English: Current-voltage (IV) graph illustrating voltage controlled negative resistance (VCNR). It shows a device with negative differential resistance, meaning the current decreases with increasing voltage in some parts of the graph, colored red It is a variety called voltage controlled negative resistance, which means the current is a single-valued function of the voltage. The curve is also called N-type, because it is shaped vaguely like the letter N, with a single decreasing negative resistance region along the voltage axis (shaded) sandwiched between two positive resistance regions. A tunnel diode has an IV curve very similar to this.