Biomedical Engineering Reference
In-Depth Information
Example Problem 9.20 describes a summing op amp circuit.
EXAMPLE PROBLEM 9.20
Find the overall gain for the following circuit.
R
a
R
2
−
+
R
b
+
+
+
+
−
+
V
a
V
b
v
n
−
v
0
v
p
−
−
−
Solution
As before, we start the solution with
v
n
¼
v
p
and note that the noninverting input is connected
to ground, yielding
v
n
¼
v
p
¼
0 V. Applying KCL at the inverting input node gives
V
a
R
a
V
b
R
b
v
o
R
2
¼
0
or
v
o
¼
R
2
R
a
V
a
þ
R
2
R
b
V
b
This circuit is a weighted summation of the input voltages. We can add additional source
resistor inputs so that in general
v
o
¼
R
2
R
a
V
a
þ
R
2
R
b
V
b
þ ...þ
R
2
R
m
V
m
