BJT Temperature Sensing With Beta Compensation for Series Resistance
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Solution Overview
Problem
Bipolar Junction Transistor (BJT) temperature sensors face inaccuracies due to the variability of beta (β) coupled with series resistance, leading to errors in temperature measurement, particularly with advanced process technologies like 3 nm and 5 nm, which affect the collector current ratio and introduce significant inaccuracies in ΔVBE calculations.
Innovation Solution
The solution involves applying multiple known currents to a BJT terminal, coupling a resistor with the base or emitter, and using analog-to-digital converters to measure voltages across the resistor for each current, determining ratios of β change to accurately calculate temperature, employing a 4-point or 3-point measurement technique with current mirrors and sense resistors to compensate for parasitic resistances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple known currents are applied to the BJT terminal with a series resistor and ADC measurement, then measurement precision is improved by accounting for β variability and series resistance, but device complexity increases due to multiple current sources and ADC converters
Solution Approach 1:
The patent segments the measurement process into multiple discrete steps: applying different known currents (first current, second current, third current) separately, measuring corresponding voltages with ADC converters, and processing these measurements to determine temperature. This segmentation allows systematic compensation for β variability and series resistance while maintaining manageable circuit complexity through structured measurement sequences
Solution Approach 2:
The patent introduces a resistive element as an intermediary component coupled with the BJT terminal. This resistor serves as a mediator to convert current measurements into voltage measurements that can be processed by ADC converters, enabling indirect measurement of β changes and series resistance effects while simplifying the overall measurement architecture
2Measurement precision
If β variability and series resistance are compensated for using multiple current measurements, then measurement precision is improved, but the number of measurement points and processing steps increases
Solution Approach 1:
The patent performs preliminary measurements by applying multiple known currents (first, second, and third currents) to the BJT terminal and recording the corresponding voltage measurements before final temperature calculation. These preliminary data points are stored and processed together to determine β changes and series resistance values, which are then used to compensate for measurement errors in the final temperature calculation
Solution Approach 2:
The patent implements feedback by using the measured voltage differences and current ratios to calculate β changes, which then feed back into the temperature determination process. The control circuit continuously adjusts and refines the temperature calculation based on the measured β variability and series resistance effects, improving measurement precision through iterative compensation
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 significantly reduces errors in temperature measurement by accounting for β variability and series resistances, providing accurate temperature sensing through improved β compensation techniques.
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
This method exploits the exponential relationship between the junction voltage and the current through the device, which is described by the diode equation.
Implementation Method 3
A resistor R is coupled in series with a base or emitter of the BJT and an analog-to-digital converter (ADC) is used to measure the voltage across the resistor R for each of the known currents.
Data Source
AI summary
Various techniques to eliminate the error caused by variable β coupled with a series resistance in BJTs are described. Multiple known currents are applied to a terminal of the BJT and a corresponding VBE is generated. A resistor R is coupled in series with a base or emitter of the BJT and an analog-to-digital converter (ADC) is used to measure the voltage across the resistor R for each of the known currents. These voltages are used to determine ratios of β change, which are then used to determine a temperature of the BJT.