Reading circuit and method for improving detection efficiency of single-photon area array laser radar

Abstract

The invention relates to a reading circuit and method for improving the detection efficiency of a single-photon area array laser radar, and belongs to the technical field of single-photon laser three-dimensional imaging. Two working modes are set, and a gray level image and a distance image can be obtained in the same detector assembly. According to the invention, the two TDCs are arranged in the reading circuit to work in turn, so that the coverage of a long continuous gating period is realized, the reading circuit is suitable for large-dynamic-range detection, and a grayscale image and a distance image in a high-dynamic range can be obtained. By arranging the TDC and the temporary storage queue to work in turn, the working efficiency of the detector is improved, that is, the laser works once, the detector can detect at least M times, the scanning efficiency is high, the laser emission power requirement is greatly reduced, and the working efficiency of the system can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of single-photon laser three-dimensional imaging, and in particular relates to a readout circuit and method for improving the detection efficiency of a single-photon area array laser radar. Background Art

[0002] The single-photon array detector is a highly sensitive photoelectric detector that can respond to photon-level signals. It is the basis of single-photon radar detection, quantum communication and other fields. With the continuous development of basic software and hardware technologies, single-photon laser three-dimensional imaging detection technology based on Geiger focal plane cameras has attracted more and more attention, and has produced many research results, which have greatly improved the effective distance and imaging effect, and have high application value. Although the use of array detectors reduces the difficulty of field scanning, compared with the unit detection method, it loses more signal processing methods and flexibility in the distance direction.

[0003] In order to reduce noise interference and the long time required for the transmission of a large amount of detection data, the existing single-photon array lidar detector mainly works in a gated state, that is, the camera needs a gated signal to work, otherwise it cannot receive the signal; in addition, after the camera opens the door once, it needs a long dead time to recover, and the effective duty cycle of the working time period is relatively low. Therefore, it has the following disadvantages in actual use:

[0004] 1. It is necessary to obtain relatively accurate prior information on the target distance and calculate the accurate arrival time of the echo signal based on the target distance in order to effectively control the delay of the gate signal so that it opens the gate at the moment the echo signal arrives. However, in the actual operation of the LiDAR, the target distance is often unknown and may change at a relatively fast speed, which causes the arrival time of the echo pulse to change in real time, which is not suitable for the detection needs of dynamic scenes.

[0005] 2. The detector gated working time is limited, and one detection cannot cover a long working distance. Currently, most single-photon array detectors can only have one triggering opportunity within the gated time, which means that the detection efficiency of complex scenes with multiple echoes is low.

[0006] 3. The detector array has a limited operating frequency. After completing one detection, it takes a long time to restore to the initial state for the next detection. The previous signal needs to be read out before the next detection can be performed. As the array increases, the readout time is prolonged, and the detector is unable to detect for a long time, which also causes a large number of spatial omissions in the laser radar.

[0007] 4. For photon echo detection in long distance intervals, although the light echo can enter the detector's field of view, since the detector does not respond, multiple laser emissions are required to cover the distance interval, resulting in low energy utilization efficiency of the entire system.

[0008] 5. For multiple echo detection in a long distance interval, since the detector is triggered a limited number of times within the gate time, it is difficult to detect weak targets in the latter part of the gate time. Since time resolution and range restrict each other, it is difficult to take into account both the distance interval length and time resolution, and the accuracy of the distance direction is also limited.

[0009] 6. Usually, because the intensity of background light changes with the scene, in order to ensure a certain detection probability, single-photon detection usually needs to adjust the echo accumulation times according to the intensity of the background light. If the background light intensity is unknown, unnecessary and redundant laser pulses may be emitted to ensure the detection probability, which is inefficient. In addition, the array detectors commonly used for three-dimensional imaging cannot directly obtain the background light count. In order to estimate the background light intensity, it is necessary to repeatedly open the door to read the signal and then accumulate the light count, which is inefficient.

