Dynamic threshold adjusting system based on silicon photomultiplier receiver and laser radar

Abstract

The invention discloses a dynamic threshold adjusting system based on a silicon photomultiplier receiver and a laser radar, and belongs to the technical field of photoelectric detection. According to the system, an incident light signal is captured in real time through a silicon photomultiplier receiver, a pulse counting rate is extracted by a signal processing module to represent ambient light intensity, and an SiPM detection threshold value is adjusted based on a dynamic feedback mechanism: when background light is enhanced, the threshold value is increased to suppress noise pulses; when the background light is weakened, the threshold is reduced to preserve the weak signal. A grey-scale map generation module is introduced, noise distribution of multi-channel SiPM is converted into a two-dimensional grey-scale map through a space mapping algorithm, and accurate positioning of a noise source and collaborative optimization of a regional threshold are achieved.

Description

Technical Field

[0001] The present invention relates to the technical fields of optoelectronic detection and lidar, and particularly to a dynamic threshold adjustment system and a lidar based on a silicon photomultiplier tube receiver, which are particularly applicable to high-precision laser ranging in scenarios with changing background light intensity. Background Art

[0002] A lidar (LiDAR) realizes target detection and ranging by emitting laser light and receiving echo signals. Its working principle is roughly as follows: In a lidar system, the laser beam emitted by the transmitting component undergoes diffuse reflection when it encounters a target object, and then the reflected light is captured by the laser receiving device. By measuring the time difference between the emission and reception of the laser signal, and combining it with the speed of light constant, through a specific calculation process (i.e., multiplying the time difference by the speed of light and then dividing by two), the distance information between the emission source and the target object can be accurately obtained. According to the number of laser lines emitted by the lidar, there are various types of products on the market, such as lidars with different configurations such as single-line, four-line, eight-line, sixteen-line, thirty-two-line, and even sixty-four-line. These devices emit a series of laser beams at multiple different angles in the vertical direction and perform scanning in the horizontal direction, thereby realizing a detailed detection of the three-dimensional shape of the target area.

[0003] As a new type of optoelectronic detection device, a silicon photomultiplier tube (SiPM) is widely used in the receiving end of lidars due to its single-photon sensitivity, high gain, and fast response characteristics. However, SiPM is extremely sensitive to background light (such as sunlight and ambient stray light), and background light noise will raise the baseline of the SiPM output signal, resulting in the following problems:

[0004] Limited performance due to fixed threshold: In traditional methods, the detection threshold of SiPM is fixed. When the background light intensity is high, a low threshold will introduce a large number of noise pulses, exceeding the capacity of the signal processing unit (such as the time-to-digital conversion module TDC); while a too high threshold will filter out valid echo signals, reducing the ranging ability.

[0005] Poor adaptability to dynamic environments: Under different weather, lighting conditions, or target reflectivities, the background light intensity varies significantly. Existing technologies cannot adjust the threshold in real time, resulting in a decrease in the signal-to-noise ratio of the system in complex environments.

[0006] Insufficient multi-channel cooperation: In a lidar with an array-type silicon photomultiplier tube receiver, each receiving channel may face different background light interferences due to different detection angles, but existing solutions lack a global optimization mechanism. Summary of the Invention

[0007] The present invention aims to solve the problems of noise interference and limited detection distance caused by the fixed threshold of the existing silicon photomultiplier tube receiver, and provides a dynamic threshold adjustment system based on a silicon photomultiplier tube receiver.

[0008] The technical solution for achieving the object of the present invention is: a dynamic threshold adjustment system based on a silicon photomultiplier tube receiver, comprising:

[0009] A plurality of silicon photomultiplier tube receivers for receiving incident light and generating corresponding electrical pulse signals; a signal processing module coupled to the silicon photomultiplier tube receivers for real-time acquisition of the intensity information of the incident light;

[0010] A control unit connected to the signal processing module and the silicon photomultiplier tube receivers for dynamically adjusting the detection threshold of the silicon photomultiplier tube receivers according to the intensity information of the incident light;

[0011] Wherein, the adjustment logic of the control unit includes:

[0012] When the intensity of the incident light increases, the detection threshold of the silicon photomultiplier tube receiver is increased;

[0013] When the intensity of the incident light decreases, the detection threshold of the silicon photomultiplier tube receiver is decreased..

