Is it well known that the transistor is an active element used to build amplifiers. But IMHO this is not true. The transistor is not active but passive element; the only thing that a transistor can do is to dissipate energy. So, it is not amplifying but attenuating element. It is just a resistor (non-linear, electrically controlled but still a resistor) that decreases the current.
The true amplification is impossible; so there are no real amplifiers. The so-called "amplification" is just an illusion, a clever trick and the "amplifier" is just a "magic box" where we see a bigger output power but this is not the amplified small input power. This is else's power.
In analog electronics, we implement such an "amplification" in the possibly most paradoxical, absurd and silly way - to obtain output power bigger than the input one, we get a big power source and then throw away a part of it (from zero up to the whole power). In comparison, in energetics, they can't afford to do it..
Am I right?
Well you could see the transistor as an active element because a minimal bias current must flow for it to operate in the "active region" as an amplifier. The amplification "appears" to happen because the gain between the base and collector/emitter is relatively constant at a given temperature and at low frequencies, thus a much larger replica of the current signal though the base flows through the emitter and collector. So yes in a way it seems silly because you need a power source that can drive the transistor, potentially with high currents for power amplifiers, but this is the only way it can be done at this scale. With nanotechnology, it may be possible to power devices purely from the energy present from the sun, so at this point it would seem less silly, but the process is still exactly the same..
I guess this could be subject to interpretation but for sure you can't 'create' energy, and existing energy cannot be 'amplified' to a larger amount of energy so to speak.
I agree with Louis and Ismat Aldmour. The amplification per say is just a process where in external energy/power supply is used to increase the signal being fed in to get an "amplified" signal.
The terms you are talking is in terms of DC voltage . It is but obvious that if we give 5V as input we would never get more than 5V at output. Transistor amplifies the amplitude of the AC signal and DC signal that we are giving is just for biasing purpose. Transistor is truly an amplifying device but not of energy or voltage but of amplitude of the incoming AC signal. Energy cannot be amplified, and if that was true then law of conservation of energy would fail. Transistor is an active element.
Maybe, we should look at the term "active/passive" from two different viewpoints - first, as a way of energy processing (producing/consuming); second, as a way of operating (controllable/non-controllable)?
The second part of the question seems to be more interesting than the first part. Is there any amplifying element at all?
First of all, I agree with Cyril, viewpoint, from a global circuit perspective, amplifiers are not able to amplify power, since the output amplification is natural consequence of the biasing power (which may not be all used for signal amplification).
Regarding the second part, if we think of a negative resistance (exotic? do these things really exist?), what would be the end result if we assemble a voltage divider with the upper branch being a negative resistance (R10)? Applying a signal at the input of the divider would produce an output which would be positive and larger than the input if R2>|R1|. Can we speak about voltage and power amplification for this case?
Luis, thank you for the interesting comment! In the second part, you talk about the negative differential resistors (exotic but absolutely real electronic elements). Your arrangement (a voltage divider with a negative resistor in one of the legs) has been exactly an amplifier just like a transistor one. The only difference is that here the "amplifying" element is a two-terminal. But it does the same as any else "amplifying" element - changes its instant resistance according to the input signal thus regulating the power applied to the load (the other resistor). So, we can speak about voltage and power amplification here in terms of electronics. I have revealed the secret of the NDR (not only what it does but how it does it) in the Wikibooks story below:
http://en.wikibooks.org/wiki/Circuit_Idea/Negative_Differential_Resistance
and, particularly, the NDR amplifier in the section below:
http://en.wikibooks.org/wiki/Circuit_Idea/Negative_Differential_Resistance#Amplification
Regards, Cyril.
Dear Cyril Mechkov, Your question is intriguing, because it can raise several interpretations. If you pick a Gaussian surface, which involves the transistor but leaves the energy source out, certainly there is no amplification at all. On the other hand, if the source is included, observing from the point of view of input and output only, the transistor amplifiers the signal.
Regarding NDRs, the problem with NDRs, as it can be seen on the picture, is that NDR are still "active" devices. In order to explore the negative resistance effect you have to select an appropriate biasing point. Thus, power balance has to include both signal power and biasing power. Such NDRs are certainly available in tunnel and Gunn diodes (able to explore tunneling and Gunn effects), or even (less useful though), in four layered devices such as TRIACs, SCRs and DIACs.
My question involves a theoretical abstraction (as far as i know, up untill now, no "passive" device was able to display negative resistance effects), a ohmic device with negative resistance, in the sense that the I-V curve is a straight line passing trough the origin with negative derivative. If such a device was made available, then we could explore the concept of power amplification and the intringuing implications arising with it.
Luis, I am glad to see that someone ask a question that "involves a theoretical abstraction" since there are only few people asking "philosophical" questions...
Only true negative resistors (negative resistance circuits like NICs) have an IV curve that is a straight line with negative slope passing through the origin. But this IV curve is not real; it is an illusion. It is a composed IV curve consisting of an ohmic IV-curve having a positive slope and an IV curve of a variable voltage source (a true negative resistor consists of two elements connected in series - a "positive" resistor and a variable voltage source).
