A 0.8-V CMOS quadrature LC VCO using capacitive coupling

A new concept for quadrature coupling of LC oscillators is introduced and demonstrated in a 4.5-GHz CMOS quadrature voltage-controlled oscillator (QVCO). By employing cupacitivc coupling of second harmonic components, quadrature outputs can be obtained at a low supply voltage without extra power consumption. Fabricated in a 0.13 mum CMOS process and operated at 0.8-V supply, the proposed QVCO measures phase noise of-112dBc/Hz at 1M offset from -1.91GHz while drawing a total current of 4mA, which corresponds to a FOM of 181 dB. The core area is 0.278mm².