Small Signal Resistance

Created at: 2025-02-02

We often deal with electronic devices for which I is not proportional to V ; in such cases there’s not much point in talking about resistance, since the ratio V /I will depend on V , rather than being a nice constant, independent of V . For these devices it is sometimes useful to know instead the slope of the V –I curve, in other words, the ratio of a small change in applied voltage to the resulting change in cur- rent through the device, ΔV /ΔI (or dV/dI). This quantity has the units of resistance (ohms) and substitutes for re- sistance in many calculations. It is called the small-signal resistance, incremental resistance, or dynamic resistance.

(The art of electronics 3rd ed.).

Zener diodes are an example of the above.