WO2022218397A1

WO2022218397A1 - Measurement method for laser radar

Info

Publication number: WO2022218397A1
Application number: PCT/CN2022/086987
Authority: WO
Inventors: 常健忠; 寿翔; 林贤华
Original assignee: 杭州宏景智驾科技有限公司
Priority date: 2021-04-16
Filing date: 2022-04-15
Publication date: 2022-10-20

Abstract

The present invention relates to a measurement method for an SPAD laser radar. The measurement method comprises: counting M Tof time units in a clock cycle of one measurement by using a ToF counter to generate a first address column and a second address column both having M storage addresses, and the storage addresses in the address columns having one-to-one correspondence to the Tof time units in the clock cycle; performing N measurements by using the SPAD laser radar, and collecting statistic on the measurement result by using the first address column and the second address column.

Description

Measurement methods for lidar

This application claims the priority of Chinese patent applications No. 202110411351.1 and No. 202110411352.6 filed on April 16, 2021, the disclosures of the above Chinese patent applications are incorporated herein in their entirety as a part of this application.

technical field

The present disclosure relates to lidar technology, and more particularly, to a measurement method for SPAD lidar.

Background technique

SPAD (Single Photon Avalanche Diode, single photon avalanche diode) as the photosensitive element of the lidar has the characteristics of high sensitivity and is widely used in multi-pixel high-resolution lidar. However, compared with the traditional APD receiver lidar, the SPAD lidar is more susceptible to the influence of ambient light, dark noise and other noises, resulting in measurement errors. In order to overcome the problems of SPAD lidar, it is necessary to process the received original signal in the measurement circuit of SPAD lidar, and use the method of multiple measurement statistics to filter noise and extract the target distance information to be measured.

In addition, compared with traditional lidars, SPAD lidars generate output errors caused by factors such as ambient light noise and dark current noise in addition to the effective output generated by the detected objects due to the influence of noise. Therefore, in the measurement circuit, it is necessary to perform noise filtering on the original output signal, and a method of multiple measurement statistics is generally used to extract the effective distance information generated by the target to be measured.

SUMMARY OF THE INVENTION

The present disclosure provides a measurement method for SPAD lidar, including:

The ToF counter is used to count M Tof time units within a clock cycle of one measurement, and a first address column and a second address column each having M storage addresses are generated. Tof time unit one-to-one correspondence;

Use the SPAD lidar to perform N measurements, and use the first address column and the second address column to perform statistics on the measurement results.

The present disclosure also provides another measurement method for a SPAD lidar. The measurement circuit of the SPAD lidar uses a statistical method of N measurements to filter out noise, N≥2, and the clock period of each measurement is determined by M Tof times. unit composition, M≥3, the method is used to perform statistics on the histogram obtained by N measurements, and the method includes the following steps:

Step 1. Use the ToF counter to count the ToF time units in each clock cycle, and at the same time, the ToF counter generates the memory addresses of the read-write memory 1 and the read-write memory 2 for storing data, so that the M generated by the ToF counter is used. The memory addresses correspond one-to-one with M Tof time units in one clock cycle;

Step 2. After power-on, initialize the data stored in all memory addresses of read-write memory one and read-write memory two to 0;

Step 3. Set n=1;

Step 4. When the nth measurement starts, the start signal is valid, and the ToF time unit of the clock cycle of the nth measurement is counted after the ToF counter is cleared, and the same storage address as the previous cycle is generated while counting;

Step 5. If n is odd, go to step 6, if n is even, go to step 7;

Step 6, according to the storage address generated by the ToF counter, the data in the read-write memory one is taken out as the original data, and the original data and the original data are added by 1 and input into the strobe one at the same time;

If the SPAD lidar receives a valid stop signal in the current Tof time unit, the first gate adds the value of the original data and stores it in the storage address of the read-write memory 2, and the storage address of the read-write memory 2 is checked by the ToF counter according to the Tof time unit count generation, enter step 8;

