[time-nuts] Fundamental limits on performance
bruce.griffiths at xtra.co.nz
Thu Sep 17 04:06:05 UTC 2009
Chris Caudle wrote:
>> From: Mark Spencer <mspencer12345 at yahoo.ca>
>> For anyone who is interested here is a bit more info about the USO's used
>> in deep space applications and some comments abou the crystal based USO's
> I found it interesting that one of the limits of stability seems to be the
> ability to process the crystals at high temperatures to drive off
> impurities. The JHU crystals are apparently in some type of glass
> enclosure which can take the high temperatures, and the paper seemed to
> indicate that the standard metal capped packages can't take the higher
Bliley BFG61 package:
> I had forgotten until I read that paper that Fox has crystals which are
> packaged in quartz packages. I couldn't find any information on how the
> packages are assembled, so I don't know if the assembly process could
> handle the higher temperatures, but obviously if the package really is
> pure quartz, it should be able to handle temperatures as high as the
> quartz resonator.
The upper temperature limit is when the crystalline quartz undergoes an
irreversible phase transition to a non piezoelectric form.
> I would assume that the package is in two parts, and
> has contacts that penetrate the lower part of the package to connect the
> resonator to the surface mount pads on the bottom surface of the package,
> so it might depend on how the penetration is sealed, and how the top and
> bottom parts of the package are attached together.
> Just seemed interesting, I would assume that the JHU guys know about those
> types of advances in packaging, but the paper didn't mention it.
Look at the JHU site there is a little on the oscillator.
The BFG61 package uses an intermediate internal ceramic plate that more
closely matches the thermal expansion of the quartz crystal.
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