Talk:Operational amplifier/Archive 3

Oscar Bonello
User RobertTanzi has been adding information about Oscar Bonello and his work on distortion, which has been removed a number of times. The text in question did not contain information about what op-amps do, so its removal was correct. Having said that, a description of what this distortion was all about might be worth including in the article, but that is not the same thing as just naming Bonello.

If Bonello has done something notable, then that should appear in an article about him or in an article on the history of op-amps rather than in this article. Man with two legs (talk) 10:44, 11 March 2009 (UTC)

About the link to Philbrick's page
Sorry, I have removed the link to the page about Philbrick absolutely involuntarily. I have no idea how it has happened and I was unpleasantly surprised when I saw Zen-in's remark. Philbrick is a legend; I highly appreciate his achievements. Circuit-fantasist (talk) 15:30, 20 March 2009 (UTC)

About the 39 kΩ resistor acting as a current source
In the internal 741 op-amp circuit, only the total power supply (VS+ - VS-) and the common 39 kΩ resistor constitute the primary current source that drives the input parts (Q12 and Q11) of the two current mirrors. "The two transistor diode junctions" do not belong to this current source; they are loads that consume the current. The two junctions reduce insignificantly the total current-creating voltage VT = VS+ - VS- - 2VF and, as a result, the generated current. Circuit-fantasist (talk) 14:56, 15 May 2009 (UTC)


 * I just made a small adjustment to the nomenclature around your edit, which seems good to me. But looking at the rest of that sub-section, I think that it is unclear in a few ways.  I'll try to clean it up.  See what you think. --Nigelj (talk) 15:46, 15 May 2009 (UTC)


 * Thank you. Only, I have an idea to apply a more system approach to explaining the 741 internal structure (see below). Circuit-fantasist (talk) 18:42, 15 May 2009 (UTC)

Archiving
The talk page was too long. So I have divided it in two parts and archived them. Circuit-fantasist (talk) 09:57, 17 May 2009 (UTC)

DC Path of non-inverting amplifier circuit diagram
The basic non-inverting amplifier, as shown, needs a DC path from the non-inverting input to earth (or whatever). Readers with a wide range of abilities will be looking at the page, and the implication from the description of ideal op-amps not needing input bias currents might make it seem that the circuit, as shown, is usable. The circuit has the assumption that the input will have a DC path provided to bias the input. I think some little comment is needed. Maitchy (talk) 20:48, 10 November 2009 (UTC)
 * I don't think any comment is needed. It is implied that a voltage source is connected to the non-inverting input, and that voltage source (whether ideal or not) provides the appropriate biasing current. There are certainly problems caused by bias currents across the source impedance of a non-ideal source, but I am not sure that discussion is appropriate in that section. Perhaps comments about complications caused by biasing (or leakage) currents could be discussed in their own section. Otherwise, the casual reader might be confused by them. &mdash;TedPavlic (talk/contrib/@) 04:23, 11 November 2009 (UTC)

History
I would love to see this section fleshed out a bit more. For example, the entries for "1961: First discrete IC op-amps" and "1962: First op-amps in potted modules" don't say which companies specifically were the pioneers. "By 1962, several companies..." sounds like weasel words to me. Which companies? I can substantiate that Philbrick was selling the PP65 by April 1963, and that Analog Devices formed in 1965 selling the AD101. ( http://www.philbrickarchive.org/1963-04_v11_no2_the_lightning_empiricist.htm and http://www.analog.com/en/corporate/historical-timeline/content/index.html ) What else have we got? Justinulysses (talk) 23:25, 26 January 2009 (UTC)

The distiction made between monolithic, discrete and hybrid ICs in the section 1962: First op-amps in potted modules is rather confusing, the definition of hybrid IC given in the wikipedia article Hybrid integrated circuit doesn't match the one given inside 1962: First op-amps in potted modules. --EleanorRugby (talk) 20:04, 16 November 2009 (UTC)


 * Can you explain where exactly you think the contradiction is? I don't quite see it. The parts of a hybrid circuit can individually have a degree of integration, but if it is still more parts than a single monolithic lump of silicon (or whatever) it is, to some extent, still hybrid.  Sp in ni  ng  Spark  20:32, 16 November 2009 (UTC)

Possible confusion over the word 'cell'
The phrase "as integrated circuit 'cells' or patterns that can be reprinted several times on one chip that is more complex, such as for a cell phone" is confusing. I removed the part "as cells" part since it seemed to imply cell phones were so named because they were made of IC "cells", which is not true as far as I know http://electronics.howstuffworks.com/cell-phone1.htm —Preceding unsigned comment added by Vhann (talk • contribs) 00:47, 15 December 2009 (UTC)


 * "Cell" is entirely appropriate terminology in this context. What is more the article actually explains the term so their is no confusion.  I have put it back, and am now the second editor to have done so making three editors (if we include the person who originally wrote it) who disagree with you.  Please do not delete it again unless you can get others to agree with you here.  The thing that is unnecessary to mention here, and not really relevant, is cell phones which is what is really causing the confusion so I have deleted that instead.  Sp in ni  ng  Spark  10:29, 21 December 2009 (UTC)


