# op amp voltage follower

Discussion in 'Homework Help' started by athulascc, Apr 21, 2015.

1. ### athulascc Thread Starter Member

Aug 15, 2014
88
1

in 2nd problem I can mark A0 , Rin and R0 with help of this model of op amp

but what are others?

2. ### WBahn Moderator

Mar 31, 2012
18,093
4,918
You need to consider what each of those parameters means and then, with that understanding, determine how you would model it in the circuit.

3. ### athulascc Thread Starter Member

Aug 15, 2014
88
1
yes. I do not know what are Ios and V0s
also how to add Ib ? it is just current (biasing current) so how to model it?

4. ### WBahn Moderator

Mar 31, 2012
18,093
4,918
Then it would seem like it is time to actually read the course material regarding non-ideal opamp parameters, wouldn't it?

Aug 15, 2014
88
1
I got it

6. ### MrAl Distinguished Member

Jun 17, 2014
2,570
521
Hello,

Since others here were nice enough to provide me with better images in times when i couldnt read the originals, i thought i would return the favor and clean up this image and rotate it so it is easier to view. Here is the enhanced image.

• ###### IMG_5.gif
File size:
28.6 KB
Views:
19
Sinus23 likes this.
7. ### kdillinger Active Member

Jul 26, 2009
141
3
Ios is input offset current and is the difference between the input bias current from each pin. Stated another way, each input pin will have a bias current: IB+ and IB-. These are both measured and the difference between them is the Input Offset Current.

Vos is the input offset voltage and it is the voltage required at the inputs to ensure the output voltage of the op-amp is 0V.

If you want to model Ib, you simply add an ideal current source on each input to circuit ground. To include Vos, you add a voltage source on the IN+ pin to circuit ground.

A really good site that explains how to build a SPICE model from an op-amp datasheet is here:

http://masteringelectronicsdesign.com/build-an-op-amp-spice-model-from-its-datasheet-part-4/

There are 4 parts, I posted the link to part 4. You will see that input bias current, input bias current, and input offset voltage are modeled.