FMCW lidar system and control method for direct current cancellation

Abstract

The application discloses a kind of FMCW laser radar systems and control method for direct current elimination, optical and detector module in system includes detector array, signal amplification conversion module includes analog amplification array, difference conversion single-end array, multiplexer and variable gain amplifier, data processing module includes analog-digital converter and FPGA, and analog amplification array adopts differential structure;The output of detector array is connected with difference conversion single-end array through analog amplification array, and the output of difference conversion single-end array is connected with variable gain amplifier through multiplexer;The output of variable gain amplifier is connected with analog-digital converter, and the output of analog-digital converter is connected with FPGA, and the address strobe output end and gain control end of FPGA are connected with multiplexer and variable gain amplifier respectively.The application increases system dynamic range by eliminating direct current component, i.e., reflects system detection distance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of integrated circuits, in particular to a FMCW laser radar system and control method for direct current elimination. BACKGROUND

[0002] The laser radar system is a system for detecting the position, speed and other characteristic quantities of a target by emitting a laser signal. In recent years, it has been widely used in the fields of unmanned driving, industrial measurement, robots, unmanned aerial vehicles and remote sensing. Among them, the frequency modulated continuous wave (FMCW) laser radar has gradually become a research hotspot due to its advantages of measurable speed, eye safety and low laser power.

[0003] FMCW mainly sends and receives continuous laser beams, interferes the return light and the local oscillator, and uses mixing detection technology to measure the frequency difference between the sending and receiving, and then converts the frequency difference to the distance of the target object. Specifically, the laser beam is reflected after hitting the target object, and the reflection affects the frequency of the light - if the target object is coming towards the vehicle, the frequency will increase; if the target object and the vehicle are moving in the same direction, the frequency will decrease; when the reflected light returns to the detector, the difference between the two frequencies can be measured compared with the frequency at the time of emission, so as to calculate the distance information of the object.

[0004] In the field of intelligent vehicle unmanned driving, laser radar has become a recognized essential technical means. Through the vehicle-mounted laser detector, the intelligent vehicle can obtain the distance information of the front road and pedestrians, perceive obstacles, and realize assisted driving and automatic driving. In the laser ranging system, the farther the distance, the weaker the return signal; the closer the distance, the stronger the return signal. When measuring outdoors, especially in bad weather such as rainy, foggy and snowy days, it is easy to be affected by external environmental background light or stray signal light, causing the signal-to-noise ratio to deteriorate and the sensitivity to decrease, thereby limiting the maximum detection distance of the system.

[0005] The detection distance of the laser radar system corresponds to the input dynamic range of the link, and a wide input dynamic range can make the system have a wider detection range, a farther detection distance and a higher detection precision, while its design difficulty is also greater.

[0006] In actual application, the detector itself has direct current and environmental light factors that will cause the detector to have direct current, especially in the FMCW system, the photocurrent used for processing is generated by the mixing of the local oscillator light and the return light after the response of the detector. The mixed light contains direct current, and the above direct current occupies part of the dynamic range after conversion and amplification by the receiving module, thereby reducing the detection distance and precision.

[0007] Therefore, how to eliminate the direct current flow is a problem to be solved urgently. In the system architecture, the direct current flow is mainly eliminated in two ways: one is to use AC coupling at the board level to filter out the direct current flow by forming a filter with capacitors and resistors; the other is to use a chip with a direct current flow elimination function to build a system architecture. The time constant corresponding to the resistance and capacitance of the first method is large, which has a delay in signal transmission and a nonlinear gain. In addition, the existence of the capacitor limits the application in the development trend of linear arrays and area arrays. The second method is to design a system architecture from the perspective of chip selection.

[0008] In order to eliminate the direct current flow, increase the dynamic range, and improve the system detection distance, it is necessary to design a FMCW laser radar system architecture for direct current flow elimination. The echoes received by each element of the linear array or area array detector are processed, which is very valuable for the development of array laser radar systems.

[0009] In the related art, a signal processing system architecture applied in an airborne laser radar is disclosed in Chinese Patent Publication No. CN106501789A, which includes an FPGA, a PMT detector, and a transimpedance amplifier. The PMT detector converts the detected laser echo signal into a current signal. The photocurrent is converted into an analog voltage signal by the transimpedance amplifier. The analog voltage signal output by the transimpedance amplifier is divided into three paths A, B, and C, which are amplified by high-gain, medium-gain, and low-gain amplifiers, respectively, and then converted into digital signals by an ADC, which are the seabed ADC output signals. The FPGA receives the seabed ADC output signals, the sea surface data of the sea and land line scanning system, and the electric local oscillator signal, thereby realizing the control of the gate circuit and the calculation of the seabed distance.

[0010] However, the application object of this scheme is a TOF laser radar, the detector object is a PMT detector (photomultiplier tube), and the core function is the I-V conversion of the transimpedance amplifier, the amplification of the analog signals output by the A / B / C three-gain amplifiers, and the conversion of the digital signals by the ADC.

