CN117434521A - DTOF sensor, ranging method, laser receiving module and ranging device - Google Patents

Abstract

The invention provides a DTOF sensor, a ranging method, a laser receiving module and a ranging device, wherein the DTOF sensor comprises an SPAD pixel and quenching circuit, a clock management circuit, M TDCs with different resolutions, M histogram circuits, a digital processing circuit and an interface circuit, the M TDCs with different resolutions work simultaneously, under the condition of limited hardware, the DTOF sensor has a large ranging range and high time resolution, data output by the TDCs with different resolutions are respectively processed by the different histogram circuits, M histograms obtained by the simultaneous processing of the M histogram circuits are output to the digital processing circuit or an external device for processing, the distance information of flight time and an object to be measured is determined, the ranging requirement can be completed by only one round of polishing, the output frame rate of the DTOF sensor is improved, meanwhile, the obtained M histograms have no problem of mutual coverage, the further processing and optimization of data are convenient for a subsequent algorithm, and the ranging accuracy is favorable for improving.

Description

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

Technical Field

The invention belongs to the technical field of sensors, and particularly relates to a DTOF sensor, a ranging method, a laser receiving module and a ranging device.

Background

The direct time of flight sensor (dtofs, direct time of flight) technology is considered as one of the most excellent sensor technologies at present, which has led to a trend of loading 3D cameras in various mobile devices, and with the development of the internet of things technology and the semiconductor technology, the application fields thereof will continue to be expanded, and in addition, corresponding researches for improving the performance thereof are also being conducted.

The DTOF sensor mainly comprises a SPAD pixel array, a quenching circuit, a clock management circuit, a TDC (time to digital converter) and a histogram circuit (comprising a plurality of memory cells).

Many ranging scenarios require that the TDC has the characteristics of ranging over a wide range and high time resolution, and when the TDC has both the characteristics, circuit modules in hardware implementation, such as clock management circuits and histogram circuits, are often added.

Conventional DTOF sensors typically contain a coarse resolution TDC and a fine resolution TDC, with the different resolution TDCs sharing a histogram circuit.

During distance measurement, a coarse histogram with coarse time resolution is generated by a coarse resolution TDC and histogram circuit through a certain number of times of polishing, and the rough distance of an object in a larger range can be determined through the coarse phase position corresponding to the maximum count of the histogram, as shown in FIG. 1, the count value corresponding to cb_k shown in 11 is the largest, namely corresponding to (k+1) T _c The approximate distance of the object to be measured is (k+1) T when the number of photons counted in the m time period is the maximum _c M is C/2, wherein T _c The period of the clock signal received by the coarse resolution TDC is represented, and m is the number of divided phase clock signals received by the coarse resolution TDC.

After determining the coarse time interval position of the object to be measured in a wide range, generating a fine histogram with a fine time resolution in a time range corresponding to the coarse phase through a fine resolution TDC and a histogram circuit by a certain number of times of polishing and through control of circuit time sequence, and determining a measurement distance with higher small range precision as shown in 12, wherein the counting value corresponding to fb_i is the largest as shown in 12, namely (i+1) T is the largest _f Time/nThe number of photons counted by the segment is the largest, and 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 divided phase clock signals received by the fine resolution TDC.

Determining the distance information of an object to be detected as [ (k x T) through two rounds of polishing _c /m+(i+1)*T _f /n)]* C/2; the first round of polishing generates a large range of contribution of a coarse histogram and a rough distance of an object, the second round of polishing generates a fine histogram contribution with high time resolution according to the position of a coarse phase corresponding to a calculated value in the coarse histogram of a measured distance determined by the first round of polishing, and the two rounds of polishing usually cover the coarse histogram generated by the first round of polishing because the two resolution TDCs share one histogram circuit, so that the coarse histogram and the fine histogram cannot be simultaneously acquired, the further processing and optimization of data by a subsequent algorithm are not facilitated, the ranging accuracy is low, and meanwhile, the frame rate of a DTOF sensor is reduced to a certain extent by the two rounds of polishing.

Disclosure of Invention

The invention aims to provide a DTOF sensor, which aims to solve the problems of low frame rate and low ranging accuracy of the traditional DTOF sensor.

An aspect of an embodiment of the present invention proposes a DTOF sensor, including:

the SPAD pixel is used for sensing single photons and generating an avalanche pulse signal, and the quenching circuit enables the SPAD photosensitive pixel to be separated from an avalanche state by reducing the voltage loaded on the SPAD pixel;

the clock management circuit is used for outputting M groups of clock signals, each group of clock signals comprises a plurality of clock signals with the same period and equal phase intervals, the number and/or the period of the clock signals of each group are unequal, and M is more than or equal to 2;

m different resolution TDCs respectively connected to the SPAD pixels, the quenching circuit and the clock management circuit simultaneously, each resolution TDC being configured to receive a set of corresponding clock signals, count time intervals from photon emission time to input time when the avalanche pulse signal is detected at corresponding phase intervals, and generate digital codes corresponding to time intervals each phase interval being a minimum measurement time unit;

The system comprises M histogram circuits which are respectively connected with M TDCs with different resolutions one by one, wherein each histogram circuit comprises a preset number of storage units, the preset number of storage units are used for respectively counting digital codes corresponding to the preset number of phase intervals and converting the digital codes into corresponding histogram data, and each histogram data is processed by a digital processing circuit, transmitted to an interface circuit and output to external equipment through the interface circuit;

the relationship between the widths of the time units corresponding to the single storage unit of the histogram data of each histogram circuit is as follows:

T _i /m _i ＝y _i+1 *T _i+1 /m _i+1 ；

wherein T is _i And m _i Respectively representing the period and the number of the equally divided phase clocks of the clock signal corresponding to the ith resolution TDC, T _i+1 、m _i+1 And y _i+1 The i is 1,2,3, and M-1, M, n, y are greater than 1, respectively representing the period of the clock signal corresponding to the i+1th resolution TDC, the number of aliquoting phase clocks, and the number of memory cells included in the corresponding histogram circuit.

