CN-121995387-A - SPAD ranging method and system based on dynamic histogram storage and multi-frame fusion

CN121995387ACN 121995387 ACN121995387 ACN 121995387ACN-121995387-A

Abstract

A SPAD ranging method based on dynamic histogram storage and multi-frame fusion includes splitting single frame measurement period into multiple sub frames, configuring corresponding phase delay amount to make each sub frame correspond to different equivalent sampling time standard, executing on each sub frame, screening photon trigger event of multiple SPAD in macro pixel in each exposure period, outputting effective photon response time and time calibration information and trigger intensity, dynamically tracking return time of echo photon based on output in current exposure period to generate processing result, integrating processing result of all exposure periods in current sub frame to generate candidate histogram, reconstructing fusion histogram based on candidate histogram corresponding to all sub frames and respective phase delay amount through data fusion, utilizing flight time extraction algorithm to analyze fusion histogram and outputting ranging result. The method can realize high-resolution three-dimensional imaging under the condition of limited hardware resources.

Inventors

MA RUI
ZHUANG RUNJIA
LI DONG
Bao Yaoqi
HU JIN
WANG XIAYU
MA JIAJI
YANG LIHONG
ZHU ZHANGMING

Assignees

西安电子科技大学

Dates

Publication Date: 20260508
Application Date: 20251229

Claims (10)

