From: sleeper75se (sleeper75se_at_yahoo.se)
Date: 2002-03-12 18:48:54
Hi Joerg and Sar,
----- 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.
>
> No. It had significantly less phase margin.
Ah, that would not be very visible in the step response I remember
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.
>
> The LT1114 performs nicely if the passive components are
> optimized for it:
>
> <snipped from other posting (not yet posted, just under
construction):>
> ...
> I have tuned the ESR compensated circuit for usage with the
> LT1114 (see picture VirtualGnd-Tuned02_bode_plot.png) by
...
Great, thanks! Looking forward to it.
----- Sar wrote:
> Those previous discussions were for the virtual ground which
> doesn't have the same constraints. As far as input circuitry,
> the specifications you
Actually, I'm still talking about the virtual ground... I know the
noise levels are not critical for the DRL-circuit, so there are many
opamps that would work just fine for that, but the VGND amplifier has
to be a good one. Of course, choosing a single-opamp package would
remove the cross-talk requirement.
For the differential inputs, I've selected LT1112 (two-opamp version
of LT1114).
> 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.
...
I think Analog is the place... but I'm not sure what types you are
talking about. If memory serves me right, a lot of the differential
amplifiers have fairly low input impedance, on the order of a few
hundred kOhms because they are mostly used for driving and receiving
low-impedance signals. Are the ones you are thinking about different
in this regard?
> Looking at the lowest level signals is a problem I frequently
> have. What is the best solution?
A lot of money => FET-probe / expensive oscilloscope ? :-)
> Has anyone built an inexpensive differential preamplifier?
...
Well, this group is all about building that sort of amplifier :-) If
you don't need bandwidth, a battery-driven inamp and an IL300 (with
proper drivers of course) should do the job nicely.
I imagine it is hard to measure EMI with an optically coupled
preamp... what kind of application do you have that requires galvanic
isolation between the scope and the circuit you are measuring? Is it
to avoid ground-loops and distortion etc...?
Regards,
Andreas
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