Optionally, the time resolutions of the first resolution TDC to the mth resolution TDC become larger in sequence, and the magnitude of each time resolution changes in inverse correlation with the phase interval of the clock signal;

the M TDCs with different resolutions work synchronously, the time interval from the emission of light pulse by the laser emission module to the detection of avalanche pulse signal by the SPAD pixel is calculated, and the time interval detected by each photon is converted into digital code.

Optionally, the total count number of the histogram data of each of the histogram circuits is equal.

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

L＝C*[(K ₁ -1)*T ₁ /m ₁ +(K ₂ -1)*T ₂ /m ₂ +...+(K _M-1 -1)*T _M-1 /m _M-1 +K _M *T _M /m _M ]/2；

wherein C represents the speed of light, K ₁ 、K ₂ To K _M The positions of the phase intervals corresponding to the maximum count peaks in the histogram data of the first histogram circuit to the mth histogram circuit are respectively represented.

Optionally, the minimum measurement time unit of each histogram circuit is:

P＝T _i /m _i 。

optionally, each histogram circuit performs +1 operation on a storage unit corresponding to the received digital code mapping, completes one photon counting, and establishes corresponding histogram data after multiple measurements;

the number of the storage units corresponding to the histogram circuit is greater than or equal to j;

where j=t/(T) _i /m _i ) T is the time measurement range corresponding to the resolution TDC.

Optionally, the M histogram circuits transmit M sets of histogram data to a digital processing circuit, and the digital processing circuit determines a corresponding time-of-flight value according to each histogram data and transmits the time-of-flight value to an external device through the interface circuit; or alternatively

The M histogram circuits transmit M groups of histogram data to the digital processing circuit, the digital processing circuit transmits the M groups of histogram data to the external device through the interface circuit, and the external device determines corresponding flight time values according to the histogram data.

A second aspect of an embodiment of the present invention proposes a laser receiving module comprising a DTOF sensor as defined in any one of the preceding claims.

A third aspect of an embodiment of the present invention provides a ranging apparatus, which is characterized by comprising a laser emitting module and a laser receiving module as described above.

A fourth aspect of the embodiment of the present invention provides a ranging method of a DTOF sensor, including:

m groups of clock signals are output by adopting a clock management circuit, each group of clock signals comprises a plurality of clock signals with the same period and equal phase intervals, the number and/or the period of the clock signals of each group are unequal, and M is more than or equal to 2;

adopting M TDCs with different resolutions for receiving and respectively receiving a group of corresponding clock signals, counting the time interval from the photon emission time to the input time of the detected avalanche pulse signal at the corresponding phase interval by each resolution TDC, and respectively generating digital codes corresponding to the time interval taking each phase interval as the minimum measurement time unit;

m histogram circuits respectively provided with a preset number of storage units are connected with M resolution TDCs one by one, the preset number of storage units are used for respectively counting digital codes corresponding to a preset number of phase intervals and converting the digital codes into corresponding histogram data, and each histogram data is processed by a digital processing circuit, transmitted to an interface circuit and output to external equipment through the interface circuit;

The relationship between the widths of the time units corresponding to the single storage unit of the histogram data of each histogram circuit is as follows:

T _i /m _i ＝y _i+1 *T _i+1 /m _i+1 ；

wherein T is _i And m _i Respectively representing the period and the number of the equally divided phase clocks of the clock signal corresponding to the ith resolution TDC, T _i+1 、m _i+1 And y _i+1 The i is 1,2,3, and M-1, M, n, y are greater than 1, respectively representing the period of the clock signal corresponding to the i+1th resolution TDC, the number of aliquoting phase clocks, and the number of memory cells included in the corresponding histogram circuit.

Compared with the prior art, the embodiment of the invention has the beneficial effects that: the DTOF sensor is provided with a plurality of TDCs with different resolutions and a plurality of histogram circuits, the TDCs with the M resolutions work simultaneously, the DTOF sensor has a large ranging range and high time resolution under the condition of limited hardware resources, data output by the TDCs with the different time resolutions are respectively processed by the different histogram circuits, M histograms obtained by the simultaneous processing of the M histogram circuits are output to a digital processing circuit or external equipment for processing, the flight time and the distance information of an object to be measured can be determined, the ranging requirement can be finished only by polishing one round, the output frame rate of the DTOF sensor is improved, meanwhile, the obtained M histograms have no problem of mutual coverage, the further processing and optimization of the data are convenient for a subsequent algorithm, and the ranging accuracy is improved.

Drawings

FIG. 1 is a schematic diagram of a histogram of two-pass lighting of a conventional DTOF sensor;

FIG. 2 is a schematic diagram of a first module of a DTOF sensor according to an embodiment of the invention;

FIG. 3 is a schematic diagram of a second module of a DTOF sensor according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a histogram circuit in the DTOF sensor shown in FIG. 3;

FIG. 5 is a schematic diagram of a third module of a DTOF sensor according to an embodiment of the present invention;

FIG. 6 is a histogram schematic of a histogram circuit in the DTOF sensor shown in FIG. 5;

fig. 7 is a schematic block diagram of a ranging apparatus according to an embodiment of the present invention;

fig. 8 is a flowchart of a ranging method of a DTOF sensor according to an embodiment of the present invention.

Detailed Description

In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

A first aspect of an embodiment of the present invention proposes a DTOF sensor 1, as shown in fig. 2, the DTOF sensor 1 comprising:

the SPAD pixel and quenching circuit 10 is used for sensing single photons and generating an avalanche pulse signal, and the quenching circuit enables the SPAD photosensitive pixel to be separated from an avalanche state by reducing the voltage loaded on the SPAD pixel;

the clock management circuit 20 is configured to output M groups of clock signals, where each group of clock signals includes a plurality of clock signals with the same period and an equal phase interval, and the number and period of the clock signals in each group are not equal, where M is greater than or equal to 2;

m different resolution TDCs respectively connected to the SPAD pixels and the quenching circuit and the clock management circuit 20 simultaneously, each resolution TDC being configured to receive a set of corresponding clock signals, count time intervals from a photon emission time to an input time when an avalanche pulse signal is detected at corresponding phase intervals, and respectively generate digital codes corresponding to time intervals each phase interval being a minimum measurement time unit;

m histogram circuits 40 connected with the M TDCs with different resolutions one by one respectively, wherein each histogram circuit comprises a preset number of storage units, the preset number of storage units are used for respectively counting digital codes corresponding to the preset number of phase intervals and converting the digital codes into corresponding histogram data, and each histogram data is processed by the digital processing circuit 50, transmitted to the interface circuit 60 and output to external equipment through the interface circuit 60;

The relationship between the widths of the time units corresponding to the single storage unit of the histogram data of each histogram circuit is as follows:

T _i /m _i ＝y _i+1 *T _i+1 /m _i+1 ；

wherein T is _i And m _i Respectively representing the period and the number of the equally divided phase clocks of the clock signal corresponding to the ith resolution TDC, T _i+1 、m _i+1 And y _i+1 The i is 1,2,3, and M-1, M, n, y are greater than 1, respectively representing the period of the clock signal corresponding to the i+1th resolution TDC, the number of aliquoting phase clocks, and the number of memory cells included in the corresponding histogram circuit.

