HF RFID transponder with phase demodulator for very high bit-rates up to 13.56 Mbit/s

Abstract

Sending larger data volumes over an air interface requires high transmission rates and a demodulator to recognize this data. Amplitude demodulators have been used in the past to detect data rates up to 848 kbit/s and phase demodulators have been used to achieve data rates of 424 kbit/s. This paper presents a 13.56 MHz HF transponder with a phase demodulator for very high bit-rates based on the passive near field coupling. The integrated phase demodulator detects phase modulated signals with a bit-rate up to 13.56 Mbit/s at an operating range of 4 cm. On the transponder chip a complete RFID analog front end is integrated. It includes a typical common HF-RFID antenna, for high data rates optimized shunt, phase demodulator and load modulator. A novel phase demodulator principle is introduced in this paper. It uses phase-locked loop (PLL) to obtain accurate time reference for the phase detectors. This allows recognizing the phase shift by the comparison of the incoming phase modulated data with the phase of the time reference. The phase demodulator reported in this paper uses two phase detectors working in an alternating mode. This solution allows to recognize phase shifts of the received data from the antenna with double data rate compared to the solution with one phase detector. The demodulator has been implemented in a 90 nm Flash CMOS technology with a supply voltage of 1.5 V and a power consumption of 0.56 mW. Measurement results show that the phase demodulator is able to recognize very small phase changes down to 5 degrees at a bit rate of 13.56 Mbit/s.