Detection circuit, receiving unit, and laser radar with adjustable output pulse width

Abstract

The present invention discloses a detection circuit with adjustable output pulse width, comprising: a single-photon avalanche diode, which can generate a photocurrent according to incident photons; a comparator, a first input terminal inputting an adjustable threshold signal, a second input terminal coupled to the single-photon avalanche diode, to input an electrical signal representing the photocurrent; and the comparator is configured to output a waveform according to the comparison result between the electrical signal and the adjustable threshold signal. The present invention provides a unit detection circuit, which has the following characteristics: when multiple photons are received by the single-photon avalanche diode in a short time, the pulse width of the circuit output signal will be widened, so that the information of the number of photons can be obtained through the signal pulse width, and the dynamic range of the single-photon avalanche diode device is expanded; in addition, the pulse width of the single-photon signal can be adjusted. In the distance measurement application, the pulse width of the single-photon signal can be configured to be close to the distance measurement light pulse width, so that the processing circuit is convenient to set a reasonable "integration time window" to obtain a better signal-to-noise ratio.

Description

Technical Field

[0001] The present invention generally relates to the field of optoelectronic technology, and in particular to a detection circuit with adjustable output pulse width, a receiving unit including the detection circuit, a laser radar, and an echo detection method. Background Art

[0002] At present, SPAD (single photon avalanche diode) units in LiDAR ranging applications can be divided into two categories, active quenching and passive quenching. Passive quenching SPAD units such as Figure 1A As shown. When the photon arrives, Figure 1A Diode 1, which is biased in Geiger mode, triggers an avalanche, generating Figure 1B The avalanche current 101 in the quenching resistor R generates a voltage ( Figure 1B The avalanche is then quenched, node 2 is discharged back to ground potential by the quenching resistor R, and diode 1 returns to the Geiger bias region. The waveform at node 2 is converted into a digital pulse with a certain driving capability after passing through the buffer and is output to the post-processing circuit (waveform 103 on the right side of Figure 1). The buffer is usually composed of multiple stages of inverters with a fixed flip threshold. The actively quenched SPAD unit is shown in Figure 2. When a photon arrives ( Figure 2B The waveform 201 in FIG. 20 shows that the diode 21 biased in the Geiger mode triggers an avalanche. At this time, the NMOS tube connected to the anode of the diode and GND is cut off (because the gate voltage 3 of the NMOS is 0V), and the NMOS is in a high-resistance state. The avalanche current generates a voltage at the drain of the NMOS tube, and then the avalanche is quenched. Node 22 maintains a high level ( Figure 2B 202), until after a delay of TDELAY (typically a few ns to tens of ns), the high level propagates to node 23 ( Figure 2B The waveform 203 in the figure makes the NMOS conduct, node 22 is discharged to 0V, and the diode returns to the Geiger bias region. The pulse width of node 22 is approximately equal to the duration of TDELAY, and the waveform of node 22 is converted into a digital pulse with a certain driving capability after buffering, and is output to the post-processing circuit ( Figure 2B The dotted line portion in waveform 204 represents the dead time of the SPAD. During the time period corresponding to the dotted line, since the NMOS tube is continuously turned on to pull the node 22 to GND, the circuit is not in a normal working state and waiting for the arrival of photons. This period of time is regarded as dead time until the NMOS tube returns to the cut-off state and the circuit returns to the working state.

[0003] In the passively quenched SPAD unit, the flip threshold of the buffer is fixed, so the width of the output pulse is fixed. When used in a lidar, the device is prone to saturation under strong ambient light, resulting in the inability to measure distance normally. In addition, since the output pulse width cannot be adjusted and cannot be adapted to the light pulse width, the optimized signal-to-noise ratio cannot be obtained in the case of certain processing circuits, and the ranging performance is reduced. In the actively quenched SPAD unit, the pulse width does not widen with the photon sequence, so the effective information required for ranging and ambient light intensity judgment is lost. In addition, there is dead time, which causes signal distortion.

[0004] The contents of the background technology section are merely the technologies known to the public and do not necessarily represent the existing technologies in the field. Summary of the invention

[0005] The present invention provides a detection circuit with adjustable output pulse width, a receiving unit that can be used for a laser radar, a laser radar comprising the receiving unit, and a method for performing echo detection using the receiving unit.

[0006] The present invention provides a detection circuit with adjustable output pulse width, comprising:

[0007] a single-photon avalanche diode configured to generate a photocurrent in response to incident photons; and

[0008] A comparator, wherein an adjustable threshold signal is input to a first input terminal of the comparator, and a second input terminal of the comparator is coupled to the single-photon avalanche diode to input an electrical signal representing the photocurrent; the comparator is configured to output a waveform according to a comparison result between the electrical signal and the adjustable threshold signal.

[0009] According to one aspect of the present invention, the cathode of the single-photon avalanche diode is coupled to a high voltage, the anode of the single-photon avalanche diode is grounded through a quenching resistor, and the anode is coupled to the second input terminal of the comparator, wherein the electrical signal is an analog voltage output by the single-photon avalanche diode.

[0010] According to one aspect of the present invention, the cathode of the single-photon avalanche diode is coupled to a high voltage through a quenching resistor, the anode of the single-photon avalanche diode is grounded, and the cathode is coupled to the second input terminal of the comparator through a capacitor, wherein the electrical signal is the change in voltage of the cathode of the single-photon avalanche diode.

