APD bias environment adaptive control method and device suitable for laser range finder

Abstract

The invention discloses an APD bias environment adaptive control method and device suitable for a laser range finder. The method comprises the following steps: setting a standard noise value; acquiring a previous environment temperature and an APD bias voltage value; acquiring the current environment temperature; the temperature difference between the current environment temperature and the last environment temperature is determined, the bias voltage variation is calculated in combination with the bias voltage temperature coefficient of the APD, and the bias voltage value of the APD is roughly adjusted through the bias voltage variation; obtaining a ranging echo signal of the laser range finder, and calculating a current noise value according to the ranging echo signal; and determining the noise value deviation between the current noise value and the standard noise value, and performing fine adjustment on the roughly adjusted APD bias voltage value by using a PID algorithm according to the noise value deviation. According to the invention, the bias voltage of the APD can be adjusted in real time according to the ambient temperature, the ranging target signal and the amplitude of the noise, the adaptive function of the bias voltage of the APD to the test environment is realized, and the method has good adaptability to environmental conditions of different ambient temperatures, illumination intensities, visibility and the like.

Description

Technical Field

[0001] The invention belongs to the field of electronic technology, and in particular relates to an APD bias environment adaptive control method and device suitable for a laser rangefinder. Background Art

[0002] Avalanche photodiode (APD) has the advantages of large current gain, high sensitivity, and fast frequency response. It is a commonly used laser echo receiving photoelectric detection device in pulsed laser rangefinders. Since the distance and type of the ranging target are different, the environmental factors of the actual ranging are also complex and changeable, and the dynamic range of the change of the laser echo signal amplitude is very large. In order to improve the ranging capability of the laser rangefinder, the current gain of the APD should be adjusted in real time according to the ranging environment. The current gain of the APD is directly related to its working bias voltage. When the bias voltage is too low, the current gain is also low, and the APD cannot perform at its best performance; when the bias voltage is too high, the noise increases, and the echo signal will be annihilated by the noise, affecting the signal extraction; when the bias voltage exceeds the breakdown voltage of the APD, it may cause damage to the APD.

[0003] like Figure 1 As shown in the figure, taking the relationship curve between the multiplication factor and working bias of the common InGaAs avalanche diode as an example, the basic principle of the relationship between APD bias and gain is explained. APD is a photovoltaic device with internal gain. When a high reverse bias voltage is applied to both ends of the PN junction, it will cause the avalanche multiplication effect of the PN junction. The effect of temperature on APD gain is mainly to change the width of the PN junction barrier layer. When the temperature rises, the barrier layer width becomes narrower, and the number of carrier ionization collisions decreases, which reduces the gain and thus increases the breakdown voltage accordingly. Figure 1 It can be seen that when the bias voltage reaches a certain value, the current is doubled; when the bias voltage is just below the breakdown voltage, the APD has a fixed gain; when the bias voltage reaches or exceeds the breakdown voltage, the current rises sharply.

[0004] The noise of APD mainly includes optical noise and electrical noise. Optical noise is generated by background radiation and signal radiation, and has little to do with the device itself; while electrical noise is inherent to it and is an important factor limiting the performance of APD. Electrical noise mainly includes thermal noise and shot noise. Adjusting the appropriate bias voltage to obtain the best multiplication factor can enable the APD to obtain the maximum signal-to-noise ratio at a given optical power. Therefore, bias voltage adaptation can not only reduce the noise level to reduce the false alarm rate, but also theoretically obtain the optimal signal-to-noise ratio of the APD.

[0005] However, in the traditional APD bias circuit design, the working bias voltage often cannot be adjusted in time according to the ranging target and environment. When the test environment (such as temperature, visibility, etc.) changes significantly, it will seriously affect the detection and extraction of the target signal. Summary of the invention

[0006] The purpose of the present invention is to provide an APD bias voltage environment adaptive control method and device suitable for a laser rangefinder, so as to solve the problem that the APD bias voltage cannot be timely adjusted according to the ranging target and environment.