Imagine you are such a negative resistor-:) and I am the input voltage source. I have set zero input voltage and you reacted to this action by setting zero internal voltage as well; so, we (the operating point) are at the coordinate origin. Now I begin increasing the input voltage. If you were a "positive resistor", you will not react to this "intervention" and the operating point will move up to the right along the IV curve of your internal positive resistor. But you are a negative resistor; so, you begin vigorously increasing your internal voltage as well. As a result, the operating point will move down to the right. You have changed the movement (the trajectory) of the operating point by subtracting an "opposing" voltage; you have made it turn to the right...
I highly recommend to you again to read thoroughly my 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
I have collected there all my insights about these great phenomena. As you can see, I have shown not only the particular negative resistance phenomenon but the evolution and the connection with other great circuit phenomena (virtual ground, bootstrapping, etc.) The negative resistance is only one (the final) stage of this evolution ladder...
Best regards, Cyril.
Dear Cyril, from what I understood, you compare negative resistance elements to variable sources. These are possible ways to realize negative resistance, using circuit emulators. I know some examples of such circuits. It is even common to explain circuit operation based on negative resistnace manifestation. However, my question involves more than that.
There is a lot of research on metamaterials and memristors. Some of the new devices that may emerge from this research may exihbit exotic phenomena, such as negative resistance. Should we expect these two be true passive devices, or will they necessarily be something close to a NDR device? Is the current passivity criterium addequate for such devices?
Today, I was also wondering if it is possible to explain inverting and non-inverting amplifiers using negative resistance concepts? It would be something very different than what is found in the literature.
Dear colleagues,
Dear Cyril,
allow me to share in your discussion about the transistor as an active or passive element.
Amplifiers are not power generators.When we speak about power generators we speak about energy conversion from one form to the other e.g. from thermal to electrical. The conversion process is subjected to energy conversion laws. We characterize such systems by a conversion efficiency which is always smaller then one.
In communication and instrumentation one has signals containing information such as the audio, the video and data, These signals must be properly processed and reformed for sake of transmission and or storage.One of the major processes for signals are amplification. They are basically built to facilitate telecommunication and broadcasting. The need to amply signals was and still a main driver for inventing amplifying devices. The amplifiers are enablers of the modern communication systems.
From the point of view of the energy conversion the amplifier increases the signal voltage or the signal current or the signal power on the cost of the DC power supply of the amplifier. With reference to input signal the output signal is amplified. This can be accomplished when a signal amplifying element exists in the circuit which is the transistor. The transistor is active concerning the signal. It is made active by the DC biasing from the power supply. Without biasing, it is passive and can not amplify the signals.
From the eyes of the DC power supplies, the amplifier circuit is a load consuming electrical power. The overall power efficiency is smaller than one.
The cost to amplify signals is Dc electrical power and a hard ware called amplifier.
One the main performance parameters of the power amplifiers is the DC conversion efficiency which is the signal output power divided by the DC input power.
Thank you
Luis, yes, true negative resistors are exactly sources... but a little special kind of sources. They are something as a "self-dependent" (2-terminal) sources. For example, a current-controlled negative resistor (VNIC) begins producing a voltage after we pass a current through it and this voltage is proportional to the current (it acts as a true current-to-voltage converter). So, "negative resistor" is only a figurative word, a metaphor, used to denote a source with such a behavior. Another electrical example: the ordinary voltage source is constant; it keeps a steady voltage when we pass a current through it. If we want to denote it with a figurative word, we can name it "negative Zener diode" or just a "negative diode". A worldly analogy from our routine: if you want to say that someone is a good man, you can name it a "negative bad man". So, the trick is to name something with its inverse; thus we have a notion about the two sides of the same thing and, what is the main use, we can make them neutralize each other...
The problem is how to make sources with such a behavior... To solve it, we use a clever trick - to obtain a negative element, we "reverse" its equivalent "positive" element by adding two times more energy that it dissipates. The paradox is that we add a (two times higher) negative resistance to obtain... a negative resistance; we already have a negative resistance before obtaining the negative resistance... and this seems as some vicious circle... That is why, a true negative resistor contains inside a positive resistor; it serves as an original to create its inverted copy...
I hope that it is possible to create a natural voltage source with such a behavior without using this artificial "reversing" technique. Well, if we pass a current through a constant voltage source, it keeps its voltage steady. Don't you think, instead, we can make it change its voltage linearly? For this purpose, we have somehow to make the source's transfer ratio (the connection between the input nonelectrical power and the output electrical power) depend linearly on the flowing current. For example, imagine we pass a current through an electromechanical generator (an alternator) with connected in series exciting and rotor coils... or a photocell whose current somehow regulates the light... The problem is that someone would say this is a circuit, not an element...
So, the new "metamaterials" mentioned by you have to extract energy from the environment proportionally to the flowing current through them. BTW neither memristors nor gyrators are negative resistors; they are not sources; they are completely passive devices mimicking some other passive devices. Negative differential resistors are also passive devices; they become active in a combination with a constant source. Thus we have two alternatives to make true negative reistors by connecting two elements in series - a constant resistor and a variable voltage source or a variable resistor and a constant voltage source.