[0011] According to one aspect of the present invention, the detection circuit further includes a threshold control unit, which is configured to output the adjustable threshold signal, and the threshold control unit is coupled to the first input terminal of the comparator to provide the adjustable threshold signal to the first input terminal.

[0012] According to one aspect of the present invention, the adjustable threshold signal increases as the intensity of the incident light increases.

[0013] The present invention also provides a receiving unit that can be used for a laser radar, comprising:

[0014] A detection circuit, the detection circuit comprising:

[0015] a single-photon avalanche diode configured to generate a photocurrent in response to incident photons; and

[0016] A comparator, wherein an adjustable threshold signal is input to a first input terminal of the comparator, and a second input terminal of the comparator is coupled to the single-photon avalanche diode to input an electrical signal representing the photocurrent; the comparator is configured to output a waveform according to a comparison result between the electrical signal and the adjustable threshold signal; and

[0017] A processing unit is coupled to the output end of the comparator of the detection circuit and is configured to calculate the incident light intensity according to the waveform output by the comparator.

[0018] According to one aspect of the present invention, the cathode of the single-photon avalanche diode is coupled to a high voltage, the anode of the single-photon avalanche diode is grounded through a quenching resistor, and the anode is coupled to the second input terminal of the comparator, wherein the electrical signal is the voltage across the quenching resistor.

[0019] According to one aspect of the present invention, the cathode of the single-photon avalanche diode is coupled to a high voltage through a quenching resistor, the anode of the single-photon avalanche diode is grounded, and the cathode is coupled to the second input terminal of the comparator through a capacitor, wherein the electrical signal is the voltage of the single-photon avalanche diode.

[0020] According to one aspect of the present invention, the receiving unit also includes a threshold control unit, which is coupled to the processing unit and configured to adjust the adjustable threshold signal according to the incident light intensity, and the threshold control unit is coupled to the first input terminal of the comparator to provide the adjustable threshold signal to the first input terminal.

[0021] According to one aspect of the present invention, the threshold control unit is configured to increase the adjustable threshold signal as the incident light intensity increases.

[0022] According to one aspect of the present invention, the receiving unit includes multiple groups of detection circuits and a summer, the output ends of the comparators of the multiple groups of detection circuits are coupled to the input ends of the summer, and the summer performs a summing operation on the outputs of the multiple groups of detection circuits.

[0023] According to one aspect of the present invention, the adjustable threshold signal of the detection circuit is set so that the width of the output waveform of the comparator of the detection circuit for a single photon matches the width of the laser pulse of the laser radar.

[0024] According to one aspect of the present invention, the adjustable threshold signal of the detection circuit is set so that: the width of the output waveform of the comparator of the detection circuit for a single photon is equal to the half-maximum full width of the laser pulse of the laser radar.

[0025] According to one aspect of the present invention, the processing unit is configured to calculate the number of incident photons based on the pulse width of the waveform output by the comparator.

[0026] The present invention also provides a laser radar, comprising:

[0027] A transmitting unit, the transmitting unit comprising a laser, the laser being configured to transmit laser pulses to the outside of the laser radar to detect a target object;

[0028] The receiving unit as described above is configured to receive an echo of the laser pulse after it is reflected on a target object;

[0029] A calculation unit is coupled to the receiving unit and is configured to calculate the distance and / or reflectivity of the target object according to the waveform output by the comparator of the receiving unit.

[0030] The present invention also provides a method for performing echo detection using the receiving unit as described above.

[0031] The present invention also provides a laser detection method, comprising:

[0032] Emitting a detection laser beam to detect a target object;

[0033] receiving an echo from the target object by a single photon avalanche diode, wherein the single photon avalanche diode generates a photocurrent according to incident photons;

[0034] By means of a comparator, the electrical signal representing the photocurrent is compared with an adjustable threshold signal to generate a digital signal output;

[0035] The adjustable threshold signal is adjusted according to the waveform of the digital signal output.

[0036] According to one aspect of the present invention, the step of adjusting the adjustable threshold signal according to the waveform of the digital signal output includes: increasing the adjustable threshold signal as the intensity of the incident light increases.

[0037] The embodiment of the present invention provides a single-photon avalanche diode unit circuit (pixel level circuit), which has two characteristics: when multiple photons are received by the single-photon avalanche diode in a short time, the pulse width of the circuit output signal will be widened, so that the information of the number of photons can be obtained through the signal pulse width, which expands the dynamic range of the single-photon avalanche diode device. The pulse width of the single-photon signal can be set and adjusted. In the dTOF ranging application, this characteristic can be used to configure the pulse width of the single-photon signal to a degree close to the ranging luminous pulse width, so as to facilitate the processing circuit to set a reasonable "integration time window" and obtain a better signal-to-noise ratio. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawings constituting a part of the present disclosure are used to provide a further understanding of the present disclosure. The illustrative embodiments of the present disclosure and their descriptions are used to explain the present disclosure and do not constitute an improper limitation on the present disclosure. In the drawings:

[0039] Figure 1A and 1B The passively quenched single photon avalanche diode detection circuit and its waveform are shown respectively;

[0040] Figure 2A and 2B The active quenching single photon avalanche diode detection circuit and its waveform are shown respectively;

[0041] Figure 3A A detection circuit according to an embodiment of the first aspect of the present invention is shown;

[0042] Figure 3B Shows Figure 3A Schematic diagram of waveforms of various nodes in the detection circuit;

[0043] Figure 4 Shown in Figure 3A Schematic diagram of adjusting pulse width by adjusting threshold in circuit;

