Properties
Figure 2 shows a graph of a negative resistor, showing the negative slope. In contrast to this, a resistor will have a positive slope. Tunnel diodes and Gunn diodes exhibit a negative resistance region in their IV (current – voltage) curve. They have two terminals like a resistor; but are not linear devices. Unijunction transistors also have negative resistance properties when a circuit is built using other components.
For negative resistance to be present there must be active components in the circuit providing a source of energy. This is because current through a negative resistance implies a source of energy just as current through positive resistance implies that energy is being dissipated. A resistor produces voltage that is proportional to the current through it according to Ohm's law. The IV curve of a true negative resistor has a negative slope and passes through the origin of the coordinate system (the curve can only enter the 2nd and 4th quadrants if energy is being supplied). This is to be compared with devices such as the tunnel diode where there is no source of energy within the device. The negative slope portion of the curve is entirely in the first quadrant and the curve passes through the origin into the third quadrant, never entering the second or fourth quadrants.
Read more about this topic: Negative Resistance
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