[time-nuts] Mini ovens packaging

Magnus Danielson magnus at rubidium.dyndns.org
Sat Aug 13 09:57:19 EDT 2016


Hi Guillermo!

Nice to see you ask questions here!

(Attila and I met Guillermo at the EFTS and had many nice discussions 
and nice time to hang out. He does his PhD in MEMS systems, which Attila 
refers to. I also met him at IFCS in New Orleans when he came up to me 
and Dr. Rohde and asked questions on phase-noise measurements. I hope he 
got that resolved eventually.)

On 08/12/2016 11:59 PM, Attila Kinali wrote:
> Hey Guillermo!
>
> How is it going?
>
> On Thu, 11 Aug 2016 09:05:02 +0000
> Guillermo Sobreviela Falces <Guillermo.Sobreviela at uab.cat> wrote:
>
>> I am currently looking for a temperature compensation system for an IC
>> (Temperature range from -40°C to 120°C and chip area of 1cm x 1cm).
>> This compensation system has to be external to the IC and, as the power
>> consumption is not the main problem, I have been looking for a crystal oven.
>> The ideal solution will be a PCB compatible oven, but it also can be an
>> external element.
>
> I guess this is for one of your MEMS chips?
>
> What is the spec of the board's environment temperature?
> How big may the oven be?
>
> And I would agree with Bob that building your own oven would be
> actually a good idea. It is not that difficult. You need a rough
> estimate of what your thermal mass inside the oven will be, an
> estimate on what the thermal resistance between the inside and
> outside is, then can apply standard control theory to design
> a PI control loop to keep it stable.

I agree with Bob and Attila, try to build your own, to get something 
working isn't all that difficult, and I think that in the end you will 
benefit from having the knowledge and additional system insight.

A good test for the trimming of the stability is to turn it on while 
cold. I learned this the hard way on a sample that a supplier had sent 
me, it oscillated wildly on turn-on, which was obvious on the current.
The remaining oscillation caused the ADEV to have a bump, which was the 
first feature I discovered.

For crystals, the oven is set to the turn-over point so that the oven 
variations has least impact on the frequency. Do you have a suitable 
turn-over point?

Another aspect to reflect on, and here I refer to Rick Karlquist's 
paper, is the temperature gradient sensitivity. Do your device have 
frequency sensitivity to temperature gradients in any directions?

Some crystal devices have achieved better performance by putting the 
temperature sensing thermicaly close to the crystal, it's a generic hint 
but it can be good to think about how it can be achieved in the long run.

Cheers,
Magnus



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