[0011] Chinese Patent Publication No. CN112782670A discloses a small signal amplification circuit suitable for laser radar analog front end, which includes an input circuit, a pre-amplification circuit, a first and second voltage amplifier, a self-triggering enable control circuit, an adaptive gain control circuit, a selector, and an output circuit. The pre-amplification circuit is connected to the input circuit. The first voltage amplifier is connected to the pre-amplification circuit. The second and first voltage amplifiers are connected. The self-triggering enable control circuit is connected to the second voltage amplifier. The adaptive gain control circuit is connected to the pre-amplification circuit and the first voltage amplifier.

[0012] The adaptive gain control circuit is connected with the self-triggering enable control circuit; the selector is connected with the pre-amplification circuit, the first and second voltage amplifiers; the selector is also connected with the adaptive gain control circuit; and the output circuit is connected with the selector.

[0013] The scheme is applied to a TOF laser radar, focuses on a circuit module architecture, and the core components include an input circuit, a pre-amplification circuit, first and second voltage amplifiers, a self-triggering enable control circuit, an adaptive gain control circuit, a selector and an output circuit, and the core mainly realizes signal amplification; the dynamic range is related to the self-triggering enable control circuit, the adaptive gain control circuit and the selector; the adaptive gain control circuit is composed of two comparators (corresponding to the two front-end amplification modules) and a logic circuit, and the high and low levels of the outputs (S1, S2 and S3) of the adaptive gain control circuit are fed back to control the front-end gain, so as to increase the dynamic range. SUMMARY

[0014] The technical problem to be solved by the application is to provide a FMCW laser radar system architecture for direct current elimination, so as to increase the dynamic range of the system by eliminating the direct current.

[0015] The application solves the above technical problems by the following technical means:

[0016] The application provides a FMCW laser radar system for direct current elimination, which comprises an optical and detector module, a signal amplification conversion module and a data processing module, the optical and detector module comprises a detector array, the signal amplification conversion module comprises an analog amplification array, a differential-to-single-end array, a multiplexer and a variable gain amplifier, and the data processing module comprises an analog-to-digital converter and an FPGA chip, and the analog amplification array adopts a differential structure.

[0017] The output of the detector array is connected with the analog amplification array and the differential-to-single-end array, the output of the differential-to-single-end array is connected with the multiplexer and the variable gain amplifier, and the output of the variable gain amplifier is connected with the analog-to-digital converter.

[0018] The output of the variable gain amplifier is connected with the analog-to-digital converter, the output of the analog-to-digital converter is connected with the FPGA chip, and the address gating output end and the gain control end of the FPGA chip are connected with the multiplexer and the variable gain amplifier respectively.

[0019] The echo light current signal output by the detector in the application is weak and not easy to process, the echo light current signal is converted and amplified by the analog amplification array, and the subsequent processing is facilitated; the analog amplification array is in a differential structure to improve the noise suppression capability, and a differential-to-single-end array is arranged to realize the synchronous control of the output of the multiplexer on the channel of the corresponding detector element, considering the difference in current signal intensity of the target when the target is close and far away, and the influence of the direct current, the gain of the receiving link is compensated by the variable gain amplifier, the amplitude of the output signal is controlled by changing the gain level, and the differential structure suppresses the common mode to eliminate the direct current of the corresponding detector element. The FMCW laser radar system for eliminating direct current proposed in the application replaces the traditional capacitor direct current elimination scheme, can avoid large signal transmission delay and signal frequency component distortion, increases the dynamic range of the system by eliminating the direct current component, that is, reflects the detection distance of the system, and the removal of the direct current increases the available space of the useful signal, indirectly improves the signal-to-noise ratio, reduces the demand for the signal-to-noise ratio of the rear end, and conforms to the development trend of laser radar line array.

[0020] Further, the analog amplification array includes a transimpedance amplifier array and a voltage amplifier array, the output of the detector array is connected with the transimpedance amplifier array, and the output of the transimpedance amplifier array is connected with the voltage amplifier array.

[0021] Further, the optical and detector module includes an optical assembly and a detector array, the optical assembly includes a laser, a fiber coupler, a fiber circulator and a power splitter;

[0022] The fiber coupler is arranged on the continuous swept frequency laser path emitted by the laser, the continuous swept frequency laser emitted by the laser is separated into two light components through the fiber coupler, the fiber circulator is arranged on the transmission path of one light component, and the power splitter is arranged at the intersection of the transmission path of the other light component and the output light path of the fiber circulator.

[0023] The output light path of the fiber circulator is arranged with a target to be measured, and the output light path of the power splitter is arranged with the detector array.

[0024] Further, the number of transimpedance amplifiers in the transimpedance amplifier array and the number of voltage amplifiers in the voltage amplifier array are the same as the number of detectors in the detector array; the total channel number of the multiplexer is the same as the number of detectors in the detector array.

