BJT Temperature Sensing With Beta Compensation and Series Resistance
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Solution Overview
Problem
Bipolar Junction Transistor (BJT)-based temperature sensing circuits face inaccuracies due to the variability of beta (β) coupled with series resistance, which affects the collector current ratio and introduces errors in temperature measurement, especially with advanced process technologies like 3nm and 5nm.
Innovation Solution
The solution involves applying multiple known currents to a BJT terminal, coupling a resistor in series with the base or emitter, and using analog-to-digital converters to measure voltages across the resistor for each current, determining ratios of beta change to accurately calculate temperature.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple known currents are applied to measure V BE for temperature sensing, then temperature measurement capability is enabled, but measurement precision deteriorates due to variable beta coupled with series resistance
Solution Approach 1:
The patent applies feedback by measuring the actual collector current using a sense resistor and using this measured current information to compensate for beta variability in the temperature calculation. The system continuously monitors the collector current and adjusts the temperature sensing calculation based on the actual current flow, thereby eliminating errors caused by beta variation coupled with series resistance.
Solution Approach 2:
The patent changes the measurement approach by introducing a sense resistor to directly measure collector current, and by applying multiple different current levels (first current, second current, third current) to the BJT. This allows the system to determine beta ratios at different operating points and compensate for beta variability, transforming the temperature sensing method from one that assumes constant beta to one that actively compensates for beta changes.
2Measurement precision
If series resistance is present in base or emitter, then device complexity is reduced, but measurement precision deteriorates due to voltage drop affecting collector current ratio
Solution Approach 1:
The patent introduces a sense resistor as an intermediary element in the collector circuit. This sense resistor allows direct measurement of the collector current without being affected by the series resistance in the base or emitter. By measuring the voltage across the sense resistor, the system obtains accurate collector current information that can be used to compensate for the effects of series resistance, thereby maintaining measurement precision without requiring elimination of the series resistance.
3Measurement precision
If beta compensation is implemented using multiple currents and sense resistors, then measurement precision improves by eliminating beta variability errors, but device complexity increases
Solution Approach 1:
The patent makes the sense resistor serve multiple functions: it is used to measure collector current for beta compensation, and it can also be used for general current sensing and monitoring purposes. The same hardware infrastructure (sense resistor, ADC) supports both the temperature sensing function and the beta compensation function, thereby reducing the overall device complexity compared to having separate dedicated circuits for each function.
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 effectively eliminates errors caused by variable beta and series resistance, providing accurate temperature measurements by utilizing beta compensation techniques.
Implementation Method 1
The voltage across the base-emitter junction of a BJT, denoted as V BE, is particularly sensitive to temperature changes. This characteristic allows BJTs to function as effective temperature sensors by correlating shifts in V BE 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.
Data Source
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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.