CN107272010B - Distance sensor, distance measuring method thereof and 3D image sensor - Google Patents
Distance sensor, distance measuring method thereof and 3D image sensor Download PDFInfo
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- CN107272010B CN107272010B CN201710477641.XA CN201710477641A CN107272010B CN 107272010 B CN107272010 B CN 107272010B CN 201710477641 A CN201710477641 A CN 201710477641A CN 107272010 B CN107272010 B CN 107272010B
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract
A distance sensor, a distance measuring method thereof and a 3D image sensor are provided, wherein the distance measuring method comprises the following steps: acquiring a plurality of counting signals, wherein each counting signal is provided with a counting start edge and a counting stop edge, the counting start edge of the first counting signal is generated when the light source emits photons, the counting stop edge of the first counting signal is generated when reflected photons reflected by a target object are detected, and the counting stop edges of other counting signals have different time delays relative to the counting stop edge of the first counting signal; counting the input clock signals in a time window defined by a counting start edge of a first counting signal and a counting stop edge of each counting signal to obtain corresponding counting values; determining a distance between the target object and the distance sensor using the respective count values. By adopting the technical scheme of the invention, the measurement precision of the 3D image sensor based on the photon detection technology can be effectively improved.
Description
Technical Field
The invention relates to the technical field of 3D image sensors, in particular to a distance sensor, a distance measuring method thereof and a 3D image sensor.
Background
Light has both wave and particle properties. Light is composed of a large number of photons, the energy of which is determined by the frequency of the light, according to its particle nature. Since the energy of a single photon in the visible band is particularly low, a special photodetector, i.e. a single photon detector, is required to be able to detect the low-energy photon. There are two main types of single photon detectors: photomultiplier tubes and Single Photon Avalanche diodes (SPADs for short). The SPAD based on the semiconductor technology has the advantages of high measurement efficiency in infrared communication bands, low power consumption, small size, large working frequency spectrum range, low working voltage and the like, is widely applied to the field of distance measurement and scenes such as 3D image reconstruction, and is particularly suitable for detecting weak light signals.
There is a 3D image sensor based on SPAD in the prior art, the 3D image sensor includes a plurality of distance sensors 100 as shown in fig. 1, wherein SPADs (see D1) in the 3D image sensor are arranged in an array. As shown in fig. 1, the distance sensor 100 performs distance measurement by detecting a Time Of Flight (TOF) Of a photon. In a specific implementation, the distance sensor 100 may include: light source control circuit 10, light source 20, SPAD, pulse generation circuit 30, and counter 40. While the light source control circuit 10 controls the light source 20 to emit photons, a count start signal counter _ start is generated to trigger the counter 40 to start counting, photons irradiated to a target object are reflected therefrom to reach the SPAD, avalanche is induced in the SPAD, and the generated avalanche current is detected by the pulse generation circuit 30 to generate a count stop signal counter _ stop. Waveforms of the count start signal counter _ start and the count stop signal counter _ stop may be referred to in fig. 2.
Referring to fig. 1 and 2 together, in an implementation, the distance from the target object to the distance sensor 100 may be obtained according to a counting result of the counter 40 to a high-speed clock (not shown) within a time window defined by a rising edge of the count start signal counter _ start and a rising edge of the count stop signal counter _ stop. Further, the 3D image sensor may reconstruct an image of the target object by controlling the light source 20 to scan the target object in an array manner, and obtaining distances from various positions on the target object to the distance sensor 100.
Since the counter 40 operates at the frequency of the high-speed clock, the time window, i.e. the flight time of the photon, is measured by the number of cycles of the high-speed clock, and the period of the high-speed clock determines the measurement accuracy of the distance sensor 100. For 3D image sensors, one counter per pixel or column of pixels is required. However, increasing the frequency of the high speed clock comes at a large cost due to area, power consumption, and process constraints. Therefore, how to improve the measurement accuracy of the 3D image sensor based on the photon detection technology is an urgent technical problem to be solved.
Disclosure of Invention
The invention solves the technical problem of how to improve the measurement precision of a 3D image sensor based on a photon detection technology.
In order to solve the above technical problem, an embodiment of the present invention provides a distance measuring method for a distance sensor, where the distance measuring method includes: acquiring a plurality of counting signals, wherein each counting signal is provided with a counting start edge and a counting stop edge, the counting start edge of the first counting signal is generated when the light source emits photons, the counting stop edge of the first counting signal is generated when reflected photons reflected by a target object are detected, and the counting stop edges of other counting signals have different time delays relative to the counting stop edge of the first counting signal; counting the input clock signals in a time window defined by a counting start edge of a first counting signal and a counting stop edge of each counting signal to obtain corresponding counting values; determining a distance between the target object and the distance sensor using the respective count values.
