UC San Diego

This thesis is directed towards the development of a digitally-assisted radio frequency power amplifier (RF PA) which is one of the potential solutions to realize a multiband and multimode transmitter with high efficiency for handset applications. To improve efficiency and linearity in multiple conditions, PA circuits and digital signal processing (DSP) algorithms are co-designed. In the dissertation, a proposed architecture employs a current- mode class-D (CMCD) configuration for high efficiency, and a polar modulation scheme driven by digital inputs. Detail design, fabrication and experimental results are given for circuit implementation and DSP of this architecture. First, a multiband watt-class complementary metal-oxide- semiconductor (CMOS) PA is demonstrated using 0.15 um CMOS integrated circuits (ICs), off-chip inductor and balun. To obtain high breakdown voltage, stacked field effect transistors (FETs) are used. The CMCD PA is tuned by band- switching capacitors, operating in the 0.7-1.8 GHz frequency band. The overall efficiencies of 27.1 / 25.6 % are achieved at 30.2 / 28.9 dBm CW output powers and 0.85 / 1.75 GHz carrier frequencies, respectively. Next, to achieve wide output power dynamic range, an architecture consisting of small segmented unti-cells is introduced into the PA, where multiple three-state unit-cells are used and the state of each unit-cell is controlled to provide a specific output power. The overall dynamic ranges are expanded to approximately 90 dB and 85 dB at and 0.85 / 1.75 GHz, respectively. The dissertation then presents digital modulation algorithms. The digital compensation techniques are developed to maintain linearity of an envelope modulator of the polar transmitter. A new digital pulse width modulation algorithm is also shown to partially suppress spurious signals associated with the digital input envelope signal. When wideband code-division multiple access (WCDMA) modulation is implemented, spur suppression of 9-10 dB is achieved while maintaining adjacent channel leakage power ratios within 3rd generation partnership project specifications