1. The SPAD ranging method based on dynamic histogram storage and multi-frame fusion is characterized by comprising the following steps of: Dividing a single frame measurement period into a plurality of subframes, and configuring corresponding phase delay amount for each subframe so that each subframe corresponds to different equivalent sampling time references, wherein each subframe corresponds to a plurality of exposure periods; for each subframe, a photon screening step and a dynamic histogram storage step are performed in sequence, wherein: in each exposure period, adaptively screening photon triggering events of a plurality of SPAD in a macro pixel in an extremum tracking mode, and outputting effective photon response time, corresponding time calibration information and triggering intensity; The dynamic histogram storage step comprises the steps of dynamically tracking the return time of echo photons based on the output of the photon screening step in the current exposure period in each exposure period to generate a corresponding processing result; And fitting, namely reconstructing a fusion histogram with time resolution higher than that of a single subframe through data fusion based on candidate histograms corresponding to all subframes and respective phase delay amounts, performing waveform analysis and nonlinear fitting on the fusion histogram by utilizing a flight time extraction algorithm, extracting flight time of echo photons and outputting a ranging result.
2. The SPAD ranging method based on dynamic histogram storage and multi-frame fusion of claim 1, wherein said multi-frame delay adjusting step comprises: Splitting the single frame measurement period into a plurality of subframes according to the ranging requirement, and generating delay selection signals corresponding to the subframes; Generating a plurality of delay signals having different fixed delay amounts using an open loop delay chain; And selecting one signal of the plurality of delay signals according to the delay selection signal corresponding to the single subframe, and adjusting the corresponding sampling clock to enable the sampling time of the subframe to deviate by a corresponding phase delay amount relative to the laser emission time, so as to establish the equivalent sampling time reference of the subframe.
3. The SPAD ranging method based on dynamic histogram storage and multiframe fusion of claim 2, wherein said photon screening step comprises: in the current exposure period, counting photon triggering times of a plurality of SPAD in the macro pixel in a summation window in an extremum tracking mode, and taking the photon triggering times as the triggering intensity of the current sampling moment; If the trigger intensity of the current sampling time is larger, updating the current maximum trigger intensity by utilizing the trigger intensity of the current sampling time and updating the current candidate response time by utilizing the current sampling time, wherein the current maximum trigger intensity is the maximum trigger frequency of the last sampling time, and the current candidate response time is the sampling time corresponding to the current maximum trigger intensity; Outputting the current candidate response time as the corresponding effective photon response time after the current exposure period is finished; And quantifying the time interval between the effective photon response time and the laser emission time as the time calibration information.
4. A SPAD ranging method based on dynamic histogram storage and multiframe fusion according to claim 1 or 3, wherein said dynamic histogram storage step comprises: nonlinear weighting is carried out on photon triggering times corresponding to effective photon response time output by the photon screening step in the current exposure period, so as to obtain weighted triggering intensity; Based on the weighted trigger intensity and the corresponding time calibration information, analyzing the distribution correlation of the photon trigger event corresponding to the weighted trigger intensity and the preset event information in the time dimension, updating the trigger time of the photon trigger event meeting the preset correlation condition into a candidate return time, and iteratively updating the event information in the dynamic histogram storage module, wherein the preset event information refers to the information of the photon trigger event meeting the correlation condition stored at the end of the last exposure period; after the current exposure period is finished, acquiring a plurality of accumulated candidate return moments, and sequentially storing the accumulated candidate return moments according to the sequence from high triggering intensity to low triggering intensity to generate corresponding candidate histograms; Summarizing the candidate histograms corresponding to all exposure periods to obtain the candidate histogram of the current subframe.
5. The SPAD ranging method based on dynamic histogram storage and multiframe fusion of claim 2, wherein said fitting process step comprises: Aligning and fusing data in the corresponding candidate histograms on a time axis according to the phase delay amount of each subframe, and reconstructing a fused histogram with time resolution higher than the measurement resolution of any subframe; Analyzing waveform distribution characteristics of the fusion histogram, and determining final return time of echo photons through nonlinear fitting; And according to the time difference between the final return time and the laser emission time, calculating by combining the light speed to obtain the final ranging result.
6. A SPAD ranging method based on dynamic histogram storage and multiframe fusion according to claim 3, wherein said summation window is a dynamic time window, and window width and/or window position thereof is dynamically determined according to the spatiotemporal distribution characteristics of photon triggering events in said macropixel.
7. The SPAD ranging method based on dynamic histogram storage and multiframe fusion according to claim 1, wherein said time scaling information is quantized by a time-to-digital converter.
8. The SPAD ranging method based on dynamic histogram storage and multiframe fusion of claim 2, wherein said open loop delay chain is comprised of a cascade of multi-stage CMOS inverters.
9. The SPAD ranging method based on dynamic histogram storage and multiframe fusion according to claim 1, further comprising an operation mode switching step of: In response to a precision priority instruction, increasing a number of subframes within the single frame measurement period; in response to a frame rate prioritization instruction, reducing a number of subframes within the single frame measurement period, or directly extracting a time of flight based on a candidate histogram of the single subframe to output a high frame rate ranging result.
10. The SPAD ranging system based on dynamic histogram storage and multi-frame fusion is characterized in that the SPAD ranging method as claimed in any one of claims 1 to 9 is deployed on the system, the system comprises a multi-frame delay adjusting module, a photon screening module, a dynamic histogram storage module and a fitting processing module, wherein: The multi-frame delay adjusting module is used for splitting a single-frame measurement period into a plurality of subframes, and configuring corresponding phase delay amount for each subframe so that each subframe corresponds to different equivalent sampling time references, wherein each subframe corresponds to a plurality of exposure periods; the photon screening module and the dynamic histogram storage module process each subframe, wherein: The photon screening module is used for adaptively screening photon triggering events of a plurality of SPAD in the macro pixel in each exposure period in an extremum tracking mode, inhibiting invalid triggering caused by background noise and outputting valid photon response time, corresponding time calibration information and triggering intensity; The dynamic histogram storage module is used for dynamically tracking the return time of echo photons based on the output of the photon screening step in the current exposure period in each exposure period to generate a corresponding processing result; The fitting processing module is used for reconstructing a fusion histogram with time resolution higher than that of a single subframe through data fusion based on candidate histograms corresponding to all subframes and respective phase delay amounts, performing waveform analysis and nonlinear fitting on the fusion histogram by utilizing a flight time extraction algorithm, extracting flight time of echo photons and outputting a ranging result.