[0014] The present invention also proposes a lidar, comprising the above dynamic threshold adjustment system, and:

[0015] A laser emission module for emitting a scanning laser beam;

[0016] A scanning drive module for controlling multi-angle scanning of the laser beam in the horizontal and vertical directions;

[0017] A time-to-digital conversion module connected to the silicon photomultiplier tube receiver for calculating the target distance according to the time difference between laser emission and echo reception. The time-to-digital conversion module transmits the distance data to the data processing module through the SPI protocol and generates a three-dimensional point cloud map.

[0018] Compared with the prior art, the present invention has the following remarkable advantages:

[0019] The present invention adjusts the SiPM detection threshold in real time according to the background light intensity, balancing noise suppression and signal capture capabilities;

[0020] The present invention supports collaborative threshold optimization of multi-channel silicon photomultiplier tube receivers, improving the global signal-to-noise ratio;

[0021] The present invention integrates a temperature compensation mechanism to ensure the working stability of the SiPM. Description of the Drawings

[0022] Figure 1 Schematic diagram of the echo signal and environmental noise of a silicon photomultiplier tube receiver.

[0023] Figure 2 Shows the flowchart of the operation of a dynamic threshold adjustment system based on a silicon photomultiplier tube receiver according to an embodiment of the present application.

[0024] Figure 3 Shows the signal pulses generated by the SiPM according to an embodiment of the present application. Detailed implementation

[0025] A dynamic threshold adjustment system based on a silicon photomultiplier tube receiver, comprising:

[0026] A plurality of silicon photomultiplier tube receivers for receiving incident light and generating corresponding electrical pulse signals;

[0027] A signal processing module coupled to the silicon photomultiplier tube receiver for real-time acquisition of the intensity information of the incident light;

[0028] A control unit connected to the signal processing module and the silicon photomultiplier tube receiver for dynamically adjusting the detection threshold of the silicon photomultiplier tube receiver according to the intensity information of the incident light;

[0029] Wherein, the adjustment logic of the control unit includes:

[0030] When the intensity of the incident light increases, the detection threshold of the silicon photomultiplier tube receiver is increased;

[0031] When the intensity of the incident light decreases, the detection threshold of the silicon photomultiplier tube receiver is decreased.

[0032] Silicon photomultiplier (SiPM) is a commonly used photodetector element. Its core component is an avalanche photodiode (SPAD). The SPAD works in cooperation with a series-connected quenching resistor and has the ability to detect single photons. When the SiPM receives photons, according to the photoelectric effect, the photons will trigger the generation of electrons and cause an avalanche effect.

[0033] Specifically, the process of converting the optical signal into an electrical signal is as follows: Photons are incident on the SPAD under the Geiger mode reverse bias voltage. There is a certain probability that the generated photoelectrons will trigger an induced avalanche effect in the depletion region, and then a stable electrical pulse is output. At this time, this pixel is regarded as "ignited". After the avalanche of the pixel occurs, the SPAD will enter the quenching state to prevent other incident photons from triggering further avalanche effects. Therefore, each pixel can only provide binary information of "yes" or "no" for the presence of photons.

[0034] Since the output ports of the SiPM are in parallel, the electrical pulses generated by each pixel will be superimposed into a larger pulse signal. By measuring the charge or amplitude of this giant pulse, the number of pixels that are lit can be calculated, thereby inferring the distribution characteristics of the incident photons, that is, the echo characteristics. The SiPM has a wide spectral response range, from near ultraviolet to near infrared, and has high photon technology capabilities and single-photon-level sensitivity.

[0035] However, when using the SiPM as the receiver of lidar, background light (mainly referring to the reflected light of ambient light on obstacles, which will generate random noise after entering the detector) will increase the baseline noise level of the SiPM output. As Figure 1 shown in the echo schematic diagram, if the threshold of the comparator is set too low, a large number of noise pulses will enter the subsequent devices (such as the time-to-digital converter TDC) for signal analysis and echo generation. Given the limited processing capacity of the device, in order to avoid signal pulses being overwhelmed by excessive noise, it is necessary to appropriately increase the threshold of the comparator.

