Op Amps for Everyone - The Repeater Builder's Technical ...

Computing Circuits
A.4.2
Noninverting Summer
This circuit adds the input voltages and multiplies them by the stage gain. R G1 , R G2 , and
R G3 in parallel should be equal to R F in parallel with R G to cancel the input bias current
using the common-mode input voltage rejection technique. V REF is added to the circuit
to enable the addition of negative values.
V OUT
V IN1 R G2
R G3
R G1
R G2
R G3
V IN2 R G1
R G3
R G2
R G1
R G3
V IN3 R G2
R G1
R G3
R G2
R G1
R F
R G
R
R G
V F
REF
R G
A–30
+ 5 V
V IN1
R G1
R G2
R G3
+
_
V OUT
V OUT — 0.5 V/Div
R G
R F
V IN2
V IN3
V IN2 = –1 V
0 V
– 2.5 V
+V CC
R F = 20 k
V IN3 — 0.5 V/Div
+ 2.5 V
V REF
V IN1 = 1.5 V
V CC = 5 V
V REF = –1.25 V
V IN3 = 5 Vp-p
Op Amp = TLV247x
R G = R G1 = R G2 = R G3 = 10 k
Figure A–25. Noninverting Summer
Single-Supply Circuit Collection
A-25