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In recent years, there has been tremendous interest in trying to implement the power amplifier in CMOS, due to its cost and integration benefits. Most of the high power (watt-level) CMOS PAs reported to date have not exhibited sufficient linearity required for next generation wireless standards. In this paper, we report a single-chip linear CMOS PA with sufficient power and linearity for emerging OFDM-based 4G WiMAX applications. This 90 nm 2.4 GHz CMOS linear power amplifier uses a two-stage transformer-based power combiner and produces a saturated output power of 30.1 dBm with 33% PAE and 28 dB small-signal gain. A novel bypass network is introduced to ensure stability without sacrificing gain. The choice of optimal biasing and capacitive compensation produces very flat AM-AM and AM-PM response up to high power. The PA has been tested with OFDM modulated signal and produces EVM better than -25 dB at 22.7 dBm average power. Graceful power back-off is demonstrated through turning off one of the stages, allowing low-power operation with enhanced efficiency.