Low-Voltage Quadrature Voltage-Controlled-Oscillator Using Twisted Transformer

For low supply voltage operation, the voltage-controlled oscillator (VCO) with low voltage swing is subject to the injection pulling effect. This letter presents a low-voltage CMOS four-phase VCO using two differential LC VCOs coupled by two cross-coupled transformers. The proposed oscillator mitigates the injection-pulling effect by the 8-shaped transformers with two lobes. The transformers cancel the interference noise coupling and offer a drain-to-source transformer feedback to swing the source voltage to below ground level and to increase the voltage swing. The die area of the quadrature voltage-controlled oscillator (QVCO) in the TSMC $0.18~\mu \text{m}$ BiCMOS process is $1.2\times0.963$ mm2. At the supply of 0.49 V, the oscillation frequency of the QVCO is 4.49 GHz and the figure of merit (FOM) is -187.032 dBc/Hz.