A 1.8GHz linear CMOS power amplifier with supply-path switching scheme for WCDMA/LTE applications

Low-cost CMOS PAs for mobile terminals have been a focus of attention in recent years. Self-contained, linear CMOS PAs are particularly attractive for smooth replacement of conventional compound semiconductor PA products. The main challenge concerning the linear CMOS PAs is to improve their power efficiency. Doherty PAs improve the average power efficiency by means of backoff efficiency boosting; however, their applicable carrier frequency range is narrow owing to the high-order output network. Supply modulation is another technique to improve the PA back-off efficiency. Although hybrid modulators have been studied for CMOS polar transmitters [1,2], none of them have satisfied full specs of modulation bandwidth and the output power for 4G cellular applications. The area overhead is also unacceptable for application to a self-contained linear PA. A class-G supply modulator relaxes the limitations by receiving external, discrete levels of supply voltages [3]. However, it still requires a costly extra DC-DC converter for multilevel supply voltages.