A readout circuit and method for improving detection efficiency of a single-photon area array laser radar

Abstract

The application relates to a readout 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 arranged, and a gray-scale image and a distance image can be acquired in the same detector assembly. In the application, two TDCs are arranged in the readout circuit to rotate and work, so that the coverage of a long continuous gate control period is realized, large dynamic range detection is suitable, and a high dynamic range gray-scale image and a distance image can be acquired. Through the rotation and work of the TDC and the temporary storage queue, the working efficiency of the detector is improved, that is, the laser works once, and the detector can detect M times at least, the scanning efficiency is high, the laser emission power demand is greatly reduced, and the system working efficiency can be effectively improved.

Description

TECHNICAL FIELD

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

[0002] A single-photon area array detector is a high-sensitivity photoelectric detector capable of responding to a photon order signal, and is the basis in the fields of single-photon radar detection and quantum communication. With the continuous development of basic hardware and software technologies, single-photon laser three-dimensional imaging detection technology based on a Geiger focal plane camera has attracted more and more attention, and many research results have been published. The action distance and imaging effect have been greatly improved, and the technology has high application value. Although the use of an area array detector reduces the difficulty of field scanning, compared with a unit detection method, more signal processing methods and flexibility are lost in the distance direction.

[0003] In order to reduce noise interference and the long time required for transmission of a large amount of detection data, the existing single-photon area array laser radar detector mainly works in a gated state, that is, the camera needs a gating signal to work, otherwise it cannot receive signals. In addition, after the camera is opened once, a long dead time is required for recovery, and the effective duty cycle of the working time period is low. Therefore, the following disadvantages exist in the actual use process:

[0004] 1. Relatively accurate target distance prior information needs to be obtained, and the accurate arrival time of the echo signal needs to be calculated according to the target distance, so as to effectively control the delay of the gating signal and make it open at the time of arrival of the echo signal. However, in the actual laser radar working process, the target distance is often unknown and may change at a relatively fast speed, which also leads to the real-time change of the arrival time of the echo pulse, and is not suitable for the detection demand of a dynamic scene.

[0005] 2. The working time of the detector is limited, and one detection cannot cover a long working distance. At present, most single-photon area array detectors can only have one trigger opportunity within the gating time, which means that the detection efficiency is low for a complex scene with multiple echoes.

[0006] 3. The working frequency of the detector array is limited. After completing one detection, a long time is required to recover the initial state for the next detection. The signal needs to be read out before the next detection. With the increase of the area array, the readout time is prolonged, and the detector is in a state of being unable to detect for a long time, which also leads to a large amount of spatial omission of the laser radar.

[0007] 4. For long-distance photon echo detection, although the optical echo can enter the field of view of the detector, the detector does not respond, and 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 detections over long distances, the detector has a limited number of triggers within the gating time, making it difficult to detect weak targets located later in the gating time. Because time resolution and range are mutually constrained, it is difficult to balance the distance interval length and time resolution, thus limiting the accuracy of the range direction.

[0009] 6. Since the intensity of background light typically changes with the scene, single-photon detection usually requires adjusting the echo accumulation count based on the background light intensity to ensure a certain detection probability. If the background light intensity is unknown, unnecessary and excessive laser pulses may be emitted to maintain the detection probability, resulting in low efficiency. Furthermore, array detectors typically used for 3D imaging cannot directly obtain the background light count. To estimate the background light intensity, it is necessary to repeatedly open the gate to read out the signal and then accumulate the light count, which is inefficient.

[0010] Therefore, although using area array detectors improves spatial coverage to some extent, range-related issues limit the application of single-photon area arrays in time-sensitive and efficiency-intensive applications. Currently, there is a lack of a method and system for reading out and processing area array single-photon lidar signals that can achieve long-distance, multi-echo detection and also include photon counting capabilities. Summary of the Invention

[0011] (a) Technical problems to be solved

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

[0013] (II) Technical Solution

[0014] To address the aforementioned technical problems, this invention provides a readout circuit for improving the detection efficiency of a single-photon array lidar. The single-photon array detector has two detector operating modes: a photon counting mode, in which the single-photon array detector acquires the number of times the photon signal of each pixel detector is triggered within the control time; and a time-of-flight measurement mode, in which the single-photon array detector acquires the time of triggering the photon signal of each pixel detector relative to the gating start signal within the control time.