[0044] Figure 5 A schematic diagram showing how to increase the dynamic range of a single-photon avalanche diode device by increasing the threshold when the ambient light is strong;

[0045] Fig. 6A A detection circuit according to another embodiment of the first aspect of the present invention is shown;

[0046] Figure 6B Shows Fig. 6A Schematic diagram of waveforms of various nodes in the detection circuit;

[0047] Figure 7 A schematic diagram of a receiving unit that can be used for a laser radar according to a second aspect of the present invention is shown;

[0048] Figure 8 A schematic diagram of a receiving unit according to a preferred embodiment of the second aspect of the present invention is shown;

[0049] Fig. 9 Shows Figure 8 A schematic diagram of waveforms of various nodes in a receiving unit is used to illustrate the selection and optimization of thresholds;

[0050] Fig.10 A schematic diagram showing a laser radar according to a third aspect of the present invention; and

[0051] Fig.11 A schematic diagram of a laser detection method according to the fourth aspect of the present invention is shown. DETAILED DESCRIPTION

[0052] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0053] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, which are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0054] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or can communicate with each other; it can be directly connected, or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0055] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply means that the first feature is lower in level than the second feature.

[0056] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can be aware of the application of other processes and / or the use of other materials.

[0057] The preferred embodiments of the present invention are described below in conjunction with the accompanying drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0058] First aspect

[0059] Figure 3A FIG. 1 shows a detection circuit 10 according to an embodiment of the first aspect of the present invention, wherein the output pulse width can be adjusted and widened, thereby reflecting the width of the light emitting pulse. Figure 3A Detailed description.

[0060] like Figure 3A As shown, the detection circuit 10 includes a single photon avalanche diode 11 and a comparator 12. The single photon avalanche diode is a photoelectric detection avalanche diode with single photon detection capability. It works in Geiger mode and can generate photocurrent according to incident photons, which can be used for the detection of extremely weak optical signals. The first input terminal ( Figure 3AThe inverting input terminal - of the comparator 12 in FIG. 3 inputs the adjustable threshold signal Threshold, and the second input terminal of the comparator 12 (the non-inverting input terminal + of the comparator 12 in FIG. 3) is coupled to the single-photon avalanche diode 11 to input the electrical signal representing the photocurrent. The comparator 12 outputs a waveform according to the comparison result between the electrical signal and the adjustable threshold signal Threshold, for example, when the electrical signal is higher than the adjustable threshold signal Threshold, it outputs a high level; when the electrical signal is higher than the adjustable threshold signal Threshold, it outputs a low level. The opposite is also true.

[0061] like Figure 3A As shown, according to a preferred embodiment of the present invention, the detection circuit 10 may further include a quenching resistor 13. The cathode of the single-photon avalanche diode 11 is coupled to a high voltage +HV, and the anode is grounded through the quenching resistor 13. In the Geiger mode, it can respond to the incident photon input stimulus P. The anode of the single-photon avalanche diode 11 is also coupled to the second input terminal (non-inverting input terminal +) of the comparator 12, so that the analog voltage output by the single-photon avalanche diode 11 is provided to the comparator 12 as an electrical signal. Figure 3A The circuit structure shown is applicable to a single-photon avalanche diode device of a P-on-N structure, because the anode of the single-photon avalanche diode of this structure does not need to be grounded, so it can be based on Figure 3A The anode of the single-photon avalanche diode of the N-on-P structure usually needs to be grounded, and its specific circuit structure will be described in detail below. Both single-photon avalanche diodes of these two structures can be used in the expandable and adjustable detection circuit of the present invention.

[0062] Figure 3B Shows Figure 3A In the circuit structure, when the single photon avalanche diode 11 receives a photon input stimulus P, the waveform A2 of the in-phase input terminal of the comparator 12 and the waveform A3 of the output terminal of the comparator 12. When the photon input stimulus P is a photon, as Figure 3BAs shown by a single arrow in the photon input stimulus P, waveform A2 at the in-phase input of comparator 12 corresponds to the signal waveform of a single photon, including a steeply rising front edge and an exponentially decaying trailing edge. The steeply rising front edge is due to the fact that the avalanche and quenching process occurs very quickly, usually in a time of <1ns, that is, the rising time of the front edge of the single photon signal is <1ns. The exponentially decaying trailing edge corresponds to the charging (Recharge) process of the single-photon avalanche diode. After the avalanche is quenched by the quenching resistor, the high-voltage power supply +HV charges the junction capacitance of the single-photon avalanche diode through the quenching resistor 13 (resistance is RQ), and the charging time constant is RQxCD, thus forming an exponentially decaying single-photon signal trailing edge. The typical value of the charging time constant is from a few ns to tens of ns. Through comparator 12, a digital waveform A3 is generated at the output end of comparator 12, where when the voltage of waveform A2 is higher than the threshold Threshold, it corresponds to the high level of waveform A3, and vice versa, it corresponds to the low level of waveform A3.

[0063] When the photon input stimulus P includes multiple consecutive photons, such as Figure 3B As shown by the three adjacent arrows in the photon input stimulus P, waveform A2 includes a corresponding number of single-photon signal waveforms, each of which includes a steeply rising leading edge and an exponentially decaying trailing edge, as described above. And because the multiple consecutive photons are closely spaced, and the value of the threshold Threshold is low, which is lower than the trough of the consecutive multiple single-photon signal waveforms, waveform A3 has a broadened output signal waveform accordingly.

