A balanced detection device based on digital post-processing

Abstract

The present invention discloses a balanced detection device based on digital post-processing, comprising: a first photoelectric conversion channel, sequentially connected to a first photodiode, a first DC-blocking capacitor, a first transimpedance amplifier, and a first analog-to-digital converter; a second photoelectric conversion channel, sequentially connected to a second photodiode, a second DC-blocking capacitor, a second transimpedance amplifier, and a second analog-to-digital converter; a digital logic processing module receives the digital waveform signals of the two analog-to-digital converters; the present invention can more effectively suppress common-mode noise.

Description

Technical Field

[0001] The present invention relates to the technical field of lidar, and particularly to a balanced detection device based on digital post-processing. Background Art

[0002] In coherent Doppler wind lidar, a high signal-to-noise ratio optoelectronic conversion technology is the balanced detection technology. In traditional balanced detection technology, two photodiodes with connected cathodes and anodes are used to suppress the common-mode signal and double the differential-mode signal. Subsequently, a transimpedance amplifier is used to perform transimpedance amplification of the photocurrent, and a voltage signal with a larger amplitude is output. This voltage signal is then filtered and analog-to-digital converted, and the obtained digital waveform is used for the inversion calculation of the Doppler wind speed.

[0003] However, in actual situations, there are deviations in the intensities of the optical signals input to the two photodiodes, and there are differences in parameters such as the optoelectronic conversion efficiency, parasitic capacitance, and temperature coefficient of the two photodiodes. It is difficult for traditional balanced detection technology to achieve sufficient suppression of the common-mode signal and sufficient amplification of the differential-mode signal, which will result in the signal-to-noise ratio of the balanced detection technology being difficult to reach the optimum. Summary of the Invention

[0004] Object of the Invention: The object of the present invention is to provide a balanced detection device based on digital post-processing, which overcomes the defects of traditional balanced detection technology and achieves the effect of improving the signal-to-noise ratio of the balanced detection technology.

[0005] Technical Solution: A balanced detection device based on digital post-processing according to the present invention includes: a first optoelectronic conversion channel, which is sequentially connected to a first photodiode, a first DC-blocking capacitor, a first transimpedance amplifier, and a first analog-to-digital converter; a second optoelectronic conversion channel, which is sequentially connected to a second photodiode, a second DC-blocking capacitor, a second transimpedance amplifier, and a second analog-to-digital converter; a digital logic processing module receives the digital waveform signals of the two analog-to-digital converters. Further, the digital logic processing module performs the following processing steps: perform mean subtraction processing on the digital waveforms of the two channels; perform amplitude adjustment according to a preset frequency-dependent amplitude difference coefficient Δg(f); perform time-delay compensation according to a preset frequency-dependent time-delay difference Δt(f); perform a differential operation to generate a differential-mode signal Y(n).

[0006] Further, the first photodiode and the second photodiode respectively have independent: bias voltage sources VBIAS1 and VBIAS2; resistors R1 and R2; transimpedance amplifier circuits. Further, the amplitude adjustment includes: when Δg(f) < 0, multiply the signal of the first channel by 1 / (Δg(f) + 1); when Δg(f) > 0, multiply the signal of the second channel by (Δg(f) + 1).

[0007] Further, the delay compensation is achieved through the following formula: Y(n)=Y A (n)-Y B (n + [Δt(f) / T]); where T is the sampling interval, and [] represents the rounding operation.

[0008] Further, the digital logic processing module further includes a feedback processing unit, which is used to extract the signal frequency f by calculating the power spectrum of the differential mode signal Y(n) and performing segmented coherent accumulation; and dynamically adjust the Δg(f) and Δt(f) parameters according to the extracted f value.

[0009] A balanced detection method based on digital post-processing according to the present invention includes the following steps: dual-channel independent photoelectric conversion and analog-to-digital conversion; digital waveform preprocessing includes: calculating and subtracting the waveform mean of each channel; performing amplitude matching adjustment based on frequency-related parameters; performing delay compensation; generating a differential signal; and feedback-adjusting dynamic parameters.

[0010] Further, the amplitude matching adjustment includes: establishing a lookup table for the Δg(f) parameter; calling the corresponding Δg(f) value in real time according to the detected signal frequency; and performing an amplitude correction operation based on multiplication.

