VCO with 8-shaped Transformer Coupled Transmission-Line

This letter presents the design and measurement of a 3.4 GHz oscillator in the TSMC $0.18 \mu \mathrm{~m}$ 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 $1.2 \times 1.2 \mathrm{~mm}^{2}$. 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 $\mathbf{1 M H z}$ frequency offset is $\mathbf{- 1 2 5. 7 3}$ $\mathrm{dBc} / \mathrm{Hz}$ at the oscillation frequency of 3.4 GHz and the figure of merit (FOM) of the proposed QVCO is $\mathbf{- 1 8 5. 3 8 d B c / H z}$.