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

[0016] The signal extraction module comprises a quenching circuit, an analog-digital conversion circuit and a digital logic circuit for converting the detector trigger signal into a digital signal and providing a quenching circuit required for single-photon detection for the photosensitive chip. The signal extraction module further comprises a comparator and a flip-flop. The quenching circuit converts the digital signal into a detector electric pulse signal. The detector electric pulse signal forms a digital pulse start TDC signal through the comparator and the flip-flop. The detector electric pulse signal and the digital pulse start TDC signal are sent to a later-stage TDC logic module for processing.

[0017] The TDC logic module comprises two TDC logic sub-circuits and a switching switch. Under the action of a mode control signal, the TDC logic module can be switched between a photon counting mode and a time-of-flight measurement mode. When the detector works in the time-of-flight measurement mode, the length of the working time of the detector is determined by a system preset gate signal. The gate signal is divided into a plurality of small time intervals by a TDC switching control signal. When the TDC switching control signal is high, the switching switch sends the digital pulse start TDC signal to the TDC logic sub-circuit one. When the TDC switching control signal is low, the switching switch sends the digital pulse start TDC signal to the TDC logic sub-circuit two. Meanwhile, the TDC switching control signal is also sent to the TDC logic module. The signal is inverted and then sent to the TDC logic sub-circuit two. 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. Conversely, the TDC logic module works in the pixel data moving-out mode. The TDC logic sub-circuit one and the TDC logic sub-circuit two output TDC serial output data to a data readout module.

[0018] The data readout module comprises two parallel data storage queues. The data storage queue is 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 storage switching signal controls whether the TDC serial output data is input to the data storage queue one or the data storage queue two. The data queue storage switching signal state is flipped once every time the laser is emitted.

[0019] Preferably, the TDC logic module has two pixel working modes, i.e., a pixel measurement mode and a pixel information moving-out mode. When in the pixel measurement mode, the TDC logic module is used for time interval measurement and photon counting. The time length measurement is realized by counting a predetermined clock interval. The accuracy of the time interval measurement depends on the clock period. The accuracy of the time interval measurement is improved by increasing the clock subdivision logic.

[0020] When the detector works in the photon counting mode, the TDC logic module counts the number of photon signals in the gating time range; the readout circuit works in the mode of two TDCs counting alternately and continuously, so that the countable photon count value of the detector pixel in the gating time range is no longer limited by the number of bits of the pixel TDC, thereby expanding the dynamic range of photon counting and realizing high dynamic range gray imaging.

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

[0022] Preferably, the two TDC logic sub-circuits in the TDC logic module work simultaneously, when one of the TDC logic sub-circuits is in the measurement mode, the other TDC logic sub-circuit is in the readout mode, and both of them alternately receive the detector electric pulse signals from the signal extraction module under the control of the TDC switching control signal; the detector trigger signal acquisition of the pixel is realized through switching, and the continuous recording of multiple detector trigger signals during the gating signal is realized; in the half cycle of the TDC switching control signal, the TDC logic sub-circuit can record the signal trigger of the detector at most once.

[0023] Preferably, in the TDC logic module, when the detector electric pulse signal arrives, the TDC logic sub-circuit starts timing, and when the falling edge of the TDC switching control signal jumps, the timing stops, and the corresponding time is t; the half cycle of the TDC switching control signal is T0, the half cycle count value is cleared from the beginning of the gating signal, 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 front edge of the gating signal is:

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

[0025] The half cycle 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 can be recorded by the TDC logic sub-circuit.

