Low cost temperature sensor can be achieved by using diode or transistor (by shorting Base and Collector). When constant current passes through the base-emitter junction it produces a voltage between the base and emitter (Vbe) that is a linear function of the absolute temperature.
The overall forward voltage drop has a temperature coefficient of approximately 2 mV/°C. The semiconductor junction sensor’s voltage versus temperature is much more linear than that of a thermocouple or resistive temperature device (RTD).
