Hello!
This is a summary of all the responses I got.
I have separated the replies with a ---------
I have had some follow up discussions with some, and I will be glad to
send further details to those interested.
Thanks to everyone who responded!
Madan
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The dutch company
SMARTEC BV
Delpratsingel 24
4811 AP Breda
Netherlands
Phone/Fax: ++31 76520 5353/4
delivers a circuit called UTI which can measure capacitances 0-2pF with < 2fF
resolution.
Regards
Torsten Eggers
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Check out the RCA corp. in USA, for their old (1980s) CD-ROM
drives. These drives are based not on laser's but on change in capacitance
directly below the electrode, they are easily sensitive to capacitance's
of the order of fF. However RCA phased them out after the advent of
semiconductor lasers, but they still produce (were till 2years ago)
components of these drives, for customer support. You could get in touch
with them their address of personnels and catalogues are available at
HTTP://www.rca.com/
Good Luck
Amit Shiwalkar
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Dont know about commercial suppliers, but I'm familiar with the
problem. Sensing such small capacitances using a commercially
produced, conventionally-packaged ICs (such as a FET op amp) as a
charge amplifier is difficult because the stray shunt capacitances
on the package pins is 3 orders of magnitude larger than the
capacitance being sensed. Mounting packaged parts on a circuit board
introduces even more capacitance, as does locating the amplifier
remote from the sensor.
We have combined MEMS-fabricated sensing elements with a custom VLSI
chip to form complex sensors. The custom IC incorporates arrays of
charge detectors, each of which is capable of resolving less than 1fF.
Perhaps incorporating a custom IC right into your sensing structure
may be useful.
Michael Mladejovsky, Phd.
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There a few.
PI Physik Instrumente, you can check their web page
MTI Advanced Product Division also makes capacitance sensing system and
sell components like pre-amps. They have a fairly knowledgable tech. rep.
Paul Slazas, 518-785-2389
Quanmin Su
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One important question is, do you want to measure VARIATIONS of 10's of fF,
or is this the absolute value of your capacitance? There is a CSEM chip
which has a (max) sensitivity of 200mV/pF; on a rest capacitance of typically
25-100 pF however!! I can send you contact person or more details if you
want.
There's also a chip from VTT Hamlin that does about the same, but for smaller
C0. I have no more details about that (yet).
Could you please forward other reply's about this subject to me. I'm looking
for an interface chip for a capacitive sensor with small C0 (a few pF's).
Best regards,
Steve.
--
Steve Reyntjens
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Check out MicroSensors's (www.microsensors.com) Universal Capacitive IC.
It's resolution is .05 fF.
Ying Hsu
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