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

Computing Circuits
A.4.3
Noninverting Summer with Buffers
V REF1 and V REF2 are added to enable the buffers to handle positive input voltages. Their
output contribution to the last stage is cancelled out by V REF3 . This configuration uses
fewer resistors at the expense of two op amps. R G1 , R G2 , and R F in parallel should be
made equal to R B to cancel the input bias current.
R
V OUT
V F
R
IN1
V F
2R
A–31
R IN2
V F
2R
G1
R REF1
V F
G2
R REF2
V
G1
R REF3
1
R F
G2 R G1
R G2
R
R
+ 5 V
V IN1
V IN2
R/2
V REF1
R
R/2
V REF2
+V CC
_
+
R
+V CC
_
+
R G1
R G2
R F
+V CC
_
+
R B
V REF3
V OUT
V OUT — 0.5 V/Div
0 V
– 2.5 V
V IN3 — 0.5 V/Div
+ 2.5 V
V IN1 = 5 Vp-p V REF1 = 1.25 V
V IN2 = 0.5 V
V REF2 = 1.25 V
V CC = 5 V
V REF3 = 2.5 V
Op Amp = TLV247x
R G1 = R G2 = R F = R = 10 k
Figure A–26. Noninverting Summer with Buffers
A-26