A 49-to-62 GHz Quadrature VCO With Bimodal Enhanced-Magnetic-Tuning Technique

A bimodal enhanced-magnetic-tuning technique is proposed to extend the frequency tuning range of millimeter-wave (mmW) quadrature VCOs (QVCOs). First, the conventional magnetic tuning is reviewed, and its limitations for the frequency tuning at mmW frequencies are high-lighted. To enlarge the variable range of the magnetic field, a new transformer-based topology called enhanced-magnetic-tuning (EMT) is proposed and analyzed. In addition, by switching the polarity of the phase shift of the coupling currents, both of the two intrinsic modes in a quadrature VCO are exploited to ideally double the frequency tuning range. With a generic model, the proposed bimodal enhanced-magnetic-tuning (B-EMT) is analyzed mathematically and compared with the conventional frequency tuning techniques. Implemented in a 65 nm CMOS process, the QVCO prototype with the proposed B-EMT technique and 1-bit digitally controlled varactor measures a tuning range of 24% from 48.8 to 62.3 GHz and phase noise of -89 to -96 dBc/Hz at 1 MHz offset while drawing 13 to 25 mA from a 1.2-V supply, corresponding to FoM from 173 to 176 dBc and FoMT from 181 to 184 dBc/Hz.