# Op-Amp Derivations

Discussion in 'General Electronics Chat' started by saifkazi, Mar 29, 2014.

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1. ### saifkazi Thread Starter New Member

Sep 4, 2013
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Hello guys
i am new here studying in 2nd year electronics and telecommunication Engineering and this is my first post.So i need help in deriving some op-amp circuit i cant figure out how this derivation work pls can some one explain me in detailed as i am having exam of Linear integration circuits so i need to become perfect in LIC

2. ### ScottWang Moderator

Aug 23, 2012
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google :how a instrument op amp working.

Jan 29, 2010
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4. ### LvW Active Member

Jun 13, 2013
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Better try "instrumentation amplifier".
More than that, each good textbook dealing with opamps shows how to find the expression for the differential gain.

5. ### ScottWang Moderator

Aug 23, 2012
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I was checked that before, if you google "instrumentation amplifier", then you can't find the video at the first page for that, and if you google "how a instrument op amp working" then you still can get a lot of infos for the circuit.

Jun 13, 2013
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7. ### ScottWang Moderator

Aug 23, 2012
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The op said that he needs a explanation to help him to understand, and the experience of a student may not like you, so I think using a similar way to learn as in the school, when he know the whole structure of that amplifier, and then to study the expression is more easier, that's what I thought.

8. ### Georacer Moderator

Nov 25, 2009
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@LvW,

I think what ScottWang is trying to say is, don't dismiss sources of knowledge presented in a thread. Each contributor gives the best resources, according to his experience and expectations of the OP.

ScottWang likes this.
9. ### ramancini8 Member

Jul 18, 2012
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Assume that the center of r is connected to a virtual ground, then each op amp has a gain of 2R1/R, and te initial stages are just buffers. The final stage is a standard diff amp.

Oct 9, 2007
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11. ### LvW Active Member

Jun 13, 2013
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Georacer, do you see any problem?
Somebody did recommend a video and what did I do? I have expressed some doubts if a video is a good way to explain how a transfer function can be derived - and I have given a link which - for my opiniuon - can be of great help. That´s all. Anything wrong with my response?

12. ### Georacer Moderator

Nov 25, 2009
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Not a problem per se. I just made the post as a reminder that such and similar expressions of doubt often cause the recipient of said doubts to write another post asking for clarification and an explanation. Just like I did for your post.

This creates a mini side-discussion in the thread which doesn't help an OP who struggles to discern learning resources in the "internet", such as this one.

To conclude, unless a resource suggestion is completely wrong or irrelevant, it isn't always for the best interest of the threads and its OP to start discussing its credibility, instead of actually helping the OP with his problem.

13. ### LvW Active Member

Jun 13, 2013
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OK - I see what you mean and, of course, I agree with you in general.
But let me say that in no way it was my intention to discuus the "crediblity" of somebody. How could I? And I don`t think I did.
My only point was the following:
If somebody wants an explanation how one could arrive at a certain function, there is always not only one single method. And if in one answer one particular method is recommended, which I do not prefer for some special reasons, I think it could be helpful for the questioner to know about some other methods or knowledge sources. And that´s all I did: I have mentioned that - according to my experience - a written text (with circuit diagrams) could be better suit the needs of the questioner. And I gave a corresponding link.
Please take into account that the english language is not my mother tongue - sometimes this may cause some misunderstandings?

14. ### #12 Expert

Nov 30, 2010
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Every questioner operates in a way that is peculiar to his own mind. This is one of the difficulties in answering on this site, finding which method works for the questioner. Saying you don't think one of the offerings is the best method to teach this person assumes you know his mind better than anybody else. Each of the helpers speaks with a different voice. (If we did not, we would only need one helper.) Each questioner has to choose among the offerings until he finds one that makes sense to him, and ignore the offerings that do not make sense to him. The, "wrong" answers might be too technical, too simple, miss the point of the question, or just foreign to the questioners internal model of how things work. The right answer is the one the questioner will respond to.

Last edited: Mar 29, 2014
15. ### LvW Active Member

Jun 13, 2013
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#12 -how could I disagree with you.
It was "only my opinion, and sometimes I´m wrong". OK?
I am really afraid both of you did misunderstand my post.
(Quote post#6: I am not sure if this is the best way to understand the derivation of the gain expression.").
I am really sorry for causing this disput. This was not my intention. Didn´t I help the questioner?

16. ### #12 Expert

Nov 30, 2010
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It depends. Did the Original Poster doubt that Scott Wang's offering was a valid method to learn about the circuit? It is up to him to decide whether a video is the best thing to speak to his level of understanding.

17. ### ScottWang Moderator

Aug 23, 2012
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Please don't take it too serious when you answering the questions, don't forget that we just offering the infos, sometimes we can't make sure that does the op will take the ideas from us, so I'm not offer too much info, I will offer some more if the op really need it, as what your keyword that I also can offer, why not, because if the op take my idea, then it's a good start and then maybe he will asking for some more infos, as ericgibbs and The Electrician mentioned that also can be find on the first page according to my keyword, what I'm trying to do is to see the video first and study the others, including what you linked.

Maybe the op will ignore my keyword and take your linked, so when offering the infos just don't take it too serious, we offering the infos according our experience, but it still depends the op to decide which one he will take it.

18. ### LvW Active Member

Jun 13, 2013
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Hi ScottWang,
I have no problem to apologize if you have the feeling that I was discussing your "credibility" (Georacer´s word). As I have mentioned already, this was not my intention.
On the other hand, was it me who did "take it too serious"?
Remember: My response was only " I am not sure if this is the best way...".
And this small sentence has caused the whole discussion ?
I deeply regret this unfortunate formulation. Next time I will write "..there is another way..." without any rating.
(But it is still my opinion that - in case of several ways to learn something - it could also be helpful for a beginner to tell him which way seems to be - in my view - most suitable.)
Kind regards
LvW

Last edited: Mar 30, 2014
19. ### Georacer Moderator

Nov 25, 2009
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I think we have spent much more time and effort for what is essentially an exercise to overcome the internet barrier inhibiting personal relations.
No one needs to apologize about anything.

Besides, we have managed to scare the OP off. Mission accomplished!

20. ### ScottWang Moderator

Aug 23, 2012
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What Georacer and #12 said that don't decide for the OP, because you are not him, if you question mine then others also can question you, if you felt that is bad, how could you question mine or some others, that's not the good way to discuss, if for the circuits maybe you can say that which part of the circuit is not so good from the theory, then point out the weakness and offer the better solution, that's what we discuss here for.