If the SPAD lidar does not receive a valid stop signal in the current Tof time unit, the gate 1 stores the original data into the storage address of the read-write memory 2, and the storage address of the read-write memory 2 is determined by the ToF counter according to the Tof time unit. The count is generated, go to step 8;

Step 7, according to the storage address generated by the ToF counter, the data in the read-write memory two is taken out as the original data, and the original data and the original data are added by 1 and input into the gate 2 at the same time;

If the SPAD lidar receives a valid stop signal within the current Tof time unit, the gate 2 stores the value of the original data plus 1 into the storage address of the read-write memory 1, and the storage address of the read-write memory 1 is checked by the ToF counter according to the Tof time unit count generation, enter step 8;

If the SPAD lidar does not receive a valid stop signal in the current Tof time unit, the gate 2 stores the original data into the storage address of the read-write memory one, and the storage address of the read-write memory one is determined by the ToF counter according to the Tof time unit. The count is generated, go to step 8;

Step 8. After the nth measurement, n=n+1, if n>N, go to step 9, otherwise return to step 4;

Step 9. If n is an even number, extract M data from the read-write memory 2 according to the M memory addresses generated by the ToF counter, and each data corresponds to the SPAD lidar counted by each Tof time unit when the effective stop signal is received. The number of times, defined as the number of stops, is to obtain the Tof time unit with the largest number of stops. In the histogram obtained by N measurements, the Tof time unit corresponds to the detected object;

If n is an even number, M data are retrieved from the read-write memory 1 according to the M memory addresses generated by the ToF counter, and each data corresponds to the number of times the SPAD lidar received a valid stop signal counted by each Tof time unit, which is defined as is the number of stops, the Tof time unit with the largest number of stops is obtained, and in the histogram obtained from N measurements, the Tof time unit corresponds to the detected object.

Preferably, the first read-write memory and the second read-write memory are implemented by RAM.

The above uses the counter to realize the dual function of ToF (time of flight) and the storage address generation of the statistical data memory, and uses the two memories to realize the statistical work on the results of the ToF measurement. Therefore, the ToF measurement and the RAM address generation are realized by the counter, and the histogram statistics function is realized by the two pieces of RAM, thereby filtering the noise of the SPAD lidar. The present invention is simple and effective, and the ToF measurement resolution is 30 cm when the counter and RAM clock are 500 MHz.

The present disclosure also provides another measurement method for SPAD lidar, the method comprising the following steps:

Step 1. Build a measurement circuit, the measurement circuit includes a dual-port read-write memory, the read address port of the dual-port read-write memory is connected to the output end of the counter, and the input end of the counter is connected to the rising edge capture unit 1; the dual-port read-write memory The write address port is connected with the output end of the counter through the delay unit one;

The write enable port of the dual-port read-write memory is connected to the output end of the gate switch 1 via the second delay unit, and the input end of the gate switch 1 is respectively connected to the high-level signal input and the rising edge capture unit 2;

The read data ports of the dual-port read-write memory are respectively connected to the latch and the input end of the gate switch 2, and the input end of the gate switch 2 also inputs -1 signal; the output end of the gate switch 2 is connected to an input end of the adder , the other input terminal of the adder inputs a +1 signal; the output terminal of the adder is connected to the write data port of the dual-port read-write memory;

The clock port of the dual-port read and write memory inputs the main clock;

Step 2. Using the gating signal, the first gating switch of the gating switch is made to input a high-level signal to enable the write data function of the dual-port read-write memory. At the same time, the second gating switch is made to input the -1 signal, and the adder will The -1 signal output by the second gate switch and the +1 signal are added together to output a 0 signal, the 0 signal is written into the dual-port read-write memory, and the data in the dual-port read-write memory is cleared;

Step 3. After the data in the dual-port read-write memory is cleared, use the gating signal to select the rising edge of the gating switch to capture the output of the second unit, and at the same time, the gating switch 2 selects the read data of the dual-port read-write memory. port;

Step 4, use the rising edge capture unit 1 to capture the rising edge of the starting signal when a certain measurement of the SPAD type lidar starts, so that the counter counts the measurement interval ToF of this measurement;

