Low-Pass Filter-Based Baseband Impedance Control Circuit for Broadband Concurrent Doherty Power Amplifier

Abstract

The baseband impedance has a significant effect on the drain efficiency (DE) of a concurrent power amplifier (PA). In this letter, a low-pass filter-based baseband impedance control circuit (BICC) is proposed for improving the concurrent efficiency of a broadband Doherty PA (DPA). The proposed BICC provides the carrier and peaking PAs with a low baseband impedance over a wide frequency range. Moreover, to extend the high-efficiency power range, asymmetrical drain bias voltages are applied to the carrier and peaking transistors. As a validation, a 1.8–2.1-GHz asymmetrical-biased DPA is implemented and measured in this work. When the fabricated DPA is stimulated by a balanced 1.8/2.1-GHz concurrent signal, it achieves a maximum concurrent output power of 40.3 dBm with a DE of 52.4%. At the 8-dB output back-off (OBO) power level, the measured concurrent DE is 47.8%.