BJT Temperature Sensor Current Ratio Error Cancellation
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Solution Overview
Problem
Current source errors in Bipolar Junction Transistor (BJT) temperature sensors lead to inaccurate temperature measurements due to inconsistencies in the supplied currents, affecting the reliability of temperature calculations.
Innovation Solution
Incorporating a resistor between the current source and the emitter terminal of the BJT, and using analog-to-digital converters to measure voltages across this resistor, allowing for the determination of current ratios that are used to calculate temperature, thereby compensating for current source errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current source is used to supply current to the BJT emitter, then temperature measurement can be performed using the exponential current-voltage relationship, but current source errors cause inaccuracies in the supplied current ratios
Solution Approach 1:
A resistor is introduced as an intermediary component between the current source and the BJT emitter. This resistor converts the current into a measurable voltage that can be used to determine the actual current ratio, thereby compensating for current source errors. The resistor serves as a mediator that allows indirect measurement of current with high precision.
Solution Approach 2:
The system measures the actual current through the resistor and uses this information to calculate the true current ratio. This feedback mechanism allows the system to compensate for current source inaccuracies by using the measured voltage across the resistor to determine the actual current being supplied to the BJT.
2Measurement precision
If two different currents are supplied to the emitter to measure ΔVBE, then temperature can be calculated using the exponential relationship, but current source errors affect the current ratio and thus the temperature calculation
Solution Approach 1:
The resistor acts as an intermediary that enables precise measurement of the actual current ratio. By measuring the voltage across the resistor for both current levels, the system can determine the true current ratio without being affected by current source inaccuracies, thus improving temperature calculation precision.
Solution Approach 2:
The system replaces direct current measurement (which is difficult and inaccurate) with voltage measurement across the resistor. This substitution allows for high-precision measurement of the current ratio using standard voltage measurement techniques, thereby improving manufacturing precision of the current ratio.
3Device complexity
If the current source is assumed to be ideal, then the temperature calculation is simplified, but the temperature measurements become inaccurate due to real-world current source errors
Solution Approach 1:
The system uses itself to measure and compensate for its own errors. By measuring the actual current through the resistor and using this information in the temperature calculation, the system performs self-correction for current source inaccuracies, maintaining both simplicity and accuracy.
Solution Approach 2:
The measured voltage across the resistor provides feedback about the actual current being supplied. This feedback is used to adjust the temperature calculation to account for current source errors, resolving the contradiction between simple calculations and accurate measurements.
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 method accurately determines temperature by eliminating the error caused by the current source, ensuring precise temperature measurements for BJT and diode sensors, which can be applied in thermal management systems for integrated circuits.
Implementation Method 1
The voltage across the base-emitter junction of a BJT, denoted as VBE, is particularly sensitive to temperature changes. This characteristic allows BJTs to function as effective temperature sensors by correlating shifts in VBE with temperature variations.
Implementation Method 2
a resistor is included between the current source and the emitter terminal of the BJT. An analog-to-digital converter (ADC) measures the voltage across the resistor R for each of the two currents.
Data Source
AI summary
Various techniques are described to accurately measure a ratio between the two currents supplied by a current source in a BJT temperature sensor. In an approach, a resistor is included between the current source and the emitter terminal of the BJT. An analog-to-digital converter (ADC) measures the voltage across the resistor R for each of the two currents. These voltages are used to determine current ratios, which are then used to determine a temperature of the BJT. The techniques are not limited to use with BJTs and are applicable to other semiconductor devices including diodes.