Nonlinear Analytical Model for Switched-Capacitor Class-D RF Power Amplifiers

This paper presents a nonlinear analytical model for an inverter-based switched-capacitor Class-D RF power amplifier (SCDPA). The root causes of the SCDPA AMAM and AMPM nonlinearities are studied. The major factors affecting SCDPA nonlinearities are identified as the unequal on-resistances of selected cell and unselected cell. Specifically, time-varying resistance of the switch, different transistor responses during the transition and parasitic resistance on the supply path (IR drop) are analyzed. Then, the system-level result, like EVM and power spectral density, can be obtained with nonlinear behavior of PA. The results of model calculation, schematic simulation, and measurement are presented and compared with validate the model both on transistor level and system level. This paper, for the first time, provides an accurate design guidance to enable fast architecture study and quick circuit-level prototype with close-to-optimum component initial parameters. It can be expanded to more architectures, therefore helps to pave the path to future design automation for highly linear SCDPAs.