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P.I.P.-XOV
E x a m p l e
Suppose that you need a 0.25
Chebyshev high-pass filter with a
400 Hz cutoff. The preceding chart
shows the correct values for K1–K3:
K1=2.018, K2=8.551, and K3=
0.1109. Next choose an arbitrary
value for C (C4, C5, C6) which yields
R4 and R5 values approximately
within the range of 2 K to 330 K ohms
and a value for R6 less than 1 M ohm.
For this example, let C=0.01 mF.
Then:R4 = (1 / 2.018) / (2 x 3.14159
x 400 x 0.01 x 10E–6) = 19,717 ohms.
Fig. 3.3 Butterworth Filters
R5 = (1 / 8.551) / (2 x 3.14159 x
400 x 0.01 x 10E–6) = 4,563 ohms.
R6 = (1 / 0.1109) / (2 x 3.14159 x
400 x 0.01 x 10E–6) = 358,800
ohms.
The 1% precision resistors with the
closest values are: R4=19.6 K
ohms, R5=4,640 ohms, and
R6=357 K ohms.
Figure 3.3 lists the resistor and ca-
pacitor values for a Butterworth fil-
ter using K1=1.392, K2=3.546, and
K3=0.2024:
Page 9
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