The silicon bandgap temperature sensor is an extremely common form of temperature sensor (thermometer) used in electronic equipment. 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 is temperature-dependent, according to the following equation:
where
T = temperature in kelvin
VG0 = bandgap voltage at absolute zero
VBE0 = bandgap voltage at temperature T0 and current IC0
K = Boltzmann's constant
q = charge on an electron
n = a device-dependent constant
By comparing the bandgap voltages at two different currents, IC1 and IC2, many of the variables in the above equation can be eliminated, resulting in 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. Above these temperatures, more exotic materials such as silicon carbide can be used instead of silicon.