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Archive 1 | Archive 2 | Archive 3 | Archive 4 | Archive 5 |
(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.
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.
Now, let's move to the electrical domain and answer the main question: What is negative resistance (resistor) versus ordinary resistance (resistor)?
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.
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.
...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?
...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)
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
Artificial "circuit" negative resistor = "positive" resistor + varying power source
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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.
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!
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.
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.
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.
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.. 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)
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.
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.
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.
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)
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.
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.
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?
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)
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)
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)
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)
Good points . I think about it some more! 8-)-- Light current 22:42, 3 August 2006 (UTC)
Could the main graph also be drawn as V against I? It would be enlightening to see dV/dI as the actual gradient.
(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)
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)
Neron, my approach is first to extract the general non-electrical idea and then to apply it in the electrical domain. From this viewpoint, the non-electrical idea is more general that the electrical one. That is why, I have placed a general conclusion in the beginning of the first section.
By the way, I realize that this page and the other pages where a have contributed have become lengthy (I have discussed this with Alfred in the end of Talk:Current_source. Maybe, I will begin implementing my circuit stories as Wikibooks and will reduce the size of my Wikipedia contributions. I would be happy, if you help me to simplify and make the Wiki articles concise. Regards, Circuit-fantasist 17:16, 11 April 2007 (UTC)
I would like to point out that there is a device that exists that exhibits negative resistance - even for a short period. This is an arc lamp during the keep-alive portion. If one looks at the V-I curve for an arc lamp, the far left portion of it, where the current is small, the voltage has a negative slope.
Redderek 20:01, 1 May 2007 (UTC)
This is the most confusing Wikipedia article of the many thousands that I have (mostly) had the pleasure to read. I stuggled to understand what was written even though I have a degree in physics, an IQ of 168, and work in electronics. Heaven help the lay reader whom Wikipedia is directed at.
The article is convoluted, overly-wordy, and appears to be too long for the subject matter. The drawings are quaint but not particularly illustrative. In fact, it reads like a webpage from one those free energy/oil conspiracy nutters. The whole things smacks of Single Author Syndrome. Others have made some attempts at tidying up but that has been like putting a Band-Aid on somebody who has fallen six storeys onto the footpath/pavement/sidewalk.
This article is in dire need of major surgery by someone with a clear grasp of the concept and able to write encyclopediacly (if that is a word). Unfortunately, that person is not me since I don't know any more about negative resistance than when I first started reading the article. Secret Squïrrel, approx 02:40, 25 January 2008 (Earth Standard Time)
This page is utter nonsense and I am willing to fix it. Most of the content has to be excised first. I'm talking about all the crayon drawings and the absurd explanations that goes with them. This stuff belongs on someone's personal web page. I don't do much Wikipedia editing but I do have an EE degree from a very well regarded Institute. This needs to be written so it A: makes sense, B: is correct, and C: Looks like and encyclopedia entry. Before this can be done a consensus has to be reached. How say you all? Zen-in ( talk) 03:10, 3 May 2008 (UTC)
![]() | This page is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
![]() | This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 | Archive 2 | Archive 3 | Archive 4 | Archive 5 |
(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.
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.
Now, let's move to the electrical domain and answer the main question: What is negative resistance (resistor) versus ordinary resistance (resistor)?
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.
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.
...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?
...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)
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
Artificial "circuit" negative resistor = "positive" resistor + varying power source
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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.
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!
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.
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.
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.
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.. 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)
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.
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.
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.
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)
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.
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.
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?
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)
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)
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)
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)
Good points . I think about it some more! 8-)-- Light current 22:42, 3 August 2006 (UTC)
Could the main graph also be drawn as V against I? It would be enlightening to see dV/dI as the actual gradient.
(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)
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)
Neron, my approach is first to extract the general non-electrical idea and then to apply it in the electrical domain. From this viewpoint, the non-electrical idea is more general that the electrical one. That is why, I have placed a general conclusion in the beginning of the first section.
By the way, I realize that this page and the other pages where a have contributed have become lengthy (I have discussed this with Alfred in the end of Talk:Current_source. Maybe, I will begin implementing my circuit stories as Wikibooks and will reduce the size of my Wikipedia contributions. I would be happy, if you help me to simplify and make the Wiki articles concise. Regards, Circuit-fantasist 17:16, 11 April 2007 (UTC)
I would like to point out that there is a device that exists that exhibits negative resistance - even for a short period. This is an arc lamp during the keep-alive portion. If one looks at the V-I curve for an arc lamp, the far left portion of it, where the current is small, the voltage has a negative slope.
Redderek 20:01, 1 May 2007 (UTC)
This is the most confusing Wikipedia article of the many thousands that I have (mostly) had the pleasure to read. I stuggled to understand what was written even though I have a degree in physics, an IQ of 168, and work in electronics. Heaven help the lay reader whom Wikipedia is directed at.
The article is convoluted, overly-wordy, and appears to be too long for the subject matter. The drawings are quaint but not particularly illustrative. In fact, it reads like a webpage from one those free energy/oil conspiracy nutters. The whole things smacks of Single Author Syndrome. Others have made some attempts at tidying up but that has been like putting a Band-Aid on somebody who has fallen six storeys onto the footpath/pavement/sidewalk.
This article is in dire need of major surgery by someone with a clear grasp of the concept and able to write encyclopediacly (if that is a word). Unfortunately, that person is not me since I don't know any more about negative resistance than when I first started reading the article. Secret Squïrrel, approx 02:40, 25 January 2008 (Earth Standard Time)
This page is utter nonsense and I am willing to fix it. Most of the content has to be excised first. I'm talking about all the crayon drawings and the absurd explanations that goes with them. This stuff belongs on someone's personal web page. I don't do much Wikipedia editing but I do have an EE degree from a very well regarded Institute. This needs to be written so it A: makes sense, B: is correct, and C: Looks like and encyclopedia entry. Before this can be done a consensus has to be reached. How say you all? Zen-in ( talk) 03:10, 3 May 2008 (UTC)
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