Silicon bandgap temperature sensor
|
|
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:
- <math>V_{BE}=V_{G0}(1-{T/T_0})+V_{BE0}(T/T_0)+(nKT/q)\ln(T_0/T)+(KT/q)\ln(IC/IC_0)<math>
where
- T = temperature in kelvins
- 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:
- <math>\Delta V_{BE}=(KT/q)\ln(IC_1/IC_2)<math>
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.