Step 5. When each measurement interval ToF arrives, the counter sends an address signal to the read address port of the dual-port read-write memory, and the address signal is sent to the write address port of the dual-port read-write memory via delay unit 1, so that the The address of the read and write data of the dual-port read-write memory uniquely corresponds to the measurement interval ToF;

Step 6. The second gate switch sends the raw data taken out from the dual-port read-write memory according to the address signal to the adder. The raw data is the intensity value of the current measurement interval corresponding to the current address signal. After the data is added by 1, it is sent to the write data port of the dual-port read-write memory. At this time, since the write enable port of the dual-port read-write memory does not receive a signal, the data sent to the write data port of the dual-port read-write memory is blocked. Give up, go to step 7;

Step 7, repeat steps 5 and 6, until the rising edge of the rising edge capture unit 2 captures the rising edge of the termination signal, and enters step 8;

Step 8. The gate switch 1 sends the pulse signal output by the rising edge capture unit 2 to the write enable port of the dual-port read-write memory through the delay unit 2, and passes through the delay unit 1 and the delay unit 2, so that the capture unit 2 sends to the dual port. The pulse signal of the write enable port of the port read-write memory is aligned with the address signal of the current measurement interval ToF sent by the counter to the write address port of the dual-port read-write memory;

Step 9. The second gate switch sends the raw data taken out from the dual-port read-write memory according to the address signal of the current measurement interval ToF to the adder, and the adder adds 1 to the intensity value of the current measurement interval and sends it to the dual-port read-write memory. Write the write data port of the memory, the updated intensity value of the current measurement interval is written into the dual-port read-write memory according to the address signal of the write address port, return to step 5, until the current measurement is completed, enter step 10;

Step 10. Return to step 4 until all measurements are completed, output the final histogram statistical information after multiple measurements in the dual-port read-write memory, and the information with the maximum intensity value is latched by the latch, and other low-intensity ones are excluded. information, that is, to complete the filtering of noise information.

Preferably, the dual-port read-write memory adopts a simple dual-port RAM.

The above method implements histogram statistics function based on a simple dual-port RAM. In particular, the present disclosure utilizes a single RAM to simultaneously realize the writing and reading of the histogram data, which reduces the RAM resource occupation by half compared to the traditional method of using one RAM for writing and reading. The present disclosure measures the measurement interval ToF (time of flight) by measuring the time difference between the start signal and the end signal (in multiple measurement statistics, the measurement period of a single measurement is composed of multiple measurement intervals ToF), that is, it represents the time of flight to be measured. target distance. At the same time, the RAM is used to realize the histogram statistics function, and the start signal counter generates the count value as the address of the RAM to characterize the measurement value of the measurement interval ToF.

Description of drawings

FIG. 1 is a schematic diagram of the method of the disclosed SPAD lidar.

FIG. 2 is a schematic circuit diagram of a specific measurement method according to the present disclosure.

FIG. 3 is a schematic circuit diagram of another specific measurement method according to the present disclosure.

Detailed ways

The present invention will be further described below in conjunction with specific embodiments. It should be understood that these examples are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the teaching content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these forms also fall within the scope defined by the appended claims of the present application.

In one or more embodiments, the measurement circuit of the SPAD lidar uses a statistical method of N measurements to filter out noise, N≥2. The clock cycle of each measurement consists of M Tof time units, M≥3, and the M Tof time units of the clock cycle of each measurement are in one-to-one correspondence, that is, the mth Tof of the clock cycle of the nth measurement The time unit corresponds to the m-th Tof time unit of the clock cycle of the n1th measurement, and the effective detection object is located in the same Tof time unit of the clock cycle of the Nth measurement. In this way, the data measured by SPAD lidar N times can be used to form a histogram, through which the noise in the original data collected by SPAD lidar can be filtered to obtain an effective detection object. For details, please refer to Figure 1.

