WO2021213103A1 - Photodetection module for laser radar, laser radar, and ambient light detection method - Google Patents

Abstract

A photodetection module for a laser radar, a laser radar, and an ambient light detection method. The photodetection module for a laser radar comprises a photodetection unit (11), a signal conditioning unit (12), and a data processing unit (13). An output end of the photodetection unit (11) is connected to an input end of the signal conditioning unit (12). An output end of the signal conditioning unit (12) is connected to an input end of the data processing unit (13). The photodetection unit (11) is used for sensing an optical signal incident thereto, and converting the sensed optical signal into an electric signal. The signal conditioning unit (12) comprises an ambient light detection subunit (121). The ambient light detection subunit (121) is used for detecting a direct current signal in the electric signal, and quantizing the direct current signal. The data processing unit (13) is used for analyzing the received quantized direct current signal. The brightness of the ambient light where the laser radar is located can be inferred according to the amplitude of the detected direct current signal, so as to adjust a corresponding parameter of the laser radar.

Description

Photoelectric detection module for lidar, lidar and ambient light detection method

Cross-references to related applications

This application claims the priority of the Chinese patent application filed on April 23, 2020, the application number is 202010329779.7, and the invention title is "Photoelectric detection module for lidar, lidar and ambient light detection method". The entire text is incorporated into this application by reference.

Technical field

This application relates to the field of laser detection, in particular to photoelectric detection modules for laser radar, laser radar and ambient light detection methods.

Background technique

Lidar is usually used to detect information about external obstacles, such as the distance between the obstacle and the lidar, and the shape of the obstacle.

The lidar includes a transmitting module and a receiving module, and the receiving module includes a photoelectric detection module. The photoelectric detection module usually receives the echo laser signal after the detection laser emitted by the transmitter module hits an obstacle.

As far as the inventor knows, it is difficult to accurately detect weak DC signals flowing out of photoelectric detection units such as APD, SPAD, and SiPM under the conditions of voltage changes. Therefore, the problems to be solved urgently are how to detect weak DC signals and how to compensate for current detection errors caused by voltage changes.

Summary of the invention

The content part of the application is provided to introduce the concepts in a brief form, and these concepts will be described in detail in the following specific embodiments. The content part of the application is not intended to identify the key features or essential features of the claimed technical solution, nor is it intended to be used to limit the scope of the claimed technical solution.

In the first aspect, the present application provides a photoelectric detection module for lidar, including: a photodetection unit, a signal conditioning unit, and a data processing unit; the output end of the photodetection unit is connected to the input end of the signal conditioning unit, The output end of the signal conditioning unit is connected to the input end of the data processing unit; the photodetection unit is used to sense the optical signal incident thereon, and convert the sensed optical signal into an electrical signal, wherein The optical signal incident on it includes the ambient light signal and the echo laser signal generated by the reflection of the laser beam after irradiating the object to be measured; the signal conditioning unit includes an ambient light detection subunit, and the ambient light detection subunit is used for The direct current signal in the electrical signal is detected and the direct current signal is quantified; wherein the direct current signal includes a direct current signal generated by a photodetection unit inducing an ambient light signal; the data processing unit is used to quantify the received The subsequent AC signal and the quantized DC signal are analyzed and processed, and the photodetector unit is adjusted according to the result of ambient light detection.

In a second aspect, an embodiment of the present application provides a lidar, which includes the photoelectric detection module for lidar described in the first aspect.

In the third aspect, an embodiment of the present application provides an ambient light detection method, which is used in the photoelectric detection module for lidar described in the first aspect; the method includes: acquiring monotonically rising signals under the control of the same clock signal The reference voltage signal is compared with the count signal of monotonically increasing counting; the reference voltage signal is compared with the actual measured voltage signal output by the current-voltage conversion module; wherein, the current-voltage conversion module is used to convert the photoelectric detection module from the detected ambient light The generated direct current signal is converted into a measured voltage signal; at the moment when the reference voltage signal rises to the same time as the measured voltage signal, the count value corresponding to the count signal at that moment is determined as the target count value; The value determines the intensity of the ambient light of the lidar.

The photoelectric detection module for lidar, lidar, and ambient light detection method provided in the embodiments of the present application detect the intensity of the DC signal caused by the ambient light by arranging the ambient light detection subunit in the photoelectric detection module. Therefore, the brightness of the ambient light where the lidar is located can be inferred by detecting the magnitude of the DC signal, which is beneficial to adjust the corresponding parameters of the lidar.

Description of the drawings

By reading the detailed description of the non-limiting embodiments with reference to the following drawings, other features, purposes and advantages of the present application will become more apparent:

FIG. 1 is a schematic structural diagram of a photoelectric detection module for lidar provided by an embodiment of the application;

2 is a schematic circuit structure diagram of an embodiment of a photoelectric detection module for lidar provided by an embodiment of the application;

3 is a schematic circuit structure diagram of another embodiment of a photoelectric detection module for lidar provided by an embodiment of the application;

Fig. 4 is a timing diagram of a multi-channel environmental light detection scheme for a photoelectric detection module of a lidar;

FIG. 5 is a schematic structural diagram of an implementation circuit of the photoelectric detection module for laser radar shown in FIG. 1 to FIG. 3;

FIG. 6 is a schematic flowchart of an embodiment of an ambient light detection method provided by an embodiment of the application.

Detailed ways

In the lidar receiving system, ambient light will affect the detection of the receiving system. The specific expression is that the ambient light forms a current on the photodetector that is proportional to the light intensity. This current value changes with the external light intensity. For example, the range may be from 0.9uA to 17uA (Avalanche Photodetection Unit, APD). The wave is a pulse current, and the peak value of the current varies greatly. It varies from a few uA to 1A. The direct current in the photodetector will increase the shot noise (the shot noise of the photogenerated current), that is, the external ambient light will affect the signal noise of the detector. Compare.

