EVB90109 Melexis Inc, EVB90109 Datasheet - Page 8

• Manufacturer Part Number: EVB90109
• Description: BOARD EVAL FOR MLX90109
• Manufacturer: Melexis Inc
• Type: Development kitr

Specifications of EVB90109

• Contents: Evaluation Board
• For Use With/related Products: MLX90109
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

A typical coil quality factor (Q
This current resonance of the parallel antenna allows to build very low power reader base stations, contrary
to serial antenna based versions. Readers using a serial antenna can leverage their voltage resonance to
drive bigger antenna’s for long distance reading up to 1m, whereas the MLX90109 is designed to drive
antennas to obtain a reading distance of 1cm up to 15cm (6”) (depending on efficiency and dimensions).
The antenna impedance is an important system design parameter for the MLX90109.
(4)
The antenna impedance can also be calculated as:
(5)
From (4) and (5):
Finally in comparison with the formula (2):
(6)
From the formula above, it is clear that Q
the antenna supply current I
Using the previous formula (6), it is possible to define the proportionality between the total number of ampere-
turns, generating the magnetic field and the inductance of the antenna (With N
antenna coil) :
(7)
Hence, to generate a strong field, it is better to choose a low antenna inductance. Limitation to this is given by
the minimal antenna impedance (Z
(8)
Remarks:
Note for equation (4): Mind that in reality the strong coupling with the tag may drastically reduce the antenna
impedance.
3901090109
Rev 008
Q
N
8.3 Antenna Impedance
ant
ant
I
ant
res
Z
Z
I
N
L
L
ant
N
ant
ant
ant
ant
min
ant
I
Q
I
ant
I
Q
V
V
DDant
DDant
res
ant
V
res
ant
ant
ant
V
Z
ant
ant
min
L
L
ant
ant
res
res
L
1
DDant
ant
ant
L
) value is 23, resulting in antenna currents of about 100mA
ant
, hence it reduces the overall current consumption.
=>
with
ant
> 1k ) and the Q that one can achieve for such an antenna:
ant
L
Q
ant
has no influence on I
ant
I
Page 8 of 15
with
DDant
N
ant
2
res
res
V
ant
= 2 *Fres
L
ant
ant
. Increasing Q
125kHz RFID Transceiver
ant
ant
the number of turns of the
MLX90109
is equivalent to reduce
Data Sheet
Jun/06