Since:

EIN = Efdbk

Then:

E

Gain = OUT

Efdbk

7-71. The feedback signal (Efdbk) can be shown in terms of the output signal (EOUT) and

the voltage divider (R1and R2). The voltage divider has the output signal on one end and

ground (0 volts) on the other end. The feedback signal is that part of the output signal

developed by R1 (at point A). Another way to look at it is that the feedback signal is the

amount of output signal left (at point A) after part of the output signal has been dropped by

R2. In either case, the feedback signal *(*Efdbk) is the ratio of R1 to the entire voltage divider

(R1 + R2) multiplied by the output signal (EOUT).

7-72. Mathematically, the relationship of the output signal, feedback signal, and voltage

divider is computed as follows:

R1

Efdbk =

(E )

R1 + R2 OUT

If you divide both sides of the equation by EOUT:

Efdbk =

R1

EOUT R1 + R2

By inverting both sides of the equation:

+

EOUT

= R1 R2

Efdbk

R1

Separating the right-hand side:

E OUT

= R1 + R2

Efdbk

R1 R1

Remember:

E

Gain = OUT

Efdbk

Therefore, by substitution:

R2

Gain =

+1

R1

7-73. You can now see that the resisters determine the gain of the noninverting

configuration. The formula is different from the one used for the inverting configuration;

however, the gain is still determined by the values of R1 and R2.