A Quad-Core VCO Incorporating Area-Saving Folded S-Shaped Tail Filtering in 28-nm CMOS

This brief reports on a 13-GHz quad-core voltage-controlled oscillator (VCO) using a folded S-shaped tail inductor. The contribution of this work is that the auxiliary resonator is folded into the main inductor, so that it leads to a more compact solution than a conventional scheme. Due to the S-shaped inductor’s electromagnetic (EM) characteristics, the proposed tail filter can achieve noise suppression without EM interference to the main tank. Designed and implemented in a 28-nm CMOS process, the proposed VCO operates between 12.32 and 13.84 GHz, for an 11.6% turning range. The measurements were carried out in the free-running mode, and the results show a phase noise (PN) of 118.3 dBc/Hz at a 1-MHz offset from the central frequency of 12.32 GHz. The power consumption of the VCO core is 24.5 mW, with a 0.9-V supply voltage, and this leads to a figure of merit (FoM) of 186.6 dBc/Hz.