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The paper presents a method for improving the phase noise performance of a CMOS quadrature LC oscillator through parasitic compensation. Owing to the parasitic resistance in the inductor, the LC oscillator suffers from a low Q-value, which degrades its phase noise performance. In this design, through the parasitic-compensation method, the LC oscillator will be made to oscillate at the frequency when the effective impedance of the parallel LC resonator is at the peak. This will increase the Q-value of the LC resonator, which improves the phase noise performance of the circuit. A 2.63 GHz quadrature CMOS LC oscillator with a phase noise of -112.3 dBc/Hz at 600 kHz offset is demonstrated, consuming 7.5 mW of power using an on-chip spiral inductor model.