It is easy to design a circuit, using operational amplifiers, for example, which produce either negative resistance, negative capacitance, or negative inductance. This is often taught in undergraduate level electronics courses. However, can anyone name one commercial or practical electronic product that actually exploits negative impedance? If there are none, why is that?
Yes, and to complete the picture we can state that a combination of two NIC units forms a very versatile block called GIC (Generalized Impedance Converter), which can be used to realize (emulate) an "ideal" grounded inductor or an FDNR element (Frequency-dependent Negative Resistor).
:-) I should have made the question clearer and asked for commercial products that exploit, say, negative resistance to cancel unwanted positive resistance.
Few days ago I was designing an feedback amplifier-based RTD linealizator, the calculated feedback was a negative resistance, I used an Esaki diode and it worked well... I don't think this device could exploit, but it is one example of the use of cancel positive resistance
we should consider that the word "negative" in the real world shows itself as a "180 deg phase shift". it means when you design an amp with input impedance -Rin, the Voltage V and Current I, will have a 180 deg difference in their wave pattern on oscilloscope. Or another example in oscillators, you use negative resistance, in fact you force another 180 deg phase shift to your circuit, and make the total circuit unstable to oscillate.
Be aware of the assumptions !!!. If you take into account the parasitic elements an electrical circuit is a fractal pattern of coupled oscillators ;-)
Negative resistances are used in many devices in microwave domain at higher frequencies:
- in oscillators,
- in filters to improve the quality factor by decreasing filer resistance
- as amplifiers such as Gunn diode and parametric amplifiers.
A negative resistance is a 2-port device and much more difficult to use than a transistor:
- it as generally lower bandwidth,
- a lot of manual tuning is necessary,
- a circulator is needed to separate input and output,
- its negative value must be quite close to the opposite of the positive value of the resistance it negates for usable effect,
- if its negative value becomes higher, the device oscillates or becomes unstable.
So, as soon as a correct transistor technology exists at a given frequency, negative resistance devices are replaced by their equivalent 4-port devices.
That is why negative resistances are not generally used in consumer equipment.
Mr. Derek Abbort,
The concept of negative Impedance is not prevalent.But negative reactance is comprehensible. As Inductive reactance is expressed as
+jX we say -jx is capacitive reactance. Impedance Z=Sqrt ( R^2+X^2) and it can never be negative.
But the concept of negative resistance is well established. Electrical arc has negative resistance.
In Electronic Devices characteristics like Tunnel Diode,Gunn Diode etc. etc.we have negative Resistance region and only in negative resistance region it can act as Oscillator.
In addition to the feedback oscillators, which use two-port amplifying active elements such as transistors and op amps, linear oscillators can also be built using one-port (two terminal) devices with negative resistance such as magnetron tubes, tunnel diodes and Gunn diodes. Negative resistance oscillators are often used at high frequencies in the microwave range and above, since at these frequencies feedback oscillators perform poorly due to excessive phase shift in the feedback path.
Dr.P.S.
concerning: "In Electronic Devices characteristics like Tunnel Diode,Gunn Diode etc. etc. we have negative Resistance region and only in negative resistance region it can act as Oscillator" above:
In the negative resistance region the small signal model is unstable. The bias point of an oscillator vary with time. Oscillators are nonlinear circuits which may be investigated as time varying linear circuits.
Mr.Erik,
You are absolutely correct in that Oscillators should operate in the negative resistance characteristic region of these devices.
In the case of negative resistance of the arc, as the current increases resistance decreases and current increase and so on.
By negative impedance we mean the impedance phase shifted by 180 degrees and the current also gets phase shifted likewise by 180 degrees but does not change in magnitude.
I am happy that the question by Mr.Abbot and the answers by you are quite interesting.
This has led to discussions on Circuit parameters and Electronic Devices,
particularly micro wave generation.,
Dr.P.S.
Dr.P.S.
Real world linear oscillators are damped circuits. The nonlinearities do not bring the poles to the imaginary axis. The Barkhausen criterion is based on the assumption of a linear circuit. A steady state linear oscillator with poles on the
imaginary axis is mathematical fiction. You cannot balance on a razor's edge. For a real world steady state oscillator the poles of the time-varying small-signal model moves between the right and the left half-plane and an energy balance is obtained.