 * Perfectly fine with me. My point wasn't that the phrase "circuits cells" was wrong by itself but rather the wording used (having "circuit cells" and "cell phone" next to each other). One way or another, your edit here is perfectly fine with me (I believe the initial problem was how I explained the problem in the very beginning so I'll take the blame here ^-^ ). Olivier Diotte (talk) 01:41, 28 December 2009 (UTC)

"Golden rules" section
The Golden rules of op-amp negative feedback section seems a little back-to-front. The second point (the fact that no current flows into either input) is a consequence of the ideal op-amp design, not a consequence of negative feedback. The first point (the fact that the two inputs are at the same voltage) is therefore a consequence of the second point (amongst other reasons).

The extrapolation about input impedance is really a restatement of the second point. This paragraph then goes on to conflate "open-loop impedance" and "closed-loop impedance", which of course are two very different things.

Given that input currents are mentioned in the following section, I think this section could be simplified to a statement that negative feedback maintains equal input voltages. Any thoughts? Oli Filth(talk&#124;contribs) 17:18, 7 May 2010 (UTC)


 * Viewing the source, the 'golden rules' have been modified. Perhaps we can find a better, and more clear, source to guide rephrasing this section? Bakkster Man (talk) 18:33, 7 May 2010 (UTC)
 * I have not seen the source, but the current wording in the article is correct. If you connected a 1 volt battery across the inputs of an opamp with no feedback, there would be a 1V difference in potential between the two inputs. Consequently, there would be a (very small) current flowing into the opamp. However, with negative feedback, the output of the opamp (if not clipped) would settle at a voltage which results in both inputs having the same voltage wrt ground. Consequently, there would be zero current flowing into the opamp. Johnuniq (talk) 02:18, 8 May 2010 (UTC)


 * Johuniq, don't forget about common mode input impedance (impedance from either input terminal to ground). As long as there is a voltage wrt ground at either input terminal, there will be a non-zero current through that input terminal regardless of feedback.  See, for example, this.  Alfred Centauri (talk) 03:11, 8 May 2010 (UTC)


 * With an ideal op amp, there would be no input current. With older op amps, the input bias current was large (input collector current divided by &beta;), so designers would set the resistances of both input circuits to be the same. That way, equal input bias currents (looking like equal independent current sources) would cancel (leaving errors due to input offset currents). Newer op amps usually have such low input bias currents (or such large offset currents) that such compensation usually isn't needed (or is not effective).


 * There were problems with overdriving the inputs. Some op amps could even latch up, so a common old-time defense was back-to-back diodes across the inputs. Perhaps the questioned 'golden rule' was a roundabout acknowledgment of either input breakdown or input protection. Step on the inputs too hard, and the amplifier isn't ideal. Glrx (talk) 04:24, 8 May 2010 (UTC)


 * Johnuniq, I'm sure we both agree that the input impedance of the op-amp itself doesn't change if negative feedback is set-up around it. All that negative feedback brings to the party is an ability to set the voltage drop across the inputs to close to zero, which in turn leads to a small input current.  But this is not an inherent feature of negative feedback, merely a consequence of small input voltages!


 * My point is that op-amps inherently have high input impedance. This in turn allows one to apply the approximation that zero current flows into the inputs, which in turn allows one to derive the fact that negative feedback produces an approximate virtual ground.  The presentation of this section therefore places cart before horse.  Oli Filth(talk&#124;contribs) 08:54, 8 May 2010 (UTC)
 * When I talk about input voltage or current, I am referring to the differential component superimposed on the DC bias values. Suppose you have an opamp that is not quite ideal. In the particular negative feedback circuit you are using, with the particular input voltage used, let's say there is 1µA input current (it takes that much input current to drive the output voltage to where it has to be). Now if you were to replace the opamp with something identical in every way except it had a much higher voltage gain, the same output voltage would occur with a much smaller input current. The input current is reduced due to the higher open-loop gain, with negative feedback. Sure, the opamp has a high input impedance (although that needs a definition!), but the negative feedback makes the effective input impedance much higher. Johnuniq (talk) 10:50, 8 May 2010 (UTC)


 * What you are saying is that for a non-ideal (input impedance < ∞) op-amp, as open-loop gain tends to infinity, input current tends to zero for a -ve feedback arrangement. I agree with this; however, as I stated before, I maintain that this is merely a consequence of the fact that as AOL tends to infinity, input voltage drop tends to zero; i.e. a trivial consequence of the first "golden rule".  And in the case of an ideal op-amp, the second "golden rule" is a given, not a consequence of -ve feedback (in contrast, the first rule is a direct consequence of feedback).


