Balance detection device based on digital post-processing

Abstract

The invention discloses a balance detection device based on digital post-processing, and the device comprises a first photoelectric conversion channel which is sequentially connected with a first photodiode, a first blocking capacitor, a first trans-impedance amplifier, and a first analog-to-digital converter; the second photoelectric conversion channel is connected with a second photodiode, a second blocking capacitor, a second transimpedance amplifier and a second analog-to-digital converter in sequence; the digital logic processing module receives digital waveform signals of the two analog-to-digital converters; according to the invention, common-mode noise can be suppressed more effectively.

Description

Technical Field

[0001] The present invention relates to the field of laser radar technology, and in particular to a balanced detection device based on digital post-processing. Background Art

[0002] In coherent Doppler wind laser radar, a high signal-to-noise ratio photoelectric conversion technology is balanced detection technology. Traditional balanced detection technology uses two photodiodes connected to the cathode and anode to suppress common-mode signals and double differential-mode signals. The photocurrent is then amplified through a transimpedance amplifier to output a voltage signal with a large amplitude. The voltage signal is then filtered and converted to analog-to-digital, and the resulting digital waveform is used for the inversion calculation of Doppler wind speed.

[0003] However, in actual situations, there is a deviation in the intensity of the optical signals input into the two photodiodes, and there are differences in parameters such as the photoelectric conversion efficiency, parasitic capacitance, and temperature coefficient of the two photodiodes. Traditional balanced detection technology is difficult to fully suppress common-mode signals and fully amplify differential-mode signals, which makes it difficult to achieve the optimal signal-to-noise ratio of balanced detection technology. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a balanced detection device based on digital post-processing to overcome the defects of traditional balanced detection technology and achieve the effect of improving the signal-to-noise ratio of balanced detection technology.

[0005] Technical solution: A balanced detection device based on digital post-processing described in the present invention includes: a first photoelectric 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 photoelectric 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 digital waveform signals from two analog-to-digital converters. Furthermore, 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-related amplitude difference coefficient Δg(f); performing delay compensation according to a preset frequency-related delay difference Δt(f); and performing differential operation to generate a differential 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; and transimpedance amplifier circuits. Further, the amplitude adjustment includes: when Δg(f)<0, multiplying the first channel signal by 1 / (Δg(f)+1); when Δg(f)>0, multiplying the second channel signal by (Δg(f)+1).

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

[0008] Furthermore, the digital logic processing module also includes a feedback processing unit for extracting the signal frequency f by power spectrum calculation and segmented coherent accumulation of the differential mode signal Y(n); and dynamically adjusting Δg(f) and Δt(f) parameters according to the extracted f value.

[0009] The balanced detection method based on digital post-processing described in the present invention includes the following steps: independent photoelectric conversion and analog-to-digital conversion of dual channels; digital waveform preprocessing including: calculating and deducting the mean value of each channel waveform; performing amplitude matching adjustment based on frequency-related parameters; performing delay compensation; generating differential signals; and feedback adjustment of dynamic parameters.

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

[0011] Furthermore, the amplitude matching adjustment also includes: establishing a Δt(f) parameter lookup table; calling the corresponding Δt(f) value in real time according to the detection 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 significant advantages: The present invention can enable the circuit to eliminate Δt(f) and Δg(f) for two optical signals at the same time, thereby more effectively suppressing common mode noise and extracting differential mode signals. It can achieve a higher signal-to-noise ratio than traditional balanced detection technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic diagram of the device of the present invention; Figure 2 is the relationship between Δg(f), Δt(f) and signal frequency of the present invention; Figure 3 ] are typical waveforms of signal A and signal B of the present invention. DETAILED DESCRIPTION

[0014] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0015] like Figure 1As shown, an embodiment of the present invention provides a balanced detection device based on digital post-processing, including: a first photoelectric conversion channel, connected in sequence 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, connected in sequence 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 digital waveform signals of 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-related amplitude difference coefficient Δg(f); performing delay compensation according to a preset frequency-related delay difference Δt(f); and performing differential operation to generate a differential signal Y(n).

[0016] like Figure 1 As 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 resistors R1 and R2 are both 10kohm, and VBIAS1 and VBIAS2 are both 10V. The capacitance values ​​of capacitors 1 and 2 are both 10nF, and the transimpedance amplifier is built with the OPA4847IDBVR chip to achieve a transimpedance gain of 30kohm. Analog-to-digital converters 1 and 2 are implemented by an ADC07D1520CIYB / NOPB, and the digital logic device is implemented by an FPGA chip model XCKU040-2FFVA1156I. A result of a 1dB higher signal-to-noise ratio than the traditional balanced detection technology is achieved.

[0017] During the circuit operation of the balanced detector, the digital waveform signal output by the analog-to-digital converter will be affected by factors such as the 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, the digital signals corresponding to the optical signals have differences in amplitude and delay.