[0064] Figure 4 FIG. 4 shows a schematic diagram of adjusting the pulse width by adjusting the threshold Threshold. Figure 4 As shown, for the same photon input stimulus P including one photon, when a lower threshold Threshold 1 is used, the width of the waveform A3 obtained at the output end of the comparator 12 is significantly wider; when a higher threshold Threshold 2 is used, the width of the waveform A3' obtained at the output end is significantly reduced. Therefore, by adjusting the threshold value of the comparator 12 flipping, the time length of the analog signal waveform output by the single-photon avalanche diode 11 exceeding the threshold value can be adjusted, thereby adjusting the width of the digital pulse output by the detection circuit 10 including the single-photon avalanche diode.

[0065] The pulse width modulation function can achieve good application results in many occasions. For example, when it is used in a laser radar system, when the ambient light is strong (such as Figure 5 As shown, the incident photon excitation P includes multiple closely adjacent arrows). By increasing the threshold Threshold, the dynamic range of the single-photon avalanche diode device can be increased, making it less prone to saturation. Specifically, Figure 5As shown, when a lower threshold Threshold 1 is used, when the ambient light is strong, the single-photon avalanche diode device 11 is frequently triggered to avalanche by the incident ambient photons, resulting in the single-photon avalanche diode 11 being triggered to avalanche again before it is fully charged after the avalanche is quenched. The waveform A3 at the output end of the comparator 12 is a waveform of a continuous high level. At this time, the detection circuit 10 can no longer perform normal distance measurement, nor can it accurately measure the ambient light intensity level. After the adjustment adopts a higher threshold Threshold 2, the signal of the waveform A3' at the output end of the comparator 12 can be changed from a continuous high level to a random pulse output. Although the ambient light noise is large at this time, the single-photon avalanche diode device is not fully saturated and still has a certain distance measurement capability (usually when the noise is large, multiple measurements are required to improve the signal-to-noise ratio to extract the effective signal), and the actual intensity of the ambient light can be evaluated through information such as the noise pulse width and frequency.

[0066] It is easy for those skilled in the art to understand that in the above embodiment, the comparator 12 uses a voltage comparator, but the present invention is not limited to this. The voltage comparator is only one embodiment, and a current comparator or other types of circuit structures with configurable flip thresholds (action thresholds) may also be used.

[0067] The above-mentioned embodiment of the present invention adds a comparator with a settable threshold value on the basis of the passive quenching SPAD unit. The comparator also acts as a buffer, and its output has a certain driving capability and can drive the subsequent processing circuit. The output signal of the single-photon signal has two characteristics: the width of the single-photon signal can be changed by adjusting the threshold; when a continuous photon sequence is reached, the output signal is widened along with the photon sequence. Those skilled in the art understand that the output signal widening is beneficial to a certain extent and can be used to judge the intensity of the incident light or the intensity of the ambient light. The specific degree of widening can be determined according to the specific usage scenario, which is not limited in the present invention.

[0068] Fig. 6A FIG. 6 shows a detection circuit 10 according to another embodiment of the present invention. The circuit structure of FIG. 6 is suitable for a single photon avalanche diode of an N-on-P structure, because its anode usually needs to be grounded. Fig. 6AAs shown, the cathode of the single-photon avalanche diode 11 is coupled to a high voltage +HV through a quenching resistor 13, and the anode of the single-photon avalanche diode 11 is grounded and is in Geiger mode. The cathode is also coupled to the second input terminal (the inverting input terminal in the figure) of the comparator 12 through a capacitor 14, so that the change in the cathode voltage of the single-photon avalanche diode 11 is provided as the electrical signal to the inverting input terminal of the comparator 12. The capacitor 14 can block direct current and pass alternating current, so only the change in the cathode voltage of the single-photon avalanche diode 11 can be provided to the inverting input terminal of the comparator 12. Similarly, the non-inverting input terminal of the comparator 12 is connected to the adjustable threshold Threshold. Figure 6B Shows Fig. 6A During the operation of the detection circuit 10, according to the incident photon stimulus P, the waveform A2 at the reverse input end of the comparator 12 and the waveform A3 at the output end of the comparator 12 are generated. Figure 3A The description is similar, the difference is, for example, in Fig. 6A In the circuit structure, the change in the cathode voltage of the single-photon avalanche diode 11 (ie, waveform A2) is a downward sharp pulse. For the specific working method, please refer to the above description of Figure 3A The description is not repeated here.

[0069] In addition, preferably, the detection circuit 10 also includes a bias resistor R B The inverting input terminal of the comparator 12 is biased by the bias resistor R B Connect to bias voltage V BIAS ,like Fig. 6A shown.

[0070] In addition, according to a preferred embodiment of the present invention, the detection circuit 10 further includes a threshold control unit, which is configured to generate and output the adjustable threshold signal according to the intensity of the ambient light, and the threshold control unit is coupled to the first input terminal of the comparator to provide the adjustable threshold signal Threshold to the first input terminal. Figure 7 The threshold control unit can, for example, dynamically adjust the adjustable threshold signal to change the width of the single photon signal in the output waveform A3 of the detection circuit, and can make the output signal widen along with the photon sequence when a continuous photon sequence is reached.

