From: Joerg Hansmann (info_at_jhansmann.de)
Date: 2002-01-09 16:54:44
Hi all,
----- Original Message -----
From: Jim Meissner <jpmeissner_at_mindspring.com>
To: <buildcheapeeg_at_yahoogroups.com>
Sent: Wednesday, January 09, 2002 1:31 PM
Subject: Re: [buildcheapeeg] New input stage
...
> Check this out with the chief engineer Joerg Hansmann.
I do not feel as a chief engineer at all, for this position
I simply do not have enough experience and knowledge nor
the required leading qualities ...
[many important points snipped due to a lack of time]
...
> Opinion: The U1 gain could be set much higher and U3 lower.
> Also U1 has half the noise at a G = 100 vs. G = 10.
For low noise high gain in the first stage is good, but not for
electrode DC offsets. (saturation of the input stage)
Therefore I have used INA114 with G=10 (according to the application
example in the INA114 datasheet for an ECG monitor ).
At gain=10, the INA114 seems to be superior to the lt1167.
Electrode offsets can easily result when combining different electrodes
(my electrode supplyer LAZINA told me, that some people really
combine different types) or when the Chloride skin of AgCl type
electrodes wears off.
I have assumed that 100mV DC electrode offset should be handled by the input
stage. But maybe I was overly cautious.
Some electrode experts here, who know about electrode offsets ?
Regards,
Joerg
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