How to calculate frequency resolution of a PLL?

[ashutosh_g]

how can i calculate my frequency resolution of PLL ?
will i able to generate frequency up to Hz mili-Hz or micro-Hz etc with PLL

 

[khouly]

pll frequency resolution

the pll resultion , as far as i know in integer N PLL is the reffence frequency , which si the minimun frequency spacing
in fractional N PLL this is not the case

if u are talking about frequcny accuracy in miili hertz , then u should use DDS for highest accuracy and u can deploy the DSS with the PLL

khouly

 

[ashutosh_g]

dds pll

well yes i am looking for frequency accuracy i want to know accurate can a frequency be from a PLL.
is it mHz Hz and how to calculate it ...i dont want to use DDS

 

[khouly]

frequency resolution pll

i mean u can use the DSS as ur oscillator which is controlled by the PLL

chech anaog devices website

khouly

 

[madengr]

dds jitter

You MAY be able to get mHz with a fractional-N PLL. The resolution is comparison_frequency/2^N where N is typically between 10 and 18. However fractional Ns are primarily used for fast tuning. It allows a high comparison frequency (tens of MHz veresus 100 KHz for integer-N) thus a wide loop bandwith, which has fast lock times. So typical 10 MHz comparison would yield 38 Hz steps using an 18 bit fractional register. Now if you could do 100 kHz comparison you would get 0.38 Hz, however that's assuming the reference divider let's you go that low. You'll just need to check.

I have not tried the DDS * PLL. I had someone from Analog Devices tell me there is too much DDS jitter so phase noise would suck, but maybe that's not the case anymore. Now if you do DDS + PLL (as in mixer) that may work better cause the phase noise won't be multiplied up by the PLL.

 

[rancohen_2000]

Re: PLL -resolution

you can donwload Analog Devices SIMPLL and ADF evaluatiun softwares. You can simualte the output frequency using it.