Single-photon ranging laser radar receiving device
By using a SPAD array and a multi-hit TDC module in the lidar receiver to monitor and store the TOF information of the highest peak value, the problem of slow scene acquisition rate in the prior art is solved, and more efficient lidar data acquisition is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2025-01-21
- Publication Date
- 2026-03-06
AI Technical Summary
Existing LiDAR technology requires the collection of histograms and the repeated storage of Time-of-Flight (TOF) data at the same point in the scene, resulting in a slow scene acquisition rate.
By employing a SPAD array, SPAD hardening circuit, current generator, transimpedance amplifier, peak hold circuit, AC coupling circuit, comparator, and multi-hit TDC module, the TOF information of the highest peak value is monitored and stored, avoiding repeated storage and post-processing, and improving the scene acquisition rate.
It enables operation in single-shot mode, improves the scene acquisition rate of lidar, reduces noise interference, and improves the accuracy and reliability of ranging.
Smart Images
Figure CN223977355U_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of single-photon ranging technology, and more specifically, to a single-photon ranging lidar receiving device. Background Technology
[0002] LiDAR systems, utilizing Time-of-Flight (TOF) technology, estimate the distance to a target object by precisely measuring the time delay from the emission of a laser pulse to its reflection and return from the target, making them particularly adept at long-range measurements. In Direct TOF applications, the system emits a pulsed laser towards the target, followed by a photodetector capturing the reflected light and activating a Time-Digital Converter (TDC) to quantify the round-trip time difference of the laser.
[0003] LiDAR typically uses pulsed laser mode, with each detector pixel independently calculating the Time-of-Flight (TOF) of its illumination point. Although flash LiDAR can theoretically capture a panoramic view with a single pulse, its high energy requirements, limited by human eye safety standards, restrict its effective range in high-background-noise environments, typically not exceeding tens of meters. In contrast, scanning LiDAR, while having a narrower field of view and a frame rate constrained by scanning speed, can achieve much greater distance measurement.
[0004] In the fields of advanced driver assistance systems (ADAS) and autonomous driving, LiDAR needs to rapidly build high-precision (centimeter-level) 3D environmental models covering a range of hundreds of meters, while requiring low-latency processing. Facing challenges such as laser echo attenuation with the square of distance, large differences in target reflectivity, and strong background light, the detector needs to possess a wide dynamic range capability.
[0005] In recent years, single-photon avalanche diodes (SPADs) have gradually become the preferred choice for LiDAR detectors due to their high sensitivity. Silicon-based SPADs (operating up to 1000nm wavelength) can operate at room temperature, have low dark count rates (DCR), and are easily integrated with on-chip electronic systems, enabling efficient Time-of-Flight (TOF) measurements and data processing. InGaAs / InP SPADs extend sensitivity to 1.7μm, but come with high DCR and require cooling. However, the inherent dead time of SPADs (tens of nanoseconds for silicon-based SPADs and microseconds for InGaAs) limits their maximum photon detection rate and cannot distinguish between single-photon and multi-photon events. Therefore, it is necessary to control the trigger probability to avoid "detector stacking," especially under high background light conditions. Increasing the optical aperture and the number of SPADs per pixel has become an effective strategy.
[0006] Due to stray triggering caused by DCR and background light, a single TOF measurement is insufficient to accurately determine the target distance. Therefore, a strategy of multiple laser pulse emission and TOF acquisition is often employed to construct a TOF histogram. The highest peak corresponds to the effective laser echo, while lower peaks may originate from multiple reflections, and the baseline reflects the random distribution of DCR and background photons. To address the "electron accumulation" problem—the information loss and histogram distortion caused by recording only the first TOF event in a single pulse—multi-hit TDCs and memory are required in high-noise environments to ensure that multiple TOF data points are captured and stored with each pulse, thus guaranteeing measurement accuracy and reliability. However, this approach requires histogram collection, and the laser repetition at the same point in the scene necessitates storing a significant amount of TOF data per frame, resulting in a slow scene acquisition rate for the lidar. Utility Model Content
[0007] The purpose of this application is to provide a single-photon ranging lidar receiving device to solve the problem that the existing technology requires the collection of histograms, and the laser repeats at the same point in the scene, and each frame also needs to store a lot of TOF data, resulting in a slow scene acquisition rate of lidar.
