This paper will summarize Noise Parameter Extraction Methods, discuss their limitations and present a novel approach to improving accuracy by incorporating an MMIC reflection coefficient synthesizer into Coplanar Waveguide probe. Products offered by ATN and Cascade Microtech, Inc. that permit automated noise parameter measurements on wafer are limited in accuracy because the variable source impedance necessary for proper operation of the system is connected through a probe which exhibits loss. This loss limits the maximum reflection coefficient presented to the device under test (DUT) and consequently impacts the accuracy of measurements as frequency increases. The reason for this stems from the manner the parameters are extracted. If all the reflection coefficients (or source admittances) presented (by the reflection coefficient synthesizer) are far removed from the optimum, the accuracy of predicting Fmin by extrapolation will suffer. If the accuracy of Fmin becomes questionable, so will the other parameters. To obtain a higher degree of accuracy and increase the diagnostic frequency, it is necessary to imbed the reflection coefficient synthesizer in the RF probe which is the subject of this paper. This is done primarily to reduce losses and take full advantage of the variable source generator capability. In addition, provisions have to be made to introduce a Noise Source into the system. This paper will address the implementation of such a reflection coefficient synthesizer using MMIC technology, compare simulated vs experimental results and discuss future plans.
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