From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2001-12-21 17:51:12
--- In buildcheapeeg_at_yahoogroups.com, "Jim Meissner" <jpmeissner_at_mindspring.com> wrote:
> Dear Group:
>
> I have hand drawn the input stage from the EEG that I built
> some years ago. Please look at my webpage under Brain Wave
> Monitor. EEG01.gif
Hi Jim, thanks for the schematic!
I've got a couple of questions:
You are using 47pF caps in a couple of places. They are there to
limit the bandwidth of the amps, right?
> If you look at the schematic you will see that this circuit is
> capable of more than 10 giga ohm input impedance, but ultimately I
> chose to use 10 meg ohms to ground. This is where the theory-
> simulation and practical collide.
>
> You will also see that this is capable to drive the shields and it
> works better with the shields grounded. Again practical.
What kind of problems did you run into before you added it?
Do you use a ground electrode as well, that is not shown in the
schematic?
> Note my clever guarded driven protective diodes.
Stupid question: Can the ESD-protection be improved if one puts a
regular double diode to the shield/amplifier output so that the
current can be diverted to the power rails as well?
> Note that I chose to DC couple the preamp.
>
> Note that I chose to run from +/- 12 volts and tried +/- 5 volts
> first. You need some common mode compliance to reduce overload
> saturation from real world events.
In what voltage range did these disturbances fall? Would an AC-
coupled amplifier that can handle offsets of around 100 - 300 mV and
transients of about 4 mV be sufficient?
/Andreas
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:35 BST