A team of researchers at North Carolina State University have developed a suite of techniques that allow them to create passive radio-frequency identification (RFID) tags that are 25 percent smaller and are less expensive that existing tags. This becomes possible as these tags no longer need to convert alternating current (AC) to direct current (DC) in order for them to function effectively.
In passive RFID technology, a “reader” transmits a radio signal that is picked up by the RFID tag. The tag then converts the AC of the radio signal into DC in order to power internal circuits. Those circuits control the signal that is bounced back to the reader. Passive RFID technology is used in everything from parking passes to merchandise and asset tracking. For example, passive RFID is the technology that tells a traffic barrier to lift when you wave a parking pass in front of the scanner.
AC-DC rectifiers and storage capacitors take up 25% or more of the chip area for cost-sensitive passive RFID tags. The researchers, in their work have demonstrated that these components can be eliminated by utilizing a RF-only circuit structure. The team was able to redesign RFID circuits to operate directly off of AC power by incorporating additional transistors into the circuits. These circuits share a few transistors that enable them to operate correctly using an AC power source.
This RF-only logic permits digital operations to be performed from AC, rather than a DC power supply. This UHF Gen-2 compatible RFID tag is designed using the RF-only logic. It has been implemented using the 0.13 µm CMOS technology. The tag dimensions are 0.6 mm × 0.3 mm and it has a sensitivity of 0 dBm in simulation.
Tags made using this new design are called “RF-only logic” RFID tags, and the prototypes and at this point do have a lower range than conventional, passive RFID tags. However, over time they plan to develop new RF-only logic tags with similar ranges to conventional tags.
By eliminating the hardware that is used to convert the AC signal to DC for powering the circuit, they have made the RFID tag much smaller and less expensive. This research was conducted with NC State Ph.D. students Wenxu Zhao and Kirti Bhanushali. They are currently looking for industry partners to help them bring this technology into the marketplace.
Learn more about this RFID Technology in their Published Paper - Design of a Rectifier-Free UHF Gen-2 Compatible RFID Tag using RF-Only Logic.
