Temperature sensing using a bipolar transistor

A circuit for sensing a temperature includes: a bipolar transistor unit 10 connected to a current source to output a voltage which is inversely proportional to temperature; a variable reference voltage unit 20 to provide a reference voltage which varies according to setting; a differential amplifier unit 30 that amplifies the difference between the temperature voltage and the set reference voltage; and a second amplifier unit 40 to amplify the output voltage of the differential amplifier using a variable feedback resistor. Temperature can be measured from the base-emitter voltage of an NPN transistor 11, whose collector is connected to the current source and emitter to ground. The reference voltage can be selected and the feedback resistor adjusted to bring the output voltage within a measurement range of either an analogue to digital converter (fig 2A, 50) or a voltage distributor (fig 2B, 50) having plural comparators comparing distributed voltages with a threshold, whilst precisely measuring over a wide range of temperature.