Optionally, the acquiring a plurality of count signals comprises: controlling the light sources to respectively emit photons at different moments, and generating a counting starting edge of a corresponding counting signal when the light sources generate the photons; generating a count stop edge of a corresponding count signal when a reflected photon reflected by the target object is detected; wherein the counting start edge of the other counting signals has a different delay with respect to the counting start edge of the first counting signal.
Optionally, the delay of the count stop edge of each of the other count signals relative to the count stop edge of the first count signal is less than or equal to the period of the input clock signal.
Optionally, for the ith count signal, the delay time is equal to T/(N-1) × (i-1), where T is the period of the input clock signal, N is the total number of the count signals, i and N are integers, and 2 ≦ i ≦ N.
Optionally, the determining the distance between the target object and the distance sensor using the respective count values comprises: and determining the distance between the target object and the distance sensor according to the average value of the obtained counting values, the period of the input clock signal and the propagation speed of the photons.
Optionally, before the determining the distance between the target object and the distance sensor by using each count value, the method further includes: comparing the count value obtained by counting at the current time with the count value obtained before the current time; and if the count value obtained by the current counting is larger than the sum of the maximum value and 1 in the count values obtained before the current counting, or is smaller than the maximum value in the count values obtained before the current counting, judging that the count value obtained by the current counting is an abnormal count value, and rejecting the abnormal count value.
In order to solve the above technical problem, an embodiment of the present invention further provides a distance sensor, including: a counting signal acquisition module, adapted to acquire a plurality of counting signals, each counting signal having a counting start edge and a counting stop edge, wherein the counting start edge of the first counting signal is generated when the light source emits photons, the counting stop edge of the first counting signal is generated when reflected photons reflected by the target object are detected, and the counting stop edges of the other counting signals have different delays with respect to the counting stop edge of the first counting signal; the counter is suitable for counting the input clock signals in a time window defined by the counting start edge of the first counting signal and the counting stop edge of each counting signal so as to obtain corresponding counting values; wherein each count value is used to determine a distance between the target object and the distance sensor.
Optionally, the count signal acquiring module includes: the time delay circuit is suitable for controlling the light sources to respectively emit photons at different moments, and the counting start edges of the corresponding counting signals are generated when the light sources generate the photons, wherein the counting start edges of other counting signals have different time delays relative to the counting start edge of the first counting signal; and the photon detection circuit is suitable for respectively detecting the reflected photons obtained by the reflection of the target object so as to obtain the counting stop edge of each counting signal.
Optionally, the delay of the count stop edge of each of the other count signals relative to the count stop edge of the first count signal is less than or equal to the period of the input clock signal.
Optionally, for the ith count signal, the delay time is equal to T/(N-1) × (i-1), where T is the period of the input clock signal, N is the total number of the count signals, i and N are integers, and 2 ≦ i ≦ N.
Optionally, the distance sensor further comprises: and the control module is suitable for determining the distance between the target object and the distance sensor according to the obtained average value of the counting values, the period of the input clock signal and the propagation speed of the photons.
Optionally, before determining the distance between the target object and the distance sensor by using each count value, the control module is further adapted to compare the count value obtained by counting at the current time with the count value obtained before the current time, and if the count value obtained by counting at the current time is greater than a sum of a maximum value of the count values obtained before the current time and 1, or is less than a maximum value of the count values obtained before the current time, determine that the count value obtained by counting at the current time is an abnormal count value, and reject the abnormal count value.
Optionally, the delay circuit comprises a controllable delay chain, a clock input end of which is connected to the input clock signal and is adapted to generate an output clock signal under the control of the phase selection signal, wherein the delay of the output clock signal relative to the input clock signal is equal to T/(N-1) × (i-1), and a flip-flop, a data input end of which is connected to the counting start edge of the first counting signal, and a data output end of which outputs the counting start edges of the other counting signals under the action of the output clock signal.
Optionally, the photon detection circuit comprises: a SPAD adapted to generate an avalanche current upon detection of the reflected photon; a pulse generating circuit adapted to generate a count-stop edge of the count signal based on the avalanche current.
In order to solve the above technical problem, an embodiment of the present invention further provides a 3D image sensor, where the 3D image sensor includes a plurality of distance sensors, and the photon detection circuits are arranged in an array.
