An optimization procedure in low-phase-noise integrated LC oscillators design

Based on a physical model, closed form expressions are derived to calculate the phase noise originating from the noise sources in a bipolar differential LC oscillator. A new spiral inductor selection criterion, which is very important to minimize the oscillator phase noise, is presented. This criterion leads to an optimization procedure for bipolar differential LC oscillator design. Following the procedure, a 900 MHz capacitive coupled LC oscillator is designed. Compared to the oscillator designed with the spiral inductors of the maximum quality factor, the simulation shows that the phase noise of the oscillator is effectively improved more than 3.6 dB when the new criterion is used.