[0071] The detection circuit according to the first aspect of the present invention is described above. Among them, when the single-photon avalanche diode is triggered to avalanche by a photon, it will then undergo a quenching and charging process and then return to a normal working state. For the detection circuit unit proposed in the embodiment of the present invention, if during the charging recovery process, another or several photons are incident on the photosensitive area of ​​the single-photon avalanche diode and trigger an avalanche, the output signal of the detection circuit will be widened. The law of widening is briefly described below. The total pulse width output by the detection circuit 10 is the total duration of the incident photon sequence plus the duration of the single-photon output pulse width (pulse width). For example, when the single-photon output pulse width is 5ns, 3 photons come continuously within a time length of 7ns, then the total pulse width output by the detection circuit is 7ns+5ns=12ns. The photon sequence in the sense of the present invention means that the maximum time interval between each adjacent photon in a photon sequence needs to be less than a single-photon pulse width. If the time interval between two adjacent photons in a photon sequence exceeds the pulse width of a single photon, then the output is not a stretched pulse, but two output pulses, and the photon sequence will be regarded as two photon sequences.

[0072] The broadening characteristic can play a significant role in the optoelectronic system. In the detection circuit of some single-photon avalanche diodes without the broadening characteristic, in the recovery time period after the avalanche (the typical value of the recovery time is several ns to tens of ns), if there are other photons incident on the photosensitive area of ​​the single-photon avalanche diode, it will not cause any change in the output signal of the single-photon avalanche diode, which is equivalent to the recovery time of the single-photon avalanche diode being the "dead time" of the detection circuit. Therefore, for the detection circuit of the single-photon avalanche diode without the broadening characteristic, when the echo signal is strong to a certain extent, it is impossible to distinguish the intensity of the signal, and the information is lost, which will cause ranging errors and the inability to measure the reflectivity. Compared with the detection circuit of the single-photon avalanche diode without the broadening characteristic, the broadening characteristic of the present invention can obtain additional information, and can distinguish whether an output pulse is caused by a single photon or multiple continuous photons from the output pulse width, thereby increasing the dynamic range of the single-photon avalanche diode detection circuit, and can still obtain pulse intensity information in the case of a strong saturation signal. Using this information, more accurate ranging results and target reflectivity measurement results can be obtained.

[0073] Second aspect

[0074] A second aspect of the present invention relates to a receiving unit 20 that can be used for a laser radar, comprising the detection circuit 10 and a processing unit 21 as described above, such as Figure 7 shown. Figure 7 The detection circuit 10 shown in FIG. Figure 3A The same as shown, but the present invention is not limited thereto, and the following may also be used Fig. 6A The detection circuit 10 shown is within the protection scope of the present invention.

[0075] The specific structure and working mode of the detection circuit 10 are as mentioned above. Figure 3A-6B The details are described above and will not be repeated here. The detection circuit 10 generates a digital waveform A3 at the output end of the comparator 12 according to the incident photon excitation P. The processing unit 21 is coupled to the output end of the comparator 12 of the detection circuit 10, so that it can receive the digital waveform A3 and calculate the intensity of the incident photon excitation P according to the waveform. According to one embodiment of the present invention, the processing unit 21 is configured to calculate the number of incident photons according to the pulse width of the waveform output by the comparator 12, and then the reflectivity of the target object can be obtained according to the calculation result.

[0076] In addition, Figure 7 As shown, the detection circuit 10 also includes a threshold control unit 15, the threshold control unit 15 is coupled to the processing unit 21, and is configured to adjust the adjustable threshold signal according to the incident light intensity, and the threshold control unit 15 is coupled to the first input terminal of the comparator 12 to provide the adjustable threshold signal Threshold to the first input terminal. For example, the threshold control unit 15 can increase the adjustable threshold signal as the incident light intensity increases. Preferably, the incident light intensity can be divided into a plurality of intervals, each interval corresponding to an adjustable threshold signal, and the higher the incident light intensity, the higher the adjustable threshold signal. The threshold control unit 15 can select an appropriate adjustable threshold signal according to the interval in which the current incident light intensity is located.

[0077] Figure 8 A preferred embodiment of the present invention is shown, wherein the receiving unit 20 of the laser radar includes multiple groups of the detection circuits 10 and the summer 22, forming a detection channel. Each detection circuit constitutes a pixel. Figure 8 Four pixels are schematically shown, namely pixels 1-4. Those skilled in the art can easily understand that Figure 8 As an illustrative example, in a ranging circuit based on a single-photon avalanche diode array, multiple single-photon avalanche diodes are usually combined into a channel (or a macro unit). In the example in the figure below, a channel / macro unit includes four single-photon avalanche diodes, but the present invention is not limited to this. A channel can be composed of any number of single-photon avalanche diodes or more. Figure 8As shown, the output ends of the comparators 12 of the plurality of detection circuits 10 are coupled to the input ends of the summer 22, and the summer 22 performs a summing operation on the outputs of the plurality of detection circuits. The output end of the summer 22 can be connected to the processing unit 21 (not shown in the figure). By using the summer 22 to perform the summing operation, the effective signal can be accumulated, so that the signal output is stronger and the signal-to-noise ratio is higher.

