A Large Signal Model to Improve Linearity of Rf Power Amplifier

Abstract

Hetero-junction Bipolar Transistors (HBTs) have become very promising devices for power amplifier design in different communication applications. This paper proposes an analytical large signal model to predict nonlinear behavior of InGaP/GaAs HBT. The proposed model is directly fitted from linear model elements using Fourier transfer functions. As a consequence, the proposed large signal model shows good insight of circuit nonlinear behavior, and can be used to analysis large signal parameters of power amplifier. Based on the proposed large signal model, power gain and phase variation of an emitter follower amplify stage under different bias conditions have been analyzed. The calculated results show that: both gain and phase properties exhibit reverse deviation in saturation compared with that in forward amplify region, and can be used to maximize the linearity of power amplifier.