[0025] Further, the analog-to-digital converter adopts a time division multiplexing structure.

[0026] In addition, the application further provides a control method of the FMCW laser radar system for eliminating direct current as described above, the method comprising:

[0027] The signal amplification conversion module converts the echo light current signal output by the optical and detector module into a voltage signal and amplifies it to obtain a voltage amplification signal;

[0028] The differential to single-ended array realizes the synchronous control of the output of the detector channel in the optical and detector module by the multiplexer, and outputs the voltage amplification signal to the variable gain amplifier, wherein the signal actually processed by the variable gain amplifier is :

[0029]

[0030]

[0031]

[0032] wherein: , are two input terminals of the variable gain amplifier, respectively; is the bias voltage of the input terminal; is the input terminal bias voltage offset caused by the direct current; is the corresponding signal voltage after the alternating current is amplified;

[0033] The data processing module is used to calculate the target distance by solving the photoelectric signal output by the variable gain amplifier;

[0034] and the data processing module is used to control the gating of the multiplexer and the gain position of the variable gain amplifier.

[0035] Further, the signal amplification conversion module converts the echo light current signal output by the optical and detector module into a voltage signal and amplifies it to obtain a voltage amplification signal, which includes:

[0036] The transimpedance amplifier array converts the echo light current signal into a voltage signal;

[0037] The voltage amplifier array amplifies the voltage signal to obtain the voltage amplification signal.

[0038] Further, the method further includes:

[0039] The optical fiber coupler separates the continuous swept frequency laser emitted by the laser into two first light components;

[0040] One of the light components is emitted after the optical fiber circulator to irradiate the target and generate echo light;

[0041] Another said first light component as the local oscillator light and echo light through the power splitter respectively produce two parts of the second light component and mixed frequency output to the detector array;

[0042] Two groups of photocurrents are generated by the detector array in response And The direct current of the two groups of photocurrents is equal in size, and the alternating current is 180° out of phase, n =1,2… N -1, N , N The total number of detectors in the detector array.

[0043] Further, the data processing module is used to calculate the target distance by solving the photoelectric signal output by the variable gain amplifier, including:

[0044] The digital signal is converted from the photoelectric signal output by the variable gain amplifier by using the digital-to-analog converter;

[0045] The digital signal is solved by using the FPGA chip to calculate the target distance.

[0046] Further, the data processing module is used to control the gating of the multiplexer and the gain position of the variable gain amplifier, including:

[0047] The FPGA chip receives the laser emission synchronization signal generated by the laser, and controls the multiplexer to select the detector address once every time the synchronization signal is received;

[0048] The gain position of the variable gain amplifier is adjusted by the FPGA chip for different output signal amplitudes of the variable gain amplifier.

[0049] The advantages of the present application are:

[0050] (1) The echo light current signal output by the detector is weak and not easy to process, and the echo light current signal is converted and amplified by setting an analog amplification array, so as to facilitate the post-processing; the analog amplification array is in a differential structure to improve the noise suppression capability, and a differential-to-single-end array is added to realize the synchronous control of the output of the pass of the corresponding detector element by the multiplexer, considering the current signal intensity gap of the target when the distance is close and far, and the influence of the direct current, the gain of the receiving link is compensated by the variable gain amplifier, the amplitude of the output signal is controlled by changing the gain level, and the differential structure eliminates the direct current of the corresponding pixel of the detector. The FMCW laser radar system for eliminating direct current proposed in the application replaces the traditional capacitor direct current elimination scheme, can avoid large signal transmission delay and signal frequency component distortion, increases the dynamic range of the system by eliminating the direct current component, that is, reflects the detection distance of the system, and the removal of the direct current increases the available space of the useful signal, indirectly improves the signal-to-noise ratio, reduces the demand for signal-to-noise ratio of the rear end, and conforms to the development trend of laser radar line array.

[0051] (2) The photoelectric current is converted into a voltage signal by a transimpedance amplifier (TIA), and each unit of the line array or surface array detector needs an independent transimpedance amplifier, so as to ensure excellent performance of the receiving link, and the gain of the TIA is generally not large, therefore, a voltage amplifier array is needed to compensate the gain and further amplify the signal.

[0052] (3) The analog-to-digital converter adopts a time division multiplexing structure, so that the analog-to-digital converter is always in a working state, and the data of the array corresponding elements are read out in turn for processing, thereby reducing the hardware cost.

[0053] (4) The FPGA chip analyzes and solves the collected digital signals by hardware, realizes laser ranging, and can improve the signal-to-noise ratio and other indicators of the system through an algorithm.