The method for real-time TDC statistics of SPAD lidar dual random memory provided by the present invention is used to count the histogram obtained through N times of measurement to obtain the Tof time unit relative to the effective detection object, so as to obtain the effective detection object through the histogram. detection object.

With reference to FIG. 2 , a method for real-time TDC statistics of SPAD lidar dual random memory provided by the present invention specifically includes the following contents:

After power-on, the data stored in all memory addresses of RAM A and RAM B are initialized to 0.

When the first measurement in N times of measurement starts, the start signal is valid, and the ToF time unit of the clock cycle of the first measurement is counted after the ToF counter is cleared. The ToF counter generates storage addresses while counting, and for each measurement, the ToF counter generates M storage addresses in total. It should be noted here that the M memory addresses generated by the ToF counter for each measurement are consistent.

In each Tof time unit, the data in RAM A is taken out as the original data according to the storage address corresponding to the current Tof time unit generated by the ToF counter. The original data and the original data plus 1 are input to the strobe one at the same time. If the SPAD lidar receives a valid stop signal in the current Tof time unit, the strobe one stores the value of the original data plus 1 into the storage address of RAM B, and the storage address of RAM B is also determined by the ToF counter according to the Tof time unit. counts are generated.

If the SPAD lidar does not receive a valid stop signal in the current Tof time unit, the strobe one stores the original data into the storage address of the read-write RAM B, and the storage address of the RAM B is also determined by the ToF counter according to the Tof time unit. Count generation.

After the first measurement, all the results of the measurement are stored in RAM B.

When the second measurement starts, the start signal is valid and the ToF counter is cleared. At this time, the read-write controller is reversed, and the data of RAM B is written into RAM A instead, and the method is the same as above. When the third measurement starts, flip again and write RAM A's data into RAM B. And so on, until all N measurements are completed.

According to the M memory addresses generated by the ToF counter, the data is retrieved from the random memory that was written in the last measurement, which may be RAM A or RAM B. Each data corresponds to the SPAD lidar counted by each Tof time unit. The number of times of receiving a valid stop signal is defined as the number of stop times, and the Tof time unit corresponding to the maximum number of stop times is the Tof time unit that needs to be found. In the histogram obtained by N times of measurement, the data of the detected object is obtained by using the Tof time unit.

FIG. 3 shows a schematic circuit diagram of another measurement method according to the present disclosure. The measurement method utilizes multiple measurements and outputs an effective signal with the highest intensity and highest reliability, so as to avoid random noises such as ambient light and dark noise. output error. The measurement method specifically includes the following contents:

Before starting, use the gating signal to set the input terminals of the first and second gate switches to the lower end. The second output of the strobe switch is always -1, that is, the adder adds -1 and 1 to generate a constant 0, and sends it to the write data port of the simple dual-port RAM. The output of the strobe switch is always 1, which enables the write data function of the simple dual-port RAM, and the 0 sent to the write data port is written into each address space of the simple dual-port RAM. The intensity value of the measurement interval ToF is cleared to prepare for the next histogram statistics.

The current histogram is obtained through multiple measurements. When statistics are performed on the current histogram, at the beginning of each measurement, the rising edge capture unit is used to capture the rising edge of a pair of start signals to generate a pulse signal for triggering the counter to start counting. The counter counts the measurement interval ToF. Each time it counts, the counter outputs an address signal, which is output through two channels. All the way is sent to the read address port of the simple dual-port RAM, which is used to read the intensity value of the current histogram in the current measurement interval ToF. The other one is sent to the write address port of the simple dual-port RAM after a delay through the delay unit, and is used to update the intensity value of the current histogram in the current measurement interval ToF when the new measurement value is valid.

The intensity value in the simple dual port RAM is not updated when the circuit does not detect a termination signal. When the termination signal is detected, a pulse signal is generated after capturing the rising edge of the termination signal by the rising edge capturing unit II. After the delay unit 2 delays, the pulse signal is aligned with the address signal of the current measurement interval ToF sent by the counter to the write address port of the simple dual-port RAM. port. After the data write function of the simple dual-port RAM is enabled, the updated intensity value of the current histogram output by the adder after adding 1 to the intensity value of the ToF in the current measurement interval is written to the current address, that is, the comparison with the current address is completed. The update of the intensity value of the corresponding measurement interval ToF.

