[lcamtuf] examines the concept of negative resistance in greater depth than expected. In ordinary resistance, current increases as voltage rises, whereas in negative resistance, current decreases when voltage increases. In negative differential resistance (NDR), the I–V curve slopes downward over certain ranges of the nonlinear voltage–current relationship. In neon lamps, increasing the current after the lamp has ignited can reduce the voltage.
There is no real passive component such as a -100 Ω resistor; such a device would supply power to the circuit and require an external source. A design using an op-amp can produce an ideal constant negative resistance within its operating range, but the circuit may be damaged if the limit is exceeded. Although the concept has limited practical use and is confined to special cases, it helps explain unusual examples such as tunnel diodes.
Why it matters
This distinction is important in circuit analysis because it shows that the term negative resistance can describe different modes of operation rather than a single physical component. The fact that NDR behavior appears only over certain ranges of the voltage–current curve means that examples such as neon lamps and tunnel diodes cannot be evaluated according to the same rules as ordinary resistors. Although a setup created with an operational amplifier allows the concept to be studied in laboratory and design contexts, it also demonstrates that reliability remains dependent on the circuit’s conditions when the operating limits are exceeded. Thus, rather than offering a search for a commonly used component in everyday circuits, the subject provides a framework for understanding nonlinear behavior; the open question is which specific applications could make this behavior practically useful.