[0007] To solve the above problems, the technical solution adopted by the present invention is as follows:

[0008] In a first aspect, the present invention provides an APD bias environment adaptive control method applicable to a laser rangefinder, the method comprising:

[0009] Set the standard noise value;

[0010] Get the last ambient temperature and APD bias value;

[0011] Get the current ambient temperature;

[0012] Determine the temperature difference between the current ambient temperature and the previous ambient temperature, calculate the bias change in combination with the APD bias temperature coefficient, and use the bias change to roughly adjust the APD bias value;

[0013] Obtain the ranging echo signal of the laser rangefinder, and calculate the current noise value according to the ranging echo signal;

[0014] The noise value deviation between the current noise value and the standard noise value is determined, and then the APD bias value after the coarse adjustment is fine-tuned using the PID algorithm according to the noise value deviation.

[0015] In the above scheme, the current noise value is calculated according to the ranging echo signal, including:

[0016] Perform AD sampling on the ranging echo signal;

[0017] Perform mean filtering and median filtering on the sampled data to remove DC potential;

[0018] After mean filtering again, the mean square error value is calculated as the current noise value.

[0019] In the above scheme, the temperature difference between the current ambient temperature and the previous ambient temperature is determined, the bias change is calculated in combination with the bias temperature coefficient of the APD, and the bias change is used to roughly adjust the APD bias value, including:

[0020] Determine the temperature difference between the current ambient temperature and the previous ambient temperature;

[0021] Multiplying the bias temperature coefficient of the APD by the temperature difference to obtain a bias change;

[0022] The previous APD bias value is added to the bias change to obtain the coarsely adjusted APD bias value.

[0023] In the above scheme, after the coarse adjustment is completed, the laser rangefinder emits laser and obtains the ranging echo signal.

[0024] In the above scheme, the method further comprises:

[0025] After fine tuning is completed, record and save the current ambient temperature and APD bias value.

[0026] In the above scheme, the PID algorithm is an incremental PID control algorithm.

[0027] In a second aspect, the present invention provides an APD bias environment adaptive control device applicable to a laser rangefinder for implementing any one of the APD bias environment adaptive control methods applicable to a laser rangefinder, the device comprising an ambient temperature acquisition unit, a digital signal processing unit and a bias adaptive control unit; wherein the ambient temperature acquisition unit comprises a temperature sensor and a single-chip microcomputer, the digital signal processing unit comprises a high-speed AD sampling circuit and a DSP digital processing circuit, and the bias adaptive unit comprises a bias generating circuit;

[0028] The temperature sensor collects the current ambient temperature;

[0029] The high-speed AD sampling circuit performs AD sampling on the ranging echo signal;

[0030] The DSP digital processing circuit is connected to the high-speed AD sampling circuit, receives sampling data from the high-speed AD sampling circuit, and processes the sampling data to calculate the current noise value;

[0031] The single chip microcomputer is connected to the temperature sensor and the DSP digital processing circuit, and is used to receive the current ambient temperature, determine the temperature difference between the current ambient temperature and the previous ambient temperature, calculate the bias change in combination with the bias temperature coefficient of the APD, use the bias change to roughly adjust the APD bias value, and determine the noise value deviation between the current noise value and the standard noise value, and then use the PID algorithm to fine-tune the roughly adjusted APD bias value according to the noise value deviation;

[0032] The bias voltage generating circuit is connected to the single chip microcomputer, and the output bias voltage is adjustable under the control of the single chip microcomputer.

[0033] In the above solution, the temperature sensor matches the voltage divider circuit to generate an analog signal, and the single chip microcomputer collects the analog signal and converts it into a temperature signal.

[0034] In the above scheme, the bias generating circuit is connected to the single-chip microcomputer through the SPI interface, and the single-chip microcomputer outputs an 8-bit code quantity CODE through the SPI interface. The bias generating circuit generates a corresponding APD bias value according to the 8-bit code quantity CODE to realize APD bias adjustment and control; wherein different code quantities CODE correspond to different APD bias voltages.

[0035] In a third aspect, the present invention further provides a laser rangefinder, which adopts any one of the above-mentioned APD bias environment adaptive control methods applicable to laser rangefinders.

[0036] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0037] The present invention can adjust the bias voltage of the APD in real time according to the ambient temperature and the amplitude of the ranging target signal and noise. The bias voltage is adjusted twice. The first time is a coarse adjustment based on the temperature difference between the two times before and after, and the coarse adjustment of the bias voltage change. The second time is a fine adjustment using a PID algorithm according to a set noise level value. By setting a suitable standard noise value and controlling the bias voltage with a noise value deviation, it can be ensured that the APD bias voltage can be finely adjusted to near the optimal operating voltage in different test environments (high and low temperatures, strong light, low visibility, etc.), thereby realizing the adaptive function of the APD bias voltage to the test environment, and having good adaptability to environmental conditions such as different ambient temperatures, light intensities and visibility.

