A new spurious component suppression technique in fractional-N frequency synthesizers

Fractional-N frequency synthesizers have long been known to suffer from a set of spurious components, often referred to as fractional spurs, which are usually attributed to the operation of the modulator. This paper presents the investigation and development of several new, advanced techniques to suppress these discrete spurs and offer substantially better performance than existing designs. The proposed technique is introducing a small amount of anti-phase cross-coupling in the system to modulate substantial affections. A synthesizer based on this proposed technique is developed by discrete components. Both simulated and measured results are shown to demonstrate a substantial improvement in performance.