[0036] In order to ensure system performance while maximizing the detection range as much as possible, the threshold needs to be controlled at the lowest possible level. In addition, since different weather conditions and target reflectivities will cause changes in the low-noise level or the magnitude of environmental noise, the performance of the dynamic threshold adjustment method has an extremely important impact on the lidar ranging performance.

[0037] In a further embodiment, the signal processing module obtains the incident light intensity information in the following manner:

[0038] Based on the current detection threshold of the silicon photomultiplier tube receiver, count the pulses generated by the incident light that are higher than the threshold to generate an incident light count value, and the count value is used to characterize the incident light intensity.

[0039] In a further embodiment, the control unit is configured to:

[0040] Take the difference between the incident light count value and the preset optimal count value as the adjustment amount, and proportionally correct the threshold of the next detection cycle of the silicon photomultiplier tube receiver.

[0041] The threshold adjustment amount (ΔTh) is determined by the following formula:

[0042] ΔTh = k·(N count -N opt )

[0043] Where, N count is the current incident light count value, N opt is the preset optimal count value (calibrated through experiments), and k is the proportionality coefficient.

[0044] The threshold for the next detection period is updated to:

[0045] Th n+1 = Th n + ΔTh

[0046] The present invention further includes:

[0047] A grayscale image generation module, connected to the control unit, for generating a two-dimensional grayscale image according to the incident light intensity information obtained by a plurality of silicon photomultiplier tube receivers at different detection angles;

[0048] Wherein, each pixel in the grayscale image corresponds to the incident light intensity of a silicon photomultiplier tube receiver at a specific angle.

[0049] The grayscale image generation module integrates background light intensity data of multiple channels and multiple angles to generate a two-dimensional grayscale image for visualizing the environmental noise distribution.

[0050] In a further embodiment, the grayscale image generation module includes:

[0051] A spatial mapping unit for establishing a spatial correspondence between the physical position coordinates of each silicon photomultiplier tube receiver and the detection angle information;

[0052] A data interpolation processor that uses a bicubic spline interpolation algorithm to perform data compensation on the incident light intensity at angles not covered;

[0053] A normalization unit that linearly maps the incident light intensity values of each channel to the 0-255 grayscale interval; a matrix generator that arranges the normalized data in a two-dimensional pixel matrix according to the spatial orientation;

[0054] A visualization interface that supports real-time display of the grayscale image and comparison of historical noise distributions.

[0055] In a further embodiment, the incident light reception operation of the silicon photomultiplier tube receiver is performed during a non-ranging period to isolate background light interference.

[0056] In a further embodiment, the control unit is further configured to:

[0057] Synchronize the currently adjusted threshold to the detection parameters of the next detection angle of the corresponding silicon photomultiplier tube receiver.

[0058] Figure 2 Shows the working process 1 of a dynamic threshold adjustment system based on a silicon photomultiplier tube receiver according to an embodiment of the present application. The following will refer to Figure 2 for a detailed description.

[0059] In step 1, incident light is received by a silicon photomultiplier tube receiver. These incident lights can be reflected laser signals that return to the silicon photomultiplier tube receiver after a laser beam emitted by lidar is reflected by an external object, or background light in the environment where the lidar is located, such as sunlight, or can include both echo signals and background light. All these situations are within the scope of protection of this disclosure.

[0060] In step 2, the intensity of the incident light is obtained. This can be achieved in various ways, such as by measuring the magnitude of the current and voltage generated by the incident light, the number of echo electrical pulses, etc. In one embodiment, the intensity can be characterized by the number of electrical pulses generated by the incident light. Those skilled in the art can also conceive of other methods for characterizing the intensity of incident light, and all of these are within the scope of protection of this disclosure.

[0061] In addition, those skilled in the art should understand that in addition to obtaining the intensity of incident light from the electrical pulses generated by the silicon photomultiplier tube receiver, it can also be obtained by other means, such as using a photoelectric sensor specifically for measuring the intensity of incident light or ambient light. All of these are within the scope of protection of this disclosure.

