From: Boris Mohar
Subject: Re: Strange going-on with a floating MOSFET gate
X-Newsreader: Forte Agent 1.92/32.572
Date: Sat, 04 Jan 2003 20:35:58 -0500
NNTP-Posting-Date: Sat, 04 Jan 2003 20:39:18 EST
Organization: Bell Sympatico
On Sun, 05 Jan 2003 00:49:58 GMT, John Popelish
>Winfield Hill wrote:
>> . ,-----+---- current -----,
>> . | | recorder |
>> . D volt +
>> . float --- G meter supply
>> . 2.04V S 695mV -
>> . | | |
>> . '-----+------------------'
>> The gate voltage should have dropped, and the drain current should
>> also have dropped. Instead the current rose from 540uA to almost
>> 900uA during the two hours. !!!
>> An additional very strange thing happened, twice. More later.
>Win, did you take any precaution to control the voltage between your
>circuit and Earth, or was the whole thing just floating (including any
>current injection between the current meter and Earth that may have
>been data dependent)?
Breathing on it will activate the surface contaminants that will start to
conduct. Now it is a tossup of surface leakage between D-G and G-S.
The best encapsulating material for experiments that excludes air and
moisture is wax. If you can find soft wax it is even better because it
minimizes weird triboelectric and piezoelectic effects that take forever
to level out.
Keithley used to give away a book titled Low Level Measurement formerly
titled Electrometer Measurements. No publication number on it. I know,
because the book is in my lap;)
Viatrack Printed Circuit Designs