TDA5200 Datasheet, PDF (24/43 Pages) Infineon Technologies AG – ASK Single Conversion Receiver

TDA 5200
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
(1)
(2)
C1 = -R---2-2---Q_Π-----f--₃--b-_d--_B--
with
Q = -----b-
a
where
in case of a Bessel filter
and thus
C2 = _{4----Q----R-----Î} --b---f--₃---_d--_B--
(3) the quality factor of the poles
a = 1.3617, b = 0.618
Q = 0.577
and in case of a Butterworth filter
and thus
a = 1.141, b = 1
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, March 2000