TDA5235
Applications
There are two different cases, which need to be checked for the desired receive
channel(s):
Elimination of in-band EMI mixing with (2*M + 1) * fLO, where M > 0:
A square wave is used as LO (Local Oscillator) for the switching-type mixer, which also
has odd harmonics. When the harmonics of the EMI source are exactly the IF frequency
away from the harmonics of the LO, these spurs will be down-converted to the IF
frequency and act as a co-channel interferer within the receiver’s channel bandwidth
mainly in the 315 MHz band.
In this case a change of the LO injection side (high side or low side injection) can be
applied.
Example (Low Side LO-injection):
Wanted channel fRF = 314.233MHz ==> fLO = 303.533MHz ==> 3*fLO = 910.599MHz
fXOSC = 21.948717 MHz ==> 41 * fXOSC = 899.8974 MHz
Resulting IF = 910.599 - 899.8974 MHz = 10.702 MHz ==> co-channel interferer
within the receiver’s channel bandwidth ==> change LO injection side
Example (High Side LO-injection):
Wanted channel fRF = 314.233 MHz ==> fLO = 324.933 MHz ==> 3*fLO = 974.799 MHz
fXOSC = 21.948717 MHz ==> 44 * fXOSC = 965.744 MHz; 45 * fXOSC = 987.692 MHz
==> both XOSC harmonics are not generating a co-channel interferer at 10.7 MHz
A final sensitivity measurement on the application hardware is recommended.
Elimination of in-band EMI mixing with 1 * fLO:
Assuming a harmonic (N * fSRC) is falling within the BW of the wanted channel and has
an impact on the sensitivity there. In this case another XTAL frequency shall be selected,
e.g. 10 kHz away
| N * fSRC - fLocalOscillator | < BWChannel
Example (e.g. EMI source TDA5235 XOSC):
fXOSC = 21.948717 MHz ==> 42 * fXOSC = 921.846114 MHz
For further details please refer to the corresponding application note or to the latest
configuration software.
3.1
Configuration Example
Please see configuration files supplied with the Explorer tool.
Data Sheet
130
V1.0, 2010-02-19
INFINEON [ Infineon ]
