I / Q Imbalance Distortion Suppression Phase Demodulation System Based on Carrier Frequency Closed-Loop Modulation

Abstract

The present invention discloses a phase demodulation system for suppressing I / Q imbalance distortion based on carrier frequency closed-loop modulation, comprising: an I / Q mixer, an I-channel conditioning circuit, a Q-channel conditioning circuit, an I-channel analog-to-digital converter, a Q-channel analog-to-digital converter, a direct digital frequency synthesizer and a microcontroller; the microcontroller includes an arctangent module, a carrier frequency generation module, a residual phase calibration module, a feedback control output module and a demodulation phase output module. The phase demodulation system for suppressing I / Q imbalance distortion based on carrier frequency closed-loop modulation of the present invention modifies the target of closed-loop control. On the basis of tracking the phase of the input signal, through feedback control, the signal after mixing is modulated at a frequency. On the one hand, the signal is separated from low-frequency noise, and on the other hand, the non-linear harmonics are modulated at this carrier frequency, thereby greatly reducing the amplitude of the non-linear harmonic components, avoiding the deterioration of the low-frequency noise floor, and being beneficial to signal detection and extraction.

Description

Technical Field

[0001] The present invention belongs to the technical field of phase demodulation detection, and particularly relates to an I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation. Background Art

[0002] In advanced sensor systems, phase modulation type sensors convert target signals into phase modulation signals, which have advantages such as high sensitivity and strong anti-interference ability. They can achieve high-precision detection of parameters such as small physical quantities, vibrations, and pressures, and are widely used in fields such as aerospace, precision manufacturing, earthquake monitoring, and biomedicine. Therefore, the application of phase modulation type sensors places higher requirements on phase demodulation technology in terms of accuracy, real-time performance, and robustness to ensure the reliability and stability of signal detection, and further promote the technological development and practical application of advanced sensor systems.

[0003] In the field of phase demodulation detection technology, phase demodulation structures based on quadrature I / Q signals are widely used. Further subdivision mainly includes direct digital sampling structures and zero intermediate frequency structures. The direct digital sampling structure directly samples radio frequency signals through a high-speed A / D converter, and combines a digital local oscillator signal and a digital phase-locked loop (DPLL) to complete phase demodulation. This structure simplifies the hardware design and avoids the influence of analog device defects on signals, but the sampling noise and bandwidth limitations of the high-speed A / D converter reduce its application in high-performance sensing systems. The zero intermediate frequency structure directly converts radio frequency signals into baseband I / Q signals through an analog quadrature local oscillator, and performs digital phase demodulation after sampling by a high-performance A / D converter. Although its sampling resolution and noise performance are superior to those of the direct digital sampling structure, the imbalance of the analog I / Q path will destroy the orthogonality of the signals, and at the same time, the low-frequency 1 / f noise of analog devices will aliase with the signals, causing problems such as image interference, noise enhancement, and a decrease in the detection signal-to-noise ratio. Currently, there is a lack of in-depth analysis of the degradation of detection performance caused by I / Q imbalance problems in sensing systems, and there are also no effective measures to improve the degradation of high-performance phase demodulation detection caused by analog signal I / Q imbalance, thus limiting the performance improvement of advanced sensor systems. Summary of the Invention

[0004] The present invention provides an I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation to solve the above-mentioned technical problems, and specifically adopts the following technical solutions:

[0005] An I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation includes: an I / Q mixer, an I-channel conditioning circuit, a Q-channel conditioning circuit, an I-channel analog-to-digital converter, a Q-channel analog-to-digital converter, a direct digital frequency synthesizer, and a microcontroller;

[0006] The I / Q mixer mixes the phase modulation signal to be measured and the reference local oscillator signal generated by the direct digital frequency synthesizer perform a mixing operation to output two orthogonal I / Q analog signals, and the phase modulation part of the phase modulation signal to be measured is expressed as ;

[0007] After the two I / Q analog signals are respectively amplified and filtered by the I / Q channel conditioning circuit, they are transmitted to the analog-to-digital converter for sampling and quantization to obtain digitized I / Q voltage signals and , and are transmitted to the microcontroller;

