A temperature sensor based on a thermal oscillator

In this paper, a temperature sensor based on the thermal diffusion constant of silicon is presented. It consists of an oscillator whose frequency is determined by the phase-shift of a thermal filter. The filter consists of two heaters and a thermopile implemented in the substrate of a standard CMOS chip. In the thermal domain, this filter has a low-pass characteristic, whose phase shift is determined solely by its physical dimensions and by the thermal diffusion constant of silicon. Since the latter is temperature dependent and essentially process independent, the oscillator's frequency can be used as a well-defined, microprocessor-compatible, measure of temperature. Measurements on 8 samples show that the sensor's inaccuracy is less than plusmn2degC over the temperature range -50degC to 125degC