Synchronous Demodulator Circuit Using Discrete Fourier Transform
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Solution Overview
Problem
Conventional synchronous demodulator circuits for phase modulation signals are complex, large, and power-consuming due to the need for multiple mixers and low-pass filters in the Costas loop, which become cumbersome with low cut-off frequencies.
Innovation Solution
A synchronous demodulator electronic circuit that employs a discrete Fourier transform unit to combine mixing and low-pass filtering operations, simplifying the demodulation process and reducing complexity by performing digital demodulation with digital conversion signals, and utilizing a digital Costas loop for phase and frequency adaptation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple mixers and low-pass filters are used in the Costas loop, then synchronous demodulation can be achieved, but the circuit complexity, size, and power consumption increase
Solution Approach 1:
The patent replaces the traditional analog Costas loop circuit (with mixers and low-pass filters) with a digital signal processing implementation using a microcontroller. The microcontroller performs correlation-based demodulation through software algorithms, substituting physical electronic components with computational operations. This digital approach maintains synchronous demodulation capability while significantly reducing circuit complexity, component count, and power consumption.
2Measurement precision
If low-pass filters with low cut-off frequencies are used, then signal filtering is improved, but the filters become cumbersome and complex
Solution Approach 1:
The patent replaces physical low-pass filters with digital filtering algorithms implemented in the microcontroller. The digital signal processing performs frequency-selective filtering through computational methods, eliminating the need for complex analog filter circuits. This approach achieves the required signal filtering precision while avoiding the physical complexity and size of traditional low-cut-off-frequency filters.
3Measurement precision
If exact carrier frequency recovery is achieved, then demodulation accuracy is improved, but the requirement for precise frequency matching increases circuit complexity
Solution Approach 1:
The patent implements a feedback-based correlation algorithm where the microcontroller adjusts the reference signal frequency based on the correlation output. The system continuously monitors the correlation between the received signal and the generated reference signal, and automatically tunes the frequency to maximize correlation. This feedback mechanism achieves exact carrier frequency recovery and optimal demodulation accuracy through software control, avoiding the need for complex analog frequency-locked loops.
Data Source
AI summary
The synchronous demodulator electronic circuit for phase modulation signals includes, in a control loop, a discrete Fourier transform unit for receiving the phase modulation signal to be demodulated, and means of recovering the carrier frequency of the phase modulation signal, so that the discrete Fourier transform unit performs in combination the operations of mixing and low-pass filtering the sampled phase modulation signal with at least one frequency and phase adapted digital conversion signal to supply at least one demodulated signal at the output of the discrete Fourier transform unit.