Compared with the prior art, the technical scheme of the embodiment of the invention has the following beneficial effects:
the distance measuring method of the distance sensor in the embodiment of the invention obtains a plurality of counting signals, each counting signal is provided with a counting start edge and a counting stop edge, wherein the counting start edge of the first counting signal is generated when a light source emits photons, the counting stop edge of the first counting signal is generated when reflected photons reflected by a target object are detected, the counting stop edges of other counting signals have different time delays relative to the counting stop edge of the first counting signal, then the counting start edge of the first counting signal and the counting stop edge of each counting signal define a time window, the input clock signals are counted to obtain corresponding counting values, and finally the distance between the target object and the distance sensor is determined by utilizing the counting values. The distance between the target object and the distance sensor corresponds to the flight time of the photons, and the counting values can indicate the proportion of the time when the flight time of the photons is not counted into the counting result to the period of the input clock signal, so that the embodiment of the invention can improve the quantization resolution of the counter to 1/N of the original counting period, can effectively improve the measurement accuracy of the distance sensor based on the photon detection technology, and further can improve the measurement accuracy of the 3D image sensor comprising the distance sensor.
Further, the embodiments of the present invention control the light sources to emit photons at different times, generate a corresponding counting start edge of the counting signal when the light source generates a photon, and generate a corresponding counting stop edge of the counting signal when a reflected photon reflected by the target object is detected, where the counting start edges of other counting signals have different delays with respect to the counting start edge of the first counting signal. That is to say, in the embodiment of the present invention, the plurality of counting signals are obtained through multiple quantization, and the same counter may be used for counting multiple times in the multiple quantization mode, so as to save resources of the counter, and reduce the influence of noise on measurement through multiple quantization.
Further, before the distance between the target object and the distance sensor is determined, the distance measuring method compares a count value obtained by current counting with a count value obtained before the current counting, and if the count value obtained by the current counting is larger than the sum of the maximum value of the count values obtained before the current counting and 1, or the count value obtained by the current counting is smaller than the maximum value of the count values obtained before the current counting, the count value obtained by the current counting is determined to be an abnormal count value, and the abnormal count value is removed, so that the measuring accuracy of the distance sensor can be further improved.
Drawings
Fig. 1 is a schematic diagram of a distance sensor in the prior art.
Fig. 2 is a schematic diagram of an operation waveform of the distance sensor shown in fig. 1.
Fig. 3 is a schematic block diagram of a distance sensor according to an embodiment of the present invention.
Fig. 4 is a schematic diagram of an operation waveform of the distance sensor shown in fig. 3.
Fig. 5 is a schematic diagram of the counter shown in fig. 3.
Fig. 6 is a schematic block diagram of another distance sensor according to an embodiment of the present invention.
Fig. 7 is a flowchart of a distance measuring method of a distance sensor according to an embodiment of the present invention.
Fig. 8 is a flowchart of another distance measuring method of the distance sensor according to the embodiment of the present invention.
Detailed Description
As described in the background section, in the prior art distance sensor based on the photon detection technology, the counter measures the flight time of photons by the number of cycles of the high speed clock, which determines the measurement accuracy of the distance sensor. For 3D image sensors, one counter per pixel or column of pixels is required. However, increasing the frequency of the high speed clock comes at a large cost due to area, power consumption, and process constraints. Therefore, how to improve the measurement accuracy of the 3D image sensor based on the photon detection technology is an urgent technical problem to be solved.
The embodiment of the invention provides a measuring method of a distance sensor, which effectively improves the quantization precision of the flight time of photons by acquiring a plurality of counting signals and counting input clock signals in a time window defined by a counting start edge of a first counting signal and a counting stop edge of each counting signal, thereby effectively improving the measuring precision of the distance sensor.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Referring to fig. 3 and 4 together, an embodiment of the invention discloses a distance sensor 200, and the distance sensor 200 may include a counting signal acquiring module 10 and a counter 20.
The count signal obtaining module 10 is adapted to obtain a plurality of count signals Ctrl, Ctr2 … …, and CtrN, where N is a positive integer, that is, N is a total number of the count signals Ctr2 to CtrN, each of the count signals Ctr1 to CtrN has a count start edge (not shown) and a count stop edge (not shown), where the count start edge of the first count signal Ctrl is generated when the light source 40 emits a photon, the count stop edge of the first count signal Ctrl is generated when a reflected photon reflected by the target object is detected, and the count stop edges of the other count signals Ctr2 to CtrN have different delays with respect to the count stop edge of the first count signal Ctrl.
The counter 20 is adapted to count the input clock signal C L Kin within a time window TOF 1-N defined by a count start edge of a first count signal Ctr1 and a count stop edge of each count signal Ctr1 to CtrN to obtain corresponding count values, each count completing one quantization.
In particular implementations, the Counter 20 may be any practicable Counter structure, such as a conventional Ripple Counter (Ripple Counter), but is not limited thereto.
