How to verify NFC antenna performance: Take PN7160 as an example
I have introduced before that there are symmetrical designs and asymmetrical designs in NFC antennas. Next, I would like to introduce to you how to verify the performance of the antenna.
Verification of card reader mode
In card reader mode, we can verify through the NCI command defined in PN7160. We can perform verification control through PN7160's own commands.
Here are the internal blocks of the RX receiver:
The RX block includes automatic gain control (AGC). The AGC regulates the voltage on the RX pin to achieve optimal receiver input voltage. To optimize the receiver input voltage, the AGC can use a voltage divider to attenuate the RX signal from the antenna. The series resistor is external to the device,
The shunt resistor is located in the RX module and can be switched within a certain range. The string value of resistor Rrx ranges from 1kΩ to 10kΩ. A value of 2.2 kΩ is a good starting value.
The Crx capacitor provides AC coupling of the RX signal. Typically a value of 1 nF can be used. After the Rrx resistor is assembled. Measurement of continuous RF fields and peak (maximum) voltage between RX and GND can be turned on as shown in Figure 36. Measurements were taken directly using the PN7160 device as described below.
Vrx voltage should be about 1.6Vp (±0.15V)
High Rrx -> Lower VRx voltage
Low Rrx -> higher VRx voltage
The PN7160 can also measure information about AGC values using NCI instructions
NCI: 2F 3D 04 02 C8 60 03.
For example :
NFC Factory Test application (NfcFactoryTestApp.c) can be used for:
Add the following two lines to the "do-while" loop at the end of the NfcFactoryTestApp.c code
The recommended AGC value is 500
0x02F6=758
AGC minimum value → 0x0000
AGC maximum value → 0x03FF
Conclusion:
The verification of the antenna in NFC is crucial. Without a good verification process, the probability of card reading failure will greatly increase.
It may also cause the common A1 error (antenna startup failure). In order to avoid such situations, NXP recommends that customers must confirm the performance verification of the antenna after completing the antenna design to ensure the normal operation of the antenna.
References:
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