[time-nuts] EPE - GPS Frequency Reference Project
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
> 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?
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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