Hello
I want to use a unity gain buffer to drive an ADC. However, I want to ask which is the difference (if any) between the first and the second op amp. Do they act the same ?

 

No.

The first is a differential amplifier. The second is a unity gain buffer.

Bob

 

Ok I understrand now. So in my case that I have a differential signal, I suppose that the first one with all the resistors equal will be fine.

 

If you use equal resistors you'll have a gain of 3. For unity gain, use R1=R2=1.5Rg, Rf=Rg.