[0078] In addition, preferably, the signal-to-noise ratio can be further optimized and improved by adjusting the single-photon signal output pulse width to match the laser radar light emission pulse width. Figure 8 In the circuit structure, the output digital signals of multiple pixels are accumulated and summed (Σ). When the accumulated result exceeds a certain numerical threshold, it is determined that there is a valid signal at this time, that is, a valid ranging echo pulse is received. The basis for determining the ranging pulse signal in this way is that the noise signal caused by ambient light or single photon avalanche diode dark count is on the time axis ( Fig. 9 The probability of these noise signals occurring simultaneously in a very narrow time window (a few ns) is extremely low. Therefore, when the detection circuits 10 of multiple single-photon avalanche diodes simultaneously generate output signals (and then accumulate a larger value) in a very narrow time window, it is very likely that this is caused by an effective echo signal light pulse. Furthermore, the processing circuit and algorithm program can extract the ranging information, target reflectivity information, etc. required to be collected by the laser radar through the pulse trigger time and pulse waveform after the output signals of multiple pixels are summed. In an embodiment of the present invention, the width of the digital pulse signal output by the pixel can be adjusted by adjusting the threshold within a single pixel. When this width is adapted to the width of the laser pulse, a more optimized ranging signal-to-noise ratio and a higher detection probability can be obtained. According to a preferred embodiment of the present invention, the threshold is adjusted so that the time width of the output digital signal of each pixel (or detection circuit) in response to a single photon input is equal to the half-maximum full width of the laser pulse. At this time, most of the energy of the signal of the light pulse emitted by the laser is concentrated in the time window corresponding to the half-maximum full width, Figure 8The processing circuit shown in will accumulate the single photon counts occurring in this time window. In other words, by setting the pulse width of the output signal, the length of an integral time window is set, and the processing circuit will accumulate the single photon events occurring in the time window. If the integral time window is set narrower than the laser pulse, the emitted light energy will be wasted, and most of the emitted effective signals will not be collected, so the ranging signal-to-noise ratio is reduced and the detection probability is reduced. If the integral time window is set wider than the laser pulse, the total signal amount does not change significantly, but the total amount of noise entering this wider time window will increase, so the ranging signal-to-noise ratio is reduced and the detection probability is reduced. Therefore, there is an optimal integral time window width. By adjusting the output signal pulse width of the detection circuit of the single-photon avalanche diode, this optimal time window width can be selected, thereby obtaining an optimized ranging signal-to-noise ratio and an optimized detection probability. Therefore, by setting the adjustable threshold signal of the detection circuit so that the width of the output waveform of the comparator of the detection circuit for single photons matches the width of the laser pulse of the laser radar, the signal-to-noise ratio of the circuit can be improved. Preferably, the width of the output waveform of the comparator of the detection circuit for a single photon is equal to the half-maximum full width of the laser pulse of the laser radar.

[0079] by Fig. 9 The waveform shown is explained in detail. Fig. 9 In the example, the time width w of the output digital signal of each pixel (i.e., the waveform A3 output by the detection circuit) is equal to the half-height full width of the laser pulse, as shown in the waveforms of pixel 1 to pixel 4. Within the time width w, four pixels generate outputs (i.e., the rising edges of the outputs of the four pixels all fall within the time width). After being accumulated and summed by the summer 22, the height of the waveform output by the summer 22 is four times the height of the waveform of a single pixel. However, since the probability of noise signals occurring simultaneously within a time width w is extremely low, the output of the noise signal is usually not accumulated. Even after passing through the summer, the height of the waveform output is only one time the height of the waveform of a single pixel. In this case, the signal-to-noise ratio of the detection unit can be characterized as 4. If the threshold is further increased so that the time width w of the output digital signal of each pixel (i.e., the waveform A3 output by the detection circuit) is reduced, then within the time width w, the outputs generated by the four pixels cannot be fully accumulated, and the height of the waveform output by the summer 22 is less than four times the height of the waveform of a single pixel, for example, it may be two or three times. In this case, the signal-to-noise ratio is significantly reduced. On the contrary, if the threshold is further lowered so that the time width w of the output digital signal of each pixel (i.e., signal waveform A3) increases, although the outputs generated by the four pixels can be fully accumulated within the time width w, the height of the waveform output by the summer 22 is equal to four times the height of the single pixel waveform, but within the time width w, the noise signal may also be accumulated through the summer, so the signal-to-noise ratio will also be reduced.

[0080] The broadening characteristic can play a significant role in the optoelectronic system. In the detection circuit of some single-photon avalanche diodes without the broadening characteristic, in the recovery time period after the avalanche (the typical value of the recovery time is several ns to tens of ns), if there are other photons incident on the photosensitive area of ​​the single-photon avalanche diode, it will not cause any change in the output signal of the single-photon avalanche diode, which is equivalent to the recovery time of the single-photon avalanche diode being the "dead time" of the detection circuit. Therefore, for the detection circuit of the single-photon avalanche diode without the broadening characteristic, when the echo signal is strong to a certain extent, it is impossible to distinguish the intensity of the signal, and the information is lost, which will cause ranging errors and the inability to measure the reflectivity. Compared with the detection circuit of the single-photon avalanche diode without the broadening characteristic, the broadening characteristic of the present invention can obtain additional information, and can distinguish whether an output pulse is caused by a single photon or multiple continuous photons from the output pulse width, thereby increasing the dynamic range of the single-photon avalanche diode detection circuit, and can still obtain pulse intensity information in the case of a strong saturation signal. Using this information, more accurate ranging results and target reflectivity measurement results can be obtained.

[0081] When the receiving unit detects that the current echo signal is too strong, the threshold of the SPAD flip can also be increased to obtain more accurate information about the signal light pulse, as shown in the reference above. Figure 4 as described.

[0082] In addition, those skilled in the art understand that the above-mentioned receiving unit 20 can be used as a unit, each unit corresponding to a channel, and arranged in an array to form a single-photon avalanche diode detection array, forming multiple receiving channels of a laser radar for measuring incident light, which are all within the protection scope of the present invention.