About your last question... Yes, in all the op-amp inverting circuits with negative feedback, the op-amp (output) acts as a true negative resistor. It adds so much voltage into the circuit as it loses across the passive element connected between the op-amp output and its inverting input. The result is an almost full voltage neutralization (a virtual ground). But note, the op-amp "acts as" (only mimics) a true negative resistor; actually, it is not exactly a negative resistor. It achieves the so desired final result (an impedance neutralization) by means of the negative feedback while the true negative resistor does the same without using a negative feedback. The first arrangement is more reliable but needs a third wire connected to the inverting input; in the second arangement, the 2-terminal negative resistor compensates "blindly" the voltage drop but can be easily connected in series... I have considered the negative impedance viewpoint at op-amp circuits in Circuit Idea wikibook:
http://en.wikibooks.org/wiki/Circuit_Idea/Voltage_Compensation#Negative_impedance_viewpoint_at_voltage_compensation
http://en.wikibooks.org/wiki/Talk:Circuit_Idea/Voltage_Compensation#A_negative_impedance_viewpoint_at_the_voltage_compensation_idea
IMO all these considerations are so important that they need separate questions.
Best regards, Cyril.
What is a passive element in a circuit ? what is an active element in a circuit ?
For passives, everybody answers : R , L and C.
For active, transistors and diodes.
What would be the answer for a system consisting of a voltage driven motor actuating an auto-transformer from the auto-transformer point of view ?
Quote: "Today, I was also wondering if it is possible to explain inverting and non-inverting amplifiers using negative resistance concepts? It would be something very different than what is found in the literature."
To Luis Alves:
perhaps the following example meets your idea?
Consider one of the classical oscillator topologies as follows:
1.) A parallel LC tank is shunted with a loss resistor Rp and forms the impedance Zp (lossy tank circuit).
2.) Together with a series resistor Rs we get a complex voltage divider Rs-Zp.
3.) Connect the output of this voltage divider to the non-inv. input of a non-inverting opamp with gain (1+R2/R1).
4.) Form a closed loop by connecting the opamp output to Rs.
5.) Oscillation condition: Rs/Rp=R2/R1
6.) Another interpretation of the same circuit:
If Rs is seen as part of the active circuit (finite gain amplifier with positive feedback), we have a lossy LC tank with another parallel resistance that is negative
Rneg=-R1*Rs/R2 .
7) Thus, the first circuit interpretation (closed loop consisting of a complex voltage divider and a fixed-gain amplifier) is identical to another interpretation (negative resistance oscillator concept).
Remark: The above result is no surprise because each oscillator circuit consisting of a closed loop (unity loop gain) can be transferred into a neg. resistance topology.
I can't stop joining this so interesting topic about the negative resistance (of course, it needs more specific questions)...
In an inverting amplifier, the op-amp behaves as a current-driven negative resistor ("VNIC") adding a voltage that is equal to the voltage drop across R2. To make it a true VNIC, we have to apply a positive feedback in addition to the existing negative one:
http://commons.wikimedia.org/wiki/File:Linear_vnic_0b_1000.jpg
In a non-inverting amplifier there is no negative resistance since there is no connection between the input and output. To make it a true voltage-driven negative resistor (INIC), we have to make such a connection by connecting a resistor between the op-amp output and the non-inverting input (in the case when the input source has some internal resistance, this means to apply a positive feedback in addition to the existing negative one):
http://commons.wikimedia.org/wiki/File:Linear_inic_0b_1000.jpg
Here are two simpler examples of INIC, in addtition to the Lutz' LC example:
http://en.wikibooks.org/wiki/Circuit_Idea/Revealing_the_Mystery_of_Negative_Impedance#Compensating_resistive_losses_by_N-shaped_negative_resistors
http://en.wikibooks.org/wiki/Circuit_Idea/Revealing_the_Mystery_of_Negative_Impedance#Generalizing_the_N-shaped_negative_resistance_idea
Regards, Cyril
Yes, Cyril - that`s exactly the circuit (neg. resistance) I was talking about in my former post.
@Cyril. I haven't had time to read the other responses, so I may be repeating something already said. But here is my view.
It all depends where you choose to draw system boundaries!
For example, if you draw a boundary around the planet and consider the sun as an external energy source we see that life produces a net order. But if we draw the boundary around the whole system then there no net increase in order.
So if we draw a boundary around the transistor and exclude the power supply as an external source, then you have amplification of energy and other variables too. But if you include the power supply within your boundary then you only see a net loss in useful energy.
But the real question at the end end of the day is: "does the transistor amplifier perform a useful function?" Yes, at the expense of external energy it is providing the 'order' we want for our signals; much in the same way that the sun provides the external energy to provide the order on this planet we call 'life.'
When you drive a car, fuel is converted to kinetic energy. View the fuel as an external source and it is providing you 'useful' conversion to kinetic energy that you want. View the system as a whole and all you see is the engine does not have a perfect Carnot efficiency and some useful fuel energy is being lost to dissipation and heat. Overall there is a loss in useful energy. But the point is that this overall loss does not stop us exploiting the car as a useful piece of technology.
Similarly we exploit transistors to our needs, despite that fact they use external energy sources.
An erbium doped fibre is still a useful way of transmitting information, despite the fact it is 'cheating' and getting amplification of photons by using a secondary pumping laser (that is acting as an external energy source).
I agree to everything Dr. Abbott has outlined.
Because it is clear (and common knowledge) that amplification of energy is not possible, we have to live with DEFINITIONS. And because we have not an infinite number of words available to give each effect a separate name, we sometimes use words which are not correct by 100%.
