Adaptive adjustment circuit and laser ranging chip

Abstract

The application discloses an adaptive adjusting circuit and a laser ranging chip. The adaptive adjusting circuit comprises a current sampling module, a transimpedance amplifier and a voltage boosting circuit. The output current of a photodetector array is obtained by the current sampling module, the output current is compared with a reference current by the transimpedance amplifier, and a corresponding voltage adjusting signal is output according to the comparison result. The driving voltage of the photodetector array is adjusted by the voltage boosting circuit according to the voltage adjusting signal, so that the photodetector array is in an avalanche breakdown state. The application samples the current flowing through the SPAD by the current sampling module, compares the current with the reference current to determine the size of the voltage boosting of the voltage boosting circuit, and does not need to adjust the temperature coefficient. The breakdown voltage required by the SPAD can be generated at any temperature, so that the photosensitive capacity and detection accuracy of the photodetector array can be ensured.

Description

Technical Field

[0001] This invention relates to the field of optical detection technology, and in particular to an adaptive adjustment circuit and a laser ranging chip. Background Technology

[0002] In recent years, Time of Flight (TOF) technology has been increasingly widely used in autonomous driving. In fields such as lidar and machine vision, TOF ranging is considered one of the most accurate and reliable ranging methods for the future. Direct Time of Flight (TOF) ranging uses light pulses emitted from the transmitter, reflected by the object, and then reaching the receiver. The round-trip flight time of the photons is recorded to achieve accurate ranging.

[0003] SPAD (Single Photon Avalanche Diode) is the most commonly used receiving device due to its excellent photon sensitivity. Normally, the power supply voltage provided to the SPAD is constant, such as 27Volt. However, the breakdown voltage (BD) across the SPAD changes with temperature. If the temperature increases, causing the BD to rise, for example to 27.5Volt, the SPAD, which was originally at the breakdown threshold, enters a sub-avalanche state. Thus, even if reflected light hits the SPAD, it will not trigger an avalanche effect, thereby reducing its photosensitivity and detection performance.

[0004] To ensure that the SPAD remains in avalanche mode even when ambient temperature changes, a common approach is to add a reference voltage generation module corresponding to the SPAD to the SPAD regulation circuit, such as... Figure 1 As shown, the reference voltage generation module generates a corresponding reference voltage VREF based on the temperature coefficient. The comparator clamps the feedback voltage VFB at the SPAD terminal to the reference voltage VREF, ultimately causing the charge pump to generate a high voltage sufficient to bring the SPAD to the avalanche critical point. In actual operation, it is necessary to first measure the temperature coefficient of VBD (i.e., SPAD breakdown voltage), and then adjust the temperature coefficient of VREF (reference voltage generation module) based on the measured VBD temperature coefficient. This method is theoretically feasible, but the actual operation process is very complex and requires a lot of CP testing (ChipProbing, wafer testing) time, resulting in a long product development cycle and high cost. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide an adaptive adjustment circuit and a laser ranging chip.

[0006] To solve the above technical problems, the present invention adopts the following technical solution:

[0007] An adaptive adjustment circuit for a photodetector, comprising:

[0008] The current sampling module is used to acquire the output current of the photodetector array;

[0009] A transimpedance amplifier is used to compare the output current with a reference current and output a corresponding voltage adjustment signal based on the comparison result.

[0010] A boost circuit is used to adjust the driving voltage of the photodetector array according to the voltage adjustment signal so that the photodetector array is in an avalanche breakdown state.

[0011] Preferably, in the adaptive adjustment circuit of the photodetector, the reference current is the current when the photodetector array breaks down, and the reference current does not change with temperature.

[0012] Preferably, in the adaptive adjustment circuit of the photodetector, the current sampling module is specifically used to obtain the average current of the output current of the photodetector array and output it to the transimpedance amplifier.

[0013] Preferably, in the adaptive adjustment circuit of the photodetector, the current sampling module includes a current mirror, the input terminal of which is connected to the positive terminal of the photodetector array, and the output terminal of which is connected to an input terminal of a transimpedance amplifier.

[0014] Preferably, in the adaptive adjustment circuit of the photodetector, the current mirror includes: a first MOS transistor and a second MOS transistor, the drain of the first MOS transistor is connected to the positive terminal of the photodetector array, the gate of the first MOS transistor and the gate of the second MOS transistor, the source of the first MOS transistor and the source of the second MOS transistor are grounded, the drain of the second MOS transistor is connected to one input terminal of a transimpedance amplifier, the other input terminal of the transimpedance amplifier is connected to a reference current output terminal, and the output terminal of the transimpedance amplifier is connected to the boost circuit.

