DToF sensor and ranging method, laser receiving module and ranging device

Abstract

The application provides a DTOF sensor, a ranging method, a laser receiving module and a ranging device. The DTOF sensor comprises a SPAD pixel and a quenching circuit, a clock management circuit, M different resolution TDCs, M histogram circuits, a digital processing circuit and an interface circuit. The M different resolution TDCs work simultaneously, have a large ranging range and high time resolution under limited hardware conditions, and the data output by the different resolution TDCs is processed by different histogram circuits. The M histograms obtained by the M histogram circuits are output to the digital processing circuit or an external device for processing to determine the time of flight and the distance information of the object to be measured. The DTOF sensor output frame rate is improved, the M histograms obtained simultaneously do not have the mutual covering problem, the subsequent algorithm can further process and optimize the data, and the ranging accuracy is improved.

Description

Technical Field

[0001] This invention belongs to the field of sensor technology, and particularly relates to a DTOF sensor and ranging method, a laser receiving module and a ranging device. Background Technology

[0002] Direct time-of-flight (DToF) sensor technology is considered one of the most advanced sensor technologies available, leading to a trend of incorporating 3D cameras into various mobile devices. With the development of IoT and semiconductor technologies, its application areas will continue to expand. Furthermore, research to improve its performance is also underway.

[0003] The DTOF sensor mainly includes a SPAD pixel array, a quenching circuit, a clock management circuit, a TDC (time-to-digital converter), and a histogram circuit (containing multiple storage units).

[0004] Many ranging scenarios require TDC to have both a large ranging range and high time resolution. When both are required, additional circuit modules are often added to the hardware implementation, such as clock management circuits and histogram circuits.

[0005] A typical DTOF sensor usually includes a coarse resolution TDC and a fine resolution TDC, with different resolution TDCs sharing a single histogram circuit.

[0006] During distance measurement, a coarse histogram with coarse time resolution is first generated through a coarse resolution TDC and histogram circuit after a certain number of illumination cycles. The approximate distance of the object within a relatively large range can be determined by the coarse phase position corresponding to the maximum count of the histogram. Figure 1 As shown in Figure 11, the count value corresponding to cb_k is the largest, which corresponds to (k+1)*T. c If the number of photons counted in the time interval / m is the highest, then the approximate distance to the object being measured is (k+1)*T. c / m*C / 2, where T c This represents the period of the clock signal received by the coarse-resolution TDC, where m is the number of equally divided phase clock signals received by the coarse-resolution TDC.

[0007] After determining the coarse time interval position of the test object within a large range, and through a certain number of illumination cycles and circuit timing control, a fine histogram with higher time resolution is generated within the time range corresponding to the coarse phase using a fine-resolution TDC and histogram circuit, as shown in Figure 12. This allows for the determination of a small range of relatively accurate measurement distances. As shown in Figure 12, the count value corresponding to fb_i is the largest, i.e., (i+1)*T. fIf the number of photons counted in the / n time period is the highest, then the high-precision measurement distance is (i+1)*Tf / n*C / 2, where Tf represents the period of the clock signal received by the fine-resolution TDC, and n is the number of equally divided phase clock signals received by the fine-resolution TDC.

[0008] The distance information of the object to be tested was determined by two rounds of illumination as [(k*T)]. c / m+(i+1)*T f The first round of illumination generates a coarse histogram, contributing significantly to the measurement range and approximate distance of the object. The second round of illumination generates a fine histogram based on the position of the coarse phase corresponding to the count value in the coarse histogram determined by the first round of illumination, contributing high time resolution. Since the two resolution TDCs share a single histogram circuit, the fine histogram generated by the histogram circuit in the second round of illumination often overwrites the coarse histogram generated in the first round, making it impossible to simultaneously acquire both the coarse and fine histograms. This hinders subsequent data processing and optimization by the algorithm, resulting in low ranging accuracy. In addition, the two rounds of illumination reduce the frame rate of the DTOF sensor to some extent. Summary of the Invention

[0009] The purpose of this invention is to provide a DTOF sensor that addresses the problems of low frame rate and low ranging accuracy in traditional DTOF sensors.

[0010] One aspect of this invention provides a DTOF sensor, comprising:

[0011] SPAD pixels and quenching circuits: the SPAD pixels are used to sense single photons and generate avalanche pulse signals, and the quenching circuits reduce the voltage applied to the SPAD pixels to remove the SPAD photosensitive pixels from the avalanche state.

[0012] A clock management circuit is used to output M groups of clock signals. Each group of clock signals includes multiple clock signals with the same period and equal phase intervals. The number and / or period of the clock signals in each group are not equal, and M≥2.

[0013] M different resolution TDCs are connected simultaneously to the SPAD pixel and quenching circuit and the clock management circuit, respectively. Each resolution TDC is used to receive a set of corresponding clock signals. Each resolution TDC simultaneously counts the time interval from the photon emission time to the detection of the avalanche pulse signal input time with corresponding phase intervals, and generates a digital code corresponding to the time interval with each phase interval as the smallest measurement time unit.

[0014] M histogram circuits are connected one-to-one with M TDCs of different resolutions. Each histogram circuit includes a preset number of storage units. The preset number of storage units are used to count the digital codes corresponding to the preset number of phase intervals and convert them into corresponding histogram data. Each histogram data is processed by a digital processing circuit and transmitted to an interface circuit, and then output to an external device through the interface circuit.

[0015] The relationship between the time unit widths corresponding to individual storage units of the histogram data in each of the histogram circuits is as follows:

[0016] T i / m i =y i+1 *T i+1 / m i+1 ;

[0017] Among them, T i and m i Let T represent the period and the number of equally divided phase clocks of the clock signal corresponding to the i-th resolution TDC, respectively. i+1 m i+1 and y i+1 These represent the period of the clock signal corresponding to the (i+1)th resolution TDC, the number of equally divided phase clocks, and the number of storage units contained in the corresponding histogram circuit, respectively, where i is 1, 2, 3, ..., M-1, and m, n, and y are all greater than 1.

