Phase-Noise Reduction in Self-Injection Locked Oscillators Using Slow-Wave Structures

An analysis of self-injection locked oscillators using a slow-wave structure for phase-noise reduction is presented. This structure is the key component of a feedback network, added to an existing oscillator and providing a stable self-injection locking signal. The unit cell of the slow-wave structure is based on a recently proposed configuration, made up of an open-ended stub and a Schiffman section. A tuning capacitor is introduced as an additional parameter, enabling an adjustment of the structure response at the desired oscillation frequency. The circuit solutions are analyzed by means of a semi-analytical formulation that incorporates the results of an electromagnetic simulation of the structure. The formulation enables a prediction of multivalued parameter regions, inherent to the long delay, which are more controllable than in the case of continuous transmission lines. An analytical derivation of the phase-noise spectral density is presented, which relates the phase-noise reduction with respect to the original free-running oscillator to the group delay of the self-injection network. The analysis and synthesis method has been applied to an oscillator at 2.75 GHz.