The Fig 20 shows the driver current ITVDD versus the antenna impedance. The target impedance to get a maximum field strength and power transfer should be close to 20Ω.(PN5180 Antenna design guide.pdf)
but the other part is 50Ohm,what is correct?
20OHM impedance is between TX line & antenna;
50OHM impedance is between signal line & GND.
Understand my explanation?
So the antenna tuning in this case should be done to match with 20Ohm or 50Ohm for maximum reading distance (not working on a battery).
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