Design and Optimization of a Highly Linear Power Amplifier with Novel Active Bias Circuit in InGaP/GaAs HBT MMIC Technology

Abstract

This paper introduces a highly linear power amplifier (PA) that utilizes a 2-μm InGaP/GaAs hetero-junction bipolar transistor (HBT) process. As communication systems evolve in complexity, the demands for the linearity and static power consumption of HBT power amplifiers are becoming more stringent. Typically, there exists a trade-off relationship between linearity and static power consumption in the design process. Hence, this paper proposes a novel active bias circuit for HBT power amplifiers, along with its layout design. The proposed active bias circuit consists of a differential pair and a current mirror structure, designed to enhance PA linearity while maintaining low quiescent current. Additionally, a novel layout structure is implemented to achieve thermal coupling between the RF transistors and the active bias, further improving PA linearity. As a result of the implementation of the proposed active bias and layout structure, the PA demonstrates high linearity in both amplitude modulation to phase modulation (AM/PM) and amplitude modulation to amplitude modulation (AM/AM) performance, while simultaneously maintaining a low quiescent current. The three-stage PA prototype achieves notable performance metrics, including a peak gain of 32.6 dB at 5.6 GHz, gain flatness of ±0.5 dB from 5.15 GHz to 5.85 GHz, and P1dB of 32.1 dBm at a quiescent emitter current of 180 mA.