Low Temperature Error Thermal Sensor Using BJT Differential Voltages
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Solution Overview
Problem
Thermal sensors calibrated at a single temperature often experience significant errors across their intended temperature range due to deviations from ideal characteristics, making it challenging to ensure accuracy over the full range of use.
Innovation Solution
The use of pairs of bipolar junction transistors (BJTs) with different current densities to generate differential base-emitter voltages, which are amplified to produce a signal with a proportional temperature dependency, allowing for single-point calibration and reduced temperature errors across the operational range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a thermal sensor is calibrated at only one or limited number of temperatures, then the calibration process is simple and fast, but the accuracy of the thermal sensor over the full temperature range deteriorates due to deviations from ideal characteristics
Solution Approach 1:
The patent applies parameter changes by utilizing the temperature-dependent characteristics of bipolar junction transistors, specifically the base-emitter voltage (Vbe) which has a known relationship with temperature. By measuring Vbe at a single calibration point and using the established physical relationship between Vbe and temperature, the system can accurately determine temperatures across the full range without requiring multiple calibration points, thus maintaining both speed and accuracy
Solution Approach 2:
The patent employs feedback mechanisms where the thermal sensor continuously monitors its own temperature through Vbe measurements and adjusts its readings based on the calibrated relationship. The single-point calibration establishes a reference that feeds into ongoing temperature measurements, allowing the system to compensate for deviations and maintain accuracy across varying temperatures
2Ease of manufacture
If thermal sensor characteristics deviate from ideal characteristics, then manufacturing variability increases, but the accuracy over the full temperature range deteriorates
Solution Approach 1:
The patent implements self-service by having the thermal sensor use its own inherent physical characteristics (the Vbe-temperature relationship of bipolar junction transistors) to perform self-calibration and self-measurement. The sensor leverages its own temperature-dependent electrical properties to determine temperature accurately, eliminating the need for external calibration equipment or complex manufacturing tolerances
Solution Approach 2:
The invention exploits parameter changes in the semiconductor materials, specifically how the base-emitter voltage of bipolar junction transistors changes predictably with temperature. This physical parameter relationship allows the sensor to compensate for manufacturing variations, as the Vbe-temperature relationship remains consistent even when other sensor characteristics vary due to manufacturing tolerances
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in thermal sensors with improved accuracy and reduced temperature errors, ensuring reliable temperature sensing from -50°C to 150°C with single-point calibration, maintaining errors within acceptable limits.
Implementation Method 1
The use of pairs of bipolar junction transistors (BJTs) with different current densities to generate differential base-emitter voltages, which are amplified to produce a signal with a proportional temperature dependency
Data Source
AI summary
A thermal sensor in some embodiments comprises two temperature-sensitive branches, each including a thermal-sensing device, such as one or more bipolar-junction transistors, and a current source for generating a current density in the thermal-sensing device to generate a temperature-dependent signal. The thermal sensor further includes a signal processor configured to multiply the temperature-dependent signal from the branches by respective and different gain factors, and combine the resultant signals to generate an output signal that is substantially proportional to the absolute temperature the thermal sensor is disposed at.