From: Sar Saloth (sarsaloth_at_yahoo.com)
Date: 2002-03-12 17:19:18
just comments here from me, no real answers....
At 08:21 AM 2002-03-12 +0000, you wrote:
>Hi Sar and Joerg,
>
>just a quick question:
>
>Joerg (?) wrote:
>
> > >In the LTSPICE simulation the addon did not perform very well ;-)
> > >(Neither did the LT1114)
>
>Did it? I thought it was a bit slower in the beginning, but the
>oscillation subsided just as fast as with the other opamp.
I couldn't see the difference either, but I guess I didn't know what I was
looking at.
>Do you
>guys have any top-of-the-head suggestions for replacements? Something
>with < -96dB channel crosstalk and > 96dB SNR would be nice.
Those previous discussions were for the virtual ground which doesn't have
the same constraints. As far as input circuitry, the specifications you
are talking about are intimately tied to the entire input circuit and the
impedances etc.. The precision low input bias current (super beta) bipolar
op-amps from LT that we are already looking are a very good candidate. I
would suggest that if you are using dual op amps in a fairly standard
package that most op amps would be able to plug into the circuit. I
haven't done any searching yet - probably tomorrow. I see that Joerg has
designed some input protection circuit, so I imagine he would have a very
good handle on the requirements for a low-noise input. As far as cross
talk, I suspect that power supply etc. are going to be significant and if
you are using dual op amps (which are probably better for optimal layout of
the signal) in the differential configuration, then in-package cross-talk
will be for the same signal pair anyway.
I have never worked with differential circuits past the very first stage.
I noticed that Analog Devices (or is it National Semiconductor ?) has (I
can't remember which) now has differential op amps, with differential
inputs and outputs and uses signal ground as a common-mode
signal. Unfortunately, I don't see how those op amps can then be used to
provide the driven reference electrode as the design has, so I don't know
if this is of any use. Joerg?
>Regards,
>
>Andreas
>
>PS.
>
>ACK means ACKnowledged. But perhaps we should use ARGH! more in our
>conversations? ;o) Just kidding.
ACK (and thanks)
>DS.
>
>PPS.
>
>A short progress report on TinyEEG:
>
>I worked a bit on the power supply this weekend and have successfully
>managed to reduce the HF noise to levels undetectable by oscilloscope.
Looking at the lowest level signals is a problem I frequently have. What
is the best solution?
Has anyone built an inexpensive differential preamplifier? As long as the
bandwidth does not need to be very large, I was thinking that a very low
noise Instrumentation amplifier and an IL300 linear optocoupler should give
excellent isolation. These things look like a couple thousand commercially
(although with higher bandwidth and protection I assume). I have had
excellent results with linear optocouplers in the past.
_________________________________________________________
Do You Yahoo!?
Get your free @yahoo.com address at http://mail.yahoo.com
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:40 BST