[0015] Preferably, in the adaptive adjustment circuit of the photodetector, the aspect ratio of the first MOS transistor is n times the aspect ratio of the second MOS transistor.

[0016] Preferably, in the adaptive adjustment circuit of the photodetector, the transimpedance amplifier includes: a differential amplifier, a comparator, a first resistor, and a second resistor. The inverting input terminal of the differential amplifier is one input terminal of the transimpedance amplifier. The inverting input terminal of the differential amplifier is connected to the drain of the second MOS transistor and is also connected to the first output terminal of the differential amplifier through the first resistor. The first output terminal of the differential amplifier is also connected to the non-inverting input terminal of the comparator. The non-inverting input terminal of the differential amplifier is the other input terminal of the transimpedance amplifier. The non-inverting input terminal of the differential amplifier is connected to the reference current output terminal and is also connected to the second output terminal of the differential amplifier through the second resistor. The second output terminal of the differential amplifier is also connected to the inverting input terminal of the comparator. The output terminal of the comparator is connected to the input terminal of the boost circuit.

[0017] Preferably, in the adaptive adjustment circuit of the photodetector, the resistance values ​​of the first resistor and the second resistor are the same.

[0018] Preferably, in the adaptive adjustment circuit of the photodetector, the boost circuit includes a charge pump. When the transimpedance amplifier outputs a high level, the charge pump increases the output voltage, causing the drive voltage of the photodetector array to increase until the sampling current is greater than or equal to the reference current.

[0019] The present invention also provides a laser ranging chip, comprising at least one photodetector array and an adaptive adjustment circuit.

[0020] Compared to existing technologies, the adaptive adjustment circuit and laser ranging chip provided by this invention utilize a current sampling module to acquire the output current of the photodetector array in the adaptive adjustment circuit. A transimpedance amplifier compares this output current with a reference current, and outputs a corresponding voltage adjustment signal based on the comparison result. A boost circuit then adjusts the drive voltage of the photodetector array according to this voltage adjustment signal, bringing the photodetector array into an avalanche breakdown state. This invention samples the current flowing through the SPAD using a current sampling module and compares it with a reference current to determine the boost voltage of the boost circuit. This eliminates the need to adjust the temperature coefficient and can generate the required breakdown voltage for the SPAD at any temperature, thereby ensuring the photosensitivity and detection accuracy of the photodetector array. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the circuit principle of a SPAD regulation circuit in the prior art.

[0022] Figure 2 This is a schematic diagram showing the breakdown voltage of a photodetector array as a function of temperature.

[0023] Figure 3 A schematic diagram of the adaptive adjustment circuit provided by the present invention.

[0024] Figure 4 This is a schematic diagram of the IV curve of a photodetector array.

[0025] Figure 5 A circuit diagram of the current sampling module in the adaptive adjustment circuit provided by the present invention.

[0026] Figure 6 A circuit diagram of the transimpedance amplifier in the adaptive adjustment circuit provided by the present invention.

[0027] Explanation of reference numerals in the attached figures

[0028] Current sampling module 10, transimpedance amplifier TIA, boost circuit 20, photodetector array 30, first MOSFET M1, second MOSFET M2, differential amplifier A1, comparator A2, first resistor Rf1, second resistor Rf2, first capacitor Cf1, second capacitor Cf2 Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0030] It should be noted that when a component is referred to as being "mounted on," "fixed to," or "set on" another component, it can be directly on the other component or may have an intervening component present. When a component is referred to as being "connected to" another component, it can be directly connected to the other component or may have an intervening component present.

[0031] It should also be noted that the directional terms such as left, right, up, and down in the embodiments of the present invention are only relative concepts or are based on the normal use state of the product, and should not be considered as restrictive.

[0032] like Figure 2 As shown in the figure, the voltage curve of the SPAD shows that the VBD (breakdown voltage) of the SPAD changes with temperature. Figure 2 As can be seen, VBD exhibits a positive temperature coefficient, with different temperature coefficients in different temperature ranges. Existing technology uses testing to obtain the temperature coefficient of VBD, and then generates a VREF (reference voltage) corresponding to the temperature coefficient to adjust the driving voltage of SPAD, so as to make the SPAD array in avalanche state at any temperature.

[0033] This invention solves the problem that traditional SPAD power supply circuits require measuring the SPAD breakdown voltage temperature coefficient first, and then adjusting the VREF (reference voltage) temperature coefficient based on the SPAD breakdown voltage temperature coefficient. This operation is very complicated, requires a lot of CP testing, and results in long development cycles and high development costs.

