can fractional-n used as clock generator?

[jasonxilion]

fractional-n pll clk generator

i need a clock whose frequency step is only 100khz or even less

i know in rf system there are fractional-n structure plls which can make the frequency step very small, but i never hear about fractional-n pll used as the clock generator.

can i use a fractional-n structure, eg ,sigma-delta as a clock generator, if needed?

or because of the low performance requirement, is there any other simpler structures to realize fraction-n function?

thx

 

[ieropsaltic]

There're other ways to make a fractional-N PLL than delta sigma. Probably the simplest way is to use an accumulator. If the overflow number of the register used at accumulator is N, and if you add k to the accumulator, then the fractional step becomes F/N. This comes at the expense of large fractional spurs.

 

[jasonxilion]

actually it is a first-order sigma-delta modulator, right?