Digital Modulator and Demodulator IC for RFID Tag Employing DSSS and Barker Code

Radio frequency identification (RFID) is lagging behind because of vendor specific solutions and expensive implementation cost. In particular, the reader is the most expensive part. A WiFi compatible tag was proposed to use the WNIC as an RFID reader. However, no specific modulator or demodulator was suggested. This paper analyzes the various IEEE 802.11 standards and their modulation and coding techniques keeping the desired properties of an RFID system in consideration. After the analysis, a digital modulator and demodulator for RFID tag in IEEE 802.11 protocol employing Direct Sequence Spread-Spectrum (DSSS) and coding is proposed. A MOD-11 synchronous counter is designed for the 11-bit encoder which generates the desired Barker code. Data are multiplied with this Barker code to modulate the data, and the received data are multiplied with the Barker code to demodulate them. The proposed modulator and demodulator are implemented in 0.18μm CMOS technology. The simulation results show that 1 bit is spread to 11 bits by the modulator and 11-bit received data are demodulated to 1 bit correctly. The proposed design is simple, resistant to multipath fading and interference and offers the highest distance with the lowest BER for an RFID tag.