[0018] Optionally, the time resolutions from the first resolution TDC to the Mth resolution TDC increase sequentially, and the magnitude of each time resolution changes inversely with the phase interval of the clock signal;

[0019] M TDCs of different resolutions work synchronously to calculate the time interval between the light pulse emitted by the photon from the laser emitting module and the avalanche pulse signal detected by the SPAD pixel, and convert the time interval detected by each of them into digital code.

[0020] Optionally, the total number of counts for the histogram data in each of the histogram circuits is equal.

[0021] Optionally, the distance information of the object to be measured is:

[0022] L=C*[(K1-1)*T1 / m1+(K2-1)*T2 / m2+...+(K M-1 -1)*T M-1 / m M-1 +K M *T M / m M ] / 2;

[0023] Where C represents the speed of light, K1, K2 to K MThese represent the positions of the phase intervals corresponding to the maximum count peaks in the histogram data of the first to the Mth histogram circuits, respectively.

[0024] Optionally, the minimum measurement time unit of each of the histogram circuits is:

[0025] P = T i / m i .

[0026] Optionally, each of the histogram circuits performs a +1 operation on the storage unit corresponding to the received digital code to complete one photon count, and establishes the corresponding histogram data after multiple measurements;

[0027] The number of storage cells corresponding to the histogram circuit is greater than or equal to j;

[0028] Where, j = T / (T) i / m i ), where T is the time measurement range corresponding to the resolution TDC.

[0029] Optionally, the M histogram circuits transmit the M sets of histogram data to the digital processing circuit, which determines the corresponding flight time value based on each histogram data and transmits it to an external device through the interface circuit; or

[0030] The M histogram circuits transmit the M sets of histogram data to the digital processing circuit. The digital processing circuit transmits the M sets of histogram data to the external device through the interface circuit, and the external device determines the corresponding flight time value based on each histogram data.

[0031] A second aspect of the present invention provides a laser receiving module, including a DTOF sensor as described in any of the preceding claims.

[0032] A third aspect of the present invention provides a ranging device, characterized in that it includes a laser emitting module and a laser receiving module as described above.

[0033] A fourth aspect of this invention provides a ranging method for a DTOF sensor, comprising:

[0034] The clock management circuit outputs M groups of clock signals. Each group of clock signals includes multiple clock signals with the same period and equal phase intervals. The number and / or period of the clock signals in each group are not equal, and M≥2.

[0035] M different resolution TDCs are used to receive a set of corresponding clock signals. Each resolution TDC simultaneously counts the time interval from the photon emission time to the input time of the detected avalanche pulse signal with a corresponding phase interval, and generates a digital code corresponding to the time interval with each phase interval as the smallest measurement time unit.

[0036] M histogram circuits, each with a preset number of storage units, are connected one-to-one to M resolution TDCs. The preset number of storage units are used to count the digital codes corresponding to the preset number of phase intervals and convert them into corresponding histogram data. Each histogram data is processed by a digital processing circuit and transmitted to an interface circuit, and then output to an external device through the interface circuit.

[0037] The relationship between the time unit widths corresponding to individual storage units of the histogram data in each of the histogram circuits is as follows:

[0038] T i / m i =y i+1 *T i+1 / m i+1 ;

[0039] Among them, T i and m i Let T represent the period and the number of equally divided phase clocks of the clock signal corresponding to the i-th resolution TDC, respectively. i+1 m i+1 and y i+1 These represent the period of the clock signal corresponding to the (i+1)th resolution TDC, the number of equally divided phase clocks, and the number of storage units contained in the corresponding histogram circuit, respectively, where i is 1, 2, 3, ..., M-1, and m, n, and y are all greater than 1.

[0040] The beneficial effects of the embodiments of the present invention compared with the prior art are as follows: The above-mentioned DTOF sensor is equipped with multiple time-division multiple control units (TDCs) of different resolutions and multiple histogram circuits. M resolution TDCs work simultaneously, which combines a large ranging range and high time resolution under limited hardware resources. The data output by the TDCs of different time resolutions are processed by different histogram circuits. The M histograms obtained by the M histogram circuits are processed simultaneously and output to the digital processing circuit or external device for processing. The flight time and distance information of the object to be measured can be determined. Only one round of lighting is needed to complete the ranging requirement, which improves the output frame rate of the DTOF sensor. At the same time, the M histograms obtained do not have the problem of mutual overlap, which facilitates the subsequent algorithm to further process and optimize the data, which is conducive to improving the ranging accuracy. Attached Figure Description

[0041] Figure 1 This is a histogram diagram of two-stage illumination for a conventional DTOF sensor.

[0042] Figure 2 A schematic diagram of a first module of the DTOF sensor provided in this embodiment of the invention;

[0043] Figure 3 This is a schematic diagram of a second module of the DTOF sensor provided in an embodiment of the present invention;

[0044] Figure 4 for Figure 3 The diagram shows a histogram of the histogram circuit in the DTOF sensor.

[0045] Figure 5 This is a schematic diagram of a third module of the DTOF sensor provided in an embodiment of the present invention;

[0046] Figure 6 for Figure 5 The diagram shows a histogram of the histogram circuit in the DTOF sensor.

[0047] Figure 7 A schematic diagram of the ranging device provided in an embodiment of the present invention;

[0048] Figure 8 This is a flowchart illustrating the ranging method of the DTOF sensor provided in an embodiment of the present invention. Detailed Implementation

[0049] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present invention and are not intended to limit the present invention.

[0050] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0051] A first aspect of the present invention provides a DTOF sensor 1, such as... Figure 2 As shown, the DTOF sensor 1 includes:

[0052] SPAD pixel and quenching circuit 10: SPAD pixel is used to sense single photons and generate avalanche pulse signal. The quenching circuit removes the SPAD photosensitive pixel from the avalanche state by reducing the voltage applied to the SPAD pixel.

[0053] The clock management circuit 20 is used to output M groups of clock signals. Each group of clock signals includes multiple clock signals with the same period and equal phase interval. The number and period of the clock signals in each group are not equal, and M≥2.

