On phase noise in quadrature cross-coupled oscillators

A cross-coupled relaxation oscillator has two outputs of the same frequency, which are in quadrature. In this paper a comparative study of the phase noise in a cross-coupled relaxation oscillator is given. We present a high level (system) study of the oscillator and analyse the oscillator stability. The derivation proves analytically that cross-coupling reduces the influence of a perturbation (noise) on the oscillator output. Both high-level and circuit simulations at 5GHz are presented to confirm the theoretical results. Close to 10dB improvement in phase noise performance due to coupling was found, and the phase noise performance compared with that of a coupled LC oscillator was achieved.