Recombination of Envelope and Phase Paths in Wideband Polar Transmitters

We investigate the recombination of discrete-time envelope and phase/frequency components of a polar transmitter, which is based here on an all-digital phase-locked loop (ADPLL) with wideband modulation capability and a digitally controlled power amplifier (DPA). A unified discrete/continuous-time analysis is introduced for the development of the interpolative transfer characteristics of the envelope and phase paths that allows their recombination to be studied in the continuous-time domain of the DPA radio-frequency output. The nonlinear recombination of the polar components in the DPA is analytically investigated in the context of a proposed characterization technique that utilizes single-tone envelope and phase signals, and conclusions on the optimal architecture of a wideband ADPLL-based polar transmitter are drawn. The harmonic distortion results obtained in the context of the proposed characterization technique effectively highlight the performance of the polar transmitter when it is driven with the wideband baseband envelope and phase-modulating signals of today's high-data-rate digital communication systems, such as wideband code-division multiple access and beyond.