For existing lidars, there is a lack of methods that can detect the influence of ambient light on the detection current in real time. Take the existing multi-line lidar that uses APD as a detector as an example. Each channel shares a high voltage and controls the high voltage based on temperature feedback. Reduce the drift of APD gain with temperature, but this scheme cannot measure the DC current of the detector, and therefore cannot quantitatively evaluate the noise influence of external ambient light on the detection of lidar.

Part of the prior art detects and quantifies the DC current into a digital signal, and requires the circuit to have two functions, one is the conversion of current to voltage, and the other is the quantization of voltage signals. For the intermediate current-voltage conversion of DC detection, the commonly used technique in the circuit is to connect a detection resistor in series with the current input branch, and complete the detection of the current value by measuring the voltage difference between the two ends of the series resistor. When considering that the DC voltage of the adjustment photodetection unit (APD) changes with temperature and process, some existing technologies use common-mode voltage differential amplifiers to perform current detection under wide common-mode voltage conditions.

The above circuit completes the conversion of current to voltage, and has the following two shortcomings. One is that the conversion resistance cannot take a larger resistance value. If it is too large, the common mode rejection of the current will become worse, resulting in an increase in output deviation. The current and transimpedance gain should not be too small, because it is of the same magnitude as the voltage noise, and a voltage that is too small cannot be effectively quantified. Therefore, to ensure effective quantization, further amplification needs to be added. Further amplification will cause the mismatch of the differential amplifier to be further amplified. Taking the smallest effective quantization value as an example, at least two additional stages of amplifiers are required. Therefore, the use of this circuit for low current detection increases the complexity of the entire detection circuit; second, in order to meet better detection accuracy, the operational amplifier is required to have Good input offset voltage and DC of the measured current will not be shunted inside the detection circuit. No shunt needs to ensure that the equivalent resistance of the positive and negative terminals of the op amp is exactly the same, the proportional error is small and the input of the op amp is small enough, and the resistance needs to be increased. The matching accuracy and the matching accuracy of the op amp input to the tube will greatly increase the area of the circuit and increase the cost.

The DC detection of the APD is carried out through the solution in this application. By setting a preset ramp voltage generating circuit related to ambient light in the synchronous logic circuit, the ramp voltage generating circuit generates a preset ramp voltage generation circuit during each ambient light detection time period. A voltage signal Vramp that varies linearly from the minimum voltage value (for example, 0V) to the preset maximum voltage value. The current-voltage converter outputs the measured voltage value output by the photodetection module according to the measured ambient light intensity. Compare the measured voltage value with Vramp, and determine the actual voltage value corresponding to the obtained ambient light through the comparison result. In this way, the direct current corresponding to the ambient light is determined, and then the intensity of the ambient light is determined. Then adjust the relevant parameters of the photodetector according to the ambient light intensity. Therefore, the power consumption of the lidar can be adjusted according to the ambient light, and the power consumption and system complexity can be reduced, and the detection accuracy can be improved on the premise that the lidar can be used to obtain accurate signals of the detected object.

The application will be further described in detail below with reference to the drawings and embodiments. It is understandable that the specific embodiments described here are only used to explain the related invention, but not to limit the invention. In addition, it should be noted that, for ease of description, only the parts related to the invention are shown in the drawings.

It should be noted that the embodiments in the application and the features in the embodiments can be combined with each other if there is no conflict. Hereinafter, the present application will be described in detail with reference to the drawings and in conjunction with the embodiments.

Please refer to FIG. 1, which shows a schematic structural diagram of a photoelectric detection module for lidar provided by an embodiment of the present application.

As shown in FIG. 1, the photoelectric detection module for lidar includes: a photodetection unit 11, a signal conditioning unit 12 and a data processing unit 13. The output terminal of the photodetection unit 11 is connected to the input terminal of the signal conditioning unit 12. The output terminal of the signal conditioning unit 12 is connected to the input terminal of the data processing unit 13.

The photodetection unit 11 is used to sense the optical signal incident on it and convert the sensed optical signal into an electrical signal. The optical signal incident on it includes the ambient light signal and the laser beam irradiated on the object to be measured. Echo laser signals generated by reflection, but electrical signals may include dark currents in addition to ambient light and echo signals.

The signal conditioning unit 12 includes an ambient light detection sub-unit 121 and an AC detection sub-unit 122. The ambient light detection sub-unit 121 is used to detect a DC signal in the electrical signal, quantize the DC signal, and pass the quantization result. Reflects the intensity of ambient light. The AC detection subunit 122 is used to amplify and quantify the AC signal in the electrical signal; wherein, the AC signal includes the AC signal generated by the photoelectric detection unit 11 inducing the echo signal, and the DC signal includes the photoelectric The detection unit 11 senses the DC signal generated by the ambient light signal.

The data processing unit 13 is used to analyze and process the received quantized AC signal and quantized DC signal. For example, the data processing unit converts the quantized DC voltage signal into a corresponding DC voltage amplitude.

In this embodiment, the ambient light detection subunit is provided in the photodetection module to detect the intensity of the DC signal caused by the ambient light. Therefore, the brightness of the ambient light where the lidar is located can be inferred by detecting the magnitude of the DC signal, which is beneficial to adjust the corresponding parameters of the lidar.

