MLX90109 Datasheet, PDF (5/9 Pages) List of Unclassifed Manufacturers – 125kHz RFID Integrated Transceiver

MLX90109
125kHz RFID Integrated Transceiver
Correction network
For a typical application, where 2kbaud date has to
be sent to a transponder using a Manchester or
Biphase encoding scheme, the most important
harmonics lie in a bandwidth between 400Hz and
3.6kHz.
As can be seen from the graphs below, the antenna
parameters can significantly reduce the available
bandwidth [FL, FH].
With a suitable correction network, the 3dB points
can be shifted to extend the possibilities.
Important system parameters are data rate, antenna
inductance (Lreader) and antenna quality factor
(Qreader).
In the time domain we optimize the shape of the
amplitude modulation on the reader antenna by
applying that correction network.
Calculation
In the graph below the transfer function of the
MLX90109 is given.
• The first Zero (Fi) is determined the by the
MLX90109 and is typically 70Hz.
• The Poles (FL and FH) are set by the Open loop
Gain (G=2mA/V) of the MLX90109 and the
Antenna Impedance Zant, which is system
dependent. In the graphs below the
dependency of both poles on applied inductance
and for 2 quality factors are reflected. It is clear
that the bandwidth reduces significantly with
increase of Qreader.
Remark: Amax = G*Zant
A correction network with a single pole/zero couple
can increase the bandwidth by moving FH to FHH.
A more complex correction network with 2 pole/zero
couples can also improve the signal loss in case of
important low frequency harmonics (DC like signals).
In the Frequency domain this means FL is shifted
towards Fi
dB(Vampl/Vmodu)
MLX90109
A_max
0
f_i f_L
f_H
Correction network with ... single pole/zero:
... double pole/zero:
0
f_i
f_L
f_H
f_HH
-A_max
A_max
0
MLX90109 + different correction networks
f_i
f_L
f_H
f_HH
Frequency Domain
MLX90109 Parallel Resonant transceiver
Page 5 of 9
F_H -> F_HH
F_L -> F_i
Time Domain
Rev 1.4 19-Dec-00