[0018] 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 the same optical signal is respectively in the two digital signals. A and t B At , the delay between the two waveforms is: Δt(f)=t A -t B (1); The amplitudes of the same optical signal in the two digital signals are g A and g B , then the amplitude difference between the two waveforms is: Δg(f)=(g A / g B)-1 (2); Through testing, the relationship between Δt(f) and signal frequency, as well as the relationship between Δg(f) and signal frequency can be calibrated. Typical results are as follows: Figure 2 As shown in Figure 2, when a sinusoidal light signal is input, the typical waveforms of signal A and signal B are as follows: Figure 3 shown.

[0019] Without correcting Δt(f) and Δg(f), a differential mode signal Y(n) is obtained. By calculating its power spectrum and performing segmented coherent accumulation, a power spectrum with a high 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, a balanced detection processing method is adopted for the original data corresponding to the power spectrum to obtain a differential mode signal Y(n) with a higher signal-to-noise ratio. This feedback-based method can still fully eliminate Δt(f) and Δg(f) when the frequency of the signal to be measured changes, thereby obtaining a differential mode signal Y(n) with a high signal-to-noise ratio.

[0020] When the frequency f of the signal to be detected is known, the method of balanced detection processing is as follows: Step 1: Calculate and subtract the mean of the two waveforms. N The sampled data are summed, and the lower N bits are cut off to obtain the mean value m of waveform A. A For the two consecutive N The sampled data are summed, and the lower N bits are cut off to obtain the mean value m of waveform B. B Then, m is subtracted from each data in waveform A. A , subtract m from each data in waveform B B , and get a waveform A with a mean of 0 (denoted as X A (n)) and waveform B with a mean of 0 (denoted by X B (n)).

[0021] Step 2: Correct the amplitude difference Δg(f) between the two waveforms. Since it is easier for FPGA to calculate multiplication than division, the correction effect is achieved by amplifying the waveform with the smaller amplitude of the two waveforms.

[0022] When Δg(f)<0, X is enlarged A (n), that is: X A Multiply each data of (n) by 1 / (Δg(f)+1) to get Y A (n).

[0023] When Δg(f)>0, X is enlarged. B (n), that is: X B Each data of (n) is multiplied by (Δg(f)+1) to obtain Y B (n).

[0024] Step 3, correct the delay Δt(f) between the two waveforms. Assuming the sampling time interval is T, the differential signal Y(n) is: Y(n)=Y A (n)-Y B (n+[Δt(f) / T]) (3); Among them, [] indicates rounding operation.

[0025] Based on the method proposed in the present invention, the circuit can eliminate Δt(f) and Δg(f) for two optical signals, thereby more effectively suppressing common-mode noise and extracting differential-mode signals, and obtaining a higher signal-to-noise ratio than a traditional balanced detector.

Claims

1. A balance detection device based on digital post-processing, characterized in that: include: A first photoelectric conversion channel 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 photoelectric 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 from the two analog-to-digital converters.

2. A balance detection device based on digital post-processing according to claim 1, characterized in that: 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-related amplitude difference coefficient Δg(f); performing delay compensation according to a preset frequency-related delay difference Δt(f); and performing differential operation to generate a differential mode signal Y(n).

3. A balance detection device based on digital post-processing according to claim 1, characterized in that: The first photodiode and the second photodiode have independent bias voltage sources VBIAS1 and VBIAS2, pull-up resistors R1 and R2, and transimpedance amplifier circuits, respectively.

4. A balance detection device based on digital post-processing according to claim 1, characterized in that: The amplitude adjustment includes: when Δg(f)<0, multiplying the first channel signal by 1 / (Δg(f)+1); when Δg(f)>0, multiplying the second channel signal by (Δg(f)+1).

5. A balance detection device based on digital post-processing according to claim 1, characterized in that: Delay compensation is achieved through the following formula: Y(n)=Y A (n)-Y B (n+[Δt(f) / T]) ; T is the sampling interval, and [] indicates rounding operation.

6. A balance detection device based on digital post-processing according to claim 1, characterized in that: The digital logic processing module also includes a feedback processing unit for extracting the signal frequency f by power spectrum calculation and segmented coherent accumulation of the differential mode signal Y(n); and dynamically adjusting Δg(f) and Δt(f) parameters according to the extracted f value.

7. A balanced detection method based on digital post-processing, characterized in that: A balanced detection device based on digital post-processing includes the following steps: independent photoelectric conversion and analog-to-digital conversion of dual channels; digital waveform preprocessing includes: calculating and deducting the mean value of each channel waveform; performing amplitude matching adjustment based on frequency-related parameters; performing delay compensation; generating differential signals; and feedback adjustment of dynamic parameters.

8. A balanced detection method based on digital post-processing according to claim 7, characterized in that: The amplitude matching adjustment includes: establishing a Δg(f) parameter lookup table; calling the corresponding Δg(f) value in real time according to the detection signal frequency; and performing an amplitude correction operation based on multiplication.

9. The balance detection method based on digital post-processing according to claim 7, characterized in that: The amplitude matching adjustment also includes: establishing a Δt(f) parameter lookup table; calling the corresponding Δt(f) value in real time according to the detection signal frequency; and performing an amplitude correction operation based on multiplication.

Images