 * I also disagree with the final paragraph; the notion that the "effective" input impedance is altered by negative feedback. IMO, "the closed-loop input impedance will be high because the inputs will be held at nearly the same voltage" doesn't make any sense.  I'm not sure I see which V/I relationship is altered by negative feedback.  Whilst the input impedance of a non-inverting amplifier topology is approximately ACL times higher than that of the op-amp, this is not true in the general case (e.g. an inverting topology).  Oli Filth(talk&#124;contribs) 11:11, 8 May 2010 (UTC)

Continuing with "increased input impedance"
I don't think today's edits by Circuit Dreamer have made the situation any clearer. In particular: Oli Filth(talk&#124;contribs) 23:12, 8 May 2010 (UTC)
 * What does it mean to talk of the "differential input impedance ... looking from the non-inverting input"? By the currently given definition, the differential input impedance is the ratio of the voltage across the input terminals divided by the current flowing from one to the other, so must be the same "viewed" from either side!
 * The input resistance of an op-amp is "about 1 megohm" without any feedback (e.g. the datasheet of a 741 datasheet picked at random).
 * "Thus the two inputs sit at the same voltage, and so the impedance between them is made artificially very high"; this still makes no sense. The impedance between the input terminals of the op-amp is not altered by negative feedback.  The only impedance that is high is that seen to ground by the single-ended input of a non-inverting amplifier.
 * "Parallel negative feedback circuits ... do not benefit from the high differential input impedance as it is shunted by the virtual ground"; it doesn't make sense to talk of a potential acting as a shunt. The op-amp inputs are in fact shunted by the feedback resistor and the op-amp output circuitry, but this is now a very convoluted way of viewing the situation.  It's much clearer to simply state that the input impedance is that of the input resistor due to the virtual ground; but this now has nothing to do with the "artificially increased" input impedance.


 * Only to note that the second and the third insertions are not mine. Circuit dreamer (talk, contribs, email) 08:01, 9 May 2010 (UTC)


 * Oh, I realise that. I was complaining about the whole thing, not just about your contribution!  Oli Filth(talk&#124;contribs) 08:46, 9 May 2010 (UTC)


 * I have read thoroughly the Horovitz & Hill's golden rules. The first rule (The output "attempts" to do whatever is necessary to make the voltage difference between the inputs zero) gives an intuitive notion about the operation of a negative feedback amplifier; it presents the op-amp as some "being" striving to reach the equilibrium (zero voltage difference between the inputs). You are right about the second rule - "it is a consequence of the ideal op-amp design, not a consequence of negative feedback". It is formulated only to help analyzing op-amp circuits with negative feedback. Circuit dreamer (talk, contribs, email) 20:43, 9 May 2010 (UTC)

Golden Rule confusion
I think too much emphasis has been placed on this "Golden Rule". It is clumsy grammar to use a singular term when there are multiple "rules"; if they can be called that. Everyone has their own idea of what the term means anyway. It would be better to just dispense with this term and cut to the chase: describing the assumptions used when op-amp circuits are analyzed. Zen-in (talk) 15:38, 9 May 2010 (UTC)


 * I've now eliminated the section, given that it comprised stuff that was already described (-ve feedback acts to make diff input voltage zero), and stuff that was tenuous (increased input impedance). Oli Filth(talk&#124;contribs) 18:06, 9 May 2010 (UTC)

Organization
Could we please get some of the basics of operational amplifiers described in the lead paragraphs before getting into our usual Wikiwaffle giving all the qualifications and restrictions in each sentence? It's very wearying to read typical "wall-o-text" Wikiprose. If you were explaining to your grandmother what an op-amp was and why it was important, that should go into the lead; all the grubby details must go later into the article. Einstein (Rutherford?) said the laws of physics should be explicable to a barmaid. --Wtshymanski (talk) 14:54, 27 August 2010 (UTC)
 * Gosh, I bet the staff in his local bar used to look forward to him coming in each evening. Oh, and I totally agree with the cleanup - good work --Nigelj (talk) 15:20, 27 August 2010 (UTC)

About the op-amp gain
The lede says: An op-amp produces an output voltage that is typically tens of thousands times larger than the voltage difference between its input terminals. But the "Limitations of real op-amps" section says: Typical devices exhibit open-loop DC gain ranging from 100,000 to over 1 million. The situation is very interesting... Circuit dreamer (talk, contribs, email) 19:57, 27 August 2010 (UTC)

play-hookey.com: In fact, the typical open-loop voltage gain for the 741 is 200,000.

All about circuits: Practical operational amplifier voltage gains are in the range of 200,000 or more...