[0054] M different resolution TDCs are connected simultaneously to the SPAD pixel and quenching circuit and the clock management circuit 20. Each resolution TDC is used to receive a set of corresponding clock signals. Each resolution TDC simultaneously counts the time interval from the photon emission time to the input time of the detected avalanche pulse signal with the corresponding phase interval, and generates a digital code corresponding to the time interval with each phase interval as the smallest measurement time unit.

[0055] M histogram circuits 40 are connected one-to-one with M TDCs of different resolutions. Each histogram circuit includes a preset number of storage units. The preset number of storage units are used to count the digital codes corresponding to the preset number of phase intervals and convert them into corresponding histogram data. Each histogram data is processed by digital processing circuit 50 and transmitted to interface circuit 60, and then output to external devices through interface circuit 60.

[0056] The relationship between the time unit widths corresponding to individual storage units of the histogram data in each histogram circuit is as follows:

[0057] T i / m i =y i+1 *T i+1 / m i+1 ;

[0058] Among them, T i and m i Let T represent the period and the number of equally divided phase clocks of the clock signal corresponding to the i-th resolution TDC, respectively. i+1 m i+1 and y i+1 These represent the period of the clock signal corresponding to the (i+1)th resolution TDC, the number of equally divided phase clocks, and the number of storage units contained in the corresponding histogram circuit, respectively, where i is 1, 2, 3, ..., M-1, and m, n, and y are all greater than 1.

[0059] In this embodiment, the corresponding control module drives the laser emitting module 110 and DTOF to work synchronously. The laser emitting module 110 emits laser pulses to the target scene. The light pulses reflected by the target scene are incident on the SPAD photosensitive pixel in Geiger mode, triggering an avalanche current signal. The quenching circuit reduces the voltage applied to the SPAD pixel to make the SPAD photosensitive pixel escape the avalanche state. After the avalanche current signal output by the SPAD passes through the quenching circuit, shaping circuit, etc., it outputs a voltage pulse signal with a fixed pulse width and amplitude to M TDCs with different resolutions.

[0060] Synchronously, the clock management circuit 20 outputs M groups of clock signals. Each group of clock signals includes multiple clock signals with varying numbers and / or periods. For example, the clock period of the first group of clock signals output to the first resolution TDC31 is T1, the number of clocks is m1, and the phase between the m1 clocks is equally divided into T1 / m1 (i.e., the phase interval between adjacent clocks in the m1 clocks is T1 / m1). The clock period of the second group of clock signals output to the second resolution TDC32 is T2, the number of clocks is m2, and so on, until the clock period of the Mth group of clock signals output to the Mth resolution TDC is T. M The number is m M。。。 To clarify: T1 / m1 > T2 / m2 > ... > T M / m M The clock signals corresponding to the number and period of each group of clocks serve as the clock signals of the corresponding resolution TDC. After each resolution TDC receives a voltage pulse signal synchronized with the driving signal of the driving laser emission module 110, it starts to count synchronously and stops counting simultaneously after receiving the avalanche pulse signal output by the SPAD pixel and the quenching circuit 10.

[0061] The time resolutions from the first resolution TDC to the Mth resolution TDC increase sequentially. The magnitude of each time resolution changes inversely with the phase interval of the clock signal. That is, the time resolution of the TDC is determined by the phase interval of the clock signal. The smaller the phase interval, the higher the time resolution of the corresponding TDC. From the first resolution TDC to the Mth resolution TDC, the time resolution increases sequentially. The M different resolution TDCs work synchronously to calculate the time interval from when the photon emits a light pulse from the laser emitting module to when the SPAD pixel detects the avalanche pulse signal. The low time resolution TDC provides a large range and low precision time interval, while the high time resolution TDC provides a small range and high precision time interval, and converts the time interval into digital code.

[0062] The first resolution TDC31 realizes the maximum measurement range of the current flight time, calculates the maximum bit value of the interval time from the emission of photon from laser emission module 110 to the detection of avalanche pulse signal, and converts the interval time into the corresponding digital code, such as binary code, thermometer code, one-thermal code, etc. The digital code is transmitted to the first histogram circuit 41, which includes y1 storage units.

[0063] The second resolution TDC32 realizes the secondary measurement range of the current flight time, calculates the second largest bit value of the interval time from the emission of photon from laser emission module 110 to the detection of avalanche pulse signal, and converts each interval time into a corresponding digital code within the measurement time range of T1 / m1. The digital code is transmitted to the second histogram circuit 42, which includes y2 storage units.

[0064] The M-th resolution TDC achieves the minimum measurement range of the current flight time, calculates the minimum bit value of the interval time from the emission of a photon from the laser emission module 110 to the detection of the avalanche pulse signal, and in T M-1 / m M-1 Within the measurement time range, the interval time is converted into a corresponding digital code, and the digital code is transmitted to the Mth histogram circuit. The Mth histogram circuit includes y M One storage unit.

[0065] The corresponding histogram circuit performs an +1 operation on the storage unit corresponding to the received digital code to complete one photon count. After multiple measurements, the corresponding histogram circuit establishes the corresponding histogram data. After a multi-lighting measurement cycle, M histogram circuits establish histogram data with different time interval widths and transmit them to the signal digital processing circuit 50 and the interface circuit 60, so as to transmit them to the external device through the interface circuit 60 to obtain the final accurate ranging information.

[0066] The interface circuit 60 is used to connect external devices, such as host computers and terminal devices. The corresponding type of interface circuit 60 can be selected according to the corresponding communication protocol. The specific type is not limited. The digital processing circuit 50 can determine the flight time or simply serve as an intermediate transmission unit for transmitting histogram data.

[0067] In this circuit, the sum of the time unit widths in the second histogram circuit 42 is equal to the minimum time unit width in the first histogram circuit 41; the sum of the time unit widths in the third histogram circuit 43 is equal to the minimum time unit width in the second histogram circuit 42; and the sum of the time unit widths in the Mth histogram circuit is equal to the minimum time unit width in the (M-1)th histogram circuit. Simultaneously, the time unit width for each histogram data is T. i / m i The time unit width of each histogram data satisfies T i / m i =y i+1 *T i+1 / m i+1 relation.

