Promising Active Abilities To A Passive RFID Tag

Written by Evan Schuman
July 5th, 2006

A Washington, D.C., IP development firm, is talking up a Patented method it says will allow low-cost passive RFID tags to monitor temperatures just as active tags can do, but for less than one-twentieth the cost.

A statement from Gentag describes the patented offering as ” an ultra-linear, low-power single-calibration temperature-sensor circuit that can be directly integrated on any chip for either the Gen 2 UHF or the 13.56 MHz global RFID markets.”

Gentag argues that because it directly integrates with the RFID chip, it can deliver a low direct cost and, because the sensor claims to need only a single-temperature calibration point at the moment of chip testing, it can also deliver cost savings during manufacturing.

The temperature control claims make this announcement, if nothing else, intriguing as that has been the centerpiece for many of RFID’s most alluring?and challenging?potential capabilities.

“Gentag’s temperature sensor is analog in nature and is specifically designed to consume minute amounts of power when it is on and reading out tag temperature − and none when off: it is always in thermal equilibrium with the tag. It can be switched on and off very quickly and can be fabricated using generic digital CMOS technology,” the company’s statement said. “Accuracy depends on the calibration temperature; when calibrated at 40 oC, the sensor?s measured accuracy is ?1 oC over the industrial temperature range (-20 to +100 C), and ?0.1 C over the medical temperature range (34 to 42 C). “

Traditional active RFID chips need their own power supplies to both boost signal distance as well as to power its sensors, said Marc Cohen, Gentag’s VP for engineering and microelectronics. Although passive tags today sell for between five and seven cents, active tags can sell for $15 to $20.

Cohen said his company’s sensor can be integrated with a passive chip and the cost will be “less than a cent” although he expects them to be sold for about one dollar.

The Gentag-equipped tag “shifts all of the power?both literally and figuratively?to the reader” which, Cohen said, “makes the tags very dumb and very cheap.”

Gentag then takes a small leap, suggesting that the temperature controls can help the chip in multiple other ways.

“This unique (temperature monitoring) circuit establishes a reference for many other possible analog RFID sensors. Most sensors are themselves temperature dependent. Therefore, it becomes essential that an independent measure of temperature be made for accurate RFID sensor calibration and robust measurements of variables such as pressure, humidity, and conductivity,” the statement said. “In addition, the same temperature sensor circuit can be utilized to establish accurate voltage or current references that are independent of temperature, references which facilitate the integration of many different kinds of sensors on passive, BAP, or active RFID sensor tags.”


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