A DETERMINISTIC APPROACH FOR DESIGNING CONDITIONALLY STABLE AMPLIFIERS

Microwave devices with the Rollet parameter (k) less than one can alwa ys be made stable by resistive loading. In cases where noise figure or output power is at a premium, the performance of an amplifier can oft en be enhanced by using a design where k is less than unity thereby av oiding resistive loading. While a simultaneous conjugate match is impo ssible for such conditionally stable designs, single-sided matching ca n be achieved. Low-noise and power designs are examples where single-s ided matching considerations naturally occur, With single-sided matchi ng and 0 < k < 1, a design method is presented that results in device impedances on both the matched and unmatched sides that are always ins ide the Unit Smith Chart, This condition is referred to as jointly (in put/output) stable. Gains resulting from jointly stable terminating im pedances are shown to be bounded, the upper bound being given by 2 . k . maximum stable gain. The design on an output-matched, conditionally stable amplifier is illustrated.