lokeshthimmapuram
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My apologies.
In the ideal working case of PFD, reset length is assumed zero. So, if Reference frequency (Fref) is leading the Feedback frequency (Ffb), only U (up pulse is seen) and the D (down pulse remains low). When Fref is lagging Ffb, only D is seen and U remains low. For this case, the S-curve of PFD ( the curve which represents the input phase difference Vs the time averaged differential output [U-D]ave ) is linear between -2Π and +2Π ( as shown in the attaced file). i.e., the range of input phase difference for which the PFD operates correctly is +/- 2Π.
By correct operation, I mean there will not be any missing edges during the comparison.
Now, lets take the case with some reset length ΔR < T ( T = Tref = Tfb ). The maximum input phase differnce for correct PFD operation without missing edges becomes 2Π-ΔR. The other way of seeing this is - if the input phase difference falls between 0 and T-ΔR, PFD operates correctly. But, if the input phase difference falls between T-ΔR and T, alternate edges gets missed. That is, wrong outputs are seen at the PFD output [ This was my Question ]. So, for the PFD to operate correctly, the input phase difference should always be < T-ΔR.
Please let me know if something is not clear (or) correct me if I'm missing something.
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