In some optional implementation manners of this embodiment, the signal conditioning unit 12 further includes a bias voltage adjustment subunit 123. The output terminal of the bias voltage adjustment subunit 123 is electrically connected to the anode of the photodetection unit 11; wherein, the bias voltage adjustment subunit 123 is used to adjust the bias voltage of the photodetection unit 11 to compensate for temperature and process deviations. The working current drift of the photodetection unit 11 is calibrated. Please combine Figure 1 and Figure 5, the bias voltage adjustment sub-unit 123 (DAC, digital-to-analog converter) outputs a voltage VB connected to the anode of the photodetection unit, and the cathode of the photodetection unit is connected to HV, so the voltage difference of the photodetection unit For HV-VB, the target quantity of the photodetection unit is current. For the photodetection unit, the physical relationship related to the current I can be expressed as I=f(HV-VB, T, P). Because the temperature T and the process P will cause different diode I values, it is necessary to adjust the HV -VB to make the value of I the same, while HV does not change, so it is necessary to adjust VB. That is, the output voltage of the bias voltage adjusting subunit 123 is used to adjust the current of the photodetection unit.

Please refer to FIG. 2, which shows a schematic circuit structure diagram of an embodiment of a photoelectric detection module for lidar provided by an embodiment of the present application.

As shown in FIG. 2, the photodetection module may include a photodetection unit 11, a signal conditioning unit 12 and a data processing unit 13. The photodetection unit 11 can be APD, Spad(s) or SiPM.

In this embodiment, the signal conditioning unit 12 includes an ambient light detection subunit 121 and an AC signal detection subunit 122 as shown in FIG. 1.

In addition, the photoelectric detection module for lidar may further include a bias voltage adjustment subunit 123 and an AC detection subunit 122 as shown in FIG. 1.

The AC detection sub-unit 122 may include a capacitor 1221, an AC current signal amplifier 1222, and an analog-to-digital converter (ADC) 1223. Among them, the capacitor is used to isolate the DC signal.

The ambient light detection sub-unit 121 includes a current-voltage conversion module. The input end of the current-voltage conversion module is electrically connected with the anode of the photodetection unit. The output terminal of the current-voltage conversion module is connected with the input terminal of the data processing unit. The current-voltage conversion module includes: a synchronous logic circuit 1211, a ramp voltage generator 1212, a counter 1213, a current-voltage converter 1214, a voltage comparator 1215, and a latch 1216; wherein the output terminal of the photodetection unit 11 is connected to the current -The input terminal of the voltage converter 1214 is connected. The signal output terminal of the synchronous logic circuit can output the same clock signal. The signal output terminal of the synchronous logic circuit 1211 is connected to the input terminal of the ramp voltage generator 1212 and the input terminal of the counter 1213, respectively. The clock signal output by the synchronous logic circuit 1211 controls the ramp voltage generator 1212 and the counter 1213 to work simultaneously. The ramp voltage generator 1212 generates a monotonically rising voltage signal that changes with time under the control of the clock signal output from the counter 1211. The counter 1213, under the control of the clock signal output from the synchronous logic circuit 1211, generates a count value that monotonically increases with time.

The inverting input terminal of the voltage comparator 1215 is connected to the output terminal of the current-voltage converter 1214; the non-inverting input terminal of the voltage comparator 1215 is connected to the output terminal of the ramp voltage generator 1212; the latch 1216 The control terminal of is connected to the output terminal of the voltage comparator 1215, and the signal input terminal of the latch 1216 is connected to the output terminal of the counter 1213. The output terminal of the latch is connected to the data processing unit 13 as the output terminal of the current-voltage conversion module.

Under the control of the signal output by the synchronous logic circuit 1211, the ramp voltage generator 1212 generates a ramp voltage signal (Vramp). In each detection period of the ambient light signal, the ramp voltage generator 1212 generates a linearly changing voltage signal from the preset minimum voltage value to the preset maximum voltage value. The counter 1213 counts (Cout) according to a preset counting frequency. When the ramp voltage signal (Vramp) input from the non-inverting input terminal of the voltage comparator 1215 is greater than the voltage signal Vout output by the current-voltage converter, the voltage comparator outputs a control signal for controlling the operation of the latch; the latch The control terminal of the input terminal inputs the control signal, the latch latches the count value input from the signal input terminal at this time, and outputs the latched count value Lout. Lout is a digital code value that does not change over time. The above-mentioned digital code value latched by the latch is controlled by the output of the voltage comparator 1215 at a high level. The voltage comparator 1215 is when the voltage Vramp output by the ramp voltage generator linearly rises from the preset minimum value to the preset maximum value, when the value of Vramp at a certain moment is just greater than (also can be regarded as equal to) the current − When the voltage Vout is output by the voltage converter, a high-level signal is output. In the case that the APD ambient light does not change for a short time, the original APD DC value can be deduced according to the code value of Lout. Therefore, the data processing unit determines the DC voltage value corresponding to the ambient light signal according to the count value.

The ramp voltage generator generates a ramp voltage signal that rises from a preset minimum voltage value to a preset maximum voltage value within a preset sampling time period; the counter increases from a preset counting frequency during the preset sampling time period. Preset the lowest value to the preset highest value count. Among them, the above-mentioned preset maximum voltage value is related to the magnitude of the expected ambient light. The stronger the expected ambient light, the greater the maximum voltage value. In specific implementation, the highest voltage value may be slightly higher than or equal to the expected ambient light level.

The photodetector used for lidar may include multiple sampling time periods when working. In each sampling period, the synchronization signal generated by the synchronization logic circuit controls the ramp voltage generator and the counter to work at the same time. During the sampling period, the ramp voltage generator generates a ramp voltage signal from the preset lowest voltage to the preset highest voltage. At the same time, during the sampling period, the counter changes from 000……0 to 111……1 (the number of counts depends on the expected quantization accuracy, such as n=8bit), so that the voltage value Vramp output by the ramp voltage generator and the counter The count value Cout increases proportionally with time.

