Introduction
Negative resistance 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, where an increase in applied voltage causes a proportional increase in current in accordance with Ohm's law, resulting in a positive resistance.
What is Negative Resistance?
Negative resistance occurs in a few nonlinear electronic components, where the relationship between voltage and current is not linear. In a nonlinear device, two types of resistance can be defined: 'static' or 'absolute resistance', the ratio of voltage to current, and differential resistance, the ratio of a change in voltage to the resulting change in current. The term negative resistance refers specifically to negative differential resistance (NDR), where the ratio of a change in voltage to the resulting change in current is less than zero.
History and Examples
Negative differential resistance is an uncommon property, but it is used in various electronic components and devices. Examples of devices with negative differential resistance include tunnel diodes, Gunn diodes, gas discharge tubes such as neon lamps, and fluorescent lights. Additionally, circuits containing amplifying devices such as transistors and op amps with positive feedback can exhibit negative differential resistance.
How Negative Resistance Works
In a device with negative differential resistance, an increase in voltage across the terminals can lead to a decrease in current through the device. This is because the device's internal resistance decreases as the voltage increases, allowing more current to flow. This property can be used to amplify an electrical signal, converting DC power applied to the terminals to AC output power.
Applications of Negative Resistance
Negative differential resistance devices are used in various applications, including electronic oscillators and amplifiers, particularly at microwave frequencies. Most microwave energy is produced with negative differential resistance devices. These devices can also be used in switching and memory circuits due to their hysteresis and bistable behavior.
Properties of Negative Resistance Devices
Negative resistance devices are nonlinear and have a more complicated behavior than ordinary resistors. Unlike most positive resistances, negative resistance varies depending on the voltage or current applied to the device. Negative resistance devices can only have negative resistance over a limited portion of their voltage or current range.
FAQ
What is the difference between negative resistance and positive resistance? Negative resistance is a property where an increase in voltage leads to a decrease in current, whereas positive resistance is a property where an increase in voltage leads to a proportional increase in current.
Can negative resistance devices be used in any type of electronic circuit? No, negative resistance devices are typically used in nonlinear circuits, such as oscillators and amplifiers, where their nonlinearity can be exploited to amplify signals.
How is negative resistance measured? Negative resistance is typically measured as the ratio of a change in voltage to the resulting change in current.
What are some common applications of negative resistance devices? Negative resistance devices are commonly used in microwave amplifiers, oscillators, and switching circuits.
Can negative resistance devices be used at any frequency range? Negative resistance devices are typically used at high frequencies, particularly in the microwave range.