User's Manual

UM2252
Component description
DocID030806 Rev 2
15/26
4.2.3 Antenna and matching network components
This schematic diagram contains the matching network and the automatic antenna tuning
capacitors as well as the alternative NFC Forum matching components.
In the default configuration, the X-NUCLEO-NFC05A1 expansion board is populated with a
VHBR tuning, which allows communication to speed up to 3.4 Mbps.
The Q-factor is doubled and bitrates up to 848kbps are supported, by switching the
components listed in the following table.
Table 3: Matching variant
VHBR Matching
NFC Forum Matching
C302
C302_NFCF
C309
C309_NFCF
R300
R300_NFCF
R301
R301_NFCF
To support VHBR bit rates, the antenna is matched to a system Q-Factor of 8.
By switching to the NFC Forum matching components, the system Q-Factor is increased to
16. This can increase read range by up to 20% depending on the communication
technology, but limits the maximum supported bit rate to 848kbps.
a
.
The etched PCB antenna can be easily removed from the expansion board to connect a
custom antenna using the connector J300.
The matching topology supports the connection of one custom differential antenna or two
single-ended antennas. The two single-ended antennas can then be multiplexed in
software using the single and rfo2 bits of IO Configuration Register 1.
a
Further information about antenna matching can be found at www.st.com/st25r