The current-voltage converter may be various existing converters that convert DC current into DC voltage. The current-voltage converter can input the analog DC current signal produced by the photodetection unit by sensing ambient light, and convert the analog DC current signal into an analog DC voltage signal Vout. The voltage signal Vout output by the current-voltage converter is input to the inverting input terminal of the voltage comparator. The voltage signal Vramp output by the ramp voltage generator is input to the non-inverting input terminal of the voltage comparator. When the voltage signal Vout is greater than the voltage signal Vramp, the voltage comparator outputs a low level. When the voltage signal Vout is less than the voltage signal Vramp, the voltage comparator outputs a high level.

When the voltage comparator 1215 outputs a low level, that is, the control terminal of the latch inputs a low level, the latch does not work, and the count value input to the latch 1216 is not latched by the latch. The latch has no output. When the voltage comparator 1215 outputs a high level, the control terminal of the latch inputs a high level, and the latch starts to work. At this time, the count value input to the latch 1216 is latched by the latch. The latch can output the count value input into it, and the output value is Lout.

Lout can be a binary number. The data processing unit can convert the binary number into a corresponding DC voltage value, or into a DC current amount related to ambient light and dark current, so as to determine information such as the size or intensity of the ambient light.

In a single-channel circuit, the DC voltage Vout is compared with Vramp. When the Vramp voltage exceeds the Vout voltage value, the comparator output voltage Vcmp reverses, and Vcmp triggers the Latch (latch) circuit to latch the Counter current count value output as Lout( Digital code value). Then the corresponding relationship between Vout and Lout at this time is

Among them, n is the preset counting digits of the counter. VFS is the preset highest voltage value that the ramp voltage generator can generate.

Assuming that the transimpedance gain of the current-voltage converter is Rt, the corresponding relationship of the count value output by the input DC current latch is

Among them, I _in (DC) is the direct current generated by the photodetector; Vout is the direct current voltage value output by the current-voltage converter; Rt is the transimpedance gain of the current-voltage converter; VFS is the voltage generated by the ramp voltage generator The highest preset voltage; Lout is the count value output by the latch; n is the preset count number of the above counter.

In this embodiment, the comparator and Latch used achieve DC quantization. This solution does not require high performance and power consumption. The circuit structure is simple. It is triggered only once when Vramp is greater than Vout, and the ramp voltage is generated before the next measurement. The device, counter and latch are reset, and the number of flips is less, so the power consumption is lower and the system complexity is lower.

Please refer to FIG. 3, which shows a schematic circuit structure diagram of another embodiment of a photoelectric detection module for lidar provided by an embodiment of the present application.

Compared with FIG. 2, the circuit structure diagram of the photoelectric detection module for laser radar shown in FIG. 3 includes a plurality of photodetection units 111, 112,... 11N. Each photoelectric detection unit corresponds to a channel. Each channel includes a photoelectric detection unit and a signal conditioning unit. As shown in Fig. 3, the photoelectric detection module for lidar includes signal conditioning units 101, 102, ..., 10N. N is the number of channels, which is an integer greater than 2.

Each signal conditioning unit may include an ambient light detection sub-unit, a bias voltage adjustment sub-unit, and an AC detection sub-unit. Among them, the ambient light detection sub-unit includes a current-voltage conversion module. The current-voltage conversion module includes a current-voltage converter 1214, a voltage comparator 1215, and a latch 1216; the AC detection sub-unit may include a capacitor 1221, an amplifier 1222, and an analog-to-digital converter 1223.

In this embodiment, the current-to-voltage conversion modules of the ambient light detection subunits 101, 102,... 10N of multiple channels can share a synchronous logic circuit, a ramp voltage generator, and a counter. Multi-channel ambient light detection sub-units share synchronous logic circuits, ramp voltage generators, and counters, which can save chip area and reduce overall system complexity and power consumption.

That is to say, in this embodiment, the non-inverting input of the voltage comparator of the ambient light detection subunit of each of the multiple channels 101, 102, ... 10N is inputted by the same ramp voltage generator. Ramp voltage signal; the input of the signal input terminal of the latch is the count value output by the same counter.

Please refer to FIG. 4, which shows a timing diagram of the environmental light detection scheme of the photoelectric detection module of the multi-channel laser radar. Figure 4 shows the timing relationship of Cout, Vramp, Vcmp, and Lout with the quantization of 3 channels as an example. At t1, the ramp voltage generator and counter are started, and the voltage Vramp generated by the ramp voltage generator starts from 0V and ramps up with a constant slope. The counter count value (Cout) starts from 0 and increases by 1 on the rising edge of the clock (not shown, each X means the clock changes once). At time t2, Vramp exceeds the Vout1 voltage of channel 101, the comparator output Vcmp1 flips, and the latch locks the count value 3 of the counter at this moment in Lout1. At time t3, Vramp exceeds the Vout2 voltage of channel 102, the comparator output Vcmp2 flips, and the latch locks the counter value 80 at this moment in Lout2. At time t4, Vramp exceeds the Vout3 voltage of channel 103, the comparator output Vcmp3 flips, and the latch locks the count value 253 of the counter at this moment in Lout3. At t5, the counter stops counting and the ramp voltage generator stops rising, waiting for the arrival of the next quantization command. Before the next quantization command comes, the latches of each channel are reset, and the counter and ramp voltage generator repeat the actions from t1 to t5. It should be noted that the time t1 may be the time after the laser detection echo is received, or it may be the time before the laser detection echo is received. In practice, in order to avoid the interference of the circuit action of the ambient light detection subunit on the received laser detection echo (causing ranging error or accuracy reduction), the ambient light detection subunit can detect the ambient light signal after receiving the laser detection echo strength.

