[time-nuts] 74HCT9046A Max. Operating Frequency

Tim Shoppa tshoppa at gmail.com
Thu Apr 24 10:29:07 EDT 2014

My feeling has always been that PC2 is most appropriate for very
wide-bandwidth (most of an octave or more) VCO's. I have used it at both
audio and in 1-2MHz region with success.

For 24.576 MHz VCXO, the fractional change in frequency will be in multiple
ppm not octaves, and I would naturally gravitate towards a simple diode DBM.


On Thu, Apr 24, 2014 at 4:41 AM, sg sg <micpreamp at yahoo.de> wrote:

> Hi,
> I'm about to implement a PLL for a 24.576 MHz VCXO using the
> phase-frequency detector (PC2) of the NXP 74HCT9046A. From the datasheet (
> www.nxp.com/documents/data_sheet/74HCT9046A.pdf) it is not clear to me
> what the maximum operating frequency for this phase detector is--from the
> enable and disable times (page 20 and figure 19) I presume 24.576 MHz is
> too much.
> So I probably need to add dividers at the inputs. Can someone advise me on
> the choice of division ratio?
> Thanks for your time,
> Samuel
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