From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-01-07 19:49:11
--- In buildcheapeeg_at_yahoogroups.com, "Joerg Hansmann" <info_at_jhansmann.de> wrote:
> Hi Andreas,
>
> ----- Original Message -----
> From: sleeper75se <sleeper75se_at_yahoo.se>
> To: <buildcheapeeg_at_yahoogroups.com>
> Sent: Monday, January 07, 2002 9:25 AM
> Subject: [buildcheapeeg] Re: Input protection
>
>
> ...
> > But... :-)
> >
> > You've only measured DC-impedance,
>
> Yes. I have had trouble setting up the AC-analysis with
> SWCAD3... (The GUI is quite different from MICROSIM)
I noticed ... I'm having trouble plotting anything. How do you set a
probe?
>
> > and unfortunately we don't get
> > those fabulous numbers for AC.
>
> You are right. But the results are nevertheless
> very usable:
> About 25.6 MegOhms impedance at 50Hz with C1=100pF and
> about 130 MegOhms impedance at 50Hz with C1=0pF.
Yes, I agree.
And for those who are interested in altered states we should mention
that the impedance gets higher for lower frequencies. Below 10Hz the
it is excellent - over 100MegOhms with a 100pF capacitor.
> As you can see the impedance depends largely on C1.
> That is the price for HF suppression (562kHz -3dB BW)
Well, it is just two capacitors. People can then choose between one
or the other depending on their situation.
>
> What is missing in this simulation is the effect of the
> DRL. It will enhance the common mode impedance by
> its gain (e.g. 1000, giving 12.8 GOhms impedance
> ( (25.6 Meg || 25.6 Meg ) * DRL_gain)
> ).
That's nice.
> > It will probably work quite nicely anyway, but perhaps not with
> > INA114
>
> I think it is ideal for INA114.
> Unlike high ohmic protection resistors the new protection circuit
> is not very susceptible for the INA114 input noise current.
>
>
> > - it would be too noisy.
>
> Why ?
> I do not understand the reason.
Ehm, you got me there, I must have punched in an extra zero on my
calculator yesterday, so I got one order of magnitude more noise.
Sorry. :-)
By the way, what do you think of this amplifier then:
http://www.linear-tech.com/pdf/1167f.pdf
Jim has commented on my design so I'm going over it now and that made
me look at Linear for instrumentation amps, and that when I found it
(just a few minutes ago).
The cost is decent (ranging from $3.70 to $7.40), and from just
browsing through the datasheet, I think it is better. Also, it comes
with sufficient ESD protection built in. Just add two 5k resistors! :-
)
Regards,
Andreas
This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:36 BST