Analysis of Parametric Oscillations in High Power Amplifiers

A large-signal analysis of sub-harmonic parametric oscillations in power amplifiers (PAs) is presented in this paper. Simplified models for current-voltage and channel charge characteristics of short-channel pseudomorphic high electron mobility transistors (pHEMTs) are adopted to investigate the effects of the device transconductance and gate-source capacitance nonlinearities on the amplifier stability. A 5-W Ku-band PA is designed to demonstrate application of the presented analysis. The MMIC PA is implemented in a 0.25-μm GaAs pHEMT process. Measurement results indicate that the PA features 37.5 dBm (5.6 W) average output power, 36% power added efficiency (PAE), and 18 dB average small signal gain.