[0068] The number of storage units in the first to Mth histogram circuits is determined based on the time resolution and measurement range of the corresponding connected TDCs. The minimum time unit width of the histogram circuit is equal to the time resolution of the connected resolution TDC (which is also the minimum phase interval of the corresponding TDC clock signal), i.e., the time resolution of each resolution TDC is T. i / m i This is equal to the smallest measurement time unit of each histogram data.

[0069] The digital processing circuit 50 can directly determine the flight time based on histogram data or obtain flight time and distance information from an external device. The flight time is:

[0070] [(K1-1)*T1 / m1+(K2-1)*T2 / m2+...+(K M-1 -1)*T M-1 / m M-1 +K M *T M / m M ];

[0071] Among them, K1, K2 to K M These represent the positions of the time intervals corresponding to the maximum count peaks in the histogram data of the first histogram circuit 41 to the Mth histogram circuit, respectively.

[0072] The digital processing circuit 50 or an external device determines the distance of the object within the corresponding measurement range by the position of the time unit width corresponding to the maximum count in the histogram, i.e., the position of the time period corresponding to the maximum peak value. Within this time unit width, the number of photons counted is the highest. For example, if the number of photons counted is the highest in the third time unit width of the first histogram data, then the approximate flight time is 3*T1 / m1. After determining the position of the time unit width of the object under test within the large range, the position of the time unit width of the maximum peak value in the second histogram data is determined as the position of the fourth time unit width. Then the flight time can be further determined as 2*T1 / m1 + 4*T2 / m2, and so on, finally obtaining the total flight time as [2*T1 / m1 + 3*T2 / m2 + ... + (K M-1 -1)*T M-1 / m M-1 +K M *T M / m M ].

[0073] The larger the value of M, the more accurate the flight time calculation. M includes at least two values, and the size of M can be set according to the actual needs of ranging accuracy, ranging range, and circuit design complexity.

[0074] For example, such as Figure 3 and Figure 4 As shown, when M equals 2, the clock management circuit 20 outputs m1 first clock signals and m2 second clock signals, with the period of the first clock signal being T. c The period of the second phase clock signal is T. fm1 first clock signals serve as the clock signals for the first resolution TDC31, which is equivalent to the coarse resolution TDC. m2 second phase clock signals serve as the clock signals for the second resolution TDC32, which is equivalent to the fine resolution TDC. The coarse resolution TDC and the fine resolution TDC start counting synchronously after receiving a voltage pulse signal synchronized with the signal driving the laser emission, and stop counting simultaneously after receiving the avalanche pulse signal output by the SPAD pixel circuit 10 again.

[0075] The coarse-resolution TDC achieves a large measurement range, calculating the approximate time interval between the emission of a photon from the laser emitting module 110 and the detection of the avalanche pulse signal. This time interval is converted into a digital code and transmitted to the first histogram circuit 41, which is equivalent to a coarse histogram circuit containing x storage units. The fine-resolution TDC achieves high-precision time measurement, within the T... c Within the measurement time range of / m1, a digital code is generated and transmitted to the second histogram circuit 42. The second histogram circuit 42 is equivalent to a fine histogram circuit, which contains y storage units.

[0076] The corresponding histogram circuit performs a +1 operation on the storage unit corresponding to the received digital code, completing one photon count. After multiple measurements, the histogram circuit establishes the corresponding histogram data. After a multi-light measurement cycle, the coarse histogram circuit and the fine histogram circuit establish the corresponding coarse histogram data and fine histogram data, respectively. After a multi-light measurement cycle, the coarse histogram and the fine histogram are generated simultaneously. The coarse histogram and the fine histogram are output to the digital processing circuit 50 for processing and then transmitted to the external device through the interface circuit 60 to obtain the final flight time and the distance information of the object under test.

[0077] Figure 3 for Figure 2 The histogram data output at the end of a measurement cycle generates both a coarse and a fine histogram at the end of each illumination round. The horizontal axis (Bin position) of the histogram represents the time period corresponding to the detected photons, and the vertical axis (Peak value) represents the number of photon counts. The left image is the coarse histogram, which contains x coarse bins, namely Coarse_Bin_0 (cb_0) to Coarse_Bin_x-1 (cb_x-1). The time unit width of each coarse bin corresponds to 1 / m1 of one clock cycle of the coarse resolution TDC, i.e., (1 / m1)*T. c This refers to the time resolution of the coarse-resolution TDC, corresponding to a time measurement range of x*T. c / m1.

[0078] The right figure is a fine histogram, which contains m2 fine bins, namely Fine_Bin_0 (fb_0) to Fine_Bin_y-1 (fb_y-1). The time unit width of each fine bin corresponds to 1 / m2 of one clock cycle of the fine resolution TDC, i.e., (1 / m2)*T. f This refers to the time resolution of the fine-resolution TDC, which corresponds to a time measurement range of y*T. f / m2, also known as T c / m1;

[0079] After one round of lighting (e.g., 20,000 lighting sessions), both the coarse resolution TDC and the fine resolution TDC will generate coarse and fine histograms simultaneously.

[0080] The mathematical relationships between Bin values ​​and Peak values ​​in the coarse and fine histograms are as follows:

[0081] The width of each coarse bin in the coarse histogram is equivalent to the sum of the widths of the y-th thin bins in the thin histogram, that is:

[0082] Bin_width(cb_i)=Bin_width(fb_0)+Bin_width(fb_1)+...+Bin_width(fb_y-1), i=1,2,...,m1 (i.e. Bin_width(cb_0)=y*T f / m2, that is, Tc / m1=y*T f / m2);

[0083] The relationship between Peak values ​​in the coarse and fine histograms is as follows:

[0084] Peak(cb_0)+Peak(cb_1)+...+Peak(cb_x-1)=Peak(fb_0)+Peak(fb_1)+...+Peak(fb_y-1);

[0085] After one round of lighting is completed, the coarse and fine histograms are generated simultaneously and output synchronously to the digital processing circuit 50. After processing, they are transmitted to the external device via the interface circuit 60. The digital processing circuit 50 or the external device calculates the coarse bin position corresponding to the largest peak (Peak) in the coarse histogram as cb_k, and the fine bin position corresponding to the largest peak (Peak) in the fine histogram as fb_i. Therefore, the time-of-flight value output by the digital processing circuit 50 or the external device after processing the histogram data for this lighting cycle is:

[0086] TOF = [(k*cb_k) + (i+1)*fb_i]

[0087] Where, cb_k=cb_0=cb_1=...=cb_x-1=(1 / m1)*T c ;

[0088] fb_i=fb_0=fb_1=...=fb_y-1=(1 / m2)*T f ;

[0089] The corresponding test distance is [(k*cb_k)+(i+1)*fb_i]*C / 2.