[0011] Further, the amplitude matching adjustment further includes: establishing a lookup table for the Δt(f) parameter; calling the corresponding Δt(f) value in real time according to the detected signal frequency; and performing an amplitude correction operation based on multiplication.

[0012] Beneficial effects: Compared with the prior art, the present invention has the following remarkable advantages: The present invention enables the circuit to simultaneously eliminate Δt(f) and Δg(f) for two optical signals, thereby more effectively suppressing the common mode noise and extracting the differential mode signal. It can achieve a higher signal-to-noise ratio than the traditional balanced detection technology. Description of the Drawings

[0013] Figure 1 is a schematic diagram of the device of the present invention;

[0014] Figure 2 is the relationship between Δg(f), Δt(f) and the signal frequency of the present invention;

[0015] Figure 3 is the typical waveforms of signal A and signal B of the present invention. Detailed Embodiments

[0016] The technical solutions of the present invention will be further described below with reference to the drawings.

[0017] As Figure 1As shown in the figure, an embodiment of the present invention provides a balanced detection device based on digital post-processing, including: a first photoelectric conversion channel, sequentially connected to a first photodiode, a first DC-blocking capacitor, a first transimpedance amplifier 1, and a first analog-to-digital converter; a second photoelectric conversion channel, sequentially connected to a second photodiode, a second DC-blocking capacitor, a second transimpedance amplifier, and a second analog-to-digital converter; a digital logic processing module receives the digital waveform signals of the two analog-to-digital converters. The digital logic processing module performs the following processing steps: performing mean subtraction processing on the digital waveforms of the two channels; performing amplitude adjustment according to a preset frequency-dependent amplitude difference coefficient Δg(f); performing time-delay compensation according to a preset frequency-dependent time-delay difference Δt(f); performing a differential operation to generate a differential-mode signal Y(n).

[0018] As Figure 1 shown, in each channel, a photodiode with a response wavelength of 1064 nm is used as the optical signal receiving element, the resistance values of R1 and R2 are both 10 kohm, and VBIAS1 and VBIAS2 are both 10 V. The capacitance values of capacitor 1 and capacitor 2 are both 10 nF, and the transimpedance amplifier is built by the OPA4847IDBVR chip to achieve a transimpedance gain of 30 kohm. The analog-to-digital converter 1 and the analog-to-digital converter 2 are implemented by an ADC07D1520CIYB / NOPB chip, and the digital logic device is implemented by an FPGA chip of model XCKU040-2FFVA1156I. The result of a 1 dB higher signal-to-noise ratio than the traditional balanced detection technology is achieved.

[0019] During the circuit operation of this balanced detector, the digital waveform signals output by the analog-to-digital converter will be affected by factors such as the time-delay and energy difference between the optical signals input to the two photodiodes, the response characteristics of the photodiodes, the parasitic capacitance of the photodiodes, and the response characteristics of the transimpedance amplifier. As a result, in the digital waveform signals corresponding to the two photodiode channels, there are differences in amplitude and time-delay of the digital signals corresponding to the optical signals.

[0020] Assume that in the digital waveform signals corresponding to the two photodiode channels, the digital signals corresponding to the optical signals are signal A and signal B respectively, and for the same optical signal, at t A and t B of the two digital signals respectively, the time-delay between the two waveforms is:

[0021] Δt(f)=t A -t B (1);

[0022] The amplitudes corresponding to the same optical signal in the two digital signals are g A and g B respectively, then the amplitude difference between the two waveforms is:

[0023] Δg(f) = (g A / g B ) - 1 (2);

[0024] The relationship between Δt(f) and the signal frequency, as well as the relationship between Δg(f) and the signal frequency, can be calibrated through testing. Typical results are as Figure 2 shown. When a sine optical signal is input, the typical waveforms of signal A and signal B are as Figure 3 shown.

[0025] Without correcting Δt(f) and Δg(f), the differential-mode signal Y(n) is obtained. By calculating its power spectrum and performing segmented coherent accumulation, a power spectrum with a higher signal-to-noise ratio is obtained, and the frequency f of the signal to be measured is identified and extracted from the power spectrum. Subsequently, for the original data corresponding to the power spectrum, a balanced detection processing method is adopted to obtain a differential-mode signal Y(n) with an even higher signal-to-noise ratio. This feedback-based method can still relatively fully eliminate Δt(f) and Δg(f) when the frequency of the signal to be measured changes, and obtain a differential-mode signal Y(n) with a high signal-to-noise ratio.

