hi W,
How can you say my symbol post was a possible cause of (misinterpretations or misunderstandings caused by incomplete information).??
Well, spark8217 is an absolute beginner.
When you present a circuit diagram and a gain formula without indicating the signal input node (one out of two alternatives) and without a correct power supply I am afraid this can cause some misunderstandings, don`t you think so? It does not matter if your main intention was to show the symbol only. A symbol as part of an incomplete and not working circuit diagram is not the best way to help a newcomer.
Was I wrong with my comments?
Am I not allowed to complete some information that you give?
Are you saying the simplified formula for Gain = Rfb/Rin is invalid in the OPA symbol I have drawn.??
Surely even though there is no input signal, the OPA symbol as posted, will still have an inherent gain which is determined by Rfb/Rin.??
E.
Yes - that`s what I am saying. The symbol does not contain any information about the open-loop gain.
Remember: The questioner speaks about Aol=1E4 - and that is the reason he should use the complete formula as given by MrAl in post#3 (and not the approximation, valid for very large Aol) - in particular because he has a specification that is expressed in % of feedback!.
What do you mean with "the OPA symbol...inherent gain which is determined by Rfb/Rin"?
This sounds very confusing. The symbol is associated with an "inherent" gain which is called "open-loop" gain Aol. In the present case: Aol=1E4.
Only for very large values for Aol (1E5...1E6) the total gain of the amplifier with feedback can be given as -Rfb/Rin. These are basics!
Regarding 0V on the OPA's Vee terminal, how do you know that the OP is not going amplify DC levels above the 0V ground or perhaps a AC signal superimposed upon a DC offset level.??
You will note I have not included in my symbol any reference to an input signal, thats because I do not what it is.!
So how would I know what the OPA biassing arrangement would have to be.??
Eric - is this really your position? When a newcomer is asking a simple question about opamps I would at first refer to the basic inverting or non-inverting configuration, which does
not require any additional considerations regarding dc offset and/or biasing circuitry. Why do you argue in such a way?
hi W,
The level of detail in my answers to an OP posts are based simply on the question being asked, if the OP wants a more in depth explanation I will answer in greater detail.
I see little purpose in filling a reply post with information the OP has not requested.
E.
I didn`t criticize not at all the "level of detail" in your answer. I just have given some additional information to the questioner - important for application of such a circuit.
Was there any error in my comments?
It is really surprising that you react in such a sensitive way.
Perhaps you have overlooked that the start of this thread was not only a question about the symbol of an opamp.
The questioner has formulated some specific questions about amplifiers, feedback, sensitivity,...
hi W,
If you choose to answer a post in greater detail , thats your choice, but I do not think it appropriate to suggest that answers that other members have given are open to,
(misinterpretations or misunderstandings caused by incomplete information).??
E.
Perhaps you remember: My first comment was only "Eric forgot to mention..." (not very unpolite).
And it was only later - as reply to your "outcry: "for goodness sake, read the posts.." - that I gave my justification for this first comment (misinterpretation, incomplete information)
However, was anything wrong from the technical viewpoint?
My only intention was and is to provide the questioners with some helpful information. I am sure that this is also your aim - even if my answer is more detailed as you consider as appropriate.
Regards
W.