When one measurement is completed by the above method, and the last measurement in multiple measurements is further completed, the read data port outputs the final histogram statistical information after multiple measurements, the latch latches the information with the highest intensity value, and excludes other intensity values. The lower information, that is, the filtering of noise information is completed.

Claims

A measurement method for SPAD lidar, comprising:

The ToF counter is used to count M Tof time units within a clock cycle of one measurement, and a first address column and a second address column each having M storage addresses are generated. Tof time unit one-to-one correspondence;

Use the SPAD lidar to perform N measurements, and use the first address column and the second address column to perform statistics on the measurement results.
The measurement method according to claim 1, wherein the first address column is generated in a first memory, and the second address column is generated in a second memory.
The measurement method according to claim 2, wherein, when performing the nth measurement,

If n is an odd number, the data in the first memory is taken out as the original data according to the storage address generated by the ToF counter, and the original data and the value of the original data plus 1 are input into the first gate at the same time, for the current Tof time unit , if the SPAD lidar receives a valid signal, the first gate will store the value of the original data plus 1 in the storage address of the second memory, if the SPAD lidar does not receive a valid signal, the first gate will The data is stored in the storage address of the second memory,

If n is an even number, the data in the second memory is taken out as the original data according to the storage address generated by the ToF counter, and the original data and the value of the original data plus 1 are input into the second gate at the same time. For the current Tof time unit, if When the SPAD lidar receives a valid signal, the second gate will store the value of the original data plus 1 into the storage address of the first memory. If the SPAD lidar receives a valid stop signal, the second gate will store the original data in the storage address. into the storage address of the first memory.
The measurement method according to claim 3, wherein for the data of the address column in the memory stored in the n=Nth measurement, the detected object is determined by taking the Tof time unit with the largest stored value.
The measurement method of claim 1, wherein the first address column and the second address column are both generated in the same memory.
The measurement method of claim 5, wherein the memory comprises:

a read address port, which is connected to the output end of the counter, and the input end of the counter is connected to the first rising edge capture unit;

write address port, which is connected with the output end of the counter through the first delay unit;

a write enable port, which is connected to the output end of the first gating switch via the second delay unit, and the input end of the first gating switch is connected to the high-level signal input and the second rising edge capture unit;

The read data port is connected to the input end of the second gating switch and the latch, the input end of the second gating switch also inputs a signal -1, and the output end of the second gating switch is connected to one of the input ends of the adder, The other input end of the adder has an input signal +1, and the output end of the adder is connected to the write data port of the memory.
The measurement method according to claim 6, wherein,

Using the gating signal, the first gating switch is made to gating the input high-level signal to enable the write data function of the memory. The output signal -1 and the signal +1 are added together to output a 0 signal, and the 0 signal is written into the memory to clear the data in the memory;

After the data is cleared, the first select switch selects the output of the second rising edge capture unit by using the select signal, and the second select switch selects the read data port of the memory.
The measurement method according to claim 6, wherein,

Use the first rising edge capture unit to capture the rising edge of the start signal at the beginning of a single measurement of the SPAD lidar, so that the counter counts the measurement interval ToF of this measurement;

When each measurement interval ToF arrives, the counter sends an address signal to the read address port of the memory, and the address signal is sent to the write address port of the memory via the first delay unit, so that the read data address and the write data address of the memory are both It uniquely corresponds to the measurement interval ToF.
The measurement method according to claim 8, wherein,

The second strobe switch sends the raw data retrieved from the memory according to the address signal to the adder, the raw data is the intensity value of the current measurement interval ToF corresponding to the current address signal, and the adder adds 1 to the raw data and sends it Write data port to memory;

When the write enable port of the memory does not receive a signal, the data sent to the write data port of the dual port read and write memory is discarded.
The measurement method according to claim 8, wherein,