Description

SPAD ranging method and system based on dynamic histogram storage and multi-frame fusion Technical Field The invention belongs to the technical field of single photon detection and integrated circuits, and particularly relates to a SPAD ranging method and system based on dynamic histogram storage and multi-frame fusion. Background Single-photon avalanche diode (SPAD, single-Photon Avalanche Diode) has become a core detector in the front edge fields of laser radar, three-dimensional sensing, weak light imaging, etc. by virtue of its Single photon level detection sensitivity and picosecond level time resolution. SPAD-based ranging systems typically employ the time-of-flight (ToF) principle, i.e., the distance is calculated by measuring the time delay between the laser emission and the echo photons. Among them, time-dependent single photon counting (TCSPC) is a mainstream technical solution for realizing high-precision ranging. The scheme needs to carry out high-resolution quantification on the arrival time of echo photons in repeated laser periods, and count the time distribution of the echo photons to construct a histogram, and finally, the accurate flight time is extracted by identifying the peak position of the histogram. However, to achieve full scale, high precision measurements, conventional TCSPC schemes must configure a high precision time-to-digital converter (TDC) with a large capacity on-chip memory within each pixel or macro-pixel to cover the entire time window and record a complete time histogram. The method leads to huge consumption of hardware resources, and obviously increases the chip area, the power consumption and the cost, thereby severely restricting the development of the SPAD array to the large-scale and high-integration direction. In order to reduce resource expenditure, in the prior art, a plurality of improved paths exist, namely firstly, the storage expenditure is reduced by reducing the time resolution, compressing the dimension of a histogram or shortening a measurement window, but the ranging accuracy and the dynamic range of a system are generally sacrificed by the method, particularly, the performance is rapidly reduced in a low signal-to-noise ratio or strong background light environment, and secondly, the accuracy is improved by adopting a multi-frame accumulation or sub-frame phase scanning mode, but the storage and the subsequent processing are required to be carried out on a multi-frame complete histogram, so that the storage and the read-write power consumption are further increased, the frame rate of the system is reduced, and the real-time requirement of a high dynamic scene is difficult to meet. Therefore, the existing SPAD ranging technology still has contradiction that is difficult to be compatible among ranging precision, on-chip storage resources, power consumption and measurement frame rate. Disclosure of Invention In order to solve the problems in the prior art, the invention provides a SPAD ranging method and a SPAD ranging system based on dynamic histogram storage and multi-frame fusion. The technical problems to be solved by the invention are realized by the following technical scheme: The invention provides a SPAD ranging method and a system based on dynamic histogram storage and multi-frame fusion, wherein the method comprises the following steps: Dividing a single frame measurement period into a plurality of subframes, and configuring corresponding phase delay amount for each subframe so that each subframe corresponds to different equivalent sampling time references, wherein each subframe corresponds to a plurality of exposure periods; for each subframe, a photon screening step and a dynamic histogram storage step are performed in sequence, wherein: in each exposure period, adaptively screening photon triggering events of a plurality of SPAD in a macro pixel in an extremum tracking mode, and outputting effective photon response time, corresponding time calibration information and triggering intensity; The dynamic histogram storage step comprises the steps of dynamically tracking the return time of echo photons based on the output of the photon screening step in the current exposure period in each exposure period to generate a corresponding processing result; And fitting, namely reconstructing a fusion histogram with time resolution higher than that of a single subframe through data fusion based on candidate histograms corresponding to all subframes and respective phase delay amounts, performing waveform analysis and nonlinear fitting on the fusion histogram by utilizing a flight time extraction algorithm, extracting flight time of echo photons and outputting a ranging result. Compared with the prior art, the invention has the beneficial effects that: Aiming at the problem that the existing SPAD ranging technology still has difficulty in considering ranging precision, on-chip storage resources, power consumption and measured frame rate, the embodiment of th