[0010] Therefore, although the use of area array detectors improves spatial coverage to a certain extent, the problems in the distance direction lead to limited applications of single-photon area arrays in time-sensitive and efficiency-intensive applications. The prior art lacks a method and system for reading and processing area array single-photon laser radar signals that can achieve long-distance spatial multiple echo detection and have photon counting functions. Summary of the invention

[0011] 1. Technical issues to be resolved

[0012] The technical problem to be solved by the present invention is to provide a single-photon laser radar array detection readout circuit and method to solve the problem that the existing single-photon laser radar with array detection cannot receive target echo signals in real time multiple times in the distance direction, resulting in low work efficiency.

[0013] (II) Technical solution

[0014] In order to solve the above technical problems, the present invention provides a readout circuit for improving the detection efficiency of a single-photon array laser radar. The single-photon array detector has two detector working modes. One is a photon counting working mode, in which the single-photon array detector obtains the number of photon signal triggering times of each pixel detector within a control time; the other is a time-of-flight measurement mode, in which the single-photon array detector obtains the time of photon signal triggering of each pixel detector within a control time relative to a gated start signal;

[0015] The two detector working modes are switched by a control signal; in order to realize the two detector working modes, the readout circuit includes a signal extraction module, a TDC logic module, and a data readout module;

[0016] The signal extraction module includes a quenching circuit, an analog-to-digital conversion circuit, and a digital logic circuit for converting the detector trigger signal into a digital signal, and providing the photosensitive chip with a quenching circuit required for single-photon detection. The signal extraction module also includes a comparator and a trigger. The quenching circuit converts the digital signal into a detector electrical pulse signal. The detector electrical pulse signal is converted into a digital pulse start TDC signal through the comparator and the trigger. The detector electrical pulse signal and the digital pulse start TDC signal are sent to the post-stage TDC logic module for processing;

[0017] The TDC logic module includes two TDC logic subcircuits and a switching switch. Under the action of the mode control signal, the TDC logic module can switch between the photon counting working mode and the flight time measurement mode. When the detector works in the flight time measurement mode, the gate signal preset by the system determines the working time length of the detector. The gate signal is divided into multiple small time intervals by the TDC switching control signal. When the TDC switching control signal is high, the switching switch sends the digital pulse to start the TDC signal into the TDC logic subcircuit 1, and when the TDC switching control signal is low, the digital pulse starts the TDC signal into the TDC logic subcircuit 2. At the same time, the TDC switching control signal is also sent to the inside of the TDC logic module, where the signal is inverted and sent to the TDC logic subcircuit 2. When the TDC logic module detects that the TDC switching control signal is high, the corresponding TDC logic module works in the pixel measurement mode, otherwise it works in the pixel data shifting mode. The TDC logic subcircuit 1 and the TDC logic subcircuit 2 output the TDC serial output data to the data readout module.

[0018] The data readout module includes two parallel data temporary storage queues, which are used to realize the pixel-level storage of the measurement results of the TDC logic module in the detector. When the TDC serial output data enters the data readout module, the data queue temporary storage switching signal controls whether it is input to data temporary storage queue one or data temporary storage queue two. Each time the laser is emitted, the state of the data queue temporary storage switching signal is flipped once.

[0019] Preferably, the TDC logic module has two pixel working modes, a pixel measurement mode and a pixel information shifting mode; when in the pixel measurement mode, the TDC logic module is used for time interval measurement and photon counting, and the time length measurement is achieved by counting the predetermined clock intervals, and the accuracy of the time interval measurement depends on the clock cycle; the accuracy of the time interval measurement is improved by adding clock subdivision logic.

[0020] When the detector working mode is set to work in the photon counting working mode, the TDC logic module counts the number of photon signal triggering times within the gated time range; the readout circuit sets the two TDCs to count and work continuously in turn, so that the photon count value that can be recorded by the detector pixel within the gated time range is no longer limited by the number of bits of the pixel TDC, so as to expand the dynamic range of photon counting and realize high dynamic range grayscale imaging.

