Example 12
2 kΩ
200 mV
6 kΩ
24 kΩ
100 mV
3 kΩ
100 mV
_
1 kΩ
10 kΩ
+
_
2.4 kΩ
+
200 Ω
500 mV
_
vo
500 Ω
+
5 kΩ
Calculate the voltage v o .
We are trying to find the output voltage of the ideal op amp circuit. Let’s try to divide the
problem into sub problems. The circuit can be divided into three blocks, a summing
amplifier, an inverting amplifier, and a difference amplifier. The output voltage of the
summing amplifier is labeled as vout1 and that of the inverting amplifier as v out 2 .
The summing amplifier output voltage is a weighted sum of the input voltages. That is
24 k
24 k
 24 k

v out1  
 200 
100 
 100 
6k
3k
 2k

 12  200  4 100  8 100   (2400  400  800 )  3600 mV  3.6V
The output voltage of the inverting amplifier is
 24 k

v out 2  
 500   6000 mV  6V
 0.2k

There are two input voltages connected to the third block. It is a difference amplifier, and
the output voltage is
v o  10  v out 2  v out1   10  (6  (3.6))  24V