VCO with 8-shaped Transformer Coupled Transmission-Line

This letter presents the design and measurement of a 3.4 GHz oscillator in the TSMC 0.18 mu m CMOS technology. The fully integrated oscillator consists of four sub-oscillators and uses four twisted transformers with the secondary inductors connected to form a twisted closed-loop transmission line for coupling the sub-oscillators. The fully-integrated chip occupies a die area of 1.2 x1.2 mm(2). The transformers are configured as 8-shaped structures to minimize the far-field magnetic field radiation from each transformer and the whole transformer. At the supply voltage of 1.7 V, the current consumption is 11.32 mA. The free-running oscillation frequency of the QVCO is tuneable. The measured phase noise at 1MHz frequency offset is -125.73 dBc/Hz at the oscillation frequency of 3.4 GHz and the figure of merit (FOM) of the proposed QVCO is -185.38dBc/Hz.