Estimation of fmax by the common-intercept method

A generally accepted traditional figure of merit of transistors is the maximum oscillation frequency f_max. This is the ultimate frequency what the device is able at for power amplification. Hence it is a well understandable metric for comparing the performance of different processes. Recent technologies allow for so high device speeds that state of the art network analyzers can not directly measure the related f_max values. Extrapolation ratios exceeding a factor of three in terms of the upper frequency limit of the VNA are to be applied in some cases. A new constrained extrapolation method based on the common intercept of "passivity" curves is proposed to reduce the uncertainty in f_max estimation.