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trond

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Glasgow, Scotland

frequency difference detector
Jul 16^th, 2005, 6:12am

I would like to build a frequency difference detector, using digital components only. It should be able to compare the signal frequency to a reference frequency and detect which frequency is faster. It should then output the difference of the two frequencies.
The signals will go in to a charge pump with a LP filter to obtain the average value.
Furthermore, it should be able to do the comparison within 1 period and also prevent slipping, meaning there should be almost no limitations on how much the reference and signal frequency can be apart for the circuit to work.

Can anyone suggest a circuit, name or paper that might address above issues?

Thanks
Svensl

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trond

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Posts: 168
Glasgow, Scotland

Re: frequency difference detector
Reply #1 - Jul 19^th, 2005, 5:54am

I had a look at "Digital Logic Implementation of the Quadricorrelators for Frequency Detector" by Yoon and Lee and implemented it in VerilogA. While the scheme does work I was wondering whether there are other circuits that might permorm better. For example, the resolution of the frequency difference could be a bit better. Could someone suggest another circuit that does frequency difference detection?

Cheers,
sven

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jbdavid Community Fellow Offline Posts: 378 Silicon Valley	Re: frequency difference detector Reply #2 - Oct 2^nd, 2005, 6:03pm This is a circuits question.. not a modeling question.. jbd
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Paul

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Switzerland

Re: frequency difference detector
Reply #3 - Oct 9^th, 2005, 2:13pm

Sven,

many phase detectors can perform (within some limits) frequency detection too. It depends whether the fact their output is proportionnal to the phase error is problematic in your case or not. I would suggest you have a look at the collection of papers in "Monolithic Phase Locked Loops and Clock Recovery Circuit", Editor B.Razavi.

Paul

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