DocID029132 Rev 3 21/25
UM2042 Antenna matching
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With the new assembled values, the matching impedance looks as in Figure 14, with a
value close to 11 + j6 Ω.
Figure 14. NFC Forum matching with an AAT setting of 11
The HW based AAT algorithm will typically adjust to an AAT value of 11. Due to the higher
Q-Factor the voltage on the antenna is also increasing. To put the receiver in an optimum
signal level range, the capacitors C401 and C412 can be increased to 100 pF.
Table 1. NFC Forum matching alternatives
Default assembly Value NFC Forum replacement Value
C403 80 pF C403_NFCF 120 pF
C410 180 pF C410_NFCF 120 pF
R401 3R9 R401_NFCF 1R96
R402 3R9 R402_NFCF 1R96
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