[0008] This application provides a single-photon ranging lidar receiving device, comprising: a SPAD array, a SPAD hardening circuit, a current generator, a transimpedance amplifier, a peak hold circuit, an AC coupling circuit, a comparator, and a multi-hit TDC module.
[0009] SPAD arrays are used to receive optical signals and generate avalanche currents;
[0010] The SPAD quenching circuit is used to quench the avalanche current and generate the first pulse signal;
[0011] The current generator is used to convert the first pulse signal into a current signal;
[0012] Transimpedance amplifiers are used to convert current signals into voltage waveform signals;
[0013] A peak hold circuit is used to detect and hold the peak value of a voltage waveform signal to obtain a shaped signal.
[0014] The AC coupling circuit is used to remove the DC component from the shaped signal to obtain the second pulse signal;
[0015] The comparator is used to convert the second pulse signal into a digital pulse according to a set threshold.
[0016] The multi-hit TDC module is used to trigger the hit TDC multiple times based on digital pulses to obtain multiple TOFs; the TOF of the last event is used as the final distance information.
[0017] In the above technical solution, the first pulse signal generated by the SPAD quenching circuit is converted into a voltage waveform signal after passing through a current generator and a transimpedance amplifier. The highest detected peak is monitored and tracked by a peak hold circuit to obtain a shaped signal. An AC coupling circuit tracks the derivative of this shaped signal. A comparator triggers a multi-hit TDC to store Time-of-Flight (TOF) information. At the end of the frame (before the next laser shot), the uniquely stored TOF value is the TOF of the last event, i.e., the highest signal peak detected in the current frame. This solution does not require histogram collection, does not require storing more TOF data per frame, and does not require post-processing. It can operate in a single-shot state, avoiding laser repetition at the same point in the scene, thereby improving the scene acquisition rate of a single-point scanning LiDAR.
[0018] In some alternative implementations, a gating module is also included; the gating module is used to filter out avalanche currents outside the gating period from the first pulse signal, and retain the avalanche currents within the gating period to obtain the third pulse signal.
[0019] In the above technical solution, the core function of the gating module is to allow avalanche current to pass only during a specific gating period, filtering out all avalanche current outside the gating period. This mechanism directly reduces false triggering events caused by detector noise (such as dark counting), thereby significantly reducing DCR and improving the signal-to-noise ratio. The gating module can also effectively reduce other types of background noise interference. Because most avalanche currents generated by background light and other non-target signals are not within the preset gating period, these noise signals are effectively shielded by the gating module, thereby improving the overall system's noise immunity. By reducing noise interference and DCR, the gating module enables the system to more accurately identify and record valid TOF data. This helps improve ranging accuracy and reliability in complex environments (such as high background noise, multiple reflections, etc.). The gating time of the gating module can be adjusted by external or internal triggers, allowing users to flexibly set the gating width and frequency according to the needs of actual application scenarios. This configurability enables the receiving device to adapt to different ranging tasks and environmental conditions, improving the system's flexibility and applicability.
[0020] In some optional implementations, a random event filter is also included; the random event filter is used to filter out random SPAD trigger events during the gating period from the third pulse signal, retain the real SPAD events that are time-related, and obtain the fourth pulse signal.
[0021] In the above technical solution, the random event filter is a configurable SPAD event filter, composed of several interconnected AND and OR gates. Since noise-triggered SPAD events are random, while genuine SPAD events are time-dependent, the random event filter can filter out random SPAD-triggered events during the gating period, while retaining genuine SPAD events. Furthermore, some SPADs can be selected for random event filtering, thereby increasing accuracy and flexibility, and further improving precision.
[0022] In some alternative implementations, a current buffer is also included; the current buffer is used to transfer the fourth pulse signal from an input source with very low impedance to an output load with high impedance to obtain the fifth pulse signal;
[0023] The current generator is used to convert the fifth pulse signal into a current signal.