[0054] Additional aspects and advantages of the application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0055] Figure 1 is a structure schematic diagram of the FMCW laser radar system for eliminating direct current in an embodiment of the application;

[0056] Figure 2 is a structure schematic diagram of an optical and detector module in an embodiment of the application;

[0057] Figure 3 is a structure schematic diagram of a signal amplification and conversion module in an embodiment of the application;

[0058] Figure 4 is a schematic diagram of a direct current elimination function waveform in an embodiment of the present application;

[0059] Figure 5 is a structural schematic diagram of a data processing module in an embodiment of the present application;

[0060] Figure 6 is a gating timing diagram of a multiplexer controlled by an FPGA chip in an embodiment of the present application;

[0061] Figure 7 is a flowchart of a control method of an FMCW laser radar system for direct current elimination in an embodiment of the present application. DETAILED DESCRIPTION

[0062] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described below in a clear and complete manner in conjunction with the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0063] As shown in Figure 1 , the first embodiment of the present application proposes an FMCW laser radar system for direct current elimination, which comprises an optical and detector module 10, a signal amplification and conversion module 20, and a data processing module 30. The optical and detector module 10 comprises a detector array 11. The signal amplification and conversion module 20 comprises an analog amplification array 21, a differential-to-single-ended array 22, a multiplexer 23, and a variable gain amplifier 24. The data processing module 30 comprises an analog-to-digital converter 31 and an FPGA chip 32. The analog amplification array 21 adopts a differential structure.

[0064] The output of the detector array 11 is connected to the differential-to-single-ended array 22 through the analog amplification array 21. The output of the differential-to-single-ended array 22 is connected to the variable gain amplifier 24 through the multiplexer 23.

[0065] The output of the variable gain amplifier 24 is connected to the analog-to-digital converter 31. The output of the analog-to-digital converter 31 is connected to the FPGA chip 32. The address gating output end and the gain control end of the FPGA chip 32 are connected to the multiplexer 23 and the variable gain amplifier 24, respectively.

[0066] The echo light current signal output by the detector array 11 in the optical and detector module 10 in the embodiment is weak and not easy to process, and the echo light current signal is converted and amplified by the analog amplification array 21, so as to facilitate the subsequent processing; the analog amplification array 21 is in a differential structure to improve the noise suppression capability, and a differential-to-single-ended array 22 is arranged to realize the output of the path of the corresponding detector element under the synchronous control of the multiplexer 23; considering the current signal intensity gap between the target at a short distance and the target at a long distance and the influence of the direct current, the reception link gain is compensated by the variable gain amplifier 24, the amplitude of the output signal is controlled by changing the gain level, and the common-mode suppression of the differential structure realizes the elimination of the direct current of the corresponding image element of the detector.

[0067] The FMCW laser radar system for direct current elimination provided by the embodiment of the application replaces the traditional capacitive direct current elimination scheme, can avoid large signal transmission delay and signal frequency component distortion, increases the dynamic range of the system by eliminating the direct current component, that is, reflects the detection distance of the system, and the elimination of the direct current increases the available space of the useful signal, indirectly improves the signal-to-noise ratio, reduces the demand for the signal-to-noise ratio of the rear end, and conforms to the development trend of laser radar linearization.

[0068] In an embodiment, as shown in Figure 2 The optical and detector module 10 includes an optical assembly and a detector array 11, the optical assembly includes a laser 12, a fiber coupler 13, a fiber circulator 14 and a power splitter 15, and the detector array 11 is a single-element, linear array or planar array balanced detector.

[0069] The fiber coupler 13 is arranged on the continuous swept laser path emitted by the laser 12, the continuous swept laser emitted by the laser 12 is separated into two light components by the fiber coupler 13, the transmission path of one light component is provided with the fiber circulator 14, and the power splitter 15 is arranged at the intersection of the transmission path of the other light component and the output light path of the fiber circulator 14.

[0070] The output light path of the fiber circulator 14 is provided with a target to be measured, and the output light path of the power splitter 15 is provided with the detector array 11.

[0071] It should be noted that in the FMCW laser radar system, the detector module includes two identical detector arrays 11 to form a balanced detector pair, and generally a common N or common P electrode PIN is selected.

[0072] Specifically, the laser 12 emits continuous swept frequency laser, and the power is separated through the fiber coupler 13. One part of the light component L1 is used to irradiate the target, and the other part of the light component is mixed with the local light L0 and the echo light (reflected by the irradiated target) to enhance the echo light signal strength. Generally, the local light L0 occupies a small part of the total laser power, and most of the laser power is used to irradiate the target to collect the echo L 1r This also has a great influence on the transmission attenuation of laser in the atmosphere, and many factors are involved.

[0073] Specifically, the laser emission, the mixing of the echo (L1) and the local light (L0) in the optical and detector module 10, and the response of the balanced detector generated by the pair of detector arrays N1 and N2 to generate photocurrent (I1 and I2) And ), wherein And contains alternating current component and direct current component, and the direct current is equal, and the alternating current is equal in size and opposite in direction.

