A Transformational Framework for Analysis of Phase Noise in LC Oscillators

Phase noise has become the single most critical factor to be addressed in the design of modern communication systems. Facing the challenging requirements of 5G cellular communication, our paper describes a new theoretical framework to calculate the phase noise of LC oscillators, relying on easy to implement closed form solutions for phase noise calculations. Using closed form phase noise solutions enables oscillator designers to easily implement multiple phase noise calculation options for a number of oscillator circuits, which would be very difficult to implement with the existing mathematically complex phase noise theories. The analytic methods of our theory rely on modeling all real oscillators as having non-ideal or latent behaviors in addition to their primary nature for generating a carrier wave operating at a single frequency with a single amplitude. It is a cascade of these non-ideal transformation processes that produce non-ideal oscillator outputs containing the phase noise sidebands. Enhanced qualitative and quantitative insights into oscillator phase noise performances are achieved by using this approach. We validate our methods by comparing their results with phase noise simulations carried out for a sample CMOS LC voltage-controlled oscillator in 90 nm RFCMOS process using SpectreRF simulator. The results for the oscillator's output 1/f2 thermal phase noise, 1/f noise upconversion into 1/f3 phase noise and the 1/f3 corner frequency of phase noise spectrum using our theory yields −136 dBc/Hz at 10 MHz offset, −21.3 dBc/Hz at 1 kHz offset and 2.6 MHz respectively. The corresponding values obtained with SpectreRF simulation are −135.9 dBc/Hz, −23.4 dBc/Hz and 2.1 MHz. The carrier frequency is 5.4 GHz with output power of 9.78 dBm.