[time-nuts] Why do crystals go bad?
jimlux
jimlux at earthlink.net
Mon Feb 14 04:29:22 UTC 2011
On 2/13/11 8:15 PM, gary wrote:
> Two authors come to mind regarding crystal oscillators: Eric Vittoz and
> Marvin Ferking. Eric Vittoz is the more modern of the two. His writings
> tend towards long term stability of crystal oscillators. Basically, most
> designs put too much energy into the crystal, which he claims wears it
> out. I'd had to dig up his papers, but my recollection is the failures
> were soft (error in frequency) rather than hard (total failure). Ferking
> covers temperature stability and crystal pulling.
>
> I haven't dealt with crystal manufacturers in a long time, but my
> recollection is the crystal is "tuned" by metal deposition. As you
> deposit metal on the crystal, the frequency lowers. Possibly today they
> laser trim, i.e. remove metal.
metal deposition is still how it works.
The real unknown is what the frequency will be after aging.. you make a
bunch, run them for a while at higher than normal temperatures, and see
which ones look like decent candidates.
Anyway, I don't think opening up the case
> and fiddling with the innards is a good idea.
>
> Back to crystal manufacturers, these companies tend to be pretty small.
> when I was working on video chip designs, it was no problem talking to
> the CEO or VP engineering. I think it is a capital intensive rather than
> labor intensive business. They have a few gurus doing product design and
> that's about it.
>
Bliley is another crystal maker.
But you're right.. there's typically very few people who actually do the
stuff for high performance crystals/oscillators. THere will be a few
techs who have the skills to put the crystal in the holder and seal it
up. A few who make the crystals (running the saws), etc.
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