In this embodiment, the corresponding control module drives the laser emitting module 110 and the DTOF to operate synchronously, the laser emitting module 110 emits laser pulses to a target scene, the light pulses reflected by the target scene are incident on the SPAD photosensitive pixels in the cover mode, avalanche current signals are induced, the quenching circuit reduces the voltage loaded on the SPAD pixels to enable the SPAD photosensitive pixels to deviate from an avalanche state, and after the avalanche current signals output by the SPAD pass through the quenching circuit, the shaping circuit and the like, voltage pulse signals with fixed pulse width and amplitude are output to M TDCs with different resolutions.

In synchronization, the clock management circuit 20 outputs M groups of clock signals, each group of clock signals including a plurality of clock signals having unequal numbers of clocks and/or periods, e.g., the clock period of the first group of clock signals output to the first resolution TDC31 is T ₁ The number of clocks is m ₁ ，m ₁ The phase between the clocks is equally divided into T ₁ /m ₁ (i.e. m) ₁ The phase interval between adjacent clocks in each clock is T ₁ /m ₁ ) The clock period of the second set of clock signals output to the second resolution TDC32 is T ₂ The number is m ₂ ,. the clock period of the M group clock signal output to the M resolution TDC is T _M The number is m _M。。。 The description is as follows: t (T) ₁ /m ₁ ＞T ₂ /m ₂ ＞....＞T _M /m _M Each group of clock signals corresponding to the number of clocks and the period is used as clock signals corresponding to the resolution TDCs, each resolution TDC starts to count synchronously after receiving a voltage pulse signal synchronous with a driving signal driving the laser emitting module 110, and stops counting simultaneously after receiving the SPAD pixel and the avalanche pulse signal output by the quenching circuit 10 synchronously again.

The time resolutions of the first resolution TDC to the Mth resolution TDC become larger in sequence, the time resolution of each time resolution is inversely related to the phase interval of the clock signal, namely, the time resolution of the TDC is determined by the phase interval of the clock signal, the smaller the phase interval is, the higher the time resolution of the corresponding TDC is, the time resolutions of the TDC are sequentially improved from the first resolution TDC to the Mth resolution TDC, M different resolution TDCs synchronously work, the time interval from the time of emitting light pulses of a laser emitting module to the time of detecting avalanche pulse signals of SPAD pixels by photons is calculated, the time interval with a large range and a low precision is provided by the low time resolution TDC, the time interval with a small range and a high precision is provided by the high time resolution TDC, and the time interval is converted into a digital code.

The first resolution TDC31 realizes the maximum measurement range of the current flight time, calculates the maximum bit number of the interval time from the emission of the photon from the laser emitting module 110 to the detection of the avalanche pulse signal, and converts the interval time into corresponding digital codes, such as binary codes, thermometer codes, single thermal codes, etc., which are transmitted to the first histogram circuit 41, wherein the first histogram circuit 41 comprises y ₁ And a memory cell.

The second resolution TDC32 achieves a sub-measurement range of the current time of flight, calculates a second largest value of the interval time from when photons are emitted from the laser emitting module 110 to when avalanche pulse signals are detected, at T ₁ /m ₁ Converts each interval time into a corresponding digital code, and the digital code is transmitted to the second histogram circuit 42, wherein the second histogram circuit 42 includes y ₂ And a memory cell.

The Mth 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 photons from the laser emission module 110 to the detection of the avalanche pulse signal, and calculates the minimum bit value of the interval time from the emission of photons to the detection of the avalanche pulse signal at T _M-1 /m _M-1 In the measurement time range of (2), converting the interval time into corresponding digital code, and transmitting the digital code to an Mth histogram circuit, wherein the Mth histogram circuit comprises y _M And a memory cell.

And the corresponding histogram circuit performs +1 operation on the storage unit corresponding to the received digital code mapping to finish photon counting, establishes corresponding histogram data through the corresponding histogram circuit after multiple measurements, establishes histogram data with different time interval widths respectively after one multiple light-emitting measurement period is finished, and transmits the histogram data to the signal digital processing circuit 50 and the interface circuit 60 to be transmitted to external equipment through the interface circuit 60, so that final accurate ranging information is obtained.

The interface circuit 60 is used for connecting with external devices, such as an upper computer, a terminal device, etc., the corresponding type of interface circuit 60 can be selected according to the corresponding communication protocol, the specific type is not limited, and the digital processing circuit 50 can determine the flight time or be used as an intermediate transmission unit only for transmitting the histogram data.

Wherein the sum of the time cell widths counted in the second histogram circuit 42 is equal to the minimum time cell width in the first histogram circuit 41, the sum of the time cell widths in the third histogram circuit 43 is equal to the minimum time cell width in the second histogram circuit 42, the sum of the time cell widths in the Mth histogram circuit is equal to the minimum time cell width in the Mth-1 histogram circuit, and at the same time, the time cell width of each histogram data is T _i /m _i The time cell width of each histogram data satisfies T _i /m _i ＝y _i+1 *T _i+1 /m _i+1 Relationship.

Wherein the number of memory cells in the first to M-th histogram circuits 41 to 41 is specifically determined according to the time resolution and measurement range in the corresponding connected TDCs, and wherein the minimum time cell width of the histogram circuit is equal to the time resolution of the connected resolution TDCs (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 I.e. the smallest unit of measurement time equal to each histogram data.

