Low Phase Noise Concurrent Dual-Band (5/7 GHz) CMOS VCO Using Gate Feedback on Nonuniformly Wound Transformer

A novel low phase noise concurrent dual-band complementary metal-oxide-semiconductor (CMOS) voltage-controlled oscillator (VCO) employing a gate-feedback enabled, nonuniform multiwinding transformer is proposed. The transformer consists of the wide-width looped main inductors and surrounding narrow-width looped feedback inductors, featuring a high degree of design freedom, owing to its controllable width, gap, and coupling coefficients. This novel topology enables both simultaneous and independent oscillation in two frequency bands using the main inductors with oscillation cores. In addition, the resonant tank's noise contribution can be reduced by boosting the loaded quality factor using gate-driving feedback inductors. The proposed VCO was fabricated in a 0.28- \mu \text{m} silicon on insulator (SOI) CMOS process. The measured results show concurrent oscillation from 4.6 to 5.6 GHz and 6.1 to 7.4 GHz with phase noise of −119.3 and −120.1 dBc/Hz at 1 MHz offset, corresponding to a figure-of-merit (FOM) of −184.4 and −185.1, whereas the FOM for low-band and high-band single-tone oscillation is −182.7 and −184.8 dBc/Hz, respectively. Finally, the FOM of the proposed VCO is compared with that of similar size concurrent dual-band VCO devices previously presented in literature.