The Non-inverting amplifier

For an ideal op-amp:
vo/vi = (R1+R2)/R2 = 1+ R1/R2

The Voltage Follower

If R1=0, R2 acts as a load and does not effect the feedback. The amplifier becomes a voltage follower.
vo/vi = 1

The Non-inverting Summer

With two inputs vo is the weighted sum of the inputs.
vo =v1 + v2 (for all resistors equal)
vo = (R1+R2)/R2 (v1 R4 + v2R3)/ (R3+R4)

vo =v1 + v2 +v3 (for R1 = 2R2 and R3=R4=R5)
vo = {(R1+R2)/R2} { (v1 R4||R5)/(R4||R5+R3) + (v2R3||R5)/(R3||R5+R4) + (v3R3||R4) /(R3||R4+R5)}

© Copyright 1996 New Mexico Institute of Mining and Technology