In this application, time t1, t2, t3, and t4 are all within the time window for measuring APD DC once, t1 represents the time when all channels start measurement, t5 represents the time when all channels end measurement, t2, t3, and t4 represent different channels ( Channel 1, channel 2, channel 3) corresponding to the end value of the measurement time, the difference between the end value of the measurement time and t1 (for example: t2-t1) is proportional to the value of the DC current on the photoelectric detection unit being detected (the length of time passed) Quantify the current amplitude).

In this embodiment, by providing a preset ramp voltage generating circuit related to ambient light in the synchronous logic circuit, the ramp voltage generating circuit generates a preset minimum voltage value (for example, 0V) during each period of ambient light detection. ) A linearly changing voltage signal Vramp to a preset maximum voltage value. The current-voltage converter outputs the measured voltage value output by the photodetection module according to the measured ambient light intensity. Compare the measured voltage value with Vramp, and determine the actual voltage value corresponding to the obtained ambient light through the comparison result. In this way, the direct current corresponding to the ambient light is determined, and then the intensity of the ambient light is determined. Then adjust the relevant parameters of the photodetector according to the ambient light intensity. Therefore, the power consumption of the lidar can be adjusted according to the ambient light, and the power consumption of the lidar can be reduced on the premise that the laser radar can be used to obtain an accurate signal of the detected object.

Compared with the digital quantization unit using multiple analog-to-digital conversion methods, the solution proposed in this application is to use a ramp voltage generator and a counter shared between channels, and a single channel through a comparator and a latch to reduce the overall system complexity and power. Consumption. The comparators and latches used do not require high performance and power consumption. The circuit structure is simple, and only triggers once when Vramp is greater than Vout. The ramp voltage generator, counter and latch are reset before the next measurement starts. The number of flips is less, so the power consumption is lower and the system complexity is lower.

Please continue to refer to FIG. 5, which shows a schematic structural diagram of an implementation circuit of the photoelectric detection module for lidar shown in FIGS. 1 to 3.

In the circuit structure of the photodetector for lidar shown in Figure 5, the photodetector is connected to the amplifier AMP of the AC signal detection subunit through a DC blocking capacitor to ensure that DC signals will not flow into the AC signal detection subunit. . In addition, the current-voltage converter of the bias voltage adjustment sub-unit (DAC) and the ambient light detection sub-unit is integrated.

As shown in FIG. 5, the bias voltage adjusting subunit DAC includes a low voltage adjusting subunit LVDAC and a medium voltage amplifying subunit (medium voltage amplifier); the medium voltage amplifying subunit includes: a direct current source I0, a first transistor M1 , A first operational amplifier A1, a first input resistor R1 and a first feedback resistor R2; wherein one end of the first input resistor R1 is connected to the ground, and the other end is connected to one end of the first feedback resistor R2; The other end of the feedback resistor R2 is electrically connected to the anode of the photodetection unit APD1, the output end of the DC current source, and the drain of the first triode; the cathode of the photodetection unit APD1 is electrically connected to the first high potential HV, The anode of the photodetection unit APD1 is also electrically connected to the output terminal of the direct current source I0; the source of the first transistor M1 is connected to the ground wire, and the drain of the first transistor M1 is connected to the direct current source I0. The output terminal of the first operational amplifier is connected to the anode of the photodetection unit; the gate of the first transistor M1 is connected to the output terminal of the first operational amplifier A1; The other end of the input resistor is connected, and the inverting input end of the first operational amplifier is connected to the output end of the low voltage regulator subunit.

The current-voltage comparison module includes a second triode M2, a third triode M3, a fourth triode M4, a third resistor R4, a voltage comparator CMP and a latch circuit latch; wherein, the second The gate of the triode M2 is connected to the gate of the first triode M1, the source of the second triode M2 is connected to ground, and the drain of the second triode M2 is connected to the first triode. The drain connection of the three-stage transistor M3;

The gate of the third triode M3 is connected to the gate of the fourth triode M4; the source of the third triode M3 is connected to the second high potential LV1, the third triode The gate of the tube M3 is connected to the drain of the third transistor M3;

The source of the fourth transistor M4 is connected to the third high potential LV2; the drain of the fourth transistor M4 is connected to one end of the third resistor R4, and is connected to the voltage comparator CMP Inverting input terminal connection;

The non-inverting input terminal of the voltage comparator CMP is connected to the output terminal of the ramp circuit generator, and the output terminal of the voltage comparator CMP is connected to the control terminal of the latch Latch;

The signal input end of the latch latch is connected to the output end of the counter, the output end of the latch latch is connected to a data processing unit, and the data processing unit is based on the output end of the latch latch. Determining the direct current voltage corresponding to the direct current;

The other end of the third resistor R4 is connected to the ground wire.

In addition, the ambient light detection subunit of the photoelectric detection module used for the lidar further includes a current compensation module (current compensation); wherein the current compensation module is electrically connected to the bias voltage adjustment subunit and the current-voltage conversion module. connect.