(Is a linear network linear? Is a sinusoidal signal really sinusoidal? Is a squarewave really a squarewave?::::::::)
Thus, if we observe that the variation of the voltage at the output node of a gain stage is larger than the variation at the input node, we use the word "amplification" without the danger of misinterpretation. It`s just a matter of definition.
Lutz vW
In the same way, we say "source" (1-port device) while it actually is a converter (2-port device)...
@Cyril. I forgot to answer the part of your question that asks '"is it an active or passive device."
We call it an active device, simply because it's operation exploits an external energy source.
Roughly speaking, any device that has a semiconductor in it is going to be an active device.
Hmmmmm...I will write this: the property of passivity is determined by sign of the product of instant values of current and voltage for the dissipative elements. The transistor can work in switch mode as well as in the amplifier mode. In both modes the u-i characteristic is in I and III quadrant of u-i characteristic which means that sign of product is positive and transistor is PASSIVE ELEMENTS.
The negative resistor have u-i characteristic ( (linear characteristic) ) in II and IV quadrant that is why he is considered as active elements.
"Roughly speaking, any device that has a semiconductor in it is going to be an active device."
What about the classical pn diode? (I would prefer "passive".)
Well, it is true there are lots of ways to define active & passive. Some people think of "passive" as something that cannot produce gain, some think of it as something that which only dissipates energy, some think of it as something that which doesn't need an external source.
I'm not so sure all these distinctions are really all that important at the end of the day.
You can't get gain with a pn diode, so some may call it "passive." On the other hand you need an external source to ensure a diode is reverse or forward biased, so some will call it "active."
In my mind, I've always thought of active and passive in terms of a device being externally powered or not in order to operate. But I acknowledge there are other ways of looking at it.
I think this discussion so far does indeed show that these concepts of active and passive are somewhat loose.
Does anyone really think they they ought to be made strict? If so, why?
Again - I agree with Dr. Abbott`s position. This classification scheme is of less importance. More important are the answers to the main question of this topic :
What means "amplification". Well - my position is as outlined one day ago under this topic - it is also a matter of definition (knowing that energy conversion is involved).
If one uses a small external magnetic field to excite a ferro-magnetic material one finds one is able to produce magnetic fields some 10,000 stronger within the material itself. This is the basis upon which all transformers etc work in that we rely or exploit the high induction that is available within the material.
Here we are not amplifying anything but rather exploiting or controlling the material properties and if we do same for wood nothing will happen.
In the same vein we have studied, designed and used smart manufacturing techniques to allow semiconductors to have similar properties whereby we may utilise smaller amounts of power / energy to control large amounts of power / energy flow through the device itself. We may also do same with hydraulic systems.
Cyril you appear to confuse the use of the term AMPLIFY and incorrectly use it as the ability to generate power rather than the ability to control the flow of power which forms the basis of Derek's use of the system boundary.
This is why using it in the context of applying power to the gate of a transistor will suddenly allow huge amounts of power out is impossible as you have said.
Where is this power going to come from? From inside the device! Impossible as you correctly state.
However, if we attach a source of power then we may use the transistor to control the flow of power through itself (not from within itself). Furthermore, through smart design and manufacturing techniques we only need small amounts of power to control the flow of substantially larger amounts of power through the device.
Thus the use of the term amplification as the ability to control the flow of power and its use as the ability to generate power are not the same as the latter defies the laws of physics.
Thus you are quite correct and I fully agree that AMPLIFICATION does not mean that one can somehow create or generate power but this was never the intention.
And the ILLUSION as you correctly note is that it appears as if the device amplifies power from within itself whereas in reality it is only controlling the flow of power through itself.
As far as passive and active devices go an active device is meant to define one in which the flow of power may be controlled. As such a resistor is passive and a transistor classed as active.
Thus a transistor as an active element may used to control the flow of substantially larger amounts of power through itself and in doing so allow amplification of the control signal. All the transistor is doing is controlling the flow of power between the source and load based on its input control signal. The amplifier used for a radio being one such example.
Amplifier is a system or a device where it enhances the power of input or the geometry or any other physical, electrical quantity, provided there are no conditions prescribed. that is the amplifier has to be supplied the required input parameter and the required energy for exercising the operation of enhancing or amplifying the given parameter. Amplifier does it's job by consuming some power from external energy sources like dc power bias, where as generators are creators of energy, then amplifiers are enhancers of any electrical quantity of given or already existing electrical parameter
In this context, the "leverage effect" just came into my mind.
Question: Does a mechanical lever provide gain?
Dear Lutz, but I still wonder what is actually the amplifier - the naked amplifier (the transistor) or the combination of the amplifier and the power supply:
I think the "naked" device should be called "amplifier". However, it can do his primary job (to amplify) only after "pumping" some external energy into the unit. The same applies to many mechanical tools: They do their job (to saw, to hammer, to drill...) only if supplied with external energy from your hand).
But Lutz, if we consider the combination amplifier + power supply as an amplifier, it will be a real power amplifier producing bigger output power than the small input power. We always use a power source; without it, the amplifier can not act. So why not combine the two components?
I have no objections.
On the other hand - coming back to my mechanical example: Can the mechanical tool (saw, drill, hammer) "act" as a tool without external energy source? Even if it lays quiet on the desk - it is what it is (a saw, a drill, a hammer).
