BJT Temperature Sensing via Resistor-Based Current Ratio Measurement
Find Innovative SolutionsGenerate Solutions
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 determination.
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 calculation of current ratios that accurately determine temperature by eliminating errors caused by the current source.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a programmable current source is used to supply currents to the BJT emitter, then temperature sensing capability is achieved, but current source errors cause inaccurate temperature measurements
Solution Approach 1:
A precision resistor is introduced as an intermediary element between the current source and the BJT emitter. This resistor converts the current ratio information into a voltage ratio that can be accurately measured by the ADC. The resistor serves as a mediator that translates current measurements into voltage measurements, eliminating the need to directly measure currents from the programmable current source.
Solution Approach 2:
The patent replaces direct current measurement with voltage measurement through the resistor. Instead of measuring currents directly from the programmable current source (which has errors), the system measures voltages across the resistor using an ADC. This substitution of measurement domain from current to voltage eliminates the current source errors while maintaining the temperature sensing function.
2Device complexity
If direct current measurement is used, then temperature determination is simplified, but current source errors directly affect measurement accuracy
Solution Approach 1:
The precision resistor acts as an intermediary that enables accurate temperature measurement without requiring direct current measurement. By converting current ratio to voltage ratio through the resistor, the system achieves both simplified measurement architecture and high precision, as voltages can be measured more accurately than currents from programmable sources.
Solution Approach 2:
The patent substitutes current measurement with voltage measurement. The ADC measures voltages across the resistor instead of directly measuring currents from the programmable current source. This substitution maintains measurement simplicity while dramatically improving precision by eliminating current source errors.
3Reliability
If a resistor is added between current source and emitter, then current source errors are eliminated, but device complexity increases
Solution Approach 1:
The precision resistor is a simple intermediary component that enables error elimination without significant complexity increase. It converts the problematic current measurements into manageable voltage measurements, allowing the use of standard ADCs to achieve high reliability temperature sensing with minimal additional circuitry.
Solution Approach 2:
By substituting current measurement with voltage measurement through the resistor, the system achieves high reliability temperature sensing. The added resistor enables the use of voltage-based measurement techniques that are inherently more accurate and easier to implement with standard ADCs, outweighing the minor complexity increase.
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 enables precise temperature measurement by eliminating the impact of current source errors, ensuring reliable temperature sensing for thermal management systems.
Implementation Method 1
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
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
Figure 1~2
Figure 3
Figure 4
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.