Rf transponder and method of measuring parameters associated with a monitored object

Abstract

A radio frequency (RF) transponder ( ) capable of measuring parameters associated with an object and transmitting data to an external reader/interrogator ( ). In use with a pneumatic tire ( ), the transponder measures temperature and pressure within the tire. The transponder includes circuitry ( ) for controlling windows of time (W and W ) during which real-time temperature and pressure measurements are made, and for storing ( ) calibration data, transponder ID number and the like, and for transmitting this information in a data stream (FIG. C) to the reader/interrogator. An excessive temperature condition may also be sensed (MTMS ) and included in the data stream. The circuitry of the transponder is preferably implemented on a single IC chip ( ), using CMOS technology, with few components external to the IC chip. The transponder is preferably passive, deriving its operating power from an RF signal provided by the exernal reader/interrogator. Data (N ) indicative of temperature and data (N ) indicative of pressure are both transmitted to the reader/interrogator, along with calibration data. A calibration data stored by the transponder and transmitted in the data stream is a slope of N /N , or the “ratioed” response of the temperature count divided by the pressure count, which is determined during calibration of the transponder.