External antenna matching or tuning on VTAP50

A matching or tuning circuit ensures that there is maximum power transmitted between the antenna and the RF transmitter device, with the antenna working only in the desired frequency band (13.56MHz), and minimum signal loss between the transmitter and antenna (Return Loss/VSWR). Tuning is essential to NFC transmission, since imperfect antenna matching or tuning can cause high power loss and poor antenna performance, and in some cases lead to circuit failure.

We have designed the matching circuits with for various off-the-shelf NFC antennas, which could be readily used with the VTAP50. (These tuning circuits are not off-the-shelf accessories, only examples of the type of design required. You will need to make design decisions about where best to accommodate the tuning circuit, refer to External antenna choices.) The example antennas are:

• Pulse Antennas W7002- NFC Wire Loop Antenna

• Pulse Antennas W7013- Small Planar NFC Antenna with Ferrite

• Molex Antennas 146236-2131 NFC Coil 45x55mm

• Molex Antennas 146236-2122 NFC Coil 34x46mm

• Molex Antennas 146236-2102 NFC Coil 15x25mm

• Molex Antennas 146236-2151 NFC Coil 15x15mm

Component values provided in the following tables to integrate the example antennas, all relate to the tuning circuit diagram Example board schematic for antenna matching or tuning above.

Matching circuit examples for off‑the‑shelf antennas