From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2002-03-08 17:32:54
Hi,
----- Original Message -----
From: sleeper75se <sleeper75se_at_yahoo.se>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Friday, March 08, 2002 6:41 AM
Subject: [buildcheapeeg] Re: High resolution EEG schematic
...
> To be honest, the control theory course was something I just took and
> forgot. :-p This is Joerg Hansmanns design and he has done thorough
> SPICE simulations (and real testing? Joerg?)
A similar circuit is working quite well in the comEEG prototype.
However I must admit, that the testing level is quite low
(on the oscilloscope I could not see oscillations).
To be sure a more thorough test should be done with a function
generator that injects a square wave into the control loop.
(any volunteers here with the right equipment ?)
IIRR the important trick in the virtual ground circuit was the
ESR of the tanatalum C at the output of the op-amp. An ESR of about
500mOhms provided a negative phase shift of about 90 degrees at the
0dB point in the bode plot of the loop gain, resulting in a total
phase margin of about 90 degrees (what is very stable)
Regards,
Joerg
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