Front end of a 900MHz RFID for biological sensing

Abstract

This thesis presents the front end of a 900MHz passive RFID for biological sensing. The components blocks of the front end consist of power harvester, switch capacitor voltage regulator, phase lock loop and a modulator and demodulator. As the RFID is passive so the power resource is limited hence the main focus while implementing all the block was low power and high efficiency power conversion. All the individual block were optimized to provide maximum efficiency. For the harvester to achieve high efficiency and high output voltage a design approach is discussed by which the device sizes are optimized and the values of the matching network components are solved. The efficiency achieved with this approach is 34% while supplying 74mA@1.2V. The switch capacitor voltage regulator would supply power to the digital core of the RFID, which will operate at subtheshold or moderate inversion. The switch capacitor implemented in this work is a adaptive voltage regulator, as I intend to use the dynamic supply voltage scaling technique to compensate for the reduction in reliability of performance of the circuit due to variation of VTH across process due to random doping effects and temperature in subthreshold.

The phase lock loop (PLL) block in this front end provide the system clock synchronized with the base station to all the backend blocks like the digital controller, memory, and the analog to digital converter ADC and the switch capacitor voltage regulator. The PLL is a low power with jitter of 24nsec and is capable of clock data recovery from EPC gen 2 protocol format data and consumes 3mW of power.

Finally a ultra low power AM (amplitude modulation) demodulator is presented which is consumes only 100nW and is capable of demodulating a double-sideband amplitude modulated (DSB-AM) signal centered at 900MHz and the modulating frequency is 160KHz. The demodulator can demodulate signal having as low as -5dBm power and 50% modulation index. The modulation for transmitting signal is achieved by BPSK(back scatter phase shift keying).