Tuning-Range Enhancement Through Deterministic Mode Selection in RF Quadrature Oscillators

Quadrature oscillators (QOs) based on parallel or series coupling mechanisms produce ambiguous phase relationships between the coupled oscillators. Deterministic mode selection is presented and analyzed for a series-coupled LC quadrature oscillator ( LC-QO) and leveraged to increase the tuning range of the QO. Series-coupled LC-QOs have been implemented in a 90-nm CMOS technology. Measured results show a frequency tuning range of 94% for a center frequency of 1.3 GHz, 60% for the oscillator operating at 3.7 GHz, and 52% for the oscillator operating at 4.4 GHz.