# How would I draw this non-inverting amplifier?

Summary: So far, I have only dealt with ideal operational amplifiers, so I am kind of lost trying to visualize how a practical op amp should look like.

A non-inverting amplifier with a gain of 10 uses 100K as its feedback resistor. It gets its input from a signal source whose source resistance is 5K. The amplifier has zero offset voltage. However, it has an input bias current of 2 µA and an input offset current of 0.2 µA.
Draw the op-amp circuit.

Is this right?
Also, is R2 = 11.11k? I used A = 1 + RF/R2 to get this value

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Seems no issues with equivalent circuit schematic above.
Regarding G=10 non-inverting opamp, i prefer to use 91k and 10k, these values are closest approximation to G=10 using E24 preferred numbers series.

Baluncore
2019 Award
You have significant input current so you need to match the source impedance of the (–) and (+) inputs. The op-amp output can be seen as having a low impedance.
So with Rf = 100k, and R = 11k11, the source impedance on the (–) input will be Rf in parallel with
R, giving 10k0. To avoid offset voltage due to input currents you need to give the (+) input the same source impedance as the (–) input. The driver has Rsource = 5k0 now, so you need to add an external Rspecial = 5k in series to match the (–) input.

Draw your potential divider so it is obviously a potential divider by keeping the current flowing in a straight line.
Don't make a hedgehog with currents radiating out from the op-amp, keep parallel currents parallel.

rude man
Homework Helper
Gold Member
Post 2 is not showing the offset current.

Baluncore
2019 Award
Post 2 is not showing the offset current.
Or post #3? The offset current was left for later. I judged that matching the source resistance was more important and enough for a first step.
I expected @marcadams267 to have noticed the missing offset current from the way it was drawn. Maybe Ios needs to be drawn as a separate current source between the two input terminals.

rude man
Homework Helper
Gold Member
Or post #3? The offset current was left for later. I judged that matching the source resistance was more important and enough for a first step.
I expected @marcadams267 to have noticed the missing offset current from the way it was drawn. Maybe Ios needs to be drawn as a separate current source between the two input terminals.
I couldn't see post#2 until now.
Offset current should be depicted exactly as the OP did in post 1, i.e. as part of bias current.

Baluncore