BJT Failure Detection Circuit With Temperature-Tracking References
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Solution Overview
Problem
Conventional bipolar junction transistor (BJT) based temperature sensors face challenges in reliably detecting failures due to the need for large temperature margins when using fixed reference voltages, which can lead to inaccurate detection and reduced reliability, especially in temperature-varying environments such as semiconductor devices in vehicles.
Innovation Solution
A semiconductor device with a failure detector that generates upper and lower limit reference voltages based on the base-emitter voltage of a second BJT, allowing for reliable failure detection by comparing the base-emitter voltage of a first BJT with these dynamically adjusted reference voltages, ensuring high reliability even under temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed reference voltage is used to monitor the emitter-base voltage VEB, then the circuit structure is simple, but the reliability of failure detection is lowered due to the need for large temperature margins
Solution Approach 1:
The reference voltage is changed from a fixed value to a dynamic value that varies with temperature. The patent uses a temperature-compensated reference voltage generated by a bandgap reference circuit, which automatically adjusts the reference voltage level according to temperature changes, thereby maintaining accurate failure detection across the entire operating temperature range without requiring excessive temperature margins.
Solution Approach 2:
The reference voltage parameter is changed from a constant fixed value to a temperature-dependent variable. By using a bandgap reference circuit, the reference voltage is made to track the temperature variations of the BJT's VEB, allowing the detection circuit to maintain high reliability across temperature changes while reducing the required temperature margin.
2Adaptability or versatility
If a large temperature margin is considered when using a fixed reference voltage, then the detection range is expanded, but the reliability of failure detection is inevitably lowered
Solution Approach 1:
The reference voltage is made dynamic and temperature-dependent through the bandgap reference circuit. This allows the detection range to remain sufficiently wide to cover all operating conditions while maintaining high detection reliability, because the reference voltage automatically adapts to temperature changes rather than requiring a fixed large margin.
Solution Approach 2:
The bandgap reference circuit provides temperature feedback to the reference voltage generation, creating a closed-loop system that automatically compensates for temperature effects. This feedback mechanism ensures that the reference voltage remains appropriately matched to the BJT's VEB across temperature variations, achieving both wide detection range and high reliability.
3Ease of manufacture
If the base-emitter voltage VEB is monitored using a fixed reference voltage, then the implementation is straightforward, but accurate detection is compromised due to temperature variations
Solution Approach 1:
The reference voltage parameter is changed from a fixed DC value to a temperature-dependent variable generated by a bandgap reference circuit. This maintains implementation simplicity as the bandgap reference is a standard circuit block, while dramatically improving measurement precision by ensuring the reference voltage tracks temperature variations and remains accurately matched to the BJT's VEB.
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
The solution enables high-reliability failure detection of BJTs with a reduced margin, preventing undetected failures in critical applications like vehicle semiconductor systems by using reference voltages that reflect temperature changes, thus enhancing the stability and safety of temperature management systems.
Implementation Method 1
a voltage generator configured to generate a first base-emitter voltage of a first bipolar junction transistor
Data Source
AI summary
A semiconductor device may include a voltage generator configured to generate a first base-emitter voltage of a first bipolar junction transistor, and a failure detector configured to generate a failure signal by comparing the first base-emitter voltage with an upper limit reference voltage and a lower limit reference voltage. The failure detector may include a second bipolar junction transistor a current source configured to generate a bias current, a first resistor coupled between the current source and a emitter of the second bipolar junction transistor to generate the upper limit reference voltage, a second resistor and a third resistor configured to divide a second base-emitter voltage of the second bipolar junction transistor to generate the lower limit reference voltage, and a first and second comparator configured to compare the first base-emitter voltage with the upper limit reference voltage and the lower limit reference voltage, respectively, to generate respective failure signals.