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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 quadrature oscillator ( -QO) and leveraged to increase the tuning range of the QO. Series-coupled -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.Index Terms-Oscillator, phase noise, quadrature, tuning range.

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