Analytical Design Method for a Low-Distortion Microwave InGaP/GaAs HBT Amplifier Based on Transient Thermal Behavior in a GaAs Substrate

Based on the transient thermal behavior in a GaAs substrate, the distortion caused by the self-heating effect in an InGaP/GaAs heterojunction bipolar transistor (HBT) has been analytically compensated. The temperature-time variation in a transistor depends on the thermal characteristics of a semiconductor substrate at the base-band range. For a wideband digital modulated signal as input, a multistage thermal resistor-thermal capacitor ladder circuit is used as a model to emulate the thermal characteristics. The distortion analysis is based on Taylor and Volterra series expansion techniques including both electrical and thermal effects. In addition, a compensation condition for the distortion caused by the thermal influence is also successfully derived based on distortion analysis. The validity of the proposed analytical method is shown for an InGaP/GaAs HBT power amplifier operating at 1.95 GHz. The analytical design results are in good agreement with the measured results.