Talk:Negative resistance

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[edit] "Nanotubes"

Removed from the article:

In conformance with the known law of conservation of energy, a plot of the negative differential resistance region of a component cannot normally pass through the origin.
More recently however, Professor Deborah Chung at the University of Buffalo has discovered a composite configuration of carbon nanotubes which actually does exhibit a negative differential resistance region throughout its entire plot, which does indeed pass though the origin. Professor Chung's device could thus be considered a negative static resistor.

What's the special case that prevents this from being a perpetual motion machine?

This is a bit strange. I'm fairly sure I can build a simple circuit that exhibits negative resistance (differential or static) at the origin. Of course, it needs a power supply, so it's not really violating conservation of energy. Madhu 22:06, 4 Mar 2005 (UTC)
I looked into this, and the Chung experiment was so obviously flawed that I am not surprised that it quietly disappeared from the news. I imagine that Buffalo University and Ms Chung were so embarrassed when they realised their error that they bought up all copies of their press releases and burnt them. As an act of mercy, I have just removed the reference from our article. Just look at this photo (on this page of some free energy nut's website), but prepare for the outbreak of at least a wry smile. In case the error isn't obvious, let me explain.
1 (The Short Explanation). To measure the resistance of something, you have to pass a current into one point on the thing and out of another point, and measure the voltage between the same two points.
2 (The Long Explanation). Refer to the photo linked above. You should be looking at two bundles of carbon fibres placed at right-angles to each other and squashed together where they cross. The four points of the cross are labelled A, B, C and D. The carbon fibres have some resistance from end to end, and there is also some conductance between the two bundles (if there isn't, then you should have put more effort into tightening up the vice in the preparation stage of the experiment). When the current source is switched on, there is a voltage gradient between points A and C, with A more positive than C. Now try to answer the question: "which two points of the current path is the voltmeter connected across?" The answer is: "anybody's guess", because the terminals B and D are connected through untidy bundles of fibres to some undefined point or collection of points in the crossover area. The geometry of this setup is such that D might be positive with respect to B, or it might be negative, depending on which fibres got squashed most tightly together. It seems that in this case D is more strongly connected to A, making it positive, and B is more strongly connected to D, making it negative. Since the experimenter has chosen to connect the positive end of his voltmeter to B, he gets a negative voltage. In conclusion, the "resistance" you are measuring is not really a resistance, but the ratio of some voltage across two points to some current flowing between two other points, and its sign and magnitude are no more meaningful than random numbers.
If anybody doubts that the original experiment could have been as simple as this reconstruction, see the original paper here. Note the proximity of the submission date to the 1st of April. --Heron 21:11, 5 August 2005 (UTC)
Given that interesting detail, it wouldn't be hard to reproduce the results with four carbon resistors -- no need for nanotubes ;-) There still seem to be references to that article floating around the Web. Not sure if I should interested or troubled... Madhu 20:47, 8 August 2005 (UTC)
5 resistors, right?
          o
          |
          Z
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o--V^V^---*---V^V^V---*---V^V^V^---o
                      |
                      Z
                      |
                      o

- Omegatron 20:59, August 8, 2005 (UTC)

I was thinking of something like a bridge, but you might be able to simplify your circuit above to only three resistors:
          o
          |
          |
o--V^V^---*---V^V^V---*---V^V^V^---o
                      |
                      |
                      o

It might not be exactly the same as the Chung circuit, but I'm guessing based on Heron's comments. Madhu 14:33, 9 August 2005 (UTC)

By the way, I completely disagree with this being removed from the article. "Mercy" should have nothing to do with it. We certainly wouldn't be mercifully censorial if it was originally from the free-energy crazies. We shouldn't be any different for this. Besides, this "mistake" has been swallowed up by those crazies and needs to be debunked.
"Now there's one for the environmental activists, if they can really get their act together. Why not swing all that power and clout they possess into action, demanding to know what has happened to Chung's negative resistor? After all, such a unit can easily be developed into systems that will power the world, once the control of the basic effect is worked out — which in this case has already been done by Chung and her team. If the Environmental Community really wishes to do something dramatic to initiate what could be a rapid solution to the hydrocarbon wastes pollution of the planet, this is their big chance."

And here's some images from the paper:

I reluctantly agree with you, Omegatron. When I originally deleted the Chung material, I didn't know that the fantasists had already latched on to it. I thought I was just decluttering Wikipedia of a piece of embarrassingly bad research. Do you agree that, in her paper, Chung displays a lack of clue about circuit theory and the physics of conduction? If, sadly, the idea has got the free energy people all excited, then I suppose we do have a duty to debunk it. --Heron 15:49, 8 July 2006 (UTC)
I'm confused as to what she's actually claiming. The paper explicitly says that it's an "apparent" negative resistance, and isn't breaking any laws, but why call it a "resistance"? Intentionally being misleading for attention? Other news articles say that she is "searching for the mystery energy source". I wonder which came first.
I think we would have a duty to debunk it even if it were only reported by academia and ignored by the crazies. A degree is no excuse for bad science. :-) The whole point of the academic scientific establishment is to attack each other's articles and research trying to disprove them, until only the Truth remains.
Also, there is nothing I hate more than trigger-happy overblown press releases of legitimate research, which appears to be a major culprit here, as well. — Omegatron 16:48, 8 July 2006 (UTC)
I can tell you where the problem started. On page 1, she directly claims to have done the impossible. First she says "True negative resistance in the former sense [absolute NR] is not possible". Then, in the next sentence, she says "apparent negative resistance in the former sense is reported here". I would say that she is claiming to have broken the laws of thermodynamics. --Heron 19:31, 8 July 2006 (UTC)
But she's making a distinction between "true" and "apparent" negative resistance. — Omegatron 21:20, 8 July 2006 (UTC)
She's making a specious distinction, since her definitions of the two terms are identical. Compare and contrast (from paras 2 and 3 of the Introduction):
"Negative resistance means that ... the current–voltage characteristic is a straight line of negative slope through the origin." (This is what she describes a few lines later as "true negative resistance in the former sense".)
"we report an apparent negative resistance phenomenon in which the entire current–voltage characteristic is a straight line of negative slope through the origin."
What's the difference? (Oh, and she is wrong about it needing to be a straight line.) --Heron 18:41, 9 July 2006 (UTC)
I guess I'm just giving her the benefit of the doubt and assuming that "apparent" means "measured at two different points". But it's misleading, whether she intended it to be or not. — Omegatron 21:53, 13 July 2006 (UTC)
Also, they were just carbon fibers, not nanotubes. — Omegatron 21:57, 13 July 2006 (UTC)

[edit] Deborah Chung s 'absolute negative resistance'

I propose removing this content as it is recent research, not relevant, not proven, and probably incorrect or at least misleading. Comments?--Light current 14:27, 1 August 2006 (UTC)

Um, no. We just added the section for good reasons. The discussion we had about adding it is right above you. Did you read it? — Omegatron 15:34, 1 August 2006 (UTC)