Analog devices MT-044 TUTORIAL: Common values are 100,000 to 1,000,000, and 10 or 100 times these figures for high precision parts. Circuit dreamer (talk, contribs, email) 20:43, 27 August 2010 (UTC)


 * The intro is getting further warped by these details. Negative feedback does not control the op amp's gain -- the gain is fixed. The op amp is a building block. It only needs sufficient loop gain for the application. The loop gain at 10 kHz may be more important. Glrx (talk) 22:14, 27 August 2010 (UTC)

Demystifying negative feedback
Glrx, I agree with you. The negative feedback (circuit) controls neither the op-amp's gain nor the op-amp's behavior nor something else; it can't control anything as it is usually a humble passive circuit (some kind of passive "something-to-something" converter). The op-amp is the one that can control the output voltage. But in this arrangement it "conforms" to the plain negative feedback circuit (we have made the active op-amp "submit" to the passive circuit by this connection) and, as a result, the whole circuit acts as a reverse copy of the passive circuit. Thus it turns out that the passive circuit "controls" the active one (just like a beautiful secretary leads her chief by the nose:); it models, shapes the op-amp's behavior. Figuratively speaking, the device connected in the negative feedback loop is a "bridle" for the uncontrollable op-amp and we have kept a curb on the op-amp:) So, we may draw a few important conclusions: any op-amp negative feedback circuit is just a reversed passive circuit; it contains the dual passive circuit; it consists of an op-amp and the opposite passive circuit. But how does the op-amp do this magic?

Assume we have connected some converter (e.g., a voltage divider, an amplifier, a voltage-to-current converter, a current-to-voltage converter, a CR differentiator, an RC integrator, an RD log converter, a DR anti-log converter, etc.), having an input and an output, in the negative feedback loop. It is interesting that we have connected its input in parallel to the op-amp's output and its output in series to the input voltage source (it is true for both the series and parallel negative feedback configurations). Thus we have made the op-amp drive the converter and observe the result of comparison between the input voltage and the converter's output voltage. The op-amp adjusts its output voltage (the converter's input voltage) so that to equalize the converter's output voltage to the input voltage. The result is amazing: the voltage divider (the attenuator) becomes an amplifier, the amplifier - an attenuator, the voltage-to-current converter - a current-to-voltage converter, the current-to-voltage converter - a voltage-to-current converter, the CR differentiator - an RC integrator, the RC integrator - a CR differentiator, the RD log converter - a DR anti-log converter, the DR anti-log converter - an RD log converter, etc.

To do all this magic, as you have noted, the op-amp needs only a sufficient gain. This gain can be (and actually is) unstable, varying, drifting, non-linear, temperature-, supply-, thermal- and time- or frequency dependent... but it has to be high enough, to be excessive... You have said, "negative feedback does not control the op amp's gain -- the gain is fixed". Yes, it is true... but, strictly speaking, the gain is constant and equal to the specified in data sheets only after the op-amp reaches the equilibrium. During the transition (at rapidly changing input voltage) the gain can be significantly less than the rated one. During this time, the op-amp is actually not an amplifier; it is an integrator changing its output voltage with the specified slew rate. Circuit dreamer (talk, contribs, email) 14:38, 29 August 2010 (UTC)


 * "During the transition (at rapidly changing input voltage) the gain can be significantly less than the rated one." This is poorly stated and basically wrong.   Most Op-amps are compensated so they will be unconditionally stable. Their open loop gain drops off at a constant rate per octave.  This gives them a constant gain bandwidth product.   When an Op-amp is used in a high frequency / high slew rate application the closed loop gain is set to a low enough value so that there is sufficient gain at the upper roll-off frequency.   No competent Engineer designs an Op-amp circuit so that it is an integrator when a high frequency signal has to be accurately processed.  The reason why an Op-amp circuit's closed loop gain is set to a low value is so that the amplifier circuit will not have variable gain when it is operating.  An amplifier that has changeable, uncontrolled gain is usually unstable.  ie:  it is an oscillator.  Zen-in (talk) 17:02, 29 August 2010 (UTC)


 * Well, let's then define more precisely the gain. Replace "...the gain can be significantly less than the rated one..." with "...the gain can be significantly less than the rated DC open loop gain..." Circuit dreamer (talk, contribs, email) 17:14, 29 August 2010 (UTC)


 * Replacing a few words here and there will not make the whole thing make any more sense. Sometimes the best correction is to just delete the whole thing  Zen-in (talk) 02:24, 30 August 2010 (UTC)

μA748 and LM071
1. What is the purpose of using an external capacitor for compensation for the μA748 when the μA741 already has one inside of it?

2. When were the μA748 and the LM071 invented?

3. What's the op-amp with the highest gain-bandwidth product?

ICE77 (talk) 19:51, 19 May 2011 (UTC)


 * The external capacitor gives an application flexibility. Circuit dreamer (talk, contribs, email) 21:05, 19 May 2011 (UTC)

I guess it's just a way to avoid the 1MHz bandwidth constraint. Am I saying it right?

ICE77 (talk) 21:34, 19 May 2011 (UTC)


 * Yes, you are right. Circuit dreamer (talk, contribs, email) 21:53, 19 May 2011 (UTC)

What is it??
Unfortunately this article doesn't actually explain to a layperson what an op-amp actually does. Having read through the article, with the limited knowledge of electronics I have, I still don't actually know what an op-amp is. The explanation that it is "a DC-coupled high-gain electronic voltage amplifier with differential inputs and, usually, a single output" neglects to explain why DC-coupling is important, what a voltage amplifier does (it makes the volts louder? ;-)) and why differential inputs are important.

