1.8-GHz CMOS Power Amplifier with Stage-Convertible Structure Using Differential Line Inductor

A 1.8 GHz power amplifier for a polar transmitter application is implemented with 0.18
μ
m RF CMOS technology, and a differential line inductor is proposed for the differential circuit. The differential line inductor is used as a low power matching network in the stage-convertible power amplifier in order to increase the efficiency of a low output power region. The power amplifier achieved a power-added efficiency of 41% at a maximum output power of 31.5 dBm. The low power efficiency improvement for the power amplifier is 81% at an output power of 20 dBm.