the output should be:

EOUT = [(2 x E1) + (4 X E2) + (3 x E3)]

EOUT = [(2 x + 12 V) + (4 x + 3 V) + (3 x + 8 V)]

EOUT = [(+24 V) + (+12 V) + (+24 V)]

EOUT = -60 V

Calculate the current for each input:

E1

IR1 =

R1

+12 V

IR1 =

6 kΩ

IR1 = + 2 mA

--------

E2

IR2 =

R2

+3 V

IR2 =

3 kΩ

IR2 = +1mA

--------

E3

IR3 =

R3

+8V

IR3 =

4 kΩ

IR3 = + 2 mA

--------

IR4 = - (IR1 + IR2 + IR3)

IR4 = - (2 mA +1mA + 2 mA)

IR4 = - 5 mA

Calculate the output voltage:

EOUT = BR4

EOUT = (IR4 x R4)

EOUT = (-5 mA) x 12 kΩ

EOUT = -60 V

You have now seen how an operational amplifier can be used in a circuit as an adder, a

summing amplifier, and a scaling amplifier.

7-91. A difference amplifier will produce an output based on the difference between the

input signals. The subtractor circuit (see Figure 7-24) will produce the following output:

EOUT = E2 - E1