[0074] In an embodiment, as shown in Figure 3 , the analog amplifier array 21 includes a transimpedance amplifier array and a voltage amplifier array, the output of the detector array 11 is connected with the transimpedance amplifier array, and the output of the transimpedance amplifier array is connected with the voltage amplifier array.

[0075] In an embodiment, the number of transimpedance amplifiers in the transimpedance amplifier array, the number of voltage amplifiers in the voltage amplifier array, and the number of detectors in the detector array 11 are the same; the total number of channels of the multiplexer 23 is the same as the number of detectors in the detector array 11.

[0076] It should be noted that the echo photocurrent signal output by the detector is weak and not easy to process, and the transimpedance amplifier TIA is used to convert the photocurrent into a voltage signal. Each unit of the line array or area array detector needs an independent transimpedance amplifier, so an equal number of transimpedance amplifier arrays need to be set according to the number of detector units of the array detector. In order to ensure excellent performance of the receiving link, the gain of the TIA is generally not too large, and a voltage amplifier array is needed to compensate for the gain to further amplify the signal.

[0077] Specifically, since the transimpedance amplifier and the voltage amplifier in this embodiment are differential structures to improve the noise suppression capability, in order to match the multiplexer 23 in the system, a differential to single-ended array 22 is added to realize the synchronous control of the output of the multiplexer 23 to the channel of the corresponding detector element, that is, the switch S1 (S2…SN) corresponding to the detector array 11N1 and the switch S1 (S2…SN) corresponding to the detector array 11N2 are synchronously controlled to be closed or opened at the same time.

[0078] It should be noted that the multiplexer 23 here can be single or multiple, but the total channels N controlled thereby are equal to the number of the detector array 11.

[0079] Specifically, the working principle of the signal conversion and amplification module is as follows: the transimpedance amplifiers N1 and N2 are connected with the detectors N1 and N2 respectively, to complete I-V conversion and amplification of the photoelectric current and The voltage amplifiers N1 and N2 further amplify the signal, and the differential-to-single-ended N1 and N2 perform single-ended output processing on the differential signal of the previous stage to obtain (V+ )+ and (V+ )- , wherein V is an output common-mode voltage, is obtained after amplification of the direct current photoelectric current, is obtained after amplification of the alternating current photoelectric current. For a balanced detector, the outputs of the differential-to-single-ended N1 and the differential-to-single-ended N2 are directly connected to the inputs of the variable gain amplifier 24, and the direct current is eliminated and the signal is further amplified by means of the amplifier characteristics, and the gain is controlled by the FPGA chip 32.

[0080] When the balanced detector is an array of N pairs, since the variable gain amplifier 24 (VGA) is 1, a multiplexer 23 N:1 is added between the differential-to-single-ended and the variable gain amplifier 24, for realizing sequential gating. Assuming that there are 4 pairs of balanced detectors, the multiplexer 23 is a 4:1 switch, i.e. a 4-to-1 switch function, S1, S2, S3, and S4 are connected to the differential-to-single-ended 11, 12, 21, 22, 31, 32, 41, and 42 respectively, and only one switch is closed to select the path at the same time. Among them, 11, 21, 31, and 41 correspond to the differential-to-single-ended array 22N1, and 12, 22, 32, and 42 correspond to the differential-to-single-ended array 22N2.

[0081] In an embodiment, the two input terminals VIP and VIN of the variable gain amplifier 24 correspond to the output terminals of the differential-to-single-ended N1 and N2 respectively:

[0082]

[0083]

[0084] , wherein is the bias voltage of the input terminal, is the input terminal bias voltage offset caused by the direct current, is the signal voltage corresponding to the alternating current after amplification.

[0085] Therefore, the signal actually processed by the variable gain amplifier 24 is , and the direct current elimination function is realized.

[0086] .

[0087] The overall goal of the system is to realize the readout, collection and analysis of the mixed continuous light signal, and eliminate the direct current in the photocurrent, as shown in Figure 4 , the mixed light signal is converted into photocurrent by the detector, and the photocurrent is converted into a voltage signal with appropriate amplitude by signal amplification conversion, and finally collected by the analog-to-digital converter 31 ADC and given to the FPGA chip 32 for signal processing.

[0088] In an embodiment, as shown in Figure 5 , the data processing module 30 includes an analog-to-digital converter 31 ADC and a field programmable gate array (FPGA), which mainly realizes the quantization of the echo signal, the gating control of the multiplexer 23, the gain selection of the variable gain amplifier 24, the collection and analysis of the echo data, and the like.

[0089] The photoelectric signal output by the variable gain amplifier 24 becomes a digital signal after being quantized by the ADC, which is received by the FPGA chip 32. The FPGA chip 32 performs hardware analysis and calculation on the collected data to realize laser ranging, and can also improve the signal-to-noise ratio and other indicators of the system through algorithm angle.

