CMOS LC oscillator using variable mean frequency

This paper presents a fully integrated CMOS LC oscillator with digital tuning. The frequency tuning is by averaging over two oscillation frequencies. The average frequency is determined by the digital input pattern, which switches a small unit of capacitance on and off the main capacitor. Measurements in a 0.18 μm CMOS test-chip shows that 5 bits of additional resolution can be achieved. With the inductor dominating the quality factor, Q, the phase noise remains almost the same, not affected by this averaging activity.