RM310 NXP Semiconductors, RM310 Datasheet - Page 10

• Manufacturer Part Number: RM310
• Description: Ht Rm 310 Hitag Tm Mini Reader Module
• Manufacturer: NXP Semiconductors

HT RM310
02-10-1998
Rev. 2.3
2.4.3.
Measuring Inductance
The inductance of the designed coil can be determined using the following measuring procedure.
A sinus signal of 125 kHz is supplied by using a function generator. If you measure the current Î
and the antenna voltage Û
, the inductance can be calculated according to the following formula:
L

U
L
L
2
f

I
2.4.4.
Antenna Tuning
The antenna has to be tuned to its final form by using the connecting cable. You must not change
anything with the antenna coil or with the connecting cable, after having finished tuning the an-
tenna. If you do, the mechanical changes will influence the electrical values and the antenna will be
detuned again.
A sinus signal of 125 kHz is fed to the antenna connectors using a frequency generator. Now you
measure the voltages Û and Û
with an oscilloscope. Then change the frequency until Û and Û
R
R
are in phase.
If the resonance frequency achieved is too high, C
has to be increased. If it is too low, C
has to
S
S
be decreased.
The aim is to arrive at a resonance frequency of 125 kHz using C
.
S
The phase of impedance has to be in the range of +/- 10°.
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Htrm310.doc/HS