Only if it is equipped with a hidden battery... and we do not know this fact:)
I think, we all know that the terminology in electronics never is "correct". Can a current flow? No. Is any circuit really linear? No. Can a wave be really sinusoidal ? No. Does a current source really provide a current (independent on the load)? No. Is an amplifier stage with RE signal feedback still a common-emitter stage? No.
The most important thing is to use terms which can avoid misinterpretations and misunderstandings. Therefore, I support the view that we have an amplifier - if it is powered or not.
Ismat and Lutz, impressive examples! I think the problem of the terminology is in this wrong word "amplifier". Without a power supply, It is not an amplifier; it is a kind of regulator (an attenuator controlled by the input source)...
I rather would say: Without any power supply it remains a circuit that is able to amplify (hence: an amplifier) - however not working.
Without power supply, The amplifier circuit has no purpose or it acts as a dummy circuit with random behavior once again depending upon the input signal amplitude and frequency. Also it can act as a random termination for the signal input, I feel An Amplifier designed for a particular parameters, and if there is no power supply is of no use. Suppose if, we try to amplify any parameter of the input signal without power source, then we are going against the Law of conservation of energy, where in we are trying to enhance the power of input signal without adding the required power to the signal externally.
My doubt is only if we assume that an amplifier without power supply is an amplifier, then we should agree that the voltage divider is a voltage source...
...."that the voltage divider is a voltage source..."
Cyril - why should we do this? It is never a "voltage source" - even if it is connected to a battery. It provides a certain voltage which - more or less - will depend on the connected load.
An amplifier (e.g., a CMOS inverter) is a (voltage-controlled) voltage divider. So, if we assume that the amplifer produces energy (voltage/current/power), we should agree that the voltage divider does the same.
My observation is that the name "voltage divider" is more appropriately chosen by the name "amplifier". So, the combination "amplifier + power supply" is an amplifier, while the voltage divider is a voltage divider... and the combination "voltage divider + power supply" is a voltage source...
"An amplifier (e.g., a CMOS inverter) is a (voltage-controlled) voltage divider".
To me, this is a really interesting view. A little improvement: Active voltage divider! This interpretation can also be applied to the classical BJT amplifier stages.
But - regarding the second part of your contribution - to me, a source is a quasi-ideal source. That means: A low-resistive divider feeding a hig-resistive load (loading error just a few percent maximum) may be called "voltage source".
Well Lutz, only few people (mainly from the area of education) would have participated in such a discussion about the most basic principles of electronics... Then let's elaborate this voltage divider viewpoint at amplifiers...
The main task of an amplifier is to produce voltage... it is a voltage-controlled voltage source... How does it produce voltage? By attenuating some else's (power supply's) voltage... How does it attenuate this voltage? By series-connected variable resistor (transistor)... But if there is no load connected (open circuit)? So, another resistor (transistor) is needed... and the two resistors (transistors) form a voltage divider...
In this voltage divider configuration, the input voltage source can control either the first or the second resistor (transistor) or the both (the powerful push-pull idea)... but this is still a voltage divider...
Yes - I like this voltage divider view. However, I think the situation changes as soon as reactive elements are involved (inuctive and/or capacitive elements).
Gentlemen,
IMHO, an OpAmp or Transistor is a type of Controller of Power.
The can accept controlling variable signals and change their state.
Resistors and Capacitors and Inductors are on the Passive pole of consideration.
Their role in the game of a circuit is basically static.
A problem arises in my immature assesment of these devices,
since the Variactor ( Tuning Diode Capacitor )
changes state in response to the DC vias.
Will be re-reading this thread to better understand the differences.
Glen
But can a variable resistor (e.g., a carbon microphone) act as an amplifier?
Cyril,
To your question about the carbon microphone,
the Voice Signal Input
is Controlling the Vcc-Vee power
to produce an Analogous Output.
Here is the thought process I go through to that opinion :
***************************************************************
Are you suggesting that the electrical control
of pre-existing power potential might be a amplifier function ?
Are we mushing the definition of amplifier and controller ?
Are we talking about Controllers or Amplifiers ?
In order to resolve this confusion in my mind,
I propose that
we must differentiate between
(1) the Physical Mechanism of a DUT
(2) the Functional Concept of the DUT.
*********************************************************************
FIRST
I will use an OpAmp single stage circuit
as the "Amplifier" DUT.
*** I recall disagreeing with Don Lancaster ( 1975 )
when he described the process of the opamp function.
He implied that the electrons of the Vsignal INPUT
actually passed over to
and exited through the Vsignal OUTPUT.
*** Then, as now, I used an intuitive approach
( I think Barrie refers to
"putting on the robes of the electron" )
to explore the workings of this op-amplifier.
So, that was 1975, and now is 40 years later.
*** It appears to me that the Signal Input is
controlling the VCC-VEE
and producing an "Analogous" Signal OutPut .
The Function of the DUT OpAmp is that
it receives a Signal Input
and produces a Vcc-Vee Analogy as the Signal Output
and may be an Amplified or Attenuated Signal value
referenced to the Signal Input.
It is easy to visualize that
the OpAmp Electron Input does not find its way
to the Electron Output.
*********************************************************************
SECOND
* From that perspective, then I look at a Transistor
as the "Amplifier" DUT.