In the embodiment of the present invention, each count value counted by the counter 20 is used to determine the distance between the target object and the distance sensor 200. It should be noted that the distance is half of the propagation path of the photon, and the propagation path of the photon is from the light source 40 to the target object and then from the target object to the photon detection circuit 102.
In this embodiment, the distance between the target object and the distance sensor 200 corresponds to a Time Of Flight (TOF), and the count values may indicate a ratio Of a Time in which the Time Of Flight Of the photon is not counted in the count result to a period Of the input clock signal C L Kin, so that the embodiment Of the present invention may increase the quantization resolution Of the counter 20 to 1/N Of the original count period T, may effectively improve the measurement accuracy Of the distance sensor 200 based on the photon detection technology, and may further improve the measurement accuracy Of the 3D image sensor including the distance sensor 200.
Preferably, the count signal acquiring module 10 may include a delay circuit 101 and a photon detecting circuit 102.
The delay circuit 101 is adapted to control the light source 40 to emit photons at different times, and generate corresponding counting start edges of the counting signals when the light source 40 generates photons, wherein the counting start edges of the other counting signals Ctr 2-CtrN have different delays with respect to the counting start edge of the first counting signal Ctr 1.
The photon detection circuit 102 is adapted to detect the reflected photons reflected by the target object, respectively, to obtain a count stop edge of each count signal Ctr 1-CtrN.
That is to say, the distance sensor 200 in the embodiment of the present invention may obtain the plurality of count signals Ctr1 to CtrN through multiple quantization, and the same counter may be used to count multiple times through multiple quantization, so as to save resources of the counter, and reduce the influence of noise on measurement through multiple quantization.
In a specific implementation, the photon detection circuit 102 may include a Single Photon Avalanche Diode (SPAD) (not shown) and a pulse generation circuit (not shown). Wherein the SPAD is adapted to generate an avalanche current upon detection of the reflected photon based on an avalanche characteristic of the SPAD; the pulse generation circuit is adapted to generate a count stop edge of the count signal Ctr 1-CtrN from the avalanche current.
In a variation of this embodiment, the photon detection circuit 102 may further include a photomultiplier tube (not shown) and a pulse generation circuit (not shown). Wherein the reflected photons are detected by the photomultiplier tube to generate a photocurrent, and the pulse generation circuit generates a count stop edge of the count signals Ctr1 to CtrN from the photocurrent.
Both the SPAD and photomultiplier tubes described above can accomplish the detection of photons. In specific implementation, the device for detecting photons can be selected according to the actual application requirements. Further, both can detect single photons, and thus have extremely high photon detection efficiency.
In a specific implementation, the delay circuit 101 may include a delay chain (not shown), and the light sources 40 may be controlled to emit photons at different times by controlling a light source control module (not shown) coupled to the light sources 40. For example, corresponding to the first quantization, the light source control module generates a light emitting control signal (not shown) to control the light source 40 to emit a photon for the first time, and the light source 40 generates a counting start edge of the first counting signal Ctr1 when generating a photon; corresponding to the second quantization, the light-emitting control signal generated by the light source control module is delayed by the delay chain, so that the light source 40 delays to emit photons with respect to the first quantization, and generates a counting start edge of a second counting signal Ctr 2; by analogy, corresponding to the nth quantization, the light-emitting control signal generated by the light source control module is delayed by the delay chain, so that the light source 40 delays to emit photons with respect to the nth-1 quantization, and generates a counting start edge of the nth counting signal CtrN. Therefore, the counting start edges of the other count signals Ctr2 to CtrN have different delays with respect to the counting start edge of the first count signal Ctr 1.
For example, when the light source 40 is a semiconductor laser, the light source control module may be a laser controller. The light source control module may perform temperature control on the light source 40 and provide current driving. It should be noted that the light source control module may be externally coupled to or internally integrated with the distance sensor 200, and the embodiment is not limited in particular.
Preferably, the delay of the count stop edge of each of the other count signals Ctr 2-CtrN with respect to the count stop edge of the first count signal Ctr1 is less than or equal to the period T of the input clock signal C L Kin.
Further preferably, the delay is equal to T/(N-1) × (i-1) for the ith count signal Ctri, where T is the period of the input clock signal C L Kin, i is an integer, and 2 ≦ i ≦ N.
Taking N-16 as an example, the delay is equal to T/15 for the second count signal Ctr2, 2 × T/15 for the third count signal Ctr3, 3 × T/15 for the fourth count signal Ctr4, … …, and T for the sixteenth count signal Ctr 16.
