NovelInstability-Prob ing Simulation forPowerAmplifiers

A novelinstability-probing simulation forpower amplifiers ispresented. Instabilities ofpoweramplifiers withuseof very-high performance pHEMT should beobserved fromasingle- gatepHEMT amongthemulti-gate configuration ofthepHEMT, wherethepoweramplifiers arenotyetsymmetric. A conventional orthogonal (even- andodd-) modeanalysis, basedonthesymmetric powercombining, isnotcomplete topredict various instabilities in thepoweramplifiers. Thispaperdemonstrates anovelinstability- probing simulation methodthatincorporates anideal transformer. The proposedmethodsuccessfully predicted microwave and millimeter-wave spurious oscillations observed fora Ku-band MMIC poweramplifier. IndexTerms-spurious oscillation, probing, poweramplifiers, multi-gate pHEMT. I.INTRODUCTION