A Wide Operating Range LC Quadrature Phase VCO With Seamless Tunability

Abstract

In this brief, we present a wide operating range quadrature phase LC oscillator with seamless tunability. A combination of series-coupling and parallel-coupling between two resonant LC tanks has been employed. Series-coupling ensures that the desired phase sequence is achieved. At the same time, variable strength parallel coupling network helps in getting a wide tuning range. Seamless tunability across the operating range is achieved by changing the polarity of the parallel coupling network without hard switching. This approach helps in getting a wide operating range without usage of varactors which are lossy at high frequencies. A VCO with the proposed architecture has been designed and fabricated in a 65-nm (low-leakage) CMOS technology. Silicon measurement results show a tuning range, with seamless tunability, of 44.7% around the center frequency of 14.3 GHz. To the best of our knowledge, this is the widest operating range LC oscillator with seamless tunability reported till date. The VCO exhibits an FOMT of 185 dB, which is comparable to the state-of-the-art reported in the literature for oscillators operating above 10 GHz.