Shouldnt this effect be called negative transresistance any way as the experimental device is simple 2 port network? 8-?--Light current 14:57, 1 August 2006 (UTC)

I was thinking of that just now, but I don't think we should include it in the article, since the word is never used in the paper and it's not an active device. As mentioned above, her measurement probably isn't even meaningful, and the experiment and its results are dubious. Citing it as an example of "transresistance" would imply more credibility than it deserves, in other words. — Omegatron 15:34, 1 August 2006 (UTC)

No, sorry I havent been following the argument. Im presenting a fresh, unsullied view. By your latter comments 'O', it seems to me that you are voting for deletion of this material also. Am I correct? If the material is to remain on WP, its proper place is on the transconductance page. Yes? Also when you say its not an 'active' device, in what way would you say it differs from one? --Light current 18:31, 1 August 2006 (UTC)

it seems to me that you are voting for deletion of this material also. Am I correct?
Absolutely not. I'm the one who added it. It was reported in the press as an instance of true, absolute "negative resistance" (with no internal source of energy, which defies the laws of physics). We've added this section to explain what was actually going on (she was measuring current at one point and voltage at another point and calling it a "resistance"). It was then reported in the press that she had discovered a room temperature superconductor (by the University no less!), or reported by cranks as a perpetual energy source (a "true negative resistance"). It is neither. We're not even sure what it's supposed to be, if anything, but we're explaining that it isn't a "true negative resistance". Please read the above discussion. — Omegatron 20:26, 1 August 2006 (UTC)

Well OK 'O' but nevertheless I think this stuff does not really belong on this page. The furore over this wild claim has surely died down now and we should present a stable, long term view on science & engineering subjects. Should we not?--Light current 20:34, 1 August 2006 (UTC)

If someone says "negative resistance? hmmm... i remember hearing about someone who made a real negative resistance a few years ago. i wonder what happened to that. maybe the big oil conspiracy covered it up. let me search wikipedia", they should find something about it. Since this is the article about negative resistance, I'd say it belongs here. If you insist, (and others agree), we can move it to somewhere else and merely link to it from here, but I don't think it deserves its own article. — Omegatron 13:21, 2 August 2006 (UTC)

I agree it doesnt deserve its own article. As I said before, since its a transresistance phenomenon it should go in the transconductance article. A link to the transconductance page should be put at the bottom of the negative resistance page--Light current 15:24, 2 August 2006 (UTC)

  • No one ever calls it a transconductance or transresistance. You might think that's what it is, but we can't publish your personal speculation.
  • Everywhere it's mentioned it's referred to as "negative resistance". By the cranks, by the newspapers, and by the original researcher.
  • I don't think it's a transconductance phenomenon, anyway. It's applying a current to a resistor network and measuring a voltage across another resistor network. It's not even a meaningful measurement from what we can tell. — Omegatron 16:24, 2 August 2006 (UTC)

You say 'No one ever calls it a transconductance or transresistance.' but negative transresistance is exacatly what she describes as measuring. Its a 2 port network!--Light current 18:05, 2 August 2006 (UTC)

If it's a two-port device (which it looks like to me), it belongs somewhere else, IMHO. Everything else on this page refers to a one-port device. I'm not exactly sure where this material should go. I haven't read the paper in great detail, but based on the experimental setup, a multimeter by itself won't tell you if you're dealing with a resistance or a current source. Either way, I am inclined to agree with Light current and recommend moving/removing the material. Madhu 19:33, 1 August 2006 (UTC)
Google search for "negative resistance". The eighth result is about Chung. The seventh through ninth are crackpottery related to Chung's results. There's no better place for this topic. — Omegatron 16:45, 2 August 2006 (UTC)
Retitled this to '..transresistance' as that is what is being described

--Light current 18:29, 15 September 2006 (UTC)

  1. She called it "negative resistance". She didn't use the word transresistance. Calling it that is original research.
  2. Besides, it's not really transresistance anyway; it's measuring four different points of a resistor network. — Omegatron 19:19, 15 September 2006 (UTC)

[edit] Two different ideas?

It seems that most of this article is about negative differential resistance, but the Negative resistance circuits section is about actual negative resistances (with a source inside them). Should we split into two articles? Move this article to Negative differential resistance? - Omegatron 23:52, August 4, 2005 (UTC)

"Many circuit topologies are capable of producing negative resistance."

Such a circuit always has a source in it, right? - Omegatron 21:46, August 5, 2005 (UTC)
Right. --Heron 22:14, 5 August 2005 (UTC)

[edit] Kron

While debunking the Chung experiment, I noticed another bad science reference to Kron and his negative resistors, so I had to fix that as well. It's obvious from this paper of his that he was talking about perfectly conventional circuits. --Heron 21:28, 5 August 2005 (UTC)

[edit] Stop confusing people!!

Whoever made up this page is a @#*^&, stop confusing people if you are not sure! I am tired of marking students' books full of crap.

Negative resistance is an amplifier, it is the working principle of a laser for example. Any amplifier of any form can be consider as negative resistor.

Notice the two references, one is apparent negative resistance, while another is negative differential resistance, i.e. NOT negative resistance.

Negative differential resistance is common in non-linear systems. In electronic it is describe as non-ohmic device. In the case of Neon lamp (where i found this page), it is a run away positive feedback effect.


The term "Negative resistance" should ONLY be use to describe amplifier (i.e. the circuit part of this page). Where the rest of the page should go under the title of "Negative differential resistance"

By "amplifier", don't you just mean "source"? — Omegatron 18:43, 11 November 2005 (UTC)
No, I don't think so... however, it's not exactly an ordinary amplifier, either. Dpbsmith (talk) 18:55, 11 November 2005 (UTC)

To "137.205.164.190:"

My longstanding impression is that "negative resistance" is a very commonly used term for negative differential resistance. I appreciate the point you're trying to make ("negative resistance" = through the origin, "negative differential resistance" = negative slope somewhere not passing through the origin).

However, the issue here is one of word usage. If you're sure that "negative resistance" isn't, hasn't, and shouldn't be used to cover both concepts, would you cite a reliable source for that—say, an electronics dictionary or recent textbook? I, for one, am not ready to update the article just on the say-so of someone who has not even created an account. Dpbsmith (talk) 18:55, 11 November 2005 (UTC)

Hmmm....

http://www.hobbyprojects.com/dictionary/n.html ... "negative resistance: A resistance such that when the current through it increases the voltage drop across the resistance decreases."

Secrets of RF Circuit Design: "The negative resistance phenomena, also called negative differential resistance..."

Practical Rf Circuit Design for Modern Wireless Systems: Active Circuits and Systems by Rowan Gilmore, Les Besser - Technology - 2003: "Negative resistance refers to a component or a circuit where an incremental increase of the applied voltage leads to a decrease of current..."

Basic Electronics by Bureau Of Naval Person U S Navy - Technology - 1973 "negative resistance of the tunnel diode..."

