TDA7200 Datasheet, PDF (21/49 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

TDA7200
Applications
3.2
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 external 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⁾.
C14
C12
FFB
OPP
22
21
R_{F1 int}
R_{F2 int}
100k
100k
SLP
19
Figure 5 Data Filter Design
with R_F1int=R_F2int=R
C14
=
2Q b
R2πf_3dB
C12
=
b
4QRπf_3dB
with
Q= ^b
a
Q is the qualify factor of the poles where, in case of a Bessel filter a=1.3617, b=0.618
and thus Q=0.577
and in case of a Butter worth filter a=1.414, b=1
and thus Q=0.71
Example: Butter worth filter with f_3dB=5kHz and R=100kΩ:
C14=450pF, C12=225pF
1) taken from Tietze/Schenk: Halbleiterschaltungstechnik, Springer Berlin, 1999
Data Sheet
21
V 1.0, 2007-05-02