Fixture De-Embedding Using Time-Domain Gating for DUT S-Parameters
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Solution Overview
Problem
Existing test fixtures introduce fixture effects that distort and attenuate signals during testing of complex electronic devices, making it difficult to accurately measure the performance of devices under test (DUTs) using network analyzers.
Innovation Solution
A fixture-effect removal device and method that utilizes time-domain gating and Mason's gain formula to derive and process S-parameters, enabling four-port fixture characterization and de-embedding to isolate the DUT's S-parameters by separating fixture effects through matrix operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If test fixtures are used to connect test devices with complex electronic devices, then connectivity and adaptability are improved, but signal attenuation and distortion occur, worsening measurement precision
Solution Approach 1:
The patent extracts the fixture effect from the total measured signal by separately characterizing the fixture's S-parameters. Through de-embedding processing, the fixture contribution is removed from the joint measurement, leaving only the DUT's true characteristics. This extraction approach resolves the contradiction by maintaining fixture connectivity while eliminating its harmful signal effects.
Solution Approach 2:
The patent introduces an intermediary calibration process using 2×-Thru fixtures to characterize the test fixtures before actual DUT measurement. This intermediary step creates a reference model of the fixture effects, which is then used to compensate for signal attenuation and distortion during DUT testing, thereby maintaining both connectivity and measurement accuracy.
2Device complexity
If traditional two-port characterization is used for fixture calibration, then simplicity is maintained, but accuracy is insufficient for complex four-port networks
Solution Approach 1:
The patent transitions from traditional two-port characterization to four-port fixture characterization by measuring all 16 S-parameters of the 2×-Thru calibration fixture. This dimensional expansion captures the complete electromagnetic behavior of complex fixtures including crosstalk and coupling effects, providing accurate characterization for modern high-speed interfaces while maintaining systematic processing through matrix operations.
3Productivity
If fixture effects are not compensated, then measurement process is simple and fast, but test results contain errors due to fixture contribution
Solution Approach 1:
The patent performs preliminary characterization of the test fixtures using 2×-Thru calibration fixtures before actual DUT measurement. The fixture S-parameters are measured and stored as reference data, enabling rapid de-embedding processing during subsequent DUT tests. This preliminary action resolves the contradiction by preparing compensation data in advance, allowing both efficient testing and accurate results.
Data Source
AI summary
An apparatus and method for removing fixture effect are disclosed herein. The device processes the calibration scattering parameters of the 2×-Thru calibration fixture pair through a time domain algorithm. The algorithm consists of time domain gating and ringing data processing to obtain partial S-parameters corresponding to the fixtures on each side of the 2×-Thru calibration fixture pair. The resulting scattering parameters are then substituted into the Mason's gain formula together with other known calibrated scattering parameters to determine all scattering parameters corresponding to the fixture on each side. Finally, in the de-embedding method, the S-parameters of the overall structure and the S-parameters of the fixtures on each side are used to obtain the scattering parameters of the DUT, thereby removing the fixture effect caused by the test fixture pair.