Asymmetrically-driven current-based chireix class-F power amplifier designed using an embedding device model

Model-based nonlinear embedding is applied for the first time to the design of an asymmetrically-driven class-F Chireix power amplifier (PA). The embedding model of a 15 W GaN HEMT is used to determine the optimum load impedances for the fundamental and multi-harmonics required at the package reference planes such that the two intrinsic transistors operate with a recently reported ideal current-based Chireix combiner. A symmetric circuit topology is used so that the phase offset of the Chireix combiner is maintained through the design from the intrinsic and packaged nodes up to the drive generators. Unlike the conventional Chireix PA, which is driven with constant envelope signals, this PA designed using embedding is found to require asymmetrical amplitude and phase modulated input drives to support the targeted equal-power input signals at the intrinsic reference planes. The Chireix PA designed exhibits a peak drain efficiency of 79.6 % and power added-efficiency (PAE) over 77/71% around peak power (43/44 dBm) and 55% at 8dB backoff power (36dBm) at 2 GHz as measured with a large-signal network analyzer (LSNA). Using a lookup table driver, the PA average drain efficiency is 50% for a 5 MHz W-CDMA signal with 9.3 dB PAPR and -41.5 dBc ACPR achieved.