[0021] When the TDC logic module operates in the pixel information shift-out mode, the measurement results of the TDC logic module can be shifted into the corresponding data temporary storage queue in a serial manner, and the measurement results already in the data temporary storage queue are correspondingly shifted backward in serial.

[0022] Preferably, two TDC logic subcircuits in the TDC logic module work simultaneously. When one of the TDC logic subcircuits is in the measurement mode, the other TDC logic subcircuit is in the readout mode. Under the control of the TDC switching control signal, the two alternately receive the detector electrical pulse signal from the signal extraction module. The detector trigger signal acquisition of the pixel is realized by switching, and the continuous recording of multiple detector trigger signals during the gating signal is realized. Within the half cycle of the TDC switching control signal, the TDC logic subcircuit can only record the detector signal trigger once at most.

[0023] Preferably, in the TDC logic module, when the detector electrical pulse signal arrives, the TDC logic subcircuit is started to start timing, and when the TDC switching control signal has a falling edge jump, the timing is stopped, and the time corresponding to the design number is t; let the half cycle of the TDC switching control signal be T0, and when the gate signal starts, the half cycle count value is reset to zero, and the half cycle count value increases by one every T0. When the current detector trigger signal arrives, the half cycle count value is N, then the time interval between the current detector trigger signal and the leading edge of the gate signal is:

[0024] Tx=(N+1)*T0-t

[0025] The half period T0 of the TDC switching control signal can be set according to the dead time determined by the detector and the detector quenching circuit and the length of time that the TDC logic subcircuit can record.

[0026] Preferably, the gate working time Tgate is set according to the storage depth of the data temporary storage queue, that is, the queue length M:

[0027] Tgate=T0*M

[0028] The width of the data temporary storage queue is consistent with the number of measurement bits of the TDC logic module, and the queue length M is set according to application needs;

[0029] The data temporary storage queue includes two queues, one of which is used to receive the measurement data of the TDC logic submodule, and the other queue moves the stored data out of the detector.

[0030] Preferably, the working timing of moving the data in the data temporary storage queue out of the detector is independent of the detector working mode setting. When the data in the data temporary storage queue is full, it can be read out of the chip through the data read-out chain. When the data is read out, the data temporary storage queues between adjacent pixels are connected together and moved out of the chip under the control of the read-out clock. At the end of the data temporary storage queue, a parallel-to-serial transmitter is set to convert the data of each pixel or several adjacent pixels into a serial code stream and send it to the outside.

[0031] The invention also provides a working method of the circuit.

[0032] The present invention also provides a method for operating a single-photon area array laser radar using the circuit and a laser in combination.

[0033] Preferably, the steps include:

[0034] (1) The single-photon array detector works in the photon counting mode to obtain the background light count of each pixel, and then obtains the corresponding high dynamic range grayscale image of the scene;

[0035] (2) Estimate the laser pulse k that needs to be emitted based on the light count value of the grayscale image and the detection probability requirement;

[0036] (3) placing the detector in a time-of-flight measurement mode, setting a wide gating signal, emitting the k laser pulses, and reading corresponding detector information;

[0037] (4) establishing a three-dimensional image in the range direction based on the detector information;

[0038] (5) according to the distribution law of the three-dimensional image in the range direction, setting the distance interval of interest in the wide gated signal and adjusting the TDC system clock;

[0039] (6) emitting laser pulses based on the TDC system clock and reading corresponding detector information;

[0040] (7) Reconstruct a range three-dimensional image based on the detector information.

[0041] The invention also provides a single-photon laser three-dimensional imaging system based on the circuit design.

[0042] (III) Beneficial effects

[0043] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0044] 1. The present invention sets two working modes, which can obtain grayscale images and distance images in the same detector assembly.

[0045] 2. In the present invention, two TDCs are arranged in the readout circuit to work in turn to achieve coverage of a long continuous gating cycle, which is suitable for large dynamic range detection and can obtain grayscale images and distance images with high dynamic range.