When the second rising edge capture unit captures the rising edge of the termination signal, the first gate switch sends the pulse signal output by the second rising edge capture unit to the write enable port of the memory via the second delay unit, and passes through the first delay unit. And the second delay unit, so that the pulse signal sent by the second capture unit to the write enable port of the memory is aligned with the address signal of the current measurement interval ToF of the write address port sent by the counter to the memory;

The second strobe switch sends the original data taken out from the memory according to the address signal of the current measurement interval ToF to the adder, and the adder adds 1 to the intensity value of the current measurement interval and sends it to the write data port of the memory. The intensity value of the current measurement interval is written into the memory according to the address signal of the write address port.
The measurement method according to claim 6, wherein,

After completing the N times of measurement, for the final histogram statistics output after multiple measurements in the memory, the information with the maximum intensity value is latched by the latch, and other information with lower intensity is eliminated to complete the noise information. filter out.
A measurement method for SPAD lidar, the measurement circuit of the SPAD lidar uses N measurement statistics method to filter out noise, N≥2, the clock cycle of each measurement consists of M Tof time units, M≥3 , then the method is used to perform statistics on the histogram obtained by N measurements, including the following steps:

Step 1. Use the ToF counter to count the ToF time units in each clock cycle, and at the same time, the ToF counter generates the memory addresses of the read-write memory 1 and the read-write memory 2 for storing data, so that the M generated by the ToF counter is used. The memory addresses correspond one-to-one with M Tof time units in one clock cycle;

Step 2. After power-on, initialize the data stored in all memory addresses of read-write memory one and read-write memory two to 0;

Step 3. Set n=1;

Step 4. When the nth measurement starts, the start signal is valid, and the ToF time unit of the clock cycle of the nth measurement is counted after the ToF counter is cleared, and the same storage address as the previous cycle is generated while counting;

Step 5. If n is odd, go to step 6, if n is even, go to step 7;

Step 6, according to the storage address generated by the ToF counter, the data in the read-write memory one is taken out as the original data, and the original data and the original data are added by 1 and input into the strobe one at the same time;

If the SPAD lidar receives a valid stop signal in the current Tof time unit, the first gate adds the value of the original data and stores it in the storage address of the read-write memory 2, and the storage address of the read-write memory 2 is checked by the ToF counter according to the Tof time unit count generation, enter step 8;

If the SPAD lidar does not receive a valid stop signal in the current Tof time unit, the gate 1 stores the original data into the storage address of the read-write memory 2, and the storage address of the read-write memory 2 is determined by the ToF counter according to the Tof time unit. The count is generated, go to step 8;

Step 7, according to the storage address generated by the ToF counter, the data in the read-write memory two is taken out as the original data, and the original data and the original data are added by 1 and input into the gate 2 at the same time;

If the SPAD lidar receives a valid stop signal within the current Tof time unit, the gate 2 stores the value of the original data plus 1 into the storage address of the read-write memory 1, and the storage address of the read-write memory 1 is checked by the ToF counter according to the Tof time unit count generation, enter step 8;

If the SPAD lidar receives a valid stop signal in the current Tof time unit, the gate 2 stores the original data into the storage address of the read-write memory 1, and the storage address of the read-write memory 1 is determined by the ToF counter according to the ToF time unit. Count generation, go to step 8;

Step 8. After the nth measurement, n=n+1, if n>N, go to step 9, otherwise return to step 4;

Step 9. If n is an odd number, extract M data from the read-write memory 2 according to the M memory addresses generated by the ToF counter, and each data corresponds to the SPAD lidar counted by each Tof time unit when the effective stop signal is received. The number of times, defined as the number of stops, is to obtain the Tof time unit with the largest number of stops. In the histogram obtained by N measurements, the Tof time unit corresponds to the detected object;

If n is an even number, M data are retrieved from the read-write memory 1 according to the M memory addresses generated by the ToF counter, and each data corresponds to the number of times the SPAD lidar received a valid stop signal counted by each Tof time unit, which is defined as is the number of stops, the Tof time unit with the largest number of stops is obtained, and in the histogram obtained from N measurements, the Tof time unit corresponds to the detected object.
The measurement method according to claim 12, wherein the first read-write memory and the second read-write memory are implemented by RAM.
A measurement method for SPAD lidar, comprising the following steps:

