While teaching op-amp circuits, which is the best way to explain the working of op-amp? I think the nullor model is useful.
Every one can visualize mathematical operations easily. Hence take examples of use op-amp in such applications is one way. Another is consider the various modes and their practical applications. Third there are lot of videos in open source which explain this very well
For my opinion, these artificial constructs like nullor, norator etc. do not help at all.
According to my experience in teaching analog electronics (and that is the question!) , there are two basic areas which are necessary to (a) analyse and (b) design operational amplifier based circuits:
(1) Amplifier technics (bias point, small-signal begaviour);
(2) Negative feedback (advantages, disadvantages, consequences).
So - finally, where is the need for an abstract model?
It is an elegant method for solving circuits with "ideal elements". But this method may "say" to beginners that it is able to do everything. But it can not :-)) The real problems begin with real elements. And this nullors can not do. See
https://www.researchgate.net/publication/281961470_MODERN_INTEGRATED_ELECTRONIC_DEVICES_IN_LINEAR_CIRCUIT_THEORY
Conference Paper MODERN INTEGRATED ELECTRONIC DEVICES IN LINEAR CIRCUIT THEORY
Dear Rohith,
I agree with the respected colleagues above and add operational amplifiers are designed and implemented to operate practically in near ideal mode to perform their function well. They are thought to be the primary building block in analog computers.
So, if they are operated under the validity of their approximations, then you can simplify the circuit analysis by assuming the equality of the inverting and the noninverting potentials as well as zero input currents. These two assumptions simplifies the analysis of the op amp application circuits.
Perhaps the most serious cause for deviation of the op amp from its nearly ideal behavior is to operate it too high frequency of switch it with too high speed.
The concept is that if the approximation is justified then you can exploit it as it makes the circuit analysis of the op amp very easy.
Best wishes
Dear Prof. Abdelhalim Zekry
I fully agree with your answer.
I tried many op-amp circuits with their nullor models. I found the circuit analysis become simpler, because, the virtual ground concept is clear due to the input nullator (input port of nullor). For a beginner in electronics, I hope this approach may be more catching. That is why I raise such a question. But the problem with nullor model is that, it doesn't has internal frequency compensation,. Additionally, All op-amp characteristics-offset currents etc., become close to its ideal values, or it represent ideal op-amp. (Same, as you said)
In my research works, many times I used op-amps as nullors and got good results. This is also a reason to think in the reverse side. Ideal op-amp is a perfect nullor, then why we can't use a nullor as an ideal op-amp.
Thanks.
I am a fan of the simple model proposed by Barrie Gilbert in this forum (as well as being a fan of Barrie himself): an ideal integrator.
Ad(s) = GBW / s.
In DC it leads back to a nullor (if you like it), but only in DC, and It does not have the unpleasant properties of an infinite Gain Bandwith product.
S.
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