A low-phase-noise wide-band CMOS quadrature VCO for multi-standard RF front-ends

A low phase noise CMOS LC quadrature VCO (QVCO) with a wide frequency range of 3.6-5.6 GHz, designed in a standard 0.18 μm process for multi-standard front-ends, is presented. A significant advantage of the topology is the larger oscillation amplitude when compared to other conventional QVCO structures. The QVCO is compared to a double cross-coupled LC-tank differential oscillator, both in theory and experiments, for evaluation of its phase noise, providing a good insight into its performance. The measured data displays up to 2 dBc/Hz lower phase noise in the 1/f2 region for the QVCO, when consuming twice the current of the differential VCO, based on an identical LC-tank. Experimental results on the QVCO show a phase noise level of -127.5 dBc/Hz at 3 MHz offset from a 5.6 GHz carrier while dissipating 8 mA of current, resulting in a figure of merit of 181.3 dBc/Hz.