I like to point to the fact that each "linear" oscillator (I ignore the always existent and necessary small non-linearity) employing positive feedback can be also seen as a "negative-resistance" oscillator. It is just a matter of the way how to explain the oscillatory process. Of course, this applies also to the known single-transistor oscillators (Clapp, Colpitt,..).
More than that, the well-known GIC topology, which is used in many high-performance filter circuits, is based on the combination of two NIC stages (NIC=Negative Impedance Convertor).
The pendulum clock is an example of an oscillator where the complex pole pair move around in the left half plane only. The impulse from the escape mechanism determine the amplitude and compensate the losses.
http://www.google.co.in/url?sa=t&rct=j&q=&esrc=s&source=web&cd=8&ved=0CHoQFjAH&url=http%3A%2F%2Fciteseerx.ist.psu.edu%2Fviewdoc%2Fdownload%3Fdoi%3D10.1.1.139.6617%26rep%3Drep1%26type%3Dpdf&ei=gSn4UM-uN4PJrAeO6YCoDg&usg=AFQjCNHzCpmrD4yQL3F_EjGtAdIp0acoDA&bvm=bv.41018144,d.bmk&cad=rja
Go through this link. It gives an explanation of reactive power and its practical implications which is due to negative impedence.
Referring to the link mentioned by Soumen Mandal, It is true that the real power consumed by reactive elements like Inductance and Capacitance is zero but only for Pure( Loss-less) Inductance and Capacitances.
However the inductance has some small resistance of the material and the capacitance has some small loss due to lossy dielectric which is represented by a pure capacitance in parallel with a large resistance.
The real Power Loss calculated in Load flow studies take int account the losses in the resistances of the lines and such practical losses in the distributed capacitances(which are not loss-less) .
Dr.P.S.
Referring to the question of Derek Abbot"Why there are no practical application of negative impedance?', I may point out that there are Practical applications of negative impedance concept in the use in Network Realization.
Just introduction of the application of Gyrator Networks in Network Realization and corresponding links are given below. This comes under Network Synthesis.
http://en.wikipedia.org/wiki/Gyrator
A gyrator is a passive, linear, lossless, two-port electrical network element proposed in 1948 by Bernard D. H. Tellegen as a hypothetical fifth linear element after the resistor, capacitor, inductor and ideal transformer.[1] Unlike the four conventional elements, the gyrator is non-reciprocal. Gyrators permit network realizations of two-(or-more)-port devices which cannot be realized with just the conventional four elements. In particular, gyrators make possible network realizations of isolators and circulators.[2] Gyrators do not however change the range of one-port devices that can be realized. Although the gyrator was conceived as a fifth linear element, its adoption makes both the ideal transformer and either the capacitor or inductor redundant. Thus the number of necessary linear elements is in fact reduced to three. Circuits that function as gyrators can be built with transistors and op amps using feedback.
http://www.beigebag.com/case_gyrator.htm
The gyrator is a two port network that is designed to transform a load impedance into an input impedance where the input impedance is proportional to the inverse of the load impedance. The gyrator network can be used to transform a load capacitance into an inductance. This feature is extremely useful in integrated circuit technology where it is difficult to realize physical inductors. The gyrator circuit can be created with just two dependent sources. The model in Figure 1 following displays the schematic of the gyrator macro:
For further details kindly refer to the links.
Dr.P.S.
Negative resistance (in the small signal sense) has been used for applications ranging from high speed logic to long line amplifiers for telephony to transmitters for deep space probes. The use is as old as the tunnel diode and as new as products in design as you read this.
Hi, everybody here!
The question is excellent and natural, and it deserves a well-founded answer. I will try to give here my modest contribution to this undertaking.