[0038] In addition, the present invention also provides an APD bias environment adaptive control device suitable for a laser rangefinder, which uses a single-chip microcomputer as a bias control unit and a DSP as a signal processing unit, and can adjust the bias of the APD in real time according to the ambient temperature and the amplitude of the ranging target signal and noise, thereby realizing the adaptive function of the APD bias to the test environment, and having good adaptability to environmental conditions such as different ambient temperatures, light intensities, and visibility. The present invention can not only control the false alarm rate of the laser rangefinder, but also improve its signal-to-noise ratio under strong light and different visibility conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of the relationship between bias voltage and gain of an APD;

[0040] Figure 2 The structure block diagram of the APD bias environment adaptive control device suitable for laser rangefinder;

[0041] Figure 3 It is the DSP signal processing flow chart;

[0042] Figure 4 is the schematic diagram of the bias control circuit;

[0043] Figure 5 It is a flow chart of the adaptive control program of APD bias voltage environment applicable to laser rangefinder;

[0044] Figure 6 This is a comparison chart of the application effects of APD bias environment adaptive digital control for laser rangefinder; among them, Figure 6 (a) is the effect diagram without applying APD bias environment adaptive digital control. Figure 6 (b) is a diagram showing the effect of applying adaptive digital control of the APD bias environment. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0046] The present invention discloses an APD bias environment adaptive control method and device suitable for laser rangefinder, which solves the problem that the detection result is easily affected by the external environment during the detection process, can accurately detect under various lighting and noise conditions, and improves the stability of detection. The present invention is suitable for industrial measurement, national defense and military applications where laser ranging is required.

[0047] The APD bias voltage environment adaptive digital control device of the present invention is suitable for a laser rangefinder, such as Figure 2 As shown, it includes an ambient temperature acquisition unit, a digital signal processing unit and a bias voltage self-adaptation unit. The ambient temperature acquisition unit includes a temperature sensor and a single-chip microcomputer; the digital signal processing unit includes a high-speed AD sampling circuit and a DSP digital processing circuit; and the bias voltage self-adaptation unit includes a bias voltage generating circuit.

[0048] The temperature sensor matches the voltage divider circuit to generate an analog signal, and the analog signal is the voltage of the temperature sensor (thermistor).

[0049] The single chip microcomputer collects and converts the temperature signal.

[0050] The high-speed AD sampling circuit samples the ranging echo signal.

[0051] The DSP digital processing circuit processes the ranging echo signal as the basis for subsequent bias adjustment.

[0052] The bias voltage generating circuit is controlled by the microcontroller through the SPI interface and the output bias voltage is adjustable.

[0053] The microcontroller has a built-in APD bias adaptive program, which adjusts the APD bias in real time according to the ambient temperature and the amplitude of the ranging target signal and noise, including coarse adjustment based on the temperature difference between the previous and next two times and fine adjustment using the PID algorithm based on the set standard noise value. The PID fine adjustment uses an incremental PID control algorithm, which only calculates two adjacent times and only considers the change in the controller output based on the previous time.

[0054] The APD bias environment adaptive digital control platform suitable for laser rangefinder of the present invention measures the ambient temperature by a temperature acquisition unit, processes and calculates the amplitude of the ranging target signal and noise by a signal processing unit, and then automatically adjusts the bias of the APD in real time by a bias adaptive unit.

[0055] Figure 3 The DSP signal processing flow of the present invention. The APD bias environment adaptive digital control device suitable for laser rangefinder of the present invention adopts a high-speed AD conversion chip (such as AD9283) to sample the ranging echo signal, the sampling rate is 30MHz, and 900 points are sampled for a single ranging. The sampled data is sent to the DSP for processing. After mean filtering and median filtering, the DC potential is removed, and after mean filtering again, the mean square error value of the sampled signal is calculated as the basis for subsequent bias adjustment. Because under the same test environment, the amplitude of the signal of the ranging target varies greatly with the different target positions, while the noise amplitude is relatively stable, the signal processing method of the present invention uses the mean square error of the sampled signal to evaluate the intensity of the overall noise, so as to avoid the change of the overall noise signal caused by the switching of the ranging target.

