The idea of small-signal modelling is that the short-cut part of the current-voltage characteristic of the semiconductor diode is not precise enough in an exact approximation and it is logical to represent the diode as a resistor at the short-cut. Using the circuit analysis technique we can find the small-signal resistance of the diode. Kirchhof equations with a diode as a load will help to calculate the ${I}_{diode}$ and ${V}_{diode}$. These values of voltage and current for the diode are called the *operating point* of the diode.

**Piecewise linear diode model:** In this model the diode is considered as an open circuit when it is off, and as a linear resistor with the offset voltage in series, when the diode is on. And close to the operating point, discussed above, the diode behaves as a small-signal resistance with: ${r}_{diode}=\frac{{{\partial}^{i}}_{diode}}{{{\partial}^{v}}_{diode}}$ calculated in the operating point. This method helps to use the semiconductor diode more accurately in its states.