Digital implementation of a demodulator for HF RFID reader device

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Abstract


This paper presents a demodulator for high frequency radio frequency identification (HF RFID) signals based on the Costas loop [1]. A description is presented of how correlation between two signals can be simplified in terms of the operations involved and implemented using a digital Costas loop [2, 3]. The demodulator is used to demodulate a subcarrier signal, after carrier direct conversion and bandpass filtering. A brief description is given of the signal characteristics of HF RFID signals at a carrier frequency of fc = 13.56 MHz and the operation of the subcarrier demodulator. Packet error rate (PER) measurement results for protocols ISO/IEC 14443 type A and type B at a bitrate fc/128 (approximately 106 kbit/s), FeliCa at fc/64 (approximately 212 kbit/s), and ISO/IEC 15693 at fc/512 (approximately 26.48 kbit/s) are presented. A comparison is given between the measured PER results and the theoretical BPSK PER limit,  and with a HF RFID reader IC ST25R3911 [4], where an almost 11 dB improvement in PER performance for ISO/IEC 14443 type B fc/128 was achieved.


Keywords


HF RFID reader; digital demodulator; correlation; Costas loop; packet error rate

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References


J. Costas, “Synchronous Communications,” Proceedings of the IEEE, vol. 44, p. 1713-1718, 1956.

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