TDA5212_06 Datasheet, PDF (25/49 Pages) Infineon Technologies AG – ASK/FSK 915MHz Single Conversion Receiver

TDA 5212
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
C₂
Pins:
22
21
19
R
R
100k
100k
Figure 4-3 Data Filter Design
Filter_Design.wmf
C1 = ^{2Q b}
R2Πf_3dB
C2 =
b
4QRΠf _3dB
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 = 1.141, b = 1
and thus Q = 0.71
Example: Butterworth filter with f_3dB = 5kHz and R = 100kΩ:
C₁ = 450pF, C₂ = 225pF
1. taken from Tietze/Schenk: Halbleiterschaltungstechnik, Springer Berlin, 1999
Wireless Components
4-4
Specification, December 2006