The digital processing circuit 50 may determine the time of flight directly from the histogram data or determine the time of flight and distance information from an external device, where the time of flight is:

[(K ₁ -1)*T ₁ /m ₁ +(K ₂ -1)*T ₂ /m ₂ +...+(K _M-1 -1)*T _M-1 /m _M-1 +K _M *T _M /m _M ]；

wherein K is ₁ 、K ₂ To K _M Respectively representing the correspondence of the maximum count peak in the histogram data of the first to mth histogram circuits 41 to 41The position of the time interval.

The digital processing circuit 50 or the external device determines the distance of the object in the corresponding measuring range by the position of the time cell width corresponding to the maximum count of the histogram, i.e. the position of the time period corresponding to the maximum peak, in which the number of counted photons is the largest, e.g. the number of photons counted in the third time cell width of the first histogram data is the largest, the coarse time of flight of the time of flight is 3*T ₁ /m ₁ After determining the time unit width position of the object to be measured in a wide range, determining the time unit width position of the maximum peak value in the second histogram data as the 4 th time unit width position, the flight time may be further determined as 2*T ₁ /m ₁ +4*T ₂ /m ₂ And so on, finally obtaining the total duration of the flight time of [2*T ] ₁ /m ₁ +3*T ₂ /m ₂ +...+(K _M-1 -1)*T _M-1 /m _M-1 +K _M *T _M /m _M ]。

The larger the value of M, the more accurate the flight time measurement and calculation, M comprises at least two, and the size of M can be specifically set according to the ranging accuracy, the ranging range and the circuit design complexity of actual requirements.

For example, as shown in FIGS. 3 and 4, when M is equal to 2, clock management circuit 20 outputs M ₁ First clock signals and m ₂ A second clock signal with period T _c The period of the second phase clock signal is T _f ，m ₁ The first clock signal is used as the clock signal of the first resolution TDC31, the first resolution TDC31 is equivalent to the coarse resolution TDC, m ₂ The second phase clock signal is used as a clock signal of the second resolution TDC32, the second resolution TDC32 is equivalent to the fine resolution TDC, and the coarse resolution TDC and the fine resolution TDC synchronously start counting after receiving a voltage pulse signal synchronized with the signal transmitted by the driving laser, and synchronously stop counting after synchronously receiving the avalanche pulse signal outputted by the SPAD pixel circuit 10 again.

Coarse resolution TDC (time-resolved digital to analog) realizes large measurement range, and photon emission from laser is calculatedThe emission module 110 emits a time interval when the avalanche pulse signal is detected, converts the time interval into a digital code, and transmits the digital code to the first histogram circuit 41, wherein the first histogram circuit 41 is equivalent to a coarse histogram circuit, and the coarse histogram circuit comprises x storage units; fine resolution TDC to achieve high time accuracy measurements at T _c /m ₁ In the measurement time range of (2), a digital code is generated and transmitted to the second histogram circuit 42, and the second histogram circuit 42 is equivalent to a fine histogram circuit, which contains y memory cells.

The corresponding histogram circuit executes +1 operation on a storage unit corresponding to the received digital code mapping to finish photon counting once, and corresponding histogram data is established in the histogram circuit after multiple times of measurement; after the end of a multiple polishing measurement period, the coarse histogram circuit and the fine histogram circuit respectively establish corresponding coarse histogram data and fine histogram data; after the multiple polishing measurement period is finished, a coarse histogram and a fine histogram are generated simultaneously, and the coarse histogram and the fine histogram are output to the digital processing circuit 50 for processing and then transmitted to external equipment through the interface circuit 60, so that the final flight time and the distance information of the object to be measured are obtained.

FIG. 3 is a graph of histogram data output at the end of the measurement period of FIG. 2, a round of lighting is completed while generating a Coarse histogram and a fine histogram, the position of the Bin on the abscissa of the histogram represents the period corresponding to the detected photon, the value of the Peak on the ordinate of the histogram represents the count number of photons, and the left graph is a Coarse histogram containing x Coarse bins, i.e., coarse_Bin_0 (cb_0) through Coarse_Bin_x-1 (cb_x-1), each of which corresponds to 1/m of one clock period of Coarse resolution TDC in terms of time cell width ₁ Namely (1/m) ₁ )*T _c That is, the time resolution of the coarse resolution TDC is x T _c /m ₁ 。

The right plot is a thin histogram comprising m ₂ Fine Bin, i.e. fine_bin_0 (fb_0) to fine_bin_y-1 (fb_y-1), each of which has a time cell width corresponding to 1/m of one clock cycle of Fine resolution TDC ₂ Namely (1/m) ₂ )*T _f That is, the time resolution of the fine resolution TDC is the time measurement range of y×T _f /m ₂ Also is T _c /m ₁ ；

The coarse resolution TDC and the fine resolution TDC generate a coarse histogram and a fine histogram at the same time when one round of polishing is finished (e.g., 20K times of polishing).

For the coarse and fine histograms, the mathematical relationship between Bin and Peak values is as follows:

The time cell width of each coarse Bin in the coarse histogram corresponds to the sum of the time cell widths of y fine bins in the fine histogram, namely:

Bin_width(cb_i)＝Bin_width(fb_0)+Bin_width(fb_1)+...+Bin_width(fb_y-1)，i＝1,2,...,m ₁ (i.e. bin_width (cb_0) =y×t) _f /m ₂ I.e. Tc/m ₁ ＝y*T _f /m ₂ )；

The relationship between Peak values in the coarse and fine histograms is:

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

after finishing the polishing of one round, synchronously outputting the rough histogram and the fine histogram to the digital processing circuit 50 for processing, then transmitting the rough histogram and the fine histogram to the external device through the interface circuit 60, calculating by the digital processing circuit 50 or the external device through an algorithm to obtain a rough Bin position corresponding to the maximum Peak in the rough histogram as cb_k, and a fine Bin position corresponding to the maximum Peak in the fine histogram as fb_i, wherein the flight time value output by the histogram data of the polishing cycle of the round after the processing by the digital processing circuit 50 or the external device is as follows:

TOF＝[(k*cb_k)+(i+1)*fb_i]

wherein cb_k=cb_0=cb_1= ₁ )*T _c ；

fb_i＝fb_0＝fb_1＝...＝fb_y-1＝(1/m ₂ )*T _f ；

The corresponding test distance is [ (k×cb_k) + (i+1) ×fb_i ] ×c/2.