The current compensation module includes a second operational amplifier A2, a fifth triode M5, a sixth triode M6, a seventh triode M7, an eighth triode M8, and a ninth triode M9; among them,

The non-inverting input terminal of the second operational amplifier A2 is connected to the inverting input terminal of the first operational amplifier A1; the inverting input terminal of the second operational amplifier A2 is connected to the source of the fifth triode and One end of the fourth resistor R3 is electrically connected; the output end of the second operational amplifier A2 is connected to the gate of the fifth transistor M5;

The other end of the fourth resistor R3 is connected to the ground wire;

The drain of the fifth transistor M5 is electrically connected to the gate and the drain of the sixth transistor M6 and the gate of the seventh transistor M7;

The source of the sixth transistor M6 is electrically connected to the fourth high potential LV3; the gate of the sixth transistor M6 is connected to the gate of the seventh transistor M7;

The source of the seventh triode M7 is electrically connected to the fifth high potential LV4; the drain of the seventh triode M7 is electrically connected to the drain of the eighth triode M8;

The source of the eighth triode M8 is connected to the ground, and the gate is electrically connected to the gate of the ninth triode M9; the drain of the eighth triode M8 is connected to the 83rd The grid of the pole tube M8 is electrically connected;

The source of the ninth transistor M9 is connected to the ground, and the drain is electrically connected to the drain of the fourth transistor M4.

DAC output voltage range is 0～M(V), M>0. The voltage output by the DAC is used to adjust the bias voltage of the photodetector. DAC is composed of two parts of circuits, one is LVDAC (low voltage DAC), and the other is MV amplifier (medium voltage amplifier). The MV amplifier includes A1, R1, R2, I0, and M1. A1 is an operational amplifier. R1 and R2 are input resistance and feedback resistance, respectively. I0 is a direct current source. M1 is the output NMOS. The gain of the MV amplifier is (1+R2/R1). The open loop impedance of the MV amplifier is the resistance ro of the M1 tube in parallel with the output impedance of the current source I0, which is approximately ro. Choosing ro value as high resistance, the equivalent of the output of the MV amplifier is a low-pass network, and the AC signal will not flow into the output of the MV DAC. The IV Converter circuit, that is, the current-voltage converter, consists of two parts. One is a resistive load current mirror circuit composed of M2, M3, M4, and R4. The second is a constant current compensation circuit (Current Compensation) with groups A2, R3, M5, M6, M7, M8, and M9. Assuming that the direct current generated by the photodetector is I _in (DC), the direct current flowing through M1 is I0+I _in (DC), and the gates of M1 and M2 are connected, and the two form a current mirror circuit, and at the same time, M3 And M4 also constitute a current mirror, continue to mirror the current of M2 to M4, assuming that the proportional relationship between the working current of M1 and M2 is p1, and the proportional relationship between the working current of M3 and M4 is p2, then the current I4 of M4 is

I4=p2×I3=p2×p1×I1=p2×p1×(I0+I _in (DC)) (3);

Among them, I4 is the working current of M4, I3 is the working current of M3; I1 is the working current of M1; I _in (DC) is the direct current generated by the photodetector; I0 is the current generated by the direct current source.

The current of M4 forms a voltage on R4. When the current compensation circuit is not considered, the output voltage Vout of the current-voltage converter (I-V Converter) is obtained as

Vout=I4×R4=p2×p1×(I0+I _in (DC))×R4 (4);

Here R4 represents the resistance value of resistor R4.

That is, Vout _{is proportional to I in} (DC) and has a DC voltage term related to I0.

In order to increase the DAC output voltage range (close to 0～MV, where M is the preset value, M is greater than zero), a single-tube PMOS is used to realize the current source of I0, so the I0 characteristic is not an ideal current source, and the I0 current will be output by the DAC voltage Vdac Influence, the approximate expression of I0 current is

I0=I0'(1+λ×Vdac) (5);

Among them, Vdac is the output voltage of the voltage regulation unit; I0' represents the direct current component that has nothing to do with the Vdac voltage, and λ is the pre-determined proportional coefficient.

When considering the current compensation circuit, the output voltage Vout of the I-V Converter is expressed as

Vout=(I4-I9)×R4=(p2×p1×(I0+I _in (DC)-I9)×R4 (6);

Among them, I9 is the working current of the ninth transistor M9; R4 represents the resistance value of the resistor R4;

And I9 is generated by the current compensation circuit. Assuming that the ratio of the current mirror formed by M6 and M7 is p3, and the ratio of the current mirror formed by M8 and M9 is p4, there is

Among them, Vlvdac is the output voltage of the low voltage DAC (LVDAC); R3 represents the resistance value of the resistor R3.

The relationship between LVDAC output voltage and DAC output voltage is

Then there is

The output voltage expression of I-V Converter is

When selecting the appropriate scale factor so that

Then the Vout output is approximately independent of the Vdac voltage.

In the Vout expression, _{the equivalent transresistance Rt reflecting the relationship between I in} (DC) and the output voltage is

Rt=Vout/I _in (DC)=p2×p1×R4 (13);

Since only a single resistor is included in the transimpedance expression, the requirement for the resistance ratio is not high. For the ratios p1 and p2 of the current mirror, a smaller ratio can be selected to ensure that the image error is small, and a larger R4 resistance value can be selected to ensure sufficient transimpedance gain. For example, choose p1=p2=3, R4=50kΩ, then Rt=450kΩ, for a 0.2uA signal, when the transimpedance is Rt=450kΩ, the output voltage increase is 0.2uA*450kΩ=90mV, which can meet general digitization The effective quantization range of the circuit.

The implementation circuit of the photoelectric detection module for lidar provided in this embodiment adopts the current mirror method to realize the conversion of the DC current converted by the ambient light into the DC voltage by the photoelectric detection unit, and uses the current mirror method to indirectly detect the conversion environment of the photodetection unit The direct current obtained by the light does not change the direct current working state of the photodetection unit.

In addition, in this embodiment, a current compensation module is used to compensate the non-linearity of the current mirror caused by the output voltage of the bias adjustment subunit, and improve the DC detection accuracy of the photodetection unit.

