Response adjustable temperature sensor for transponder

Abstract

A response-adjustable temperature sensor ( , Rext), particularly for a transponder ( ) capable of measuring one or more parameters (e.g., temperature, pressure) and transmitting a data stream (FIGS. C, B) to an external reader/interrogator ( ). The transponder typically operates in a passive mode, deriving its power (Vxx, Vcc, Vdd) from an RF interrogation signal received by an antenna system ( ), but can also operate in a battery-powered active mode. The transponder includes memory ( ) for storing measurements, calibration data, programmable trim settings ( ), transponder ID and the like. The temperature sensor is a temperature measurement device characterized by a resistance (Rext, ) and a temperature sensing circuit ( ) comprising a temperature sensing transistor (Q ) which exhibits a predictable change in its base-emitter voltage due to temperature, and transistors (P , N , P , N ) connected for mirroring a current (I(T)) through the temperature sensing transistor and through the resistance. The resistance may be a fixed, temperature-independent resistor or a resistance that has a resistance value that predictably varies with temperature, such as a thermistor ( ). Temperature response and resolution can be adjusted while maintaining desired current levels by varying the value of the resistance and also by selecting a thermistor with a suitable temperature coefficient. User-settable trimming bits can be used to determine scaling of the transponder output. Replacing an external pressure-sensing capacitor with a fixed-value capacitor allows further flexibility in scaling of the output when only temperature readings are needed.