Design of CMOS millimeter-wave cross-coupled LC quadrature VCOs with varactorless frequency tuning

We present the analysis and design of a 60 GHz LC QVCO in a 90nm RF CMOS process based on the disconnected-source parallel coupled QVCO topology. We introduce a first order linear model of an LC QVCO at millimeter wave frequencies and derive the oscillator steady-state parameters. Varactor size optimization for maximum quality factor at millimeter wave frequencies is thoroughly analyzed. To overcome the classical tradeoff between the varactor quality factor and tuning range, we suggest an alternative wide-band linear frequency tuning technique based on the fundamental operation of LC QVCOs. By changing the bias of the coupling transistors (G(Mc)-tuning), a wide frequency tuning range of 5GHz (57.5 GHz -> 62.5 GHz) can be achieved with very linear characteristics. The G(Mc)-tuning technique exhibits 4dBc/Hz lower phase noise than a varactor solution. The circuit draws a maximum of 17.6mA (excluding buffer circuits) from a 1V supply.