I think you are wrong, or overly prescriptive. "Negative resistance" is, in fact, the common term, and "negative differential resistance" is an alternative term that can also be used that some people prefer as being clearer. Dpbsmith (talk) 19:07, 11 November 2005 (UTC)

I agree that using the term "negative resistance" to mean "negative differential resistance" is terribly misleading.
I think we should be "overly prescriptive" in this article, and only leave it as a note that the term can be used for either meaning. (And I am not the anon.) — Omegatron 19:50, 11 November 2005 (UTC)
Of course not... your style is much calmer and dispassionate. I just asked a colleague, who took out his copy of Horowitz and Hill, and they give an example using a tunnel diode in which they refer to it simply as "negative resistance." I'm thinking that negative "differential" resistance is a fairly common characteristic of passive circuit elements. On the other hand, "true" through-the-origin negative resistance only occurs in active circuits, rarely in a pure form, and is not a customary building block in circuit designs.
Someone designing a circuit might well say "I'll use an operational amplifier here," and buy one off the shelf. But you wouldn't say, "Oh, I think I'll use a negative resistor in here," and buy a little modular two-terminal device marked "-10,000 ohms" containing a little lithium battery inside. Or anything like that. And I'm thinking that ("true") negative resistance is something that happens to occur in certain circuit designs, not a common design element, so it's relatively rarely talked about. So, negative differential resistance is common, "true" negative resistance is rare, and the tendency is to use a short, convenient term for the commonly-talked-about thing.
Anyway, I've shown a recent citation that includes the sentence "Negative resistance refers to a component or a circuit where an incremental increase of the applied voltage leads to a decrease of current." Someone show me one that says that's wrong.
I don't think we should be overly prescriptive unless we're sure that the use of the phrase "negative resistance" for "negative differential resistance" is generally deprecated as of 2005.
I'm perfectly happy to have the article set an example by using "negative differential resistance" throughout, where applicable, because it's perfectly clear and unambiguous. I'm not going to waltz through and strike out the word "differential" or anything like that. But at the moment I am not happy with saying "negative resistance" is incorrect usage. I can easily be convinced otherwise, if someone will bother to show me something convincing. Dpbsmith (talk) 20:17, 11 November 2005 (UTC)
I'm perfectly happy to have the article set an example by using "negative differential resistance" throughout, where applicable, because it's perfectly clear and unambiguous.
That's exactly what I meant. :-)
Especially because we talk about both in this article, and you probably wouldn't see both concepts in the same place otherwise, so it's ok to be loose with terminology in those contexts. — Omegatron 20:28, 11 November 2005 (UTC)


[edit] Another fresh viewpoint at negative resistance

(See also my stories about negative resistance:

Hi everybody! I would like to join this so interesting discussion. I have noted for a long time that in electronics Negative resistance and its most popular circuit implementation - Negative impedance converter - are almost mysteries. What is more, they are real nightmares for students and not only for them:)

Browsing through the article I have been noting that it looks quite solid and scientific (especially the last part describing in details a scientific experiment with a lot of links pointing to original sources). However, frankly speaking, I am not sure if visitors would understand what negative resistance is from this page. In my opinion, reading this page, they will know what negative resistance is (for example, "a situation when current is a decreasing function of voltage"), but they will not really understand it...

From many years, I have been thinking about the phenomenon of negative resistance. Finally, I have managed to build my own philosophy about it; now, I would like to share my penetrations with you. Maybe, I have first to define accurately who I am and what my goals are. Simply, I am just a human being who loves circuits; so, I will expose here a "circuit viewpoint" at the phenomenon.

The point is that we are human beings needing something more than scientific facts, reports, formal explanations and definitions. In order to really comprehend the phenomenon of negative resistance (and of every new thing in this life), we need first to know what the general idea behind it is. Only, basic circuit ideas are in fact "non-electrical". They do not depend on the specific implementation (tube, transistor, op-amp etc.); they are eternal. So, we may find them in our routine. Then, let's ask the first question.

[edit] What is the basic idea behind negative resistance?

[edit] Extracting the general idea from our routine

Generally speaking, we may observe this phenomenon in situations where someone (something) interferes to some extent in our life. He/she/it may help or impede us in three degrees (under-, exactly- or over-). Negative resistance represents the last degree when someone "over-helps" or "over-impedes" us - see more examples in my page about the "over-helping" negative resistance (the dual page about "over-impeding" negative resistance is under construction). We can already make the first conclusion:

A negative resistance phenomenon is a process of injecting an additional excessive power to an existing power source.

[edit] Comparison between "ordinary" and negative resistance

Now, let's move to the electrical domain and answer the main question: What is negative resistance (resistor) versus ordinary resistance (resistor)?


A voltage source acting as a negative resistor (connected in series with the load)
Fig. 1a: An "ordinary" positive resistor Fig. 1b: An "over-helping" voltage source Fig. 1c: An "over-impeding" voltage source
Fig. 1a: An "ordinary" positive resistor
Fig. 1b: An "over-helping" voltage source
Fig. 1c: An "over-impeding" voltage source


In order to compare an ordinary "positive" resistor R with a negative resistor -R, let's assemble two circuits where these components are connected in series with the loads so that the same current passes through them. As a result, a voltage drop VR = R.I appears across the "positive" resistor R (Fig. 1a) and the same voltage VH = VR = R.I appears across the negative resistor -R (Fig. 1b). Only, the resistor R sucks the voltage V = R.I from the circuit (it is a voltage drop) while the negative resistor -R adds the voltage V = R.I into the circuit. So, a resistor acts as a current-to-voltage drop converter while a negative resistor acts as a current-to-voltage converter. The element named "resistor" is really a resistor while here the "negative resistor" is actually a voltage source, whose voltage is proportional to the current passing through it. Now, we can answer the main question "What is negative resistor?"; the answer is simple and clear.

A negative resistor is just a voltage source, whose voltage is proportional to the current passing through it. Shortly, a negative resistor acts as a "current-controlled voltage source".

If we connect the additional voltage source in the opposite direction versus the input voltage source (Fig. 1c), it will act as an "over-impeding" voltage source.


A current source acting as a negative resistor (connected in parallel with the load)
Fig. 2a: An "ordinary" positive resistor Fig. 2b: An "over-helping" current source Fig. 2c: An "over-impeding" current source
Fig. 2a: An "ordinary" positive resistor
Fig. 2b: An "over-helping" current source
Fig. 2c: An "over-impeding" current source


Now, let's assemble two circuits where these components are connected in parallel to the loads so that the same voltage is applied across them. As a result, a current IR = VL/R passes through the resistor R (Fig. 2a) and the same current IH = VL/R passes through the negative resistor -R (Fig. 2b). Only, the resistor R sucks the current from the circuit while the negative resistor -R injects the current into the circuit. The element named "resistor" is really a resistor while here the "negative resistor" is actually a current source, whose current is proportional to the voltage across it. Thus we have found another answer to the main question "What is negative resistor?"

A negative resistor is just a current source, whose current is proportional to the voltage across it. Shortly, a negative resistor acts as a "voltage-controlled current source".

If we connect the additional current source in the opposite direction versus the input current source (Fig. 2c), it will act as an "over-impeding" current source.

[edit] How do we make negative resistors?

