Analysis and design consideration of hybrid supply modulator for envelope tracking power amplifier

Hybrid supply modulator consisting of parallel operation of a linear amplifier and a switching amplifier is often used in envelope tracking power amplifier systems to improve power efficiency at different back-off levels. This paper features a detailed analysis of current slew rate of hybrid supply modulator, which is lacking in many papers. Based on this slew rate analysis, one new methodology to accurately distinguish between supply modulator´s two operation regions is proposed. In addition, theoretical analysis of operation principle for the two regions and practical design considerations are included as well. An example hybrid supply modulator was implemented and simulated in 65nm CMOS technology, and it achieves a maximum efficiency of 83.5% with ripple error less than 3.5mV when tracking a 20MHz envelop signal.