NXP Semiconductors
AN11740
PN5180 Antenna design
AN11740
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Application note
COMPANY PUBLIC
Rev. 1.1 — 19 June 2018
345311
13 of 62
3. Generic PCD antenna design rules
Some of the antenna and analog design rules are very common for NXP NFC Reader
designs, i.e. they do neither specifically depend on the used standard (ISO, NFC or
EMVCo) nor depend on the NXP Reader IC but rather on physical or technical basics.
3.1 Optimum Antenna Coil
The optimum antenna coil size for a standard PCD can be derived from the Biot-Savart
law. The major prerequisites are some simplifications like the assumption that the
antenna system is optimized based on the parallel operation of smart cards on top of the
PCD antenna. The optimization is derived for the operating distance, i.e. the target is to
show the optimum PCD antenna size for a given required operating distance.
The principle and simplified electrical circuit is shown in Fig 9.
(1) Index 1: PCD
(2) Index 2: PICC
Fig 9.
PCD & PICC Antenna coil system
The index 2 indicates the parameters of the PICC. Here the PICC is taken as given, i.e.
the parameters with the index 2 cannot be modified. This is another simplification, but
also refers to the reality, where the reader antenna optimization does not allow to change
card parameters.
The PCD antenna is taken as a circular antenna to allow a simple calculation. The impact
of different form factors is discussed later.
Out of this law the coupling coefficient
k
between PCD and PICC antenna can be
described as following:
