Abstract
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.
Highlights
Phase noise is an undesired characteristic of oscillator circuits, which degrades their spectral purity and can induce demodulation errors
The possibility to reduce the phase noise of an existing oscillator through self-injection locking with long transmission lines has been demonstrated in several previous works [1]-[3]
Oscillators based on slow-wave resonators with excellent performance have been demonstrated in the literature [6]-[7]
Summary
Phase noise is an undesired characteristic of oscillator circuits, which degrades their spectral purity and can induce demodulation errors. The possibility to reduce the phase noise of an existing oscillator through self-injection locking with long transmission lines has been demonstrated in several previous works [1]-[3]. This is generally inconvenient [3], since the overall system becomes bulky due to the long lengths required to achieve a significant phase-noise improvement. The slow-wave structure is included in the external feedback loop of an existing oscillator, in order to reduce its phase noise. The problem of coexistence of solutions in some parameter intervals, demonstrated in [3] and inherent to the long delay, will be shown to be less critical when using slow-wave structures. The analysis and synthesis method will be applied to an oscillator at 2.75 GHz, obtaining a phase-noise reduction of more than 13 dB
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