[0090] Further, the FPGA chip 32 is also used to receive a laser emission synchronization signal generated by the laser 12. Each time a synchronization signal is received, it indicates that a cycle of detection signal is completed. The FPGA controls the multiplexer 23 to be selected once, and each time a synchronization signal is received, it indicates that the selection address completes a detection of all elements of the array detector. The FPGA realizes the above-mentioned successive selection configuration of the multiplexer 23, as shown in Figure 6 .

[0091] In an embodiment, the analog-to-digital converter 31 adopts a time division multiplexing structure.

[0092] It should be noted that if all data is uploaded for analysis, the ADC requires a higher requirement, and the huge amount of data consumes a large amount of backend resources and finally cannot process the data. Therefore, the time division multiplexing structure is adopted, so that the ADC is always in working state, and the array corresponding elements are read out in turn to process the data, thereby reducing the hardware cost.

[0093] The embodiment generates the same direct current and the same alternating current by the optical and detector module 10, converts and amplifies by the transimpedance amplifier and the voltage amplifier, and finally eliminates the direct current in the signal by the differential to single-ended and variable gain amplifier 24 to ensure that the final output is the effective signal component, so as to improve the dynamic range and signal-to-noise ratio. The system architecture provides a solution for eliminating the direct current of the FMCW laser radar, and can eliminate the direct current, convert and amplify, collect, store and analyze the laser echo signal of each unit of the unit, linear array or surface array balanced detector, improve the signal-to-noise ratio, dynamic range and detection distance range of the system, comply with the development trend of the linear array of the laser radar, and provide a reference for the design of the subsequent laser radar system processing architecture.

[0094] In addition, as Figure 7 shown, the second embodiment of the present application provides a control method for the FMCW laser radar system for eliminating the direct current, and the method comprises the following steps:

[0095] S10, converting and amplifying the echo photoelectric current signal output by the optical and detector module into a voltage signal by the signal amplification and conversion module, to obtain a voltage amplified signal;

[0096] S20, synchronously controlling the output of the detector path in the optical and detector module by the multi-channel selector by using the differential to single-ended array, and outputting the voltage amplified signal to the variable gain amplifier, wherein the signal actually processed by the variable gain amplifier is :

[0097]

[0098]

[0099]

[0100] In the formula: , are two input terminals of the variable gain amplifier, respectively; is the bias voltage of the input terminal; is the input terminal bias voltage offset caused by the direct current; is the signal voltage corresponding to the alternating current after amplification;

[0101] S30, calculating the target distance by calculating the photoelectric signal output by the variable gain amplifier by using the data processing module.

[0102] S40, controlling the gating of the multi-channel selector and the gain gear of the variable gain amplifier by using the data processing module.

[0103] The embodiment converts and amplifies the echo photoelectric signal output by the optical and detector module by using the analog amplification array, and finally eliminates the direct current amount in the signal by means of the amplifier itself characteristics of the differential to single-ended and variable gain amplifier, so as to ensure that the final output is the effective signal component, and to realize the improvement of dynamic range and signal-to-noise ratio. Meanwhile, considering the current signal intensity gap of the target at close and far distances, and the influence of the direct current amount, the gain of the receiving link is compensated by the variable gain amplifier, and the amplitude of the output signal is controlled by changing the gain gear, that is, high gear gain is configured for far distance, and low gear gain is configured for close distance.

[0104] In an embodiment, the step S10 of converting and amplifying the echo photocurrent signal output by the optical and detector module into a voltage signal by using the signal amplification conversion module includes the following steps:

[0105] Converting the echo photocurrent signal into a voltage signal by using the transimpedance amplifier array;

[0106] Amplifying the voltage signal by using the voltage amplifier array to obtain the voltage amplified signal.

[0107] In an embodiment, the method further includes the following steps:

[0108] Separating the continuous swept frequency laser emitted by the laser into two first light components by using the fiber coupler;

[0109] One of the first light components is emitted after the fiber circulator to irradiate the target and generate echo light;

[0110] The other first light component is used as the local oscillator light and echo light, and passes through the power splitter to generate two second light components and mixed frequency output to the detector array;

[0111] Generating two groups of photocurrents by using the detector array And The direct current amounts of the two groups of photocurrents are equal, and the alternating current amounts are 180° out of phase, n =1,2… N -1, N , N The total number of detectors in the detector array.

[0112] Further, the laser emits continuous swept frequency laser, and power separation is realized through the optical fiber coupler. A part of light component L1 is used to irradiate the target, and another part of light component is used as the local light L0 and the echo light (reflected by the irradiated target) to mix and enhance the echo light signal strength. Generally, the local light L0 occupies a small component of the total laser power, and most of the laser power is used as the irradiated target to collect the echo L1r. This is also related to the fact that the laser transmission in the atmosphere is greatly attenuated, and there are many influencing factors. The formula is as follows:

[0113]

[0114] In the formula: is the optical power of the light component is the optical power of the light component is the transmission efficiency of the laser in the atmosphere, is the reflectivity of the target, is the area of the target, is the distance of the target.