[0024] In the above technical solution, the main function of the current buffer is to transmit the signal from an input source with extremely low impedance (such as the fourth pulse signal output by a random event filter) to an output load with high impedance without introducing significant signal attenuation or distortion. This ensures signal integrity and quality, reducing signal loss due to impedance mismatch during signal transmission. Current buffers typically have high current gain and bandwidth, enhancing the signal's driving capability and enabling more stable and reliable signal transmission to subsequent processing circuits or devices. This is particularly important for lidar receivers requiring high sensitivity and high-speed response.
[0025] In some optional implementations, multiple SPAD arrays are included, each SPAD array corresponding to a SPAD hardening circuit, a gating module, a random event filter, and a current buffer.
[0026] The outputs of multiple current buffers are coupled and output to the current generator.
[0027] In the above technical solution, multiple parallel-connected SPAD arrays aggregate photon detection events, reducing the impact of background noise and saturation. Furthermore, the outputs of multiple current buffers are coupled and output to a current generator. Due to the effect of the current buffers, the input source with extremely low impedance (effective resistance) is transmitted to the output load with high impedance, preventing the signal source from being affected by any difference in the amount of current absorbed by the output load. This allows the output currents of the two SPAD arrays to be aggregated, reducing current loss, and output to the current generator.
[0028] This application provides a control method for a single-photon ranging lidar receiver, comprising:
[0029] Using a SPAD array, optical signals are received and avalanche currents are generated;
[0030] The SPAD quenching circuit is used to quench the avalanche current and generate the first pulse signal.
[0031] The first pulse signal is converted into a current signal using a current generator.
[0032] A transimpedance amplifier is used to convert the current signal into a voltage waveform signal;
[0033] A peak hold circuit is used to detect and hold the peak value of the voltage waveform signal to obtain the shaped signal.
[0034] By using an AC coupling circuit, the DC component is removed from the shaped signal to obtain the second pulse signal;
[0035] Using a comparator, the second pulse signal is converted into a digital pulse according to a set threshold.
[0036] Using a multi-hit TDC module, multiple time-of-flight (TOF) events are obtained by triggering the TDC multiple times based on digital pulses; the TOF of the last event is used as the final distance information.
[0037] In some alternative implementations, it also includes:
[0038] Using a gating module, the avalanche current outside the gating period is filtered out from the first pulse signal, while the avalanche current within the gating period is retained, to obtain the third pulse signal.
[0039] In some alternative implementations, it also includes:
[0040] By using a random event filter, the random SPAD trigger events during the gating period are filtered out from the third pulse signal, and the real SPAD events related to time are retained to obtain the fourth pulse signal.
[0041] In some alternative implementations, it also includes:
[0042] A current buffer is used to transfer the fourth pulse signal from an input source with very low impedance to an output load with high impedance, thus obtaining the fifth pulse signal.
[0043] The fifth pulse signal is converted into a current signal using a current generator.
[0044] In some alternative implementations, it also includes:
[0045] The avalanche current generated by each SPAD array is processed sequentially through the corresponding SPAD hardening circuit, gating module, random event filter, and current buffer.
[0046] The outputs of multiple current buffers are coupled and output to the current generator. Attached Figure Description
[0047] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0048] Figure 1 A functional block diagram of a single-photon ranging lidar receiving device provided in this application embodiment;
[0049] Figure 2 This is a waveform diagram of a SPAD trigger event provided in an embodiment of this application;
[0050] Figure 3 The peak hold output waveform diagram provided in the embodiments of this application;
[0051] Figure 4 The output waveform diagram of the AC coupling circuit provided in the embodiment of this application;
[0052] Figure 5 The comparator output waveform diagram provided in the embodiments of this application;
[0053] Figure 6 A flowchart illustrating the operation of the single-photon ranging lidar receiving device provided in the embodiments of this application;
[0054] Figure 7 A schematic diagram illustrating the gateless mode and gated mode provided in the embodiments of this application;
[0055] Figure 8 A schematic diagram illustrating random SPAD triggering events and actual SPAD triggering events provided in the embodiments of this application;
[0056] Figure 9 A flowchart illustrating the control method steps of a single-photon ranging lidar receiving device provided in this application embodiment. Detailed Implementation
[0057] The technical solutions in the embodiments of this application will now be described with reference to the accompanying drawings.
