A study of capacitor-coupled varactor VCO to investigate flicker noise up-conversion mechanism

CCV-VCO (capacitor-coupled varactor VCO) has been studied with a view to suppressing flicker noise up-conversion. The mechanisms of flicker noise up-conversion to f/sup 3/ phase noise utilize three paths; direct modulation, folding by non-linearity of oscillation, and tail current up-conversion at common node. Designed NMOS-VCO satisfied to avoid f/sup 3/ phase noise by direct modulation pass. Measured phase noise at 10 kHz offset from carrier was -74 dBc/Hz at 2.9 GHz oscillation frequency, and the corner frequency between f/sup 3/ phase noise and f/sup 2/ phase noise was approximately 20 kHz. The current consumption was 6 mA with 1.8 V. The 1 MHz FOM of VCO was 182 dB and 10 kHz FOM of VCO was 173 dB.