Page 304

CHAP. 12]

FREQUENCY RESPONSE, FILTERS, AND RESONANCE

293

Solved Problems 12.1

In the two-port network shown in Fig. 12-33, R1 ¼ 7 k and R2 ¼ 3 k . ratio V2 =V1 (a) at no-load, (b) for RL ¼ 20 k .

Obtain the voltage

Fig. 12-33

(a) At no-load, voltage division gives V2 R2 3 ¼ 0:30 ¼ ¼ V1 R1 þ R2 7 þ 3 (b) With RL ¼ 20 k , Rp ¼

and

R2 RL 60 ¼ R2 þ RL 23

k

Rp V2 60 ¼ 0:27 ¼ ¼ V1 R1 þ Rp 221

The voltage ratio is independent of frequency. The load resistance, 20 k , reduced the ratio from 0.30 to 0.27.

12.2

(a) Find L2 in the high-pass circuit shown in Fig. 12-34, if jHv ð!Þj ¼ 0:50 at a frequency of 50 MHz. (b) At what frequency is jHv j ¼ 0:90? (a) From Section 12.2, with !x  R1 =L2 , 1 jHv ð!Þj ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 þ ð!x =!Þ2 Then,

1 0:50 ¼ qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 þ ð fx =50Þ2

Fig. 12-34

or

pffiffiffi fx ¼ 50 3 MHz

Mahmood_Nahvi_eBook_Schaum_s_Outlines_Theory_An  
Mahmood_Nahvi_eBook_Schaum_s_Outlines_Theory_An  
Advertisement