Then why are we able to give input to this non-linear circuit from 1mV to 1000mV in LTspice Simulator. It should show some sort of error, as we are going out of non-linearity
Thanks..
Hanumantas, as I have mentioned - the signal (independent on its real value) is TREATED by the simulator as if it would be small enough to stay within the linear range of the part.
Or - other way round: The part is TREATED (idealized) as if it would have a linear transfer characteristic through its bias point. This is equivalent to a tangent drawn through the dc bias point.
The user of the simulator must know that the ac analysis does not recognize any non-linearity and that this particular analysis does nothing else than to use the SLOPE of the nonlinear characteristic for calculation.
Therefore, this analysis primarily is used for gain calculations or any other calculations which involve the RATIO of two quantities - like input or output resistances of amplifiers.
Counter example: It is not a good idea to use the ac analysis for calculating the current through a diode as function of the applied voltage (because the desired result is not a ratio of two parameters).
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Another explanation: The ac analysis does nothing else the you do with pencil and paper when you try to calculate currents and voltages in a
linear network consisting of R, L, C .
In this case, the results also are independent on the sources and its (fictitious) values