[time-nuts] Super stable BVA Quartz resonators... BVA??

Jeff Mock jeff at mock.com
Sat Dec 8 13:49:00 EST 2007


Thanks for the description, it is very interesting.  I have a follow up 
question if you don't mind.

How does crystal aging look on a graph of temp versus frequency.  This 
graph has some temperature point where the slope of frequency variation 
goes to zero and the crystal is quite stable around this temperature.

What does this graph look like as a crystal ages?  Does the optimal 
operating temperature change over time, that is, does the graph tend to 
move left and right, or does aging tend to move the graph vertically 
(the optimal freq stays the same, but the optimal operating temperature 
changes as a result of aging).

I hope this makes sense...
jeff


Bernd T-Online wrote:
> Hi all,
> 
> For explanation how the BVA works, please see the attached slide which 
> shows schematically its internal construction. (The explaning text is in 
> German, as it is from my periodically given crystal seminar.)
> The key points which yield the BVA's improved aging are, that
> - the whole resonator package is made from quartz, consisting of the 
> resonationg quartz plate in the middle section and the two mounting & 
> sealing plaates on top and bottem - you may call it a Hamburger style ;-)
> - the resonating plate is held through quartz bridges rather than metal 
> suspensions, thus reducing mounting stress.
> - the BVA is "electrodeless", as the electrodes are evaporated on the 
> inner side of the upper and lower mounting plates. Therefore no stress 
> between the quartz surface and the metal eletrode.
> - Therefore the energizing electrical field is applied through an 
> airgap, which represents two small load capacitors in series to the 
> resonator, thus making the resonator electrically "stiffer" and less 
> sensitive to circuit influences.
> 
> On the other side you may imagine the main problems associated with such 
> a construction:
> - The difficulty to manufacture the convex and concave shaped parts with 
> such a precision, that the curvature yields a constant and very small 
> airgap.
> - To realize the fine adjustment to frequency, because the unit cannot 
> be tuned in the conventional way, i.e. by plating some metal on the 
> electrode.
> - The frequency accuracy to which the resonator has to manufactured, 
> because the resonator frequency cannot be pulled with the external 
> circuit elements by more than some hundred ppb.
> 
> It may be interesting to note, that there was a company "BVA 
> Industries", which wanted to generate their income solely from making 
> BVA - which failed. Maybe because of the cost could not be covered by 
> the revenues from the rather limited market.
> 
> Bernd DK1AG
> __________________
> AXTAL GmbH & Co. KG
> Facility MOS
> Wasemweg 5
> D-74821 Mosbach / Germany
> fon: +49 (6261) 939834
> fax: +49 (6261) 939836
> www.axtal.com
> 
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.




More information about the time-nuts mailing list