[0046] 3. By setting TDC and temporary queue to work in turns, the working efficiency of the detector is improved. That is, the laser works once and the detector can detect at least M times. The scanning efficiency is high, which greatly reduces the laser emission power demand and can effectively improve the system working efficiency.

[0047] 3. Similarly, by setting the TDC and the temporary storage queue to work in turns, the detection process can be carried out simultaneously with the information reading detector component process, thereby improving the real-time response capability of the system.

[0048] 4. By adjusting the TDC system working clock, large distance range and high-precision distance resolution detection can be achieved in the same detector component, which can better meet the system application requirements.

[0049] 5. The readout circuit technical solution of the present invention does not limit the array scale, the pixel architecture design modules are clearly divided, and the connection between modules is simple, which is conducive to large-scale integration through three-dimensional stacking technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic diagram of the working timing of the traditional single photon array;

[0051] Figure 2 is a block diagram of the composition of the detector pixel of the present invention;

[0052] Figure 3 It is a schematic diagram of the pixel working timing in the flight time measurement working mode of the present invention;

[0053] Figure 4 Schematic diagram of the pixel working timing in the photon counting working mode of the present invention;

[0054] Figure 5 is a TDC logic block diagram of an embodiment of the present invention;

[0055] Figure 6 A schematic diagram of a data organization method for a data temporary storage queue according to an embodiment of the present invention;

[0056] Figure 7 A schematic diagram of detector array data readout according to an embodiment of the present invention;

[0057] Figure 8 A comprehensive workflow diagram of a single-photon area array laser radar according to an embodiment of the present invention;

[0058] Fig. 9 The figure is a schematic diagram of the anti-interference working sequence of the single-photon array laser radar according to an embodiment of the present invention. DETAILED DESCRIPTION

[0059] In order to make the purpose, content and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below in conjunction with the drawings and examples.

[0060] The present invention relates to a single-photon array laser radar signal readout circuit and a processing method thereof, which solves the problem in the prior art that the single-photon array laser radar readout circuit has a short gating time, cannot receive the target echo signal in real time, and has low efficiency. Each pixel in the readout circuit includes two TDC logic modules and two data temporary storage queues. The detector trigger signal is accessed in turn by the TDC logic module, which reduces the probability of the detector trigger signal being missed and improves the laser emission efficiency. The data temporary storage queue is used to improve the efficiency of TDC data transfer. At the same time, the readout circuit can also realize the photon counting function and the time interval measurement function. With the mode setting, the single-photon array laser radar can realize long-distance depth imaging. With the laser coding setting, the single-photon array laser radar has anti-interference working ability.

[0061] In the working process of the traditional single-photon laser radar system, Figure 1 As shown, the target distance is unknown. On the one hand, it is impossible to accurately place the possible target trigger photon signal within the gated range. Limited by the measurement time length of the detector unit pixel TDC, it is impossible to use a long gated signal to increase the chance of the signal being within the gated range. On the other hand, background and dark noise will also be triggered within the gated range. Short gated signals cause signals outside the gate to be lost. When the detector signal is read out, the signal photon can no longer be detected when the gate is opened next time. Therefore, in long-distance detection applications, traditional area array single-photon lidar cannot receive echo signals in real time over long distances, and needs to emit multiple lasers to cover a longer distance range. In addition, traditional area array single-photon radars have limited ability to process multiple echoes, which affects the accurate presentation of complex scenes.

[0062] like Figure 2 The figure shows a schematic diagram of the pixel architecture of a planar array single-photon detection component. It can be seen from the figure that it can be divided into four parts: a photosensitive chip, a signal extraction module, a TDC logic module, and a data readout module. Among them, the photosensitive chip is mainly a detector unit with single-photon detection capability. In this embodiment, the photosensitive chip adopts a Geiger mode APD detector, which can be a silicon-based single-photon detector or a compound-based (such as indium gallium arsenide) single-photon detector. When the detector receives an incident photon, the photon is converted into a photoelectron with a certain probability, and then multiplied to form a current signal that can be sensed by the subsequent circuit, and is connected to the signal extraction circuit.

