Design of LC Resonator for Low Phase Noise Oscillators

Abstract

The effects of resonator topology on the phase noise of LC oscillators are studied in this paper. It is shown that there is a neglected factor that can considerably influence the phase noise behavior of the oscillator. We designate this factor as the Inductance Energy Factor (IEF), which directly depends on the topology of the resonator. It is shown that through proper design of the resonator for a better IEF, the oscillator phase noise can be improved. It is also shown that by modifying the resonator structure to improve IEF, the phase noise does not have to be constrained by the minimum realizable inductance and its maximum quality factor. Therefore, the power-phase noise trade-off remains effective beyond this point. In the following, a general method to design the resonator circuit by a so-called evolutionary modification of the conventional LC tank is given. Illustrated simulations further help to confirm that phase noise improvements of more than 10 dB can be readily achieved by judicious design of the resonator circuit.