Understanding Fractional-N PLL

Presentation (pdf)

There are many misconceptions around Fractional N PLLs. One of them is that they require different design equations and simulation techniques that are used for integer N PLLs. In fact, they use the same concepts and equations. The difference, though, is the performance. By having smaller N value, Fractional N PLLs theoretically have better phase noise performance. Although Fractional N PLLs contain compensation circuitry for the fractional spurs, typically it is still a net improvement.

This webinar will address some of the misunderstanding of fractional N PLLs, introduce the advantages and disadvantages of fractional N PLLs over integer N PLLs, fractional N PLL design consideration as well as design tricks.

Topics covered in this online seminar include:

• Basic PLL Overview and Benefit of Fractional N PLL
• The Mis-Use of Fractional N
• Fractional N PLL Details
• Spurs and Their Reduction Methodology
• Summary