[0090] The multi-histogram circuit can combine a large ranging range and high time resolution. The test only requires one round of lighting, which does not affect the output frame rate of the DTOF sensor 1. It can also output coarse and fine histograms at the same time, which can facilitate further optimization of the subsequent digital processing circuit 50 and external equipment to improve ranging accuracy.

[0091] And when M=3, such as Figure 5 and Figure 6 As shown, the clock management circuit 20 outputs m1 first clock signals, m2 second clock signals, and m3 clock signals. The period of the first clock signal is T. c The period of the second clock signal is T. m The period of the third clock signal is T. f m1 first clock signals serve as the clock signals for the first resolution TDC31, which is equivalent to the coarse resolution TDC. m2 second clock signals serve as the clock signals for the second resolution TDC32, which is equivalent to the medium resolution TDC. m3 third clock signals serve as the clock signals for the third resolution TDC33, which is equivalent to the fine resolution TDC. (Here, coarse and fine refer to the phase interval of the multi-phase clock signals, and the relationship between the phase intervals is: first clock signal > second clock signal > third clock signal). The coarse resolution TDC, medium resolution TDC, and fine resolution TDC start counting synchronously after receiving the light pulse signal emitted by the laser emitting module 110. They stop counting simultaneously after receiving the avalanche pulse signal output by the SPAD pixel circuit 10.

[0092] The coarse resolution TDC achieves a large ranging range, calculates the approximate time interval between the emission of a photon from the laser emission module 110 and the detection of the avalanche pulse signal, and converts the time interval into a digital code to be transmitted to the coarse histogram circuit, which contains x storage units.

[0093] Medium-resolution TDC achieves ranging with medium time accuracy, in T c Within the measurement time range of / m1, a digital code is generated and transmitted to the middle histogram circuit, which contains z storage units.

[0094] Fine-resolution TDC enables high-time-accuracy ranging, in T m Within a measurement time range of / m2, a digital code is generated and transmitted to a fine histogram circuit, which contains y storage units.

[0095] The corresponding histogram circuit performs a +1 operation on the storage unit corresponding to the received digital code, completing one photon count. After multiple measurements, the histogram circuit establishes the corresponding histogram data. After a multi-light measurement cycle, the coarse histogram circuit, the medium histogram circuit, and the fine histogram circuit establish the corresponding coarse histogram data, medium histogram data, and fine histogram data, respectively. After a measurement cycle, the coarse histogram, medium histogram, and fine histogram are generated simultaneously and output to the digital processing circuit 50 for processing. After processing, the data is transmitted to the external device through the interface circuit 60 to obtain the final flight time and the distance information of the object under test.

[0096] Figure 6 for Figure 5 The histogram output at the end of a measurement cycle generates a coarse, medium, and fine histogram simultaneously during a single illumination cycle. The horizontal axis (Bin position) of the histogram represents the time period corresponding to the detected photons, and the vertical axis (Peak value) represents the number of photon counts. The left image is the coarse histogram, which contains x coarse bins, i.e., Coarse_Bin_0 (cb_0) to Coarse_Bin_x-1 (cb_x-1). The time unit width of each coarse bin corresponds to 1 / m1 of one clock cycle of the coarse resolution TDC, i.e., (1 / m1)*T. c This refers to the time resolution of the coarse-resolution TDC, corresponding to a time measurement range of x*T. c / m1; The middle graph is a histogram containing z middle bins, namely Middle_Bin_0 (mb_0) to Middle_Bin_z-1 (mb_z-1). The time unit width of each middle bin corresponds to 1 / m2 of one clock cycle of the medium resolution TDC, i.e., (1 / m2)*T. m This refers to the time resolution of the medium-resolution TDC, which corresponds to a time measurement range of z*T. m / m2, the right figure is a fine histogram, which contains y fine bins, namely Fine_Bin_0(fb_0) to Fine_Bin_y-1(fb_y-1). The time unit width of each fine bin corresponds to 1 / m3 of one clock cycle of the fine resolution TDC, i.e., (1 / m3)*T. f This refers to the time resolution of the fine-resolution TDC, which corresponds to a time measurement range of y*T. f / m3.

[0097] After one round of lighting is completed, the coarse resolution TDC, medium resolution TDC, and fine resolution TDC will simultaneously generate coarse histograms, medium histograms, and fine histograms.

[0098] The mathematical relationships between Bin values ​​and Peak values ​​in coarse, medium, and fine histograms are as follows:

[0099] The width of each coarse bin in the coarse histogram is equivalent to the sum of the widths of the z middle bins in the medium histogram, and the width of each middle bin in the medium histogram is equivalent to the sum of the widths of the y fine bins in the fine histogram.

[0100] Bin_width(cb_i)=Bin_width(mb_0)+Bin_width(mb_1)+...+

[0101] Bin_width(mb_z-1), i=1,2,...,m2 (i.e. Bin_width(cb_0)=z*T m / m2, that is

[0102] Tc / m1=z*T m / m2);

[0103] Bin_width(mb_j)=Bin_width(fb_0)+Bin_width(fb_1)+...+Bin_width(fb_y-1), i=1,2,...,m3 (i.e. Bin_width(cb_0)=y*T f / m3, i.e., T m / m2=y*T f / m3);

[0104] The relationship between Peak values ​​in the coarse, medium, and fine histograms is as follows:

[0105] Peak(cb_0)+Peak(cb_1)+...+Peak(cb_x-1)=Peak(mb_0)+Peak(mb_1)+...+Peak(mb_z-1)=Peak(fb_0)+Peak(fb_1)+...+Peak(fb_y-1).