An embodiment of the present application also provides a lidar. The lidar includes the photoelectric detection module for lidar provided by the embodiment shown in one of FIGS. 1 to 3.

With further reference to FIG. 6, it shows an ambient light detection method used in the photoelectric detection module for lidar provided by the embodiment shown in one of FIGS. 1 to 4.

As shown in Figure 6, the ambient light detection method includes the following steps:

Step 601: Obtain a monotonically increasing reference voltage signal and a monotonically increasing counting signal under the control of the same clock signal, and the reference voltage signal monotonically increasing between a preset minimum voltage value and a preset maximum voltage value.

Step 602: Compare the reference voltage signal with the measured voltage signal output by the current-voltage conversion module; wherein the current-voltage conversion module is used to convert the DC current signal generated by the photoelectric detection module from the detected ambient light into a measured voltage signal.

Step 603: At the moment when the reference voltage signal rises to the same time as the actual measured voltage signal, the count value corresponding to the count signal at that moment is determined as the target count value.

Step 604: Determine the intensity of the ambient light of the lidar according to the target count value.

The data processing unit can determine the magnitude of the direct current corresponding to the ambient light through the above-mentioned count value, and then determine the magnitude of the ambient light.

In each sampling period, for example, the same synchronous clock signal output by the synchronous logic unit is used to control the ramp voltage generator to work synchronously with the counter.

In practice, the analog voltage signal output by the current-voltage conversion module can be input to the inverting input terminal of the voltage comparator; the ramp voltage signal output from the output terminal of the ramp voltage generator can be input to the non-inverting input terminal of the comparator. The analog voltage signal has a preset relationship with the current signal generated by the photodetection module inducing ambient light. When the ramp voltage signal rises to the analog voltage signal, the voltage comparator outputs a control signal to control the operation of the latch, and the latch latches the current corresponding count value of the counter input from the input terminal , And output the latched count value to the data processing unit. The physical relationship between the DC current signal caused by the ambient light and the preset maximum count and target count value and the transimpedance gain of the current-voltage conversion module according to the predetermined physical relationship between the data processing unit (please refer to formula (2)) , To determine the DC current signal corresponding to the ambient light, so as to determine the ambient light intensity of the lidar.

For detailed description of step 601 to step 604, reference may be made to the description part of the embodiment shown in FIG. 2 and FIG. 3, which will not be repeated here.

The above description is only a preferred embodiment of the present application and an explanation of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solution formed by the specific combination of the above technical features, and should also cover the above technical features without departing from the inventive concept. Or other technical solutions formed by any combination of its equivalent features. For example, the above-mentioned features and the technical features disclosed in this application (but not limited to) with similar functions are mutually replaced to form a technical solution.

Although the subject matter has been described in language specific to structural features and/or logical actions of the method, it should be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or actions described above. On the contrary, the specific features and actions described above are merely exemplary forms of implementing the claims.

Claims (13)

1. A photoelectric detection module for lidar, which is characterized by comprising: a photodetection unit, a signal conditioning unit, and a data processing unit; the output end of the photodetection unit is connected to the input end of the signal conditioning unit, and the signal conditioning The output terminal of the unit is connected with the input terminal of the data processing unit;

   The photodetection unit is used to sense the light signal incident on it, and convert the sensed light signal into an electrical signal, where the light signal incident on it includes the ambient light signal and the laser beam irradiating the measured object Echo laser signal generated after being reflected;

   The signal conditioning unit includes an ambient light detection subunit, and the ambient light detection subunit is used to detect a DC signal in the electrical signal and quantify the DC signal; wherein the DC signal includes a photodetection unit sensing DC signal generated by ambient light signal;

   The data processing unit is used to analyze and process the received quantized AC signal and quantized DC signal, and adjust the photodetector unit according to the result of ambient light detection.
2. The photoelectric detection module for lidar according to claim 1, wherein the ambient light detection subunit comprises a current-voltage conversion module, and the input terminal of the current-voltage conversion module is connected to the anode of the photoelectric detection unit. Electrical connection;

   The current-voltage conversion module includes: a synchronous logic circuit, a ramp voltage generator, a counter, a current-voltage converter, a voltage comparator, and a latch; wherein

   The output terminal of the photoelectric detection unit is connected with the input terminal of the current-voltage converter;

   The signal output by the synchronous logic circuit controls the ramp voltage generator and the counter to work at the same time;

   The inverting input terminal of the voltage comparator is connected with the output terminal of the current-voltage converter; the non-inverting input terminal of the voltage comparator is connected with the output terminal of the ramp voltage generator;

   The control terminal of the latch is connected with the output terminal of the voltage comparator, and the signal input terminal of the latch is connected with the output terminal of the counter.
3. The photoelectric detection module for lidar according to claim 2, wherein the photoelectric detection module includes a plurality of channels, and each channel of the plurality of channels includes the photoelectric detection unit, the Signal conditioning unit;

   Wherein, the signal conditioning unit of each channel includes a current-voltage conversion module, and the current-voltage conversion module of each channel includes a current-voltage converter, a voltage comparator, and a latch; and

   The current-voltage conversion modules of the multiple channels share the same synchronous logic circuit, ramp voltage generator, and counter.
4. The photoelectric detection module for lidar according to claim 2 or 3, wherein:

   Under the control of the signal output by the synchronous logic circuit, the ramp voltage generator generates a ramp voltage signal and the counter counts according to a preset counting frequency;

   When the ramp voltage signal input from the non-inverting input terminal of the voltage comparator is greater than the voltage signal output by the current-voltage converter, the voltage comparator outputs a control signal for controlling the operation of the latch;

