TDA 5210
Applications
4.2 Data Filter Design
Utilising the on-board voltage follower and the two 100kΩ on-chip resistors a
2nd order Sallen-Key low pass data filter can be constructed by adding 2 exter-
nal capacitors between pins 19 (SLP) and 22 (FFB) and to pin 21 (OPP) as
depicted in the following figure and described in the following formulas1.
C1
22
C2
21
Pins:
19
R
R
100k
100k
Filter_Design.wmf
Figure 4-3
(1)(2)
Data Filter Design
b
2Q b
R2Πf3dB
C2 = ---------------------------
4QRΠf3dB
C1 = ----------------------
with
b
a
(3)the quality factor of the poles
Q = ------
where
in case of a Bessel filter a = 1.3617, b = 0.618
and thus Q = 0.577
and in case of a Butterworth filter a = 1.414, b = 1
and thus Q = 0.71
Example: Butterworth filter with f3dB = 5kHz and R = 100kΩ:
C1 = 450pF, C2 = 225pF
1. taken from Tietze/Schenk: Halbleiterschaltungstechnik, Springer Berlin, 1999
Wireless Components
4 - 4
Specification, May 2001
INFINEON [ Infineon ]