[0026] Preferably, the gating 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 the application needs;

[0029] The data temporary storage queue comprises two queues, one of which is used to receive the measurement data of the TDC logic sub-module, and the other is used to remove the stored data out of the detector.

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

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

[0032] The application also provides a single-photon area array laser radar working method completed by combining the circuit with a laser.

[0033] Preferably, the method comprises the following steps:

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

[0035] (2) Estimate the laser pulses k to be emitted according to the light count value of the gray scale image and the detection probability requirement;

[0036] (3) Put the detector into a time-of-flight measurement mode, set a wide gate signal, emit the k laser pulses, and read the corresponding detector information;

[0037] (4) Establish a distance-oriented three-dimensional image based on the detector information;

[0038] (5) According to the distribution rule of the distance-oriented three-dimensional image, set a distance interval of interest within the wide gate signal, and adjust the TDC system clock;

[0039] (6) Emit laser pulses based on the TDC system clock, and read the corresponding detector information;

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

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

[0042] (Three) Beneficial effects

[0043] Compared with the prior art, the application can at least realize one of the following beneficial effects:

[0044] 1. The application sets two working modes, and can obtain a gray scale image and a distance image in the same detector assembly.

[0045] 2. In the application, two-way TDC is set in the readout circuit to realize long continuous gate period coverage, is suitable for large dynamic range detection, and can obtain high dynamic range gray scale image and distance image.

[0046] 3. By setting TDC and temporary storage queue to work alternately, the working efficiency of the detector is improved, that is, the laser works once, and the detector can detect M times at least, the scanning efficiency is high, the laser emission power demand is greatly reduced, and the system working efficiency can be effectively improved.

[0047] 3. Also by setting TDC and temporary storage queue to work alternately, the detection process can be carried out at the same time as the information readout detector assembly process, and the real-time response ability of the system is improved.

[0048] 4. By adjusting the TDC system working clock, large distance range and high precision distance resolution detection can be realized in the same detector assembly, and the application requirements of the system can be better met.

[0049] 5. The readout circuit technical scheme of the application is not limited by array size, the pixel architecture design module is clear in division, the connection between modules is simple, and large-scale integration can be realized by three-dimensional stacking technology. BRIEF DESCRIPTION OF DRAWINGS

[0050] Figure 1 It is a traditional single photon array working time sequence schematic diagram;

[0051] Figure 2 It is a composition block diagram of the detector pixel of the application;

[0052] Figure 3 It is a pixel working time sequence schematic diagram in the time-of-flight measurement working mode of the application;

[0053] Figure 4 It is a pixel working time sequence schematic diagram in the photon counting working mode of the application;

[0054] Figure 5 It is a TDC logic block diagram of the embodiment of the application;

[0055] Figure 6 It is a data storage queue data organization method schematic diagram of the embodiment of the application;

[0056] Figure 7 It is a detector array data readout schematic diagram of the embodiment of the application;

[0057] Figure 8 It is a single photon area array laser radar comprehensive working flowchart of the embodiment of the application;

[0058] Figure 9 The figure is a single-photon area array laser radar anti-interference working timing diagram of an embodiment of the present application. DETAILED DESCRIPTION

[0059] In order to make the purpose, content and advantages of the present application clearer, the specific embodiments of the present application are described in further detail below in combination with the drawings and examples.

[0060] The present application relates to a single-photon area array laser radar signal readout circuit and a processing method thereof, which solves the problem of short gating time of the single-photon area array laser radar readout circuit in the prior art, which cannot receive target echo signals in real time and is low in efficiency. Each pixel in the readout circuit includes two TDC logic modules and two data temporary storage queues. The TDC logic modules are used to alternately access the detector trigger signal, so as to reduce the probability of the detector trigger signal being missed and improve the laser emission efficiency. The data temporary storage queues are used to improve the efficiency of TDC data storage. Meanwhile, the readout circuit can also realize photon counting and time interval measurement functions, and can realize single-photon area array laser radar long-distance depth imaging in cooperation with mode setting, and can make the single-photon area array laser radar have anti-interference working capability in cooperation with laser coding setting.