[0026] When the frequency f of the signal to be detected is known, the balanced detection processing method is as follows:

[0027] Step 1, calculate and subtract the mean values of the two waveforms. Sum the consecutive 2 N sampling data in waveform A, truncate the low N bits of the sum data to obtain the mean value m A of waveform A. Sum the consecutive 2 N sampling data in waveform B, truncate the low N bits of the sum data to obtain the mean value m B of waveform B. Subsequently, subtract m A from each data in waveform A, and subtract m B from each data in waveform B to obtain waveform A with a mean value of 0 (denoted as X A (n)) and waveform B with a mean value of 0 (denoted as X B (n)).

[0028] Step 2, correct the amplitude difference Δg(f) between the two waveforms. Since it is easier for the FPGA to calculate multiplication than division, the waveform with the smaller amplitude among the two waveforms is amplified to achieve the correction effect.

[0029] When Δg(f) < 0, then amplify X A (n), that is: multiply each data of X A (n) by 1 / (Δg(f) + 1) to obtain Y A (n).

[0030] When Δg(f) > 0, then amplify XB (n), that is: X B Multiply each data of (n) by (Δg(f) + 1) to obtain Y B (n).

[0031] Step 3, correct the delay Δt(f) between the two waveforms. Let the sampling time interval be T, then the differential-mode signal Y(n) is:

[0032] Y(n)=Y A (n)-Y B (n + [Δt(f) / T]) (3);

[0033] Where, [] represents the rounding operation.

[0034] Based on the method proposed by the present invention, the circuit can eliminate Δt(f) and Δg(f) for two optical signals, thereby more effectively suppressing the common-mode noise and extracting the differential-mode signal, and obtaining a higher signal-to-noise ratio than the traditional balanced detector.

Claims

1. A balanced detection device based on digital post - processing, characterized in that, Including: The first optoelectronic conversion channel is successively connected to a first photodiode, a first DC-blocking capacitor, a first transimpedance amplifier, and a first analog-to-digital converter; The second optoelectronic conversion channel is sequentially connected to a second photodiode, a second DC-blocking capacitor, a second transimpedance amplifier, and a second analog-to-digital converter; the digital logic processing module receives the digital waveform signals of the two analog-to-digital converters; among them, the digital logic processing module performs the following processing steps: performing mean subtraction processing on the digital waveforms of the two channels; performing amplitude matching adjustment according to a preset frequency-dependent amplitude difference coefficient Δg(f); performing time-delay compensation according to a preset frequency-dependent time-delay difference Δt(f) and then performing a differential operation to generate a differential-mode signal Y(n); the amplitude matching adjustment includes: when Δg(f)<0, multiplying the signal of the first channel by 1 / (Δg(f)+1); when Δg(f)>0, multiplying the signal of the second channel by (Δg(f)+1); the differential-mode signal is achieved through the following formula: Y(n)=Y A (n)-Y B (n+[Δt(f) / T]); where T is the sampling interval, and [] represents the rounding operation; the digital logic processing module also includes a feedback processing unit for extracting the signal frequency f through the power spectrum calculation and segmented coherent accumulation of the differential-mode signal Y(n); dynamically adjusting the Δg(f) and Δt(f) parameters according to the extracted f value.

2. The balanced detection device based on digital post-processing according to claim 1, wherein The first photodiode has a bias voltage source VBIAS1 and a pull-up resistor R1; the second photodiode has a bias voltage source VBIAS2 and a pull-up resistor R2.

3. A balanced detection method based on digital post - processing, for the balanced detection device based on digital post - processing as described in any one of claims 1 - 2, comprising the following steps: Dual-channel independent optoelectronic conversion and analog-to-digital conversion; The digital waveform preprocessing includes: calculating and subtracting the waveform mean value of each channel; performing amplitude matching adjustment based on frequency-related parameters; performing time-delay compensation; generating a differential signal; and feedback-adjusting dynamic parameters.

4. A balance detection method based on digital post-processing according to claim 3, characterized in that The amplitude matching adjustment includes: establishing a Δg(f) parameter look-up table; real-time calling the corresponding Δg(f) value according to the detected signal frequency; and performing a multiplication-based amplitude correction operation.

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