Temperature Sensor Circuit Using Four-Current Resistance Cancellation
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Solution Overview
Problem
Existing temperature sensor circuits in integrated circuits suffer from errors due to intrinsic resistances in transistors, leading to inaccuracies of approximately ±0.5° C in temperature measurements.
Innovation Solution
A circuit design that applies four different currents (A, B, C, and D) to transistors, where specific relationships between these currents cancel out the effects of inherent base and emitter resistances, allowing for accurate temperature sensing without requiring additional information about resistance values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If base resistance RB and emitter resistance RE are non-zero in actual bipolar transistors, then the transistor structure becomes more realistic and manufacturable, but the temperature measurement accuracy deteriorates with errors of approximately ±0.5° C due to temperature-dependent resistance values affecting ΔVBE
Solution Approach 1:
The patent segments the temperature measurement process into multiple discrete steps, applying four different current values (IA, IB, IC, ID) to the transistor at different times. This temporal segmentation allows the circuit to collect multiple voltage measurements (VBE1, VBE2, VBE3, VBE4) under different operating conditions, which are then processed to eliminate the effects of temperature-dependent resistances RB and RE from the final temperature calculation.
Solution Approach 2:
The patent changes the operating parameters of the transistor by varying the collector current through four different current sources. By measuring VBE at different current levels (IA, IB, IC, ID) and using the relationship between these measurements, the circuit derives a temperature calculation that is independent of the temperature-dependent resistance values RB(T) and RE(T), thereby maintaining accuracy despite parameter variations.
2Measurement precision
If four different currents are applied to the transistor through multiple current sources, then temperature measurement accuracy is improved by eliminating resistance effects, but the circuit complexity increases with additional current sources and measurement steps
Solution Approach 1:
The patent employs periodic action by sequentially applying four different current values (IA, IB, IC, ID) to the transistor in a repeating cycle. Each current level is applied for a specific duration to allow VBE measurement, then switched to the next current level. This periodic measurement approach enables the extraction of temperature information while eliminating resistance effects, as the systematic variation of current levels provides the necessary data points for accurate calculation.
Solution Approach 2:
The circuit uses the transistor's own VBE characteristics under different current conditions to self-determine its temperature. By measuring the VBE voltage at four different current levels and processing these measurements through the patent's calculation method, the circuit inherently compensates for its own temperature-dependent resistance variations without requiring external calibration or additional temperature sensing components.
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 circuit achieves accurate temperature measurement by simplifying the temperature calculation, eliminating the impact of intrinsic resistances and improving measurement accuracy, enabling precise temperature determination.
Implementation Method 1
a first voltage potential between the emitter of the at least one transistor and the base during application of the current A to the emitter of the at least one transistor, a second voltage potential between the emitter of the at least one transistor and the base during application of the current B to the emitter of the at least one transistor
Data Source
AI summary
In one embodiment, a circuit includes at least one transistor with a base and collector being electrically connected to a ground, and at least one current source being configured to apply four different currents (A, B, C, and D) to the emitter. A sum of the currents A and C are substantially equivalent to a sum of the currents B and D, or a sum of the currents A and D are substantially equivalent to a sum of the currents B and C. The circuit outputs first, second, third, and fourth voltage potentials between the emitter and the base during application of the currents A, B, C, and D, respectively.