[0061] In the working process of the traditional area array single-photon laser radar system, as shown in FIG. 1, the target distance is unknown, on the one hand, the possible target trigger photon signal cannot be accurately placed in the gating range, and on the other hand, the background and dark noise can also trigger in the gating range. The short gating signal causes the signal outside the gate to be discarded. When the detector signal is read out, the signal photon cannot be detected when the gate is opened again. Therefore, the traditional area array single-photon laser radar cannot realize real-time reception of echo signals in a long distance interval in the application of long-distance detection, needs to emit multiple lasers to cover a long distance range, and the traditional area array single-photon radar has limited ability to process multiple echoes, which affects the accurate presentation of a complex scene. Figure 1 As shown in FIG. 2, it is a pixel architecture schematic diagram of an area array single-photon detection assembly. As shown in the figure, it can be divided into four parts, namely a photosensitive chip, a signal extraction module, a TDC logic module and a data readout module. 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 incident photons, the photons are converted into photoelectrons at a certain probability, and then form a current signal that can be perceived by the subsequent circuit after multiplication, and access the signal extraction circuit.

[0062] Figure 2 As shown in FIG. 2, it is a pixel architecture schematic diagram of an area array single-photon detection assembly. As shown in the figure, it can be divided into four parts, namely a photosensitive chip, a signal extraction module, a TDC logic module and a data readout module. 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 incident photons, the photons are converted into photoelectrons at a certain probability, and then form a current signal that can be perceived by the subsequent circuit after multiplication, and access the signal extraction circuit.​

[0063] In the signal extraction circuit part, the quenching circuit avoids the risk of burning the detector caused by the continuous increase of the multiplied avalanche current of the detector, and then forms an electric pulse signal, which is sent into the TDC logic module after the comparator and the flip-flop to form a digital pulse to start the TDC signal; the quenching circuit also contains the dead time adjustment function of the detector, and the dead time represents the minimum time interval that the detector can respond to the input photons. If the dead time set by the quenching circuit is too short, the detector has not exited the last trigger, and the trigger frequency is too high, which leads to the burning of the detector or no response. If the dead time is too long, the detector does not respond to the input photons successively, and the photon detection efficiency is reduced. Therefore, the dead time should be set according to the performance of the detector itself and the application requirements.

[0064] In the TDC logic module, two TDC logics are contained, and under the action of the mode control signal, the TDC logic module can be switched between the photon counting mode and the time of flight measurement mode.

[0065] The switching switch is controlled by the TDC switching signal to send the start TDC signal generated by the detector trigger into the TDC logic subcircuit 1 or the TDC logic subcircuit 2. When the detector works in the time of flight measurement mode, the working time sequence relationship of the two TDC logic subcircuits is shown in the figure. The working time length of the detector is determined by the system preset gate signal. 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 start TDC signal into the TDC logic subcircuit 1, and when the TDC switching control signal is low, the switching switch sends the start TDC signal into the TDC logic subcircuit 2. At the same time, the TDC switching control signal is also sent into the TDC logic module, and the signal is inverted and then sent into 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, and vice versa. The TDC switching control signal is generated by the TDC switching signal. 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, the TDC measures the time interval. The start point of the measured time interval is corresponding to the current detector trigger signal, that is, the pulse front edge of the current start TDC signal. When the falling edge of the TDC switching signal, the TDC stops timing. The corresponding time is t. Assuming that the half cycle of the TDC switching control signal is T0, the half cycle count value is cleared from the start of the gate signal, 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, and the time interval of the current detector trigger signal relative to the front edge of the gate signal is

[0067] Tx = (N + l) * To - t

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

[0069] If it is necessary to further extend the Tgate time, it can be achieved by reducing the TDC system clock frequency, i.e., extending the clock period T1.

