Parameter characterisation and automatic impedance matching of 13.56 MHz NFC antennas

The underlying paper and investigations deal with the main functionality and physical parameters of contactless smartcard and NFC (Near Field Communication) devices. The specific need of impedance matching for reader devices is pointed out in particular, as the correct matching represents a major performance indicator of the system. Therefore, in a first step, the dedicated parameters are analyzed for a reader device. Based on these insights, detailed analysis of the concept, the implementation and the verification of an automatic impedance matching circuit for NFC antennas with a frequency of 13.56 MHz is given. Besides an introduction to manual tuning and its issues, the fundamental components of an automatic tuning system are outlined. A lab-scaled prototype is built and demonstrated. Finally, the successful operation of this system is tested with several different antennas. Furthermore, the effects of detuning due to dynamic behavior are pointed out, characterizing the need for further investigations.