An Investigation of Efficiency Limiting Mechanisms in GaAs MESFET Amplifiers

An advanced large signal, physics based MESFET model is used to investigate the effects of gate-drain breakdown on high efficiency amplifier operation. As the drain bias relative to breakdown and the input power drive level are varied, the device input and output impedances shift causing impedance matching difficulties. Optimal tuning and bias for high efficiency operation can be achieved by modification of the position of the dynamic load line relative to the MESFET breakdown characteristic. In this manner the maximum achievable efficiency is obtained. Harmonic tuning is confirmed to be critical for obtaining maximum efficiency.