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CHAP. 5]

AMPLIFIERS AND OPERATIONAL AMPLIFIER CIRCUITS

81

Fig. 5-28

Fig. 5-29

5.13

LOW-PASS FILTER

A frequency-selective amplifier whose gain decreases from a finite value to zero as the frequency of the sinusoidal input increases from dc to infinity is called a low-pass filter. The plot of gain versus frequency is called a frequency response. An easy technique for finding the frequency response of filters will be developed in Chapter 13. The leaky integrator of Fig. 5-24 is a low-pass filter, as illustrated in the following example. EXAMPLE 5.22 In Example 5.18 let v1 ¼ sin ! t. Find jv2 j for ! ¼ 0; 10; 100; 103 ; 104 , and 105 rad/s. By repeating the procedure of Example 5.18, the frequency response is found and given in Table 5-1. response amplitude decreases with frequency. The circuit is a low-pass filter.

Table 5-1. Frequency Response of the Low-pass Filter !, rad/s

0

f , Hz jv2 =v1 j

0 1

10 1.59 1

100 15.9 0.995

103 159 0.707

104

105

1:59  103 0.1

15:9  103 0.01

The

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