15.1 An 88%-Efficiency Supply Modulator Achieving 1.08μs/V Fast Transition and 100MHz Envelope-Tracking Bandwidth for 5G New Radio RF Power Amplifier

In the recent 3GPP standard, 5G New Radio (NR) in the sub-6GHz frequency band supports up to 100MHz bandwidth (BW) for uplink channel and requires fast on/off transition below $10 \mu \mathrm {s}$ to support short transition-time interval (TTI). Thus, it forces the supply modulator (SM) to track the NR-100MHz envelope signal for power saving of an RF power amplifier (RF-PA) and requires a fast dynamic voltage-scaling (DVS) transition. For the 3G/LTE uplink, the SM has to satisfy low receiver-band noise (RxBN) for LTE-FDD bands [1] and a boosted output for Power Class 2 high-power user equipment (HPUE) in TD-LTE [2], [3]. In order to support the 100MHz envelope tracking (ET) BW, the SM must have a 3dB bandwidth of at least 125MHz while keeping sufficient phase margin in the presence of few-hundred-pF load capacitance. Furthermore, a typical linear-assisted SM topology has maximum efficiency limitation due to the AB bias current, sinking- and sourcing-current of the linear amplifier. In this work, a voltage-buffer-compensated (VBC) Class-AB linear amplifier (LA) and a feed-forward fast-switching (FFFS) buck converter are proposed to achieve the 100MHz ET BW and high system-power efficiency.