A class-C VCO IC with an amplitude feed-back loop for ultra-low supply voltage is designed, fabricated and fully evaluated in 65-nm CMOS technology. The class-C VCO IC consists of an LC-VCO and a feedback loop to shift VCO bias condition from class-AB start-up to class-C steady-state. The feedback loop includes a power detector and a comparator.
The VCO IC has exhibited 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. The frequency tuning range is from 2.25 to 2.48 GHz.