Preamplifier circuit and control method suitable for laser coherent speed and distance measurement system

Abstract

The present invention belongs to the field of laser radar technology, and discloses a preamplifier circuit suitable for a laser coherent speed and distance measurement system, including a first-stage amplification module for amplifying a photocurrent signal by a transimpedance amplifier circuit, a low-pass filter module for removing the aliasing phenomenon of high-frequency signals folded into a low-frequency band during the digitization of analog signals by a low-pass filter, a channel selection module for controlling the passband of echo signals in both speed measurement and distance measurement by a channel selection circuit, a filter switching module for switching signals to pass through an all-pass filter or a high-pass filter, and a second-stage amplification module for converting the differential voltage signal output by the all-pass filter or the high-pass filter into a single-ended signal by a differential amplifier circuit. The present invention realizes the measurement of two types of information, namely, target speed and distance, under the same device, and can accurately extract and amplify the target echo signal, thereby improving the flexibility and accuracy of signal extraction and processing.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser radar, and in particular relates to a preamplifier circuit suitable for a laser coherent speed and distance measurement system and a control method thereof. Background Art

[0002] At present, the mainstream amplifier circuit uses a single passband to measure both speed and distance information. If an all-pass filter is used alone, the extremely high-energy DC signal cannot be removed during the ranging stage. After the pre-amplifier, the DC signal has greater energy, which masks the weak echo of the distant target and affects the ranging result. If a high-pass filter is used, the speed Doppler frequency of the target that is far away and weak but useful will be suppressed during the speed measurement stage, resulting in speed measurement errors. At present, LiDAR is a radar that uses laser as a carrier. It is a combination of traditional radar technology and modern laser technology. Compared with microwave radar, it has higher resolution. With the development and maturity of lasers and various related technologies, LiDAR has made great progress and has been widely used in various measurements.

[0003] The coherent laser rangefinder system is divided into three parts: fiber optics, telescope and electronics. The electronics part includes laser drive and temperature control circuit, detector and preamplifier circuit, and information processing circuit. The detector and preamplifier circuit realize the photoelectric conversion and amplification of the signal output by the optical bridge. When the target is far away, the laser echo signal reflected from the surface of the measured object is extremely weak. In this system, the echo energy is only in the pW level, which is easily submerged in the clutter. Therefore, the preamplifier circuit must ensure the amplification factor while removing the interference signal. It is the key circuit of the receiving part of the entire system.

[0004] In the laser coherent speed and distance measurement system, in order to realize the two functions of speed measurement and distance measurement in the same system, a fixed-frequency signal is first used to measure the target speed, and then a positive linear continuous frequency modulation signal or a negative linear continuous frequency modulation signal is generated according to the speed direction to measure the distance information of the target.

[0005] In the speed measurement stage, due to the point frequency signal used, there will be no other obvious interference signals in the target echo, and an all-pass filter is usually used in the amplification circuit to not attenuate signals of any frequency. In the distance measurement stage, since there are a large number of circulators, lenses, coatings and other devices in the optical system that will produce backward light path reflections, and these devices are relatively close to the detection process, a DC signal with energy far higher than the target echo energy will be generated during the detection process. When the energy reaches a certain level, the intermediate frequency signal of the receiving branch will be saturated, thereby covering up the weak echo signal of the distant target and causing the target to be lost. Therefore, a high-pass filter is usually used in the existing amplification circuit to remove interference signals such as the optical system's own light path reflection.

[0006] Therefore, the amplifier circuit needs to be able to process different characteristic small signals of speed measurement and distance measurement echo at the same time. If the middle channel of the amplifier circuit simply selects an all-pass filter, the DC signal with energy of uW level cannot be removed in the distance measurement stage, and the accurate echo signal cannot be obtained, which affects the distance measurement. If the middle passband of the amplifier circuit selects a high-pass filter, the passband will suppress the weak but useful speed Doppler frequency when the target distance is far and the energy intensity is insufficient, causing speed measurement errors. Therefore, a single passband is used in the circuit to measure both speed and distance information, and one of the information will inevitably have a measurement error when using the amplifier circuit in the prior art.

