A 4.4-GHz 193.2-dB FoM 8-Shaped-Inductor Based LC-VCO Using Orthogonal-Coupled Triple-Coil Transformer

A 4.2-to-4.6 GHz 8-shaped-inductor based LC-VCO with an orthogonal-coupled triple-coil transformer is presented in this brief. The orthogonal-coupled triple-coil transformer is designed to reduce magnetic coupling and improve phase noise. The mutual inductance between the 8-shaped inductor and the tail-filtering inductor is negligible due to the symmetrical and reversal magnetic field generated by the two loops of the 8-shaped inductor, which avoids the additional chip area occupation of the bulky tail-filtering inductor. In addition, an 8-shaped transformer with thin line width is proposed to bias the varactor instead of using resistors, which avoids the resistor thermal noise contribution. The VCO is implemented in a 180 nm CMOS process, which consumes 7.4 mA current from a 1 V power supply. By adopting the 8-shaped inductor with noise filtering and noise-free biasing technique from the orthogonal-coupled triple-coil transformer, the measured phase noise achieves -149.3 dBc/Hz at 10 MHz offset away from a 4.3 GHz carrier and the resulting figure-of-merit (FoM) is -193.2 dB. To the best knowledge of the authors, this brief presents the VCO with the best FoM among published 8-shaped-inductor based LC-VCOs.