A Coupler-Based Differential Doherty Power Amplifier with Built-In Baluns for High Mm-Wave Linear-Yet-Efficient Gbit/s Amplifications

Abstract

We propose a Doherty power amplifier architecture with impedance inverting balun and impedance scaling balun to support Doherty active load modulation and Power Back-Off (PBO) efficiency enhancement at high mm-Wave frequencies. Unlike transformer baluns often used at RF frequencies, mm-Wave coupler-based baluns are employed to provide well balanced differential-to-single-ended conversion and absorb device output parasitic capacitance. Moreover, this paper reports that coupler-based balun with 45° electrical length exhibits impedance inverting behavior, which is utilized to construct Doherty active load modulation network in the reported PA design. Adaptive biasing circuit further enhances the Main/Auxiliary PA cooperation. The measured Doherty PA exhibits 20.1dBm Psat, 19.3dBm P1dB, and 26% peak PAE. At 7dB PBO, the measured PAE is 16.6%, demonstrating 1.45× efficiency enhancement compared to an ideal class-B PA with the same peak PAE at P1dB.