[0056] Figure 4 The bias control circuit diagram of the present invention. The core of the circuit is the bias generating chip, whose actual output voltage is related to the sampling voltage divider resistor. By configuring the resistance value of the voltage divider resistor and the pin output of the digital adjustment signal, an adjustable bias voltage that meets the APD input range requirements can be generated. The digital adjustment signal can be controlled in real time by the single-chip microcomputer through the SPI interface.

[0057] The specific control method is that the microcontroller controls the 8-bit code CODE through SPI. When CODE=00hex, the DAC register is reset; when CODE changes between 01hex and FFhex, DACout generates a discrete bias value between 0.01V and 1.25V, thereby controlling the APD bias to change between 40V and 70V. By configuring appropriate voltage divider resistors, when CODE=FFhex, the APD bias is 70V; when CODE=01hex, the APD bias is 40V; that is, for every 01hex increase in CODE, the APD bias decreases by about 0.12V.

[0058] The APD bias adaptation program mainly includes the main program, the microcontroller initialization program, the ambient temperature acquisition subroutine, the FLASH erasing and reading and writing program, the laser emission program, the PID control subroutine, the SPI bias output adjustment subroutine and other parts.

[0059] Figure 5 This is a flow chart of an APD bias voltage environment adaptive program suitable for a laser rangefinder according to the present invention. The bias voltage is adjusted twice in the program. The first time is a coarse adjustment based on the temperature difference between the two times before and after, and the bias voltage change is roughly adjusted. The bias voltage temperature coefficient of the APD is related to the APD's own characteristics. Taking the common InGaAs avalanche diode as an example, the APD temperature coefficient is 0.14V / ℃, that is, for every 1℃ increase in temperature, the corresponding optimal operating voltage and breakdown voltage increase by 0.14V. Coarse adjustment can prevent bias voltage anomalies caused by sudden changes in temperature between the two tests, and prepare for the next step of fine adjustment. The second time is to use the PID algorithm for fine adjustment based on the set noise level value. By setting a suitable standard noise value and controlling the bias voltage with the noise value, it can be ensured that the bias voltage can be fine-tuned to near the optimal operating voltage in different test environments (high and low temperatures, strong light, low visibility, etc.).

[0060] Figure 6 This is the comparison result of the laser rangefinder echo signal in a complex application environment before and after applying the APD bias environment adaptive digital control platform for laser rangefinder described in the present invention. The horizontal axis represents the sampling point, each sampling point corresponds to 5m; the vertical axis represents the signal sampling value. Figure 6 As shown in (a), before the APD bias environment adaptive digital control platform for laser rangefinder of the present invention is applied, the laser echo signal and noise are generally high in a complex application environment. After calculation, the signal-to-noise ratio at this time is -2.04dB. Figure 6 As shown in (b), the bias voltage adaptive platform will adaptively adjust the APD bias voltage according to the noise in a complex application environment. At this time, the signal and noise are relatively low overall. After calculation, the signal-to-noise ratio at this time is -1.56dB. After testing, the APD bias voltage environment adaptive digital control device suitable for laser rangefinder of the present invention can improve the signal-to-noise ratio of the measured target in a complex application environment.

[0061] In addition, the present invention also provides a laser rangefinder, which adopts the APD bias environment adaptive control method applicable to the laser rangefinder described in any one of the above technical solutions.

[0062] In summary, the present invention provides an APD bias environment adaptive digital control method and device suitable for laser rangefinders. The device uses a single-chip microcomputer as a bias control unit and a DSP as a signal processing unit. The bias of the APD can be adjusted in real time according to the ambient temperature and the amplitude of the ranging target signal and noise, so as to realize the adaptive function of the APD bias to the test environment, and has good adaptability to environmental conditions such as different ambient temperatures, light intensities, and visibility. The present invention can not only control the false alarm rate of the laser rangefinder, but also improve its signal-to-noise ratio under strong light and different visibility conditions.

[0063] It should be noted that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0064] It should be pointed out that, according to the needs of implementation, the various steps / components described in this application can be split into more steps / components, and two or more steps / components or partial operations of steps / components can be combined into new steps / components to achieve the purpose of the present invention.

