A 2.4-GHz, 2.2-W, 2-V fully integrated circular geometry power amplifier with 50Ω input and output matching is fabricated using 2.5V, 0.35μm CMOS transistors. It can also produce 450mW using a 1V supply. Harmonic suppression is 64dB or better. An on-chip circular geometry active-transformer is used to combine several push-pull low-voltage amplifiers efficiently to produce a larger output power while maintaining a 50Ω match. This new on-chip power combining and impedance matching method uses virtual ac grounds and magnetic couplings extensively to eliminate the need for any off chip component such as wirebonds. It also desensitizes the operation of the amplifier to the inductance of bonding wires and makes the design more reproducible. This new topology makes possible a fully-integrated 2.2W, 2.4GHz, low voltage CMOS power amplifier for the first time.