Basics of Dual Fractional-N Synthesizers/PLLs - Sponsored Whitepaper

The term fractional-N describes a family of synthesizers that allow the minimum frequency step to be a fraction of the reference frequency. Over the years, a number of methods have been proposed to realize fractional-N frequency synthesis that are based on the basic concepts of traditional integer-N synthesis [1,5]. Among these methods, three techniques are best known in the industry: fractional divider-based, current injection-based, and ∆Σ modulator-based fractional-N.

This white paper describes these methods and provides a general discussion of the use of fractional-N synthesizers in a low-cost, low-power radio.