[0008] The microcontroller includes an arctangent module, a carrier frequency generation module, a residual phase calibration module, a feedback control output module, and a demodulation phase output module;

[0009] The arctangent module performs an arctangent phase calculation on the voltage signals and after digital quantization, so as to extract the phase difference information contained in the I / Q signals , and the carrier frequency generation module takes the sampling rate as the beat and generates a phase value that accumulates over time at a fixed frequency , and outputs it to the residual phase calibration module for residual phase separation to remove the part of the resolved phase residual information, and only retains the phase tracking residual dynamically caused by the signal to be measured . The phase tracking residual is input to the feedback control output module for calculating the feedback control quantity, which is used to configure the direct digital frequency synthesizer in real time, so as to control the real-time phase of the direct digital frequency synthesizer to achieve phase tracking demodulation of the input signal. The phase tracking residual is input to the demodulation phase output module, and the demodulation phase output module combines the phase difference information and the feedback control quantity to generate the final phase demodulation result .

[0010] Furthermore, the I / Q mixer performs a mixing operation on the phase modulation signal to be measured and the reference local oscillator signal generated by the direct digital frequency synthesizer to generate sum-frequency and difference-frequency components. Among them, the difference-frequency component converts the high-frequency signal to the baseband to obtain two orthogonal I / Q analog signals in space for subsequent phase demodulation.

[0011] Further, the I / Q channel conditioning circuit amplifies and low-pass filters the I / Q signals output by the I / Q mixer, amplifies the signal level to the input level range adapted to the subsequent analog-to-digital converter, improves detectability, and while implementing anti-aliasing filtering, filters out the sum-frequency components of the mixer and retains the difference-frequency components.

[0012] Further, the I / Q channel analog-to-digital converter quantizes and samples the I / Q voltage output by the conditioning circuit at a sampling rate to obtain a digitally quantized voltage signal.

[0013] Further, under the digital control of the microcontroller, the direct digital frequency synthesizer dynamically adjusts its output phase-frequency characteristics in real time, and the digital control frequency is consistent with the sampling frequency; the adjustment method of the direct digital frequency synthesizer is to only use frequency control, and the phase adjustment amount is obtained by integrating the frequency adjustment amount within each control period to achieve tracking of the phase modulation part of the signal to be measured.

[0014] Further, a reconstruction filter is cascaded at the output end of the direct digital frequency synthesizer, and the bandwidth covers the output nominal frequency to effectively remove possible spurious signals and noise, thereby improving the signal quality and spectral purity at the output end of the direct digital frequency synthesizer.

[0015] Further, the I / Q channel conditioning circuit and the I / Q channel analog-to-digital converter are consistent in device selection and symmetric in circuit design, so as to reduce the imbalance of the I / Q signals and avoid excessive deterioration of the orthogonality of the I / Q signals.

[0016] Further, the analog bandwidth design of the I / Q channel conditioning circuit comprehensively considers the feedback control algorithm design of the microcontroller. Under the closed-loop system, the phase part of the I / Q channel signal is expressed as the superposition of the residual phase and the linearly increasing phase introduced by the control carrier frequency, that is , and the maximum frequency deviation caused by this phase part can be expressed as , and the bandwidth of the analog conditioning is greater than or equal to .

[0017] Further, the arctangent module performs an arctangent calculation on the quantized I / Q voltage signal, uses the Arctangent function to achieve phase calculation within the range, and obtains the phase difference information contained in the I / Q signal .

[0018] Further, the carrier frequency generation module takes the sampling rate as the beat and generates a phase value that accumulates with time at a fixed frequency ; ;

[0019] The phase accumulation module uses the sampling rate as the beat to generate a phase value that accumulates over time, and then outputs it to the feedback control output module for calculating the feedback control quantity;

[0020] The feedback control output module combines the phase difference information obtained by the arctangent module and the phase accumulation value output by the phase accumulation module to calculate the feedback control quantity and feedback it to the direct digital frequency synthesizer, dynamically adjusting the phase-frequency characteristics of the output of the direct digital frequency synthesizer. On the one hand, it tracks the phase modulation part of the signal to be measured, and on the other hand, it introduces a control carrier frequency in the I / Q signal output by mixing, forming a carrier frequency modulation of the I / Q signal;

[0021] The demodulation phase output module combines the phase difference information obtained by the arctangent module and the feedback control quantity output by the feedback control output module to restore and estimate the phase modulation information of the signal to be measured, realizing phase demodulation and output.

