what is the differences between a small signal model and a large signal model?

Question

how to differentiate both

Answer 1

A small signal model takes a circuit and based on an operating point (bias) and linearizes all the components. Nothing changes because the assumption is that the signal is so small that the operating point (gain, capacitance etc) doesn't change. A large signal model takes into account the fact that the large signal actually affects the operating point and takes into account that elements are nonlinear and that circuits can be limited by power supply values. You can't get 10 volts out of a 1.5 volt supply without transformers. A small signal model ignores supply values.

Answer 2

Wow, I have read transistor/VLSI circuit books that explain small vs. large signal analysis very poorly, and then some guy on Yahoo puts it all in focus.

Eugene has a very elegant response; pick that one for best answer.

I can only add a simple example to his answer. Imagine a simple transistor amplifier circuit that proportionally amplifies over a small region of input voltage. If we keep that input within a certain range (small signal analysis), our amplifier behaves linearly. If we put in too large a signal, our amplifier will not necessarily give us a proportional amplification (large signal analysis where the transistor may enter triode or cutoff regions). We generally like our amplifiers linear in analog circuit design.

Answer 3

small model wont be catchy enough and it will not have enough space to give out whatever you want to explain.but big model is advantageous.but for what is the models required?