An S-shaped negative differential resistor
An S-shaped negative differential resistor

[edit] "Natural" negative differential resistors...

...based on constant-voltage dynamic resistors . We may obtain them, if we begin dynamically decreasing the ordinary ohmic resistor. First, we decrease slightly the ohmic resistance R (section 1-2) thus getting decreased differential resistance. Then, we decrease considerably enough the ohmic resistance (section 2-3), in order to get zero differential resistance (a voltage-stable dynamic resistor, a voltage stabilizer). Finally, decreasing enormously the ohmic resistance (section 3-4), we go so far that the IV curve changes its slope; as a result, we obtain the desired S-negative differential resistance. In this way, following the sequence: ohmic > decreased > zero > S-negative differential resistance, we come to conclusion: An S-shaped negative differential resistor is actually an "over-acting" voltage-stable dynamic resistor.

Examples: neon lamps, thyristors etc. See also my new story about negative differential resistors:

How do We Make Decreased, Zero and Negative Differential Resistance?

An N-shaped negative differential resistor
An N-shaped negative differential resistor

...based on constant-current dynamic resistors. Similarly, we may obtain the dual negative resistors, if we begin dynamically increasing the ordinary ohmic resistor. First, we increase slightly the ohmic resistance R (section 1-2) thus getting increased differential resistance. Then, we increase considerably enough the ohmic resistance (section 2-3), in order to get infinite differential resistance (a current-stable dynamic resistor, a current stabilizer). Finally, increasing enormously the ohmic resistance (section 3-4), we go so far that the IV curve changes its slope; as a result, we obtain the desired N-negative differential resistance. In this way, following the sequence: ohmic > increased > infinite > N-negative differential resistance, we come to conclusion: An N-negative differential resistor is actually an "over-acting" current-stable dynamic resistor.

Examples: tunnel and Gunn diodes etc.

A general conclusion: The negative differential resistor acts as a dynamic resistor with considerably varying resistance.

Discuss. Circuit-fantasist 17:14, 13 September 2006 (UTC)

[edit] True negative resistors

Only, the negative differential resistor that we have obtained is not a true negative resistor as it does not contain a source; it is just a part of such a negative resistor. In order to get a true negative resistor, we have to connect in series an additional constant voltage source:

Negative differential resistor + constant voltage source = true negative resistor

[edit] Artificial "circuit" negative resistors

Artificial "circuit" negative resistor = "positive" resistor + varying power source


A negative resistor connected in series with the load
Fig. 3a: An "ordinary" positive resistor Fig. 3b: An "over-helping" negative resistor Fig. 3c: An "over-impeding" negative resistor
Fig. 3a: An "ordinary" positive resistor
Fig. 3b: An "over-helping" negative resistor
Fig. 3c: An "over-impeding" negative resistor


A negative resistor connected in parallel with the load
Fig. 4a: An "ordinary" positive resistor Fig. 4b: An "over-helping" negative resistor Fig. 4c: An "over-impeding" negative resistor
Fig. 4a: An "ordinary" positive resistor
Fig. 4b: An "over-helping" negative resistor
Fig. 4c: An "over-impeding" negative resistor


[edit] Negative resistor applications

[edit] 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.

[edit] Negative resistor acting as a bistable component (a flip-flop)

To be continued... Circuit-fantasist 10:43, 24 August 2006 (UTC)


Interesting. Perhaps you could generalise it further, and say that all resistances, whether negative or positive, are current-controlled voltage sources. That way, you could merge your two diagrams into one. Positive resistances have a positive current-to-voltage coefficient, which causes the product of voltage and current, or the power consumption, to be positive. They do not therefore need a power source (although you could make such a device with a power source - I suppose that's what an active load is). Negative resistances have a negative I-V coefficient, which causes the product of current and voltage to be negative, and hence they emit power. They therefore need a power source. Or am I overcomplicating things? --Heron 19:04, 9 July 2006 (UTC)
Neron, thank you for the support. Really, Wikipedia is a great idea; now, I have the feeling that I am in the right place at the right time. Imagine, I am an initial excitation voltage source, which experiences a decrased resistance because of you acting as a "helping" voltage source:) If you continue working in this direction, I will experience zero:)) and finally negative resistance:)))
I accept your text; I admire its laconism and precision. You have made it just for an encyclopedia. Maybe, we might generalize the two components into one block diagram of a current-to-voltage converter.
From one side, to say that an ordinary "positive" resistor is a current-controlled voltage source sounds quite strange. Generally speaking, sources and loads (for example resistors) are converters - sources transfer energy from outside world to circuit while resistors transfer energy from circuits to outside world. However, there is something confusing to use here the term current-to-voltage converter as it is more informational rather energetical device. Actually, we do not convert current into voltage; we just change the carrier of analog information (current with voltage).
From the other side, you are right to think of a resistor as a voltage source - this is just a Norton's idea to build a voltage source by using a current one (Norton's theorem). The situation is similar to the dispute "Is a voltage divider a voltage source?" Let's think a little more...
Finally, don't you think that there is something confusing in the fact that ordinary resistance is something negative (harmful) but yet it is named "positive" resistance? Also, note that its power disappears but we say that it is positive. And v.v., why although a negative resistor add energy into circuit, we name it "negative" resistor? Don't you think that is more natural to reverse this terminology (of curse, we will not afford to do that:)
Continue thinking... Circuit-fantasist 19:27, 11 July 2006 (UTC)
Hi again! I have finally made a decision about your suggestion to combine the positive and negative resistors into the concept of current-controlled voltage source. Sorry, I can't accept it because of reasons above. I will repeat them again below.
A "positive" resistor is just a resistor. Really, a voltage appears across the resistor but it is not its voltage; this is the voltage of the excitation electrical source (current source or a voltage source with a series connected resistor). The whole combination current source + resistor acts as a source; similarly, the combination voltage source + voltage divider acts as a new derivative voltage source.
Again, the "positive" resistor is a load while the negative resistor is a source. They both are converters. --Circuit-fantasist 18:01, 21 July 2006 (UTC)
I have found an interesting picture comparison between the positive and negative resistance. --Circuit-fantasist 19:12, 22 July 2006 (UTC)