[0007] Through the above analysis, the problems and defects of the prior art are as follows:

[0008] In the amplifier circuit of the existing laser coherent speed and distance measurement system, a single passband is used to measure both speed and distance information, which may lead to measurement errors in one of the information. Summary of the invention

[0009] In view of the problems existing in the prior art, the present invention provides a preamplifier circuit and a control method thereof suitable for a laser coherent speed and distance measurement system.

[0010] The present invention is implemented in this way: a preamplifier circuit suitable for a laser coherent speed and distance measurement system comprises:

[0011] A primary amplification module, used for performing primary amplification of the photocurrent signal using a transimpedance amplifier circuit;

[0012] A low-pass filter module is used to remove the aliasing phenomenon of high-frequency signals folding into low-frequency bands during the digitization of analog signals by using a low-pass filter;

[0013] A channel selection module, used for controlling the passband of the echo signal in the speed measurement and distance measurement by using the channel selection circuit;

[0014] A filter switching module, used for switching the signal to pass through an all-pass filter or a high-pass filter according to a control signal of a channel selection circuit;

[0015] The secondary amplification module is used to convert the differential voltage signal output by the all-pass filter or the high-pass filter into a single-ended signal using a differential amplification circuit.

[0016] Further, the transimpedance amplifier circuit includes a first-stage preamplifier and a first-stage main amplifier;

[0017] The first-stage preamplifier is used to amplify the converted current signal and convert the signal into a voltage signal;

[0018] The first-stage main amplifier is used to increase the signal amplitude by passing the voltage signal through a variable gain main amplifier.

[0019] Furthermore, the channel selection circuit includes a signal input terminal, an output terminal, and a logic switch circuit connected to the signal input terminal.

[0020] Furthermore, the high-pass filter comprises an SLFH series laminated chip high-pass filter.

[0021] Furthermore, the low-pass filter comprises a ZL2012PXX series industrial-grade laminated chip low-pass filter.

[0022] Furthermore, the transimpedance amplifier includes a chip of AD80XX series.

[0023] Another object of the present invention is to provide a control method for a preamplifier circuit applicable to a laser coherent speed and distance measurement system, the control method for a preamplifier circuit applicable to a laser coherent speed and distance measurement system comprising:

[0024] Step 1: After the laser echo signal is reflected back, it is received by the receiving optical system, converted into a current signal and then enters the first-stage amplifier circuit. The transimpedance preamplifier amplifies the converted current signal, and then the signal becomes a voltage signal, and then the signal amplitude is increased by the variable gain main amplifier.

[0025] Step 2: the signal passing through the transimpedance amplifier enters a low-pass filter to filter out the frequency components that cause frequency aliasing;

[0026] Step 3, using a channel selection circuit to control the passband of the echo signal in both speed measurement and distance measurement, using an all-pass filter in speed measurement and a high-pass filter in distance measurement;

[0027] Step 4: The differential voltage signal outputted by the all-pass filter or the low-pass filter is connected to the input end of the differential receiving amplifier, and an amplified single-ended signal is outputted, which is the second stage amplification.

[0028] Furthermore, the channel selection circuit in step 2 is controlled by the switching signals SW1 and SW2 of the logic switch circuit, and the selected signal is output from the output end after passing through a high-pass filter or an all-pass filter.

[0029] Further, in the speed measurement mode, the switching signal SW2 of the logic switch circuit is high level H, the input signal input2 enters PIN2 of the IC and is set to be connected to PIN2B, and PIN2B passes through the capacitor C3 and is output after passing through the all-pass filter; at the same time, the switching signal SW1 is low level L, the input signal input1 enters PIN1 of the IC and is set to be connected to PIN1A. Since PIN1A is grounded through the third capacitor C2, the input signal input1 is short-circuited.

[0030] Furthermore, in the ranging mode, the logic switch circuit switches the signal SW2 to a low level L and SW1 to a high level H, and the input signal input2 is short-circuited; the input signal input1 passes through the second capacitor C1 from pin1B and is output after passing through a high-pass filter.

