TDA5250D2_07 Datasheet, PDF (75/94 Pages) Infineon Technologies AG – ASK/FSK 868MHz Wireless Transceiver

TDA5250 D2
Version 1.7
Application
The best sensitivity performance can be achieved using a data filter bandwidth of 1.25 times the
maximum occuring data frequency.
The IQ filter setting is depending on the modulation type. ASK needs an IQ filter of 50kHz, 50kHz
deviation at FSK recommend a 100kHz IQ filter and 100kHz deviation were measured with a
150kHz IQ filter
A very practicable configuration is to set the chip-internal adjustable IQ filter to the sum of FSK peak
deviation and maximum datafrequency. Concerning these aspects the bandwidth should be chosen
small enough. With respect to both, the crystal tolerances and the tolerances of the crystal oscillator
circuit of receiver and transmitter as well, a too small IQ filter bandwidth will reduce the sensitivity
again. So a compromise has to be made. For further details on chip tolerances see also Section
3.2.7
3.10.2 Sensitivity depending on the ambient Temperature
Demonstrating a wide band of application possibilities the temperature behavior must not be
forgotten. In automotive systems the required temperature range is from -40 °C to +85 °C. The
receivers very good performance is documented in the following graph. The selected supply
voltage is 5V, the influence of the supply voltage can be seen in the following Section 3.10.3
The IQ filter setting can be taken from the legend of Figure 3-37.
BER_Temp_5V.wmf
Figure 3-37 Temperature Behaviour
Figure 3-37 shows that ASK as well as FSK sensitivity is in the range of -110 to -111dBm at 20°C
ambient temperature for a BER of 2E-3.
Notice that the sensitivity variation in this temperature range of -40 °C to +85 °C is only about 1.5
to 2 dB.
Data Sheet
75
2007-02-26