Application specific design methods of RF CMOS power amplifier for power-efficient transmitter

Abstract

The efficiency of PA is one of the most important characteristics in mobile or battery-powered wireless communications system. Unfortunately, any common efficiency enhancement approach does not lead to the improvement of efficiency in every application. Therefore, the method specified to a given application should be developed to improve the overall system efficiency maximally. In this dissertation, we have investigated the efficiency improvement of the CMOS PAs in the specified applications; Class-E CMOS PAs in wireless sensor network (WSN) applications and high-power linear CMOS PAs in non-constant envelope modulation schemes such as QPSK and QAM. It is challenging to achieve a high transmit efficiency in such a low transmit-power application as WSN because power consumptions in the former stages of PA are no more negligible compared with the transmitted signal power and hence severely degrade the overall efficiency. The proposed injection-locked Class-E PA (Class E 1LPA) is based on the Class-E power oscillator and injection locking concept. Since the injection-locking requires only small signal input into a Class-E power oscillator, the demand on high driving capability in the preamplifier is no longer necessary. And we can minimize the driving power as well as the DC power consumption in preamplifier, while maintaining the final power stage fully driven with high drain efficiency (DE). The 2.4GHz Class-E ILPA with the inverter preamplifier fully integrated on the 0.18㎛ CMOS process achieves PAE of 44.5%, while delivering the output power of 11dBm with 49.3% drain efficiency at 1.2V supply voltage. It shows the efficiency improvement of approximately 13% compared with the conventional Class-E PA. The power-efficient injection-locked (sub-harmonic injection-locked) transmitters were fabricated based on the proposed Class-E ILPA. With 1 V supply voltage, the fabricated injection-locked transmitter achieves the overall TX efficiency of 42.3%, while delivering ...