[0034] The adaptive adjustment circuit of the photodetector of this invention does not require adjustment of the temperature coefficient of the VREF and can generate the breakdown voltage required for SPAD at any temperature. Please refer to [link to relevant documentation]. Figure 3 The adaptive adjustment circuit of the photodetector is connected to the photodetector array 30, and includes: a current sampling module 10, a transimpedance amplifier TIA, and a boost circuit 20.

[0035] The photodetector array 30 is a SPAD array composed of several SPADs. The input terminal of the current sampling module 10 is connected to the positive terminal of the photodetector array 30, and the output terminal of the current sampling module 10 is connected to an input terminal of the transimpedance amplifier TIA. The current sampling module 10 is used to obtain the output current of the photodetector array 30 and send it to the transimpedance amplifier TIA.

[0036] The other input terminal of the transimpedance amplifier TIA is connected to a reference current generator (such as a bandgap reference unit) to receive the reference current output by the reference current generator. The output terminal of the transimpedance amplifier TIA is connected to a boost circuit 20 to compare the output current with the reference current and output a corresponding voltage adjustment signal to the boost circuit 20 according to the comparison result. The voltage adjustment signal is either a high-level signal or a low-level signal.

[0037] The boost circuit 20 is connected to the negative terminal of the photodetector array 30 and is used to adjust the driving voltage of the photodetector array 30 according to the voltage adjustment signal, so that the photodetector array 30 is in an avalanche breakdown state. For example, when the voltage adjustment signal is a high-level signal, the boost circuit 20 boosts the voltage according to the first boost command and outputs a higher voltage (e.g., 29V); when the voltage adjustment signal is a low-level signal, the boost circuit boosts the voltage according to the second boost command and outputs a lower voltage (e.g., 27V). The duty cycle of the first boost command is higher than that of the second boost command.

[0038] In the adaptive adjustment circuit provided by this invention, the SPAD current is sampled by the current sampling module 10. The sampled current Is is compared with a preset reference current by the transimpedance amplifier TIA. If the sampled current Is is less than the reference current Iref, the transimpedance amplifier TIA outputs a high level. The boost circuit 20 boosts the voltage according to the pulse signal of the first duty cycle, thereby increasing the HVOUT voltage and thus increasing the current of the SPAD array. When the sampled current is greater than or equal to the reference current, the transimpedance amplifier TIA outputs a low level. The boost circuit 20 boosts the voltage according to the pulse signal of the second duty cycle. This voltage will be less than the initial state HVOUT until the sampled current is less than or equal to the reference current. At this time, the circuit adjustment reaches a balance and keeps the HVOUT voltage greater than the SPAD breakdown voltage VBD.

[0039] Furthermore, the HVOUT voltage automatically adjusts with temperature changes. Assuming an initial state where the duty cycle of the pulse signal controlling the output current in the boost circuit is 50%, when the temperature rises, the SPAD array requires a higher HVOUT voltage to trigger avalanche breakdown. At this time, the sampling current decreases and falls below the reference current, causing the transimpedance amplifier TIA to output a high level. This high level lasts longer than in the initial state, resulting in a pulse signal duty cycle greater than 50%. Consequently, the output voltage will be higher than the initial HVOUT voltage until the sampling current is greater than or equal to the reference current. When the temperature drops, the SPAD array requires a lower HVOUT voltage to trigger avalanche breakdown. At this time, the sampling current rises and rises above the reference current, causing the transimpedance amplifier TIA to output a low level. This low level lasts shorter than in the initial state, resulting in a pulse signal duty cycle less than 50%. The output voltage is then controlled by the external capacitor C (…). Figure 3 The capacitor shown is connected between HVOUT and ground. When powered, the output voltage will be less than the initial state HVOUT until the sampling current is less than or equal to the reference current, which greatly improves the stability and light sensitivity of the photodetector array 30 when the temperature changes, and improves the detection accuracy.

[0040] In this embodiment of the invention, the reference current is the current at which the photodetector array 30 breaks down. The reference current does not change with temperature, while the sampling current is related to whether the SPAD in the photodetector array 30 breaks down. The magnitude of the current at which the SPAD breaks down can be determined experimentally. Figure 4 As shown in the figure, SPAD is a single-photon avalanche diode, APD is an avalanche diode, and PD is a photodiode. The reference current Iref can be directly measured experimentally.

[0041] Preferably, the current sampling module 10 includes a current mirror 101, the input terminal of which is connected to the positive terminal of the photodetector array 30, and the output terminal of which is connected to an input terminal of the transimpedance amplifier TIA. The current mirror 101 is specifically used to obtain the average current value of the output current of the photodetector array 30 and output it to the transimpedance amplifier TIA, thereby improving the accuracy of the sampling current.

