An Analysis of Phase Noise in Transformer-Based Dual-Tank Oscillators

This paper introduces a new phase noise analysis for one-port and two-port dual mode transformer-based (T-based) oscillators. In this paper we differentiate through linear time variant analysis between the noise response of L-based oscillators and dual-tank dual-mode T-based oscillators. Through derivations, we show that the open loop quality factor definition, commonly used in LC oscillators, is not a valid alternative definition for quality factor in T-based oscillators. We derive the traditional quality factor and the open loop quality factor for both the one- and two-port T-based oscillators. In addition, we investigate through calculation and simulation the impulse sensitivity function (ISF) for noise in the signal path of differential T-based oscillators. SpectreRF noise simulations are then used to verify the derived ISFs in one- and two-port models of T-based oscillators. Finally a case study of a dual-mode T-based oscillator is implemented in a commercially available 130 nm technology. The oscillator is used as an example to show how the different quality factors can affect phase noise performance in the two modes of oscillation available in transformer-based oscillators.