[0083] The present invention also relates to a method for performing echo detection using the receiving unit as described above.

[0084] In addition, when used in laser radar, the output pulse width and recovery time of the single-photon avalanche diode detection circuit are required to be as short as possible. Such optimization can make the dynamic range of the single-photon avalanche diode device larger and less likely to saturate under ambient light noise. Some designs are needed to make the output pulse width and recovery time of the single-photon avalanche diode detection circuit as short as possible. In the single-photon avalanche diode detection circuit of this patent, the recovery time or quenching time constant is determined by the quenching resistance value and the junction capacitance of the single-photon avalanche diode. Reducing the quenching resistance value or reducing the junction capacitance of the diode can shorten the quenching time constant. If the quenching resistance value is too small, the quenching may fail, and the lower limit is usually tens of k ohms. Reducing the junction capacitance usually requires reducing the photosensitivity area of ​​a single single-photon avalanche diode, and reducing the photosensitivity surface of a single single-photon avalanche diode means that more single-photon avalanche diode units can be placed under the same total photosensitivity surface area, which also increases the dynamic range of a channel / macro unit (less prone to saturation due to ambient light). Therefore, according to a preferred embodiment of the present invention, in laser radar applications, the photosensitivity area of ​​a single single-photon avalanche diode usually does not exceed 500um. 2 .

[0085] The third aspect

[0086] Fig.10A laser radar 30 according to the third aspect of the present invention is shown. As shown in the figure, the laser radar 30 includes a transmitting unit 31 and a receiving unit 20 as described above. The transmitting unit 31 includes a laser array, and the laser array is configured to emit multiple laser beams for detecting the target object OB. The laser beam is diffusely reflected after encountering the target object OB, and part of the reflected echo returns to the laser radar and is received by the receiving unit 20. As shown above, the receiving unit 20 includes a single-photon avalanche diode and a comparator, which can receive the echo reflected by the laser beam after detecting the target object OB and convert it into a digital signal output. Although not shown, it is easy for a person skilled in the art to understand that the transmitting unit 31 may also include a transmitting lens group, located downstream of the optical path of the laser array, for modulating (collimating) the laser beam emitted by the laser array into parallel light and emitting it into the ambient space around the laser radar 30. Similarly, the receiving unit 20 may also include a receiving lens group, and the single-photon avalanche diode is located on its focal plane, which is used to converge the echo reflected by the outgoing laser beam after detecting the target object OB onto the single-photon avalanche diode. As shown in the figure, the laser beam L1 emitted by the transmitting unit 31 is projected onto the target object OB, and diffuse reflection occurs, and a portion of the laser beam is reflected back to form an echo L1′. The receiving unit 20 receives the reflected echo L1′ and converts it into an electrical signal. The processing unit 21 of the receiving unit 20 is configured to calculate the distance and / or reflectivity of the target object based on the waveform output by the comparator of the receiving unit. For example, the processing unit 21 can calculate the distance of the target object based on the time of flight TOF (the time period from the laser emission to the single photon avalanche diode reception) of the echo according to the speed of light. In addition or alternatively, the processing unit 21 calculates the reflectivity of the target object based on the pulse width of the signal.

[0087] The fourth aspect

[0088] A fourth aspect of the present invention provides a laser detection method 40, such as Fig.11 As shown below, refer to Fig.11 Detailed description.

[0089] In step S41, a detection laser beam is emitted to detect a target object.

[0090] In step S42, an echo from the target object is received by a single photon avalanche diode, wherein the single photon avalanche diode generates a photocurrent according to incident photons.

[0091] In step S43, the electrical signal representing the photocurrent is compared with an adjustable threshold signal through a comparator to generate a digital signal output.

[0092] In step S44, the adjustable threshold signal is adjusted according to the waveform of the digital signal output.

[0093] According to a preferred embodiment of the present invention, the step of adjusting the adjustable threshold signal according to the waveform of the digital signal output includes: increasing the adjustable threshold signal as the intensity of the incident light increases. After obtaining the digital signal output of the comparator, the intensity of the incident light can be obtained according to its waveform, for example, by calculating the number of incident photons to evaluate the intensity of the incident light, and then the adjustable threshold signal can be increased simultaneously according to the increase in the intensity.

[0094] The preferred embodiments of the four aspects of the present invention are described in detail above. Through the scheme of the preferred embodiment of the present invention, when the ambient light is strong, by raising the threshold of the detection circuit, the dynamic range of the single-photon avalanche photodiode device can be increased, making it less likely to saturate. By adjusting the output pulse width of the single-photon signal to match the laser radar light pulse width, an optimized signal-to-noise ratio can be achieved. Compared with the detection unit of the single-photon avalanche photodiode without a broadening characteristic, this broadening characteristic can obtain additional information, and can distinguish from the output pulse width whether an output pulse is caused by a single photon or multiple continuous photons, thereby increasing the dynamic range of the single-photon avalanche photodiode device, and can obtain pulse intensity information in the case of a strong saturation signal. Using this information, more accurate ranging results and target reflectivity measurement results can be obtained. In addition, by adjusting the output pulse width of the single-photon signal to match the laser radar light pulse width, an optimized signal-to-noise ratio can be achieved.

