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What's the most temperature stable capacitor?

I've been asked to design a low pass filter, but, it's to work over the range -40C to +65C (maybe +75C). The frequencies of interest are around

2Hz so it looks like I'll need capacitors in the range 1uF to 4u7. Oh, and it's meant to be small so surface mount components would be best (but I'd be happy to sacrifice that requirement if necessary).

What's the best kind of capacitor to use here? I don't think the usual dielectrics - X7R, etc - are characterised to -40C and I'm sure they will be 20% or more out by that temperature. Are there more exotic capacitors available, perhaps from non mainstream suppliers, for this kind of application, that might reach 1uF?

Thank you

Nemo

Reply to
Nemo
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"Nemo" skrev i meddelandet news:hZyWmkBmn64GFwm+@furfur.demon.co.uk...

One of the stable ceramic dielectrics is COG which has a temp. coefficient

Reply to
Stig Carlsson

Stig Carlsson suggests ...

Comprehensive answer with nice plot twist at the end - thank you - sounds extremely useful!

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Nemo
Reply to
Nemo

Use smaller components, and synthesise the required value. Possibly use a gyrator, and an inductor. Or go for a complete active filter design. The most _accurate_ solution, will be to do this using a DSP (at this frequency, you could even potentially use quite normal processors, rather than DSP designs). With crystal timing, it'll beat anything possible with pssive components. You are not going to get small accurate bipolar capacitors. Even if you sacrifice the 'size' requirement, the cost will be silly....

Best Wishes

Reply to
Roger Hamlett

How sharp a cutoff do you want?

Can you do it in the digital world? (Quartz crystals are pretty stable over temperature.)

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These are my opinions, not necessarily my employer's.  I hate spam.
Reply to
Hal Murray

Nemo schrieb:

Also have a look at the MKM capacitors by WIMA - they are made of such a mixed dielectric, especially for (relative) temperature independent capacity.

Tilmann

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http://www.autometer.de - Elektronik nach Maß.
Reply to
Tilmann Reh

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