[0058] Please refer to Figure 1 , Figure 1A functional block diagram of a single-photon ranging lidar receiver provided in this application embodiment includes: a SPAD array, a SPAD quenching circuit, a current generator, a transimpedance amplifier, a peak hold circuit, an AC coupling circuit, a comparator, and a multi-hit TDC module. The SPAD array is used to receive optical signals and generate avalanche currents. The SPAD quenching circuit is used to quench the avalanche currents and generate a first pulse signal. Each SPAD and its quenching circuit constitute a miniature unit. The current generator is used to convert the first pulse signal into a current signal. The transimpedance amplifier is used to convert the current signal into a voltage waveform signal. The peak hold circuit is used to detect and hold the peak value of the voltage waveform signal to obtain a shaped signal. The AC coupling circuit is used to remove the DC component from the shaped signal to obtain a second pulse signal. The comparator is used to convert the second pulse signal into a digital pulse according to a set threshold. The multi-hit TDC module is used to trigger the hit TDC multiple times according to the digital pulses to obtain multiple Time of Flight (TOF). The TOF of the last event is used as the final distance information.
[0059] Specifically, please refer to Figures 2-5 , Figure 2 This is a waveform diagram of a SPAD trigger event provided in an embodiment of this application. Figure 3 This is a waveform diagram of the peak hold circuit provided in an embodiment of this application. Figure 4 This is a waveform diagram of the output of the AC coupling circuit provided in an embodiment of this application. Figure 5 The comparator output waveform diagram provided in the embodiments of this application.
[0060] In this embodiment, the SPAD quenching circuit can employ a variable load quenching circuit (VLQC), with a dead time adjustable within the range of 10–200 ns. The adjustable duration of the VLQC output digital pulse is set to 5 ns, equal to the pulse width of the laser. The peak detection method used in the peak hold circuit of this embodiment requires timestamping all peaks detected by the peak detector and overwriting the previously stored TOF value with the latest TOF value. Therefore, it is necessary to employ a multi-hit TDC with a sufficiently long FSR, good resolution, and low dead time in subsequent conversions within the same frame.
[0061] Regarding multi-hit TDC, due to the dead time of SPADs, the resulting pileup phenomenon (photon accumulation) can cause premature TDC triggering (false triggering). For single-hit TDCs, it may be impossible to continue responding to and recording subsequent genuine SPAD triggering events. Multi-hit TDC aims to solve this problem by detecting SPAD events multiple times and recording the corresponding Time-of-Flight (TOF) information. In this scheme, since multiple SPAD triggering events need to be measured and recorded, each subsequent event is derived from the previous event and overwrites the TOF of the previous event. Multi-hit TDC uses the TOF of the last event as the final distance information.
[0062] The AC coupling circuit isolates DC and only allows AC current to pass through. In this embodiment, the AC coupling circuit can be considered as differentiating the output of the peak hold circuit to generate a pulse at each incremental peak value. That is, a pulse is generated only when the subsequent peak value is higher than the previous peak value (an incremental pulse exists).
[0063] In this embodiment, the first pulse signal generated by the SPAD quenching circuit is converted into a voltage waveform signal after passing through a current generator and a transimpedance amplifier. A peak hold circuit monitors and tracks the detected highest peak to obtain a shaped signal. An AC coupling circuit tracks the derivative of this shaped signal. A comparator triggers a multi-hit TDC to store Time-of-Flight (TOF) information. At the end of the frame (before the next laser shot), the uniquely stored TOF value is the TOF of the last event, i.e., the highest signal peak detected in the current frame. This scheme does not require histogram collection, does not require storing more TOF data per frame, and does not require post-processing. It can operate in a single-shot state, avoiding laser repetition at the same point in the scene, thereby improving the scene acquisition rate of a single-point scanning LiDAR.
[0064] Please refer to Figure 6 , Figure 6 A flowchart illustrating the operation of the single-photon ranging lidar receiving device provided in the embodiments of this application.
[0065] In some alternative implementations, a gating module is also included; the gating module is used to filter out avalanche currents outside the gating period from the first pulse signal, and retain the avalanche currents within the gating period to obtain the third pulse signal.