[0095] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A detection circuit with adjustable output pulse width, comprising: a single photon avalanche diode configured to generate a photocurrent in response to incident photons; and A comparator, wherein a first input terminal of the comparator inputs an adjustable threshold signal, and a second input terminal of the comparator is coupled to the single photon avalanche diode to input an electrical signal representing the photocurrent; the comparator is configured to output a waveform according to a comparison result between the electrical signal and the adjustable threshold signal, wherein the adjustable threshold signal increases with an increase in the intensity of the incident light, The total pulse width output by the detection circuit is determined based on the total duration of the incident photon sequence and the duration of the single photon output pulse width, and the maximum time interval between adjacent photons in the photon sequence is smaller than the duration of the single photon output pulse width.

2. The detection circuit as described in claim 1, wherein the cathode of the single-photon avalanche diode is coupled to a high voltage, the anode of the single-photon avalanche diode is grounded through a quenching resistor, and the anode is coupled to the second input terminal of the comparator, wherein the electrical signal is an analog voltage output by the single-photon avalanche diode.

3. The detection circuit as described in claim 1, wherein the cathode of the single-photon avalanche diode is coupled to a high voltage through a quenching resistor, the anode of the single-photon avalanche diode is grounded, and the cathode is coupled to the second input terminal of the comparator through a capacitor, wherein the electrical signal is the change in voltage of the cathode of the single-photon avalanche diode.

4. The detection circuit according to any one of claims 1 to 3 further comprises a threshold control unit, wherein the threshold control unit is configured to output the adjustable threshold signal, and the threshold control unit is coupled to the first input terminal of the comparator to provide the adjustable threshold signal to the first input terminal.

5. A receiving unit that can be used for laser radar, comprising: A detection circuit, the detection circuit comprising: a single-photon avalanche diode configured to generate a photocurrent in response to incident photons; and A comparator, wherein an adjustable threshold signal is input to a first input terminal of the comparator, and a second input terminal of the comparator is coupled to the single-photon avalanche diode to input an electrical signal representing the photocurrent; the comparator is configured to output a waveform according to a comparison result between the electrical signal and the adjustable threshold signal, wherein the adjustable threshold signal increases as the intensity of incident light increases; and a processing unit, the processing unit being coupled to the output end of the comparator of the detection circuit and configured to calculate the distance of the target object and / or the incident light intensity according to the waveform output by the comparator, The total pulse width output by the detection circuit is determined based on the total duration of the incident photon sequence and the duration of the single photon output pulse width, and the maximum time interval between adjacent photons in the photon sequence is smaller than the duration of the single photon output pulse width.

6. A receiving unit as described in claim 5, wherein the cathode of the single-photon avalanche diode is coupled to a high voltage, the anode of the single-photon avalanche diode is grounded through a quenching resistor, and the anode is coupled to the second input terminal of the comparator, wherein the electrical signal is the voltage across the quenching resistor.

7. A receiving unit as described in claim 5, wherein the cathode of the single-photon avalanche diode is coupled to a high voltage through a quenching resistor, the anode of the single-photon avalanche diode is grounded, and the cathode is coupled to the second input terminal of the comparator through a capacitor, wherein the electrical signal is the voltage of the single-photon avalanche diode.

8. The receiving unit as described in any one of claims 5-7 further includes a threshold control unit, which is coupled to the processing unit and configured to adjust the adjustable threshold signal according to the incident light intensity, and the threshold control unit is coupled to the first input terminal of the comparator to provide the adjustable threshold signal to the first input terminal. 9 . The receiving unit of claim 8 , wherein the threshold control unit is configured to increase the adjustable threshold signal as the incident light intensity increases.

10. A receiving unit as described in any one of claims 5-7, wherein the receiving unit comprises multiple groups of detection circuits and a summer, the output ends of the comparators of the multiple groups of detection circuits are coupled to the input ends of the summer, and the summer performs a summing operation on the outputs of the multiple groups of detection circuits.

11. A receiving unit as described in any one of claims 5-7, wherein the adjustable threshold signal of the detection circuit is set so that: the width of the output waveform of the comparator of the detection circuit for a single photon matches the width of the laser pulse of the lidar.

12. A receiving unit as described in claim 11, wherein the adjustable threshold signal of the detection circuit is set so that: the width of the output waveform of the comparator of the detection circuit for a single photon is equal to the half-maximum full width of the laser pulse of the laser radar.

13. The receiving unit according to any one of claims 5 to 7, wherein the processing unit is configured to calculate the number of incident photons based on the pulse width of the waveform output by the comparator.

14. A laser radar, comprising: A transmitting unit, the transmitting unit comprising a laser, the laser being configured to transmit laser pulses to the outside of the laser radar to detect a target object; The receiving unit according to any one of claims 5 to 13, wherein the receiving unit is configured to receive an echo of the laser pulse after being reflected on a target object.

15. A method for performing echo detection using the receiving unit according to any one of claims 5 to 13.

16. A laser detection method, comprising: Emitting a detection laser beam to detect a target object; receiving an echo from the target object by a single photon avalanche diode, wherein the single photon avalanche diode generates a photocurrent according to incident photons; By means of a comparator, the electrical signal representing the photocurrent is compared with an adjustable threshold signal to generate a digital signal output; According to the waveform of the digital signal output, the adjustable threshold signal is adjusted, The step of adjusting the adjustable threshold signal according to the waveform of the digital signal output comprises: increasing the adjustable threshold signal as the incident light intensity increases, The detection circuit includes the single-photon avalanche diode and the comparator, and the total pulse width output by the detection circuit is determined based on the total duration of the incident photon sequence and the duration of the single-photon output pulse width, and the maximum time interval between adjacent photons in the photon sequence is less than the duration of the single-photon output pulse width.

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