Internal Bandgap Voltage Error Reduction in High Gradient Layouts
Internal bandgap voltage errors in high gradient layouts are reduced by common-centroid matching, thermal isolation trenching, and package stress mitigation.
Complementary to Absolute Temperature
Voltage Behavior
An analog voltage or current source exhibits a negative temperature coefficient when its magnitude decreases linearly with rising thermodynamic temperature. This characteristic defines a complementary to absolute temperature signal, which exhibits a highly predictable change of approximately two millivolts per degree Celsius.
Silicon Implementation
Bipolar junction transistors provide the physical mechanism for generating these outputs. The base-emitter voltage of a forward-biased transistor decreases as temperature rises. Designing the bias current to be stable across the operating range ensures that the negative slope remains linear and repeatable.
Reference Synthesis
Combining this signal with its positive temperature coefficient counterpart creates a stable bandgap reference. The addition of the two opposing slopes produces an output voltage that remains virtually unchanged across the specified temperature range. Precise resistor ratios determine the exact point where the thermal drift is minimized.
Because the individual coefficients are around two millivolts per degree, the scaling circuit must use stable materials to prevent drift over time.
Sensor Calibration
In digital temperature sensors, the linear change of the base-emitter voltage is converted to a digital output. Linearity is verified during manufacturing at single or multiple temperature points. The residual errors are stored in nonvolatile registers to adjust the final output.