[0031] In combination with the above technical solutions and the technical problems solved, please analyze the advantages and positive effects of the technical solutions to be protected by the present invention from the following aspects:

[0032] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving the problems, the technical solutions to be protected by the present invention and the results and data during the research and development process are closely combined to analyze in detail and deeply how the technical solutions of the present invention solve the technical problems, and some creative technical effects brought about after solving the problems. The specific description is as follows:

[0033] The present invention adds a channel selection circuit between the secondary amplification circuits, and the main control system (external circuit) gives a passband selection signal to control the passband of the echo signal to be full-pass filtering or high-pass filtering. When the full-pass filter is used in the speed measurement mode, any useful signal will not be attenuated, thereby improving the speed measurement accuracy.

[0034] In the ranging mode, a high-pass filter is used to effectively remove the interference signal generated by the reflection of the optical system itself and prevent the intermediate frequency signal of the receiving branch from being saturated. The present invention realizes the measurement of both target speed and distance information in the same device. The target echo signal can be accurately extracted and amplified through the preamplifier circuit, thereby improving the flexibility and accuracy of signal extraction and processing.

[0035] Second, considering the technical solution as a whole or from the perspective of the product, the technical effects and advantages of the technical solution to be protected by the present invention are described in detail as follows:

[0036] The present invention realizes the measurement of two kinds of information, namely, target speed and distance, under the same device. The echo signals of target speed and distance can be accurately extracted and amplified in a targeted manner through the preamplifier circuit, thereby improving the flexibility and accuracy of signal extraction and processing.

[0037] Third, as auxiliary evidence of the inventiveness of the claims of the present invention, it is also reflected in the following important aspects:

[0038] The expected benefits and commercial value of the technical solution of the present invention after transformation are:

[0039] After the technical solution of the present invention is transformed, the target speed and distance can be measured in the same device. Compared with the commonly used amplification circuit, the flexibility and accuracy of subsequent signal extraction and processing are improved, and the difficulty of signal processing and chip cost are effectively reduced. It can be used in a large number of fields such as long-distance target detection, obstacle avoidance, command guidance, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a structural principle diagram of a preamplifier circuit applicable to a laser coherent speed and distance measurement system provided by an embodiment of the present invention;

[0041] Figure 2 is a principle block diagram of a transimpedance amplifier circuit provided by an embodiment of the present invention;

[0042] Figure 3 It is a connection principle diagram of a preamplifier circuit for a laser coherent speed and distance measurement system provided by an embodiment of the present invention;

[0043] Figure 4 A channel selection circuit provided by an embodiment of the present invention;

[0044] Figure 5 is a spectrum diagram of a speed measurement signal after passing through an all-pass filter provided by an embodiment of the present invention;

[0045] Figure 6 is a spectrum diagram of the ranging original echo signal provided by an embodiment of the present invention;

[0046] Figure 7 This is a spectrum diagram of a ranging signal after passing through a high-pass filter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0047] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] 1. Explanatory Examples In order to enable those skilled in the art to fully understand how to implement the present invention, this section provides an illustrative example that expands and describes the technical solution of the claims.

[0049] like Figure 1 As shown, the preamplifier circuit applicable to the laser coherent speed and distance measurement system provided by the embodiment of the present invention includes:

[0050] A primary amplification module, used for performing primary amplification of the photocurrent signal using a transimpedance amplifier circuit;

[0051] A low-pass filter module is used to remove the aliasing phenomenon of high-frequency signals folding into low-frequency bands during the digitization of analog signals by using a low-pass filter;

[0052] A channel selection module, used for controlling the passband of the echo signal in the speed measurement and distance measurement by using the channel selection circuit;

[0053] A filter switching module, used for switching the signal to pass through an all-pass filter or a high-pass filter according to a control signal of a channel selection circuit;

[0054] The secondary amplification module is used to convert the differential voltage signal output by the all-pass filter or the high-pass filter into a single-ended signal using a differential amplification circuit.

