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Design >> Analog Design >> XTAL for 32kHz operation
https://designers-guide.org/forum/YaBB.pl?num=1360002289

Message started by ic_engr on Feb 4^th, 2013, 10:24am

Title: XTAL for 32kHz operation
Post by ic_engr on Feb 4^th, 2013, 10:24am

Hello

We have had a customer usig 32kHz crystal with our designed oscillator which was pierce topology.

What we are told, is that if the metal lid of teh crystal is left floating teh system is very sensitive to Charge accumulation of 2kV using balloon charged by rubbing.

If the metal lid is grounded the problem goes away.

Does anyone know if this phenomenon is expected that the crystal parameters change due to 2kV charge ?

Regards

ic_engr

Title: Re: XTAL for 32kHz operation
Post by wave on Feb 4^th, 2013, 6:36pm

ROFL! LMAO!

Ok, I've fielded hundreds of crystal questions. None this funny.

Balloon?! Is that a scientifically repeatable condition?
ISO calibrated lab ?

Try thinking in terms of ESD rather than xtal parameters, for charge accumulation.

WAVE
;D

Title: Re: XTAL for 32kHz operation
Post by ic_engr on Feb 5^th, 2013, 6:38pm

Hello Wave,

Let me give you a bit more details. The system being body worn, the person wearing it noted that while jogging or running with poly-ester shirt, the time base moved few second in 5mins time span.

In the lab, the way to replicate was using a balloon rubbed and checkd for static chagre of 2kV.

Any ideas, or still hard to believe, eh?

ic_engr

Title: Re: XTAL for 32kHz operation
Post by loose-electron on Feb 8^th, 2013, 6:45pm

you are probably crashing something due to ESD event

The crystal will run at its frequency, however what you are describing can mess up everything attached to the the crystal.

Title: Re: XTAL for 32kHz operation
Post by ic_engr on Feb 11^th, 2013, 5:44am

Grounding the casing of the crystal seems to fix the issue, so wonder is groundign the casing a standard practice or leaving it floating.

ic_engr

Title: Re: XTAL for 32kHz operation
Post by ywguo on Feb 12^th, 2013, 7:29pm

Funny.

Quote:

Grounding the casing of the crystal seems to fix the issue,

How do you ground the case of the crystal?

Yawei

Title: Re: XTAL for 32kHz operation
Post by Lex on Feb 13^th, 2013, 6:42am

ic_engr wrote on Feb 4^th, 2013, 10:24am:

Doesn't sound odd to me. The vibrating crystal is converting mechanical resonance into an electric resonance by piezoelectric properties. Since it is made of piezoelectric material, a large voltage can have mechanical effects, which on their turn change the frequency. Over time it can cause damage in the crystal, affecting reliability. So I guess you should do something about it. ;)

Title: Re: XTAL for 32kHz operation
Post by RobG on Feb 23^rd, 2013, 1:29pm

Maybe the ESD event is shutting down the amp so the time you lose is the amount of time it takes to restart? Or maybe causing some chatter if you are gaining time.

It also doesn't take a lot of leakage to debias the amp...