TDA5220 Datasheet, PDF (28/44 Pages) Infineon Technologies AG – ASK/FSK Single Conversion Receiver

confidential
TDA 5220
preliminary
Applications
4.6 ASK/FSK Switch Functional Description
from RSSI Gen
(ASK signal)
FSK PLL Demodulator
0.18 mV/kHz
typ. 2 V
1.5 V......2.5 V
The TDA5220 is containing an ASK/FSK switch which can be controlled via
Pin 15 (MSEL). This switch is actually consisting of 2 operational amplifiers that
are having a gain of 1 in case of the ASK amplifier and a gain of 11 in case of
the FSK amplifier in order to achieve an appropriate demodulation gain charac-
teristic. In order to compensate for the DC-offset generated especially in case
of the FSK PLL demodulator there is a feedback connection between the
threshold voltage of the bit slicer comparator (Pin 20) to the negative input of
the FSK switch amplifier.
In ASK-mode alternatively to the voltage at Pin 20 (SLN) a value of approx. 87%
of the peak-detector output-voltage at Pin 26 (PDO) can be used as the slicer-
reference level. The selection between these modes is controlled by Pin 16
(SSEL). This is shown in the following figure.
MSEL
15
H=ASK
L=FSK
ASK/FSK Switch
-
+ _ASK
+ ^FSK
-
R₁=100k
Data Filter
R₂=100k
v=1
R₃=300k
PEAK
DETECTOR
R=56k
PDO
26
C=100 nF
R=390k
Comp
-
+ _CP
25
+ ^CM
-
H=CP
L=CM
DATA Out
R₄=30k
ASK mode: v=1
FSK mode: v=11
22
21
FFB
OOP
19
SLP
20
16
SLN
SSEL
C₁
R
C₂
C
Figure 4-7 ASK/FSK mode datapath
ask_fsk_datapath.WMF
Wireless Components
4-8
Target Specification, October 2001