Re: EDN: Measuring Nanoamperes

On Fri, 04 May 2007 07:37:56 GMT, Robert Baer
<robertbaer@xxxxxxxxxxxxx> wrote:

John Larkin wrote:

On Fri, 04 May 2007 00:20:26 +0000, Mike Monett <No@xxxxxxxxx> wrote:


To All,

Paul Rako has an interesting article in the April 26 issue of EDN,
titled "Measuring nanoamperes". He measures the 1uA current in a
32,768 Hz watch crystal using a Tektronix CT-1 current probe. (This
is beyond the max frequency spec, but additional calibration
indicates it may be ok. Also see my article below on analyzing
crystal oscillators in SPICE.)

The main part of the article is a companion to the articles Bob
Pease wrote on measuring the input current of the National LMC662.
They are "What's All This Teflon Stuff, Anyhow?":

http://www.national.com/rap/Story/0,1562,4,00.html

and "What's All This Femtoampere Stuff, Anyhow?":

http://www.national.com/rap/Story/0,1562,5,00.html

He includes additional circuit details by Paul Grohe, plus photos of
the actual setup.

There are two reference sections with some good links, including
"Counting Electrons: How to measure currents in the attoampere
range", by Adam Daire, Keithley Instruments:



Except they never actually count electrons.

I've always wanted to build a circuit that could clearly resolve
single electrons. 1 electron into 1 pF is about 160 nV, hard to dig
out of the noise.

I think maybe you could use an eprom cell to demonstrate
single-electron steps. Or possibly some sort of varicap-based
parametric amplifier.

John

What about a "micro cell" that has an oil drop and field plates - to
make a minature version of the infanous Millikan oil drop experiment?

I still want to do it with an uncooled electronic circuit that can be
made with available parts.

John

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