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dB<br />

90°<br />

45°<br />

0°<br />

–45°<br />

–90°<br />

v (A v )<br />

EXAMPLE 23.11 For the filter of Fig. 23.75:<br />

a. Sketch the curve of AvdB versus frequency using a log scale.<br />

b. Sketch the curve of v versus frequency using a log scale.<br />

Solutions:<br />

a. For the break frequencies:<br />

1<br />

1<br />

f1 ������ �37.2 Hz<br />

2pR1C 2p(9.1 k�)(0.47 mF)<br />

1<br />

1<br />

fc �–––– ���� �376.25 Hz<br />

R1R2<br />

2p(0.9 k�)(0.47 mF)<br />

2p��� R1 � �C The maximum low-level attentuation is<br />

�20 log 10<br />

R 2<br />

R 1 � R 2<br />

� R2<br />

��20 log 10<br />

��20 log10 10.1 � �20.09 dB<br />

The resulting plot appears in Fig. 23.76.<br />

b. For the break frequencies:<br />

At f � f1 � 37.2 Hz,<br />

v ��tan �1 � tan �1 f1 fc � �<br />

f f<br />

��tan �1 1 � tan �1<br />

��45° � 84.35°<br />

� 39.35°<br />

At f � fc � 376.26 Hz,<br />

v ��tan �1<br />

37.2 Hz<br />

��<br />

376.26 Hz<br />

9.1 k��1 k�<br />

��<br />

1 k�<br />

376.25 Hz<br />

��<br />

37.2 Hz<br />

� tan �1 1<br />

HIGH-PASS FILTER WITH LIMITED ATTENUATION ⏐⏐⏐ 1065<br />

1 2<br />

3<br />

4<br />

5<br />

f1 /10 fc /10 f1 fc 10f1 10fc FIG. 23.74<br />

Phase response for the high-pass filter of Fig. 23.68.<br />

+<br />

V i<br />

–<br />

R 1<br />

9.1 k�<br />

C<br />

0.47 mF<br />

R 2<br />

FIG. 23.75<br />

Example 23.11.<br />

f (log scale)<br />

1 k�<br />

+<br />

V o<br />

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