection of M5 and M6 using a diode connection creates an equivalent large impedance between Vx and Vdiff, making the closed-loop gain of the switched capacitor amplifier closer to the ratio of the capacitances of C1 and C2. This improves the closed-loop gain accuracy of the switched capacitor amplifier, thereby improving the accuracy of the output data of the dynamic vision sensor chip.

Claims

1. A switched capacitor amplifier for a dynamic vision sensor chip based on a pseudo-resistance switch, comprising an input capacitor C1, a feedback capacitor C2, and an operational amplifier AMP; the AMP's positive input terminal Vref, negative input terminal Vx, and output terminal Vdiff are respectively connected to an external reference voltage source, the output terminal Vlog of a preceding voltage follower, and the positive input terminal and negative input terminal of a subsequent high-threshold comparator and low-threshold comparator; C1 is loaded between Vlog and Vx; C2 is loaded between Vx and Vdiff; and the invention is characterized in that: The device further includes a pseudo-resistance switch consisting of a reset switch P-type complementary metal oxide semiconductor (PMOS) transistor M1 and one or more parallel N-type complementary metal oxide semiconductor (NMOS) transistor groups, each of which includes a first NMOS transistor M2 and a second NMOS transistor M3 connected in a diode connection manner. The reset switch PMOS transistor M1 has a gate terminal connected to an external logic circuit reset signal output terminal RST, a substrate connected to a power supply VDD, a source terminal connected to Vdiff, and a drain terminal connected to Vx. The on and off of M1 are controlled by an external logic circuit reset signal. When the external logic circuit reset signal is at a low level, M1 is turned on; when the external logic circuit reset signal is at a high level, M1 is turned off. The drain and gate terminals of the first NMOS transistor M2 are connected to Vx, and the substrate is connected to ground GND. The drain and gate terminals of the second NMOS transistor M3 are connected to Vdiff, the substrate is connected to GND, and the source terminal is connected to the source terminal of M2. M2 and M3 are both connected in series in a diode connection manner.

2. A switched capacitor amplifier for a dynamic vision sensor chip based on a pseudo-resistance switch, comprising an input capacitor C1, a feedback capacitor C2, and an operational amplifier AMP; the AMP's positive input terminal Vref, negative input terminal Vx, and output terminal Vdiff are respectively connected to an external reference voltage source, the output terminal Vlog of a preceding voltage follower, the positive input terminal of a subsequent high-threshold comparator, and the negative input terminal of a subsequent low-threshold comparator; C1 is loaded between Vlog and Vx; C2 is loaded between Vx and Vdiff; and the invention is characterized in that: The device further includes a pseudo-resistance switch consisting of a reset switch NMOS transistor M4 and one or more parallel PMOS transistor groups, each PMOS transistor group including a first PMOS transistor M5 and a second PMOS transistor M6 connected in a diode connection manner. The reset switch NMOS transistor M4 has a gate terminal connected to an external logic circuit reset signal output terminal RST, a substrate connected to GND, a source terminal connected to Vx, and a drain terminal connected to Vdiff. The on and off of M4 is controlled by an external logic circuit reset signal. When the external logic circuit reset signal is at a low level, M4 is turned on; when the external logic circuit reset signal is at a high level, M4 is turned off. The drain and gate terminals of the first PMOS transistor M5 are connected to Vx, and the substrate is connected to a power supply VDD. The drain and gate terminals of the second PMOS transistor M6 are connected to Vdiff, the substrate is connected to VDD, and the source terminal is connected to the source terminal of M5. M5 and M6 are both connected in series in a diode connection manner.

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