[0062] In step 3, the threshold Th of the silicon photomultiplier tube receiver is adjusted according to the obtained intensity of the incident light. For example, when the intensity of the incident light is too high, such as when the silicon photomultiplier tube receiver is in a strong sunlight environment, the threshold Th of the silicon photomultiplier tube receiver can be increased to avoid a large number of noise pulses from entering the subsequent devices or circuits for analyzing signals and generating echoes, thereby preventing signal pulses from being overwhelmed by a large amount of noise. On the contrary, when the intensity of the incident light is low, such as when the silicon photomultiplier tube receiver is detecting in a dark environment at night, the threshold Th of the silicon photomultiplier tube receiver can be decreased to ensure that normal echo signals are not filtered out and can enter the subsequent devices or circuits for signal analysis and echo generation.

[0063] After adjusting the threshold for the silicon photomultiplier tube receiver, subsequent devices, circuits, or software can use the adjusted threshold to filter out noise signals or background light signals. For example, among the electrical pulses generated by the silicon photomultiplier tube receiver due to incident light, those electrical pulses with amplitudes equal to or higher than the adjusted threshold are identified as valid echo signals; while those electrical pulses with amplitudes lower than the adjusted threshold are identified as noise signals or background light signals and are directly filtered out. This can improve the signal-to-noise ratio of the lidar, effectively analyze the echo signals, and increase the accuracy and reliability of radar ranging.

[0064] The above working method 1 can be continuously executed to dynamically adjust the threshold of the silicon photomultiplier tube receiver to ensure that it is within a reasonable range. In addition, in the case of an array with multiple silicon photomultiplier tube receivers, the threshold of each silicon photomultiplier tube receiver can be adjusted individually or as a whole. In the case of individual adjustment, the above steps 1, 2, and 3 are respectively executed for each silicon photomultiplier tube receiver. In the case of overall adjustment, for example, the threshold of all silicon photomultiplier tube receivers can be dynamically adjusted by obtaining the intensity of the incident light through one of the silicon photomultiplier tube receivers. Although the accuracy of this method is slightly lower, the processing speed is faster and the structure is simpler.

[0065] By adjusting the threshold through real-time feedback, taking into account noise suppression and signal capture, the ranging accuracy in complex environments is significantly improved;

[0066] Based on the grayscale image, global noise monitoring and threshold optimization of multiple silicon photomultiplier tube receivers are realized;

[0067] Integrate the temperature compensation mechanism to avoid the influence of environmental temperature drift on the performance of SiPM;

[0068] It can be adapted to the array-type silicon photomultiplier tube receiver and support the generation of high-resolution three-dimensional point clouds.

[0069] Embodiment 1: Dynamic Threshold Adjustment Process

[0070] Background Light Intensity Monitoring:

[0071] The silicon photomultiplier tube receiver receives the incident light during the non-ranging period (such as the laser emission interval);

[0072] The signal processing module counts the number of pulses higher than the current threshold (Th n ) to obtain N count .

[0073] Threshold Calculation and Update:

[0074] The control unit calculates ΔTh according to the formula and updates the threshold Th n+1 ;

[0075] The updated threshold is sent to the corresponding silicon photomultiplier tube receiver through the SPI protocol.

[0076] Ranging and Signal Processing:

[0077] After the laser is emitted, the echo signal is converted into an electrical pulse by the silicon photomultiplier tube receiver;

[0078] Only the pulses with an amplitude higher than Th n+1 are transmitted to the TDC module to calculate the flight time and generate the target distance data.

[0079] Example 2: Grayscale Map Generation and Multi-channel Optimization

[0080] The control unit aggregates the N count values of each silicon photomultiplier tube receiver at different angles;

[0081] The grayscale map generation module maps the data into a two-dimensional matrix, and the grayscale value of each pixel in the matrix corresponds to the background light intensity of a specific SiPM channel at a specific angle;

[0082] According to the grayscale map distribution, a higher threshold adjustment weight is applied to the SiPM channels in high-noise areas (such as the direction of strong sunlight irradiation).

[0083] Example 3: Temperature Compensation Mechanism

[0084] The temperature sensor monitors the working temperature of the SiPM in real time;

[0085] The temperature compensation module adjusts the SiPM bias voltage according to the preset voltage-temperature curve to ensure its gain stability.