Continuing with fig. 4, taking the counter 20 triggered to count by the rising edge of the input clock signal C L Kin as an example, assuming that the input clock signal C L Kin is counted by the time window TOF1 defined by the counting start edge and the counting stop edge of the first counting signal Ctr1 in the prior art, Δ T1 in fig. 4 cannot be counted into the counting result due to the inability to wait until the next rising edge arrives, so that when the flight time of the photon corresponding to the distance between the target object and the distance sensor 200 changes within the period T of the input clock signal C L Kin, the distance sensor 200 cannot recognize the next rising edge, and the smaller the period T of the input clock signal C L Kin, the smaller the distance change that the distance sensor 200 can recognize is, the higher the measurement resolution is.
Referring to fig. 4 and 5 together, the dashed line in fig. 5 represents the total number of count signals in the present embodiment, i.e. N is 16, wherein the 1 st dashed line represents the count stop edge of the first count signal Ctr1, the 2 nd dashed line represents the count stop edge of the second count signal Ctr2, and so on, the 16 th dashed line represents the count stop edge of the sixteenth count signal Ctr16, the time length between the 2 nd and 16 th dashed lines is equal to the period T of the input clock signal C L Kin, in the present embodiment, it is assumed that the count value in the time window TOF1 is a, a is a positive integer, the count value in the time window TOF1 to 8656 is also a, the count value in the time window TOF7 to 16 becomes a +1, i.e. 6 times is a, 10 times is a +1, therefore, the average value of the count values is [ 6A +10 × (a +1) ]/6316 is a +5/8, which indicates that the fraction between the count value of the target photon distance in the sensor 364 and the target photon count result is greater, the accurate as the fraction of the input photon count distance into the sensor 364 is equal to Δ T1.
In summary, in the N quantization processes, assuming that N (N is an integer greater than or equal to 0 and less than N) times of counting results are a, and the remaining N-N times of counting results are a +1, the final quantization result should be the average value of the counting results:
the embodiment can obtain the average value of each count value
The period T of the input clock signal C L Kin and the photon propagation velocity C determine the distance between the target object and the range sensor 200
The distance of the target object to the distance sensor 200
The embodiment of the invention can improve the quantization resolution of the counter 20 to 1/N of the original counting period through multiple quantization, and can effectively improve the measurement precision of the distance sensor 200 based on the photon detection technology. If N is 2mAnd m is a positive integer, the distance sensor 200 improves the distance measurement precision by m bits compared with the prior art.
It should be noted that, in the prior art, there is also a scheme for improving the Time measurement resolution by using a Time-to-digital converter (TDC) technique. The embodiment of the invention can be combined with the TDC technology to further improve the ranging precision of the distance sensor 200.
It should be noted that, in the embodiments of the present invention, the delay of the count stop edge of the other count signals Ctr2 to CtrN relative to the count stop edge of the first count signal Ctr1 is not particularly limited, and the delays may be equal to or different from each other.
It should be noted that, in the specific implementation, the counter 20 may count the rising edge or the falling edge of the input clock signal C L Kin, and this embodiment is not particularly limited, although an error may affect the measurement result of measuring the distance of one pixel of the target object at the start point of the counting, when measuring a plurality of pixels, the error may be eliminated as an offset value as a whole, and the depth of field when reconstructing the image of the target object is not affected.
Optionally, the distance sensor 200 may further include a lens or lens assembly (not shown) disposed between the target object and the photon detection circuit 102, and adapted to optically modify (e.g., image) the reflected photons before being detected by the photon detection circuit 102.
In another embodiment of the present invention, the delay circuit 20 may further delay the count stop edge of the first count signal Ctr1 to obtain the count stop edges of the other count signals Ctr2 to CtrN, so that the count stop edges of the other count signals Ctr2 to CtrN have different delays with respect to the count stop edge of the first count signal Ctr 1.
Fig. 6 is a schematic block diagram of another distance sensor according to an embodiment of the present invention.
Preferably, the distance sensor 300 shown in FIG. 6 may comprise a delay circuit 101, a photon detection circuit 102, a counter 20 and a control module 50, wherein the control module 50 is adapted to determine the distance between the target object and the distance sensor 300 according to the average value of the obtained respective count values, the period of the input clock signal C L Kin and the propagation speed of the photons.
In a specific implementation, the control module 50 may be a control component such as a single chip, a Programmable logic Device (Programmable L analog Device, abbreviated as P L D), a Field Programmable gate array (Field Programmable gate array, abbreviated as FPGA), and the like.
It should be noted that the control module 50 may be externally coupled or internally integrated with the distance sensor 300, and the embodiment is not particularly limited.
Preferably, the control module 50 is further adapted to compare the count value obtained by the current counting with the count value obtained before the current counting before determining the distance between the target object and the distance sensor 300 by using each count value, and if the count value obtained by the current counting is greater than the sum of the maximum value of the count values obtained before the current counting and 1 or less than the maximum value of the count values obtained before the current counting, determine that the count value obtained by the current counting is an abnormal count value, and reject the abnormal count value.