(1) I can visulize that there is a mixture of Electrons Input
flowing into the Electrons Output.
That is part of the Physical Method.
The Function of the DUT Transistor is that
it receives a Signal Input
and produces a Vcc-Vee Analogy as the Signal Output
and may be an Amplified or Attenuated Signal value
referenced to the Signal Input.
It is easy to visualize that
the Transistor Electron Input
does partially find its way to the Electron Output.
********************************************************************
Both examples are DUT circuits which , in Functional Concept,
(1) receive a Signal Input
(2) produce a Vcc-Vee Analogy as the Signal Output.
IMHO, that is the Functional Nature of an Amplifier.
********************************************************************
I do expect academic comments
and some erudite critique.
Glen
Very interesting perspective at the topic... I need time to realize it...
But can a variable resistor (e.g., a carbon microphone) act as an amplifier?
Theoretically, we can certainly compare the acoustic power ( a control power) and output electric power. But rather probably be appropriate to talk about the transfer: acoustic energie to electric one.
Must pay the law of conservation of energy. At the very least they must be provided with additional energy source.
Well... but still we can think of the combination "speaker+microphone" as of a kind of an "electromechanical transistor".
Cyril,
DUT is Device Under Test .
In my post :
Device #1 is an OpAmp.
Device #2 is a Transistor.
Glen
Thanks Glen. I asked you since my notion about DUT is as of an element inserted into some tester (e.g., a curve tracer)...
I admire your philosophy about amplification... especially to present the output signal as an "analogy" of the input one. Very, very powerful and colorful functional view at so called "amplifying elements"... It is so nice that, in the grayness of this world, still there are colorful thinking people as you...
I will add only that, in conventional amplifiers, really the input signal does not appear at the output; we have replaced it by its more powerful "analogy":) But another configuration is also possible - instead to replace, to add the output signal to the input one (to second it)... and to use their sum as an output. We can add either voltage or current... and eventually - power. We can do this addition in two manners - in series (summing voltages) and in parallel (summing currents)... It is interesting to see these techniques in practice...
. It is interesting to see these techniques in practice...
Cyril, yes - this would be interesting. Can you provide an example?
Dear Lutz, welcome again in the club of circuit philosophers:)
Examples of amplification by voltage addition can be all the inverting circuits where the op-amp adds its output voltage to the input one thus enhancing it (e.g., in an inverting op-amp integrator, the RC circuit is driven by increased input voltage). Another example can be the VINIC.
An example of amplification by current addition can be the Howland current pump where the op-amp adds (injects) its output current to the input one thus enhancing it. More examples can be the IINIC and current booster in the attached picture below.
Cyril,
How is it that the Howland Pump is doing anything more than controlling the Vcc-Vee source power ?
The Vin is controlling the Vcc-Vee , producing the Vout.
At the same time, almost, the Vout is controlling drive currents for two transistors which control the Vcc and Vee power to make available much more power than the OpAmp can supply.
* Are you saying that the 10mA OpAmp Iout is "added" to the dual transistor Iout ?
? That would be enough "added" current for it to be called an "amplifier" ?
* Looks like an OpAmp directly driving the collector and emitter of two transistors, like an odd Class-B circuit. I commonly have an OpAmp drive two transistors directly at their combined bases, and pull negative feedback directly from their combined outputs. This let the OpAmp do all the bias and control directly on the transistors.
* Maybe I am pre-mature in my response,
so will research the design philosophy for the Howland Pump.
* Interesting path this has taken.
"Examples of amplification by voltage addition can be all the inverting circuits where the op-amp adds its output voltage to the input one thus enhancing it (e.g., in an inverting op-amp integrator, the RC circuit is driven by increased input voltage)."
Cyril - where does such an addition of voltages takes place?
Do you speak about the feedback effect? In an inverting opamp configuration we have two currents which are subtracted from each other in the common node (inv. input terminal). That`s all (for my opinion).
Hi Cyril
In this circuit creates internal output transistors of OPA a cascode connection with the external transistors.
Very critical can be working point of external transistors - if no DC feedback (as well as with it).
Josef
Maibe the humble emitter follower is the simplest example of this amplification by adding? Let's see why...
The input voltage source begins "lifting" the emitter voltage trying to make it (almost) equal to its own voltage. For this purpose, it passes a base current via the base-emitter junction through the load. The transistor "feels" this by its input part (the base-emitter junction) and "helps" the input source by adding a collector current through its output part (the collector-emitter junction). Thus the total output emitter current is a sum of the input base current and the partial "helping" collector current.
So, in the CC configuration, the input base current is used for something useful while, in the case of the CE configuration, it is unused and goes to ground; there the output current is formed only by the "analogous" collector current...
Cyril, I am afraid that your conclusion (the last part of your contribution) is not compatible with the working principle of a transistor.
Lutz, this explanation is not precise; it is figurative. Its role is to show the "helping" principle - the output current is formed by adding a suplemental current to the input current instead by replacing it by another current...
Yes - you are right, it is not very precise. But - it is no "explanation" at all. Just a statement. It was my only intention to express my disagreement. Not more.
I think, just the opposite is true: There is one current (Ib) that is subtracted from another one (Ie) - and the result is Ic.