(True) negative impedance is a fundamental circuit concept (like positive feedback, virtual ground, bootstrapping, etc.) and variety of circuits are based on this phenomenon... but people usually are unaware of its existence. A typical example of this wide-spread situation is the comprehensive TI material below dedicated to the legendary Howland current pump:
http://www.ti.com/lit/an/snoa474/snoa474.pdf
Browsing through the well-written TI material, you will not find even a gentle hint at existing of some negative resistance subcircuit. Instead, the circuit is considered as consisting of four resistors and an op-amp, and then is thoroughly analyzed and “explained” on half a page (as they say, “the authors have not seen the forest for the trees”:). If they saw the negative “resistor” (NIC) inside the Howland pump, they could consider the circuit as consisting only of two components (negative and positive) and analyze it in a few lines... So, negative impedance helps us to build convenient current sources that “can be used to force currents into sensors or other materials. They can be used in experiments, or in production test. They can bias up diodes or transistors, or set test conditions.”
So, the negative impedance exists and we have only to discern it in its various circuit implementations. For this purpose, we have first to realize what the negative impedance actually is.
We may think of the (true) negative impedance element as of a "mirror copy" of the equivalent "positive" impedance element (resistor, capacitor or inductor) since the negative element adds the energy (voltage, current) that the corresponding positive element would consume. The negative impedance is not used independently but together with a portion of "positive" impedance. Depending on the proportion between the two ingredients of this "mixture", the result of this neutralization can be positive, zero, infinite or negative impedance. Most frequently, two equivalent (positive and negative) impedances are mixed to obtain virtual zero or infinite impedance.
If a current-controlled negative impedance element (voltage-inversion NIC) is connected in series with an equivalent positive impedance element, the result is zero impedance. This arrangement is used in line repeaters to compensate (zero) the line resistance or in real voltage sources to compensate (zero) their internal resistance:
http://www.lucent.com/bstj/vol10-1931/articles/bstj10-3-485.pdf
If a voltage-controlled negative impedance element (current-inversion NIC) is connected in parallel to an equivalent positive impedance element, the result is infinite impedance. This configuration is used for topological reasons (the grounded load) in the Howland current source mentioned above. Another famous application of this circuit is the Deboo integrator (it is invented independently by Gordon Deboo in the 60’s when working for NASA) what is nothing else than a Howland current source driving a grounded capacitor. In these circuits, the negative resistance neutralizes (in the sense that makes infinite) the internal resistance of the imperfect current source (MAXIM specialists have managed “to see the forest for the trees “:)
http://www.maximintegrated.com/app-notes/index.mvp/id/1155
Similarly, in the exotic circuit of a load canceller, the negative resistance neutralizes (makes infinite) the load resistance:
http://pdfserv.maximintegrated.com/en/an/AN815.pdf
And finally, in the similar exotic circuit of the capacitance neutralizer invented in the distant 60’s, the negative capacitance neutralizes the “positive” stray capacitance:
http://www.philbrickarchive.org/1964-1_v12_no1_the_lightning_empiricist.htm
I have considered in detail the negative impedance (resistance) and its implementations in a series of materials uploaded on my profile. I recommend to see at least the two Wikibooks stories about the true and differential negative resistance:
http://en.wikibooks.org/wiki/Circuit_Idea/Revealing_the_Mystery_of_Negative_Impedance
http://en.wikibooks.org/wiki/Circuit_Idea/Negative_Differential_Resistance
Some time ago I found: http://www.circuit-fantasia.com/circuit_stories/understanding_circuits/nic/vnic/vnic.htm and du to the fact that you were asking about applications for negative impedance, I wanted to bring up this once more. I think there is even something at wikipedia about the negative impedance converter. In the IEEE journal of solid state circuits there were also some publications about CMOS negative impedance converters published.
To me, a voltage-controlled negative resistor (NIC) is nothing else than a voltage-controlled current source with a current that flows through the controlling node into the voltage source.
Similarly, a current-controlled negative resistor (NIC) is nothing else than a current-controlled voltage source with a voltage that adds to the voltage of the exciting voltage source (creating the input current). Maybe we have only to add that both the dependent sources are two-terminal (a sort of "self-dependent" sources).
Yes, and to complete the picture we can state that a combination of two NIC units forms a very versatile block called GIC (Generalized Impedance Converter), which can be used to realize (emulate) an "ideal" grounded inductor or an FDNR element (Frequency-dependent Negative Resistor).
