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This paper presents a theoretical analysis and control procedure of the bimodal oscillation phenomenon inherent to LC-tuned Quadrature voltage-controlled oscillators (QVCOs). A systematic start-up procedure is proposed to drive the quadrature VCO (QVCO) into the desirable mode of operation by controlling its initial conditions. By means of this approach, two parallel tuning curves can be obtained without switching capacitor or inductor banks, thus no penalty on phase noise and circuit complexity. The tuning frequency of the QVCO is from 11.7 to 14.5 GHz under 1 V supply and 0 to 1 V control voltage. This corresponds to a 21.4% tuning range with a moderate phase noise of -108 dBc/Hz at 1 MHz offset frequency. The core dc power consumption is 10.6 mW. A phase-locked loop (PLL) control methodology for forcing the QVCO into the desirable mode is also proposed for practical applications.
Date of Conference: 17-19 Jan. 2011