Efficiency improvement in nanometre CMOS outphasing power amplifiers

The outphasing transmitter is one such technique that warrants research as it has yet to achieve commercial viability. It operates by decomposing a modulated signal into two constant-amplitude signals with a phase difference corresponding to the normalised envelope amplitude, amplifying them with high-efficiency PAs, and then summing them to reconstruct the envelope.<br><br>Silicon is a promising semiconductor for outphasing as the signal processing circuitry and PA can reside on the same die however silicon PAs suffer from low output power due to the sub-1V supply voltages and lossy passive components.

This thesis focuses on improving the design of CMOS outphasing PAs which utilise unisolated power combiners and switched-mode voltage-source PA stages.<br><br>Power combiner design is advanced with the creation of two novel three-port coupled coils which allow multiple inductors to be merged into a single compact low-loss structure. Four Wilkinson power combiners were fabricated to demonstrate and evaluate the coupled coils with one combiner requiring only three components by harnessing resistive coil parasitics.<br><br>The most popular voltage-source CMOS PA, the complementary Class-D, suffers from shoot-through current losses where the supply voltage is shorted to ground during switching.