[0055] like Figure 3 As shown, it is a connection schematic diagram of the preamplifier circuit for the laser coherent speed and ranging system provided by an embodiment of the present invention. The echo signal received by the receiving optical system is converted into an electrical signal by an avalanche photodiode and enters the transimpedance amplifier circuit for primary amplification. After the primary amplification, the signal enters the low-pass filter to remove aliasing. According to the current measurement mode, the channel selection circuit controls the signal to pass through an all-pass filter or a high-pass filter. The all-pass filter is used in the speed measurement stage, which will not attenuate the echo signal of the weak target. The high-pass filter is used in the ranging stage, which can effectively remove the DC signal with energy in the uW order and obtain an accurate echo. The signal passing through the channel selection circuit is converted into a single-ended signal using a differential to single-ended amplifier, and the secondary amplification is completed.

[0056] After the echo light is detected by the balanced detector, the balanced detector will output a weak photocurrent signal containing effective information of the echo light and amplify it. The amplification circuit is implemented using two-stage amplification, the first stage is a transimpedance amplifier circuit, and the second stage is a differential amplifier circuit. A low-pass filter is connected between the two-stage amplifier circuits. A channel selection circuit is added after the low-pass filter. The channel selection circuit is used to control the passband of the echo signal. In the case of speed measurement, an all-pass filter is used, and in the case of distance measurement, a high-pass filter is used.

[0057] Step 1: After the laser echo signal is reflected back, it is received by the receiving optical system and collected by the avalanche photodiode receiver as much as possible. After being converted into a current signal, it enters the first-stage amplifier circuit. The transimpedance preamplifier amplifies the converted current signal. At this time, the signal becomes a voltage signal, and then the signal amplitude is increased by the variable gain main amplifier. Figure 2 shown.

[0058] The transimpedance amplifier includes a chip of the AD80XX series, which is a wide bandwidth, single-power supply transimpedance amplifier optimized for fiber optic receiver circuit applications. This series of chips has the advantages of low power consumption, low noise, and wide bandwidth, and an operational amplifier and feedback device are integrated inside, so no additional discrete components are required, and the circuit control is simple.

[0059] Step 2: The signal passing through the transimpedance amplifier enters the low-pass filter to filter out the frequency components that produce frequency aliasing and prevent frequency aliasing.

[0060] As mentioned above, in this system, the ADC sampling clock of the analog-to-digital converter (the signal is sampled by the analog-to-digital converter (ADC) after passing through the preamplifier circuit, and the ADC sampling clock used in this system is 100Mhz.) is 100Mhz, that is, f s =100MHz, the frequency of the low-pass filter should satisfy f s ≥2f c , the cut-off frequency f of the low-pass filter in the present invention is c =50MHz.

[0061] The low-pass filter includes the ZL2012PXX series industrial-grade laminated chip low-pass filter. Its laminated structure and small size are suitable for high-density mounting, and its steep attenuation characteristics effectively suppress noise.

[0062] Step 3: Add a channel selection circuit after the low-pass filter. This circuit is used to control the passband of the echo signal in both speed measurement and distance measurement. When measuring speed, an all-pass filter is used, and when measuring distance, a high-pass filter is used. The channel selection circuit of this embodiment is as follows: Figure 5 As shown, it includes a signal input terminal, an output terminal and a logic switch circuit connected to the signal input terminal. Under the control of the switching signals SW1 and SW2 of the logic switch circuit, the selected signal is output from the output terminal after passing through a high-pass filter or an all-pass filter.

[0063] As described above, in the speed measurement mode, the switching signal SW2 is at a high level H, the input signal input2 enters PIN2 of the IC and is set to be connected to PIN2B, and PIN2B passes through the capacitor C3 and is output after passing through the all-pass filter; at the same time, the switching signal SW1 is at a low level L, the input signal input1 enters PIN1 of the IC and is set to be connected to PIN1A. Since PIN1A is grounded through the third capacitor C2, the input signal input1 is short-circuited.

[0064] Similarly, in the ranging mode, the switching signal SW2 is at a low level L, SW1 is at a high level H, the input signal input2 is short-circuited; the input signal input1 passes through the second capacitor C1 from pin1B and is output after passing through a high-pass filter.

