From: Andreas Robinson (sleeper75se_at_yahoo.se)
Date: 2002-02-01 16:16:58
--- In buildcheapeeg_at_yahoogroups.com, "Joerg Hansmann"
<info_at_jhansmann.de> wrote:
Hi Joerg,
> > Oops. I meant "in parallel" of course... when the
> > capacitor shuts of at low frequencies, you
> > basically have a 1Mohm resistor
>
> 10 Mohm ? At least this was the value I have written
> in the schematic...
Double fault. I meant 10. :-)
[snip]
> > By the way, why don't you use an integrator
plugged
> > into the REF-input?
>
> I have seen this sort of hp in the datasheets and bm
> schematic and do not understand the point.
> IMO it is effectively a hp-filter. However I could
> also get the same characteristic with a simple RC
> hp. So why waste an additional op-amp ?
Ok, I've attached an image that might change your
mind. It shows two instrumentation amplifiers, running
at +/- 2.5V. Both have G=100 (approximately), but one
is DC coupled and the other AC coupled using an
integrator. I'm feeding both a 1mV signal with a 25mV
offset.
The one with DC coupling is saturated, while the other
one is still working. As you pointed out, this is not
a true AC-coupling effect, as both amplifiers are
saturated at 30mV. Anyway, the DC-coupled version
begins to distort the signal at around 15mV offset, so
you get an extra +/-10mV (66% increase) offset range
without lowering the gain or using hp-filters (with
noisy resistors) at the inputs.
[snip]
> > I had to play around a bit with the DC-current of
> > I1 (60000 amperes, how does that sound? :-)
>
> It sounds like only a theoretical diode would
> survive this ;-)
Or a really big one, you can probably find those
puppys at power plants. Hmm, they are probably bigger
than puppys too. :)
> > It's just
> > "plug in equation A into equation B and give it to
> > the supercomputer (My HP-48 calculator)".
>
> The portable math-lab ... or even better ?
Slower at least. :) But a lot faster than doing things
by hand.
> I do not have anything comparable on my PC,
> so for future equations I fully rely on you
> and your supercomputer ;-)
Well, you can have a HP48 too! Sort of. It is out of
production, but there are emulators... (that are
faster than the original)
A beginner's page:
http://www.area48.com/index.html
Latest emulator version:
http://privat.swol.de/ChristophGiesselink/emu48.htm
Regards,
Andreas
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This archive was generated by hypermail 2.1.4 : 2002-07-27 12:28:37 BST