A 30 GHz Inductively Coupled VCO With a FoMT of −191.8 dBc/Hz in 40-nm CMOS

Abstract

This letter reports an inductively coupled voltage-controlled oscillator (VCO) operating at millimeter-wave (mm-wave) frequencies. The VCO core incorporates a dual-tapped transformer, an NMOS cross-coupled pair, a varactor, and a four-bit binary-weighted capacitor bank. Independent biasing of the drain and gate of the cross-coupled pair is achieved through the transformer center taps, preventing the core transistors from entering the deep triode region. Low phase-noise (PN) performance is obtained by maximizing the LC-tank quality factor and by incorporating a tail filter. In addition, the oscillator figure-of-merit (FoM) and FoM_T are evaluated as a function of the gate bias voltage. The proposed VCO was designed and fabricated in a 40-nm CMOS process. On-die measurements indicate a tuning range of 15.9% from 25.47 to 29.88 GHz, with a PN of −107.66 dBc/Hz at 1-MHz offset from a 25.47-GHz carrier. The VCO dissipates 6.3 mW from a 1.1-V supply and achieves a FoM of −187 dBc/Hz and a FoM_T of −191.8 dBc/Hz.