Efficiency optimization in linear-assisted switching power converters for envelope tracking in RF power amplifiers

Linear-assisted switchers are based on the idea of combining high efficiency of switching converters with wide-bandwidth capabilities of linear amplifiers. Such linear-assisted switching power converters have been proposed for implementation of wide-bandwidth envelope-tracking power supplies for RF power amplifiers in polar modulation architectures. This paper presents modeling of the overall linear-assisted switcher efficiency as a function of the band separation frequency between the signals processed by the switching and the linear parts. The efficiency model, which is based on the statistical amplitude distributions of the signals, is used to derive the optimum band separation frequency to maximize the overall efficiency. Application examples, including a two-tone test and a CDMA signal in a polar modulation RF transmitter, are presented to illustrate the approach.