Proportional Behavior
An analog electrical response increases linearly in direct proportion to the absolute temperature in kelvins. This proportional to absolute temperature characteristic forms the basis for integrated silicon temperature sensors. High-precision circuitry uses this predictable change to measure temperature or to stabilize reference voltages.
Generation Mechanism
The difference between the base-emitter voltages of two bipolar transistors operating at different current densities generates this linear voltage signal. Since this difference is determined by the ratio of the junction areas and the bias currents, the output voltage is highly stable and repeatable. Precision current mirrors drive the transistors to maintain a constant current ratio across all operating conditions.
Drift Sensitivity
Mechanical tension caused by packaging stress can introduce non-linearities into the measured signal. Silicon dies subjected to bending forces exhibit piezoresistive changes that disturb the proportional to absolute temperature output. Minimizing this physical stress is necessary to preserving the accuracy of the temperature measurement.
Compensation Application
A bandgap reference circuit combines a positive temperature coefficient voltage with a negative temperature coefficient voltage to produce a temperature-independent output. By adding the proportional to absolute temperature voltage to a complementary voltage, the primary temperature dependencies cancel each other out. This method achieves a reference output that varies by only a few parts per million over a very wide temperature range, making it ideal for high-resolution data converters.
