Question

In regard to pn junction diode, what is the difference between a small and large signal model, and what are they both used for?

Also, how do both models relate to the I-V behavior/characteristics for the diode?

Answer 1

Small Signal is an small magnitude AC Signal . All components are treated as linear components since the small signal magnitude is so small that it does not push the circuit into non linear region.

Small signal analysis is primarily used to determine the Capacitance of PN Diode, since capacitance is the dQ/dV i.e. small change in charge with respect to small change in V.

Large signal Analysis is done to find the operating point of the device/circuit. Primarily large signal analysis is used to descrive non linear components in terms of non linear equations.

In case of PN Diode small signal analyis is used for calculating Diffusion Capacitance and large singal analysis is primarily used to analyze diode for digital applications i.e. to analyze how the current changes if switching is made instantly.