AFAIK, any source that adjusts its o/p voltage to keep its output current constant has a -ve o/p impedance, so if the load impedance increases, so will the o/p voltage and this is equivalent to the source having its o/p impedance being reduced. This is basically a constant current source action. Does this make sense, or am I way off track...? Rohitbd 12:16, 10 July 2006 (UTC)
There isn't a voltage divider connected in the non-inverting input of the op-amp INIC; as a result, the op-amp acts as an "over-impeding" voltage source producing two times higher compensating voltage in point B.
There isn't a voltage divider connected in the non-inverting input of the op-amp INIC; as a result, the op-amp acts as an "over-impeding" voltage source producing two times higher compensating voltage in point B.
Hi, Rohitbd. Thank you for joining the dispute. The topic of constant current creating is very interesting. That is why, I have created a special page about the philosophy of constant current source creating and a few more specific pages about practical CCS. Yes, I think that when the over protection circuit of a power supply comes into operation, it usually begins behaving as a CCS (as far as know, there are also other circuits with trigger action).
We may use CCS concept to introduce the second kind of negative resistance (I have named it figuratively "over-impeding" negative resistance). The ordinary CCS keeps a constant current by varying its internal voltage or resistance. In order to convert this circuit into NIC, we have just to "mislead" the op-amp making it "over-act". For example, compare the two circuits of Op-amp Widlar current source and INIC on the right and you will see that there is only one difference between them - the voltage divider R3-R4. In the first circuit, it prevents the "over-compensating". As a result, the voltage VB follows exactly the voltage VA (bootstrapping). In the second circuit, there isn't a voltage divider. As a result, the op-amp produces 2 times higher voltage VB than VA and a negative resistance appears. Circuit-fantasist 19:27, 11 July 2006 (UTC)
Your explanation is interesting from an intuitive point of view, but it's really quite simple mathematically and electrically. The sign of the voltage drop in your above drawings is opposite for positive and negative resistances. Heron's observation that negative resistance is a power source rather than a power sink is a direct consequence from the definition of power (or energy). Rohitbd's observation is partly correct. A regulated power supply appears as a negative resistance at it's input. The output impedance is zero for a voltage source and infinite for a current source. Madhu 14:12, 10 July 2006 (UTC)
Hello, Madhu. Thank you for the feedback. As I can see, we are quite different person - I rely mainly on my imagination, intuition and emotions while you rely on reasoning and formal analysis. Wikipedia gives us a chance to combine, not to oppose, both the approaches: I might reveal circuit phenomena and build circuits; you might analyze them. Famous circuits are invented by using this complementary principle, for example CMOS. Let's solve "qualitative" problems (introducing, explaining and revealing the basic ideas behind circuits) by qualitative means and "quantitative" ones - by using quantitative means.
I have corrected the sign of VI = R.I on fig. 2 and removed some confusing signs in the text.
What do you mean saying "A regulated power supply appears as a negative resistance at it's input"? --Circuit-fantasist 17:26, 12 July 2006 (UTC)
You can look at it both intuitively and analytically. An ideal regulator is 100% efficient, so all input power is avaiable at the output, i.e. power is conserved. The only difference is the input/output voltage. If the output voltage is constant and connected to a fixed resistive load, the output power is constant. The input power must also be constant since power is conserved. If the input voltage is increased, the input current drops to maintain constant power. This is negative differential resistance: current goes down when voltage goes up (and vice-versa). It's not hard to relax the 100% efficiency constraint and show that non-ideal regulated supplies also exhibit negative resistance.
Here are a couple of negative resistance circuits which might not be intuitive: Wien bridge oscillator and Colpitts oscillator. Of course, one could intuitively argue that any harmonic oscillator exhibits negative resistance at some port. Madhu 20:36, 12 July 2006 (UTC)
Thank you for the example; I have already known another interesting circuit phenomenon. As far as I can see, you mean a "clever" voltage regulator (for example pulse regulator), which does not regulate the output voltage by dissipating the surplus power on an analog regulating element (transistor). Instead, it "observes" the output voltage by a feedback and changes the pulse width thus regulating the current needed. Another more primitive but clear example: someone regulates AC voltage by observing it on the transformer's output (that is, using feedback) and changing the transformer ratio (for example, switching over the winds or moving a slider). Maybe, (hydro) power stations in energetics use this phenomenon when regulate their electrical outputs; maybe, they behave as negative resistors at their hydraulic inputs? Well, let's finalize these thoughts in a conclusion:
The input part of the circuit consuming a constant power behaves as a negative resistor.
Voltage versus current. However I am confused by the assertion "This is negative differential resistance: current goes down when voltage goes up (and vice-versa)" or the same "current is a decreasing function of voltage" (Negative resistance). Look at the picture of an op-amp NIC that I have inserted above; it has a negative resistance but here the current goes down when the voltage goes down and vice-versa (similarly to the behavior of a bare resistor)! It comes out that both the cases exist; therefore, there is no sense in this assertion!? What do you think about this paradox?
I'm missing your point. If current goes down as voltage goes down, how is that negative resistance? Isn't that the definition of positive resistance? Madhu 22:11, 13 July 2006 (UTC)
Negative resistor versus amplifier. Madhu, since you are so clever, can you answer what the relationship is between a negative resistor and an amplifier? As we know, it is considered that a negative resistor is an amplifier. If it is true, are there any difference between a negative resistor and an amplifier? If yes, what is the difference? I will show my viewpoint in "2.1. Negative resistor acts as an odd amplifier" but now I give an opportunity to express first your view:)
I wouldn't call myself clever, in fact, I'm fairly sure I'm not ;-) To answer your question, I would say that a negative resistor is like a one port amplifer. Of course, this is entirely my opinion. Others probably have their own way of looking at it, and that's perfectly fine. I personally don't have much interest in debating opinions, but that's just me. You're more than welcome to come up with your own answers in your own way, but I prefer to analyze circuits mathematically. It works for me. Madhu 22:11, 13 July 2006 (UTC)
Hi Madhu! Sorry for the delay; these days, I was seized by the idea how to evade NOR (see below). Now, I would like to resume the discussion about the negative resistor acting as an amplifier. Maybe, your idea to think of negative resistor as a one-port amplifier is great. Only, there is a "little" problem - I do not know what a one port amplifier actually is:) Can you give me more info about it? It would be very well, if it is a 2-terminal device; then, we might merge our explanations.
Madhu, thank you for your correct replies. As I can see, for now I manage to keep some dialogue only with a few Wikipedians and you are one of them. I have the feeling that I become disappointed in the Wiki society in the area of electronics:( There are too many people dealing with routine editorial activities and only few people eager to discuss circuit phenomena:( --Circuit-fantasist 18:04, 20 July 2006 (UTC)
Well, I don't think my idea about the one port amplifier is great at all, it's just the first answer that came to mind. By one port, I mean that the input and output are the same. Conventional amplifiers usually have two ports: a distinct input and output. Further, a negative resistor isn't a great replacement for a conventional, two port amplifier, IMHO. You bring up some interesting topics, but as you say, we probably look at circuits differently. If you like, we can continue the discussion offline. You can find my email address here: Madhu 22:15, 20 July 2006 (UTC)
Thank you for the elucidation. I am happy that I think in this direction also. I don't know why but I like 2-terminal devices, maybe because of their perfect simplicity. I have found an interesting message about this topic. See also an interesting picture comparison between the positive and negative resistance corresponding to my wievpoint.
Madhu, it is interesting for me to communicate with you. Of course, I will use the email, if the topic discussed is not so interesting for the other Wikipedians. --Circuit-fantasist 19:38, 22 July 2006 (UTC)
I don't think that Wien bridge oscillator and Colpitts oscillator are non-intuitive. I think that they have invented them and then they have hidden the key:) I haven't yet an intuitive notion about them but I know I will ever have. For now, I have some intuitive notion about Hartley generator. --Circuit-fantasist 20:17, 13 July 2006 (UTC)
I didn't have an intuitive understanding of them either, until I did the analysis. In my opinion, the Hartley and Colpitts circuits are electrical duals. If you can understand one, you can understand the other. Madhu 22:11, 13 July 2006 (UTC)

[edit] A damper

I hate to put a damper on all this enthusiasm, but we must be careful here to abide by WP:NOR. Ie these ways of explaining things are OK if someone else has already published them. Yes?--Light current 02:09, 12 July 2006 (UTC)

Well, merely coming up with a new way of explaining something probably isn't OR, just good writing. But coming up with a new concept certainly would be OR.
Atlant 17:41, 12 July 2006 (UTC)

Well.. you know Atlant, Im not sure about that. Ive put forward a number of new explanations of things only to be shot down in flames by some editors firing the NOR missile at me! 8-(--Light current 23:49, 12 July 2006 (UTC)


[edit] How to evade NOR (The King is naked!)