Cyril - as mentioned above, I have explained why I don`t think that your example can proove the principle of "amplification by adding".
On the other hand, I think your idea can be - and is - realized by the following circuitry:
Take a simple non-inverting opamp configuration with a closed-loop gain of "2" (6dB) using two equal resistors in the negative feedback path. If we now - in addition - provide a certain amount of positive feedback (but smaller than the negative feedback factor of k=0.5) the gain will be larger than 6 dB.
Explanation: A small part of the output signal is added to the input signal and causes a larger gain. Hence, we can say: The extra portion of gain is causes by the superposition (addition) of two signals (in phase).
Do you agree?
Yes Lutz, I agree... This is an example of negative resistance created by a positive feedback. Actually, all kind of circuits adding the output quantity to the input one, tend to possess negative resistance. Howland current pump is one of them; it adds a suplemental current to the input one. Well, let's consider this arrangement to answer the Glen's question above...
An input current source (a voltage source with a resistor in series) passes the input current through a load. The Howland op-amp circuit (an INIC or more figuratively, a negative resistor) "feels" it by sensing the voltage drop across the load and "helps" the input source by injecting an additional current through the load. Thus the total load current is a sum of the input current and the additional "helping" current.
So the Howland current pump amplifies the input current by adding its output current to the input current instead to replace it by an "analogous" current.
In the attached picture below, R1, R2 , R3 and the op-amp form the "helping" Howland pump; VREF and R form the "helped" input current source:)
http://www.circuit-fantasia.com/circuit_stories/understanding_circuits/current_source/howland_current_source/howland_current_source.htm
Now let's consider the other odd circuit solution deeply impressing Glen. I was also deeply impressed when seeing it many years ago... and in general, I always admire when I see such a powerful circuit idea... maybe because I myself have lots ideas ... while people who do not have their own ideas not admire... but happily use others' ideas...
I have found a more clear circuit solution and attached it below. Well, what can we see here?
Josef sees cascode connections between the internal and external transistors. It is true... and if we draw the internal op-amp structure, really we will see them. But I see more than this...
I see a weak op-amp inverting amplifier (LT1210 and the two resistors of 1.8 k and 3.6. k) that tries to drive a heavy load (not shown in the figure)... and it would not be able to do it... But fortunately for it, the complementary output of a power amplifier (composed by the two CE drivers Q1 and Q2) is connected in parallel at the output of its low-power companion.
The stronger "brother" vigilantly observes the weaker by sensing its current consumed by the power supply. So when the "little brother" starts travailing... and begins consuming more current... converted to voltages by R1 and R2... the "big brother" converts them into currents... and, as a result, a big additional "helping" current is injected (in parallel to the initial low current) into the common load.
Figuratively speaking, we can think of this composed amplifier consisting of two nested one inside subamplifiers, as of a sort of a Russian "Matryoshka":)
If you prefer more serious analogies, recall how the brake servo helps you when pressing the brake pedal (you are the op-amp; the servo is the power booster).
So Glen, here "an OpAmp does not drive two transistors directly at their combined bases." The power transistors are driven by the efforts of a weak op-amp to drive a heavy load.
http://bec.physics.monash.edu.au/wiki/Main/SpinorCoilDriver
Cyril,
Belated, thanks on 160421.
Right! We do not have to directly drive the BJT 'base' structure.
The Power Boosted OpAmp is familiar. Interesting the way you tweaked the bias from the power side, rather than diodes on the bases.
I have experimented with 'base biasing' diodes on shunt limiters, also,
which I found actually worked predictably, Bode plots show two distinct diode curves, mixing together. (linked below only for clarity.)
Could not download of the SpinorCoilDriver ,
but I have drawn the schematic and will be running in Spice to explore.
I have reviewed all your postings on this Question
... always expert.
Your responses to me are kind gestures
and encouraging to my study.
the old apprentice, Glen.
http://www.geocities.ws/glene77is/bmp_et_limiter/AFX_Limiter-Shunt2-S-140821-b.png
http://www.geocities.ws/glene77is/bmp_et_limiter/a-OAD-base-bias-1-T.jpg
http://www.geocities.ws/glene77is/articles_ET_files/article_ET_AFX_CW_Limiter.html
From the viewpoint of energy are active element sources only. The other elements "controls" only the energy from source in accordance with the signal .
However, it is customary to name transistors (Tubes ...) as active elements - due to resistances (convert the energy into heat), capacitors, and inductors (energy only accumulate).
Yes Josef... It is interesting fact that just this morning, I discussed with my students the philosophy of the so-called "amplification" (i.e., "attenuation")...
Yea Cyril, we sometimes fergot to discuss the most important "simple" problems :-)
Josef
Now I want to share something intimate with you...
Now here is already after midnight... but I am very excited and I can not sleep because two remarkable for me events simultaneously happened...
The first is that, for the first time, my (10-years old) grandson showed a spontaneous interest in my very distant (60s) years when I made my first steps in electronics. In 1969, together with one of my classmates, we built a real robot ... so he asked me what was this robot, what it contained, what it did, etc.
What so impressed me was that so far he was only interested in your smartphone... and now, for the first time, it was interested in something different... something more real and material...
(Glen, thanks... Here is the robot...)