The multiple histogram circuit can have a large ranging range and high time resolution, only one round of polishing is needed for testing, the output frame rate of the DTOF sensor 1 is not affected, and coarse and fine histograms are output at the same time, so that further optimization of the subsequent digital processing circuit 50 and external equipment is facilitated, and the ranging accuracy is improved.

And when m=3, as shown in fig. 5 and 6, the clock management circuit 20 outputs M ₁ First clock signal, m ₂ Second clock signal m ₃ A clock signal of period T _c The period of the second clock signal is T _m The period of the third clock signal is T _f ，m ₁ The first clock signal is used as the clock signal of the first resolution TDC31, the first resolution TDC31 is equivalent to the coarse resolution TDC, m ₂ The second clock signal is used as the clock signal of the second resolution TDC32, the second resolution TDC32 is equivalent to the middle resolution TDC, m ₃ The third clock signal is used as the clock signal of the third resolution TDC33, the third resolution TDC33 is equivalent to the fine resolution TDC, (the thickness is the phase interval size of the multi-phase clock signal, the relationship between the phase interval size is that the first clock signal > the second clock signal > the third clock signal), the coarse resolution TDC, the middle resolution TDC and the fine resolution TDC start counting synchronously after receiving the signal of the light pulse sent by the laser emitting module 110, and stop counting after receiving the avalanche pulse signal output by the SPAD pixel circuit 10 again.

The coarse resolution TDC achieves a large range, calculates the approximate time interval between when photons are emitted from the laser emitting module 110 until an avalanche pulse signal is detected, and converts the time interval into a digital code for transmission to a coarse histogram circuit, which contains x memory cells.

Middle resolution TDC to achieve medium time accuracy ranging at T _c /m ₁ In the measurement time range of (1), a digital code is generated and transmitted to a middle histogram circuit, wherein the middle histogram circuit comprises z storage units.

Fine resolution TDC to achieve high time accuracy ranging at T _m /m ₂ In the measurement time range of (1), generates digital code and transmits it to a fine histogram circuit, the fine histogram circuit comprisesy memory cells.

The corresponding histogram circuit executes +1 operation on the storage unit corresponding to the received digital code mapping to finish photon counting once, and corresponding histogram data is established in the histogram circuit after multiple measurements; after the end of one multiple polishing measurement period, the coarse histogram circuit, the middle histogram circuit and the fine histogram circuit respectively establish corresponding coarse histogram data, middle histogram data and fine histogram data; after the measurement period is finished, a coarse histogram, a medium histogram and a fine histogram are generated simultaneously, and are output to the digital processing circuit 50 for processing and then transmitted to external equipment through the interface circuit 60, so that the final flight time and the distance information of the object to be measured are obtained.

FIG. 6 is a graph of the histogram output at the end of the measurement period of FIG. 5, a round of lighting generating Coarse, medium and fine histograms simultaneously, the position of the Bin on the abscissa of the histogram representing the period of time corresponding to the detected photon, the Peak value of the histogram representing the count number of photons, the left graph being a Coarse histogram containing x Coarse bins, namely Coarse_Bin_0 (cb_0) through Coarse_Bin_x-1 (cb_x-1), each Coarse Bin having a time cell width corresponding to 1/m of one clock period of Coarse resolution TDC ₁ Namely (1/m) ₁ )*T _c That is, the time resolution of the coarse resolution TDC is x T _c /m ₁ The method comprises the steps of carrying out a first treatment on the surface of the The Middle graph is a Middle histogram containing z Middle bins, namely middle_bin_0 (mb_0) to middle_bin_z-1 (mb_z-1), each of which has a time cell width corresponding to 1/m of one clock cycle of the Middle resolution TDC ₂ Namely (1/m) ₂ )*T _m That is, the time resolution of the middle resolution TDC, the time measurement range corresponding to the middle resolution TDC is z×T _m /m ₂ The right graph is a Fine histogram containing y Fine bins, namely fine_bin_0 (fb_0) to fine_bin_y-1 (fb_y-1), each of which has a time cell width corresponding to 1/m of one clock cycle of the Fine resolution TDC ₃ Namely (1/m) ₃ )*T _f That is, the time resolution of the fine resolution TDC is the time measurement range of y×T _f /m ₃ 。

At the end of one round of polishing, the coarse resolution TDC, the medium resolution TDC and the fine resolution TDC generate a coarse histogram, a medium histogram and a fine histogram at the same time.

For coarse, medium and fine histograms, the mathematical relationship between Bin and Peak values is as follows:

the time cell width of each coarse Bin in the coarse histogram corresponds to the sum of the time cell widths of the z bins in the medium histogram, and the time cell width of each Bin in the medium histogram corresponds to the sum of the time cell widths of the y fine bins in the fine histogram, namely:

Bin_width(cb_i)＝Bin_width(mb_0)+Bin_width(mb_1)+...+

Bin_width(mb_z-1)，i＝1,2,...,m ₂ (i.e. bin_width (cb_0) =z×t) _m /m ₂ I.e.

