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This letter presents an injection-locked CMOS power amplifier for pulse width modulation (PWM) digitized polar transmitter. A power oscillator combined with injection-locking technique reduces the required driving power and provide high drain efficiency in the power stage. The switched power oscillator is proposed for PWM digitized polar transmitter. To achieve differential to single output and impedance transformation, a lumped element balun, employing a minimum number of discrete components, is used. The power amplifier achieved a power-added efficiency of 70.7% at a maximum output power of 29.05 dBm. The measured drain efficiency in the power stage was 72.7% at 820 MHz. The chip is implemented with a 0.18 μm CMOS process. The total chip size is 0.48 mm2.