A low-power smart temperature sensor for passive UHF RFID tags and Sensor nets

A low-power wide-range CMOS temperature sensor architecture is proposed for RFID and Sensor Networks based on temperature-to-frequency conversion using supply voltage controlled sub-threshold ring oscillator. The principles of operation are investigated and proved via simulation results. Most errors are canceled out by this ratio-metric design. An inaccuracy of −0.84°C to +0.34°C occurs over a range of −40°C to 80°C after using a novel in-field digital two-point calibration. The entire sensor consumes less than 93nW to 305nW over the temperature range and can be digitally reconfigured for setting sample rate and resolution in a tradeoff.