Talk:Circuit Idea/Revealing the Mystery of Differential Negative Resistance

I start here maybe the most interesting discussion about differential negative resistors concerning two unique operation modes - linear and bistable. Linear applications include various exotic 1-port amplifiers (e.g., legendary tunnel diode amplifier). A lot of interesting negative resistor applications are based on bistable mode: exotic switching circuits with dual-treshold action (hysteresis), memory circuits (flip-flops), etc. Later, we might copy or move this discussion to negative differential resistance page where its place is but now we have to ascertain if the differential negative resistors obey the definition. Please, join the discussion; the topic is extremely interesting and important.

Differential negative resistor operating in linear mode
Obviously, this definition is formulated especially for differential negative resistance but, unfortunately, it has problems even in this case. The definition is correct only if the differential negative resistor operates in linear mode (i.e., if we drive a current-driven differential negative resistor by a current and if we drive a voltage-driven differential negative resistor by a voltage). Let's ascertain it.





As a rule, electronics resources show the IV curve of a differential negative resistance in its final N or S shape (e.g., see a bare curve) and note there is a section with a negative slope. But nobody shows how this magic is done and what it actually means. Only, in order to grasp the idea of differential negative resistance, it is extremely important to show exactly how and why this part of the curve is inclined to the left. Here is the secret of the phenomenon.

The trick is extremely simple, clear and intuitive: this is the great dynamizing idea that is brought here to the utmost degree. A differential negative resistor is notning more than a kind of "self-varying", dynamic resistor that changes extremely its instant (ohmic, "positive") resistance depending on the current passing through the resistor or on the voltage applied across it; a differential negative resistor is actually an over-dynamic resistor. I have shown the evolution of this great idea in a circuit story about S-shaped differential negative resistors (I have placed a reference to this story for your convenience, not to promote myself).

Applying a voltage across a voltage-driven differential negative resistance
Look at Fig. 3 to see how a voltage-driven differential resistor having an N-shaped IV curve behaves, in order to do this magic in the area of the negative resistance. In this graphical representation, I have superimposed the IV curves of the input voltage source (in a red color) and the differential negative resistor (in blue) on a common coordinate system. In addition, to make things absolutely clear, I have superimposed the IV curve of the instant ohmic resistance R (in orange) as well. Now, turn on your most human mental faculty - your imagination, and visualize in your mind's eye what happens when the input voltage begins varying.

For example, when the input voltage begins increasing, its IV curve moves horizontally from left to right remaining parallel to itself. If the resistor was "static", the crossing (operating) point would slide along the IV curve of its ohmic resistance having a positive slope. But it is a more "clever":) dynamic resistor (like my opponents in this talk page:). So, it begins changing (in this case, increasing) its instant ohmic resistance R and rotating vigorously its IV curve clockwise. As a result, a wonder happens and the operating point slides along a hew IV curve having a negative slope. Note this is not a real curve as the ohmic IV curve is. It is an artificial, a synthetic, an imaginative IV curve; it is an illusion.

Does this case obey the definition, "...an increasing current in the circuit results in a decreasing voltage..."? No, as the voltage jumps in the negative resistance region (see below).

Passing a current through a current-driven differential negative resistance
A current-driven differential resistor with an S-shaped IV curve (Fig. 4) has the opposite crafty behavior:) - when the input current increases, it decreases its instant ohmic resistance R and rotates vigorously its IV curve contraclockwise. Now, the operating point slides upwards along a hew IV curve having a negative slope as above.

Does this case obey the definition now? Yes, if we only replace "voltage" with "voltage drop":



Differential negative resistor operating in bistable mode
If the differential negative resistor operates in bistable mode (i.e., if we drive a current-driven differential negative resistor by a voltage and if we drive a voltage-driven differential negative resistor by a current), the definition is not true.

I give an opportunity to you to see why the definition has failed in these cases. If you do not manage, I will elucidate why. Circuit-fantasist (talk) 22:05, 15 February 2009 (UTC)

Applying a voltage across a current-driven differential negative resistance






Passing a current through a voltage-driven differential negative resistance