Hi Light current, Atlant and all members of Wikipedia society in this area of electronics! I realize that I have disturbed to some extent your calmness:); so, maybe I have to say some words about me, my reasons and my intentions. Simply speaking, I have to say what I (will) do on talk and article pages of Wikipedia.

[edit] Yes, I do original research!

Honestly, I realize that I actually do an original research on talk pages of Wikipedia contrary to NOR. According to its definitions, I do "research that consists of collecting and organizing information from existing primary or secondary sources (generalization, analysis, synthesis, interpretation, or evaluation of information or data)..." What is more, my explanations on talk pages are based on my "self-published resources" available to readers from my web site of circuit-fantasia.com. In addition, I do all the "bad" things listed in What is excluded? As far as I know, there is nothing wrong with it, if I stay at talk pages. But what have I to do, in order to join the article pages abiding by NOR? Below, I share some tips about how to evade Wikipedia NOR barrier.

[edit] But yet, how do we evade NOR? (a tip for creatively thinking Wikipedians)

My idea is extremely simple - to explain circuits so simply, clearly and evidently that there is no any need to verify these explanations (NOR stipulates such a possibility - to use sources "the accuracy of which is easily verifiable by any reasonable adult without specialist knowledge..."). For this purpose, I present circuits relying only on human (web visitor's) experience, imagination and intuition. I implement this approach by using a 3-step "scenario" (see my teaching philosophy). First, I extract the basic idea from many everyday situations formulating it verbally and in a form of block-diagram, then I show the possibly simplest equivalent electrical circuit diagram and finally I draw the specific electronic circuit solution.

You probably guess why I can't cite "verifiable sources", which reveal circuit phenomena - just because there are not such sources! I have been looking for them on the web from years but I have not found yet. I don't know why but it is true that the existing "verifiable sources" are dull and formal. Maybe, their authors pursue other goals (for example, to climb up the scientific ladder); that is why they make the simple complex while I try to make the complex simple, the simple - simpler and the simpler - simplest.... Figuratively speaking, I am just the boy from Andersen's story who says "The King is naked!":)

I have refused a long time ago to publish my ideas in the so-called "verifiable sources" since they consider this human-friendly approach as a non-scientific (in the bad sense of the word). Note - they do not reveal the ideas behind circuits but if you do that, they will probably shout, "This is non-scientific"! I can't stop showing some example of this paradox; here is such a story about it.

[edit] An example of this approach

[edit] Bob Pease's viewpoint at transimpedance amplifier

Electronic design magazine is an extremely reputable source and Bob Pease is an extremely reputable author. Well, let's then try to understand what the op-amp actually does in the circuit of a transimpedance amplifier following the link from the bottom of this Wiki page pointing to Bob's reputable article What's All This Transimpedance Amplifier Stuff, Anyhow?. I have formatted his text in bold italic and inserted my comments into the original text between his thoughts.

"One of the first things you learn about operational amplifiers (op amps) is that the op amp's gain is very high", Mr. Pease begins his story. Only, the gain is the most insignificant op-amp's feature, if we try to understand what the op-amp does in the circuit discussed. What is the problem to be solved?

"Now, let's connect a feedback resistor across it, from the output to the −input (Fig. 1)." I ask, "Why?" Is there any reasonable need to do that? Because we, human beings, do something, only if there is some reason to do that.

"When you put some input current into the −input..." Again, I ask, "Why?" What is the need to put the current just into there?

"...(also known as the summing point),..." Is the −input a summing point here? If yes, what does it sum here (recall that the op-amp has extremely high input impedance)? As far as I know, we need at least two inputs and one output, in order to sum something.

"...the gain is so high that all of the current must go through the feedback resistor." Can you see any direct connection between the very high gain and the behavior of the current? Has the current any other alternative to flow? No, as the op-amp has extremely high input impedance.

"So, the output will be VOUT = −(IIN × RF). That's neat." Again, "Why?" Can you see any connection between this speculation and the previous one from above? It is only evident (according to Ohm's law) that the voltage drop across the resistor R is VR = IIN × RF; however, I wonder why "the output will be VOUT = −(IIN × RF)"? I would like to know why.

"While we used to call this a "current-to-voltage converter," which it is indeed, it's also sometimes referred to as a "transimpedance amplifier," where the "gain" or "transimpedance" is equal to RF", concludes Mr. Pease at the end.


Now, answer honestly to my questions. What have you understood from this reputable source? Have you known what the problem actually is? Have you realized how the problem was solved? Have you made sense of connecting an op-amp? Do you understand what it actually does in this circuit? Simply speaking, what is the basic idea behind the circuit? Can you elaborate it, in order to get circuits that are more complex (for example, circuits with negative resistance)? Can you simplify it, in order to get circuits that are simpler (for example, op-amp ammeter)?

Try to find ahswers to these questions yourself. As for me, I will prepare a human-friendly story about this legendary circuit and will place a link to this "non-verifiable" source on transimpedance amplifier page. This circuit deserves attention. --Circuit-fantasist 07:59, 16 July 2006 (UTC)

[edit] My viewpoint at transimpedance amplifier

As I can see, there aren't any suggestions; as usual, I have first to expose my viewpoint. If I have to express briefly the main idea, I will say:

In transimpedance amplifier, the op-amp compensates the voltage drop across the resistor adding as much voltage as it loses; the compensating voltage serves as an output voltage.

