A fully integrated CMOS differential power amplifier driver(PAD) is proposed for WiMAX applications. In order to fulfill the differential application requirements,a transmission line transformer is used as the output matching network.A differential inductance constitutes an inter-stage matching network.Meanwhile,an on chip balun realizes input matching as well as single-end to differential conversion.The PAD is fabricated in a 0.13μm RFCMOS process.The chip size is 1.1×1.1 mm~2 with all of the matching network integrated on chip. The saturated power is around 10 dBm and power gain is about 12 dB. A fully integrated CMOS differential power amplifier driver (PAD) is proposed for WiMAX applications. In order to fulfill the differential application requirements, a transmission line transformer is used as the output matching network. A differential inductance constitutes an inter-stage matching network. , an on chip balun realizes input matching as well as single-end to differential conversion. The PAD is fabricated in a 0.13 μm RFCMOS process. The chip size is 1.1 × 1.1 mm ~ 2 with all of the matching network integrated on chip. saturated power is around 10 dBm and power gain is about 12 dB.