Lutz you are completly right, but the question of Derek was if there is a commercial product. And if I concenctrate on this question than I would clearly state yes the negative impedance converter circuit is an application, as for example TI is mentiong it in http://www.ti.com/lit/ds/symlink/opa861.pdf . Maybe this is not the correct interpretation of negative impedance but then we have to discuss this.
Hi Andreas,
for my opinion, the question has been answered already (NIC applicatins).
However, I am afraid the link as provided by you does not help too much because it shows how a commercial unit (OTA) can be used as an active device to realize an NIC. That means - it is not an example how and where the NIC is used.
Or am I wrong?
I guess gunn diodes, tunnel diodes are designed to work on negative differential resistance.
Suggest me whether i am wright or wrong
In Gunn Diode also,just like an ordinary Diode we have D.C and A.C (Differential) Resstances. Differential Resistance is the Resistance offered to A.C.
In Gunn Diode ( Gunn Oscillator) as you said only A.C.Resitance (in the negative Region ) is used.
Dr.P.S.
I second Pisupati. It seems the question is about the true negative impedance.
Negative impedance/resistance is used in LC resonators for implementing voltage controlled oscillators (e.g. PLLs in radioelectronics). Regarding product example, you can find it in a lot (most?) GSM cellular phones exploiting TI's "Digital RF Processor" as part of all-digital PLL [Staszewski ISSCC 2005; R. B. Staszewski and P. T. Balsara, “All-Digital Frequency Synthesizer in Deep-Submicron CMOS,” New Jersey: John Wiley & Sons, 2006].
hi Derek Abbott,
a common (and commercial) application may be considered a (lossless, auto-) transformer. The voltage V1 (winding in coil1) and current I2 (winding in coil2), may have a max. of 180o phase difference. It is, also, an educational example for the acknowledgement of certain (variable but stable) phase differences observed with Lissajous curves.
PS1: These lissajous curves are very sensitive to coupling conditions (distance and/or direction of coils, coupling core material etc.).
PS2: Transformer like (trans-) functions will come soon in applications of (new thermoelectic etc.) nanomaterials having alike (topological) morphology. Such a coupling in nanomaterials may be almost lossless due to nano-size coupling (distance and/or direction of "nano-coils", coupling material etc.).
Ioannis,
I am afraid that any transformer can not be considered as a (true) negative resistor because there is no additional source of energy in this system...
... or a Gunn diode... or a neon lamp... or each thing not containing a source...
also, the phenomenon of "microphonism" (avoid or permit) transduction concerning devices that convert mechanical vibrations into electrical energy and vice versa. As a practical application for "permitted microphonism" we may propose some modes of medical ultrasound images. The ultrasound images are based actually on negative impedance of the transducer.
Interesting... I have not known about this effect...
Ioannis, I still hope that telling us these amusing stories, you make a difference between "true negative resistance"...
https://en.wikibooks.org/wiki/Circuit_Idea/Revealing_the_Mystery_of_Negative_Impedance
...and "differential negative resistance"...
https://en.wikibooks.org/wiki/Circuit_Idea/Negative_Differential_Resistance
dear Cyril Mechkov,
if you enrich your criteria in your classification then you will have new multi-physics examples. A proposal "hidden dimension" may be the frequency f (f=1/time). This additional dimension will permit us to include phenomena having limited frequency negative (electrical) resistance for selective spot or band domain frequencies. There is a big family of old (classic) and new quantum phenomena having frequency f selective electric permittivity ε(f), magnetic permeability μ(f) and mechanical coefficients, as well as electromechanical coupling coefficients. So, an example under proposal enriched criteria may be the "negative refractive index" class of materials (in optics) and metamaterials (in microwave regime) having selective frequency values of ε(f), μ(f). On the other frequency domain side and under enriched proposal criteria, nanomaterials associated new phenomena in the low frequency (~mHz) will be referred soon'ref], also.
ref:[https://www.researchgate.net/publication/283052751_EIS_studies_of_unconventional_topological_pseudo-insulator_phases_in_incandescent_lamps%27_tungsten_wires]
Conference Paper EIS studies of unconventional topological pseudo-insulator p...
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