[time-nuts] Improving the stability of crystal oscillators

Enrico Rubiola rubiola at femto-st.fr
Mon Oct 15 11:19:59 EDT 2007

Dear all,

the major problem for the use of a Peltier cell with
a quartz oscillator is that the cell maximum operating
temperature is of the order of 80 degrees Celsius.
This is due to the low melting point of the metal pairs
suitable to produce the Peltier effect (reversed thermocouple).

The resonator inversion temperature occurs at 70-80
degrees Celsius, depending on the cut angles.

A more general problem is that
a good temperature controlled oven has high thermal
resistance, limited by the dissipation inside the oven.
Unfortunately, the Peltier cell has low thermal resistance,
which means poor isolation from the oven.

This problem is made worse by the joule effect, which
always go with the Peltier effect.  For this reason, the
temperature fluctuations of the Peltier heat sink tend
to be larger than the environment fluctuations (unless
you use water cooling!).  Thus, the thermal fluctuations
propagating through the Peltier cell tend to be an amplified
version of the environment fluctuation.
This phenomenon is dramatic when the Peltier cools down,
and a minor problem when the Peltier cell heats up.

Very best,


On 13 Oct 2007, at 22:13 , Don Collie wrote:

> ); SAEximRunCond expanded to false
> Errors-To: time-nuts-bounces+rubiola=femto-st.fr at febo.com RETRY
> Has anyone concidered using a small Peltier pile to maintain the  
> crystal`s
> temparature. I understand that these devices will heat or cool, so  
> it would
> be possible to maintain the crystal temparature at , say, 25 degrees
> celcius, over a range of ambient temparatures
> [perhaps 0 to 70  degrees]. There would be several advantages in this
> approach.
> Cheers!,................................Don Collie jnr.
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Enrico Rubiola
professor of electronics

web:	http://rubiola.org
e-mail:	rubiola at femto-st.fr

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