In the previous post the transfer function of an op-amp differentiator was derived:
To check this function isn’t way off, I’ve compared the step response using GNU Octave (a freeware Matlab competitor I’ve only recently discovered) with the step response in LTspice. For the purposes of the comparison I used the following values:
|A||100||kV/V||Op-amp DC voltage gain|
|τ||1/(2π)||rad/s||Op-amp corner frequency of 1 Hz|
A first-order op-amp model was used to derive the transfer function that’s being verified. Luckily, LTspice includes such a model: the three terminal “opamp” model which is described as an “ideal single-pole operational amplifier”. This model is very useful in situations where you’re more interested in testing a theory than attempting to simulate a real device. Here is the test circuit:
The two plots are very similar which gives me some faith in the transfer function.
I used the Mingw32 Windows install of Octave version 3.6.1 with the Control toolbox. Installation instructions can be found here: http://wiki.octave.org/Octave_for_Windows