Since the later the time when the counter 20 finishes counting, the larger the counting result will be, if the actual counting result appears smaller or too large, it will be determined as a counting error, recognized by the control module 50, and control the counter 20 to count again. Finally, the abnormal count values are removed, and the correct count values are averaged, thereby improving the measurement accuracy of the distance sensor 300.
Continuing with the example of N-16 shown in fig. 5, if it is known that the respective 6 count values obtained are A, A, A, A, A, A, it is normal when the 7 th count value is a +1, and it is abnormal when it is a-1 or less or a +1 or even more; if the 6 counts obtained are known to be A, A, A, A, A and A +1, respectively, the 7 th count is A +1 is normal, A is smaller or A +2 is even larger, and is abnormal.
In a specific implementation, the delay circuit 101 includes a controllable delay chain 1011 and a flip-flop 1012.
The clock input Clk of the controllable Delay chain 1011 is connected to the input clock signal C L Kin, and is adapted to generate an output clock signal C L Kout under the control of a phase selection signal Sel, where the Delay of the output clock signal C L Kout relative to the input clock signal C L Kin is equal to T/(N-1) × (i-1), where the phase selection signal Sel may be provided by the control module 50, but is not limited thereto.
The data input end D of the flip-flop 1012 is connected to the count start edge Ctr1_ Up of the first count signal Ctr1, and under the action of the output clock signal C L Kout, the data output end Q outputs the count start edges Ctr2 to CtrN of the other count signals Ctr 2-CtrN, N _ Up. are well known to those skilled in the art, and for simplicity, the description is omitted here.
In a specific implementation, the phase selection signal Sel may control the delay of the output clock signal C L Kout output by the controllable delay chain 1011 with a value T/(N-1) × (i-1) with respect to the input clock signal C L Kin, for example, the counter 20 counts up the rising edge, and the flip-flop 1012 also triggers up the rising edge, when the rising edge of the output clock signal C L Kout acts on the flip-flop 1012, the logic level of the data output Q of the flip-flop 1012 is equal to the logic level of the data input D thereof, that is, the counting start edge of each counting signal may be generated and transmitted to the light source 40 according to the delay provided by the controllable delay chain 1011 to control the light source to emit photons at different times.
It should be noted that the delay circuit 101 is not limited to the above-mentioned scheme, for example, it may also only include a controllable delay chain, and the controllable delay chain may include a buffer and several switches. The controllable delay chain can directly count the start edge Ctr1_ Up of the first counting signal Ctr1 under the action of the phase selection signal Sel to obtain the start edge of each counting signal.
For more information on the distance sensor 300, please refer to the related description of the distance sensor 200, which is not repeated herein.
The embodiment of the invention provides a distance measuring method of a distance sensor. Referring to fig. 7, 3 and 4 together, the distance measuring method of the distance sensor 200 may include the steps of:
step S101, obtaining a plurality of count signals Ctrl, Ctr2 … …, and CtrN, where N is a positive integer, that is, N is the total number of the count signals Ctr2 to CtrN, each of the count signals Ctr1 to CtrN has a count start edge (not shown in the figure) and a count stop edge (not shown in the figure), where the count start edge of the first count signal Ctrl is generated when the light source 40 emits photons, the count stop edge of the first count signal Ctrl is generated when reflected photons obtained by reflection from the target object are detected, and the count stop edges of the other count signals Ctr2 to CtrN have different delays relative to the count stop edge of the first count signal Ctrl;
step S102, counting the input clock signal C L Kin within a time window TOF 1-N defined by a counting start edge of the first counting signal Ctr1 and a counting stop edge of each counting signal Ctr1 to CtrN to obtain a corresponding counting value;
step S103, determining the distance between the target object and the distance sensor 200 using the respective count values.
In this embodiment, the distance between the target object and the distance sensor 200 corresponds to a Time Of Flight (TOF) Of a photon, and the count values may indicate a ratio Of a Time in which the Time Of Flight Of the photon is not counted in the counting result to a period Of the input clock signal C L Kin, so that the embodiment Of the present invention may increase the quantization resolution Of counting to 1/N Of the original counting period, and may effectively improve the measurement accuracy Of the distance sensor 200 based on the photon detection technology.
Preferably, the acquiring the plurality of count signals Ctr1 to CtrN in step S101 may include the following steps: controlling the light sources 40 to emit photons at different times, and generating a counting start edge of a corresponding counting signal when the light sources 40 generate the photons; generating a count stop edge of a corresponding count signal when a reflected photon reflected by the target object is detected; wherein the counting start edges of the other counting signals Ctr 2-CtrN have different delays relative to the counting start edge of the first counting signal Ctr 1.
