Capacitor Values Expanding Antenna Tuning Range To Higher Values - Texas Instruments 2000 Series Reference Manual

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Note: It is not recommended to use antennas with Q factors lower than 50. Antennas with
inductances lower than 13.7 µH or more than 37.8 µH should not be used except when
connecting two antennas in series since the additional capacitor values become very
large. Antennas with fewer turns (i.e. smaller inductance) generate less charge-up field
strength under the same operating conditions and in addition also have less receive
sensitivity. Using capacitors parallel to the antenna resonator changes the coupling of the
RFM's transmitter power stage thus reducing the generated field strength.
In order to avoid adaptation problems, it is strongly recommended to use standard
TI-RFid antennas.
SCBU022 – November 2002
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Table A-2. Capacitor Values Expanding Antenna
Tuning Range to Higher Values
Antenna inductance range
28.0 µH to 29.3 µH
29.4 µH to 31.0 µH
31.1 µH to 32.4 µH
32.5 µH to 33.8 µH
33.9 µH to 35.0 µH
35.1 µH to 36.2 µH
36.3 µH to 37.6 µH
Two serial connected TI-RFid
standard antennas
(1)
C1, C2, and C3 = 47 nF
(1)
Capacitor Value
C4 = 18.3 nF
(parallel 6.8 nF, 6.8 nF, 4.7 nF)
C4 = 13.6 nF
(parallel 6.8 nF, 6.8 nF)
C4 = 10 nF
C4 = 6.8 nF
C4 = 3.98 nF
(parallel 3.3 nF, 0.68 nF)
C4 = 2.2 nF
C4 not needed
C4 = 3.3 nF
C2 and C3 not needed
Expanding Antenna Tuning Inductance Range
Appendix A
35