Switching-Converter-Only Multiphase Envelope Modulator With Slew Rate Enhancer for LTE Power Amplifier Applications

Abstract

With ever-growing energy crisis in wireless communication, effective envelope tracking solutions are in high demand for efficient operation of power amplifiers. Conventionally, a linear regulator is utilized to assist a switching converter to achieve fast tracking performance, but is highly inefficient. To overcome such an efficiency limitation, a dual-phase switching-converter-only topology is proposed in this paper. Synchronized adaptive voltage tracking control is introduced, which enables both clock synchronization and fast response for high-speed envelope tracking. To mitigate the inductor current slew rate limit of the switching converter, a push-pull slew rate enhancer (SRE) is designed. The SRE only operates when the switching converter reaches its inductor current slew rate limit, thereby maximizing the efficiency. The proposed envelope modulator is fabricated with a 0.18-μm CMOS process, achieving 85.8% peak efficiency at 1.5 W, tracking a 10-MHz LTE envelope.