[0042] Please refer to the following: Figure 5 The current mirror 101 includes a first MOS transistor M1 and a second MOS transistor M2. Both the first MOS transistor M1 and the second MOS transistor M2 are N-channel field-effect transistors, which are turned on when their gates are at a high level and turned off when their gates are at a low level.

[0043] In this embodiment, the drain of the first MOS transistor M1 is connected to the positive terminal of the photodetector array 30, the gate of the first MOS transistor M1, and the gate of the second MOS transistor M2. The source of the first MOS transistor M1 and the source of the second MOS transistor M2 are grounded. The drain of the second MOS transistor M2 is connected to one input terminal of the transimpedance amplifier TIA. The other input terminal of the transimpedance amplifier TIA is connected to the reference current output terminal. The output terminal of the transimpedance amplifier TIA is connected to the boost circuit 20.

[0044] For example, the photodetector array 30 has m photodetectors, of which n photodetectors are triggered by photons, generating n current outputs, where m>n. This invention adds up the n currents and averages them to obtain the sampling current. The size of the first MOS transistor M1 is n*W / L, and the size of the second MOS transistor M2 is W / L, where W is the width and L is the length. The current from each SPAD in the photodetector array 30 is input from the drain of the first MOS transistor M1 (i.e., I1 to In). After processing by the first MOS transistor M1 and the second MOS transistor M2, the sampling current obtained through the drain of the second MOS transistor M2 is... The width-to-length ratio of the first MOSFET M1 is n times that of the second MOSFET M2. The sum of the currents of all triggered SPADs can be sampled through the first MOSFET M1. The average value of the sampled current is then mirrored to the second MOSFET M2 through current mirroring. The sampled current Is is then input to the transimpedance amplifier TIA.

[0045] Please refer to the following: Figure 6 The transimpedance amplifier TIA includes: a differential amplifier A1, a comparator A2, a first resistor Rf1, and a second resistor Rf2, wherein the first resistor Rf1 and the second resistor Rf2 are two feedback resistors. Preferably, the resistance value of the first resistor Rf1 and the resistance value of the second resistor Rf2 are the same to ensure that the differential amplifier A1 only amplifies the current difference and ensures control accuracy.

[0046] The differential amplifier A1 has two input terminals and two output terminals. The inverting input terminal of the differential amplifier A1 is one input terminal of the transimpedance amplifier TIA. The inverting input terminal of the differential amplifier A1 is connected to the drain of the second MOS transistor M2 and is also connected to the first output terminal of the differential amplifier A1 through the first resistor Rf1. The first output terminal of the differential amplifier A1 is also connected to the non-inverting input terminal of the comparator A2. The non-inverting input terminal of the differential amplifier A1 is the other input terminal of the transimpedance amplifier TIA. The non-inverting input terminal of the differential amplifier A1 is connected to the reference current output terminal and is also connected to the second output terminal of the differential amplifier A1 through the second resistor Rf2. The second output terminal of the differential amplifier A1 is also connected to the inverting input terminal of the comparator A2. The output terminal of the comparator A2 is connected to the input terminal of the boost circuit 20.

[0047] Optionally, a first capacitor Cf1 is connected in parallel across the two ends of the first resistor Rf1, and a second capacitor Cf2 is connected in parallel across the two ends of the second resistor Rf2. Both the first capacitor Cf1 and the second capacitor Cf2 are filter capacitors used to filter out noise and enable the differential amplifier A1 to work reliably.

[0048] Specifically, the sampling current Is and the reference current Iref are amplified by differential amplifier A1 to generate voltages V1 and V2, respectively, where V1 = Is * Rf1 and V2 = Iref * Rf2. Since Rf1 = Rf2 = R, V1 = Is * R and V2 = Iref * R. V1 and V2 are then passed through comparator A2 to generate a high level or a low level Vout.

[0049] Furthermore, the boost circuit 20 includes a charge pump (not shown in the figure). When the transimpedance amplifier TIA outputs a high level, the charge pump increases the output voltage, thereby increasing the driving voltage of the photodetector array 30. At this time, the sampling current will increase accordingly until the sampling current is greater than or equal to the reference current, making the HVOUT voltage greater than the VDB voltage.

[0050] For example, the function of the charge pump is to increase the supply voltage from 3.3V to 27V-29V, with 27V-29V corresponding to a temperature range of -40℃ to 85℃. At a normal temperature of 40℃, the corresponding voltage is 28V; when the temperature rises to 85℃, the charge pump output voltage is 29V, and when the temperature drops to -40℃, the charge pump output voltage is 27V. As the temperature changes, the voltage of HVOUT is adjusted accordingly to ensure that the current generated during the avalanche breakdown of the SPAD remains stable near the reference current IREF.

