[ntp:questions] 500ppm - is it too small?
david at ex.djwhome.demon.co.uk.invalid
Fri May 8 07:29:19 UTC 2009
David J Taylor wrote:
> David Woolley wrote:
>> A reasonable expectation of a cheap crystal is 50ppm static plus
>> <10ppm temperature dependent. When one gets >500ppm it suggests the
>> problem is rather worse than poor crystal tolerancing.
> I am inclined to agree. One reference I found was this:
This seems to suggest crystals have quadratic temperature dependency.
My understanding is that normal cuts have cubic dependency. Of course,
32kHz crystals are often cut for wrist watch use, and using a cut with
quadratic characteristics might give a flatter response close to body
temperature, at the expense of poorer behaviour for signficant deviation.
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