A CMOS RF Power Amplifier Using an Off-ChipIEEE MICROWAVE AND WIRELESS COMPONENTS LETTERS, VOL. 17, NO. 5, MAY 2007 385 A CMOS RF Power Amplier Using an Off-Chip Transmision Line Transformer With 62% PAE Jaemin Jang, Student Member, IEEE, Changkun Park, Haksun Kim, and Songcheol Hong, Member, IEEE Abstract―In this letter, a two-stage 900-MHz CMOS differential power amplier (PA) is designed and implemented in a 0.18- 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 ampliers are used as driver ampliers. The PA delivers an output power of 31.7 dBm and a power-added efciency of 62.4% with a power gain of 30.3 dB, including the losses of the bond-wires and ……