0195136047.pdf

PROBLEMS 259

5.1.6Consider Example 5.1.2. LetA=1 andRi=Ro.
Show that no matter what values ofRThandRLare
used, the power gain as defined in that example is
less than unity, and find the maximum value it can
have.

5.1.7(a) Figure P5.1.7 shows a circuit containing an
amplifier block. Find the open-circuit voltage
amplification of the circuit.
(b) Let the output terminals be connected to a load
resistanceRL. Find the input resistanceRi′.

5.1.8(a) Consider the amplifier block in the circuit
configuration of Figure P5.1.8. Find an ex-
pression forv 2 /v 1 in terms ofRi,Ro, andAof
the amplifier.

(b) Determine the output resistance of the circuit.

*5.1.9(a) Two amplifiers, which can be represented by

the model of Figure 5.1.1 of the text, are con-

nected incascade(that is, head to tail), as

shown in Figure P5.1.9. Let their parameters

beRi 1 ,Ro 1 ,A 1 , andRi 2 ,Ro 2 ,A 2 , respectively.

Findvx/v 1.

(b) Discuss how the answer is influenced by the

ratioRi 2 /Ro 1 , particularly when this ratio ap-

proaches zero or infinity.

5.1.10Reconsider Problem 5.1.9. If we define a power

gainGPas the ratio of the power dissipated inRL

to the power produced by the sourcev 1 , find an

R 2

A

R 1

R 3

Ai 1

vout

i 1

+

−

Vi

Figure P5.1.3

R 1 R 2

Ai 1

B

+ i 1 A

−

v 1 (t)

Figure P5.1.4

ri

hfii

D

C

ii

+

+

−

−

hrvo ro vo

B

A

Figure P5.1.5

+

−

vout

+

−

vin

R 1

Figure P5.1.7

+

−

v 2

D

C

B

A Amplifier

+ (in) block (out)

−

v 1

Figure P5.1.8

+ +

− −

Amplifier v 2 RL iL vx

1

Amplifier

2

+

−

v 1

i 1 Figure P5.1.9