Claims

1. A dynamic threshold adjustment system based on a silicon photomultiplier tube receiver, characterized in that Comprising: A plurality of silicon photomultiplier tube receivers for receiving incident light and generating corresponding electrical pulse signals; A signal processing module coupled to the silicon photomultiplier tube receiver for real-time acquisition of the intensity information of the incident light; A control unit connected to the signal processing module and the silicon photomultiplier tube receiver for dynamically adjusting the detection threshold of the silicon photomultiplier tube receiver according to the intensity information of the incident light; Wherein, the adjustment logic of the control unit includes: When the intensity of the incident light increases, the detection threshold of the silicon photomultiplier tube receiver is increased; When the intensity of the incident light decreases, the detection threshold of the silicon photomultiplier tube receiver is decreased.

2. The dynamic threshold adjustment system based on a silicon photomultiplier tube receiver according to claim 1, wherein The signal processing module obtains the incident light intensity information in the following manner: Based on the current detection threshold of the silicon photomultiplier tube receiver, count the pulses of the incident light that are higher than the threshold to generate an incident light count value, and the count value is used to characterize the intensity of the incident light.

3. The dynamic threshold adjustment system based on a silicon photomultiplier tube receiver according to claim 2, wherein, The control unit is configured to: Take the difference between the incident light count value and the preset optimal count value as the adjustment amount, and proportionally correct the threshold of the next detection period of the silicon photomultiplier tube receiver.

4. The dynamic threshold adjustment system based on a silicon photomultiplier tube receiver according to claim 1, wherein Further comprising: A grayscale map generation module connected to the control unit for generating a two-dimensional grayscale map according to the incident light intensity information obtained by a plurality of silicon photomultiplier tube receivers at different detection angles; Wherein, each pixel in the grayscale map corresponds to the incident light intensity of a silicon photomultiplier tube receiver at a specific angle. The grayscale map generation module integrates the background light intensity data of multiple channels and multiple angles to generate a two-dimensional grayscale map for visualizing the environmental noise distribution.

5. The dynamic threshold adjustment system based on a silicon photomultiplier tube receiver according to claim 4, characterized in that The grayscale map generation module includes: A space mapping unit for establishing a spatial correspondence between the physical position coordinates of each silicon photomultiplier tube receiver and the detection angle information; A data interpolation processor that uses a bicubic spline interpolation algorithm to perform data compensation on the incident light intensity of the uncovered angle; A normalization unit that linearly maps the incident light intensity values of each channel to the 0-255 grayscale interval; a matrix generator that arranges the normalized data in a two-dimensional pixel matrix according to the spatial orientation; A visualization interface that supports real-time display of the grayscale map and comparison of historical noise distributions.

6. The dynamic threshold adjustment system based on a silicon photomultiplier tube receiver according to claim 1, characterized in that The incident light receiving operation of the silicon photomultiplier tube receiver is performed during the non-ranging period to isolate background light interference.

7. The dynamic threshold adjustment system based on a silicon photomultiplier tube receiver according to claim 1, characterized in that, The control unit is further configured to: Synchronize the currently adjusted threshold to the detection parameters of the next detection angle of the corresponding silicon photomultiplier tube receiver.

8. A lidar, characterized in that, Including the dynamic threshold adjustment system according to any one of claims 1-7, and: A laser emission module for emitting a scanning laser beam; A scanning drive module for controlling the multi-angle scanning of the laser beam in the horizontal and vertical directions; A time-to-digital conversion module connected to the silicon photomultiplier tube receiver for calculating the target distance according to the time difference between laser emission and echo reception. The time-to-digital conversion module transmits the distance data to the data processing module through the SPI protocol and generates a three-dimensional point cloud map.

9. The lidar according to claim 7, wherein The scanning drive module works in coordination with the control unit so that the threshold adjustment of each silicon photomultiplier tube receiver is synchronously updated with its corresponding next scanning angle.

10. The lidar according to claim 7, characterized in that, Further comprising: A temperature compensation module, connected to the silicon photomultiplier tube receiver, is used to adjust the operating voltage of the SiPM in real time according to the ambient temperature to maintain a constant overvoltage state.

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