TDA5255E1_07 Datasheet, PDF (53/91 Pages) Infineon Technologies AG – ASK/FSK 434MHz Wireless Transceiver

TDA5255 E1
Version 1.2
Application
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 / 24,
e.g.
[3 – 22]
f_COSC = 434,16E6 / 24= 18.09MHz
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----v----1----+-----C----t--u----n---e---1----⁾---^â‹---⁽---C----v---2-----+-----C----v----3----+-----C----t--u----n---e---2----⁾
Cv1
+
Ct
un
e
1
+
Cv2
+
C
v3
+
Ct
un
e2
[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.
3.2.3 Parasitics
For the correct calculation of the external capacitors the parasitic capacitances of the pins and the
switches (C₂₀, C₂₁, C₂₂) have to be taken into account.
Data Sheet
53
2007-02-26