Negative resistance

In <a href="/facts/Electronics/E4JhgISq">electronics</a>, negative resistance (NR) is a property of some <a href="/facts/Electrical_circuit/zt94kTW0">electrical circuits</a> and devices in which an increase in <a href="/facts/Voltage/EN2po6N2">voltage</a> across the device's terminals results in a decrease in <a href="/facts/Electric_current/Dc1xdnUX">electric current</a> through it.
This is in contrast to an ordinary <a href="/facts/Resistor/JrsGReM6">resistor</a> in which an increase of applied voltage causes a proportional increase in current due to <a href="/facts/Ohm%2527s_law/PjfEyTgI">Ohm's law</a>, resulting in a positive <a href="/facts/Electrical_resistance/hxSt0UAj">resistance</a>. Under certain conditions it can increase the power of an electrical signal, <a href="/facts/Amplifier/pnRgxncC">amplifying</a> it.
Negative resistance is an uncommon property which occurs in a few <a href="/facts/Linear_circuit/eDxQYWo2">nonlinear</a> 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 <a href="/facts/Amplifier/pnRgxncC">amplify</a>, converting <a href="/facts/Direct_current/r9MNUx84">DC</a> power applied to its terminals to <a href="/facts/Alternating_current/qxICS3xa">AC</a> output power to amplify an AC signal applied to the same terminals. They are used in <a href="/facts/Electronic_oscillator/6NaXsSzJ">electronic oscillators</a> and <a href="/facts/Amplifier/pnRgxncC">amplifiers</a>, particularly at <a href="/facts/Microwave/HmVSN31Y">microwave</a> frequencies. Most microwave energy is produced with negative differential resistance devices. They can also have <a href="/facts/Hysteresis/9M2pwR62">hysteresis</a> and be <a href="/facts/Bistability/Rvxss5V4">bistable</a>, and so are used in <a href="/facts/Switching_circuit/6ogJWSyx">switching</a> and <a href="/facts/Semiconductor_memory/XXP0CacJ">memory</a> circuits. Examples of devices with negative differential resistance are <a href="/facts/Tunnel_diode/BVtMxHzU">tunnel diodes</a>, <a href="/facts/Gunn_diode/oAt1B8md">Gunn diodes</a>, and <a href="/facts/Gas_discharge_tube/uPNhhy7I">gas discharge tubes</a> such as <a href="/facts/Neon_lamp/dVz7h0B4">neon lamps</a>, and <a href="/facts/Fluorescent_lights/R8SlXCyg">fluorescent lights</a>. In addition, circuits containing amplifying devices such as <a href="/facts/Transistor/Bmr8zwL0">transistors</a> and <a href="/facts/Op_amp/hunKdYb9">op amps</a> with <a href="/facts/Positive_feedback/eFGatCpF">positive feedback</a> can have negative differential resistance. These are used in <a href="/facts/Electronic_oscillator/6NaXsSzJ">oscillators</a> and <a href="/facts/Active_filter/NsyjIJ4L">active filters</a>.
Because they are nonlinear, negative resistance devices have a more complicated behavior than the positive "ohmic" resistances usually encountered in <a href="/facts/Electric_circuit/zt94kTW0">electric circuits</a>. Unlike most positive resistances, negative resistance varies depending on the voltage or current applied to the device, and negative resistance devices can only have negative resistance over a limited portion of their voltage or current range.

Negative resistance open-in-new

Negative resistance