Saturated PAs for High Efficiency: Operation of Saturated Amplifiers Having the Optimum Voltage Waveform to Achieve Maximum Efficiency

Abstract

High efficiency is a crucial design consideration. This is true not only for power amplifiers (PAs), but also for transmitters such as the Doherty PA and the supply-modulated PA, due to thermal management, reliability, and size [1]-[3] issues. Several PA topologies, e.g., class E, class F, and class F-1, have been proposed to achieve high efficiency [3]-[17]. In the class-E PA, a transistor acts as a switch, which has very low loss. The voltage of the class-E amplifier is supported through the charging and discharging of a transistor's output capacitor, which is parallel with the switch. Because this amplifier tunes all the harmonic components using the LC resonator, it delivers the highest efficiency among the proposed amplifiers. The capacitor's charging step, however, cannot be abrupt; above the theoretical maximum frequency fmax,E, the capacitor cannot be discharged quickly enough to support the ideal waveform [3], [4]. As a result, the efficiency of the class-E PA is significantly degraded at a frequency above fmax,E [3]-[6]. Also, the power density of the class-E amplifier is low because of the low content of the fundamental voltage component.