[0022] The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation of the present application modifies the target of closed-loop control. On the basis of tracking the phase of the input signal, through feedback control, the mixed signal is modulated at a frequency. On the one hand, it separates the signal from the low-frequency noise, and on the other hand, it modulates the non-linear harmonics at this carrier frequency, thereby greatly reducing the amplitude of the non-linear harmonic components. The combination of the two avoids the deterioration of the low-frequency noise floor and is beneficial to signal detection and extraction.

[0023] The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation of the present application introduces a direct digital frequency synthesizer to generate the local oscillator signal on the basis of the traditional zero-intermediate frequency I / Q phase demodulation structure. The local oscillator signal generated by the DDS is adjusted in real time and dynamically under the control of the controller to accurately track the phase modulation part of the signal to be detected, thereby effectively suppressing the phase fluctuation in the analog I / Q signal and compressing the bandwidth of the I / Q signal. This method significantly suppresses the non-linear distortion caused by I / Q imbalance, and at the same time, by compressing the signal bandwidth, it reduces the requirement for the bandwidth of the analog signal acquisition circuit. On the one hand, the use of low-noise analog devices (such as operational amplifiers and ADCs) helps to optimize the detection noise of the system; on the other hand, it simplifies the design of the analog conditioning circuit, avoids the dependence on high-speed ADCs, and reduces the design cost of the demodulation system.

[0024] The advantages of the present invention lie in the provided I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation, which combines analog homodyne carrier phase tracking with residual carrier frequency modulation, integrating the advantages of homodyne closed-loop tracking in expanding the detection dynamic range and improving nonlinearity, and combining the carrier frequency modulation method to secondarily modulate the phase residual after homodyne closed-loop tracking onto a fixed carrier frequency to construct a carrier frequency closed-loop phase demodulation structure. This structure effectively eliminates the problems of I / Q imbalance, local oscillator leakage, low-frequency flicker noise, and image interference caused by analog components in the I / Q channels, thereby suppressing the detection noise floor across the entire frequency range and ensuring high-precision detection and extraction of signals. Such a structure does not require complex I / Q imbalance digital estimation and compensation algorithms, reducing the requirements for algorithm performance and ensuring real-time performance. At the same time, the carrier frequency closed-loop phase demodulation structure effectively compresses the bandwidth of the I / Q signals by suppressing phase fluctuations in the analog I / Q signals, reducing the requirements for the bandwidth of the analog signal acquisition circuit. On the one hand, using low-noise analog devices (such as operational amplifiers and ADCs) helps optimize the detection noise of the system; on the other hand, it simplifies the design of the analog conditioning circuit, avoids dependence on high-speed ADCs, and reduces the design cost of the demodulation system. In summary, the proposed I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation combines a control algorithm to introduce a controlled carrier frequency on the basis of tracking the phase modulation of the signal to be measured, ultimately realizing the carrier frequency closed-loop tracking demodulation of the baseband I / Q signals, successfully solving the problem of signal demodulation distortion caused by I / Q signal imbalance, and improving the detection signal-to-noise ratio of the system. Brief Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic diagram of an I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation of the present invention;

[0027] Figure 2 It is a schematic diagram of an embodiment of an I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation of the present invention;

[0028] Figure 3 It is a frequency-domain simulation diagram of the phase detection result of an embodiment of the present invention, including a comparison with the traditional zero-intermediate-frequency phase detection structure.

