Once concept I find ignored quite a bit – including myself among the guilty – are the assumptions for “small-signal” analysis.
As taught in introductory classes, small-signal analysis occurs over an infinitesimal increment about some fixed operation point (which used to be known as the “Q” point – for “quiescent”. Is it still? I haven’t heard the term in years).
The incremental change required dealing with derivatives but in the incremental model, the derivative became a linear change “
“. While this is correct given the basic assumptions, it seems we get in the habit of thinking that “linear systems” are indeed always linear. Even resistors are not necessarily linear over temperature if a 2nd-order tempco term is significant (and included in the model).
Computers only calculate functions given to them. If the underlying model is flawed, so will be the result. Trouble is, one can get by in the vast majority of situations. But for precise work, getting by isn’t good enough.
Read the article.