Synthesizer Questions?

[liberal]

I want to build a synthesizer,with a variable PFD Ref Frequency(Fref) and variable integer Divider (N),the PLL output is Fout.
I want to know the relationships between the variable Fref and the variable Divider N.As we know Fout=NFref.But now the N and the Fref are variable,how to cal their ralationships?any references?Thank you!

 

[toonafishy]

Except for the Fout formula yu gave, there is no relationship between Fref and N. You choose both in order to get the final Fout needed.

 

[liberal]

No.
As we konw if the Fref is constant but the N is variable ,then we can cal the range of N is 171/N---249/N.But now the Fref is variable too,then how to Cal?