Granted the current description is probably fine for electrical engineers, but an explanation for a layperson would be really useful! -- Malvineous (talk) 10:45, 1 February 2010 (UTC)


 * Why explain DC coupling's importance, gain, and voltage amplifier in this article? Isn't that the role of the articles that are the subject of the wikilinks here? Alfred Centauri (talk) 13:19, 1 February 2010 (UTC)


 * You don't have to explain all those things here, but the explanation of an op-amp should be understandable if you're unfamiliar with those aspects. You shouldn't need to read a dozen different articles if you only want a basic idea of what this one thing does! -- Malvineous (talk) 02:07, 3 February 2010 (UTC)

I have added a simple explanation. Man with two legs (talk) 19:48, 3 February 2010 (UTC)


 * That's great, now I understand what it does :-) Thanks for that.  Re the posts below I tend to agree with the quote "a little inaccuracy sometimes saves tons of explanation."  You can be a little inaccurate up front for the benefit of non-experts like me, then spend the rest of the article explaining all the detail more accurately. -- Malvineous (talk) 02:42, 13 February 2010 (UTC)


 * An Operational Amplifier is a device originally devised for high-precision measurement/implementation of mathematical operations in early analogue computers and associated analogue systems. That's why they needed to be accurate and with a high enough gain. — Preceding unsigned comment added by 80.4.57.101 (talk) 20:57, 10 October 2011 (UTC)

Subject is op amps not op amp applications
I trimmed or moved several external links that were about operational amplifier applications rather than the op amp itself. The further reading section may need similar trimming but I'm not familiar with the books. Glrx (talk) 22:16, 7 February 2012 (UTC)

Flash external links
I added two links to the external links section for two Flash Animations that I had made. These two animations shows the relationship between the input and output voltages for the inverting and non inverting amplifiers. But someone has removed them. Can they please explane why. Please note that this is my 1st ever edit of a Wikipedia page. Not sure what I should call myself here. 19 September 2011. — Preceding unsigned comment added by 121.91.13.186 (talk) 20:44, 18 September 2011 (UTC)
 * I moved your comment to the bottom of the page as that is where editors expect to find new comments. The two external links added and removed are:
 * Non-inverting Operational Amplifier - Flash Animation
 * Inverting Operational Amplifier - Flash Animation
 * Wikipedia can be a rough place because there are hundreds of people trying to add external links to articles every day (most are removed); the procedure is that the person proposing a link needs to justify it based on the external links guideline. The proposed links are good for education but are not suitable here as they don't add information not already in the article (and there are already too many external links). Johnuniq (talk) 01:50, 19 September 2011 (UTC)

The heading of this page says "This article may be too technical for most readers to understand. Please help improve the article to make it understandable to non-experts, without removing the technical details. The talk page may contain suggestions. (September 2010". I would have thought that these two external links would have helped in this regard for non-experts. I reckon these two external linkes should be added. R Wall, 5th October 2011.  — Preceding unsigned comment added by 121.91.22.164 (talk) 21:16, 4 October 2011 (UTC)

I agree that these flash animations are very helpful. I'm taking a class on circuits and those flash animations really helped simplify the purpose of op-amps for me. Jojojlj (talk) 03:25, 9 February 2012 (UTC)

Opamp does not amplify the voltage itself; But the change (delta) in voltage.
This needs to be updated all over the doc. I have made correction at first occurence. — Preceding unsigned comment added by 120.61.25.154 (talk) 17:54, 23 March 2012 (UTC)

"Crucial" Difference Edit
Man with two legs, there is no crucial difference between your original phrasing, "the difference between the two input voltages", and my phrasing "voltage across the input terminals". In fact, they mean precisely the same thing.

The voltage across the input terminals is defined as (V+ - V-) AKA "the difference between the two input voltages"

However, your latest phrasing, "difference in voltage between its input terminals", is problematic. The voltage between its input terminals is the difference so your phrasing amounts to "the difference in the difference voltage".

For this reason, I will edit your new phrasing back to your old phrasing as you seem to attached to that rather than the "across" phrasing. Alfred Centauri (talk) 13:52, 4 February 2010 (UTC)
 * (Apologies for not noticing this section was here before my last edit)
 * I am certain that your interpretation of my phrasing is not correct and it does not mean "difference in the difference".
 * I don't agree that "voltage across..." is accurate but even if I am wrong on that, my point is that phrasing is more obscure to someone who is not familiar with electronic jargon. The word "difference" is clear to any intelligent person even if they don't know much about electricity while "voltage across" is not.  There is nobody out there who knows anything much about electricity who would need to look up Wikipedia to find out what an op-amp is, so for the article to have any value it needs to be written in a way that is comprehensible to someone who is new to the subject. Man with two legs (talk) 22:53, 4 February 2010 (UTC)
 * Man with two legs, your last revert seems odd. Did you not notice that my latest edit (which you just reverted) restored in part your original phrasing?  Did you not write as a comment to a previous edit "I still prefer the original version though."?  Do you honestly believe the current phrasing is better than your original phrasing?


