Universal Demodulation Circuit for ASK and FSK Signals
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Solution Overview
Problem
Existing digital microwave communication systems face challenges in demodulating both Amplitude Shift Keying (ASK) and Frequency Shift Keying (FSK) signals due to broadband switch noises and interference, which require complex filtering and can result in error codes, and existing demodulation circuits are not versatile enough to handle different modulation signals from different equipment manufacturers without hardware changes.
Innovation Solution
A demodulation circuit that includes bandpass filtering, signal gain amplification, pulse extraction, and data decision circuits capable of demodulating both ASK and FSK signals, allowing for flexible configuration without requiring hardware changes in indoor or outdoor units, using a combination of bandpass filtering, amplification, pulse extraction, and data decision based on label information to output digital demodulation data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a bandpass filter is used to filter switch noises in ASK demodulation, then the filtering capability is improved, but the filter cannot completely eliminate broadband switch noises which still form pulse interferences after envelope detection
Solution Approach 1:
The patent divides the filtering process into multiple stages: a bandpass filter for initial noise reduction, followed by a differentiator circuit to convert pulse interferences into detectable signals, and a threshold comparison circuit to eliminate residual errors. This segmented approach addresses the limitation of single-stage filtering by progressively treating different aspects of noise and interference.
Solution Approach 2:
The patent introduces a differentiator circuit as an intermediary between the bandpass filter and the threshold comparison circuit. This intermediary converts the difficult-to-filter pulse interferences into signals with distinct characteristics that can be easily distinguished from valid data through threshold comparison, effectively mediating between filtering and decision-making.
2Measurement precision
If the threshold value of the decision circuit is set low to improve signal detection, then the sensitivity is improved, but error codes occur more frequently due to residual pulse interferences
Solution Approach 1:
The patent performs preliminary processing of the signal through bandpass filtering and differentiation before the final threshold comparison. This preliminary action transforms the signal and interference characteristics in advance, allowing the threshold comparison circuit to operate with a higher threshold that is less susceptible to pulse interferences, thereby preventing error codes while maintaining sensitivity.
3Reliability
If separate demodulation circuits are designed for ASK and FSK signals to ensure optimal performance, then the demodulation capability is improved, but the device complexity increases and hardware changes are required when switching between modulation types
Solution Approach 1:
The patent designs a universal demodulation circuit that can handle both ASK and FSK signals using the same hardware components. The circuit uses a bandpass filter, differentiator, and threshold comparison circuit that work effectively for both modulation types, eliminating the need for separate dedicated circuits and reducing hardware complexity while maintaining demodulation performance.
4Object-affected harmful factors
If FSK demodulation is implemented with separate loops for two frequencies to improve filtering capability, then the frequency separation is improved, but the design complexity increases and the filter design becomes difficult when frequencies are close
Solution Approach 1:
The patent extracts the frequency separation function from complex multi-loop filtering structures. Instead of using separate filtering loops for each frequency, the patent uses a single bandpass filter followed by a differentiator that naturally separates the frequency components through mathematical differentiation, simplifying the overall design while maintaining effective frequency separation even when frequencies are close together.
Data Source
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AI summary
A demodulation circuit, a digital microwave system including the demodulation circuit, and a signal demodulation method are provided. The demodulation circuit includes a first circuit, a second circuit, a third circuit, and a fourth circuit connected in turn. The fourth circuit includes a pulse counting unit and a data decision unit connected in turn. The signal demodulation method includes: performing bandpass filtering on input signals; increasing gains of the bandpass filtered signals; extracting pulse signals are extracted from the gain-increased signals; counting the extracted pulse signals; filtering the pulse signals with counting values beyond a set value range, and outputting obtained signals.