3-39
Compute the voltage developed by R3 (ER3):
Add this to the voltage at point A to compute the output voltage (Eout):
As you can see, the circuit shown in figure 3-25 functions as a subtractor. But just as an adder is only
one kind of summing amplifier, a subtractor is only one kind of difference amplifier. A difference
amplifier can amplify the difference between two signals. For example, with two inputs (E1 and E2) and a
gain of five, a difference amplifier will produce an output signal which is:
The difference amplifier that will produce that output is shown in figure 3-26. Notice that this circuit
is the same as the subtractor shown in figure 3-25 except for the values of R3 and R4. The gain of this
difference amplifier is:
Figure 3-26.—Difference amplifier.
