Abstract: We propose a dual band CMOS power amplifier for mobile WiMAX systems.The power amplifier,combined with an active matching transformer,is fully integrated and fabricated in a 0.13μm CMOS process.The transformer operates at dual bands with active matching circuit.The measured result shows that the transformer efficiency of 78.2% and 70.4% at 2.5 and 3.5GHz are realized,respectively,and 26.5 and 24.8dB gain are achieved.The PAE reaches 20% and 28% at 2.5 and 3.5GHz,respectively.The third inter-modulation (IM3) is lower than -30dBc at the 25dBm average power.

Key words: RF CMOS, power amplifier, transformer, WiMAX