Negative resistance - for what purpose

[Grossel]

Hi.

I just came over the circuit on wikipedia - named Negative impedance converter (NiC).

I understand that the current is opposite proportional to the voltage. Question is - What can I do with a NiC?

What potentional reason should I ever have in order to put together a NiC on a breadboard? I cannot think of any reasons, and wikipedia just tell me how it works, not what I can use it for.

Any suggestions?

 

[Speakerguy]

Did you miss the GIANT section on "Application" in the wiki article? Or the other giant "Application" section in the linked wiki article on Negative Resistance?

Oscillators

All feedback oscillators imply the presence of negative resistance. There are many such topologies, including the Dynatron oscillator, Colpitts oscillator, Hartley oscillator, Wien bridge oscillator, and some types of relaxation oscillators. If the feedback loop is broken and the input impedance examined it will be found to include negative resistance.[10] Negative resistance characteristics of Gunn diodes are often used in microwave frequencies as well.
[edit] Amplifiers
Figure 4: Negative resistance microwave amplifier using a circulator
Figure 5: 8 - 12 GHz tunnel diode amplifier, circa 1970

A device exhibiting negative resistance can be used to amplify a signal and this is an especially useful technique at microwave frequencies. Such devices do not present as pure negative resistance at these frequencies (in the case of the tunnel diode a large parallel capacitance is also present) and a matching filter is usually required. The reactive components of the device's equivalent circuit can be absorbed into the filter design so the circuit can be represented as a pure resistance followed by a bandpass filter. The output of this arrangement is fed into one port of a three-port circulator. The other two ports constitute the input and output of the amplifier with the direction of circulation as shown in the diagram. Treating R0 as being positive, the reflection coefficients at the two ends of the filter are given by;

    \Gamma_1 = \frac{Z_1 - R_0}{Z_1 + R_0} and, \Gamma_2 = \frac{Z_2 - R_1}{Z_2 + R_1}

Since the filter has no resistive elements, there is no dissipation and the magnitudes of the two reflection coefficients must be equal,

    \left| \Gamma_1 \right| = \left| \Gamma_2 \right| 

The input power entering the cirulator is directed at the matching filter, is reflected at both the input and output of the filter and a portion finally arrives at the load. This portion is given by;

    \frac{P_\mbox{out}}{P_\mbox{in}} = \left| \Gamma_1 \right|^2

For a well matched filter, the reflection coefficients will be very small in the passband and very little power will reach the load. On the other hand if R0 is replaced by a negative resistance such that,

    R_0' = - R_0 \,\! then,

    \Gamma_1' = \frac{Z_1 + R_0}{Z_1 - R_0} and,

    \left| \Gamma_1' \right| = \left| \Gamma_2' \right| = \frac{1}{\left| \Gamma_1 \right|}

Now the reflection coefficients are very large and more power is reaching the load than was injected in the input port. The net result of terminating one port in a negative resistance is amplification between the remaining two ports.[11]
[edit] Mixers and frequency converters

The highly non-linear characteristics of tunnel diodes makes them useful as frequency mixers. The conversion gain of a tunnel diode mixer can be as high as 20 dB if it is biased to operate in the negative resistance region.[12]
[edit] Antenna design

Another concept of negative resistance exists in the domain of radio frequency antenna design. This is also known as negative impedance. It is not uncommon for an antenna containing multiple driven elements to exhibit apparent negative impedance in one or more of the driven elements.
[edit] Impedance cancellation

Negative impedances can be used to cancel the effects of positive impedances, for example, by eliminating the internal resistance of a voltage source or making the internal resistance of a current source infinite. This property is used in telephony line repeaters[13] and in circuits such as the Howland current source[14], Deboo integrator[15] and load cancellers.[16][17]

 

[Grossel]

Did you miss the GIANT section on "Application" in the wiki article? Or the other giant "Application" section in the linked wiki article on Negative Resistance?

I cannot find that text on the wiki page I'm linking to. Can you provide a link to that text?