How to decide PLL LoopBandwidths？

[option318]

Who can tell me, how to decide PLL LoopBandwidths？please tell me thanks.

 

[amarnath]

the loop bandwidth should not exceed 1/10 of the input frequency.It should be decided based on whether your input noise is dominant or whether your VCO noise is dominant. For input noise you need keep a low bandwidth, for vco noise a large bandwidth is needed to cut it off. Another factor is the lock time , though you can still keep a low bandwidth and lock faster using loop bandwidth enhancement techniques to settle faster.I would suggest you to refer the thesis available on PLL's. I found Fuding Ge's thesis to be pretty good.You can refer to that for your design.


amarnath

 

[quanble]

Could you tell me why the bandwidth should choose less than 1/10 of input frequency in more deepth ?or do you have some doc about this topic?

 

[amarnath]

The PLL can be approximated as a continious time system only when we have no finite sampling effects, so to meet this requirement we need to keep the bandwidth less than 1/10 input frequency and another requirement is stability. You can refer to any text book on PLL's, for more info on the same


amarnath

 

[lijianheng]

First, it depends on what your PLL used for?

 

[docini]

one correction to what amarnath has said. the loop bandwidth is 1/10th of reference frequency, not input frequency. reference frequency is the rate at which phase detector compares the phase of the input and feedback clocks.

 

[option318]

Thank you for amarnath of explanation. but how can find Fuding Ge's thesis？

 

[amarnath]

just search "fuding ge thesis pll" in google.


amarnath

 

[satyasiva]

Hi amarnath,

I didn't get the thesis from google. I f u have the link please give it.

 

[amarnath]

http://www.geocities.com/fudinggepll/PLLProj.pdf

 

[jecyhale]

Who can tell me, how to decide PLL LoopBandwidths？please tell me thanks.

it is up to your lock time which the system requires.