Talk:Circuit Idea/Negative Differential 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. Please, join the discussion; the topic is extremely interesting and important. Circuit-fantasist (discuss • contribs) 16:49, 25 June 2012 (UTC)

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






How to create negative resistance
(an extract from an old Wikipedia discussion)

In the very beginning, I have tried to show in only one definition the general idea behind the two possible kinds of negative resistances (differential and true): "Negative resistance can be created in some limited region of resistor IV curve by vigorously changing the resistance or the magnitude of additional voltage." Here is what I mean. I would like to say that negative resistance is created on the base of (by modifying) some positive resistance. Negative resistance cannot exist independently. It cannot exist in the whole operating range; it can exist only in a limited region of the range. Accordingly, negative resistance cannot occupy the whole IV curve; we can create a negative slope (fold up the curve) only in some limited middle part of the whole IV curve of a positive resistor. In the end parts, the resistance is positive; thus the odd "S" or "N" shape. For this purpose, we have somehow to change the monotonous motion of the operating point (that draws the IV curve) when the input quantity (voltage or current) changes within the negative resistance region; we have to revert its direction. The trick is simple but clever: in the one-variable function IOUT = VIN/R (Ohm's law) we begin changing another (second) variable simultaneously with the first one. For example, we can change the very resistance R or we can change the voltage of an additional voltage source connected in series with the resistor. Thus, in this region, we actually have a function of two variables (IOUT = VIN/RIN or IOUT = (VIN1 + VIN2)/R) but we consider it as a function of one variable (we see only the one variable - the input voltage). Thus, we have artificially changed the resistance in this region; we have made dynamic resistance. As a result, the curve changes its slope up to negative but only within the borders in the negative resistance region where we have what (resistance) to change. After the end of the region, the reserve of high resistance (S-shaped curve) or high conductance (N-shaped curve) is depleted and the resistance reaches its minimum (S-shaped curve) or maximum (N-shaped curve). The magic of negative resistance ceases and the ordinary positive resistance establishes in the final part of the IV curve (the negative resistor is saturated). Similar considerations can be written for the first part with positive resistance where the initial resistance is maximum (S-shaped curve) or minimum (N-shaped curve) and the negative resistor is saturated. These end parts of saturation can be seen very well in the IV curves of the op-amp negative impedance converters - INIC (Fig. 5a) and VNIC (Fig. 5b). So, I have tried to put all the wisdom above in one sentence.

"The use of the terms "true negative resistance" and "absolute negative resistance" have been opposed..." Please, suggest the right terms then to denote the existing phenomenon. I have tried everything to solve the problem: I have explained that actually there is no true negative resistance exactly as there are no true sources; I have explained what a true negative resistor is (a circuit with power supply); then, I have put "true" in quotes to show that this is a metaphoric name... But what have you done to solve the problem? You continue repeating, "True negative resistor" is even more unacceptable - there is no such component." There is no a component but there is a circuit that can be figuratively named "true negative resistor". See this funny movie of Professor Horowitz (in contrast to wikipedians, he has a sense of humor:) where he has hidden an op-amp NIC supplied by two 9 V batteries in a cardboard box with a label of 10 kΩ to mimic a component (a resistor). Circuit dreamer (talk, contribs, email) 18:20, 3 July 2011 (UTC)

Negative resistor applications
(an extract from a very old Wikipedia discussion about NDR applications)

I have placed it here to help the discussion about using the NDR as an amplifier.Circuit-fantasist (discuss • contribs) 05:59, 1 July 2012 (UTC)

Negative resistor acting as an amplifer
It is considered that a negative resistor can act as an amplifier. If this is true, are there any difference between a negative resistor and an amplifier? If yes, what is the difference? Let's clarify the topic.

What is amplification?

I hope you agree with me that amplification is impossible. We cannot amplify energy (power); we can only regulate it. Then what is amplification? How do we amplify? How do we make an amplifier? It sounds bluntly, but it is true that in (analog) electronics we use the possibly silliest idea for this purpose.

In order to amplify some small input power (in electronics, usually presented by input voltage), we get many times bigger (at least, VPS = K.VINmax) power source (a constant voltage source acting as a power supply) and then, imagine, we throw out the excessive power?!? An example of this absurd: in order to "amplify" 10 times 1V input voltage by a 24V supplied amplifier, we throw out (as a heat) the power according to the rest 14V (in energetics, they never do that!) Doing that, we actually dissipate, attenuate power. As a result, there is not amplification; there is only attenuation!

How do we make an "ordinary" amplifier?

Components. Following the silly idea above (obviously, we have no choice), we may assemble an amplifier by using only two components: a power supply and a regulating element.

A power supply. According to the chosen structure (see below), we need a constant-voltage or a constant-current power supply.

A regulating element. The function of this component is to resist the current (in order to dissipate a power), proportionally to the magnitude of the input voltage source. So, it acts as an electrically controlled resistor (carbon microphone, a tube, a transistor etc.) whith input and output part.
 * In the 4-terminal regulating elements (e.g., carbon microphone, magnetic amplifier etc.) the input and output part are electrically separated; so, they do not interact each other.
 * In the 3-terminal regulating elements (e.g., tubes, transistors etc.) the input and output part are electrically connected by the common terminal (emitter, base, collector etc.) In some arrangements (e.g., common emitter amplifier), they do not interact each other while, in other cases (e.g., common collector amplifier), the output influences the input by feedback.
 * But what do we have to do, if we have only a humble 2-terminal regulating element, which input and output parts are the same? If you do not guess, see the answer below.

Amplifier structures. We can connect these components, according to the basic electrical circuits, in series or in parallel to the load.

A series amplifier. In some cases, we connect in series a constant-voltage power supply, the output part of the regulating element and the load.

A parallel amplifier. In other cases, we connect in parallel a constant-current power supply (constant-voltage source + resistor), the output part of the regulating element and the load.

 How do we make a negative resistance amplifier?

A negative resistor acting as a regulating element. In the past, striving to build an extremely simple amplifier by using a 2-terminal regulating element, maybe they asked themselves, "How to reach the regulating element, in order to control its resistance?" or, "Where to apply the input signal?" Then they guessed to use an odd regulating element - dynamic resistor, which resistance depends considerably on the current passing through the same element (i.e., a negative differential resistor). In this odd 2-terminal element, the input and the output part are the same; so, they could apply the input signal to the output part. It looks quite strange, doesn't it?

An amplifier structure. So, we can build an odd negative resistance amplifier by connecting in series all the components needed: a constant-voltage power supply V, a negative differential resistor, an input voltage source VIN and a "positive" resistor. The negative differential resistor and the "positive" resistor constitute a voltage divider, which ratio depends on the input voltage. So, we may think of this circuit as a voltage divider supplied by a slightly varying voltage source V + VIN.

An amplifier operation. When we vary slightly the input voltage, the negative differential resistor changes considerably its resistance according to the input voltage; so, the voltage divider changes noteceably its ratio. As a result, the voltage drops across the "positive" and negative resistors vary considerably; so, we may use some of them as an output voltage.

Negative resistor acting as a bistable component (a flip-flop)
To be continued... Circuit-fantasist 10:43, 24 August 2006 (UTC)