 * As to whether it is clearer or not or to what level Wikipedia articles are to be written to, I suggest you consider taking a look at the physics and particularly the math related articles. Your statement "so for the article to have any value it needs to be written in a way that is comprehensible to someone who is new to the subject" is just plain silly, in my not so humble opinion.


 * At any rate, the half-life of edits to this article are not very long so I'm happy to leave your edits alone. Alfred Centauri (talk) 13:54, 5 February 2010 (UTC)
 * P.S. Re the accuracy of "voltage across", here's a quote from the Wikipedia "Voltage" article:  "A common use of the term "voltage" is in specifying how many volts are dropped across an electrical device (such as a resistor). In this case, the "voltage", or more accurately, the "voltage drop across the device", can usefully be understood as the difference between two measurements."  And no, I didn't write that and sure, if you feel that it's inaccurate, have a go at fixing it. ;^)  Alfred Centauri (talk) 22:17, 5 February 2010 (UTC)

Having read this, and re-read the lead-in paragraph, I agree that the current phrasing (voltage difference between its input terminals) is incorrect. I propose the following solution, which I hope will satisfy everyone above - change "voltage" in that sentence to "potential." This way, we can keep the "crucial" word "difference," but since we're referring to the difference in potential it is actually correct. I'm implementing this edit now, and I will also add to the beginning of the second sentence "In this configuration, ..." - making it clear that the situation described in the second sentence describes the more technical description in sentence one. Pyrilium (talk) 18:05, 1 July 2013 (UTC)

Textual edits in portion titled "Internal circuitry of 741 type op-amp"
I propose to introduce edits to the document portion titled "Internal circuitry of 741 type op-amp". Please let me know if these are unwelcome.


 * Make grammar more consistent with English
 * Make vocabulary more consistent with common usage in Electrical Engineering
 * Attempt to clarify explanations when they may bear improvement

Respectfully submitted ArthurOgawa (talk) 23:45, 18 February 2014 (UTC)


 * All of the things you propose look like welcome improvements. Go ahead, be WP:BOLD and see what happens. Binksternet (talk) 02:01, 19 February 2014 (UTC)

My edits have now been submitted. I dunno if I clobbered any edits others have made in the last two days.ArthurOgawa (talk) 00:03, 21 February 2014 (UTC)

input impedance
The input stage does not form a darlington stage - so the current description is definitely wrong. The Impedance value is about right - the typical value in the data sheets is 3 MOhm. I have not found a specific source explaining this, but simple, basic circuit analysis gives an input impedance of about 4 * beta(Q1) * kT/ e / I(Q1), which is twice that of a simple long tailed pair (due to Q2 and Q4). The rather large differential impedance is because of the relatively small current, not so much because of the different circuit.--Ulrich67 (talk) 18:17, 23 October 2014 (UTC)

Major lacunae in the article (and on Wikipedia)
There's no mention of (SPICE) macromodels, even though these are really important in practice. Unlike for transistor models there's no page at all on Wikipedia for any opamp models, like the Boyle macromodel, MPZ macromodel and so forth. The Burr Brown (now TI) app note http://www.ti.com/lit/an/sboa027/sboa027.pdf has some basics on these. December Rush (talk) 12:47, 27 December 2014 (UTC)

If you want a more academic source, Johan Huijsing's book Operational Amplifiers: Theory and Design, 2nd Edition, has a chapter on that (the 2nd one). December Rush (talk) 16:29, 28 December 2014 (UTC)

Op amp Test
In industry, op amps are tested with specific circuits that amplify certain nonidealities to a measurable range. This isn't touched upon in this article and I would like to add the section on it. I think it would fit well in section 2 after "real op amps" becasue it would be relevant there but it could also be its own section closer to the end of the article. Closer to the end would probably flow better because the user would have a better understanding of op amps after section 3 which explains basics of design and behavior. If no one has any objections to this or advice on writing this section, I will start working on it. There is an external link talking about simple op amp measurements: Simple Op Amp Measurements and essentially what I am proposing is to devote a section for that. Another concern might be that this section will grow too big or doesn't belong on this page, in which case we could move it to another page like Operational amplifier applications, which is its own page.

Some public resources I have to start with are this EDN series:Part 1 Part 2Part 3 Part 4 and An Introduction to Mixed-Signal IC Test & Measurement; 2nd Ed; Gordon Roberts, Friedrich Taenzler, and Mark Burns; Oxford University Press; 836 pages; 2012; ISBN 978-0-19-979621-2. Salazar126 (talk) 00:12, 27 May 2015 (UTC)

Dead Link - Example for expensive OP
The Link under Ref. 3 is currently a dead link. It could be relatively easy be repaired. However I don't think this part is a good example, being an high-end audio part, that does not offer superior scientific measurable performance. In this context prices are not always rational. A better example would be a high Power / high Voltage part like Apex - PA95, which is priced at about $200. The trouble is finding a good reference for this - links to a distributor site, like the one before are candidates for dead links and not really good Refs anyway.Ulrich67 (talk) 20:11, 22 October 2014 (UTC)
 * Changed this to a better example. Though there might be a better reference for a similar example. --Ulrich67 (talk) 18:19, 8 November 2015 (UTC)

