RF tags reduced in size for direct energy harvesting

May 11, 2016 // By Nick Flaherty
direct energy harvesting RFID die
Researchers at North Carolina State University have removed the need for DC rectification and charge pumps in RF tags so they can be used directly with an energy harvesting source, reducing the size of the tags by 25%.

The team has developed a suite of techniques that allow them to create passive radio-frequency identification (RFID) tags that can be run directly off harvested incident RF energy, without the need to rectify the incident RF and build the voltage through a charge pump.

The RF-DC conversion requires substantial circuitry and substantial chip area, so eliminating the need for RF-DC conversion can save considerable die size in a cost sensitive market. The RF-DC conversion efficiency is also poor when the incident electric field is low, so this new scheme has potential to achieve more efficiency.

"By eliminating the hardware that is used to convert the AC signal to DC for powering the circuit, we are able to make the RFID tag much smaller and less expensive," says Paul Franzon, a professor of electrical and computer engineering at NC State and senior author of a paper on the work. The research was conducted with NC State Ph.D. students Wenxu Zhao and Kirti Bhanushali.

Franzon's team was able to redesign RFID circuits to operate directly off of AC power by incorporating additional transistors into the circuits. The circuits share a few transistors that enable them to operate correctly using an AC or energy harvesting power source.

The researchers have developed the design of a complete UHF passive RFID chip based on test circuits, the implemention of a CAD flow and design of a cell library. These "RF-only logic" RFID tags have less range than conventional, passive RFID tags. However, Franzon and his team have plans to develop new RF-only logic tags that they anticipate will have similar range to conventional tags. 

"We're currently looking for industry partners to help us bring this technology into the marketplace," he said.

http://www.ece.ncsu.edu/erl/faculty/paulfwww/Research/RF.htm