How to decide the bandwidth of a PLL?

[zhangljz]

Hello,

Since the bandwidth is related with the divider ratio N, so if we increase the N, the bandwidth will decrease, then we may increase the charge pump current to maintain a constant bandwidth.

Is it common to configure the charge pump regarding to different output frequencies?

For a 10MHz reference frequency, is the bandwidth from 700KHz to 200KHz suitable, for output frequency 30MHz ~ 120MHz

Thanks

 

[BigBoss]

I think you confuse " Loop Bandwidth" and " Filter Bandwidth" ..
These are different things.You may adjust Filter Bandwidth freely but Loop Bandwidth is depended on-as you said-other components too including Filter...

 

[zhangljz]

Yes. The loop bandwidth should be around 1/20 of reference clock frequency, but it also changes according to the ratio N, charge pump current, filter ,etc.

So if I want to have a proper loop bandwidth for all output frequencies, I need to configure something, like charge pump or filter. Changing which parameter is better to do this job?

Thanks