I recently design an OTA based filter, and simulate it with LTspice IV. I was surprised to see that the gain vary with frequency (of course) but also with the input amplitude of the signal.
So I decided to simulate a basic RC filter to see how if the gain change with input amplitude, and the same thing happened.
Here is the schematic, with a variable AC amplitude (0.1, 0.2, 0.5, 1) :
And here is the plot :
I don't understand, the frequency response of a filter characterized by a transfert function V(out)/V(in) should vary only with frequency, and not with V(in), isn't it?