NXP Semiconductors
AN145715
PN544 Antenna Design Guide
145715
© NXP B.V. 2006. All rights reserved.
Application Note
Rev. 1.5 — 28th August 2009
11 of 43
Decreasing the amplitude rise time after a modulation phase
Increasing the receiving bandwidth
The EMC filter and the matching circuit must transform the antenna impedance to the
required TX matching resistance Z
match
(f) at the operating frequency of f = 13.56 MHz.
Fig. 6 Impedance transformation
The measured Z
match(f)
can be remodeled in an equivalent circuit loading each TX pin with
R
match/2
.
When cutting the circuitry after the EMC filter the precondition Rmatch/2 needs to be
introduced to calculate the remaining components.
Note, that R
match/2
does not reflect the driver resistance!
Fig. 7 Definition of transformation impedance Ztr
tr
tr
tr
jX
R
Z
+
=
tr
tr
tr
jX
R
Z
−
=
*
EMC filter general design rules:
L
0
= 390nH - 1µH
