TDA5250D2_07 Datasheet, PDF (55/94 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

TDA5250 D2
Version 1.7
Application
QOSC_FSK.wmf
Figure 3-17 FSK modulation
In receive mode the crystal oscillator frequency is set to yield a direct-to-zero conversion of the
receive data. Thus the frequency may be calculated as
f_COSC = f_RF / 48,
e.g.
[3 – 22]
f_COSC = 868,3E6 / 48 = 18.0833MHz
which is identical to the ASK transmit case.
XOUT 19
L
f, C_L
XIN 21
C_V1
XSWF 20
XSWA 22
C_V2
C_V3
XGND 23
-R
C_tune1
C_tune2
Figure 3-18 FSK receive
In this case the ASK-switch is closed. The necessary C_vm is given by:
QOSC_ASK.wmf
Cvm = -⁽--C-C---v--v--1-1---+--+---C-C---t--tu--u--n-n--e--e-1--1--⁾--+-^â‹---⁽-C--C---v-v--2-2---+--+---C--C---v-v--3--3---+-+---C--C---t-t-u-u--n--n--e-e--2-2----⁾
[3 – 23]
The C-bank C_tune2 can be varied over a range of 16 pF in steps of 250fF for finetuning of the FSK
receive frequency. In this case the switches of the C-bank are controlled by the bits D0 to D5 of the
XTAL_TUNING register (subaddress 02H, see Table 3-5).
3.2.2.2 ASK-mode:
In transmit mode the crystal oscillator frequency is the same as in the FSK receive case, see
Figure 3-18.
In receive mode a receive frequency offset is necessary as the limiters feedback is AC-coupled.
This offset is achieved by setting the oscillator frequency to the FSK HIGH transmit frequency, see
Figure 3-17.
Data Sheet
55
2007-02-26