Distortion Analysis Circuit Using Reference Signal Subtraction
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Solution Overview
Problem
Conventional methods for analyzing distortion and noise in sinusoidal wave signals are inefficient, as they require multiple notch filters, are time-consuming with phase-locked loops, or have high distortion and slow processing with spectrum analyzers, especially when dealing with low distortion signals.
Innovation Solution
A method that determines the amplitude and relative phase of a signal under test, generates a reference signal based on these parameters, and combines it with the test signal to produce a residual signal indicative of distortion, which is then measured using analog-to-digital and digital-to-analog converters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a notch filter is used to measure distortion, then the fundamental frequency can be rejected, but multiple separate notch filters are required for every frequency and parts of noise are removed
Solution Approach 1:
The patent implements a universal distortion measurement system that can analyze multiple frequency components using a single set of circuits. The system generates reference signals at different frequencies and uses a single combining circuit to process all frequency components, eliminating the need for multiple separate notch filters while maintaining measurement precision across the entire frequency spectrum
Solution Approach 2:
The system dynamically adjusts the reference signal frequency to match the fundamental frequency of the input signal. By using a phase-locked loop to track the fundamental frequency and dynamically generating reference signals at the appropriate frequency, the system achieves accurate distortion measurement without requiring fixed-frequency notch filters for each possible frequency
2Measurement precision
If a phase-locked loop is used to generate reference signal, then the fundamental frequency can be tracked, but it requires a great deal of time and has aggressive distortion constraints
Solution Approach 1:
The system performs preliminary frequency estimation using a fast Fourier transform (FFT) or other spectral analysis method before engaging the phase-locked loop. This preliminary action provides an initial estimate of the fundamental frequency, allowing the phase-locked loop to start from a known proximity rather than searching from scratch, thereby significantly reducing the time required to acquire and track the fundamental frequency while maintaining measurement precision
3Measurement precision
If a spectrum analyzer is used to measure frequency components, then individual frequencies can be measured, but the analyzer itself introduces distortion and the process is slow
Solution Approach 1:
The patent introduces reference signals as intermediaries that represent the ideal fundamental frequency components. By subtracting these reference signals from the input signal before analysis, the system isolates only the distortion components for measurement. This intermediary approach eliminates the need for a spectrum analyzer to directly measure and display all frequency components, thereby removing the spectrum analyzer's own distortion from the measurement equation and significantly reducing measurement time
Data Source
AI summary
A method, circuit and system for determining at least one of an amplitude and a relative phase of a signal under test. A reference signal is generated based, at least in part, upon the at least one of the amplitude and the relative phase of the signal under test. The reference signal is combined with the signal under test to generate a residual signal indicative of a distortion within the signal under test. The residual signal is measured.