[0070] A TDC switching control signal half cycle is composed of Q TDC system clock periods

[0071] To = Q * T1

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

[0073] In the photon counting mode, the TDC logic only records the number of arrival start TDC signals, and does not measure the time interval. As shown in Figure 4 At this time, the TDC switching signal does 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 TDC switching control signal half cycle. 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 moving out mode, the measurement result of the TDC is moved out of the TDC logic through serial shift, and is sent to the data readout part after the switching switch.

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

[0076] The counting / timing logic of the TDC is composed of linear shift register feedback logic, in this embodiment, 10 bits. The input TDC switching signal, mode control, start TDC signal, and the like output necessary control signals to control the TDC logic to work normally after passing through the state machine. When the start TDC signal is input, the TDC logic outputs a pulse reset signal to the front-stage signal extraction, which resets 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 different time intervals corresponding to digital states through the cyclic feedback shift of the register. At this time, the clock for counting is the system working clock, and the clock frequency in this embodiment is 250M. In order to improve the time resolution, sub-clock resolution bits can be introduced. For example, in this embodiment, two sub-clock time resolution bits are added by clock phase shift, and the time resolution at this time can reach 1ns. When the TDC logic is in the pixel information moving out mode, the state machine controls to disconnect the feedback chain of the TDC, and the sub-clock resolution bits are connected to the register chain. The state machine generates a shift clock signal, and controls the data result in the TDC to move out through 12 times of shift clock.

[0077] When the detector assembly is in the photon counting working mode, the state machine controls the output clock to be the TDC switching signal, that is, the TDC logic counts once when a TDC switching signal occurs. In the photon counting working mode, the sub-clock resolution bits are disabled to work, that is, there are at most 10 bits of data at this time.

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

[0079] Tgate=T0*M

[0080] In this embodiment, M is 20.

[0081] When the TDC serial output data enters the data readout module, the data queue storage switching signal controls whether the data is input to the data storage queue 1 or the queue 2. The data queue storage switching signal state flips once every time the laser is emitted, so that the data storage queue switches once.

[0082] In this embodiment, as Figure 6As shown in Figure a, the data temporary storage queue has a depth of 20, designated as R1 to R20, with each temporary data entry containing 12 bits. During the pixel information shift-out working time, the TDC logic serially shifts the current TDC measurement result into R20. Simultaneously, the existing data in R20 is also sequentially shifted into R19, R19 into R18, and so on. After half a cycle T0 of 20 DC switching control signals, the temporary data queue is full. After one 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 As shown in b, R20 is connected to the previous pixel readout, and R1 is connected to the next pixel readout input.

[0084] Assuming 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 moves towards the end of the row driven by a clock. At the end of each row, the M-sequence is converted into natural binary information by a decoder and then sent to a high-speed parallel-to-serial converter transmitter. The data is then transmitted to the host computer processing system for further processing via a high-speed serial bus. In this embodiment, assuming the detector array is 128*512 and the readout clock is 250MHz, reading 512 columns requires 40.48 microseconds. Considering that 4 rows share one high-speed parallel-to-serial transmitter, a total of 32 high-speed transmitters are needed, resulting in a data burst rate of 12G / s.

[0085] Another processing method, which does not use a serial data transmitter, decodes the data and stores it in a high-speed memory, which can be directly accessed by a processor integrated with the detector array for further processing to obtain the data processing results, reducing the need for high-speed data transmission. This will not be elaborated here.

[0086] Based on the above embodiments, in practical applications, the above mode control and application methods can be combined to improve the flexibility and efficiency of system applications.

[0087] For scenarios with unknown distances and unknown background light intensity, the following methods can be used: Figure 8 The diagram shows the workflow of a lidar system.

