Combined Discrete/Normal Statistical Modeling of Microwave Devices

This paper deals with statistical characterization of the equivalent circuit parameters for microwave FET devices. The statistics are derived from the S-parameters measured for a sample of devices. The use of a multidimensional normal distribution seems justified for most parameters. For parameters exhibiting sample distributions substantially different from normal we propose a combined discrete/normal approach that can preserve the means, standard deviations, correlations and marginal distributions derived from the sample. This provides enhanced accuracy of the model while retaining the simplicity of the normal distribution. The problem of the size of the sample is also addressed in terms of confidence levels and confidence intervals.