A CMOS RF Power Amplifier Using an Off-Chip Transmision Line Transformer With 62% PAE

In this letter, a two-stage 900-MHz CMOS differential power amplifier (PA) is designed and implemented in a 0.18- $\mu$m radio frequency CMOS process. A transmission line transformer on a printed circuit board is used as an output power combiner and matching circuits of a class-E power stage. To drive the power stage effectively, cascaded class-D amplifiers are used as driver amplifiers. The PA delivers an output power of 31.7 dBm and a power-added efficiency of 62.4% with a power gain of 30.3 dB, including the losses of the bond-wires and the output transformer.