TDA5250D2_07 Datasheet, PDF (21/94 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

TDA5250 D2
Version 1.7
Functional Description
2.4.8 FSK Demodulator
The output differential signals of the I/Q limiters are fed to a quadrature correlator circuit that is used
to demodulate frequency shift keyed (FSK) signals. The demodulator gain is 2.4mV/kHz, the
maximum frequency deviation is ±300kHz as shown in Figure 2-4 below.
The demodulated signal is applied to the ASK/FSK mode switch which is connected to the input of
the data filter. The switch can be controlled by the ASKFSK pin (pin 4) and via the D11 bit in the
CONFIG register.
The modulation index m must be significantly larger than 2 and the deviation at least larger than
25kHz for correct demodulation of the signal.
1,6
1,5
1,4
1,3
1,2
1,1
1
0,9
0,8
0,7
0,6
0,5
-350 -300 -250 -200 -150 -100 -50 0 50 100 150 200 250 300 350
f /kHz
Figure 2-4 Quadricorrelator Demodulation Characteristic
Qaudricorrelator.wmf
2.4.9 Data Filter
The 2-pole data filter has a Sallen-Key architecture and is implemented fully on-chip. The bandwidth
can be adjusted between approximately 5kHz and 102kHz via the bits D4 to D7 of the LPF register
as shown in Table 3-10.
Data Sheet
21
2007-02-26