Hi guys,

I have a generalised op-amp question.  I am having trouble trying to
extrapolate what I need to know from manuals and datasheets, so maybe one of
you experts here in analog electronics (something I definately am not) can
help me with understanding the concept.  This may seem like a dumb question
to some of you, but here goes...

Do op-amps have a limit on the amount they can amplify a signal ?  What I am
finding is that if you increase the difference in resistance in the divider
in a differential amplification setup, at a certain point, the signal
becomes non-linear at the peaks.  Increasing the reference voltage into the
op-amp does not seem to help.  At a certain point in the divider value, the
output simply shifts further up from zero, rather than increasing the gain,
and the peaks are flattened out.  Note that this is not the same as getting
the low point to zero on a non rail-to-rail op-amp by providing a negative
reference - I am already doing this.  I am having a great deal of trouble
getting much more than about 20x gain from an LM358.  I would like 100x
gain, but this seems impossible to achieve with this op-amp, even though it
is marketted as a "HiGain" op-amp.

I am pretty sure of my observations.  I am not proto testing it, but SPICE
testing it with CircuitMaker, so I can see a sine wave amplified output
compared to a sine wave input - a good way to graphically see with a SPICE
transient analysis what is going on.

PS: I am good with digital electronics, but I wish I was better at analog
...

Rgs
Ian.

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