[0115] Further, the local light and the echo light pass through the power beam splitter to generate two parts of light components and mix, and the N pairs of balanced detectors composed of the detector arrays N1 and N2 respond to generate two groups of photocurrents In1 and In2 (n=1, 2…N-1, N). The photocurrents have the characteristics that the direct current amount is equal, and the alternating current amount has a phase difference of 180°. The formula is as follows:

[0116]

[0117]

[0118] In the formula, is the direct current amount of the current, is the alternating current amount of the current.

[0119] In an embodiment, the step S30 of calculating the target distance by using the data processing module to solve the photoelectric signal output by the variable gain amplifier includes the following steps:

[0120] Converting the photoelectric signal output by the variable gain amplifier into a digital signal by using the digital-to-analog converter;

[0121] Solving the digital signal by using the FPGA chip to calculate the target distance.

[0122] In an embodiment, the step S40 of controlling the gating of the multiplexer and the gain position of the variable gain amplifier by using the data processing module includes the following steps:

[0123] The FPGA chip is used for receiving a laser emission synchronization signal generated by the laser, and the multiplexer is controlled to select a detector address once every time the synchronization signal is received;

[0124] The FPGA chip is used for adjusting the gain level of the variable gain amplifier according to different output signal amplitudes of the variable gain amplifier.

[0125] In the embodiment of the application, it is assumed that the line array balance detector is a 4-line array (two identical 4-line PINs), and according to the above analysis, the photoelectric current generated by the detector arrays N1 and N2 is and ( n =1,2,3,4), the photoelectric current is converted into a voltage through the transimpedance amplifier in the corresponding array, the voltage is amplified by the voltage amplifier, and the differential signal is converted into a single-ended signal for output. The multiplexer is a 4-to-1 multiplexer, and two identical multiplexers are connected to the differential-to-single-ended array, and the switches S1, S2, S3 and S4 in the multiplexer are connected to the four single-ended outputs in the differential-to-single-ended array, respectively. The closing of S1, S2, S3 and S4 in turn represents the selection of the signal output to the variable gain amplifier, and the selection timing can be controlled by the FPGA chip, for example, Figure 6 , where the high level represents the closing of the switch, and T represents a selected period, which is generally consistent with the laser repetition frequency.

[0126] The two multiplexers output a signal as the input signal of the variable gain amplifier, respectively VIP and VIN, and the variable gain amplifier suppresses the DC voltage offset caused by the DC current as a common mode to achieve the function of DC cancellation and further amplify the useful signal to the analog-to-digital converter. The gain of the variable gain amplifier is adjusted by the FPGA chip, and after the output of the variable gain amplifier is sampled, quantized and read out by the analog-to-digital converter, the FPGA analyzes the output of the analog-to-digital converter and feeds back to the variable gain amplifier whether the gain needs to be changed.

[0127] Specifically, when the gain of the variable gain amplifier is a non-continuous adjustable 3-level (high, medium and low) and the full-scale range of the analog-to-digital converter is 1V, the FPGA sends a command to configure the variable gain amplifier to adjust the gain to the medium gain level if the output peak value is less than 500mV when it starts at the low gain level, and the FPGA sends a command to configure the variable gain amplifier to adjust the gain to the high gain level if the output peak value is still less than 500mV. If the output peak value is greater than 1V when it starts at the high gain level, the FPGA sends a command to configure the variable gain amplifier to adjust the gain to the medium gain level, and the FPGA sends a command to configure the variable gain amplifier to adjust the gain to the high gain level if the output peak value is still less than 1V.

[0128] It should be noted that the input dynamic range of the front-end processing circuit is an important performance indicator, especially for the FMCW laser radar system, the existence of the local oscillator light introduces a large amount of direct current, and the ambient light such as sunlight will also introduce the direct current, the existence of the direct current occupies the swing space of the useful signal, causing the dynamic range to decrease. The embodiment of the application proposes a system architecture for eliminating direct current based on the FMCW laser radar, instead of the traditional capacitor direct current elimination scheme to avoid large signal transmission delay and signal frequency component distortion, by eliminating the direct current component to increase the system dynamic range, that is, to reflect the system detection distance, at the same time, the removal of the direct current increases the available space of the useful signal, indirectly improves the signal-to-noise ratio, reduces the demand for the signal-to-noise ratio of the back-end, and conforms to the development trend of laser radar linearization.

