Negative impedance converter

A negative impedance converter, in English as abbreviated Negative Impedance Converter NIC refers is a form of impedance conversion, which is a negative electrical resistance. This electronic circuit, it is possible to convert the more positive resistance value of an electric resistance component in a negative resistance value.

A negative resistance is an inverse of the well-known Ohm's Law as the relationship between the electric voltage U and the current flowing through the constant resistance R is the electrical current I:

A negative impedance converter, as shown in the adjacent circuit diagram, realized at its terminals for the external voltage source Vs in R3 is R2, the following relationship:

This means that the external voltage source Vs, a large current flows even more, the higher the voltage. In other words, it flows an electric power in the voltage source.

The voltage source is connected to the negative resistance Rin

Loaded. As mentioned this is output from the voltage source, and can therefore in principle be realized with an active electronic circuits, which consist, for example, of operational amplifiers.

Since the above equation is also valid with voltage, the resistor R1 can be in the converter by a complex impedance Z, consisting of coils or capacitors, replace it. In this configuration, the NIC thus formed the basis of the gyrator, a circuit with which you can convert any impedance to their dual impedance, such as an electrical capacitance in an inductor.

The practical benefit is that electric capacity in the form of capacitors can be significantly easier to manufacture and cheaper than is the case with inductances in the form of coils. Therefore, the negative impedance converter makes the realization of analog electrical filters without coils a significant role.

Another application of this circuit is to compensate unavoidable but unwanted internal resistances of the real sources. In the adjacent figure is a real current source with unwanted internal resistance Rs, shown in red trim. Through external parallel connection of a magnitude equal negative resistance Rs can be so realized from the perspective of consumer ZL an ideal current source with the ideal internal resistance of an infinitely high value ( ∞ Ω ).