Accuracy of Microwave Transistor fT and fMAX Extractions

We present a complete methodology to evaluate the accuracy of microwave transistor figures-of-merit fT (current gain cut-off frequency) and fMAX (maximum oscillation frequency). These figures-of-merit are usually extracted from calibrated S-parameter measurements affected by residual calibration and measurement uncertainties. Thus, the uncertainties associated to fT and fMAX can be evaluated only after an accurate computation of the S-parameters uncertainties, including the contribution from de-embedding. This was done with the aid of two recently released software tools. We also present an analysis on how different interpolation/extrapolation methodologies affect uncertainty. Finally, an overview of the possible causes of errors and suggestions on how to avoid them are given. With the continued rise of reported fT /fMAX values, this study has become necessary in order to add confidence intervals to these figures-of-meri

A W-Band On-Wafer Active Load-Pull System Based on Down-Conversion Techniques

A new W-band active load-pull system is presented. It is the first load-pull system to implement a 94 GHz load by means of an active loop exploiting frequency conversion techniques. The active loop configuration demonstrates a number of advantages that overcome the typical limitations of W-band passive tuners or conventional active open loop techniques in a cost effective way: load reflection coefficients Γ L as high as 0.95 in magnitude can be achieved at 94 GHz, thus providing a nearly full coverage of the Smith Chart. Possible applications of the setup include technology assessment, large-signal device model verification at sub-THz frequencies, and W-band MMIC design and characterization. The availability of direct and accurate load-pull measurements at W-band should prove an asset in the development of sub-THz integrated circuits. First measure- ments performed on high performance InP double heterojunction bipolar transistors (DHBTs) and GaN high electron mobility transistors (HEMTs) are presente