Tc/m ₁ ＝z*T _m /m ₂ )；

Bin_width(mb_j)＝Bin_width(fb_0)+Bin_width(fb_1)+...+Bin_width(fb_y-1)，i＝1,2,...,m ₃ (i.e. bin_width (cb_0) =y×t) _f /m ₃ T, i.e _m /m ₂ ＝y*T _f /m ₃ )；

The relationship between Peak values in the coarse, medium and fine histograms is:

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)。

after finishing the polishing of one round, synchronously outputting the rough histogram, the medium histogram and the fine histogram to the digital processing circuit 50 after the rough histogram, the medium histogram and the fine histogram are simultaneously generated, wherein the rough Bin position corresponding to the maximum Peak in the rough histogram is cb_k, the medium Bin position corresponding to the maximum Peak in the medium histogram is mb_j, the fine Bin position corresponding to the maximum Peak in the fine histogram is fb_i, and the flight value output after the histogram data of the polishing cycle of the round is processed by the digital processing circuit 50 and the external device is as follows:

TOF＝[(k*cb_k)+(j*mb_j)+(i+1)*fb_i]；

wherein cb_k=cb_0=cb_1= ₁ )*T _c ；

mb_j＝mb_0＝mb_1＝...＝mb_z-1＝(1/m ₂ )*T _m ；

fb_i＝fb_0＝fb_1＝...＝fb_y-1＝(1/m ₃ )*T _f ；

The corresponding test distance is [ (k_cb_k) + (j_mb_j) + (i+1) ×fb_i ]. Times.C/2, the multiple histogram circuit can have a large ranging range and high time resolution, only one round of polishing is needed for testing, the output frame rate of the DTOF sensor 1 is not influenced, and coarse and fine histograms are output at the same time, so that the subsequent digital processing circuit 50 and external equipment can be further optimized, and the ranging accuracy is improved.

Of course, the resolution TDC and the histogram circuit may be equal to 4 or more, and resolution TDCs with different time resolutions are used together, which are all within the protection scope of the present invention and will not be described in detail.

Each histogram circuit executes +1 operation on a storage unit corresponding to the received digital code mapping, completes one photon counting, and establishes corresponding histogram data after multiple measurements;

the number of the storage units of the histogram circuit is greater than or equal to j;

where j=t/(T) _i /m _i ) T is the time measurement range of the corresponding resolution TDC.

I.e. the number of memory cells of the histogram circuit is determined by the range and phase interval of the corresponding connected TDC, e.g. the phase interval of the TDC is T _i /m _i The number of memory cells of the histogram circuit at least comprises T/(T) when the measurement range is T _i /m _i )。

Meanwhile, the digital processing circuit 50 may process or not process the histogram data, optionally, M histogram circuits are connected to the digital processing circuit 50, the digital processing circuit 50 is connected to the interface circuit 60, and the interface circuit 60 is used for transmitting the data to an external device such as an upper computer;

the M histogram circuits transmit M groups of histogram data to the digital processing circuit 50, and the digital processing circuit 50 determines corresponding flight time values according to the histogram data and transmits the flight time values to external equipment such as an upper computer and the like through the interface circuit 60; or alternatively

The M histogram circuits transmit the M sets of histogram data to the digital processing circuit 50, and the digital processing circuit 50 does not process the histograms, and directly transmits the M sets of histogram data to external devices such as an upper computer through the interface circuit 60, so as to provide sufficient data support for subsequent algorithm optimization.

Compared with the prior art, the embodiment of the invention has the beneficial effects that: the DTOF sensor 1 is provided with a plurality of TDCs with different resolutions and a plurality of histogram circuits, the M TDCs with different resolutions work simultaneously, the DTOF sensor has a large ranging range and high time resolution under the condition of limited hardware resources, data output by the TDCs with different time resolutions are respectively processed by the different histogram circuits, the M histograms obtained by the simultaneous processing of the M histogram circuits are output to the digital processing circuit 50 or external equipment for processing, the flight time and the distance information of an object to be measured can be determined, the ranging requirement can be completed only by one round of polishing, the output frame rate of the DTOF sensor is improved, meanwhile, the obtained M histograms have no problem of mutual coverage, the further processing and optimization of the data are convenient for a subsequent algorithm, and the ranging accuracy is improved.

As shown in fig. 7, the present invention further proposes a laser receiving module 120, where the laser receiving module 120 includes a DTOF sensor 1, and the specific structure of the DTOF sensor 1 refers to the above embodiment, and since the laser receiving module 120 adopts all the technical solutions of all the embodiments, at least has all the beneficial effects brought by the technical solutions of the embodiments, which are not described herein again.

The laser receiving module 120 is disposed opposite to the laser emitting module 110, the laser receiving module 120 receives photons corresponding to the lighting period and generates corresponding histogram data, the laser receiving module 120 directly calculates corresponding flight time according to the histogram data or outputs the histogram data to the external device, and the external device determines flight time and specific distance information.

The present invention also proposes a ranging device 100, as shown in fig. 7, where the ranging device 100 includes a laser emitting module 110 and a laser receiving module 120, and the specific structure of the laser receiving module 120 refers to the above embodiment, and since the ranging device 100 adopts all the technical solutions of all the embodiments, at least has all the beneficial effects brought by the technical solutions of the embodiments, and will not be described in detail herein.

The distance measuring device 100 may be a camera, a video camera, etc. to measure distance, depth information and image information.

Corresponding to the structure of the DTOF sensor 1 as above, a fourth aspect of the embodiment of the present invention proposes a ranging method of the DTOF sensor 1, as shown in fig. 8, including:

step S10, a clock management circuit 20 is adopted to output M groups of clock signals, the clock signals have the same period and a plurality of clock signals with equal phase intervals, the number and/or the period of the clock signals of each group are unequal, and M is more than or equal to 2;

Step S20, M TDCs with different resolutions are adopted to receive and respectively receive a group of corresponding clock signals, each TDC with different resolutions counts the time interval from the photon emission time to the input time of the detected avalanche pulse signal at the corresponding phase interval, and each TDC generates a digital code corresponding to the time interval taking each phase interval as the minimum measurement time unit;

step S30, M histogram circuits respectively provided with a preset number of storage units are connected with M resolution TDCs one by one, the preset number of storage units are used for respectively counting digital codes corresponding to a preset number of phase intervals and converting the digital codes into corresponding histogram data, and each histogram data is processed by the digital processing circuit 50, transmitted to the interface circuit 60 and output to external equipment through the interface circuit 60;

the relationship between the widths of the time units corresponding to the single storage unit of the histogram data of each histogram circuit is as follows:

T _i /m _i ＝y _i+1 *T _i+1 /m _i+1 ；

wherein T is _i And m _i Respectively represent the period sum and the like of the clock signals corresponding to the ith resolution TDCNumber of phase-separated clocks, T _i+1 、m _i+1 And y _i+1 The i is 1,2,3, and M-1, M, n, y are greater than 1, respectively representing the period of the clock signal corresponding to the i+1th resolution TDC, the number of aliquoting phase clocks, and the number of memory cells included in the corresponding histogram circuit.

