What is the physical meaning of loop bandwidth of PLL?

hi

what is the physical meaning of loop bandwidth of pll?
why it is said that the noise of charge pump is dominant inside the PLL bandwidth?

thanks.

I think you can refer to :
http://www-mtl.mit.edu/researchgroup...4_meninger.pdf

The transfer function of each noise source to the vco output is different. The noise coming from PFD/charge pump is low-pass filtered, and the noise from VCO itself is high-pass filtered.

the physicall meaning of the loop BW , is the 3 dB BW of the loop transfer funcation when u say the loop tansfer funcation consider the input of the PD is the input , and VCO is the output

khouly

Think of your VCO as a wild bucking bronco!

Think of your PLL as a cowboy holding the leash! If he has a short leash, he can control the bronco well--equivalent to a wide PLL bandwidth. If he has a very long leash, he can not control the bronco very well, but just generally steer him in the right direction--that is like the PLL with a very narrow loop bandwidth.

But lets say the cowpoke was out drinking all last night, and can barely sit on the horse. You might do better with a long leash/small PLL bandwidth, as the cowpoke is polluted! Similarly, if you have a poor crystal oscillator clock with lots of phase noise, you do not want to lock the VCO too tightly to the poor source.

Judging how sober your cowboy is or not, you can determine the best length of leash (PLL bandwidth) to get the best ride! Judging how ornery your bronco is also is a factor in determining leash length!

Dear Biff , it is a great example , and explanation of the PLL

:D

khouly

Hi Biff, it's the most profound comments I have seen about PLL bandwidth. Le

thats the apt consideration welldone biff

hi,

If you don't mind can any body upload the following pdfs to me...

>>00845184.pdf or A low-noise phase-locked loop design by loop bandwidth optimization
>>00600281.pdf or Optimal loop bandwidth design for low noise PLL applications

These are IEEE papers.

Thanks in advance
SavithRu

good explaination