Using an idea of compensation is not a good way to think of it. Think of it as servoing. In an idealized, simple transimpedance amplifier circuit, an injected current most go somewhere, it's not going into the amplifier. The current must be drawn through the feedback resistor. Well, how does that happen? The op amp must create an output voltage that forces this to occur, and using the inverting input allows the resulting output voltage to stabilize at the required output voltage. (I think you know that using the non-inverting input would drive the output to a rail.) So when you inject a new current into the circuit's input, the output voltage slews in a direction towards the voltage that will drag all the input current through the feedback resistor and then settles (if everything is stable), perhaps oscillating a little, on the exact required output voltage. It's really very simple, but you have to understand current, current sources, and the physics of having a complete circuit (from source to sink). (I hope you're not offended by that last comment, it is not intended. I remember when I was learning about these things, it took a while. And BTW most (even PhD) researchers don't know that they're supposed to use transimpedance amplifiers to convert a photodiode's output to a voltage. If you don't do it, you can create an output that sorta looks ok so they say, well it looks like a pretty go presentation of the input light signal, and perhaps it's not necessary to get a better signal, but it is far from a linear representation of the input current. It's one of those gotchas.) blackcloak 17:00, 28 July 2006 (UTC)
Hi Blackcloak! Thank you for the feedback. This subject is extremely important and interesting for me that I can discuss it as long as you want:) IMO, there isn't any contradiction between as; actually, we both think similarly. Maybe, the problem is that I have gone too far trying to penetrate in these phenomena; then, I have gone too far trying to reach the perfect simplicity in presenting them to students.
Browsing through your text I can see that you have thoroughly explained how the op-amp does the servoing (how it keeps the virtual ground). Yes, this is wonderful; I have also shown the op-amp action step-by-step in a flash movie dedicated to op-amp inverting summer (transimpedance amplifier is an important part of this circuit). Only, Blackcloak, believe me, this is insufficiently. As human beings, we need before to know why it does this work! Also, we need to know what the problem the op-amp solves (why have we connected it there?). Simply speaking, we need to know what the basic idea is.
Many ideas can stay behind some specific circuit implementation but only one of them is the main, essential, substantial idea. In order to understand and then to explain really the circuit discussed, we have first to reveal and then to show this idea. For the circuit of the so called transimpedance amplifier, the main idea is exactly compensation, not negative feedback (servoing). Negative feedback is a great idea; but here, negative feedback is just a possible way of implementation. Compensation and negative feedback are not exactly equivalent ideas. We might make (passive) compensation without negative feedback and v.v. - (series) negative feedback without compensation.
Circuits with parallel feedback possess the property to interfere in the input sources - they may "help" or "oppose" the excitation voltage source. In the circuit of transimpedance amplifier, the op-amp "helps" the input source. It acts just as a small battery, which adds so much voltage as it loses across the resistor R. See how simple it sounds - just add a small battery in series with the resistor and make its voltage to be equal to the voltage drop across the resistor! In order to understand this bare truth, you needn't to know what servoing is; we just do it! For this purpose, we usually copy the "harmful" voltage drop across the resistor. The perfect "copying" is "active copying" (that is, negative feedback). That is why, we use it here. Let's say it again by little rewording.
In transimpedance amplifier, we (that is, the op-amp) copy the voltage drop across the resistor by using a negative feedback, then add the "copy" voltage into the circuit and finally use the compensating "mirror" voltage as an output voltage.
If you have time and enthusiasm enough, please visit the resources below that I have dedicated to this great idea (compensation, removing voltage by an "antivoltage", "helping", "zeroing" etc.)
Blackcloak, if I have an inspiration enough during the holidays, I will create a page about transimpedance amplifier especially for you:) --Circuit-fantasist 09:24, 29 July 2006 (UTC)


Blackcloak, where are you? You have disappeared just like a voltage drop across the resistor in the circuit of a transimpedance amplifier:) I have also disappeared for a week, in order to create my new page about transimpedance amplifier (as you can see, I keep my word). I would like to dedicate this exciting story about the legendary circuit to you. Only, there is a small problem - I don't know who you are actually:) --Circuit-fantasist 19:15, 5 August 2006 (UTC)


If I have to express in details the main idea, I will build the circuit in three successive logically connected steps. In the beginning, imagine we have to measure a current flowing through a part of some circuit (for example, imagine that we have to measure the current acquired from a real voltage source when it is shorted). However, we have a voltmeter instead an ammeter; so, we decide to convert the current into voltage. For this purpose, we break the circuit and connect a resistor R acting as a simple current-to-voltage converter.


What does the op-amp actually do in the circuit of transimpedance amplifier?
Step 1: Passive current-to-voltage converter Step 2: Active current-to-voltage converter Step 3: Op-amp current-to-voltage converter
Step 1: Passive current-to-voltage converter
Step 2: Active current-to-voltage converter
Step 3: Op-amp current-to-voltage converter


Step 1: The problem. Only, a problem appears here: from one side, the voltage drop VR = R.I across the resistor (the output voltage) is useful for us; from the other side, this voltage is harmful as it enervates the excitation voltage (not shown on the picture). As a result, the current IIN decreases. What do we do to solve this contradiction?

There is no problem and there is no contracdiction. A current source is a current source, the voltage required to create the current is continuously varying (if necessary) to produce the desired current. blackcloak 17:00, 28 July 2006 (UTC)
I have clarified the arrangement above. I mean the common case - a real voltage source feeding the circuit (see this picture of a transimpedance amplifier). Well, I will discuss the situation with a great pleasure:)
Here, we solve the well-known problem - how to obtain a constant current. There isn't any problem, if we drive the imperfect current load by a perfect current source or, if we drive a perfect current load (shorted output) by an imperfect current source. There is a problem in our situation as we drive the imperfect current load by an imperfect current source. How to solve the problem?
You say, "A current source is a current source, the voltage required to create the current is continuously varying (if necessary) to produce the desired current." Right, this is one of the possible ways of creating a constant current source - by simple varying the excitation voltage or by negative feedback (the best solution). In this arrangement, the excitation voltage source (as a part of a constant current source), increasing additionally its voltage, compensates the losses into the imperfect current load (and not only them). It is wonderful! Unfortunately:(, in the most cases, we can't do that trick as we just can't reach (can't drive) the excitation voltage source! An analogy: can we control the sun, in order to adjust the light or the temperature inside the room:)?
That is why, we apply more frequently the other trick - we connect an additional voltage source, which compensates (only the local) losses into the imperfect current load. An analogy: we connect additional light or thermal sources inside the room, in order to "help" the sun (instead to control directly it).
In this way, we actually convert the imperfect current load into a perfect one with zero resistance (a kind of an active "superconductor":) You probably guest that using this technique, we can make almost ideal diodes without VF, "botomless" capacitors with infinite capacitance, perfect ammeters with zero resistance etc. Another advantage of this trick is using the compensating "anti-voltage" as an output voltage; so that we can connect as much low resistance load as we want - see the explanations below. --Circuit-fantasist 10:30, 29 July 2006 (UTC)

Step 2: The remedy. Obviously, we have to compensate the voltage losses across the resistor R. For this purpose, we connect an additional voltage source VH and adjust its voltage so that VH = VR. As a result, the "harmful" voltage VR and the resistance R disappears; the point A becomes a virtual ground (VA = 0). Actually, the additional voltage source VH "helps" the excitation voltage in its efforts to create the current IIN. Note that the two voltage sources are connected in series, in one and the same direction (- +, - +) so that their voltages are added. Then we take the compensating voltage VH = -VR = -R.I as a "mirror" output. The advantage: the load consumes energy from the "helping" voltage source instead from the excitation voltage source.