Step 1. Build a measurement circuit, the measurement circuit includes a dual-port read-write memory, the read address port of the dual-port read-write memory is connected to the output end of the counter, and the input end of the counter is connected to the rising edge capture unit 1; the dual-port read-write memory The write address port is connected with the output end of the counter through the delay unit one;

The write enable port of the dual-port read-write memory is connected to the output end of the gate switch 1 via the second delay unit, and the input end of the gate switch 1 is respectively connected to the high-level signal input and the rising edge capture unit 2;

The read data ports of the dual-port read-write memory are respectively connected to the latch and the input end of the gate switch 2, and the input end of the gate switch 2 also inputs -1 signal; the output end of the gate switch 2 is connected to an input end of the adder , the other input terminal of the adder inputs a +1 signal; the output terminal of the adder is connected to the write data port of the dual-port read-write memory;

The clock port of the dual-port read and write memory inputs the main clock;

Step 2. Using the gating signal, the first gating switch of the gating switch is made to input a high-level signal to enable the write data function of the dual-port read-write memory. At the same time, the second gating switch is made to input the -1 signal, and the adder will The -1 signal output by the second gate switch and the +1 signal are added together to output a 0 signal, the 0 signal is written into the dual-port read-write memory, and the data in the dual-port read-write memory is cleared;

Step 3. After the data in the dual-port read-write memory is cleared, use the gating signal to select the rising edge of the gating switch to capture the output of the second unit, and at the same time, the gating switch 2 selects the read data of the dual-port read-write memory. port;

Step 4, use the rising edge capture unit 1 to capture the rising edge of the starting signal when a certain measurement of the SPAD type lidar starts, so that the counter counts the measurement interval ToF of this measurement;

Step 5. When each measurement interval ToF arrives, the counter sends an address signal to the read address port of the dual-port read-write memory, and the address signal is sent to the write address port of the dual-port read-write memory via delay unit 1, so that the The address of the read and write data of the dual-port read-write memory uniquely corresponds to the measurement interval ToF;

Step 6. The second gate switch sends the raw data taken out from the dual-port read-write memory according to the address signal to the adder. The raw data is the intensity value of the current measurement interval corresponding to the current address signal. After the data is added by 1, it is sent to the write data port of the dual-port read-write memory. At this time, since the write enable port of the dual-port read-write memory does not receive a signal, the data sent to the write data port of the dual-port read-write memory is blocked. Give up, go to step 7;

Step 7, repeat steps 5 and 6, until the rising edge of the rising edge capture unit 2 captures the rising edge of the termination signal, and enters step 8;

Step 8. The gate switch 1 sends the pulse signal output by the rising edge capture unit 2 to the write enable port of the dual-port read-write memory through the delay unit 2, and passes through the delay unit 1 and the delay unit 2, so that the capture unit 2 sends to the dual port. The pulse signal of the write enable port of the port read-write memory is aligned with the address signal of the current measurement interval ToF sent by the counter to the write address port of the dual-port read-write memory;

Step 9. The second gate switch sends the raw data taken out from the dual-port read-write memory according to the address signal of the current measurement interval ToF to the adder, and the adder adds 1 to the intensity value of the current measurement interval and sends it to the dual-port read-write memory. Write the write data port of the memory, the updated intensity value of the current measurement interval is written into the dual-port read-write memory according to the address signal of the write address port, return to step 5, until the current measurement is completed, enter step 10;

Step 10. Return to step 4 until all measurements are completed, output the final histogram statistical information after multiple measurements in the dual-port read-write memory, and the information with the maximum intensity value is latched by the latch, and other low-intensity ones are excluded. information, that is, to complete the filtering of noise information.
The measurement method according to claim 14, wherein the dual-port read-write memory adopts a simple dual-port RAM.