[0066] Please refer to Figure 7 , Figure 7This diagram illustrates the gateless and gated modes provided in the embodiments of this application. The core function of the gating module is to allow avalanche current to pass only during a specific gating period, filtering out all avalanche current outside the gating period. This mechanism directly reduces false triggering events caused by detector noise (such as dark counting), thereby significantly reducing DCR and improving the signal-to-noise ratio. The gating module can also effectively reduce other types of background noise interference. Because most avalanche currents generated by background light and other non-target signals are not within the preset gating period, these noise signals are effectively shielded by the gating module, thereby improving the overall system's noise immunity. By reducing noise interference and DCR, the gating module enables the system to more accurately identify and record valid TOF data. This helps improve ranging accuracy and reliability in complex environments (such as high background noise, multiple reflections, etc.). The gating time of the gating module can be adjusted by external or internal triggers, allowing users to flexibly set the gating width and frequency according to the needs of actual application scenarios. This configurability enables the receiving device to adapt to different ranging tasks and environmental conditions, improving the system's flexibility and applicability.
[0067] In some optional implementations, a random event filter is also included; the random event filter is used to filter out random SPAD trigger events during the gating period from the third pulse signal, retain the real SPAD events that are time-related, and obtain the fourth pulse signal.
[0068] Please refer to Figure 8 , Figure 8 This diagram illustrates random SPAD triggering events and genuine SPAD triggering events provided in this embodiment. The random event filter is a configurable SPAD event filter, composed of interconnected AND and OR gates. Since noise-triggered SPAD events are random, while genuine SPAD events are time-dependent, the random event filter can filter out random SPAD triggering events during the gating period, while retaining genuine SPAD events. Furthermore, some SPADs can be selected for random event filtering, thereby increasing accuracy and flexibility, and further enhancing precision.
[0069] In some alternative implementations, a current buffer is also included; the current buffer is used to transfer the fourth pulse signal from an input source with very low impedance to an output load with high impedance to obtain the fifth pulse signal;
[0070] The current generator is used to convert the fifth pulse signal into a current signal.
[0071] In this embodiment, the primary function of the current buffer is to transmit a signal from an input source with extremely low impedance (such as the fourth pulse signal output by a random event filter) to an output load with high impedance without introducing significant signal attenuation or distortion. This ensures signal integrity and quality, reducing signal loss due to impedance mismatch during transmission. Current buffers typically have high current gain and bandwidth, enhancing signal driving capability and enabling more stable and reliable signal transmission to subsequent processing circuits or devices. This is particularly important for lidar receivers requiring high sensitivity and high-speed response.
[0072] In some optional implementations, multiple SPAD arrays are included, each SPAD array corresponding to a SPAD hardening circuit, a gating module, a random event filter, and a current buffer.
[0073] The outputs of multiple current buffers are coupled and output to the current generator.
[0074] In this embodiment, multiple parallel-connected SPAD arrays aggregate photon detection events, reducing the impact of background noise and saturation. Furthermore, the outputs of multiple current buffers are coupled and output to a current generator. Due to the effect of the current buffers, the input source with extremely low impedance (effective resistance) is transmitted to the output load with high impedance, preventing the signal source from being affected by any difference in the amount of current absorbed by the output load. This allows the output currents of the two SPAD arrays to be aggregated, reducing current loss, and output to the current generator.
[0075] Specifically, this embodiment uses multiple parallel-connected SPAD arrays as laser echo receivers. Digital pulses are generated through SPAD quenching circuits, each of which is a variable load quenching circuit (VLQC) with an adjustable dead time duration ranging from 10 to 100 ns. The adjustable duration of the VLQC output digital pulse is set to 5 ns, equal to the laser's pulse width. This digital pulse is output to a transimpedance amplifier (TIA) via a current generation circuit, achieving digital-to-analog conversion from current to total voltage waveform. The analog signal is then processed by on-chip analog electronics, using a peak hold circuit to monitor the highest peak detected since laser emission. An AC coupler tracks the signal's variation, and a comparator triggers a multi-hit TDC to store Time-of-Flight (TOF) information. At the end of the frame, before the next laser firing, the only stored TOF value will be the last one, corresponding to the highest signal peak detected within the frame.
