Study of second-harmonic self-injection impact on [formula omitted] phase noise of CMOS parallel LC-tank oscillators

Abstract

This article studies the impact of injecting the second harmonic of the oscillation to the tail transistor, as a self-injection, in CMOS parallel LC-tank oscillators. In this scheme, the second harmonic of the oscillation is generated, delayed, and then fed back to the tail transistor. Employing the injection locking theory, closed-form formulas are derived that predicts 1/f2 phase noise arising from various noise sources in the oscillator. These formulas are validated against SpectreRF simulation results for different injection amplitudes and phases. It is shown that the phase-noise performance is improved by increasing the injection strength while the phase shift of the injected signal is set to zero. This improvement is attributed to increase oscillation amplitude and decrease phase noise factor. The amplitude and phase stability of the architecture is also analyzed in this article. Furthermore, as a case study that employs the described self-injection technique, a self-switching bias oscillator is investigated. Phase noise simulations show that the studied circuit, delivers 5 dB better phase noise, compared to the conventional class-B tail-biased oscillator.