[0088] Firstly, the detector array is set in the photon counting mode, the light self-counting value of each pixel in the gated integration time is obtained as a gray scale image, and the background light intensity is estimated. According to the background light intensity and the required detection probability, the maximum likelihood estimation or other estimation algorithm is used to obtain the required laser emission times. Then the detector array is set in the time-of-flight measurement mode, the wide gating signal is set, the laser pulse is emitted, the detector array signal is read, and the large-range distance photon echo signal is obtained. After accumulating enough laser emission times, the three-dimensional image of large distance depth is obtained by algorithm reconstruction. Further analysis of the three-dimensional image features, according to the needs, the interested distance interval is selected, the corresponding distance gating signal is set, a certain number of laser pulses are emitted, the small-range distance photon echo signal is obtained, and the high-precision three-dimensional image of the interested region is obtained by algorithm processing. Repeating this process can obtain the continuous detection of unknown distance and unknown background light intensity scene.

[0089] Another application supported by the present application is the anti-interference of single-photon array lidar. Since the detector array supports the reading of continuous photon pulse trigger events, in the case that the laser can support pulse modulation, the laser pulse position modulation can be used to encode the continuous outgoing laser pulse string. As shown in Figure 9 When the detector receives the normal laser echo signal, it also receives part of the interference signal. By using a pulse string of appropriate length, the laser pulse position modulation sequence is correlated with the received detector trigger event time sequence, the influence of the interference signal and the false alarm signal can be removed, and the relative time of flight of the pulse sequence can be accurately obtained. The suppression of pulse interference is realized.

[0090] The above only describes the preferred embodiments of the present application. It should be noted that for those skilled in the art, without departing from the technical principles of the present application, a number of improvements and modifications can be made, and these improvements and modifications should also be considered as the protection scope of the present application.

Claims

1. A readout circuit for improving the detection efficiency of a single-photon area array lidar, characterized in that, The single photon area array detector has two working modes, one is a photon counting working mode, and the single photon area array detector acquires the number of single photon area array detector photon signal triggers in a control time; and the other is a time of flight measurement mode, and the single photon area array detector acquires the time of single photon area array detector photon signal trigger relative to a gate start signal in a control time; The two working modes of the single photon area array detector are switched through a control signal; in order to realize the two working modes of the single photon area array detector, the readout circuit comprises a signal extraction module, a TDC logic module and a data readout module; The signal extraction module is used for converting the single photon area array detector trigger signal into a digital signal and providing a quenching circuit required by the photosensitive chip for single photon detection, and the signal extraction module further comprises a comparator and a flip-flop; the quenching circuit converts the digital signal into a single photon area array detector electric pulse signal; the single photon area array detector electric pulse signal forms a digital pulse start TDC signal through the comparator and the flip-flop; and the single photon area array detector electric pulse signal and the digital pulse start TDC signal are sent to the later-stage TDC logic module for processing; The TDC logic module comprises two TDC logic sub-circuits and a switching switch; under the action of a mode control signal, the TDC logic module can be switched between the photon counting working mode and the time of flight measurement mode; when the single photon area array detector works in the time of flight measurement mode, the length of the single photon area array detector working time is determined by a system preset gate start signal; the gate start signal is divided into a plurality of small time intervals by a TDC switching control signal; when the TDC switching control signal is high, the switching switch sends the digital pulse start TDC signal to the TDC logic sub-circuit one; when the TDC switching control signal is low, the switching switch sends the digital pulse start TDC signal to the TDC logic sub-circuit two; meanwhile, the TDC switching control signal is also sent to the TDC logic module, and the signal is inverted and then sent to the TDC logic sub-circuit two; 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, and vice versa; the TDC logic sub-circuit one and the TDC logic sub-circuit two output TDC serial output data to the data readout module; The data readout module comprises two parallel data storage queues, and the data storage queue is used for realizing the pixel-level storage of the measurement results of the TDC logic module in the single photon area array detector; when the TDC serial output data enters the data readout module, the data queue storage switching signal controls whether the TDC serial output data is input to the data storage queue one or the data storage queue two; the data queue storage switching signal state is flipped once for each laser emission.