[0076] Please refer to Figure 9 , Figure 9A flowchart illustrating the control method steps of a single-photon ranging lidar receiver provided in this application embodiment includes:
[0077] Step S1: Using a SPAD array, receive optical signals and generate avalanche current;
[0078] Step S2: Use the SPAD quenching circuit to quench the avalanche current and generate the first pulse signal;
[0079] Step S3: Use a current generator to convert the first pulse signal into a current signal;
[0080] Step S4: Use a transimpedance amplifier to convert the current signal into a voltage waveform signal;
[0081] Step S5: Using a peak hold circuit, detect and hold the peak value of the voltage waveform signal to obtain the shaped signal;
[0082] Step S6: Using an AC coupling circuit, the DC component is removed from the shaped signal to obtain the second pulse signal;
[0083] Step S7: Using a comparator, the second pulse signal is converted into a digital pulse according to a set threshold.
[0084] Step S8: Using the multi-hit TDC module, trigger the hit TDC multiple times according to the digital pulse to obtain multiple TOFs; take the TOF of the last event as the final distance information.
[0085] In some alternative implementations, it also includes:
[0086] Using a gating module, the avalanche current outside the gating period is filtered out from the first pulse signal, while the avalanche current within the gating period is retained, to obtain the third pulse signal.
[0087] In some alternative implementations, it also includes:
[0088] By using a random event filter, the random SPAD trigger events during the gating period are filtered out from the third pulse signal, and the real SPAD events related to time are retained to obtain the fourth pulse signal.
[0089] In some alternative implementations, it also includes:
[0090] A current buffer is used to transfer the fourth pulse signal from an input source with very low impedance to an output load with high impedance, thus obtaining the fifth pulse signal.
[0091] The fifth pulse signal is converted into a current signal using a current generator.
[0092] In some alternative implementations, it also includes:
[0093] The avalanche current generated by each SPAD array is processed sequentially through the corresponding SPAD hardening circuit, gating module, random event filter, and current buffer.
[0094] The outputs of multiple current buffers are coupled and output to the current generator.
[0095] In the embodiments provided in this application, it should be understood that the disclosed apparatus and methods can be implemented in other ways. The apparatus embodiments described above are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. Furthermore, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Additionally, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some communication interfaces; indirect couplings or communication connections between devices or units may be electrical, mechanical, or other forms.
[0096] Furthermore, the units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.
[0097] Furthermore, the functional modules in the various embodiments of this application can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.
[0098] In this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, without necessarily requiring or implying any such actual relationship or order between these entities or operations.
[0099] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.
Claims
1. A single-photon range finding lidar receiving apparatus characterized by comprising: Comprise: a SPAD array, a SPAD quenching circuit, a current generator, a trans-impedance amplifier, a peak holder, an AC coupling circuit, a comparator and a multi-hit TDC module; the SPAD array is used for receiving an optical signal and generating an avalanche current; the SPAD quenching circuit is used for quenching the avalanche current to generate a first pulse signal; the current generator is used for converting the first pulse signal into a current signal; the trans-impedance amplifier is used for converting the current signal into a voltage waveform signal; the peak holder is used for detecting and holding the peak of the voltage waveform signal to obtain a reshaped signal; the AC coupling circuit is used for removing the direct current component of the reshaped signal to obtain a second pulse signal; the comparator is used for converting the second pulse signal into a digital pulse according to a set threshold value; the multi-hit TDC module is used for triggering a hit TDC multiple times according to the digital pulse to obtain multiple TOFs; and taking the TOF of the last event as final distance information.
2. The apparatus of claim 1, wherein, Further comprise: a gating module; the gating module is used for filtering out the avalanche current outside the gating period and retaining the avalanche current in the gating period to obtain a third pulse signal.
3. The apparatus of claim 2, wherein, Further comprise: a random event filter; the random event filter is used for filtering out the random SPAD trigger event in the gating period and retaining the time-related true SPAD event to obtain a fourth pulse signal.
4. The apparatus of claim 3, wherein, Further comprise a current buffer; the current buffer is used for transmitting the fourth pulse signal from an input source with extremely small impedance to an output load with high impedance to obtain a fifth pulse signal; the current generator is used for converting the fifth pulse signal into a current signal.
5. The apparatus of claim 4, wherein, Comprise a plurality of SPAD arrays, each SPAD array corresponds to a SPAD quenching circuit, a gating module, a random event filter and a current buffer: the outputs of the plurality of current buffers are coupled and output to the current generator.