[0065] Thus, under the control of the switching signal of the logic switch circuit, the signal passes through the all-pass filter or the high-pass filter. When the system is in the speed measurement stage, the signal is connected to the all-pass filter. When the system is in the distance measurement stage, the signal is connected to the high-pass filter.

[0066] The high-pass filter includes an SLFH series laminated chip high-pass filter, which has customizable center frequency, suppression and other characteristics.

[0067] Step 4: The output signal after full-pass or low-pass filtering is a differential voltage signal, which needs to be converted into a single-ended signal. The output signal is connected to the input of the differential receiving amplifier, and the amplified single-ended signal is output, which is the second stage amplification.

[0068] The differential amplifier includes chips of the AD81XX series. AD8129 / AD8130 are differential to single-ended amplifiers with extremely high common-mode rejection ratio (CMRR) at high frequencies. They are powered by a single power supply and have a wide voltage range of +5V to ±12V. They support wide common-mode and differential-mode voltage ranges while maintaining signal integrity.

[0069] 2. Application Examples: In order to prove the creativity and technical value of the technical solution of the present invention, this section provides application examples of the technical solution of the claims on specific products or related technologies.

[0070] The present invention is used in a certain space-based model application mission to provide the navigation system with the distance and speed of the target. During the entire mission process, the product continuously and effectively provides corresponding information of the target, ensuring the success of the mission.

[0071] 3. Evidence of the effects of the embodiments. The embodiments of the present invention have achieved some positive effects during the development or use process, and indeed have great advantages over the prior art. The following content is described in conjunction with the data, charts, etc. of the experimental process.

[0072] In the speed measurement mode, for a weak target with a long detection distance and a low speed, after applying this embodiment, an all-pass filter is used, which will not attenuate any useful information. Figure 4 For the echo of a long-distance slow target that has passed through an all-pass filter, a 1024-point fast Fourier transform will not cause attenuation of the useful signal.

[0073] In the ranging mode, due to the self-reflection of the optical system, there will always be a DC signal with energy much higher than the echo target, causing the target to be lost, such as Figure 5 After applying this embodiment, since a high-pass filter is added to the amplifier circuit, the low-frequency DC signal is eliminated and an accurate echo of the target is obtained, as shown in FIG. Figure 6 .

[0074] A slow-moving target is placed at a long distance. First, the commonly used preamplifier circuit is used for experiment, and the passband is an all-pass filter. The speed echo signal can be effectively amplified to measure the target speed, but the DC signal will drown the real echo during distance measurement, resulting in distance measurement errors. Then, an amplifier circuit with a passband of a high-pass filter is used for testing. Due to the long distance of the target and insufficient energy intensity, the weak but useful speed Doppler frequency is suppressed, and there is a speed measurement error after the signal amplified by the amplifier circuit is resolved. Finally, this embodiment is used. When measuring speed, the speed echo can be accurately obtained and effectively amplified, and the Doppler frequency shift of the speed is obtained to calculate the speed. When measuring distance, the DC signal is eliminated and amplified to obtain the real distance echo, and the distance information can be obtained by decoupling from the speed. Through experimental verification, the preamplifier circuit design proposed by the present invention is suitable for laser coherent speed and distance measurement system. In the speed measurement mode, an all-pass filter is used, which will not attenuate any useful signal, thereby improving the speed measurement accuracy. In the distance measurement mode, a high-pass filter is used to effectively remove the interference signal generated by the reflection of the optical system itself, and prevent the intermediate frequency signal of the receiving branch from saturation. The measurement of target speed and distance information is realized in the same device. The target echo signal can be accurately extracted and amplified through the preamplifier circuit, which improves the flexibility and accuracy of signal extraction and processing.

[0075] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered within the protection scope of the present invention.