[0106] After one round of lighting, the coarse, medium, and fine histograms are generated simultaneously and output to the digital processing circuit 50. The digital processing circuit 50 and the external device calculate, using an algorithm, that the coarse bin position corresponding to the largest peak (Peak) in the coarse histogram is cb_k, the medium bin position corresponding to the largest peak (Peak) in the medium histogram is mb_j, and the fine bin position corresponding to the largest peak (Peak) in the fine histogram is fb_i. Therefore, the flight value output after processing by the digital processing circuit 50 and the external device for this lighting cycle is:

[0107] TOF=[(k*cb_k)+(j*mb_j)+(i+1)*fb_i];

[0108] Where, cb_k=cb_0=cb_1=...=cb_x-1=(1 / m1)*T c ;

[0109] mb_j=mb_0=mb_1=...=mb_z-1=(1 / m2)*T m ;

[0110] fb_i=fb_0=fb_1=...=fb_y-1=(1 / m3)*T f ;

[0111] The corresponding test distance is [(k*cb_k)+(j*mb_j)+(i+1)*fb_i]*C / 2. The multi-histogram circuit can combine a large ranging range and high time resolution. The test only requires one round of lighting, which does not affect the output frame rate of DTOF sensor 1. It also outputs coarse and fine histograms at the same time, which facilitates further optimization of the subsequent digital processing circuit 50 and external equipment to improve the ranging accuracy.

[0112] Of course, the number of resolution TDCs and histogram circuits can also be four or more. The use of different time resolution TDCs in combination is within the scope of protection of this invention, and will not be described in detail hereafter.

[0113] Each histogram circuit performs an +1 operation on the storage unit corresponding to the received digital code, completes one photon count, and establishes the corresponding histogram data after multiple measurements.

[0114] The number of storage cells in a histogram circuit is greater than or equal to j;

[0115] Where, j = T / (T) i / m i ), where T is the time measurement range of the corresponding resolution TDC.

[0116] The number of storage cells in a histogram circuit is determined by the range and phase interval of the corresponding connected TDC. For example, if the phase interval of the TDC is T... i / m i If the measurement range is T, then the minimum number of storage units in the histogram circuit includes T / (T i / m i ).

[0117] Meanwhile, the digital processing circuit 50 can process the histogram data or not. Optionally, M histogram circuits are connected to the digital processing circuit 50, and the digital processing circuit 50 is connected to the interface circuit 60. The interface circuit 60 is used to transmit data to external devices such as a host computer.

[0118] M histogram circuits transmit M sets of histogram data to digital processing circuit 50. Digital processing circuit 50 determines the corresponding flight time value based on each histogram data and transmits it to external devices such as a host computer via interface circuit 60; or

[0119] M histogram circuits transmit M sets of histogram data to digital processing circuit 50. Digital processing circuit 50 does not process the histograms but directly transmits the M sets of histogram data to external devices such as host computers through interface circuit 60, providing sufficient data support for subsequent algorithm optimization.

[0120] The beneficial effects of this invention embodiment compared with the prior art are as follows: The DTOF sensor 1 described above is equipped with multiple time-division multiple control units (TDCs) of different resolutions and multiple histogram circuits. M resolution TDCs work simultaneously, achieving both a large ranging range and high time resolution under limited hardware resources. The data output by the TDCs of different time resolutions are processed by different histogram circuits. The M histograms obtained from the simultaneous processing by the M histogram circuits are output to the digital processing circuit 50 or an external device for processing, which can determine the flight time and the distance information of the object to be measured. Only one round of illumination is needed to complete the ranging requirement, which improves the output frame rate of the DTOF sensor. At the same time, the M histograms obtained do not have the problem of mutual overlap, which facilitates the subsequent algorithm to further process and optimize the data, and is conducive to improving the ranging accuracy.

[0121] like Figure 7 As shown, the present invention also proposes a laser receiving module 120, which includes a DTOF sensor 1. The specific structure of the DTOF sensor 1 is as described in the above embodiments. Since the laser receiving module 120 adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0122] The laser receiving module 120 is positioned opposite to the laser emitting module 110. The laser receiving module 120 receives photons for the corresponding light emission period and generates corresponding histogram data. The laser receiving module 120 directly calculates the corresponding flight time based on the histogram data or outputs the histogram data to an external device, which then determines the flight time and specific distance information.

[0123] The present invention also proposes a ranging device 100, such as... Figure 7 As shown, the ranging device 100 includes a laser emitting module 110 and a laser receiving module 120. The specific structure of the laser receiving module 120 is as described in the above embodiments. Since the ranging device 100 adopts all the technical solutions of all the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be described in detail here.

[0124] Among them, the ranging device 100 can be a camera, webcam, or other device to complete the measurement of distance, depth information, and image information.

[0125] Corresponding to the structure of the DTOF sensor 1 described above, a fourth aspect of this invention proposes a ranging method for the DTOF sensor 1, as follows: Figure 8 As shown, it includes:

[0126] Step S10: The clock management circuit 20 outputs M groups of clock signals, which are multiple clock signals with the same period and equal phase interval. The number and / or period of each group of clock signals are not equal, and M≥2.

[0127] Step S20: Use M different resolution TDCs to receive a set of corresponding clock signals. Each resolution TDC simultaneously counts the time interval from the photon emission time to the input time of the detected avalanche pulse signal with the corresponding phase interval, and generates a digital code corresponding to the time interval with each phase interval as the smallest measurement time unit.

[0128] Step S30: M histogram circuits, each with a preset number of storage units, are connected one-to-one to M resolution TDCs. The preset number of storage units are used to count the digital codes corresponding to the preset number of phase intervals and convert them into corresponding histogram data. Each histogram data is processed by the digital processing circuit 50 and transmitted to the interface circuit 60, and then output to the external device through the interface circuit 60.

