Adjustable duty cycle ASK demodulator for passive UHF RFID tags

In order to improve the sensitivity of passive ultrahigh frequency (UHF) radio frequency identification (RFID) tags and increase the operation distance, usually the threshold voltage compensation technology was used to reduce the drop voltage of the charge transfer transistor in the envelope circuit of the demodulator. In this paper, the duty cycle of the signal is calibrated so that it is not affected by the difference between the drive capability of PMOS and NMOS transistors, and by the fluctuation of process, voltage and temperature (PVT). The proposed demodulator has been implemented in TSMC 0.18μm CMOS process. With the carrier frequency of 920 MHz and the data rates of 80 Kbit/s, the minimum input RF signal amplitude of the demodulator is 100 mV, and the minimum modulation index is 20%. The power consumption of the demodulator is 0.24 μW with the supply of 1 V, and the duty cycle that the circuit can calibrate ranges from 40% to 60%.