Operational Amplifiers

[rgsparber]

The equation that fully describes an ideal operational amplifier is simple, yet its meaning is complex. I have written a tutorial that attempts to explain it.

If you are interested, please, click here


Your comments are welcome. All of us are smarter than any one of us.


Thanks,

Rick

[BuffaloJohn]

You spent half your document doing Ohm's and Kirchhoff's Laws which didn't do anything to explain op-amps.

Then, rather than trying to explain the gain function, you dive back into the same confusing analysis. You don't define k and shortly after - you declare "I hereby drop ≈ and just use =."

ARRRRRRRRGH!!!!!!!!!!!!!!!!!!!!!!

There are many, many much better articles online for learning about opamps. Seriously, if you want to understand an opamp, look elsewhere.

And - you didn't even explain gain for anything but DC. The word "gain" was used only once.

What is k? It is the open loop gain!

What do the resistors you add to the opamp do? They bound the open loop gain to a function. Using the figure on pg8, R1 is the input resistor and R2 is the feedback resistor and the gain of that circuit is R2/R1.

[rgsparber]

It sounds like you understand op amps and feedback well. That tells me you are not my target audience. My students were confused by the text book but said my explanation helped.

Rick

[BuffaloJohn]

Of course your "students" told you that.

But do they actually understand open loop gain and the gain function of the resistors?

You still spent 14 pages to explain something poorly and left out basic terminology that is important to understanding further characteristics of opamps.

[rgsparber]

John,

Sorry if this sounds snippy, but yes, I do understand open-loop gain and feedback. My Masters is in EE is from Berkeley and I worked at Bell Labs for 28 years. These students do not receive a grade from me so are not obligated to say anything positive about the material. They came in confused and left understanding the material.

Rick

[BuffaloJohn]

I didn't ask if you understood those things, I asked if your students understood open loop gain and feedback.

I don't have a masters. I didn't think when I graduated with my EE in 1977 and still don't think it is useful. I spent my time in industry - designing hardware and software.

[rgsparber]

Four weeks ago these students learned ohm's law. Two weeks ago they started to write nodal equations. Last week they were introduced to opamps. So, no, they do "understand" open-loop gain and feedback. My challenge was to use what they barely knew and move them towards an appreciation of what feedback could do at a very basic level. Feedback is not an easy thing to grasp.

I didn't understand feedback until I learned about the complex plane, poles, zeros, root locus, and control theory.

Rick

[BuffaloJohn]

Feedback is not an easy thing to grasp.

I didn't understand feedback until I learned about the complex plane, poles, zeros, root locus, and control theory.

Feedback is easy to understand if taught properly and a basic understanding of opamps doesn't need complex plane/poles/zeros/root locus. Basic control theory is a little bit useful - just the beginning parts - because that teaches summing, amplification, and feedback.

Too much math and too complicated explaining get in the way of learning the basics... These folks only learned ohms law four weeks ago...

[rgsparber]

John,

I think I see what is going on here.

You are focused on the general concept of feedback. I agree that the basics are simple and can be explained by presenting open loop gain, the feedback network, and the difference node. There is no need for much math. To fully understand and apply feedback, all of the heavy-duty math I mentioned is needed.

I failed to explain the intent of this tutorial. The students had three homework problems they couldn't solve. I was walking them through these problems. It was a narrow focus that involved feedback without directly talking about it. That comes after they do a lab.

I will add a preamble to the article explaining the goal.

Thanks for helping me see this shortcoming,

Rick

[rgsparber]

I have updated the article to include non-ideal behavior of the opamp.

Rick