Expanding Antenna Tuning Inductance Range; Circuit For Expanding Antenna Tuning Range To Lower Values - Texas Instruments 2000 Series Reference Manual

Expanding Antenna Tuning Inductance Range

It is possible to expand the tuning range of the antenna inductance. This may be necessary when TI-RFid
standard antennas are used close to metal, when antenna extension cables are used or when customer
specific antennas which might not be within the necessary antenna tuning inductance range are used.
Note: Please remember that the capacitors of external modules have to be able to withstand
higher voltages when used together with a RFM.
Expanding the antenna tuning inductance range to lower or higher values can be done by connecting
additional capacitors in parallel and in series to the antenna resonator.
The capacitors have to be connected in parallel and in series in order to withstand high voltages and
currents occurring at the antenna resonance circuit.
THERE
RESONATOR COMPONENTS, WHICH MAY BE HARMFUL TO
HEALTH. THE RFM MUST BE SWITCHED OFF WHILE WORKING
ON IT. EXTERNAL COMPONENTS MUST BE MOUNTED SUCH
THAT THEY CANNOT BE ACCIDENTALLY TOUCHED.
To ensure that the RFM functions correctly when the antenna tuning inductance range is expanded,
special capacitors, as listed below, must be used:
Capacitor type:
• Polypropylene film capacitor
• Minimum 1250V DC operating voltage
• Capacitance tolerance: max. ±5%
• Type: SIEMENS "KP" or WIMA "FKP1
The antenna tuning inductance range can be decreased to 13.7 µH in six ranges, as shown in
and Table A-1.
Figure A-1. Circuit for Expanding Antenna Tuning Range to Lower Values
SCBU022 – November 2002
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IS HIGH VOLTAGE
ANT 2
ANT 1
WARNING
PRESENT AT
C1
Expanding Antenna Tuning Inductance Range
Appendix A
SCBU022 – November 2002
ALL ANTENNA
Figure A-1
C3
C4
33