DSP techniques for linearity and efficiency enhancement of multi-band envelope tracking transmitters

Due to the increasing demands for large capacity and high performance wireless transmitters, multi-band transmitter architectures play an important role in modern communications. Thus, advances in the design techniques of radio frequency (RF) power amplifiers (PAs) have promoted the use of a single multi-band PA and RF components in order to concurrently process multiple input signals located in different frequency bands. In this paper, digital signal processing (DSP) techniques for linearity and efficiency enhancement of multi-band envelope tracking (ET) transmitters are discussed. A two-dimensional digital predistortion (2D-DPD) is used for linearization of the dual-band PA around each band separately, relaxing the high speed requirements needed by wideband DPD. Power efficiency enhancement of the dual band PA is accomplished by adopting bandwidth reduced envelope shaping functions that depend on the original envelopes of the two concurrent signals driving the PA, which provides a good compromise between efficiency and linearity. The proposed architecture is experimentally validated where linearization and efficiency enhancement results are presented.