[0051] The present invention also provides a laser ranging chip, including an adaptive adjustment circuit and at least one photodetector array. The output terminal of the adaptive adjustment circuit is connected to the negative terminal of the photodetector array and is used for the voltage of the photodetector array to make the photodetector array in an avalanche state, as mentioned above.

[0052] In summary, this invention samples the current flowing through the SPAD using a current sampling module, compares it with a reference current to determine the boost voltage of the boost circuit, manually adjusts the SPAD breakdown voltage temperature coefficient, saves CP testing costs, and can generate the required breakdown voltage for the SPAD at any temperature, thereby ensuring the photosensitivity and detection accuracy of the photodetector array. Furthermore, this invention simplifies the circuit structure of the adaptive adjustment circuit, simultaneously reducing hardware costs.

[0053] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. An adaptive biasing circuit for a photodetector, comprising: include: The current sampling module is used to acquire the output current of the photodetector array; A transimpedance amplifier is used to compare the output current with a reference current and output a corresponding voltage adjustment signal based on the comparison result. A boost circuit is used to adjust the driving voltage of the photodetector array according to the voltage adjustment signal, so that the photodetector array is in an avalanche breakdown state; The reference current is the current at which the photodetector array breaks down. The reference current does not change with temperature. When the output current is less than the reference current, the transimpedance amplifier outputs a high level. The boost circuit boosts the voltage of the photodetector array according to the pulse signal of the first duty cycle, thereby increasing the current of the photodetector array. When the output current is greater than or equal to the reference current, the transimpedance amplifier outputs a low level. The boost circuit boosts the voltage according to the pulse signal of the second duty cycle. This voltage is less than the initial voltage of the photodetector array until the output current is less than or equal to the reference current. At this point, the circuit adjustment reaches balance and keeps the voltage of the photodetector array greater than the SPAD breakdown voltage.

2. The adaptive adjustment circuit of the photodetector according to claim 1, characterized in that, The current sampling module is specifically used to obtain the average current of the output current of the photodetector array and output it to the transimpedance amplifier.

3. The adaptive adjustment circuit of the photodetector according to claim 2, characterized in that, The current sampling module includes a current mirror, the input of which is connected to the positive terminal of the photodetector array, and the output of which is connected to an input of a transimpedance amplifier.

4. The adaptive adjustment circuit of the photodetector according to claim 3, characterized in that, The current mirror includes a first MOS transistor and a second MOS transistor. The drain of the first MOS transistor is connected to the positive terminal of the photodetector array, the gate of the first MOS transistor, and the gate of the second MOS transistor. The source of the first MOS transistor and the source of the second MOS transistor are grounded. The drain of the second MOS transistor is connected to one input terminal of a transimpedance amplifier. The other input terminal of the transimpedance amplifier is connected to the reference current output terminal. The output terminal of the transimpedance amplifier is connected to the boost circuit.

5. The adaptive adjustment circuit of the photodetector according to claim 4, characterized in that, The width-to-length ratio of the first MOS transistor is n times that of the second MOS transistor.

6. The adaptive adjustment circuit of the photodetector according to claim 4, characterized in that, The transimpedance amplifier includes: a differential amplifier, a comparator, a first resistor, and a second resistor. The inverting input terminal of the differential amplifier is one input terminal of the transimpedance amplifier. The inverting input terminal of the differential amplifier is connected to the drain of the second MOSFET and is also connected to the first output terminal of the differential amplifier through the first resistor. The first output terminal of the differential amplifier is also connected to the non-inverting input terminal of the comparator. The non-inverting input terminal of the differential amplifier is the other input terminal of the transimpedance amplifier. The non-inverting input terminal of the differential amplifier is connected to the reference current output terminal and is also connected to the second output terminal of the differential amplifier through the second resistor. The second output terminal of the differential amplifier is also connected to the inverting input terminal of the comparator. The output terminal of the comparator is connected to the input terminal of the boost circuit.

7. The adaptive adjustment circuit of the photodetector according to claim 6, characterized in that, The resistance values ​​of the first resistor and the second resistor are the same.

8. The adaptive biasing circuit for a photodetector of claim 1, wherein, The boost circuit includes a charge pump. When the transimpedance amplifier outputs a high level, the charge pump increases the output voltage, causing the drive voltage of the photodetector array to increase until the sampling current is greater than or equal to the reference current.

9. A laser ranging chip, comprising at least one photodetector array, characterized in that, Also included are adaptive regulation circuits as claimed in claims 1-8.

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