Furthermore, in the embodiment of the present invention, the plurality of count signals Ctr1 to CtrN may be obtained through multiple quantization, and the same counter may be used for multiple counting in the multiple quantization mode, so as to save resources of the counter and reduce the influence of noise on measurement through multiple quantization.
Preferably, the delay of the count stop edge of each of the other count signals Ctr 2-CtrN with respect to the count stop edge of the first count signal Ctr1 is less than or equal to the period T of the input clock signal C L Kin.
Further preferably, the delay is equal to T/(N-1) × (i-1) for the ith count signal Ctri, where T is the period of the input clock signal C L Kin, i is an integer, and 2 ≦ i ≦ N.
In a specific implementation, the step S103 may include the step of determining the distance between the target object and the distance sensor 200 according to the average value of the obtained respective count values, the period of the input clock signal C L Kin, and the propagation speed of the photon.
The embodiment of the invention also provides another distance measuring method of the distance sensor. Referring to fig. 8 and 6 together, the distance measuring method of the distance sensor 300 may include the steps of:
step S101, obtaining a plurality of count signals Ctrl, Ctr2 … …, and CtrN, where N is a positive integer, each of the count signals Ctr1 to CtrN has a count start edge (not shown) and a count stop edge (not shown), where the count start edge of the first count signal Ctrl is generated when the light source 40 emits photons, the count stop edge of the first count signal Ctrl is generated when reflected photons obtained by reflection of the target object are detected, and the count stop edges of the other count signals Ctr2 to CtrN have different delays with respect to the count stop edge of the first count signal Ctrl;
step S102, counting the input clock signal C L Kin within a time window TOF 1-N defined by a counting start edge of the first counting signal Ctr1 and a counting stop edge of each counting signal Ctr1 to CtrN to obtain a corresponding counting value;
step S104, comparing the count value obtained by counting at the current time with the count value obtained before the current time;
step S105, judging whether the count value obtained by current counting is larger than the sum of the maximum value and 1 in the count values obtained before the current counting, or smaller than the maximum value in the count values obtained before the current counting; if yes, executing step S106, judging the counting value obtained by counting at the current time as an abnormal counting value, and rejecting the abnormal counting value; if not, step S103 is executed.
Wherein, step S106: judging the counting value obtained by current counting as an abnormal counting value; step S103: the distance between the target object and the distance sensor 300 is determined using the respective count values.
Since the later the counter 20 finishes counting, the larger the counting result will be, if the actual counting result appears smaller or too large, it will be determined as a counting error, and when it is identified, the counting should be performed again. Finally, the abnormal count values are removed, and the correct count values are averaged, thereby improving the measurement accuracy of the distance sensor 300.
For more information on the steps S101, S102 and S103, please refer to the related description of fig. 7, which is not repeated herein.
For more information on the distance measuring method of the distance sensor 200 or 300, please refer to the related description of the distance sensors 200 and 300, which is not repeated herein.
The embodiment of the invention also discloses a 3D image sensor, which can comprise a plurality of distance sensors 200 or 300, wherein the photon detection circuit 102 is arranged in an array. Compared with the distance sensor in the prior art, the distance sensor 200 or 300 in the embodiment of the invention has higher measurement accuracy, so that the 3D image sensor has higher reconstruction accuracy on a 3D image and can be used for detecting a finer 3D image.
In specific implementation, the 3D image sensor can be applied to 3D image reconstruction devices such as single photon cameras, 3D printers and the like. Further, the photon detection circuit 102 adopted by the 3D image sensor in this embodiment can detect single photons, so that a 3D scene can be efficiently, quickly, and accurately reconstructed in a low-light environment.
Although the present invention is disclosed above, the present invention is not limited thereto. Various changes and modifications may be effected therein by one skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
Claims (13)
1. A distance measuring method of a distance sensor, comprising:
acquiring a plurality of counting signals, wherein each counting signal is provided with a counting start edge and a counting stop edge, the counting start edge of the first counting signal is generated when the light source emits photons, the counting stop edge of the first counting signal is generated when reflected photons reflected by a target object are detected, and the counting stop edges of other counting signals have different time delays relative to the counting stop edge of the first counting signal;
counting the input clock signals in a time window defined by a counting start edge of a first counting signal and a counting stop edge of each counting signal to obtain corresponding counting values;
determining a distance between the target object and the distance sensor using the respective count values;
and for the ith counting signal, the delay is equal to T/(N-1) × (i-1), wherein T is the period of the input clock signal, N is the total number of the counting signals, i and N are integers, and i is more than or equal to 2 and less than or equal to N.
