Page 1121 - Basic Electrical Engineering

R = R,
f

Then,
V = −(V + V + V )
0
2
1
3
The output voltage, V is equal to the algebraic sum of the input voltages.
0
By choosing a suitable ratio of R /R, the output voltage can be made equal to
f
the sum of the desired ratio of the input voltages. The circuit is called a

summing amplifier circuit.

17.6.2 Op-amp As a Differential Amplifier (Subtractor)

Fig. 17.6 (b) shows a differential amplifier, or a difference amplifier, or

simply a subtractor. Here, the difference between two voltages, viz V and V 1
2
can be amplified using this circuit. Again, assume that the amplifier has

infinite gain and infinite input impedance, point Q and Q at virtual ground,
1
2
i.e., zero potential. Amplifier allows no current flow through it. Looking at
the inverting input terminal and feedback path

From the non-inverting input terminal

Subtracting equation (iv) from equation (v), we have

or,