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Loop bandwidth of PLL

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haadi20

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pll loop bandwidth

How do i define the loop bandwidth for a PLL ? Is there a standard way of doing that ?

Lets say i have to design a PLL whose tuning range is 6GHz, and the reference frequency is 100MHz.

What factors does loop bandwidth depend upon? The loop bandwidth is needed to further design the components of the filter, but how to decide a reasonable value of the loop bandwidth ?

PLL gurus...show ur expertise....
 

loop bandwidth of pll

pll loop bandwidth design is not trivial. but there are many papers on it. basically it is a trade off of setting time and loop phase noise optimization.
 
loop bandwidth pll

mainly loop bandwidth related to the speed of the loop "lock time"
and the phase noise performance of the loop

so u must know ur requirements to get the loop bandwidth

in normal design procedure the loop bandwidth taken to be 1/20 of the reffernce frequency

wish this help

khouly
 
pll bandwidth

you can refer some book:
 

pll natural frequency bandwith

Hi :

Nature frequency and loop bandwidth is difference,right ?. I always have some question. That is when we calculate H(s) we can get nature-frequency and damping factor. but loop bandwidth is how get ? and if the fact is right about which nature frequency or loop bandwith is 1/10-1/20 input frequency ? Why is this ? Have any book discuss this ?

Thank you .
 

define loop bandwidth

The loop bandwidth defines the follows:
1. As the loop bandwidth increases, the loop settling time decrease.
2. As the loop bandwidth increases, the spurs attenuation decrease.
3. As the loop bandwidth increases, the VCO phase noise is more cleaned.

So according to ur target specs, u can define the loop BW. In most cases the loop BW is about Fref/10 to have an acceptable spur level and not a slow loop. It all depend on the standard u want to target.
 

what is loop bandwidth in a pll ?

Thank you .

But I have a question. loop badwidth has these relation. Then what is the function about nature-frequency from close-loop H(s). We kown damping factor have the characteristic of overshunt and undershunt. What is function or definition about nature-frequency ?
 

pll 3db bandwidth

I summarized several key pLL parameters relationship and reasons behind:

1. closed loop W-3db (bandwidth) ~0.05*Wo; Wo is PD input signal frequency.
Reason: keep continous assumption of switch circuit valid.

2. Open loop bandwidth (loop bandwidth) Wt ~ 1.55*Wn (natural frequency);
Reason: derivitation from laplace equation.

3. W-3dB = 2.06*Wn
Reason: derivitation from laplace equation.

Wn is so critical that it determines
lock time: (2π/ωn);
Lock range: πζωn;
Pull in time and almost everything;
 

loop bandwidth 1/10 of reference frequency

Today most important topic is phase noise of the closed loop PLL. That is because nearly all new developed system specs use higher order symbol constellations (64QAM) and have wideband RX channel (>10MHz). So the error vector magnitude of the phase noise integrated over the RX bandwidth is the most important. If you minimze all second order contributors the VCO and the reference remain. The VCO deliver 1/f contribution and the reference in the interessting band a flat contribution. The PLL bandwidth determine the amount of the contribution of VCO and reference. At a specific bandwidth the total is minimum. That is the first order design decision.
 

pll loop bandwidth equation

i could not understand fully the description upstair.
Could you give me some paper for reference,Thanks
 

pll loop equations dennis fischette

RFsystem means PLL loop is a low-pass system for reference input noise, and a high pass system for VCO noise.

If we consider only 1st order noise contributor, we trace off closed loop bandwidth for these two parameters. Using environment normally will decide loop bandwidth.
 

pll laplace

TO neoflash and all guy:

Thank you for your help.But in the first point , I have seen another paper say that loop bandwidth < 1/20 Reference frequency . The result is difference.
This may confuse me. Anybody have any opinion.

Thank you
 

bandwidth of pll

This is to alleviate the inaccuracy induced by laplace approximation of the system.

One basic assumption in PLL loop analysis theory is continuous operation of loop. If loop bandwidth is too large, this basic assumption will break.
 

pll loop bandwidth calculation

To neoflash and everybody:

I really not understand what your mean ? Can you explain to more detail. Or have any document discuss this topic ?

Added after 54 minutes:

To neoflash and everybody:
I have two document :

1. Deisgn of A PLL with Fast -Lock and Low Jitter

It say loop bandwidth < 1/20 reference frequency

2. Pratical Phase-Locked Loop Design
2004 ISSCC Tutorial Dennis Fischette
Websit : https://www.delroy.com

It say natural-frequency < 1/20 reference frequency

What kind is right ???
 

define loop bandwidth of pll

Neoflash figure out that the <1/20 is only a guide for a simplified loop calculation. The problem is that the PLL is not a continuous system but is modelled more easy as a continuous system. If the VCO voltage change it take about a reference cycle before the frequency change result in a phase change at the phase detector. That is also not exactly true because changes in the VCO frequency shortly before the divided output signal have to wait less. A main assumption is to introduce a delay element in the time continuous modelling exp(-i*omega*T/2) which model the mean delay of T/2. At 1/20 of the reference the phase the phase shift is not low:

360*angle(exp(-i*2*pi*(1/20)*1/2))/(2*pi)=-9 [degree] sorry that is matlab

So 1/20 is only a modelling issue not a design issue!
 

pll 3db bandwidth fref 1/10

Tuki:

I suggest you go for PLL book for more detailed information if you are really interested in PLL design.

I suggest you read the book by Rolland Best.
 

wn 3db bandwidth

you can refer to the book by Dean Banerjee about the natural frequency and -3db
bandwidth of pll!
 

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