> Yes, that is tight. However, I have now been told that 6min/year is
> acceptable. Thats still +/-11.4ppm however.
>
> > If you can maintain a constant ambient temp this
>
> No chance of that. Its automotive after all! sPEC IS -40 TO +80 Deg.C (which
> is the industrial temp range).
>
> >best crystal (coldweld package) you can get is going to be 5ppm over
>
> Thanks for your suggestion... I'll look into cold welded crystals.

>You are likely going to have to use some type of temp stabiliser to
>get the accuracy you require.  If you can spare the energy then you
>could use a heater (classic crystal oven principal) to hold the
>occilator at a temp of between 60 and 80 Deg.C with a simple
>controller.  Insulation would then reduce fluctuations and if would
>not spend a lot of time away from 60 C.

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How about using a temperature sensor to make a software-controlled
TCXO (temperature compensated crystal oscialltor). The frequency
response curve of a crystal is a fairly well known "S" curve; you
could measure the temperature and know how off it is. If you wanted
to get really fancy, you could use an '84 and have that calibration
as part of the production process; or you might find that one
calibration curve could fit a family or lot of crystals.

Cheap GPS receivers use this technique to know their osciallator's
frequency precisely.


John Maushammer
jmaushammer@SMTPLINK.CTA.COM