[0129] In the description of the present specification, the description referring to the terms “one embodiment”, “some embodiments”, “an example”, “a specific example”, or “some examples” and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0130] In addition, the terms “first”, “second” are only used for description purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Therefore, the features defined with “first”, “second” can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of “a plurality of” is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0131] Although the embodiments of the present application have been shown and described above, it can be understood that the above-described embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. An FMCW lidar system for direct current cancellation, characterized in that, The system includes: an optical and detector module, a signal amplification and conversion module, and a data processing module. The optical and detector module includes a detector array. The signal amplification and conversion module includes an analog amplification array, a differential-to-single-ended array, a multiplexer, and a variable gain amplifier. The data processing module includes an analog-to-digital converter and an FPGA chip. The analog amplification array adopts a differential structure. The output of the detector array is connected to the differential-to-single-ended array via the analog amplifier array, and the output of the differential-to-single-ended array is connected to the variable gain amplifier via the multiplexer. The output of the variable gain amplifier is connected to the analog-to-digital converter, the output of the analog-to-digital converter is connected to the FPGA chip, and the address strobe output and gain control terminal of the FPGA chip are respectively connected to the multiplexer and the variable gain amplifier. The signal amplification and conversion module converts the echo photocurrent signal output by the optical and detector module into a voltage signal and amplifies it to obtain a voltage amplified signal. The differential-to-single-ended array is used to achieve synchronous control of the output of the detector path in the optical and detector module by the multiplexer. The output voltage amplified signal is sent to the variable gain amplifier, wherein the variable gain amplifier actually processes the signal as follows: : In the formula: , These are the two input terminals of the variable gain amplifier; It is the bias voltage at the input terminal; It is the input bias offset caused by the DC power supply. It is the signal voltage corresponding to the amplified AC quantity; The data processing module is used to process the photoelectric signal output by the variable gain amplifier to calculate the target distance; The data processing module is used to control the selection of the multiplexer and the gain level of the variable gain amplifier. A fiber optic coupler is used to separate the continuously sweeping laser emitted by the laser into two first optical components. The first optical component described in one path illuminates the target after being emitted through the fiber optic circulator and generates an echo light; The other first optical component, as the local oscillator and echo light, is passed through a power beam splitter to generate two second optical components, which are then mixed and output to the detector array. Two sets of photocurrents are generated using the detector array response. and The DC currents of the two sets of photocurrents are equal in magnitude, while the AC currents are 180° out of phase. n =1,2… N -1, N , N This represents the total number of detectors in the detector array.

2. The FMCW lidar system for direct current cancellation as described in claim 1, characterized in that, The analog amplifier array includes a transimpedance amplifier array and a voltage amplifier array. The output of the detector array is connected to the transimpedance amplifier array, and the output of the transimpedance amplifier array is connected to the voltage amplifier array.

3. The FMCW lidar system for direct current cancellation as described in claim 1, characterized in that, The optical and detector module includes optical components and a detector array. The optical components include a laser, a fiber coupler, a fiber circulator, and a power beam splitter. The detector array is a unit, linear, or area array balanced detector. The fiber coupler is arranged on the path of the continuously swept laser emitted by the laser. The continuously swept laser emitted by the laser is separated into two optical components by the fiber coupler. The fiber circulator is arranged on the transmission path of one optical component, and the power beam splitter is arranged at the intersection of the transmission path of the other optical component and the output optical path of the fiber circulator. The target to be measured is arranged on the output optical path of the fiber optic circulator, and the detector array is arranged on the output optical path of the power beam splitter.

4. The FMCW lidar system for direct current cancellation as described in claim 2, characterized in that, The number of transimpedance amplifiers in the transimpedance amplifier array and the number of voltage amplifiers in the voltage amplifier array are the same as the number of detectors in the detector array; the total number of channels in the multiplexer is the same as the number of detectors in the detector array.

5. The FMCW lidar system for direct current cancellation as described in claim 1, characterized in that, The analog-to-digital converter adopts a time-division multiplexing structure.

6. A control method for an FMCW lidar system with direct current cancellation as described in any one of claims 1-5, characterized in that, The step of using the signal amplification and conversion module to convert the echo photocurrent signal output by the optical and detector module into a voltage signal and amplifying it to obtain a voltage amplified signal includes: The echo photocurrent signal is converted into a voltage signal using a transimpedance amplifier array; The voltage signal is amplified using a voltage amplifier array to obtain the amplified voltage signal.

7. The control method for an FMCW lidar system with direct current cancellation as described in claim 6, characterized in that, The step of using the data processing module to process the photoelectric signal output by the variable gain amplifier and calculate the target distance includes: The photoelectric signal output from the variable gain amplifier is converted into a digital signal using the analog-to-digital converter. The FPGA chip is used to decode the digital signal and calculate the target distance.

8. The control method for an FMCW lidar system with direct current cancellation as described in claim 6, characterized in that, The method of controlling the selection of the multiplexer and the gain level of the variable gain amplifier using the data processing module includes: The FPGA chip is used to receive the laser emission synchronization signal generated by the laser, and the multiplexer is controlled to perform detector address selection once each time a synchronization signal is received; The gain level of the variable gain amplifier is adjusted using the FPGA chip for different output signal amplitudes.

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