A linear, wide-range absolute temperature thermometer using a novel p–n diode sensing technique

We describe a novel application arising from earlier observations that under several different constant currents the p–n diode exhibits different diode voltages at the same temperature. Firstly, we show by theory, simulation and experiment that this voltage difference increases linearly with temperature. Secondly, we show that the approach allows direct measurement of absolute temperatures. These two facts have, to the best of our knowledge, not been reported before. The approach alleviates complexity issues typically associated with p–n diode thermal sensors by reducing conditioning circuits and eliminating delicate voltage references and calibration. In the test application the current through the diode is switched between two values by a micro-controller. The buffered diode voltage is fed into the analog to digital converter (ADC) of the microcontroller to facilitate direct temperature readout on an appropriate device with a minimum of programming. Finally, the performance of the prototype against two standards is shown to validate the present approach.

► We show diode voltage difference at two constant currents increases linearly with temperature.
► We show how direct absolute temperature measurement is then possible.
► We present a test microcontroller application for direct temperature readout on the principle.
► We validate the approach by comparing test design with two standard instruments.