doctorworm
Newbie level 6
Hi folks,
I'm having trouble finding equations or literature on how to design a suitable frequency divider.
Ignoring the sigma-delta stuff (for now), I want to know how to "hit" every channel in a fractional-N PLL synth. Let's say I know the frequency step (channel spacing), reference (comparison) frequency and the VCO output range.
I have the choice of a dual-modulus divider or a multi-modulus divider. Apparently the dual-modulus divider might not give me all the channels in the range but I don't know how true this is!
The reference frequency has to be an integer division of whatever the Xtal frequency is and I guess the accumulator size, n, means that the total number of cycles has to be 2^n. These limitations don't make life easier.
So... how can I choose which type of divider will achieve this and also how can I work out which division ratios (N/N+1 etc) will give me every single channel in the output range?
Apologies if I've broken any rules - this is my first (or second) post so please go easy on me!
Cheers!
I'm having trouble finding equations or literature on how to design a suitable frequency divider.
Ignoring the sigma-delta stuff (for now), I want to know how to "hit" every channel in a fractional-N PLL synth. Let's say I know the frequency step (channel spacing), reference (comparison) frequency and the VCO output range.
I have the choice of a dual-modulus divider or a multi-modulus divider. Apparently the dual-modulus divider might not give me all the channels in the range but I don't know how true this is!
The reference frequency has to be an integer division of whatever the Xtal frequency is and I guess the accumulator size, n, means that the total number of cycles has to be 2^n. These limitations don't make life easier.
So... how can I choose which type of divider will achieve this and also how can I work out which division ratios (N/N+1 etc) will give me every single channel in the output range?
Apologies if I've broken any rules - this is my first (or second) post so please go easy on me!
Cheers!