Differentiating ASK Demodulator for Contactless Smart Cards Supporting VHBR

This brief proposes an amplitude shift keying (ASK) demodulator that uses switched-capacitor differentiators to make it compliant with the very high bit rate amendment to the ISO/IEC 14443 standard for contactless smart card applications. These differentiators detect transitions in modulated ASK signals with a carrier frequency of 13.56 MHz at data rates up to 6.78 Mb/s. The demodulator has been implemented in 0.18 μm CMOS technology. The total power consumption is under 350 μW. Measured results confirm correct operation, and it is further shown that this differentiating scheme allows the modulation index to be reduced to 2.56%.