Step 3: The implementation. Finally, we make an op-amp do this donkeywork. Now, it "observes" the virtual ground and adjusts its output voltage VH = -VR = -R.I. See also:

--Circuit-fantasist 06:47, 17 July 2006 (UTC)

[edit] Unhappy with lede

A differential negative resistance component can also be employed as an amplifier. A tunnel diode is a good example. THe lede says the component must contain an energy source. That is not correct. --Light current 22:02, 2 August 2006 (UTC)

How can it be used as an amplifier if it has no energy source? — Omegatron 13:41, 3 August 2006 (UTC)

Well there must be an energy source somwhere but not necessarily in the component. Put a neg diffl res device across a tl. Rather than act as an attenuator (which a pos res would) it acts as an amplifier. THe energy comes from dc supplied by the line. 8-)--Light current 13:47, 3 August 2006 (UTC)

Hi everybody here! You carry on very, very interesting discussion! Let me join it. Here are a few thoughts about the topic (discuss). For more explanations, see above Negative resistor acting as an amplifier (discuss).
In the beginning, let's say that amplification is impossible. We cannot amplify energy (power); we can only regulate (attenuate) it. For this purpose, we need regulating elements, which do that work.
The classic 3-terminal regulating element (e.g., tube, transistor etc.) acts as an electrically controlled resistor with separate input and output ports. The voltage (current) applied across (through) the input port controls the resistance between the two terminals of the output port.
The odd 2-terminal regulating element (e.g., tunnel diode) acts as an electrically controlled resistor, which input and output are the same. The voltage (current) applied across (through) the two terminals of the element controls the resistance between the same two terminals. In order to do that magic, such a regulating element is actually an "over-acting" dynamic resistor, i.e. negative resistor.
In order to build such a Negative resistance amplifier, we may connect in series an input voltage source, a constant-voltage power supply, a "positive" resistor and a negative differential resistor. When the input voltage varies slightly, the negative differential resistor changes considerably its resistance according to the input voltage; so, the voltage divider changes noticeably 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.
In this arrangement, the differential negative resistor is not an amplifier; it is just a part of an amplifier (the differential negative resistor is just a 2-terminal regulating element). The combination of the differential negative resistor acting as a regulating element and the power supply constitutes an amplifier:
Differential negative resistor + power supply = negative resistance amplifier
From other viewpoint, this combination forms a truly negative resistor:
Differential negative resistor + power supply = truly negative resistor
So, we can make a conclusion:
Truly negative resistor = negative resistance (2-terminal, 1-port) amplifier
(see also Madhu's viewpoint above). Circuit-fantasist 08:18, 25 August 2006 (UTC)

[edit] Positive feedback -> negative resistance?

To obtain a negative resistance characteristic in a circuit using only positive impedance components, it is necessary to apply positive feedback at some point in the cct by means of an amplifier supplied by a suitable energy source. Discuss--Light current 22:09, 2 August 2006 (UTC)

Maybe reword that a bit. If you say positive impedance, that might exclude capacitors, which have a negative reactance and small positive series resistance (or large parallel resistance). Arguably, an ideal capacitor has a negative impedance. How about "using only passive components with non-negative resistance"? Maybe reword "positive feedback" also, it could be a negative feedback amplifier and 180 degree phase shift. Madhu 20:06, 3 August 2006 (UTC)

Good points . I think about it some more! 8-)--Light current 22:42, 3 August 2006 (UTC)


Hi Light current and Madhu! Thank you for the posing so interesting problem for discussion. Here, I will try to expose my viewpoint at the topic. I hope that you will scrutinize my speculations and will react to them (I have not yet searched the web about this topic).
There are different kinds of feedback arrangements in an N-shaped IV curve of a negative differential resistor.
There are different kinds of feedback arrangements in an N-shaped IV curve of a negative differential resistor.
IMO, in a circuit containing negative resistor, we may observe all the three possible situations:
  • there is negative feedback,
  • there is no feedback,
  • there is positive feedback.
Lets for concreteness consider a simple circuit, consisting of three connected in series components: a voltage source V, a "positive" resistor Ri (it might represent the internal source resistance) and a negative differential resistor -R. Depending on the kind of the negative resistor and the interrelation between the two resistances (the magnitude of Ri versus R), we may observe the cases below:
N-type negative resistor (based on an "over-acting" current-stable dynamic resistor)
  • Ri < R - there is negative feedback
  • Ri = R - there is no feedback
  • Ri > R - there is positive feedback
S-type negative resistor (based on an "over-acting" voltage-stable dynamic resistor [1])
  • Ri < R - there is positive feedback
  • Ri = R - there is no feedback
  • Ri > R - there is negative feedback
There are different kinds of feedback arrangements in an S-shaped IV curve of a negative differential resistor.
There are different kinds of feedback arrangements in an S-shaped IV curve of a negative differential resistor.
Well, let's consider the picture on the right (only suppose that there is an ohmic resistor Ri instead the constant current source showed). Imagine that we have created this curve by applying different kinds of feedback arrangements as follows:
  • Section 0-1, ohmic resistance, we have not applied any feedback.
  • Section 1-2, decreased differential resistance, we have applied only imperfect negative feedback (e.g., by using an amplifier with little K).
  • Section 2-3, zero differential resistance, we have applied only perfect negative feedback thus obtaining a voltage stabilizer (Ri > R).
  • Section 3-4, negative differential resistance, we have added small positive feedback to the existing negative feedback (still Ri > R).
  • Then, if we make equal the positive and the negative feedback (Ri = R), we will have no feedback again.
  • Finally, if we increase the positive feedback so that it becomes stronger than negative one (Ri < R), we will obtain a flip-flop (memory) component.
Do you accept this chain of thoughts? Discuss.
See also my new stories about negative resistance: A heuristic approach to teaching negative resistance phenomenon and How do We Make Decreased, Zero and Negative Differential Resistance? Circuit-fantasist 18:20, 10 September 2006 (UTC)


I have finally realized why there is a need of positive feedback in negative resistance circuits. If you want, we might discuss this extremely interesting topic. Circuit-fantasist 11:25, 30 September 2006 (UTC)


[edit] wish: show the graph rotated too

Could the main graph also be drawn as V against I? It would be enlightening to see dV/dI as the actual gradient.

Yes. Madhu 21:42, 16 October 2006 (UTC)

[edit] Fair-use image discussion

(moved here from image page Image:Chung negative resistance setup.png):

I believe this is fair use as it is for "analysis or criticism". — Omegatron 19:14, 11 November 2005 (UTC)

Source

I don't feel that this qualifies for fair use because it could easily be recreated with a free-use image. Kevin 12:49, 1 August 2006 (UTC)

It is needed to show the device as she presented it. — Omegatron 13:35, 1 August 2006 (UTC)
I'm deleting it (and the other image) for the reasons Kevin said. You can easily recreate a diagram containing the same information, and source the information to the paper by Chung. Fut.Perf. ☼ 12:11, 11 February 2007 (UTC)
Actually, I've had second thoughts and I'm undeleting it again. See image page for rationale. Sorry, my first day on the replaceable-fair-use speedy deletion queue. Fut.Perf. ☼ 14:23, 11 February 2007 (UTC)
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