Nonlinear Distortion Detection Using Cross-Correlation
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Solution Overview
Problem
Conventional methods for measuring nonlinear distortion in signal generators struggle to distinguish between distortion caused by the generator and the device under test (DUT), leading to inaccurate characterization of nonlinear distortion in DUTs, especially due to the introduction of noise by semiconductor components in signal generators.
Innovation Solution
A system comprising a signal generator, a splitter, a DUT, and a network analyzer is used to generate and split a periodically modulated RF signal, allowing the network analyzer to measure the input and output signals separately, enabling the determination of nonlinear distortion specific to the DUT by performing cross-correlation and applying a fitting function to isolate the frequency response function and nonlinear distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional noise-power-ratio or adjacent channel power ratio methods are used to measure nonlinear distortion, then the measurement process is simple, but the measurement precision is poor because the method cannot distinguish between distortion from the signal generator and distortion from the DUT
Solution Approach 1:
The patent segments the measurement process into distinct components: the signal generator produces a multi-tone signal with a controlled notch, the DUT processes this signal, and the measurement system separately analyzes the input and output signals. By segmenting the distortion sources and measuring them independently through cross-correlation, the system achieves precise distinction between generator-induced and DUT-induced distortion.
Solution Approach 2:
The patent introduces cross-correlation as an intermediary mathematical operation between the input signal X(ω) and output signal Y(ω). This intermediary process enables the separation of distortion components by correlating the known input signal spectrum with the measured output spectrum, thereby isolating the DUT's contribution to nonlinear distortion from the signal generator's contribution.
2Power
If signal generators are built with semiconductor components to provide necessary output power, then the power output is sufficient, but nonlinear distortion is introduced that fills the notch and degrades measurement accuracy
Solution Approach 1:
The patent extracts the distortion component caused by the signal generator from the total measured distortion. By using cross-correlation between the input signal X(ω) and output signal Y(ω), the system identifies and separates the generator-induced distortion E_gen(ω) from the DUT-induced distortion, allowing accurate characterization of the DUT's nonlinear properties despite the presence of generator distortion.
Solution Approach 2:
The patent changes the spectral parameters of the input signal by introducing a controlled notch at specific frequencies where distortion measurement is desired. This parameter modification allows the system to create a reference condition where the absence of input signal energy at notch frequencies enables precise measurement of distortion components while maintaining sufficient overall output power for DUT operation.
3Adaptability or versatility
If error-vector-magnitude method is used to determine nonlinear distortion, then the method can work with modern communication standards, but the measurement accuracy is compromised by assumptions about H(ω) and reliance on communication standards
Solution Approach 1:
The patent enables the measurement system to self-determine the frequency response function H(ω) through cross-correlation of the measured input and output signals, without relying on external communication standards or assumptions. This self-service approach allows the system to adapt to any DUT while maintaining high measurement accuracy, as H(ω) is empirically derived rather than assumed.
Data Source
AI summary
Nonlinear distortion of a device under test (DUT) is detected by obtaining measurements of a multi-tone input signal from a signal generator to a DUT, to obtain a measured multi-tone input signal. Measurements are also obtained of a multi-tone output signal from the DUT that is generated based on the multi-tone input signal, to obtain a measured multi-tone output signal. A correlated part of the measured multi-tone output signal that is correlated with the measured multi-tone input signal is determined insofar as the correlated part corresponds to a frequency response function of the DUT.