Junction Thermometry
Semiconductor junction thermometry measures local silicon die temperature based on the temperature dependency of forward-biased p-n junction voltages. Utilizing temperature diode sensing within integrated circuits enables real-time thermal monitoring of high-power microprocessors and optical sensor dies. Operational limits restrict accurate sensing to temperatures below one hundred fifty degrees Celsius, where silicon reverse leakage currents begin to dominate junction behavior.
Electrical Behavior
Forward junction voltage decreases linearly at approximately minus two millivolts per degree Celsius under constant forward bias current. Implementing temperature diode sensing relies on forced current ratios to eliminate process-dependent saturation current variables. Dual-current excitation measures junction voltage differences at two distinct current levels, producing a voltage output proportional to absolute temperature.
Process variations in diode ideality factors introduce offset errors that require factory calibration or digital correction factors. Integrated analog front-end circuits convert small millivolt signal changes into high-resolution digital temperature readings.
Current Switching
Precision current sources switch between high and low current levels at kilohertz rates to cancel series resistance drops. Filtering circuit noise ensures accurate measurement of small differential junction voltages.
Calibration Accuracy
Metrological verification requires two-point thermal calibration against traceable platinum resistance thermometers. On-chip calibration registers store individual diode offset values to achieve temperature accuracy within 0.5 degrees Celsius. Test protocols verify linearity across the full industrial operating temperature range.
