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LS204IN View Datasheet(PDF) - STMicroelectronics

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Description
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LS204IN Datasheet PDF : 16 Pages
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Application information for active low-pass filters
4.5
Example
Figure 14. 5th order low-pass filter (Butterworth) with unity gain configuration
C2
C4
Ri
R1
Ci
R2
C1
R3
R4
C3
LS204
In the circuit of Figure 14, for Fc = 3.4 kHz and Ri = R1 = R2 = R3 = 10 kW, we obtain:
Ci = 1.354 -1-- -----1------ = 6.33nF
R 2πfc
C1 = 0.421
-1--
R
2----π-1---f--c-
= 1.97nF
C2 = 1.753
-1--
R
2----π-1---f--c-
= 8.20nF
C3 = 0.309 -1-- -----1------ = 1.45nF
R 2πfc
C4 = 3.325 -1-- -----1------ = 15.14nF
R 2πfc
The attenuation of the filter is 30 dB at 6.8 kHz and better than 60 dB at 15 kHz.
The same method, referring to Table 7 and Figure 15 is used to design high-pass filters.
In this case the damping factor is found by taking the reciprocal of the numbers in Table 7.
For Fc = 5 kHz and Ci = C1 = C2 = C3 = 1 nF we obtain:
Ri
=
------1--------
0.354
-1--
C
2----π-1---f--c-
= 25.5kΩ
R1
=
------1--------
0.421
-1--
C
-----1------
2πfc
= 75.6kΩ
R2 = ------1-------- -1-- -----1------ = 18.2kΩ
1.753 C 2πfc
R3
=
------1--------
0.309
-1--
C
2----π-1---f--c-
= 103kΩ
R4
=
------1--------
3.325
-1--
C
2----π-1---f--c-
= 9.6kΩ
Figure 15. 5th order high-pass filter (Butterworth) with unity gain configuration
R2
R4
Ci
C1
C2
Ri
R1
C3
C4
R3
10/16
 

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