Voltage-Controlled-Oscillator Using an 8-shaped Transformer-coupled Transmission Line

This letter presents a 3:1 8-shaped transformer used to form an 8-shaped transformer-coupled transmission line consisting of four back-to-back connected transformers. The stacked transformers form a closed loop. By placing cross-coupled inverter pairs in the loop, a VCO is built. The die area of the VCO in the TSMC 0.18 mu m CMOS process is 1.2x1.2 mm(2). The measured phase noise of the eight/four-phase VCO at 5.43 GHz is -114.82 dBc/Hz and the VCO figure of merit (FOM) is -180.128 dBc/Hz. The wave on the loop is a traveling wave. The 8-shaped transformer reduces magnetic field coupling and limits the Electro-Magnetic Compatibility (EMC) issue.