Negative resistance

In electronics, negative resistance (NR) is a property of some electrical circuits and devices in which an increase in voltage across the device's terminals results in a decrease in electric current through it.

This is in contrast to an ordinary resistor, in which an increase in applied voltage causes a proportional increase in current in accordance with Ohm's law, resulting in a positive resistance. Under certain conditions, negative resistance can increase the power of an electrical signal, amplifying it.

Negative resistance is an uncommon property which occurs in a few nonlinear electronic components. In a nonlinear device, two types of resistance can be defined: 'static' or 'absolute resistance', the ratio of voltage to current

v

/

i

{\displaystyle v/i}

, and differential resistance, the ratio of a change in voltage to the resulting change in current

Δ

v

/

Δ

i

{\displaystyle \Delta v/\Delta i}

. The term negative resistance means negative differential resistance (NDR),

Δ

v

/

Δ

i

<

0

{\displaystyle \Delta v/\Delta i<0}

. In general, a negative differential resistance is a two-terminal component which can amplify, converting DC power applied to its terminals to AC output power to amplify an AC signal applied to the same terminals. They are used in electronic oscillators and amplifiers, particularly at microwave frequencies. Most microwave energy is produced with negative differential resistance devices. They can also have hysteresis and be bistable, and so are used in switching and memory circuits.