[0065] It will be easily understood by those skilled in the art that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for adaptively controlling the APD bias voltage environment of a laser rangefinder, characterized in that: The method includes: Set the standard noise value; Get the last ambient temperature and APD bias value; Get the current ambient temperature; Determine the temperature difference between the current ambient temperature and the previous ambient temperature, calculate the bias change in combination with the APD bias temperature coefficient, and use the bias change to roughly adjust the APD bias value; Obtain the ranging echo signal of the laser rangefinder, and calculate the current noise value according to the ranging echo signal; The noise value deviation between the current noise value and the standard noise value is determined, and then the APD bias value after the coarse adjustment is fine-tuned using the PID algorithm according to the noise value deviation.

2. The APD bias environment adaptive control method for a laser rangefinder according to claim 1, characterized in that: Calculate the current noise value based on the ranging echo signal, including: Perform AD sampling on the ranging echo signal; Perform mean filtering and median filtering on the sampled data to remove DC potential; After mean filtering again, the mean square error value is calculated as the current noise value.

3. The APD bias environment adaptive control method for a laser rangefinder according to claim 1, characterized in that: Determine the temperature difference between the current ambient temperature and the previous ambient temperature, calculate the bias change in combination with the APD bias temperature coefficient, and use the bias change to roughly adjust the APD bias value, including: Determine the temperature difference between the current ambient temperature and the previous ambient temperature; Multiplying the bias temperature coefficient of the APD by the temperature difference to obtain a bias change; The previous APD bias value is added to the bias change to obtain the coarsely adjusted APD bias value.

4. The APD bias environment adaptive control method for a laser rangefinder according to claim 1, characterized in that: After the coarse adjustment is completed, the laser rangefinder emits laser and obtains the ranging echo signal.

5. The APD bias environment adaptive control method for a laser rangefinder according to claim 1, characterized in that: The method further includes: After fine tuning is completed, record and save the current ambient temperature and APD bias value.

6. The APD bias environment adaptive control method for a laser rangefinder according to claim 1, characterized in that: The PID algorithm is an incremental PID control algorithm.

7. An APD bias environment adaptive control device applicable to a laser rangefinder for implementing the APD bias environment adaptive control method applicable to a laser rangefinder as claimed in any one of claims 1 to 6, characterized in that: The device comprises an ambient temperature acquisition unit, a digital signal processing unit and a bias voltage adaptive control unit; wherein the ambient temperature acquisition unit comprises a temperature sensor and a single chip microcomputer, the digital signal processing unit comprises a high-speed AD sampling circuit and a DSP digital processing circuit, and the bias voltage adaptive unit comprises a bias voltage generating circuit; The temperature sensor collects the current ambient temperature; The high-speed AD sampling circuit performs AD sampling on the ranging echo signal; The DSP digital processing circuit is connected to the high-speed AD sampling circuit, receives sampling data from the high-speed AD sampling circuit, and processes the sampling data to calculate the current noise value; The single chip microcomputer is connected to the temperature sensor and the DSP digital processing circuit, and is used to receive the current ambient temperature, determine the temperature difference between the current ambient temperature and the previous ambient temperature, calculate the bias change in combination with the bias temperature coefficient of the APD, use the bias change to roughly adjust the APD bias value, and determine the noise value deviation between the current noise value and the standard noise value, and then use the PID algorithm to fine-tune the roughly adjusted APD bias value according to the noise value deviation; The bias voltage generating circuit is connected to the single chip microcomputer, and the output bias voltage is adjustable under the control of the single chip microcomputer.

8. The APD bias environment adaptive control device for a laser rangefinder according to claim 7, characterized in that: The temperature sensor matches the voltage divider circuit to generate an analog signal, and the single chip microcomputer collects the analog signal and converts it into a temperature signal.

9. The APD bias environment adaptive control device for a laser rangefinder according to claim 7, characterized in that: The bias generating circuit is connected to the single-chip microcomputer via an SPI interface, and the single-chip microcomputer outputs an 8-bit code quantity CODE via the SPI interface. The bias generating circuit generates a corresponding APD bias value according to the 8-bit code quantity CODE to achieve APD bias adjustment and control; wherein different code quantities CODE correspond to different APD biases.

10. A laser rangefinder, characterized in that: The laser rangefinder adopts the APD bias environment adaptive control method applicable to the laser rangefinder as claimed in any one of claims 1 to 6.

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