External links modified
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I have just added archive links to 4 one external links on Operational amplifier. Please take a moment to review my edit. If necessary, add after the link to keep me from modifying it. Alternatively, you can add to keep me off the page altogether. I made the following changes:
 * Added archive http://web.archive.org/web/20140306140238/http://www.edn.com/contents/images/45890.pdf to http://www.edn.com/contents/images/45890.pdf
 * Added archive http://web.archive.org/web/20110720114249/http://ecow.engr.wisc.edu/cgi-bin/get/ece/342/schowalter/notes/chapter10/theua741operationalamplifier.ppt to http://ecow.engr.wisc.edu/cgi-bin/get/ece/342/schowalter/notes/chapter10/theua741operationalamplifier.ppt
 * Added archive http://web.archive.org/web/20120616161548/http://lyle.smu.edu:80/ee/7321/MOS_op-amp_design.pdf to http://lyle.smu.edu/ee/7321/MOS_op-amp_design.pdf
 * Added archive http://web.archive.org/web/20110823212009/http://electronicdesign.com:80/article/analog-and-mixed-signal/what-s-all-this-julie-stuff-anyhow-6071.aspx to http://electronicdesign.com/article/analog-and-mixed-signal/what-s-all-this-julie-stuff-anyhow-6071.aspx

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Minor niggles...

 * I think it is not the best to say it has a "single-ended output" - you either say "it is a single-ended amplifier (or output stage, more likely)" or you say it has a single output. "Single-ended output" is a kind of tautology, isn't it? Maitchy (talk) 07:48, 1 September 2010 (UTC)


 * This links to Single-ended signaling so is describing the way the output is used, not a clear tautology IMO. ~Kvng (talk) 15:10, 11 July 2020 (UTC)


 * I think the opening remarks could still start off a little less daunting for lay readers, giving the important aspects of why opamps are so darned useful before getting bogged down in lots of technicalities. How about something like: "Operational amplifiers ("opamps") are a very important building block in a wide range of electronic circuits, from audio to video.  They had their origins in analog computers, from which many linear, non-linear and frequency-dependent circuits have found uses in many other applications. Their popularity in general amplifier designs largely stems from the fact designers can determine their important characteristics (such as gain) by choice of external resistor values with little effect from temperature or transistor variations, etc." Not perfect, but gives a reasonable introduction?  Maitchy (talk) 07:48, 1 September 2010 (UTC)


 * Agreed, especially with the last sentence. Circuit dreamer (talk, contribs, email) 08:37, 1 September 2010 (UTC)
 * Thanks for those who made the appropriate insertion and tidy-up. Fun to see the flurry of changes-to-changes from such a small number of words, and nice to see the article starts in a way that isn't too off-putting for average readers yet still is accurate and encompasses what is important. Wiki works! Maitchy (talk) 22:20, 1 September 2010 (UTC)


 * It needs to say somewhere that the old accepted symbol for an op-amp was different, a rounded "front" to the symbol, and only one (inverting) input. Related to that, what do people consider is the "correct" way to place inverting and non-inverting inputs - "+" on top or "-" on top? I see both; some publications religiously stick with "-" to the top; some use whatever is convenient in the circuit (even - gasp - having the op-amp facing right!) and some have "+" at the top (so it matches where the "+" power supply goes on the symbol?).


 * We'll need a source and a picture of the old style (which I'm somehow too young to have ever seen!) would be nice too. Maybe improve Electronic_symbol while we're at it? ~Kvng (talk) 15:10, 11 July 2020 (UTC)


 * There are more (and sometimes subtle) limitations of real operational amplifiers - such as latch-up, static damage, input voltage range below V-. I think this article is about the right size, so what about a new article expanding on op-amp specifications and limitations, and tabulating some of the more common IC's with their characteristics? Note there is already a List of vacuum tubes page and a List of Intel microprocessors for example. I don't think there needs to be an attempt to comprehensively list many op-amps, but some are so famous (or so commonly used, or so unique!) they could be worthwhile to tabulate (such as: 709, 741/747/748 LM301/7/8 (and LM101/7 - note LM108 is different!!, early RCA CA-series, some OP*, LT*, LMH*, TL* devices) with open-loop gain, supply voltage range, etc and notes like "subject to latch-up" or "noise < ...".  Thoughts? Maitchy (talk) 22:20, 1 September 2010 (UTC)


 * We do have Operational amplifier applications. I think we are already deep into the minutia in this article. If anyone wants to go deeper, that should be in notes or a separate article. That level of detail is really what technical papers and books are for. ~Kvng (talk) 15:10, 11 July 2020 (UTC)

Hyphens
The hyphen usage on this page is incorrect. Putting a hyphen between two words creates a compound adjective. Thus, "operational amplifier" is a noun, but "operational-amplifier" is an adjective. Likewise in the abbreviation, "op amp" is a noun, and "op-amp" is an adjective. For example, "This high-speed op amp doesn't work in this op-amp circuit." I know that there are many "common" examples of incorrect usage, but ask an English teacher: "op-amp" is not a noun. (Also, "opamp" is an abomination.) — Preceding unsigned comment added by 24.147.65.117 (talk) 00:07, 11 July 2012 (UTC)

