ib technology

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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.

60v peak-to-peak measured

across the antenna coil

Antenna waveform

13.56 MHz

NO card in field – RF duty cycle

7.5 ms

100ms (default polling delay)

NOTE THAT OPTIMUM PERFORMANCE (BEST SIGNAL TO NOISE RATIO) IS ACHIEVED

WHEN PEAK-TO-PEAK ANTENNA VOLTAGE IS APPROXIMATELY 50 VOLTS.