Abstract:
Today RFID technology is mostly used as a medium for numerous tasks including
managing supply chains, healthcare, tracking livestock, preventing counterfeiting, controlling building access, and supporting automated checkout. Contactless RFID technology is adding speed, accuracy, efficiency and security to an ever-expanding range of
applications. As RFID transponders are embedded in the objects for tracking purposes
it is necessary to make the transponders as small as possible. The passive type transponders do not require any battery of their own to operate; they retrieve the power from
the radio signal of the reader. RFID technology can operate in low frequency (LF),
high frequency (HF), ultra-high frequency (UHF) and microwave frequency. Higher
the frequency better the read range of the transponder. So, to keep the read range higher
this research work focuses on the design of a passive RFID transponder at 2.45 GHz
microwave frequency. Analog circuits of the transponder i.e voltage controlled oscillator (VCO), rectifier, charge pump and voltage regulator circuits are designed for the
transponder in such a way that the device consume less power as well as require small
area.
The VCO works as the clock generator for the transponder. In this work a low
power, low phase noise, small area 3-stage differential ring VCO is designed and analyzed. The transponder receives the RF signal when it is within the read range of the
reader and with the help of a rectifier circuit it converts the RF power to DC. To enhance the rectified output voltage a charge pump circuit is used. In this work, to reduce
the circuit area the rectifier and the charge pump circuit is designed together. To protect the circuit from high or unstable voltage, a low power linear regulator is designed
which produces stable DC output. Moreover, to assess all the circuits in diversified environments process corner analysis, temperature sweeping, Monte Carlo analysis and
stability analysis has been performed in this research. Designed in a 90nm CMOS
technology, the proposed VCO oscillates at 2.45 GHz microwave frequency with an
area of 1316 µm 2 and consumes only 2.27 mW power. The charge pumped rectifier
circuit occupies 3884 µm 2 space having a high power conversion efficiency of 78.5%.
With an active chip area of 1557.7 µm 2, the proposed voltage regulator circuit gives a
stable output of 1 V with a low power consumption of 10 µW only. Finally, after the
post-layout simulation in each circuit, it is found that the parasitic components didn’t
change the circuit performances drastically from the schematic based simulations.
