A High-Efficiency Two-Stage GaAs HBT Doherty Power Amplifier With Thermal Compensation for WLAN Application

In this paper, a high-efficiency Doherty power amplifier (DPA) using an InGaP/GaAs heterojunction bipolar transistor (HBT) process is presented. The DPA aims for the application of 2.4 GHz wireless local area network (WLAN) systems with a high peak-to-average power ratio (PAPR). The traditional bulky quarter-wavelength line is realized using a low-pass n-type network for miniaturization and low loss. A thermally compensated dynamic bias circuit is applied to increase thermal stability. Under the excitation of a 40-MHz 64-quadratic-amplitude modu-lation(QAM) signal, the proposed DPA achieves a gain of 29 dB gain, an average power of 26 dBm, and an average power added efficiency (PAE) up to 21%. Good error vector magnitude (EVM) and adjacent channel leakage ratio (ACLR) performance are also measured, which demonstrates EVM and ACLR after digital pre-distortion (DPD) are -42 dB and -50.7 dBc. respectively.