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The negative impedance converter (NIC) is a configuration of an operational amplifier which acts as a negative load. This is achieved by introducing a phase shift of 180° (inversion) between the voltage and the current for any signal generator. The basic circuit of an NIC and its analysis is shown below.

Contents 1 Basic circuit and analysis 2 Application 3 See also 4 External links

If the operational amplifier is ideal, the inverting and non-inverting inputs have the same voltage, so the current I₂ is simply given by:

Then, considering the voltage from one ground to the other one, it is possible to write:

Replacing the previous relationship and rearranging we get:

from which we get the input resistance:

Main article: Negative resistance

By using an NIC as a negative resistor, it is possible to let a real generator behave (almost) like an ideal generator, i.e. the magnitude of the current or of the voltage generated does not depend on the load.

An example is shown in the following picture:

The current generator and the resistor within the dotted line is the Norton representation of a circuit comprising a real generator and R_s is its internal resistance. If an NIC is placed in parallel to that internal resistance, and the NIC has the same magnitude but inverted resistance value, there will be R_s and − R_s in parallel, thus the equivalent resistance is:

so the real generator will now behave like an ideal one, and the generator's entire current will go to the load Z_L, whatever the value of Z_L and R_s.

• Negative resistance
• Negatron yields real natural frequency, Alexander Bell, USA, EDN, 08/1993

• A heuristic approach to teaching negative resistance phenomenon
• Understanding Negative Impedance Converter (NIC) - reveals in four consecutive steps the basic idea behind NIC.
• What Is the Idea behind Howland Current Source? - a famous circuit using NIC to obtain a constant current.
• Keeping a constant current by adding an additional current - using NIC to make a perfect Deboo integrator.
• How do we make an "over-helping" negative resistance? - reveals the basic idea behind the NIC.

• Negatrons enrich filter, oscillator designs, Alexander Bell, USA, EDN, July 21, 1994
• Improved frequency modulator uses "Negatron", Alexander Bell, USA, EDN, 07/11/2002
• Programmable impedance has 12-bit resolution, Alexander Bell, USA, EDN, May 23, 1996
• Network forms digital-to-impedance converter, Alexander Bell, USA, EDN, March 14, 1996

• MDAC makes digital-to-inductance converter, Alexander Bell, EDN, 09/1996