High-swing class-C VCO

By removing the tail current source of a class-C VCO, a high-swing VCO core has been introduced. The use of a transformer has added an additional degree of freedom so that a bias control circuit can adjust gate bias of the switching pair to a low voltage for the highest tank swing. High efficiency of class-C operation combined with high output swing led to a first class phase noise performance. The VCO oscillating at 5.11 GHz, draws 1.44 mA from a 0.6 V power supply. The measured phase noise is -127 dBc/Hz at 3 MHz offset frequency resulting in a FoM of 192.3 dB.