A 12.5-to-15.4GHz, -118.9dBc/Hz PN at 1MHz offset, and 191.0dBc/Hz FoM VCO with Common-Mode Resonance Expansion and Simultaneous Differential 2ND-Harmonic Output using a Single Three-Coil Transformer in 65nm CMOS

In recent years, common-mode resonance at twice the oscillation frequency has been proven to be an effective method to improve the FoM and phase noise performance of LC VCOs [1]–[4]. In [2], the implicit common-mode is proposed to merge the common-mode resonance tank into the VCO's main tank to save the chip area as shown in the left of Fig. 1. The VCO in [3] boosts both the common-mode impedance at 2ND harmonic and differential-mode impedance at 3RD harmonic frequency to improve the FoM as shown in the middle of Fig. 1. However, manual harmonic tuning to align those harmonic resonance frequencies is needed in both VCOs in [2] and [3] to uphold an optimal performance over the tuning range. To avoid the manual harmonic tuning, an extra resonator is added to the main tank in [4], improving phase noise over a wide bandwidth. However, the extra head resonator inevitably increases the VCO's chip area.