I agree. At some stage I'll go about removing the hyphens if no one else objects?Accidentprone104 (talk) 17:43, 11 December 2012 (UTC)


 * I have removed unnecessary hyphens. ~Kvng (talk) 15:41, 11 July 2020 (UTC)

Seperate page for the μA741?
The μA741 seems important enough in it's own right to have a separate page. I nominate a potential split from Internal circuitry of 741-type op-amp into a new article. The Manic Puppeteer (talk) 15:51, 28 July 2015 (UTC)
 * Seems like a good idea and the basic WP:N stuff is well surpassed by the huge sourcing for both aspects.
 * Couple of questions though:
 * Split or duplicate? We can choose to do either (see below).
 * Is the internal structure of the 741 relevant to an op-amp article that it primarily about the use of op-amps as building blocks, secondarily (and very importantly) as explaining the internal structure of an op-amp? This is "op-amp", and not "history of op-amps". The history is important, but it's a big enough overall topic, and there's a big enough need for a "current status only" article that too much history shouldn't be in this top level article.  So, ignoring the later developments like high impedance inputs, is the 741 circuit still relevant as a block-structure level explanation of op-amp internals?  If it is, we keep it in here (i.e. duplicative overlap rather than simple split). If it's an evolutionary dead-end or misleading per contemporary practice, we remove it through a straightforward split.  Of course both copies, here and at 741, may then develop either broadly or more narrowly.
 * Is the internal structure of the 741 specific and novel to the 741? (dim memory suggests it is) Or is it merely a development of the 702? (709 / 101 or whatever). If it's novel to the 741, then it belongs in a 741 article. If it's just gradual evolution, then maybe the split should be Operational amplifier and History of operational amplifiers / History of integrated circuit operational amplifiers, rather than prioritising the 741 uniquely. There are whole books on op-amps, so even having two history articles would be permissible. You could certainly write them as two, then merge later. Andy Dingley (talk) 16:09, 28 July 2015 (UTC)
 * I believe that the 741 has a unique internal structure, though it was technically a development of the 702, it diverged far enough from the original design to merit a separate article. I'm also taking into consideration the fact that the 741 is the effective "555 of op-amps" owing to it's ease of use, relative stability, reliable performance, and wide prevalence. I also believe that the 741 is still relevant to op-amp construction, as it's architecture is somewhat of a standard even in contemporary op-amps, so perhaps a duplicate would be better. The Manic Puppeteer (talk) 18:59, 28 July 2015 (UTC)
 * In which case, copy a bunch of content from here into a new article on the 741, trim down anything here that isn't generic or a precis of the 741 and then let the two articles grow independently. Andy Dingley (talk) 19:17, 28 July 2015 (UTC)


 * Not sure, leaning oppose. The &mu;A741 was a dominant op amp, but I'm not sure there's a whole lot to say about it in an encyclopedia. IIRC, the history is Robert Noyce let Bob Widlar experiment with analog circuits. Widlar used RTL as an amplifier. Then he made the &mu;A702 using a vacuum tube level shifting circuit. Then there was the &mu;A709 (and the side branch instrumentation amplifier &mu;A725). The 709 set the basic pattern of diff amp, CE gain, and push-pull output. I think the 709 was the significant op amp, but the frequency comp issues were a little daunting. The following designs refined the stages (e.g., lower bias currents; short-circuit protection), made better use of the crummy PNPs, and improved the process. LM301. The 741 used internal compensation, so it was the user-friendly opamp. The better article would be one about the evolution of the opamp's internal circuitry. I think Solomon wrote about that. Glrx (talk) 19:13, 30 July 2015 (UTC)
 * I aggree that there will not be a long article on the 741 alone. But does that matter - short articles are not bad. It's more the 500+ lines articles that are a problem. The internal circuit is not that unique - the lm101 is rather similar, except for internal compensation. So one could handle both OPs in a single article. The 741 internals are also different from many modern OPs - so having the detailed describtion of the old circuit may be a little misplaced in the general OP article.--Ulrich67 (talk) 18:44, 8 November 2015 (UTC)

- As an alternate point of view, this "internals" section you propose to move was _exactly_ what I was looking for when I came to this page. TdewolfWiki (talk) 05:27, 23 September 2016 (UTC)

This discussion is nearly two years old so I am being WP:BOLD and removing the tag from the main page. Martin of Sheffield (talk) 13:03, 6 April 2017 (UTC)


 * Support The 741 definitely qualifies for a separate article but that doesn't mean it needs to have a separate article. 741 theory of operation is instructive to understanding the internals of an op amp but it would be just as effective in this role as a link to a stand-alone article. Having this material inline in this article takes readers into the weeds and we don't want to do that so I support splitting this into a stand-alone article. ~Kvng (talk) 15:50, 11 July 2020 (UTC)