Page 1119 - Basic Electrical Engineering

The negative sign indicates that the output voltage is inverted. The closed

loop voltage gain is . Thus, the input voltage appears at the output terminal

multiplied by a and gets inverted.

Fig. 17.5 (b) shows a non-inverting amplifier. The output voltage, V can
0
be calculated as

The output is positive, i.e., non-inverted and is multiplied by a factor,

In Fig. 17.5 (c), R has been made zero, i.e., output terminal is directly
f
connected to point Q so that using equation (iii), we can write

V = (1+0)V = V in
in
0
This circuit is called a unity gain voltage follower. Such a circuit is used

for impedance matching in electronic devices and circuits.

17.6.1 Op-amp As a Summing Amplifier

Op-amps can be used for adding and subtracting two input signals. They can

also be used as differentiators and integrators. Analog computers use
extensive op-amp circuits for these functions. These are discussed in brief as
follows.

Fig. 17.6 shows an adder, i.e., a summing amplifier and a subtractor, i.e., a
differential amplifier circuit.