2. The readout circuit of claim 1, wherein, The TDC logic module has two pixel working modes, namely a pixel measurement mode and a pixel information removal mode; when in the pixel measurement mode, the TDC logic module is used for time interval measurement and photon counting; the time interval measurement is realized by counting a predetermined clock interval, and the accuracy of the time interval measurement depends on the clock period. When the single photon array detector is set to work in the photon counting mode, the TDC logic module counts the number of photon signal triggers in the gating time range; When the TDC logic module works in the pixel information moving out mode, the measurement results of the TDC logic module can be moved into the corresponding data temporary storage queue in a serial manner, and the measurement results already in the data temporary storage queue are correspondingly moved backward in a serial manner.

3. The sense circuit of claim 2, wherein, The two TDC logic sub-circuits in the TDC logic module work simultaneously, when one of the two TDC logic sub-circuits is in the measurement mode, the other one is in the readout mode, and the two TDC logic sub-circuits alternately receive the single photon array detector electric pulse signals from the signal extraction module under the control of the TDC switching control signal; the single photon array detector trigger signal acquisition of the pixel is realized through switching, and the continuous recording of multiple single photon array detector trigger signals during the gating start signal is realized; in the half cycle of the TDC switching control signal, the TDC logic sub-circuit can record the signal trigger of the single photon array detector at most once.

4. The sense circuit of claim 3, wherein, When the single photon array detector electric pulse signal arrives, the TDC switching control signal starts timing, and when the TDC switching control signal appears a falling edge jump, the timing stops, and the corresponding time is t; the half cycle of the TDC switching control signal is T0, and the half cycle count value is cleared from the start of the gating start signal, and the half cycle count value increases by one every T0, and when the current single photon array detector trigger signal arrives, the half cycle count value is N, then the time interval of the current single photon array detector trigger signal relative to the front edge of the gating start signal is: Tx=(N+1)*T0-t The half cycle T0 of the TDC switching control signal is set according to the dead time determined by the single photon array detector and the quenching circuit of the single photon array detector and the length of time that can be recorded by the TDC logic sub-circuit.

5. The sense circuit of claim 4, wherein, The gating 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 measurement bits of the TDC logic module, and the queue length M is set according to the application requirement; The data temporary storage queue contains two queues, one of which is used to receive the measurement data of the TDC logic sub-module, and the other queue moves the stored data out of the single photon array detector.

6. The sense circuit of claim 5, wherein, The working timing of moving the data in the data temporary storage queue out of the single photon array detector is independent of the single photon array detector working mode setting, when the data in the data temporary storage queue is full, the data can be read out to the outside of the chip through the data readout chain; during the data readout, the data temporary storage queues between adjacent pixels are connected together, and under the control of the readout clock, the data temporary storage queues move to the outside of the chip, at the end of the data temporary storage queue, the data of each pixel or several adjacent pixels is converted into a serial code stream through the setting of the parallel-to-serial converter, and then transmitted to the outside.

7. A method of operating a single-photon area array lidar comprising a readout circuit and a laser as in any one of claims 1 to 5, wherein, The method comprises the following steps: (1) the single photon array detector works in the photon counting mode, the background light count of each pixel is obtained, and then the corresponding scene high dynamic range gray scale image is obtained; (2) estimating the k laser pulses to be emitted according to the light count value of the gray-scale image and the detection probability requirement; (3) placing the single-photon area array detector in a time-of-flight measurement mode, setting a gate start signal, emitting the k laser pulses, and reading the corresponding single-photon area array detector information; (4) establishing a distance-direction three-dimensional image based on the single-photon area array detector information; (5) setting a distance range of interest within the gate start signal according to the distribution rule of the distance-direction three-dimensional image, and adjusting the TDC system clock; (6) emitting laser pulses based on the TDC system clock, and reading the corresponding single-photon area array detector information; (7) reconstructing a distance-direction three-dimensional image based on the single-photon area array detector information.

8. A single-photon laser three-dimensional imaging system based on the readout circuit design according to any one of claims 1 to 5.

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