I was just looking at the opamp worksheet. The negative feed back non-inverting opamp gain formula was given as Av=r1/r2 1. I believe it should be Av=r1/r2 +1

 

You are correct.

 

Thanks. *1 didn't make much sense.

 

Moved from Feedback & Suggestions forum

 

The plus 1 depends on whether it is a positive or negative amp. Negative gets a - sign and Positive gets a 1+.

 

I use Rf/Ri to avoid confusion. I dislike confusion. And 1+Rf/Ri, as well.

 

I use Rf/Ri to avoid confusion. I dislike confusion. And 1+Rf/Ri, as well.

I must admit that your answer has caused some confusion for me

 

OK, sorry about that. Ri= the resistor in series with the input voltage to the inverting input. Rf = the feedback resistor connected between the opamp output and the inverting input.
The added "+1" is because with an input to the non-inverting side there is always at least a gain of one (unity gain).

 

"I must admit that your answer has caused some confusion for me"
I actually thought that was a bit of humour in response to your statement "I dislike confusion"?

 

"I must admit that your answer has caused some confusion for me"
I actually thought that was a bit of humour in response to your statement "I dislike confusion"?

Some writers utilize conventions that are unknown to large segments of the population, for reasons that I do not see. Unconventional uses of words, in the manner of London schoolboy slang, can certainly convey incorrect meanings and cause problems.
For op-amp basics, though, input and feedback are rather the most basic concepts, and thus Ri and Rf should be clear, while R1 and R2 must reference some circuit drawing.

 

I wonder if @LvW would clarify

 

OK, sorry about that. Ri= the resistor in series with the input voltage to the inverting input. Rf = the feedback resistor connected between the opamp output and the inverting input.
The added "+1" is because with an input to the non-inverting side there is always at least a gain of one (unity gain).

You can believe me - I was able to imagine what you mean with "Ri" and "Rf"
However, from your sentence " I dislike confusion. And 1+Rf/Ri, as well" I have derived that you dislike the expression (1+Rf/Ri) "as well".
THIS has caused some confusion for me.

 

I was just looking at the opamp worksheet. The negative feed back non-inverting opamp gain formula was given as Av=r1/r2 1. I believe it should be Av=r1/r2 +1

For those of us who don't know what worksheet you're referring to, could you post a schematic and link?

Assuming you spelled things correctly, which I doubt because we use R as resistor designators, and r1 is the feedback resistor and r2 is the input resistor, the plus sign is indeed missing. That would be a critical error in something supposed intended to be educational.

 

I guess it wasn't what I thought!

 

Some writers utilize conventions that are unknown to large segments of the population, for reasons that I do not see. Unconventional uses of words, in the manner of London schoolboy slang, can certainly convey incorrect meanings and cause problems.

Yes - I totally agree with you.
However, even "conventional" uses of words/terms can and will convey incorrect meanings and, thus, cause problems for a correct understanding. Examples?

* "Current source" (in fact, a voltage source with a large static or dynamic internal source resistance)
* "Injecting a current" (in fact, we cannot "inject" a current - we realize a voltage divider with Rload<<Rsource)
* "Transistor current gain" (this is not really a "gain" because Ib is not the cause of Ic).
* "Current I creates a voltage across R" according to V=I*R (the formula is, of course, correct - but a current never can "create" a voltage. The other way round: A current needs a driving voltage)

 

You can believe me - I was able to imagine what you mean with "Ri" and "Rf"
However, from your sentence " I dislike confusion. And 1+Rf/Ri, as well" I have derived that you dislike the expression (1+Rf/Ri) "as well".
THIS has caused some confusion for me.

OK, AND, FOR THE RECORD!! That was an error on my part!
It is the confusion created that I dislike.
Op-amp gain expressions are friends that help me. I like them.
Sentence sequence can lead to delivering wrong impressions, which I demonstrated quite well in that instance.

 

OK, AND, FOR THE RECORD!! That was an error on my part!
It is the confusion created that I dislike.
Op-amp gain expressions are friends that help me. I like them.
Sentence sequence can lead to delivering wrong impressions, which I demonstrated quite well in that instance.

Thanks for these honest words.