Silicon bandgap temperature sensor

Its main advantage is that it can be included in a silicon integrated circuit at very low cost.

The principle of the sensor is that the forward voltage of a silicon diode, which may be the base-emitter junction of a bipolar junction transistor (BJT), is temperature-dependent, according to the following equation:[1] where By comparing the voltages of two junctions at the same temperature, but at two different currents, IC1 and IC2, many of the variables in the above equation can be eliminated, resulting in the relationship: Note that the junction voltage is a function of current density, i.e. current/junction area, and a similar output voltage can be obtained by operating the two junctions at the same current, if one is of a different area to the other.

A circuit that forces IC1 and IC2 to have a fixed N:1 ratio,[2] gives the relationship: An electronic circuit, such as the Brokaw bandgap reference, that measures ΔVBE can therefore be used to calculate the temperature of the diode.

The result remains valid up to about 200 °C to 250 °C, when leakage currents become large enough to corrupt the measurement.

[2][3][4] If high precision is not required it is enough to bias a diode with any constant low current and use its −2 mV/˚C thermal coefficient for temperature calculation, however this requires calibration for each diode type.