In this embodiment, the corresponding control module drives the laser emitting module 110 and the DTOF to operate synchronously, the laser emitting module 110 emits laser pulses to a target scene, the light pulses reflected by the target scene are incident on the SPAD photosensitive pixels in the cover mode, avalanche current signals are induced, the quenching circuit reduces the voltage loaded on the SPAD pixels to enable the SPAD photosensitive pixels to deviate from an avalanche state, and after the avalanche current signals output by the SPAD pass through the quenching circuit, the shaping circuit and the like, voltage pulse signals with fixed pulse width and amplitude are output to M TDCs with different resolutions.

In synchronization, the clock management circuit 20 outputs M groups of clock signals, each group of clock signals including a plurality of clock signals having unequal numbers of clocks and/or periods, e.g., the clock period of the first group of clock signals output to the first resolution TDC31 is T ₁ The number of clocks is m ₁ ，m ₁ The phase between the clocks is equally divided into T ₁ /m ₁ (i.e. m) ₁ The phase interval between adjacent clocks in each clock is T ₁ /m ₁ ) The clock period of the second set of clock signals output to the second resolution TDC32 is T ₂ The number is m ₂ ,. the clock period of the M group clock signal output to the M resolution TDC is T _M The number is m _M . . . The description is as follows: t (T) ₁ /m ₁ ＞T ₂ /m ₂ ＞....＞T _M /m _M Each group of clock signals corresponding to the number of clocks and the period is used as clock signals corresponding to the resolution TDCs, each resolution TDC starts to count synchronously after receiving a voltage pulse signal synchronous with a driving signal driving the laser emitting module 110, and stops counting simultaneously after receiving the SPAD pixel and the avalanche pulse signal output by the quenching circuit 10 synchronously again.

The time resolutions of the first resolution TDC to the Mth resolution TDC become larger in sequence, the time resolution of each time resolution is inversely related to the phase interval of the clock signal, namely, the time resolution of the TDC is determined by the phase interval of the clock signal, the smaller the phase interval is, the higher the time resolution of the corresponding TDC is, the time resolutions of the TDC are sequentially improved from the first resolution TDC to the Mth resolution TDC, M different resolution TDCs synchronously work, the time interval from the time of emitting light pulses of a laser emitting module to the time of detecting avalanche pulse signals of SPAD pixels by photons is calculated, the time interval with a large range and a low precision is provided by the low time resolution TDC, the time interval with a small range and a high precision is provided by the high time resolution TDC, and the time interval is converted into a digital code.

The first resolution TDC31 realizes the maximum measurement range of the current flight time, calculates the maximum bit number of the interval time from the emission of the photon from the laser emitting module 110 to the detection of the avalanche pulse signal, and converts the interval time into corresponding digital codes, such as binary codes, thermometer codes, single thermal codes, etc., which are transmitted to the first histogram circuit 41, wherein the first histogram circuit 41 comprises y ₁ And a memory cell.

The second resolution TDC32 achieves a sub-measurement range of the current time of flight, calculates a second largest value of the interval time from when photons are emitted from the laser emitting module 110 to when avalanche pulse signals are detected, at T ₁ /m ₁ Converts each interval time into a corresponding digital code, and the digital code is transmitted to the second histogram circuit 42, wherein the second histogram circuit 42 includes y ₂ And a memory cell.

The Mth 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 photons from the laser emission module 110 to the detection of the avalanche pulse signal, and calculates the minimum bit value of the interval time from the emission of photons to the detection of the avalanche pulse signal at T _M-1 /m _M-1 In the measurement time range of (2), converting the interval time into corresponding digital code, and transmitting the digital code to an Mth histogram circuit, wherein the Mth histogram circuit comprises y _M And a memory cell.

And the corresponding histogram circuit performs +1 operation on the storage unit corresponding to the received digital code mapping to finish photon counting, establishes corresponding histogram data through the corresponding histogram circuit after multiple measurements, establishes histogram data with different time interval widths respectively after one multiple light-emitting measurement period is finished, and transmits the histogram data to the signal digital processing circuit 50 and the interface circuit 60 to be transmitted to external equipment through the interface circuit 60, so that final accurate ranging information is obtained.

Wherein the sum of the time cell widths counted in the second histogram circuit 42 is equal to the minimum time cell width in the first histogram circuit 41, the sum of the time cell widths in the third histogram circuit 43 is equal to the minimum time cell width in the second histogram circuit 42, the sum of the time cell widths in the Mth histogram circuit is equal to the minimum time cell width in the Mth-1 histogram circuit, and the time cell width of each histogram data is T _i /m _i The time cell width of each histogram data satisfies T _i /m _i ＝y _i+1 *T _i+1 /m _i+1 Relationship.

Wherein the number of memory cells in the first to M-th histogram circuits 41 to 41 is specifically determined according to the time resolution and measurement range in the corresponding connected TDCs, and wherein the minimum time cell width of the histogram circuit is equal to the time resolution of the connected resolution TDCs (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 I.e. the smallest unit of measurement time equal to each histogram data.

The digital processing circuit 50 may determine the time of flight directly from the histogram data or determine the time of flight and distance information from an external device, where the time of flight is:

[(K ₁ -1)*T ₁ /m ₁ +(K ₂ -1)*T ₂ /m ₂ +...+(K _M-1 -1)*T _M-1 /m _M-1 +K _M *T _M /m _M ]；

Wherein K is ₁ 、K ₂ To K _M The positions of time intervals corresponding to the maximum count peaks in the histogram data of the first to mth histogram circuits 41 to M-th histogram circuits are indicated, respectively.

The digital processing circuit 50 or the external device determines the distance of the object in the corresponding measuring range by the position of the time cell width corresponding to the maximum count of the histogram, i.e. the position of the time period corresponding to the maximum peak, in which the number of counted photons is the largest, e.g. the number of photons counted in the third time cell width of the first histogram data is the largest, the coarse time of flight of the time of flight is 3*T ₁ /m ₁ After determining the time unit width position of the object to be measured in a wide range, determining the time unit width position of the maximum peak value in the second histogram data as the 4 th time unit width position, the flight time may be further determined as 2*T ₁ /m ₁ +4*T ₂ /m ₂ And so on, finally obtaining the total duration of the flight time of [2*T ] ₁ /m ₁ +3*T ₂ /m ₂ +...+(K _M-1 -1)*T _M-1 /m _M-1 +K _M *T _M /m _M ]。

The larger the value of M, the more accurate the flight time measurement and calculation, M comprises at least two, and the size of M can be specifically set according to the ranging accuracy, the ranging range and the circuit design complexity of actual requirements.