[0063] In the signal extraction circuit part, the quenching circuit avoids the risk of detector burning caused by the continuous increase of the avalanche current after the detector is multiplied, and then forms an electrical pulse signal, which is formed into a digital pulse start TDC signal through the comparator and trigger, and sent to the subsequent TDC logic module for processing; the quenching circuit also includes the dead time adjustment function of the detector. The dead time represents the minimum time interval that the detector can respond to the photon input. If the dead time of the quenching circuit is set too short, the detector will not exit the last trigger. The trigger frequency is too high, causing the detector to burn or not respond. If the dead time is too long, the detector will not respond to the successively input photons, reducing the photon detection efficiency. Therefore, the dead time should be set based on the detector's own performance and application requirements.

[0064] The TDC logic module includes two TDC logics. Under the action of the mode control signal, the TDC logic module can switch between the photon counting working mode and the flight time measurement mode.

[0065] The switching switch controlled by the TDC switching signal sends the start TDC signal generated by the detector trigger to TDC logic sub-circuit 1 or TDC logic sub-circuit 2. When the detector works in the time-of-flight measurement mode, the working timing relationship of the two TDC logic sub-circuits is shown in the figure. The working time length of the detector is determined by the gating signal preset by the system. The gating signal is divided into multiple small time intervals by the TDC switching control signal. When the TDC switching control signal is high, the switching switch sends the start TDC signal to TDC logic sub-circuit 1. When the TDC switching control signal is low, the start TDC signal is sent to TDC logic sub-circuit 2. At the same time, the TDC switching control signal is also sent to the TDC logic module, where the signal is inverted and sent to TDC logic sub-circuit 2. When the TDC logic module detects that the TDC switching control signal is high, the corresponding TDC logic module works in the pixel measurement mode, otherwise it works in the pixel data shift-out mode. Figure 3 It can be seen that at the same time, the two TDC logics are in different working modes.

[0066] It should be noted that in the time-of-flight measurement mode, TDC measures the time interval. The starting point of the measured time interval corresponds to the current detector trigger signal, that is, the pulse leading edge of the current TDC start signal. When the TDC switching signal falls, TDC stops timing. The time corresponding to the design number is t. Suppose the half-cycle of the TDC switching control signal is T0. When the gate signal starts, the half-cycle count value is reset to zero. Every time T0 passes, the half-cycle count value increases by one. When the current detector trigger signal arrives, the half-cycle count value is N. Then the time interval of the current detector trigger signal relative to the leading edge of the gate signal is

[0067] Tx=(N+1)*T0-t

[0068] In this embodiment, the gate signal Tgate is 20 microseconds, and the achievable gate distance is 3 kilometers. T0 is 1 microsecond, and the gate signal is divided into 20 time intervals.

[0069] If the Tgate time needs to be further extended, it can be achieved by reducing the TDC system clock frequency, that is, extending the clock cycle T1.

[0070] The TDC switching control signal half cycle consists of Q TDC system clock cycles.

[0071] T0=Q*T1

[0072] In the embodiment, Q=400, T1=4 nanoseconds. For example, if T1 is extended to 8 nanoseconds, Tgate is increased to 40 microseconds. If T1 is reduced to 2 nanoseconds, Tgate is shortened to 10 microseconds. Similarly, the Q value can be reduced to improve the photon counting resolution, thereby improving the signal resolution capability in the distance direction.

[0073] In photon counting mode, the TDC logic only counts the number of times the start TDC signal arrives, and does not measure the time interval. Figure 4 As shown. At this time, the TDC switching signal will not frequently switch the TDC logic. In this example, the designed TDC bit width is 10 bits, so a maximum of 1023 photon signal trigger events can be counted in a half cycle of the TDC switching control signal. Assuming that the photon event rate does not exceed 1M / s, the half-cycle signal T0 at this time can be as long as 1 millisecond.

[0074] In the TDC logic, when in the pixel information shift-out mode, the TDC measurement result is shifted out of the TDC logic through serial shifting and sent to the data readout part after switching the switch.

