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This technical note from Analog Devices indicates that low dielectric absorption is a prime requirement for choosing a capacitor for a sample-and-hold circuit (see page 11). It also suggests to look for capacitors advertised as low dielectric absorption.

How do I go about searching for capacitors designed for low dielectric absorption? On Digikey and Mouser, it's not one of the listed parameters.

I also tried searching based on dielectric type, based on information from Kemet and Wikipedia linking dielectric absorption to material. In this case, it seems like film capacitors are the best candidates (still can't find any datasheets that actually report absorption), but they have very low capacitance. Ideally I want 1uF or more capacitance, to limit the effects of charge injection from the analog switching logic.

What terms and parameters should I use to guide my search?

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The dielectrics with lowest absorbtion are vacuum and air (which is jinxed in normal conditions by porcellain, glass or saphire). Out of normal dielectrics, teflon was the best in last century. There possibly some improvements done for polypropylene and plyester caps. There is an article by Bob Pease about the phenomena http://electronicdesign.com/article/analog-and-mixed-signal/what-s-all-this-soakage-stuff-anyhow-6096

So you solution may involve teflon or normal plastics. But if you are designing new 9 digit voltmeter, then the capacitor design becomes very interesting, as interesting as real analog trade secret can be.

BTW the percentages for DA cited on Analog Devices pages are in range of 0.001%..

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  • \$\begingroup\$ You have any idea where to look for the papers formerly found in the "good technical stuff" section of his website, which no longer can be found at www.national.com/rap ? \$\endgroup\$ – Ben Voigt Sep 6 '12 at 2:17
  • \$\begingroup\$ Found it: The Best of Bob Pease, linked from ti.com/ww/en/bobpease/index.html \$\endgroup\$ – Ben Voigt Sep 6 '12 at 2:31
  • \$\begingroup\$ And where are these Analog Devices datasheets with 0.001% DA? AFAIK, Analog doesn't make capacitors... \$\endgroup\$ – Ben Voigt Sep 6 '12 at 4:09
  • \$\begingroup\$ analog.com/library/analogDialogue/Anniversary/21.html at the end of page there is list of dielectrics \$\endgroup\$ – user924 Sep 6 '12 at 11:11
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The best are Teflon, followed by polystyrene and polypropylene. Polyester is not so good. Ceramics are also bad. Only polypropylene is really easy to find. Are you sure this is what you need?

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