I'd have to agree, about ANY op amp out there can amplify more than 100x,
assuming you're not close to unity gain frequency. What frequencies are we
talking about? TTYL

> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Richard Prosser
> Sent: February 20, 2003 20:46
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: Differential Amplifiers
>
>
> Are you sure that you're not getting close to either of the
> supply rails? -
> Otherwise I can't think of much!
> 100x gain should be OK provided that the input offsets don't get out of
> hand - do both input have the same effective source impedance (or near
> enough the same).
>
> What frequency are you simulating your circuit - could you be hitting a
> slew rate limit - or the simulated effect of one?
>
> Can you send the circuit or put it on a website somewhere?
>
> Richard P
>
>
>
>
> 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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