A Wide Tuning Range LC Quadrature Phase Oscillator Employing Mode Switching

We present a wide tuning range quadrature phase LC oscillator in this paper. A combination of series-coupled and parallel-coupled topologies between the two LC tanks in the oscillator is used. Series-coupled topology ensures that a desired phase sequence is achieved, whereas, tunability and switching of parallel-coupling helps in achieving very wide tuning range. Furthermore, use of varactors, which are unsuitable for high frequencies because of their losses, is avoided as significant frequency tuning can be achieved by varying the coupling strength itself. Circuit simulation results show that an 11 GHz oscillator, designed in a standard 90 nm CMOS technology in this topology, achieves a tuning range of more than 46%.