Claims

1. A preamplifier circuit suitable for a laser coherent speed and distance measurement system, characterized in that: The preamplifier circuit suitable for the laser coherent speed and distance measurement system comprises: A primary amplification module, used for performing primary amplification of the photocurrent signal using a transimpedance amplifier circuit; A low-pass filter module is used to remove the aliasing phenomenon of high-frequency signals folding into low-frequency bands during the digitization of analog signals by using a low-pass filter; A channel selection module, used for controlling the passband of the echo signal in the speed measurement and distance measurement by using the channel selection circuit; A filter switching module, used for switching the signal to pass through an all-pass filter or a high-pass filter according to a control signal of a channel selection circuit; A secondary amplification module is used to convert the differential voltage signal output by the all-pass filter or the high-pass filter into a single-ended signal using a differential amplification circuit; The preamplifier circuit can measure two kinds of information, namely, target speed and distance, by using the same device, and accurately extract the echo signals of the target speed and distance.

2. The preamplifier circuit suitable for the laser coherent speed and distance measurement system as claimed in claim 1, characterized in that: The transimpedance amplifier circuit comprises a first-stage preamplifier and a first-stage main amplifier; The first-stage preamplifier is used to amplify the converted current signal and convert the signal into a voltage signal; The first-stage main amplifier is used to increase the signal amplitude by passing the voltage signal through a variable gain main amplifier.

3. The preamplifier circuit suitable for the laser coherent speed and distance measurement system as claimed in claim 1, characterized in that: The channel selection circuit includes a signal input terminal, an output terminal, and a logic switch circuit connected to the signal input terminal.

4. The preamplifier circuit suitable for the laser coherent speed and distance measurement system as claimed in claim 1, characterized in that: The high-pass filter includes an SLFH series multilayer chip high-pass filter.

5. The preamplifier circuit suitable for the laser coherent speed and distance measurement system as claimed in claim 1, characterized in that: The low-pass filter includes a ZL2012PXX series industrial-grade laminated chip low-pass filter.

6. The preamplifier circuit suitable for the laser coherent speed and distance measurement system as claimed in claim 1, characterized in that: The transimpedance amplifier circuit includes a chip of AD80XX series.

7. A control method for a preamplifier circuit applicable to a laser coherent speed and distance measurement system for implementing any one of claims 1 to 6, characterized in that: The preamplifier circuit applicable to the laser coherent speed and distance measurement system realizes measuring two kinds of information, namely, target speed and distance, by using the same device, and its control method includes: Step 1: After the laser echo signal is reflected back, it is received by the receiving optical system, converted into a current signal and then enters the first-stage amplifier circuit. The transimpedance preamplifier amplifies the converted current signal, and then the signal becomes a voltage signal, and then the signal amplitude is increased by the variable gain main amplifier. Step 2: the signal passing through the transimpedance amplifier enters a low-pass filter to filter out the frequency components that cause frequency aliasing; Step 3, using a channel selection circuit to control the passband of the echo signal in both speed measurement and distance measurement, using an all-pass filter in speed measurement and a high-pass filter in distance measurement; Step 4: Connect the differential voltage signal output by the all-pass filter or the high-pass filter to the input end of the differential receiving amplifier, and output the amplified single-ended signal, which is the second stage amplification.

8. The control method for the preamplifier circuit applicable to the laser coherent speed and distance measurement system as claimed in claim 7, characterized in that: The channel selection circuit in step 2 is controlled by the switching signals SW1 and SW2 of the logic switch circuit, and the selected signal is output from the output end after passing through a high-pass filter or an all-pass filter.

9. The control method for the preamplifier circuit applicable to the laser coherent speed and distance measurement system as claimed in claim 8, characterized in that: In the speed measurement mode, the switching signal SW2 of the logic switch circuit is high level H, the input signal input2 enters PIN2 of the IC and is set to be connected to PIN2B, and PIN2B passes through the capacitor C3 and is output after passing through the all-pass filter; at the same time, the switching signal SW1 is low level L, the input signal input1 enters PIN1 of the IC and is set to be connected to PIN1A. Since PIN1A is grounded through the third capacitor C2, the input signal input1 is short-circuited to the ground.

10. The control method for the preamplifier circuit applicable to the laser coherent speed and distance measurement system as claimed in claim 8, characterized in that: In the ranging mode, the logic switch circuit switches the signal SW2 to a low level L, SW1 to a high level H, and the input signal input2 is short-circuited to the ground; the input signal input1 passes through the second capacitor C1 from pin1B and is output after passing through a high-pass filter.

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