Why the DLL locking range be limited in the range of .......

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huanchou

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dll false lock 1.5t 0.5t

Dear all:

I am a DLL-disign newer. I have read some papers about the DLL,
but I still don't know Why the DLL locking range is limited in the range
of 0.5T ~ 1.5 T.
Can any export answer the question for me, or where can I find the reference?

Thanks!
 

Re: Why the DLL locking range be limited in the range of ...

The DLL locking range is limited by the phase detector.
If you try to extend the detector range or to add the anti-false lock circuit , the DLL will not have the issue.
 

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    huanchou

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Re: Why the DLL locking range be limited in the range of ...

The DLL locking range is limited by the phase detector.
If you try to extend the detector range or to add the anti-false lock circuit , the DLL will not have the issue.
Click to expand...

Yes, you can extend the range of DLL, but it is still limited in some range and can't like PFD.

Yibin.
 

Dear huanchou
What is the difference between DLL and PLL?
 

Re: Why the DLL locking range be limited in the range of ...

the dll has cap
pfd bw
and cp bw
they all limit the range
 

Re: Why the DLL locking range be limited in the range of ...

yes, lock range is determined by characteristic of pd. For example, if the delay between out clk and ref cll is in (0.5T,T), pd will give down signal and increase the delay to T. If the delay between out clk and ref cll is in (T,1.5T), pd will give up signal and decrease the delay to T. But if delay >1.5T, pd will give down signal and decrease delay to 2T, which is a false locking. It is same for delay < 0.5T. Now most DLLs introduce a pd which can avoid the false locking when delay <0.5T. Althrough compliex pfds are introduced to extend lock range to some extent, but it is still a phase detector not a phase and frequency detector as in PLLs, thus lock range is still limited by pd.
 

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