Bandwidth Enhancement of Frequency Dispersive Doherty Power Amplifier
Hao-Yu Liu, Xiaohu Fang, Kwok‐Keung M. Cheng
Abstract
This letter presents a modified Doherty power amplifier (DPA) combining network with wide bandwidth (BW) and high power utilization factor (PUF). For the first time, the impact of the excessive phase dispersion of matching networks on the performance of conventional broadband DPA is analytically revealed. For dispersion compensation, an optimized adaptive combining load is introduced to enhance the achievable DPA BW and PUF. For verification, a 42-dBm equal-cell DPA is prototyped to cover 1.4-2.55 GHz. Measurement results indicate that, over the prescribed frequency range, a PUF of over 0.95, back-off efficiency (6 dB) of 48%-58%, and saturation efficiency of 62%-74% can be achieved. Moreover, under WCDMA excitation, the adjacent channel leakage ratio (ACLR) was found to be better than -32 dBc with average efficiency of over 45% without applying digital predistortion techniques.