tda5235 Infineon Technologies Corporation, tda5235 Datasheet - Page 130

• Manufacturer Part Number: tda5235
• Description: Enhanced Sensitivity Double-configuration Receiver With Digital Baseband Processing
• Manufacturer: Infineon Technologies Corporation

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) * f
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):
Example (High Side LO-injection):
A final sensitivity measurement on the application hardware is recommended.
Elimination of in-band EMI mixing with 1 * f
Assuming a harmonic (N * f
an impact on the sensitivity there. In this case another XTAL frequency shall be selected,
e.g. 10 kHz away
Example (e.g. EMI source TDA5235 XOSC):
For further details please refer to the corresponding application note or to the latest
configuration software.
3.1
Please see configuration files supplied with the Explorer tool.
Data Sheet
Wanted channel f
f
Resulting IF = 910.599 - 899.8974 MHz = 10.702 MHz ==> co-channel interferer
Wanted channel f
f
==> both XOSC harmonics are not generating a co-channel interferer at 10.7 MHz
| N * f
f
XOSC
XOSC
XOSC
within the receiver’s channel bandwidth ==> change LO injection side
= 21.948717 MHz ==> 41 * f
= 21.948717 MHz ==> 44 * f
SRC
= 21.948717 MHz ==> 42 * f
Configuration Example
- f
LocalOscillator
RF
RF
= 314.233 MHz ==> f
= 314.233MHz ==> f
| < BW
SRC
) is falling within the BW of the wanted channel and has
Channel
XOSC
XOSC
XOSC
130
= 899.8974 MHz
= 965.744 MHz; 45 * f
= 921.846114 MHz
LO
LO
= 324.933 MHz ==> 3*f
LO
= 303.533MHz ==> 3*f
:
LO
, where M > 0:
XOSC
LO
LO
= 987.692 MHz
V1.0, 2010-02-19
= 974.799 MHz
= 910.599MHz
Applications
TDA5235