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What's the relationship of noise bandwidth to loop bandwidth in PLL?

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hmsheng

hmsheng

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What's PLL noise bandwidth? What's the relationship of noise bandwidth to loop bandwidth?
Can we minimaze PLL integrated phase noise by reduce PLL noise bandwidth?
 

noise bandwidth

this is not a simple question, first you look at some book,for example, RAZAVI's
 

bandwidth of pll

the bandwidth of the PLL is the PLL noise bandwidth

but every noise source in the PLL has it's transfer function

so if you r talking about phase noise of the Xtal reffernce the noise transfer funcation is low pass filter so to minimize the the noise , decresae tha bandwidth

but the noise in VCO the transfer funcation is high pass filter to to minimize the VCO noise increase the bandwidth

read R. Best Book about PLL it is very goog

khouly
 

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pll noise bandwidth

khouly said:
the bandwidth of the PLL is the PLL noise bandwidth

...

khouly
Click to expand...

I can't agree with you that the bandwidth of the PLL is the PLL noise bandwidth.
The PLL bandwidth is defined as the cross frequency at gain=1 of open loop. But noise bandwith is defined as following:
 
phase locked loop phase noise bandwidth

i think it wioll depend what is ur defintion of the bandwidth closed loop or open loop , when i am talking about PLL bandwidth i consider the pll is closed loop in lock state

khouly
 

noise bandwidth of pll

hmsheng said:
The PLL bandwidth is defined as the cross frequency at gain=1 of open loop. But noise bandwith is defined as following:
Click to expand...
i do not agree with u about this definision to the pll BW because the pll is used as a closed system not as an open loop system
 

pll integration noise bandwidth

This paper gives a clear relation between PLL bandwidth and jitter (assuming noise sources in each block causes jitter)



Original question : Can we minimaze PLL integrated phase noise by reduce PLL noise bandwidth?

The answer to this original question can be found in the paper. If noise from input clock source is dominant, then reducing the PLL (noise) bandwdith reduces the integrated phase noise at the output. But, if the VCO noise is dominant, then you need to have a high bandwidth to reduce the output integrated phase noise. Refer to the paper for an in-depth analysis.

Bharath
 

pll noise loop bandwidth

Thanks for tsb_nph's material.

But I will say more about pll loop bandwidth.

Here is the loop bandwidth defined in PLL Performance, Simulation, and Design, writen by Dean Banerjee.

On page 91: ...where wc is the closed loop bandwidth, that is the frequency where the open loop response is equal to 1.

Also please see page 12, 118 for loop bandwidth defination.

MODERATOR ACTION: book download from : **broken link removed**
 
increase pll bandwidth

hmsheng said:
What's PLL noise bandwidth? What's the relationship of noise bandwidth to loop bandwidth?
Can we minimaze PLL integrated phase noise by reduce PLL noise bandwidth?
Click to expand...

Noise bandwidth depend on PLL bandwidth and noise characteriscs.
Integrating noise power density function in the whole PLL bandwidth and dividing it with dc noise value leads to noise bandwidth. For white noise, it has uniform value in its bandwidth. So for white noise PLL's noise bandwidth is equal to PLL's bandwidth.
PLL has two main noise source: input clock jitter and VCO noise. We can reduce PLL bandwidth to supress the former but have to enlarge the bandwidth to reduce the latter. There is a trade-off.
 

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