[0075] A preferred embodiment of TDC logic is shown in Figure 5 shown.

[0076] The counting / timing logic of TDC is composed of linear shift register feedback logic, which is 10 bits in this embodiment. The input TDC switching signal, mode control, start TDC signal, etc. are passed through the state machine to output the necessary control signal to control the normal operation of TDC logic. When the start TDC signal is input, the TDC logic outputs a pulse reset signal, which is sent to the previous stage signal extraction to reset the register set by the detector trigger signal. When the detector is in the time-of-flight measurement mode, the TDC logic working in the pixel measurement mode represents the digital state corresponding to different time intervals through the cyclic feedback shift of the register. At this time, the counting clock is the system working clock, and the clock frequency in the embodiment is 250M. In order to improve the time resolution, a sub-clock resolution bit can be introduced. For example, in the embodiment, two sub-clock time resolution bits are added by clock phase shifting, and the time resolution at this time can reach 1ns. When the TDC logic is in the pixel information shift-out mode, the state machine controls the disconnection of the TDC feedback chain, connects the sub-clock resolution bit to the register chain, and the state machine generates a shift clock signal, and controls the data results in the TDC to shift out through 12 shift clocks.

[0077] When the detector assembly is in the photon counting working mode, the clock output by the state machine control is the TDC switching signal, that is, a TDC switching signal appears and the TDC logic counts once. In the photon counting working mode, the sub-clock resolution bit is prohibited from working, that is, at most 10 bits of data are available at this time.

[0078] In the data readout module, two data temporary storage queues are also set. In the flight time measurement working mode, the relationship between the queue depth M and the gate time is:

[0079] Tgate=T0*M

[0080] In an embodiment, M is 20.

[0081] When the TDC serial output data enters the data readout module, the data queue temporary storage switching signal controls whether it is input to data temporary storage queue 1 or queue 2. Each time the laser is emitted, the state of the data queue temporary storage switching signal is flipped once, thereby switching the data temporary storage queue once.

[0082] In this embodiment, if Figure 6As shown in a, the data temporary storage queue depth is 20, namely R1..R20, and each temporary storage data has 12 bits. During the pixel information shift-out working time, the TDC logic shifts the current TDC measurement result into R20 by serial shifting the data. At the same time, the existing data in R20 is also serially shifted into R19, R19 into R18, ..., and after 20 half cycles T0 of the DC switching control signal, the temporary storage data queue is full. After a data queue temporary storage switching signal state flip, the current data temporary storage queue can enter the detector component information readout state.

[0083] In the detector component information readout state, R1 to R20 form a 12-bit wide shift register array, such as Figure 6 b, where R20 is connected to the previous pixel readout and R1 is connected to the next pixel readout input.

[0084] Assuming that the detector array consists of M rows and N columns, the information readout chain of the detector array is as follows: Figure 7 As shown. Each pixel has a data temporary queue with a depth of 20, which is connected end to end and moves to the end of the row under the clock drive. At the end of each row, the M sequence is converted into natural binary information by the decoder, and then sent to the high-speed parallel-to-serial conversion transmitter, and sent to the host computer processing system through the high-speed serial bus for further processing. In this embodiment, assuming that the detector array is 128*512 and the readout clock is 250M, it takes 40.48 microseconds to read out 512 columns. Considering that 4 rows share one high-speed parallel-to-serial transmitter, a total of 32 high-speed transmitters are required, and the data burst rate is 12G / s.

[0085] Another processing method does not use a serial data transmitter. After the data is decoded, it is stored in a high-speed memory, which can be directly accessed by a processor integrated with the detector array for further processing to obtain data processing results, reducing the demand for high-speed data transmission. It will not be repeated here.

[0086] According to the above embodiments, in actual application, the above mode control and application methods can be combined to improve the flexibility and efficiency of system application.

[0087] For scenes with unknown distance and unknown background light intensity, the following can be used: Figure 8 The lidar system workflow is shown.