2. The distance measurement method according to claim 1, wherein said acquiring a plurality of count signals comprises:
controlling the light sources to respectively emit photons at different moments, and generating a counting starting edge of a corresponding counting signal when the light sources generate the photons;
generating a count stop edge of a corresponding count signal when a reflected photon reflected by the target object is detected;
wherein the counting start edge of the other counting signals has a different delay with respect to the counting start edge of the first counting signal.
3. The distance measuring method according to claim 1, wherein the delay of the count stop edge of each of the other count signals with respect to the count stop edge of the first count signal is less than or equal to the period of the input clock signal.
4. The distance measurement method according to claim 3, wherein the determining the distance between the target object and the distance sensor using the respective count values includes: and determining the distance between the target object and the distance sensor according to the average value of the obtained counting values, the period of the input clock signal and the propagation speed of the photons.
5. The distance measuring method according to claim 1, further comprising, before said determining the distance between the target object and the distance sensor using the respective count values:
comparing the count value obtained by counting at the current time with the count value obtained before the current time;
and if the count value obtained by the current counting is larger than the sum of the maximum value and 1 in the count values obtained before the current counting, or is smaller than the maximum value in the count values obtained before the current counting, judging that the count value obtained by the current counting is an abnormal count value, and rejecting the abnormal count value.
6. A distance sensor, comprising:
a counting signal acquisition module, adapted to acquire a plurality of counting signals, each counting signal having a counting start edge and a counting stop edge, wherein the counting start edge of the first counting signal is generated when the light source emits photons, the counting stop edge of the first counting signal is generated when reflected photons reflected by the target object are detected, and the counting stop edges of the other counting signals have different delays with respect to the counting stop edge of the first counting signal;
the counter is suitable for counting the input clock signals in a time window defined by the counting start edge of the first counting signal and the counting stop edge of each counting signal so as to obtain corresponding counting values;
wherein each count value is used to determine a distance between the target object and the distance sensor;
and for the ith counting signal, the delay is equal to T/(N-1) × (i-1), wherein T is the period of the input clock signal, N is the total number of the counting signals, i and N are integers, and i is more than or equal to 2 and less than or equal to N.
7. The distance sensor of claim 6, wherein said count signal acquisition module comprises:
the time delay circuit is suitable for controlling the light sources to respectively emit photons at different moments, and the counting start edges of the corresponding counting signals are generated when the light sources generate the photons, wherein the counting start edges of other counting signals have different time delays relative to the counting start edge of the first counting signal;
and the photon detection circuit is suitable for respectively detecting the reflected photons obtained by the reflection of the target object so as to obtain the counting stop edge of each counting signal.
8. The distance sensor of claim 7, wherein the count stop edges of said other count signals each have a delay relative to the count stop edge of said first count signal that is less than or equal to the period of said input clock signal.
9. The distance sensor of claim 8, further comprising: and the control module is suitable for determining the distance between the target object and the distance sensor according to the obtained average value of the counting values, the period of the input clock signal and the propagation speed of the photons.
10. The distance sensor according to claim 9, wherein the control module is further adapted to compare a count value obtained by a current counting with a count value obtained before the current counting before determining the distance between the target object and the distance sensor using each count value, and determine the count value obtained by the current counting as an abnormal count value and reject the abnormal count value if the count value obtained by the current counting is greater than a sum of a maximum value of the count values obtained before the current counting and 1 or less than a maximum value of the count values obtained before the current counting.
11. The distance sensor of claim 8, wherein said delay circuit comprises:
a controllable delay chain having a clock input connected to said input clock signal and adapted to generate an output clock signal under control of a phase selection signal, said output clock signal having a delay relative to said input clock signal equal to T/(N-1) × (i-1);
and the data input end of the trigger is connected with the counting start edge of the first counting signal, and the data output end of the trigger outputs the counting start edges of the other counting signals under the action of the output clock signal.
12. The distance sensor of any of claims 6 to 11, wherein said photon detection circuit comprises:
a SPAD adapted to generate an avalanche current upon detection of the reflected photon;
a pulse generating circuit adapted to generate a count-stop edge of the count signal based on the avalanche current.
13. A 3D image sensor comprising a plurality of the distance sensors of any one of claims 7 to 12, wherein the photon detection circuits are arranged in an array.
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| US11353563B2 (en) * | 2018-09-13 | 2022-06-07 | Pixart Imaging Inc. | Avalanche diode based object detection device |
| CN114270208A (en) * | 2020-11-13 | 2022-04-01 | 深圳市汇顶科技股份有限公司 | Time-of-flight measurement circuit and related system, electronic device and method |
| CN113009455B (en) * | 2021-04-14 | 2022-06-03 | 吉林大学 | Method and system for improving pulse laser ranging precision |
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