A Class-C Eight-Phase Voltage-Controlled Oscillator With 184.2 dBc/Hz FoM and Loop-Based Superharmonic Coupling in 65-nm CMOS

This brief presents the design and implementation of a class-C eight-phase voltage-controlled oscillator (VCO) with loop-based superharmonic coupling (LBSC). By inserting a series inductor in the control core, LBSC works as a ring oscillator and the second-harmonic common-mode (CM) nodes of the four VCO cores are forced to lock orthogonally, which contributes to eight-phase generation. This represents a significant improvement over conventional superharmonic coupling which is limited to generating only quadrature phases. Furthermore, the application of class-C technology achieves a remarkable increase in energy efficiency ratio (EER) and significantly suppresses flicker noise by removing the tail current transistor. The proposed VCO is implemented in UMC 65nm LL CMOS and achieves an oscillation frequency of 12.4-13.56 GHz, an EER of 38%, a figure of merit (FoM) of 184.2 dBc/Hz and a FoMT of 183.2 dBc/Hz at 1 MHz offset. The 1/f(3) phase noise (PN) corner is < 250 kHz, and the phase error is < 1.8 degrees.