NXP Semiconductors
AN11740
PN5180 Antenna design
AN11740
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Application note
COMPANY PUBLIC
Rev. 1.1 — 19 June 2018
345311
29 of 62
a. Symmetrical tuning (requires DPC)
b. Asymmetrical tuning (requires DPC disabled)
Fig 24. Tuning options
Asymmetrical tuning
The asymmetrical tuning is the standard tuning as taken e.g. from the existing CLRC663
design recommendations. It uses EMC cut off frequencies >17MHz, which results in an
asymmetrical transfer function, but shows a good detuning and loading behavior (see
section 4.2.2). The asymmetrical transfer function has some disadvantages regarding the
pulse shapes and receiver performance, and requires a slightly reduced Q factor of the
antenna coil circuit itself.
This tuning is available with the PN5180 like with any other NXP Reader IC and shown in
the following sections, too.
Based on this the following EMC filter values are chosen:
L0 = L0A = L0B = 470nH
C0 = C0A = C0B = 56pF + 68pF
f
Cutoffasym
= 20.9MHz
Note:
This EMC filter is taken from the existing CLRC663 designs. The chosen values
of the inductance, the cut off frequency and the corresponding capacitance have
shown to be a reasonable trade-off between the transfer function for the transmit
signal as well as for the receive signal on one hand and the filter function to
suppress the higher harmonics on the other hand.
Note:
The standard “asymmetrical” antenna tuning requires the DPC to be disabled.
Symmetrical tuning
The symmetrical tuning, which is required for the DPC, provides a better transfer function
and allows a higher Q factor compared to the asymmetrical tuning. However, the related
disadvantage is typically a much higher field strength under loading conditions as well as
a much higher ITVDD under loading conditions. This might even exceed the ISO or