[0029] I / Q Imbalance Distortion Suppression Phase Demodulation System Based on Carrier Frequency Closed-Loop Modulation, including phase modulation signal input 1, I / Q mixer 2, I-channel conditioning circuit 3, Q-channel conditioning circuit 4, I-channel analog-to-digital converter (ADC) 5, Q-channel analog-to-digital converter (ADC) 6, direct digital frequency synthesizer (DDS) 7, microcontroller 8, arctangent module 801, carrier frequency generation module 802, residual phase calibration module 803, feedback control output module 804 and demodulated phase output module 805. Detailed Implementation Manner

[0030] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the accompanying drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to explain the present application, and should not be construed as a limitation of the present application.

[0031] As Figure 1 shown, an I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation of the present application includes: phase modulation signal input 1, I / Q mixer 2, I-channel conditioning circuit 3, Q-channel conditioning circuit 4, I-channel analog-to-digital converter (ADC) 5, Q-channel analog-to-digital converter (ADC) 6, direct digital frequency synthesizer (DDS) 7 and microcontroller 8. Among them, the microcontroller 8 includes an arctangent module 801, a carrier frequency generation module 802, a residual phase calibration module 803, a feedback control output module 804 and a demodulated phase output module 805. The I / Q mixer 2 mixes the phase modulation signal to be measured 1 with the reference local oscillator signal generated by the direct digital frequency synthesizer (DDS) 7 to perform a mixing operation and output a pair of quadrature voltage signals ( and ). The I-channel conditioning circuit 3 and the Q-channel conditioning circuit 4 perform signal conditioning on the I / Q voltage signals, complete the amplification and low-pass filtering of the analog signals, amplify the signal level to the input level range suitable for the subsequent ADC, improve the detectability, and obtain the I / Q voltage output by the conditioning circuit ( and ). The I-channel analog-to-digital converter (ADC) 5 and the Q-channel analog-to-digital converter (ADC) 6 perform digital sampling on the conditioned analog I / Q voltage signals to obtain digitally quantized voltage signals ( and ), which are transmitted to the microcontroller 8. The microcontroller 8 is responsible for digital logic operations. The arctangent module 801 in it performs phase calculation on the digitally quantized voltage signals ( and ) to extract the phase difference information contained in the I / Q signals , the carrier frequency generation module 802 uses the sampling rate as the beat, and generates a phase value that accumulates over time at a fixed frequency (), and outputs it to the residual phase calibration module 803 for residual phase separation, removing the resolved phase residual information in , and only retaining the phase tracking residual dynamically caused by the signal to be measured . Subsequently, it is input to the feedback control output module 804 for calculating the feedback control quantity, so as to configure the DDS in real time, thereby controlling the real-time phase of the DDS ( ) to achieve phase tracking demodulation of the input signal. At the same time, the input demodulated phase output module 805 generates the final phase demodulation result by combining the control output and the phase tracking residual.

[0032] Specifically, the phase difference between the signal to be measured and the local oscillator signal is obtained by solving through the four-quadrant arctangent algorithm . The obtained phase difference is further transmitted to the closed-loop controller, and the feedback control output is calculated based on the control algorithm to dynamically adjust the phase of the DDS output signal in real time . The control objective of the closed-loop control combines homodyne phase closed-loop tracking and residual phase carrier frequency modulation. On the one hand, the phase of the output signal dynamically adjusted by the DDS should achieve real-time tracking of the phase modulation part of the input PM signal to be measured , that is, the dynamic adjustment part should be as consistent as possible with the fluctuation, so as to ensure effective homodyne phase closed-loop tracking of ; on the other hand, on the basis of homodyne phase closed-loop tracking, carrier frequency generation and residual phase carrier frequency modulation are introduced, and the residual phase under the aforementioned homodyne phase closed-loop tracking is further modulated on the fixed carrier frequency , and also makes the signal to be measured and the local oscillator signal maintain a stable frequency difference between them, so as to achieve carrier frequency closed-loop tracking demodulation of the input signal to be measured. At this time, the closed-loop residual phase contains two parts at the same time, the tracking residual part of and the linearly increasing phase part introduced by the control carrier frequency , that is, . Finally, the demodulated phase output module combines the phase difference information obtained by arctangent calculation and the feedback control output information, and outputs the phase demodulation result of the PM signal to be measured . Compared with the existing I / Q phase demodulation structure based on zero intermediate frequency, in the present invention, the local oscillator signal generator uses DDS to realize the output of a dynamically phase-frequency modulated signal. The control algorithm introduces a control carrier frequency on the basis of tracking the phase modulation of the signal to be measured, integrating the advantages of zero-difference closed-loop tracking in the expansion of the detection dynamic range and the improvement of nonlinearity, and combining the carrier frequency modulation method. The phase residual after zero-difference closed-loop tracking is secondarily modulated on a fixed carrier frequency to construct a carrier frequency closed-loop phase demodulation structure, realizing the carrier frequency closed-loop tracking demodulation of the baseband I / Q signal, and specifically solving the problem of signal demodulation distortion caused by I / Q signal imbalance.

