A 2.4 GHz CMOS quadrature LC-oscillator/mixer

Coupled LC oscillators are very often used to achieve quadrature outputs. In this paper we present an expression for the oscillation frequency of a coupled oscillator considering the effect of mismatches. Then we calculate the new value of the resonator effective Q due to varying of the oscillation frequency, and we evaluate the correspondent phase noise degradation. We show that this degradation is critical for high quality factor inductors. We evaluate the capability of a coupled LC oscillator to perform the mixing function by inserting a signal in the oscillator feedback structure. The theoretical results are confirmed by simulation.