ib technology
2) The Micro RWD is designed to generate a 13.56 MHz carrier frequency in short
bursts of energy with a peak-to-peak voltage of up to 60 volts. This RF field is only
turned-on whenever there is card communication and for the remainder of time the
RF field is off. This dramatically reduces the average current consumption to around
20ma with short bursts of up to 200ma.
3) Generally for 65mm diameter wound antenna or similar sized PCB antenna the
range is around 5 cm, larger antenna (10 – 15cm diameter) can achieve up to 10cm
range under ideal conditions. Lower burst current can be achieved by adjusting the
series resistors in the antenna loop circuit (ensuring Q value is around 35-40).
4) Sample antenna supplied are for evaluation only. The characteristics of an antenna
for EMC approval will vary according to shape of coil, type of wire, style of
winding, bobbin material, spacing between windings or PCB track design and PCB
material etc.
5) The antenna coil (PCB or wire wound) should be positioned as close to the capacitor
components as possible and the coil-capacitor (LC) arrangement should be no more
than 3cm from the MicroRWD module for optimum performance. For longer
distances a screened twisted-pair antenna cable can be used with an impedance
matching transformer, this technique is not described here.
6) The position and environment of the antenna in the final applications should be
taken into account and a trimming capacitor can be used to adjust the capacitance to
fine tune the LC arrangement back to 13.56 MHz resonance. An oscilloscope should
be connected ACROSS the antenna coil connections. With NO transponder card in
the field a pulsed 13.56 MHz sine wave will be seen with a peak-to-peak voltage of
up to 60 volts. The trimming capacitor should be adjusted to achieve the highest
amplitude of sine wave. The antenna resistance should then be checked to ensure the
Quality factor is correct. The capacitor and coil inductance values have been
carefully chosen for optimum performance so any custom antenna should be
designed to be as close to this arrangement as possible.
7.5 ms
100ms (default polling delay)
Antenna waveform
13.56 MHz
NO card in field – RF duty cycle
60v peak-to-peak measured
across the antenna coil
NOTE THAT OPTIMUM PERFORMANCE (BEST SIGNAL TO NOISE RATIO) IS ACHIEVED
WHEN PEAK-TO-PEAK ANTENNA VOLTAGE IS APPROXIMATELY 50 VOLTS.
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