[0088] First, the detector array is placed in the photon counting mode, and the light self-count value of each pixel within the gated integration time is obtained as a grayscale image, and the background light intensity is estimated based on this. According to this background light intensity and the required detection probability, the maximum likelihood estimation or other estimation algorithms are used to obtain the required number of laser shots. Then the detector array is placed in the time-of-flight measurement mode, a wide gated signal is set, laser pulses are emitted, the detector array signal is read, and a large range of distance photon echo signals are obtained. After accumulating enough laser shots, a three-dimensional image with a large distance and depth is reconstructed by the algorithm. Further analyze the three-dimensional image features, select the distance interval of interest as needed, set the corresponding distance gated signal, emit a certain number of laser pulses, obtain a small range of distance photon echo signals, and reconstruct a high-precision three-dimensional image of the area of ​​interest after algorithm processing. Repeating this process can obtain continuous detection of scenes with unknown distances and unknown background light intensity.

[0089] Another application supported by the present invention is the anti-interference of single-photon array laser radar. Since the detector array supports the reading of continuous photon pulse triggering events, if the laser can support pulse modulation, laser pulse position modulation can be used to encode the continuously emitted laser pulse train. Fig. 9 As shown in the figure, when the detector receives the normal laser echo signal, it also receives some interference signals. By transmitting a pulse train of appropriate length and correlating the laser pulse position modulation sequence with the received detector trigger event time sequence, the influence of interference signals and missed alarm signals can be removed, and the relative flight time of the pulse sequence can be accurately obtained, thus suppressing pulse interference.

[0090] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A readout circuit for improving the detection efficiency of a single-photon array laser radar, characterized in that: The single-photon array detector has two detector working modes: one is the photon counting working mode, in which the single-photon array detector obtains the number of photon signal triggers per pixel detector within the control time; the other is the time-of-flight measurement mode, in which the single-photon array detector obtains the time of photon signal triggering per pixel detector within the control time relative to the gate start signal; The two detector working modes are switched by a control signal; in order to realize the two detector working modes, the readout circuit includes a signal extraction module, a TDC logic module, and a data readout module; The signal extraction module is used to convert the detector trigger signal into a digital signal and provide the photosensitive chip with a quenching circuit required for single-photon detection. The signal extraction module also includes a comparator and a trigger. The quenching circuit converts the digital signal into a detector electrical pulse signal. The detector electrical pulse signal is converted into a digital pulse start TDC signal through the comparator and the trigger. The detector electrical pulse signal and the digital pulse start TDC signal are sent to the post-stage TDC logic module for processing. The TDC logic module includes two TDC logic subcircuits and a switching switch. Under the action of the mode control signal, the TDC logic module can switch between the photon counting working mode and the flight time measurement mode. When the detector works in the flight time measurement mode, the gate signal preset by the system determines the working time length of the detector. The gate signal is divided into multiple small time intervals by the TDC switching control signal. When the TDC switching control signal is high, the switching switch sends the digital pulse to start the TDC signal into the TDC logic subcircuit 1, and when the TDC switching control signal is low, the digital pulse starts the TDC signal into the TDC logic subcircuit 2. At the same time, the TDC switching control signal is also sent to the inside of the TDC logic module, where the signal is inverted and sent to the TDC logic subcircuit 2. When the TDC logic module detects that the TDC switching control signal is high, the corresponding TDC logic module works in the pixel measurement mode, otherwise it works in the pixel data shifting mode. The TDC logic subcircuit 1 and the TDC logic subcircuit 2 output the TDC serial output data to the data readout module. The data readout module includes two parallel data temporary storage queues, which are used to realize the pixel-level storage of the measurement results of the TDC logic module in the detector. When the TDC serial output data enters the data readout module, the data queue temporary storage switching signal controls whether it is input to data temporary storage queue one or data temporary storage queue two. Each time the laser is emitted, the state of the data queue temporary storage switching signal is flipped once.

