NXP Semiconductors
AN11740
PN5180 Antenna design
AN11740
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Application note
COMPANY PUBLIC
Rev. 1.1 — 19 June 2018
345311
47 of 62
Fig 43. PN5180 Rx block diagram
The optimum register settings might be different from the default values stored in the
EEPROM. So, for the optimization and testing typically the registers can be tuned and
changed directly. As soon as the optimum settings are derived, the new settings might be
changed and stored in the corresponding EEPROM area for the LOAD_RF_CONFIG.
Then in the final application simply the standard LOAD__RF_CONFIG command can be
used again with the optimized settings, and no modification of the application sw is
required.
The NFC Cockpit (GUI) supports this optimization procedure, refer to [9] for details
regarding the evaluation board and the use of the GUI.
The default settings in the EEPROM are optimized for the PN5180 based on the 65mm x
65mm evaluation board antenna. Some of these settings typically must be adjusted and
optimized for other antenna designs.
4.5.1 External Rx components
The RxP and RxN are connected to the antenna circuit. Typically, there is a standard
coupling capacitor used to connect the Rx circuit to the EMC filter (see Fig 19). External
filtering normally is not required.
The voltage level at the RxN and RxP must be high enough to achieve a good sensitivity,
but must not exceed the given limit (see [1]).
Typically, the serial resistor
R1A and R1B is in the range of 1…10kΩ. The exact value
can be chosen with the help of the AGC: the Rx resistor values must be chosen in such
way that
AGC_VALUE ≈ 300dec (in RM, antenna design for full NFC)
AGC_VALUE ≈ 600dec (in RM, antenna design for RM only)
The test can be done in the following steps:
1.
Choose R1A and R1B (e.g. start with 4.7kΩ).
2. Apply the default AGC settings, e.g. with the default LOAD_RF_CONFIGfor type
A@106, ensure the gear 0 is used (if DPC is enabled), ensure that the antenna is not
loaded and switch on the carrier.
3. Read the AGC_VALUE.
4. Decrease R1A and R1B, if AGC_VALUE > 350 (or 700 for pure RM).
5. Increase R1A and R1B, if AGC_VALUE < 250 (or 500 for pure RM).
