Compute the voltage developed by R3 (ER3):

ER3 = (R3) x (IR3)

ER3 = (I kΩ) x (+3 mA)

ER3 = +3 V

Add this to the voltage at point A to compute the output voltage (EOUT):

EOUT = (ER3) + (voltage at point A)

EOUT = (+3 V) + (+6 V)

EOUT = +9 V

7-94. The circuit shown in Figure 7-24 functions as a subtractor. 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

that is:

EOUT = 5 (E2 - E1)

7-95. The difference amplifier that will produce that output is shown in Figure 7-25.

Notice that this circuit is the same as the subtractor shown in Figure 7-24 except for the

values of R3 and R4. The gain of this difference amplifier is:

R3

Gain =

R1

5k Ω

Gain =

1k Ω

Gain = 5

and since:

R3

R4

=

R1

R2

then, for a difference amplifier:

R3

R4

Gain =

=

R1

R2