[0129] The relationship between the time unit widths corresponding to individual storage units of the histogram data in each histogram circuit is as follows:

[0130] T i / m i =y i+1 *T i+1 / mi+1 ;

[0131] Among them, T i and m i Let T represent the period and the number of equally divided phase clocks of the clock signal corresponding to the i-th resolution TDC, respectively. i+1 m i+1 and y i+1 These represent the period of the clock signal corresponding to the (i+1)th resolution TDC, the number of equally divided phase clocks, and the number of storage units contained in the corresponding histogram circuit, respectively, where i is 1, 2, 3, ..., M-1, and m, n, and y are all greater than 1.

[0132] In this embodiment, the corresponding control module drives the laser emitting module 110 and DTOF to work synchronously. The laser emitting module 110 emits laser pulses to the target scene. The light pulses reflected by the target scene are incident on the SPAD photosensitive pixel in Geiger mode, triggering an avalanche current signal. The quenching circuit reduces the voltage applied to the SPAD pixel to make the SPAD photosensitive pixel escape the avalanche state. After the avalanche current signal output by the SPAD passes through the quenching circuit, shaping circuit, etc., it outputs a voltage pulse signal with a fixed pulse width and amplitude to M TDCs with different resolutions.

[0133] Synchronously, the clock management circuit 20 outputs M groups of clock signals. Each group of clock signals includes multiple clock signals with varying numbers and / or periods. For example, the clock period of the first group of clock signals output to the first resolution TDC31 is T1, the number of clocks is m1, and the phase between the m1 clocks is equally divided into T1 / m1 (i.e., the phase interval between adjacent clocks in the m1 clocks is T1 / m1). The clock period of the second group of clock signals output to the second resolution TDC32 is T2, the number of clocks is m2, and so on, until the clock period of the Mth group of clock signals output to the Mth resolution TDC is T. M The number is m M ...To clarify: T1 / m1 > T2 / m2 > ... > T M / m M The clock signals corresponding to the number and period of each group of clocks serve as the clock signals of the corresponding resolution TDC. After each resolution TDC receives a voltage pulse signal synchronized with the driving signal of the driving laser emission module 110, it starts to count synchronously and stops counting simultaneously after receiving the avalanche pulse signal output by the SPAD pixel and the quenching circuit 10.

[0134] The time resolutions from the first resolution TDC to the Mth resolution TDC increase sequentially. The magnitude of each time resolution changes inversely with the phase interval of the clock signal. That is, the time resolution of the TDC is determined by the phase interval of the clock signal. The smaller the phase interval, the higher the time resolution of the corresponding TDC. From the first resolution TDC to the Mth resolution TDC, the time resolution increases sequentially. The M different resolution TDCs work synchronously to calculate the time interval from when the photon emits a light pulse from the laser emitting module to when the SPAD pixel detects the avalanche pulse signal. The low time resolution TDC provides a large range and low precision time interval, while the high time resolution TDC provides a small range and high precision time interval, and converts the time interval into digital code.

[0135] The first resolution TDC31 realizes the maximum measurement range of the current flight time, calculates the maximum bit value of the interval time from the emission of photon from laser emission module 110 to the detection of avalanche pulse signal, and converts the interval time into the corresponding digital code, such as binary code, thermometer code, one-thermal code, etc. The digital code is transmitted to the first histogram circuit 41, which includes y1 storage units.

[0136] The second resolution TDC32 realizes the secondary measurement range of the current flight time, calculates the second largest bit value of the interval time from the emission of photon from laser emission module 110 to the detection of avalanche pulse signal, and converts each interval time into a corresponding digital code within the measurement time range of T1 / m1. The digital code is transmitted to the second histogram circuit 42, which includes y2 storage units.

[0137] The M-th resolution TDC achieves the minimum measurement range of the current flight time, calculates the minimum bit value of the interval time from the emission of a photon from the laser emission module 110 to the detection of the avalanche pulse signal, and in T M-1 / m M-1 Within the measurement time range, the interval time is converted into a corresponding digital code, and the digital code is transmitted to the Mth histogram circuit. The Mth histogram circuit includes y M One storage unit.

[0138] The corresponding histogram circuit performs an +1 operation on the storage unit corresponding to the received digital code to complete one photon count. After multiple measurements, the corresponding histogram circuit establishes the corresponding histogram data. After a multi-lighting measurement cycle, M histogram circuits establish histogram data with different time interval widths and transmit them to the signal digital processing circuit 50 and the interface circuit 60, so as to transmit them to the external device through the interface circuit 60 to obtain the final accurate ranging information.

[0139] In this circuit, the sum of the time unit widths in the second histogram circuit 42 is equal to the minimum time unit width in the first histogram circuit 41; the sum of the time unit widths in the third histogram circuit 43 is equal to the minimum time unit width in the second histogram circuit 42; and the sum of the time unit widths in the Mth histogram circuit is equal to the minimum time unit width in the (M-1)th histogram circuit. Simultaneously, the time unit width for each histogram data is T. i / m i The time unit width of each histogram data satisfies T i / m i =y i+1 *T i+1 / m i+1 relation.

[0140] The number of storage units in the first to Mth histogram circuits is determined based on the time resolution and measurement range of the corresponding connected TDCs. The minimum time unit width of the histogram circuit is equal to the time resolution of the connected resolution TDC (which is also the minimum phase interval of the corresponding TDC clock signal), i.e., the time resolution of each resolution TDC is T. i / m i This is equal to the smallest measurement time unit of each histogram data.

[0141] The digital processing circuit 50 can directly determine the flight time based on histogram data or obtain flight time and distance information from an external device. The flight time is:

[0142] [(K1-1)*T1 / m1+(K2-1)*T2 / m2+...+(K M-1 -1)*T M-1 / m M-1 +K M *T M / m M ];

[0143] Among them, K1, K2 to K M These represent the positions of the time intervals corresponding to the maximum count peaks in the histogram data of the first histogram circuit 41 to the Mth histogram circuit, respectively.

