A Hybrid Supply Modulator for 10-MHz LTE Power Amplifier with 17.3% PAE Improvement

Abstract

A hybrid supply modulator (HSM) is proposed for the envelope-tracking power amplifier (ET-PA) to improve its power- added efficiency (PAE). The proposed HSM consists of a linear amplifier (LA) and a switching amplifier (SA). The LA adopts a current-recycling OTA (CROTA) followed by an IQ-controlled class- AB output stage. The CROTA enhances gain and slew rate of the LA first stage. In the class-AB output stage, the quiescent current (IQ) is regulated to reduce its sensitivity to process and supply variations. The SA employs a zero-peaked hysteresis comparator for switching control, which reduces the time delay of the SA control loop, and leads to better power efficiency. Measurement results shows that the HSM reaches 75.2% efficiency at 29.3-dBm output power. When tested with a commercial PA, the PAE improves by 17.3% at 22-dBm RF output power with 34.9-dB power gain.