PLL Bandwidth definition and calculation?

[flesher]

pll bandwidth

1,
When designing PLL, it is always said that PLL's bandwidth should be set to be smaller than Fref/10. what's the PLL bandwidth? Is it Wc(open loop unit gain bandwidth), Wn( Natural frequency) or W-3db ( closed loop -3db frequency)?
2,
and I know Wc means the frequency where gain=1. W-3db means the frequency where gain decrease 3db. what does natural frequency mean?

3, If all the parameters are know, like Ich, Kvco, R,C1,C2. How to get Wc, Wn,
W-3db, Phase Margin, Damping factor. can anyone give the formulars ? I found some thing for internet:

Natural Freq: Wn=sqrt[(Kvco*Icp)/(2*pi*Cbig*N)]
Damping Factor: zeta=(Rlpf/2)*sqrt[(Icp*Cbig*Kvco/2*pi*N)]
Open loop bandwidh Freq: w0=(Icp*Kvco*Rlpf)/2*pi*N
3dB Bandwidth: w3dB=wn*sqrt(1+2*zeta^2+sqrt(2+4*zeta^2+4*zeta^4))

Are these equations are correct?


Regards,

 

[kbksharma]

definition of pll bandwidth

ur pll bandwidth depends upon the settling time requirements of ur PLL and the type of pll ur using i.e fractional or integer PLL design

what is the settling time requirement of ur PLL

 

[bengilbert]

calculate pll bandwidth

Sounds like you need to read Dean Banjeree's **broken link removed**. You might also want to check out **broken link removed**.

To answer you question the bandwidth of the loop is the open loop bandwidth Wc.

The natural frequency Wn is the frequency that the loop will oscillate at when it is settling to a new frequency.

You can find the formulas in Dean's book.

 

[sainiparvesh]

Re: calculate pll bandwidth

Hi
Can we use the "allmargin(loopgain)" function of MATLAB to determine the loopbandwith Wc(PMFrequency) of higher(any) order PLLs instead of relying on above equations which are valid only for type2 3rd order PLL only?
Pravesh