[0144] The digital processing circuit 50 or an external device determines the distance of the object within the corresponding measurement range by the position of the time unit width corresponding to the maximum count in the histogram, i.e., the position of the time period corresponding to the maximum peak value. Within this time unit width, the number of photons counted is the highest. For example, if the number of photons counted is the highest in the third time unit width of the first histogram data, then the approximate flight time is 3*T1 / m1. After determining the position of the time unit width of the object under test within the large range, the position of the time unit width of the maximum peak value in the second histogram data is determined as the position of the fourth time unit width. Then the flight time can be further determined as 2*T1 / m1 + 4*T2 / m2, and so on, finally obtaining the total flight time as [2*T1 / m1 + 3*T2 / m2 + ... + (K M-1 -1)*T M-1 / m M-1 +K M *T M / m M ].

[0145] The larger the value of M, the more accurate the flight time calculation. M includes at least two values, and the size of M can be set according to the actual needs of ranging accuracy, ranging range, and circuit design complexity.

[0146] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A DTOF sensor, characterized by, include: SPAD pixels and quenching circuits: the SPAD pixels are used to sense single photons and generate avalanche pulse signals, and the quenching circuits reduce the voltage applied to the SPAD pixels to remove the SPAD photosensitive pixels from the avalanche state. A clock management circuit is used to output M groups of clock signals. Each group of clock signals includes multiple clock signals with the same period and equal phase intervals. The number and / or period of the clock signals in each group are not equal, and M≥2. M different resolution TDCs are connected simultaneously to the SPAD pixel and quenching circuit and the clock management circuit, respectively. Each resolution TDC is used to receive a set of corresponding clock signals. Each resolution TDC simultaneously counts the time interval from the photon emission time to the detection of the avalanche pulse signal input time with corresponding phase intervals, and generates a digital code corresponding to the time interval with each phase interval as the smallest measurement time unit. M histogram circuits are connected one-to-one with M TDCs of different resolutions. Each histogram circuit includes a preset number of storage units. The preset number of storage units are used to count the digital codes corresponding to the preset number of phase intervals and convert them into corresponding histogram data. Each histogram data is processed by a digital processing circuit and transmitted to an interface circuit, and then output to an external device through the interface circuit. The relationship between the time unit widths corresponding to individual storage units of the histogram data in each of the histogram circuits is as follows: T i / m i =y i+1 *T i+1 / m i+1 ; Among them, T i and m i Let T represent the period and the number of equally divided phase clocks of the clock signal corresponding to the i-th resolution TDC, respectively. i+1 m i+1 and y i+1 These represent the period of the clock signal corresponding to the (i+1)th resolution TDC, the number of equally divided phase clocks, and the number of storage units contained in the corresponding histogram circuit, respectively, where i is 1, 2, 3, ..., M-1, and m, n, and y are all greater than 1.

2. The DTOF sensor of claim 1, wherein, The time resolutions from the first resolution TDC to the Mth resolution TDC increase sequentially, and the magnitude of each time resolution changes inversely with the phase interval of the clock signal. M TDCs of different resolutions work synchronously to calculate the time interval between the light pulse emitted by the photon from the laser emitting module and the avalanche pulse signal detected by the SPAD pixel, and convert the time interval detected by each of them into digital code.

3. The DTOF sensor as described in claim 1, characterized in that, The total number of counts for the histogram data in each of the aforementioned histogram circuits is equal.

4. The DTOF sensor as described in claim 1, characterized in that, The distance information of the object to be measured is: L=C*[(K1-1)*T1 / m1+(K2-1)*T2 / m2+...+(K M-1 -1)*T M-1 / m M-1 +K M *T M / m M ] / 2; Where C represents the speed of light, K1, K2 to K M These represent the positions of the phase intervals corresponding to the maximum count peaks in the histogram data of the first to the Mth histogram circuits, respectively.

5. The DTOF sensor as described in claim 1, characterized in that, The minimum measurement time unit for each of the histogram circuits is: P = T i / m i .

6. The DTOF sensor of claim 1, wherein, Each of the histogram circuits performs an +1 operation on the storage unit corresponding to the received digital code, completes one photon count, and establishes the corresponding histogram data after multiple measurements. The number of storage cells corresponding to the histogram circuit is greater than or equal to j; Where, j = T / (T) i / m i ), where T is the time measurement range corresponding to the resolution TDC.

7. The DTOF sensor as described in claim 1, characterized in that, M histogram circuits transmit M sets of histogram data to a digital processing circuit. The digital processing circuit determines the corresponding flight time value based on each histogram data and transmits it to an external device via the interface circuit; or The M histogram circuits transmit the M sets of histogram data to the digital processing circuit. The digital processing circuit transmits the M sets of histogram data to the external device through the interface circuit, and the external device determines the corresponding flight time value based on each histogram data.

8. A laser receiving module, characterized in that, Including the DTOF sensor as described in any one of claims 1 to 7.

9. A ranging device, characterized by It includes a laser emitting module and a laser receiving module as described in claim 8.

10. A ranging method using a DTOF sensor, characterized in that, include: The clock management circuit outputs M groups of clock signals. Each group of clock signals includes multiple clock signals with the same period and equal phase intervals. The number and / or period of the clock signals in each group are not equal, and M≥2. M different resolution TDCs are used to receive a set of corresponding clock signals. Each resolution TDC simultaneously counts the time interval from the photon emission time to the input time of the detected avalanche pulse signal with a corresponding phase interval, and generates a digital code corresponding to the time interval with each phase interval as the smallest measurement time unit. M histogram circuits, each with a preset number of storage units, are connected one-to-one to M resolution TDCs. The preset number of storage units are used to count the digital codes corresponding to the preset number of phase intervals and convert them into corresponding histogram data. Each histogram data is processed by a digital processing circuit and transmitted to an interface circuit, and then output to an external device through the interface circuit. The relationship between the time unit widths corresponding to individual storage units of the histogram data in each of the histogram circuits is as follows: T i / m i =y i+1 *T i+1 / m i+1 ; Among them, T i and m i Let T represent the period and the number of equally divided phase clocks of the clock signal corresponding to the i-th resolution TDC, respectively. i+1 m i+1 and y i+1 These represent the period of the clock signal corresponding to the (i+1)th resolution TDC, the number of equally divided phase clocks, and the number of storage units contained in the corresponding histogram circuit, respectively, where i is 1, 2, 3, ..., M-1, and m, n, and y are all greater than 1.

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