[0033] As Figure 2 shown in the schematic diagram of an embodiment of the I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation of the present invention. The I / Q mixer 2 mixes the phase-modulated signal 1 to be measured with the reference local oscillator signal generated by the direct digital frequency synthesizer (DDS) 7, and performs a mixing operation to obtain the quadrature signal ( and ) of the mixing output, which includes sum-frequency components and difference-frequency components. The phase-modulated signal to be measured can be expressed as , and the quadrature reference local oscillator signal generated by the DDS can be expressed in complex form . Among them, and represent the voltage amplitudes of the signals for mixing, represents the nominal carrier frequency of the signal, represents the phase part of the phase-modulated signal to be detected, represents the phase part dynamically adjusted by the reference local oscillator signal generated by the DDS. The difference-frequency component in the mixing output converts the carrier signal into a baseband signal, obtaining a pair of mutually orthogonal I / Q signals for subsequent phase demodulation. The sum-frequency component is not the signal required for phase detection and is filtered out by the low-pass filter after the I / Q mixer.

[0034] The I-channel conditioning circuit 3 and the Q-channel conditioning circuit 4 condition the I / Q signals output by the I / Q mixer, complete the amplification and low-pass filtering of the analog signals, amplify the signal level to the input level range suitable for the subsequent ADC, improve the detectability, and obtain the I / Q voltage output by the conditioning circuit. At the same time, while realizing anti-aliasing filtering in the front stage of signal sampling, the sum-frequency component of the mixer is further filtered out, and the difference-frequency component is retained. Due to the non-ideality of analog devices themselves and the limitation of processing errors, there are inevitable amplitude imbalance, phase imbalance and DC offset in the I / Q channel output, and the orthogonality deteriorates. At this time, the I / Q voltage ( and ) output by the conditioning circuit is affected by the I / Q channel imbalance and noise and is expressed as the following formula. Among them, represents a low-pass filter function, represents the gain imbalance coefficient, represents the phase imbalance coefficient, and represents the DC bias voltage of the I / Q signal, and represents the independent noise signal superimposed on the I / Q signal.

[0035]

[0036] The I / Q channel conditioning circuit and the I / Q channel analog-to-digital converter are consistent in device selection and symmetric in circuit design, so as to reduce the imbalance of the I / Q signal and avoid excessive deterioration of the orthogonality of the I / Q signal.

[0037] The analog bandwidth design of the I / Q channel conditioning circuit comprehensively considers the feedback control algorithm design of the microcontroller. Under the closed-loop system, the phase part of the I / Q channel signal is expressed as the superposition of the residual phase and the linearly increasing phase introduced by the control carrier frequency, that is , and the maximum frequency deviation caused by this phase part can be expressed as , and the bandwidth of the analog conditioning is greater than or equal to .

[0038] The I-channel analog-to-digital converter (ADC) 5 and the Q-channel analog-to-digital converter (ADC) 6 sample the I / Q voltage ( and and ) output by the conditioning circuit at the sampling rate and ) to obtain the digitally quantized voltage signals ( and ), where n represents the nth sampling moment, that is

[0039]

[0040] The microcontroller 8 first performs an arctangent calculation on the quantized I / Q voltage signal through the arctangent module 801 to obtain the phase difference information contained in the I / Q signal, expressed as: . The Atan2 function is a four-quadrant arctangent function. It can calculate the polar coordinate angle (in radians) relative to the origin according to the input I / Q values, and the phase discrimination range is , which can solve the quadrant recognition problem.

