TDA5230 Datasheet, PDF (89/186 Pages) Infineon Technologies AG – Universal Low Power ASK/FSK Single Conversion Multi-Channel Image-Reject Receiver

2.4.10 Digital FSK Demodulator
TDA523x
Functional Description
from
IF-Limiter
DIGITAL-DOWN-CONVERTER
I
Q
Direct Digital
Synthesizer
Filter
CIC
I
Decimator
CIC
Q
Decimator
Demodulator
DAM
to
Digital-
Receiver
Figure 43 Digital FSK Demodulator
The Digital FSK Demodulator has three major units:
• Digital Down Converter
• CIC Filter
• Demodulator
Digital Down Converter
The output signal of the limiter amplifier at an IF-center-frequency from 10.7 MHz is
converted to near baseband by an I/Q mixer, driven from a programmable Direct Digital
Synthesizer.
The programming of the Direct Digital Synthesizer is done with the registers FSKNCO0,
FSKNCO1 and FSKNCO2.
NCO value calculation:
TDA5230:
For Lo-Side LO Injection mode operation:
NCO_dec

= round_2²⁴ *

f _SYS
4
− ( f_SYS −
f _SYS
f
IF
)






Data Sheet
85
Version 4.0, 2007-06-01