   The control terminal of the latch inputs the control signal, and the latch latches the count value input from the signal input terminal at this time, and outputs the count value;

   The data processing unit determines the DC voltage value corresponding to the ambient light signal according to the count value.
5. The photoelectric detection module for lidar according to claim 4, wherein the ramp voltage generator generates a ramp voltage signal that rises from a preset minimum voltage value to a maximum voltage value within a preset sampling time period; The counter counts from a preset lowest value to a preset highest value according to a preset counting frequency within the preset sampling time period.
6. The photoelectric detection module for lidar according to claim 2 or 3, wherein the signal conditioning unit further comprises a bias voltage adjusting subunit;

   The output end of the bias voltage adjusting subunit is electrically connected to the anode of the photodetection unit; wherein

   The bias voltage adjustment subunit is used to adjust the bias voltage of the photodetection unit to calibrate the drift of the operating current of the photodetection unit caused by temperature and process deviation.
7. The photoelectric detection module for lidar according to claim 6, wherein the ambient light detection subunit further comprises a current compensation module; wherein

   The current compensation module is electrically connected with the bias voltage adjustment subunit and the current-voltage conversion module, respectively.
8. The photoelectric detection module for lidar according to claim 7, wherein the bias voltage adjustment subunit comprises a low voltage adjustment subunit and a medium voltage amplification subunit;

   The medium voltage amplifying subunit includes: a direct current source, a first triode, a first operational amplifier, a first input resistance and a first feedback resistance; wherein

   One end of the first input resistor is connected to the ground, and the other end is connected to one end of the first feedback resistor;

   The other end of the first feedback resistor is electrically connected to the anode of the photodetection unit, the output end of the direct current source, and the drain of the first triode;

   The cathode of the photodetection unit is electrically connected with the first high potential, and the anode of the photodetection unit is also electrically connected with the output terminal of the direct current source;

   The source of the first triode is connected to the ground, the drain of the first triode is connected to the output end of the direct current and the anode of the photodetection unit; the gate of the first triode is connected to The output terminal of the first operational amplifier is connected; the non-inverting input terminal of the first operational amplifier is connected to the other end of the first input resistor, and the inverting input terminal of the first operational amplifier is connected to a low-voltage regulator The output terminal of the unit is connected.
9. The photoelectric detection module for lidar according to claim 8, wherein the current-to-voltage conversion module comprises a second triode, a third triode, a fourth triode, a third resistor, and a voltage Comparator and latch circuit; among them

   The grid of the second triode is connected to the grid of the first triode, the source of the second triode is connected to ground, and the drain of the second triode is connected to the first triode. The drain connection of the three-stage transistor;

   The gate of the third triode is connected to the gate of the fourth triode; the source of the third triode is connected to the second high potential, and the gate of the third triode is connected Connected to the drain of the third triode;

   The source of the fourth triode is connected to the third high potential; the drain of the fourth triode is connected to one end of the third resistor, and the inverting input terminal of the voltage comparator is connected;

   The non-inverting input terminal of the voltage comparator is connected with the output terminal of the ramp circuit generator, and the output terminal of the voltage comparator is connected with the control terminal of the latch;

   The signal input end of the latch is connected to the output end of the counter, the output end of the latch is connected to a data processing unit, and the data processing unit determines the DC voltage corresponding to DC current;

   The other end of the third resistor is connected to the ground wire.
10. The photoelectric detection module for lidar according to claim 9, wherein the current compensation module includes a second operational amplifier, a fifth triode, a sixth triode, a seventh triode, and a Eight transistors and ninth transistors; among them

    The non-inverting input terminal of the second operational amplifier is connected to the inverting input terminal of the first operational amplifier; the inverting input terminal of the second operational amplifier is connected to the source of the fifth transistor and the first operational amplifier. One end of the four resistors is electrically connected; the output end of the second operational amplifier is connected to the gate of the fifth triode;

    The other end of the fourth resistor is connected to the ground wire;

    The drain of the fifth triode is electrically connected to the gate and the drain of the sixth triode, and the gate of the seventh triode;

    The source of the sixth triode is electrically connected to the fourth high potential; the grid of the sixth triode is connected to the grid of the seventh triode;

    The source of the seventh triode is electrically connected to the fifth high potential; the drain of the seventh triode is electrically connected to the drain of the eighth triode;

    The source of the eighth triode is connected to the ground, and the gate is electrically connected to the gate of the ninth triode; the drain of the eighth triode is connected to the gate of the eighth triode. The grid is electrically connected;

    The source of the ninth triode is connected to the ground, and the drain is electrically connected to the drain of the fourth triode.
11. The photoelectric detection module for lidar according to claim 1, wherein the signal conditioning unit further comprises an AC detection sub-unit, and the AC detection sub-unit is used to perform an AC signal in the electric signal. Amplification and quantification; wherein, the AC signal includes an AC signal generated by the photodetection unit inducing the echo signal.
12. A laser radar, characterized in that, the laser radar includes the photoelectric detection module for laser radar described in one of 1-11.
13. An ambient light detection method used in the photoelectric detection module used for lidar of one of 1-11; the method includes:

    Obtain a monotonically increasing reference voltage signal and a monotonically increasing counting signal under the control of the synchronous clock signal;

    Comparing the reference voltage signal with the measured voltage signal output by the current-voltage conversion module; wherein the current-voltage conversion module is used to convert the direct current signal generated by the photoelectric detection module from the detected ambient light into the measured voltage signal;

    At the moment when the reference voltage signal rises to the same time as the actual measured voltage signal, determining the count value corresponding to the count signal at that moment as the target count value;

    The intensity of the ambient light of the lidar is determined according to the target count value.

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