[0041] Furthermore, the carrier frequency generation module 802 takes the sampling rate as the beat and generates a fixed frequency Generate a phase value that accumulates over time ( ), specifically, the carrier frequency generation module uses a numerically controlled oscillator (NCO) to generate it. The digitally quantized phase accumulation output is , representing the phase accumulation value at the th sampling moment.

[0042] Furthermore, the residual phase calibration module 803 combines the residual phase information output by the arctangent module 801 and the phase information output by the carrier frequency generation module 802 to perform residual phase separation, removing the part in the resolved phase residual information , and only retaining the phase tracking residual dynamically caused by the signal to be measured . Specifically, the separated residual phase is expressed as .

[0043] Furthermore, the feedback control output module 804 calculates the feedback control quantity based on the separated residual phase . The feedback control quantity is used to configure the DDS in real time, thereby controlling the real-time phase of the DDS ( ) to achieve phase tracking demodulation of the input signal. Specifically, the real-time phase output of the DDS is an integral output, and the control output in each sampling period can be expressed by the following formula. Under the accumulation of the control output in each sampling period, the real-time phase output of the DDS is as shown in the following formula.

[0044]

[0045] Furthermore, the demodulated phase output module 805 generates the final phase demodulation result by combining the control output and the phase tracking residual. Specifically, the final phase demodulation result is expressed as .

[0046] Furthermore, the direct digital synthesizer (DDS) 7 dynamically modulates its output phase and frequency under the real-time control of the microcontroller 8. A reconstruction filter is cascaded at its output end, and the bandwidth covers the output nominal frequency to effectively remove possible spurious signals and noise, thereby improving the signal quality and spectral purity at the output end of the direct digital synthesizer (DDS) 7. The adjustment method of the direct digital synthesizer (DDS) 7 is to only use frequency control. By integrating the frequency adjustment amount within each control period , the phase adjustment amount is obtained to achieve tracking of the phase modulation part of the signal to be measured.

[0047] Furthermore, the real-time phase output of the direct digital synthesizer (DDS) 7 simultaneously includes the part for phase modulation of the input to be measured the residual error to be tracked and the fixed frequency introduced by the phase accumulation module . At this time, compared with the traditional zero-IF structure, the phase tracking residual error is modulated at a fixed frequency , that is a fixed frequency is superimposed on . The DC bias voltage of the I / Q signal and and the independent noise signals superimposed in the I / Q signal and can be separated from the signal in the frequency domain, thus avoiding the deterioration of the detection signal-to-noise ratio caused by noise coupling. At the same time, due to the effect of closed-loop frequency modulation, the nonlinear effects caused by the imbalance and nonlinearity of the I / Q signal are reduced, so that the intensity of the nonlinear harmonic components in the detected spectrum is greatly attenuated, thus ensuring the total harmonic distortion of the detection and improving the detection performance.

[0048] The frequency-domain simulation diagram of the phase detection result of an embodiment of the present invention is as Figure 3 shown, including the comparison with the traditional zero-IF phase detection result. Among them, the phase part of the phase modulation signal to be detected is , that is, the modulation frequency is 57 Hz and the modulation depth is 1 radian. The phase spectrum curve demodulated by the zero-IF method is represented by a black dotted line, and the phase spectrum curve demodulated by the carrier frequency closed-loop modulation method of the present invention is represented by a black solid line. It can be seen that there are a large number of 57-Hz nonlinear distortion harmonics in the result of phase demodulation based on the zero-IF method, while there is only a clean 57-Hz spectral line in the result of phase demodulation based on the carrier frequency closed-loop modulation method of the present invention. At the same time, from the signal detection noise floor in the low-frequency band, it can be seen that the carrier frequency closed-loop modulation method of the present invention can achieve a lower detection noise floor and has a higher phase detection signal-to-noise ratio, thus ensuring the weak signal detection performance of the phase modulation type advanced sensing system.

[0049] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any form. Any technical solutions obtained by using equivalent replacement or equivalent transformation fall within the protection scope of the present invention.

