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This paper presents a CMOS RF amplitude detector as a practical integrated test device and demonstrates its application for on-chip testing. The proposed circuit performs full-wave rectification and generates a dc voltage proportional to the amplitude of an RF signal over a wide frequency range. The design considerations and analysis of operation for the employed class-AB rectifier are described. Fabricated in a standard 0.35-mum CMOS process, the RF detector uses only 0.031 of area and presents an equivalent input capacitance of 13 fF. Measurements show that this RF test device has a detection dynamic range of 30 dB from 900 MHz to 2.4 GHz. Experimental results for the application of the RF amplitude detector in the built-in measurement of the gain and compression of a 1.6-GHz low-noise amplifier fabricated in the same chip are also presented.