Current-voltage
Ohm’s law describes the common current-voltage relationship, which has a linear, positive slope (see the figure). Fundamentally ohmic devices are found in every electronic product as discrete resistors and within ICs. But while linear resistance is comfortably familiar, nonlinearity and negative resistance are complementary topics that deserve equal attention.
Nonlinearity is just as necessary, as its linear counterpart to perform many useful functions. Weak nonlinearities may be ignored for practical purposes in many cases or exploited purposefully and advantageously in others. Both linear and nonlinear behaviors can be understood concurrently. The subject is found laced throughout electrical engineering, from physics to chemistry, the biological sciences, and other disciplines. Ultimately, thinking outside the limitations of Ohm’s law may allow us to discover new ways to make circuits perform.
As is simply stated by S.A. Maas in Nonlinear Microwave and RF Circuits (2nd edition, Boston: Artech House, 2003): “All electronic circuits are nonlinear: this is a fundamental truth of electronic engineering.”