A wideband CMOS Power Amplifier（PA）operating from 700 MHz to 3GHz with 23.6dBm maximum output power is presented in this paper.The PA consists of a single-stage amplifier with fully differential cascode topology.On-chip transformers paralleled with switched-capacitors are applied in the input and output of this PA.The wideband input and output matches are realized by digitally controlling the states of switches to change the value of capacitors

while tuning the operating frequency of this PA to realize wide range operation.This wideband PA including on-chip transformers is designed based on TSMC 0.18μm CMOS model and simulated using Agilent’s ADS.Layout’s post-simulation results indicate that the input match S11 is perfectly matched（less than-10dB）from 700 MHz to 3GHz and the gain of S21 reaches 27dB at 1.7GHz with only 0.75mm2 chip area.