TDA5250D2 Datasheet, PDF (59/97 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

confidential
TDA 5250 D2
preliminary
Applications
In this case the ASK-switch is closed. The necessary C_vm is given by:
C_vm
=
(_---C_{----v---1----}+_-----C_{----t--u--n---e--1---})_----⋅_---(_--C_{----v---2----}+_-----C_----v---3---+_-----C_{-----t-u---n---e--2---})
C_v1 + C_tune1 + C_v2 + C_v3 + C_tune2
[4 – 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 4-5).
4.2.2.2 ASK-mode:
In transmit mode the crystal oscillator frequency is the same as in the FSK
receive case, see Figure 4-18.
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 4-17.
4.2.3 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.
XOUT 19
f, C_L
XIN 21
C_V1
XSWF 20
XSWA 22
C_V2
C_V3
XGND 23
L
-R
C₂₁
C_tune1
C₂₂
C₂₀
C_tune2
Figure 4-19 parasitics of the switching network
QOSC_parasitics.wmf
Wireless Components
4 - 19
Specification, July 2002