[time-nuts] EPE - GPS Frequency Reference Project

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Sep 26 23:17:02 UTC 2009

GandalfG8 at aol.com wrote:
> In a message dated 26/09/2009 13:33:12 GMT Daylight Time,  
> ximac at btinternet.com writes:
> Boring  mode - ON
> With reference to the subject matter and my previous posting,  I can
> confirm in the true Orwellian manner that all 74HC4046 devices are  equal
> except that some are more equal than others. Mine, a NS labeled  device,
> will not tolerate DC coupling along with long pulse inputs  whereas
> others (I think those from NXP [Philips]) will. Another, but  messy
> solution, is to AC couple them and clamp the negative-going peaks  to
> ground.
> Boring mode - OFF
> Not boring at all, such information is always useful.
> Did you establish whether or not the EPE version uses the original  Silicon 
> Chip circuit or the corrected one?
> regards
> Nigel
There's a subtle difference between 3rd phase detectors in the 74HC4046A
(Philips/NXP, ON, TI) and the 74HC4046 (Fairchild, NS)
The 3rd Phase detector in the 74HC4046A works as the designer intended
in the GPSDO circuit, the 3rd phase detector in the 74HC4046 does not.

The 74HC4046 uses an RS flipflop for the 3rd phase detector and requires
narrow pulses on the R and S inputs.
The 74HC4046A uses extra internal gates to ensure that only narrow
pulses are seen by the RS flipflop in the 3rd phase detector.


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