Claims

1. An I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation, characterized in that: include: I / Q mixer, I channel conditioning circuit, Q channel conditioning circuit, I channel analog-to-digital converter, Q channel analog-to-digital converter, direct digital frequency synthesizer and microcontroller; The I / Q mixer modulates the phase of the signal to be measured. The reference local oscillator signal generated by the direct digital frequency synthesizer is mixed to output orthogonal I / Q two-way analog signals, the phase modulation signal to be measured The phase modulation part is expressed as ; The I / Q two-way analog signals are amplified and filtered by the I / Q channel conditioning circuit respectively, and then transmitted to the analog-to-digital converter for sampling and quantization to obtain digital I / Q voltage signals. and , transmitted to the microcontroller; The microcontroller comprises an inverse tangent module, a carrier frequency generation module, a residual phase calibration module, a feedback control output module and a demodulation phase output module; The inverse tangent module performs digital quantization on the voltage signal and Perform inverse tangent phase calculation to extract the phase difference information contained in the I / Q signal The carrier frequency generation module uses a sampling rate For the beat, at a fixed frequency Generates a phase value accumulated over time , and output it to the residual phase calibration module for residual phase separation, removing the solved phase residual information In part, only the signal to be tested is retained Phase tracking residual caused by dynamics , phase tracking residual The feedback control output module is input to calculate the feedback control amount to configure the direct digital frequency synthesizer in real time, thereby controlling the real-time phase of the direct digital frequency synthesizer. To achieve phase tracking demodulation of the input signal, phase tracking residual Input demodulation phase output module, the demodulation phase output module combines the phase difference information and feedback control quantity to generate the final phase demodulation result .

2. The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation according to claim 1, characterized in that: The I / Q mixer is a phase modulated signal to be measured. The reference local oscillator signal generated by the direct digital frequency synthesizer A mixing operation is performed to generate sum frequency and difference frequency components, wherein the difference frequency component converts the high-frequency signal to baseband to obtain two-way I / Q analog signals that are spatially orthogonal to each other for subsequent phase demodulation.

3. The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation according to claim 1, characterized in that: The I / Q channel conditioning circuit amplifies and low-pass filters the I / Q signal output by the I / Q mixer, amplifies the signal level to adapt to the input level range of the subsequent analog-to-digital converter, and filters out the mixer sum frequency component while realizing anti-aliasing filtering and retaining the difference frequency component.

4. The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation according to claim 1, characterized in that: The I / Q channel analog-to-digital converter is sampled at a rate The I / Q voltage output by the conditioning circuit is quantized and sampled to obtain a digitally quantized voltage signal.

5. The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation according to claim 1, characterized in that: The direct digital frequency synthesizer dynamically adjusts the phase-frequency characteristics of its output in real time under the digital control of the microcontroller, and the digital control frequency and sampling frequency The adjustment method of the direct digital frequency synthesizer is to use only frequency control, through each control cycle The integral of the frequency adjustment amount is used to obtain the phase adjustment amount, thereby tracking the phase modulation part of the signal to be measured.

6. The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation according to claim 1, characterized in that: A reconstruction filter is cascaded at the output end of the direct digital frequency synthesizer, and the bandwidth covers the output nominal frequency.

7. The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation according to claim 1, characterized in that: The I / Q channel conditioning circuit and the I / Q channel analog-to-digital converter are consistent in device selection and symmetrical in circuit design.

8. The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation according to claim 1, characterized in that: The analog bandwidth design of the I / Q channel conditioning circuit comprehensively considers the feedback control algorithm design of the microcontroller. The phase part of the I / Q channel signal in the closed-loop system is represented by the superposition of the residual phase and the linear growth phase introduced by the control carrier frequency, that is, The maximum frequency deviation caused by this phase part can be expressed as , the bandwidth of the analog conditioning is greater than or equal to .

9. The I / Q imbalance distortion suppression phase demodulation system based on carrier frequency closed-loop modulation according to claim 1, characterized in that: The inverse tangent module performs inverse tangent calculation on the quantized I / Q voltage signal using the Arctangent function to achieve Phase calculation of the range to obtain the phase difference information contained in the I / Q signal .

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