Asymmetric multilevel outphasing transmitter using Class-E PAs with discrete pulse width modulation

Abstract

We present a high-efficiency transmitter architecture based on asymmetric multilevel outphasing (AMO), but with a new method of generating discrete amplitude levels from the constituent amplifiers. AMO and multilevel LINC (ML-LINC) transmitters improve their efficiency over LINC by switching the supplies of the power amplifiers (PAs) among a discrete set of voltages. This allows them to minimize the occurrence of large outphasing angles. However, it is also possible to generate a discrete set of amplitudes by varying the duty cycle of the waveform that drives the PAs. The chief advantage of this discrete pulse width modulation (DPWM) is hardware simplicity, as it eliminates the need for a fast, low-loss switching network and a selection of power supply voltages. We demonstrate this concept with a 48-MHz, 20-W peak output power AMO transmitter using a four-level DPWM. At peak output power, the measured power-added efficiency is 77.7%. For a 16-QAM signal with a 6.5-dB peak-to-average power ratio, the AMO prototype improves the average efficiency from 17.1% to 36.5% compared to the standard LINC system.