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wylee
Joined: 17 Feb 2004
Posts: 113
Helped: 5
Location: Malaysia
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 14 Sep 2006 5:07 cycle slipping pll |
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Referring to the circuit posted by safwatonline, http://www.edaboard.com/viewtopic.php?p=597721#597721
For lock detection,
what are the problems/disadvantages of using a cycle slip detector (cycle slipping detector) connected as below?
1. Will there be any false detection? (e.g: when same clocks phase but different frequencies)
2. How accurrate is the detector?
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rfsystem
Joined: 25 Feb 2002
Posts: 858
Helped: 96
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16 Sep 2006 16:11 pll cycle slip |
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There two different topics here:
1. Lock detection
2. Cycle slip detection
The circuit above detect a single slip. The slip detection is used to
a. accumulate the slips to have a phase synchronious switching between 2 frequencies
b. increase gain of the chargepump if some slips accumulate (only 1 slip decrease stability) to speedup settling
Lock detection used different circuits to have various trades of lock phase range, sensitivity,..
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wylee
Joined: 17 Feb 2004
Posts: 113
Helped: 5
Location: Malaysia
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19 Sep 2006 2:48 Re: PLL: Cycle slipping detector, lock detection, please hel |
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Reply from safwatonline,
Hello wylee,
i dont have too much information about the lock detector except the basic operation, but here is what i think anyway:
the cycle slipping seems to be good and simple way to detect the lock but it has a main disadvantage that u cannot accuratly detect the lock as in some application like in CDR u need to get the lock detection in terms of UI and switch to the phase allignment loop acording to this value (and vice versa), but on the other hand it makes a really simple solution for non-accurate detection, if u want an accurate detection i suggest the counter methode.
anyway to be exactly sure , there is an obvious solution which is making a large signal model \"using verilog-A for instance\" and do some simulations , this must be done anyway \"i guess\" during the PLL design and if u choosed to do the Cycle slipping Lock Detector then as u can see it is nothing more than the extra to FF\'s which u should have already made in ur model.
sorry that i couldn\'t help any more .
regards
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