A Class-C voltage-control-oscillator (VCO) IC with an amplitude feedback loop for ultra-low-voltage application is proposed. The Class-C VCO consists of an LC-VCO circuit and an amplitude feedback loop to shift LC-VCO bias condition from initial Class-AB start-up to steady Class-C low current oscillation. The amplitude feedback loop is formed by a detector and a comparator with low voltage supply. The LC-VCO IC has been designed, fabricated and fully evaluated using 65-nm CMOS technology. The fabricated Class-C VCO IC exhibits a measured phase noise of -111 dBc/Hz at 1 MHz offset from the 2.43 GHz carrier frequency at a supply voltage of only 0.3 V.
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