The next amazing (for me) event this evening was that after almost 50 years, and precisely at this point, when my grandson sent me the message through Viber, I was talking on the phone with my friend who told me that owns and can give me the most valuable for me book that first brought me into electronics ... and what is most interesting is that, in this remarkable book, in 1967, I saw for the first time real robots... and I immediately decided to do such a robot... and we began making it a year later...
I am not religious... and I do not believe in miracles... but now I am just shocked...
Here is how some things can change fatefully our life...
Cyril and Josef,
Such honest admissions from practicing electrical engineers !
I am curious, now, about "amplifying" vs "attenuation".
Yes, Cyril - as Glen has recommended in his last sentence:
What was the outcome of your discussions with your students about "the philosophy of the so-called "amplification"? Anything new?
Final question: What about a simple mechanical system realzing the well-known lever rule? Is the lever a power amplifier?
Hi Lutz
Is the lever and power amplifier?
I'd rather likened to the transformer.
Josef
Lutz, as they say, the new is the well-known old:)
So, there is no amplification... it is impossible... there is only attenuation... The so-called amplification is only an illusion... where we do not (want to) see the additional power supply... We see only the input power at the port 1-2 and the output power at the port 3-4... then make the ratio between them and name it "gain"...
A new thought is that we began thinking about the "amplifying" (controlling, regulating...) element as another load that dissipates power. Thus actually we have two loads dissipating two kinds of power - useful and harmful... as though the power is steered between them...
Hi Cyril
In terms of energy it is always process with losses. But signal is amplified.
Josef
Yes Josef - I also think that this is a pure matter of definition. Certainly, input excursions are "amplified" if the amplitude at the output is larger than at the input.
Of course, power "amplification" is another thing. I think, Cyril had only "power amplification" in his mind while writing "..there is only attenuation... The so-called amplification is only an illusion".
Cyril - correct?
Yes, these are power considerations...
"Attenuation" expresses the relation (ratio) between the partial load power and the total supply power... while "amplification" gives the relation (ratio) between the partial load power and the input source power...
From this perspective, it seems that "attenuation" is more real and true term since it gives the proportion between two powers produced by the same power source... while "amplification" gives the proportion between powers produced by different power sources... although there are exceptions... A similar situation is when using terms as "resistance" and "transresistance"... "conductance" and "transconductance"...
A "transistor" is a man-made physical structure, system, for which all of us have a lot of fun setting up mathematical models for discussion !
How do you define "amplification" ?
How do you define "active" ?
How do you define "passive" ?
Our nonlinear differential equations models for physical systems are not complete !
Hi Erik,
Only to note the math is the last thing that would help this discussion. The elementary technical sense... and even the common sense is more useful here...
Also, I do not want to define anything... I want to understand what actually it is...
Hi Cyril,
Math is our common language for discussing our observations !
We must agree about the meaning of the words in this language in order to have a good discussion :
To Cyril and Erik,
I would suggest :
How do you define mathematics? - ResearchGate. Available from: https://www.researchgate.net/post/How_do_you_define_mathematics#571b50ac615e2791fb6a0412 [accessed Apr 23, 2016].
Coming back to the main question "Is the transistor an amplifying element?" my answer is: NO.
The transistor as a stand-alone unit does not amplify anything. For my opinion,"to amplify somethig" requires a comparison (ratio) of two physical quantities of the same kind (V/V, I/I). Hence, the transistor is a "transfer element" that transfers voltage excursions at its input to current excursions at the output (VCCS) - and the desribing parameter is the transconductance gm.
In this context - the term "current gain" B=Ic/Ib is a misleading name.
Interesting thoughts, Lutz... But we can go even further in this direction...
The output (collector-emitter) part of the transistor does not produce current... it is not a source... Then what is it?
It is something that impedes (opposes, resists) the current caused by the power supply in the output part of the circuit... it is a kind of resistance... non-linear, current stabilizing... but still resistance...
From this viewpoint, the transistor is a kind of a voltage-to-resistance converter... a voltage-controlled (nonlinear) resistor... Only, in terms of geometry, the input base-emitter voltage controls not the angle of the IV curve but its horizontal position...
Is it possible to amplify energy at all?
No, we can transform one form on another form only.
According to my considerations above, here is a possible definition of "amplification":
The amplification is an electrically controlled attenuation.
The trick is that we attenuate a more powerful (than the input) source... so the resulting partial power is always bigger than the input one... as though it is an "amplified" input power... and we take it as output power...
Amplification is an electrically controlled attenuation
Cyril, may be, this is a possible (and even correct) definition - however, I think a definition should be clear, easy to understand, easy to appply, not confusing, unequivocal,...
And I am not quite sure if this applies to the quoted definition. On the other hand, I really don`t know if there is already a commonly accepted and general defintion?
My attempt:
Amplification is the process by which increases (linearly or by defined manner) value of the voltage (current, power). Input signal supplies the required input energy. Output power is drawn from the power supply. The process always exhibits some power losses.
Well, it is obvious that either voltage or current amplification also implies a power amplification. But is it correct to say "power amplification"... since saying "amplification", we mean a constant ratio... linear device?
IMO the word "amplification" is reserved for linear applications. As a rule, the power ratio is not constant (although there are some exceptions)... and the "power amplifier" will be not linear...
Maybe they are "nonlinear amplifiers", "functional amplifiers"...
And what about cascode circuits?
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