2. The circuit according to claim 1, characterized in that The TDC logic module has two pixel working modes, pixel measurement mode and pixel information shifting mode. In the pixel measurement mode, the TDC logic module is used for time interval measurement and photon counting. The time length measurement is achieved by counting the predetermined clock intervals. The accuracy of the time interval measurement depends on the clock cycle. When the detector working mode is set to work in the photon counting working mode, the TDC logic module counts the number of photon signal triggers within the gated time range; When the TDC logic module operates in the pixel information shift-out mode, the measurement results of the TDC logic module can be shifted into the corresponding data temporary storage queue in a serial manner, and the measurement results already in the data temporary storage queue are correspondingly shifted backward in serial.

3. The circuit according to claim 2, characterized in that The two TDC logic subcircuits in the TDC logic module work simultaneously. When one of the TDC logic subcircuits is in the measurement mode, the other TDC logic subcircuits is in the readout mode. Under the control of the TDC switching control signal, the two TDC logic subcircuits alternately receive the detector electrical pulse signal from the signal extraction module. The detector trigger signal acquisition of the pixel is realized by switching, and the continuous recording of multiple detector trigger signals during the gate signal is realized. Within the half cycle of the TDC switching control signal, the TDC logic subcircuit can only record the signal trigger of the detector once at most.

4. The circuit according to claim 3, characterized in that In the TDC logic module, when the detector electrical pulse signal arrives, the TDC is started to start timing, and when the TDC switching control signal has a falling edge jump, the timing is stopped, and the time corresponding to the design number is t; let the half cycle of the TDC switching control signal be T0, and when the gate signal starts, the half cycle count value is reset to zero, and the half cycle count value increases by one every T0. When the current detector trigger signal arrives, the half cycle count value is N, then the time interval of the current detector trigger signal relative to the leading edge of the gate signal is: Tx=(N+1)*T0-t The half period T0 of the TDC switching control signal can be set according to the dead time determined by the detector and the detector quenching circuit and the length of time that the TDC logic subcircuit can record.

5. The circuit according to claim 4, characterized in that The gate working time Tgate is set according to the storage depth of the data temporary storage queue, that is, the queue length M: Tgate=T0*M The width of the data temporary storage queue is consistent with the number of measurement bits of the TDC logic module, and the queue length M is set according to application needs; The data temporary storage queue includes two queues, one of which is used to receive the measurement data of the TDC logic submodule, and the other queue moves the stored data out of the detector.

6. The circuit according to claim 5, characterized in that The timing of moving the data in the data temporary storage queue out of the detector is independent of the detector working mode setting. When the data in the data temporary storage queue is full, it can be read out of the chip through the data readout chain. When the data is read out, the data temporary storage queues between adjacent pixels are connected together and moved out of the chip under the control of the readout clock. At the end of the data temporary storage queue, a parallel-to-serial transmitter is set to convert the data of each pixel or several adjacent pixels into a serial code stream and send it to the outside.

7. A method of operating the circuit as claimed in any one of claims 1 to 6.

8. A method for operating a single-photon array laser radar using a combination of the circuit described in any one of claims 1 to 6 and a laser.

9. The method according to claim 8, characterized in that The following steps are involved: (1) The single-photon array detector works in the photon counting mode to obtain the background light count of each pixel, and then obtains the corresponding high dynamic range grayscale image of the scene; (2) Estimate the laser pulse k that needs to be emitted based on the light count value of the grayscale image and the detection probability requirement; (3) placing the detector in a time-of-flight measurement mode, setting a wide gating signal, emitting the k laser pulses, and reading corresponding detector information; (4) establishing a three-dimensional image in the range direction based on the detector information; (5) according to the distribution law of the three-dimensional image in the range direction, setting the distance interval of interest in the wide gated signal and adjusting the TDC system clock; (6) emitting laser pulses based on the TDC system clock and reading corresponding detector information; (7) Reconstruct a range three-dimensional image based on the detector information.

10. A single-photon laser three-dimensional imaging system based on the circuit design according to any one of claims 1 to 6.

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