TDA7210 Datasheet, PDF (25/52 Pages) Infineon Technologies AG – Wireless Components ASK/FSK Single Conversion Receiver

TDA7210
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.
C₁₄
C₁₂
Pins:
22
21
19
R
R
100k
100k
Figure 4-3 Data Filter Design
Filter_Design.wmf
C14 = ^{2Q b}
R2πf_3dB
C12 =
b
4QR πf _{3 dB}
with
Q= ^b
a
the quality 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 Butterworth filter a = 1.414, b = 1
and thus Q = 0.71
Example: Butterworth filter with f_3dB = 5kHz and R = 100kΩ:
C₁₄ = 450pF, C₁₂ = 225pF
1. taken from Tietze/Schenk: Halbleiterschaltungstechnik, Springer Berlin, 1999
Wireless Components
4-4
Data Sheet, December 2008