The above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention, and are intended to be included in the scope of the present invention.

Claims (10)

1. A DTOF sensor, comprising:

the SPAD pixel is used for sensing single photons and generating an avalanche pulse signal, and the quenching circuit enables the SPAD photosensitive pixel to be separated from an avalanche state by reducing the voltage loaded on the SPAD pixel;

the clock management circuit is used for outputting M groups of clock signals, each group of clock signals comprises a plurality of clock signals with the same period and equal phase intervals, the number and/or the period of the clock signals of each group are unequal, and M is more than or equal to 2;

m different resolution TDCs respectively connected to the SPAD pixels, the quenching circuit and the clock management circuit simultaneously, each resolution TDC being configured to receive a set of corresponding clock signals, count time intervals from photon emission time to input time when the avalanche pulse signal is detected at corresponding phase intervals, and generate digital codes corresponding to time intervals each phase interval being a minimum measurement time unit;

the system comprises M histogram circuits which are respectively connected with M TDCs with different resolutions one by one, wherein each histogram circuit comprises a preset number of storage units, the preset number of storage units are used for respectively counting digital codes corresponding to the preset number of phase intervals and converting the digital codes into corresponding histogram data, and each histogram data is processed by a digital processing circuit, transmitted to an interface circuit and output to external equipment through the interface circuit;

The relationship between the widths of the time units corresponding to the single storage unit of the histogram data of each histogram circuit is as follows:

T _i /m _i ＝y _i+1 *T _i+1 /m _i+1 ；

wherein T is _i And m _i Respectively representing the period and the number of the equally divided phase clocks of the clock signal corresponding to the ith resolution TDC, T _i+1 、m _i+1 And y _i+1 The i is 1,2,3, and M-1, M, n, y are greater than 1, respectively representing the period of the clock signal corresponding to the i+1th resolution TDC, the number of aliquoting phase clocks, and the number of memory cells included in the corresponding histogram circuit.

2. The DTOF sensor as recited in claim 1, wherein the time resolution from the first resolution TDC to the mth resolution TDC becomes sequentially larger, and the magnitude of each time resolution changes inversely with the phase interval of the clock signal;

the M TDCs with different resolutions work synchronously, the time interval from the emission of light pulse by the laser emission module to the detection of avalanche pulse signal by the SPAD pixel is calculated, and the time interval detected by each photon is converted into digital code.

3. The DTOF sensor as recited in claim 1, wherein a total count of histogram data for each of the histogram circuits is equal.

4. The DTOF sensor as recited in claim 1, wherein the distance information of the object to be measured is:

L＝C*[(K ₁ -1)*T ₁ /m ₁ +(K ₂ -1)*T ₂ /m ₂ +...+(K _M-1 -1)*T _M-1 /m _M-1 +K _M *T _M /m _M ]/2；

Wherein C represents the speed of light, K ₁ 、K ₂ To K _M The positions of the phase intervals corresponding to the maximum count peaks in the histogram data of the first histogram circuit to the mth histogram circuit are respectively represented.

5. The DTOF sensor as recited in claim 1, wherein a minimum measurement time unit for each of the histogram circuits is:

P＝T _i /m _i 。

6. the DTOF sensor as recited in claim 1, wherein each of the histogram circuits performs +1 operation on the corresponding memory location of the received digital code map to complete one photon count, and establishes corresponding histogram data after multiple measurements;

the number of the storage units corresponding to the histogram circuit is greater than or equal to j;

where j=t/(T) _i /m _i ) T is the time measurement range corresponding to the resolution TDC.

7. The DTOF sensor as recited in claim 1, wherein,

the M histogram circuits transmit M groups of histogram data to a digital processing circuit, and the digital processing circuit determines corresponding flight time values according to the histogram data and transmits the flight time values to external equipment through the interface circuit; or alternatively

The M histogram circuits transmit M groups of histogram data to the digital processing circuit, the digital processing circuit transmits the M groups of histogram data to the external device through the interface circuit, and the external device determines corresponding flight time values according to the histogram data.

8. A laser receiving module comprising a DTOF sensor as claimed in any one of claims 1 to 7.

9. A distance measuring device comprising a laser emitting module and a laser receiving module according to claim 8.

10. A method of ranging a DTOF sensor, comprising:

m groups of clock signals are output by adopting a clock management circuit, each group of clock signals comprises a plurality of clock signals with the same period and equal phase intervals, the number and/or the period of the clock signals of each group are unequal, and M is more than or equal to 2;

adopting M TDCs with different resolutions for receiving and respectively receiving a group of corresponding clock signals, counting the time interval from the photon emission time to the input time of the detected avalanche pulse signal at the corresponding phase interval by each resolution TDC, and respectively generating digital codes corresponding to the time interval taking each phase interval as the minimum measurement time unit;

m histogram circuits respectively provided with a preset number of storage units are connected with M resolution TDCs one by one, the preset number of storage units are used for respectively counting digital codes corresponding to a preset number of phase intervals and converting the digital codes into corresponding histogram data, and each histogram data is processed by a digital processing circuit, transmitted to an interface circuit and output to external equipment through the interface circuit;

The relationship between the widths of the time units corresponding to the single storage unit of the histogram data of each histogram circuit is as follows:

T _i /m _i ＝y _i+1 *T _i+1 /m _i+1 ；

wherein T is _i And m _i Respectively representing the period and the number of the equally divided phase clocks of the clock signal corresponding to the ith resolution TDC, T _i+1 、m _i+1 And y _i+1 The i is 1,2,3, and M-1, M, n, y are greater than 1, respectively representing the period of the clock signal corresponding to the i+1th resolution TDC, the number of aliquoting phase clocks, and the number of memory cells included in the corresponding histogram circuit.