0195136047.pdf

3.4 FREQUENCY RESPONSE 167

TABLE 3.4.1Some of the Block Diagram Reduction Manipulations

Cascaded elements

Addition or subtraction

(eliminating auxiliary

forward path)

Shifting of pickoff

point ahead of block

Shifting of pickoff

point behind block

Shifting summing

point ahead of block

Shifting summing

point behind block

Removing H from

feedback path

Eliminating

feedback path

Original Block Diagram Manipulation Modified Block Diagram

G 1 G 2 C R G 1 G 2 C

G

1 + GH

R C

R G 1 ± G 2 C

R

R G C G

G

R C

G C

E

C

R

G C

C

R

G 2

G 1 +

−+

R

C

1/G

1/H

G

−

R +

H

1/G

G

+

−

RC

G

G

+

−

RE

H

G

+

−

RC

HG

+

−

R C

G

+

−

RE

C

G

+

−

RE

EXAMPLE 3.4.4

Feedback amplifiers are of great importance in electronic circuits. The block diagram of a class
of feedback amplifier is shown in Figure E3.4.4(a). Determine the transfer functionC/Rfor the
block diagram.

G 0

G 3

R C

G 2

H

(a)

Σ G 1

+

+

+

−

Σ

Figure E3.4.4