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A self-biased low-power CMOS power detector (PD) is proposed and demonstrated in this paper. The detector utilizes the nonlinear characteristics of short-channel MOS devices operating in either a saturation or subthreshold regime to generate a dc current that is proportional to the input RF signal power. The operating regimes of MOS devices depend on input RF power levels. A quasi-T-coil matching network providing 50- matching from 0.5 to 20 GHz is designed and analyzed. An embedded amplifier is added to enhance the sensitivity of the PD when the input power level is low. The circuit that is implemented in a 0.13- CMOS process occupies an active area of 0.085 . In the matched frequency range, the measured input dynamic range is 47 dB with an overall sensitivity of 26.8 mV/dB. The output dc voltage response is nearly frequency-independent in the linear operating range, varying by less than 1.9 dB for a given input RF power level, as the RF frequency is swept across the operating frequency range. With a standard 1.2-V supply, the static power consumption is about 0.1 mW, which decreases to with a 0.5-V supply, while the operating frequency remains unchanged.