Envelope-tracking common-drain CMOS power amplifier with a switching-only supply modulator for LTE applications

This paper proposes an integrated envelope tracking CMOS power amplifier for LTE application. It is shown in the paper that a common-drain power amplifier has improved linearity performance and less switching-ripple leakage of the supply voltage, as compared to its common-source counterpart. Hence, the proposed envelope tracking power amplifier is designed with a common-drain structure and post-simulated in a 0.18 μm CMOS process. By utilizing the common-drain structure, the supply modulator can be implemented using a switching-only regulator, and neither a linear regulator nor a hybrid technique is required. For a signal at 1.85 GHz with a 5-MHz bandwidth and 6.5 dB PAPR, the CMOS envelope tracking power amplifier achieves a power added efficiency of 30% and an Adjacent Channel Leakage Power Ratio (ACLR) of −32 dBc at an average output power of 22 dBm. By employing envelope tracking technique, the power added efficiency is improved by up to 5 dB, as compared to that of the stand-alone power amplifier.