Bandgap Temperature Sensing Circuit for Process-Independent Accuracy
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Solution Overview
Problem
Existing temperature sensing circuits in low voltage single chip systems are prone to inaccuracy due to manufacturing process variations and channel length modulation, affecting the reliability of temperature sensing.
Innovation Solution
A temperature sensing circuit comprising a current source circuit, resistor, bandgap voltage generation circuit, voltage-equalizing circuit, and temperature determining circuit, which uses a pair of bipolar junction transistors and a sampling capacitor to calculate temperature values with high accuracy, independent of manufacturing process effects, by equalizing voltages and determining temperature through voltage differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a delay line or current mirror is used for temperature sensing, then the circuit can operate in low voltage single chip systems, but the temperature sensing accuracy deteriorates due to manufacturing process variations and channel length modulation
Solution Approach 1:
The patent changes the sensing parameter from current-based (prone to process variations) to voltage-based measurement. By using a bandgap voltage reference and measuring voltage differences across resistors that are less sensitive to process variations, the circuit achieves more accurate temperature sensing that is not affected by manufacturing process variations or channel length modulation.
Solution Approach 2:
The patent introduces a bandgap voltage reference circuit as an intermediary to provide a stable voltage reference that is independent of process variations. This intermediary element enables accurate temperature measurement by comparing voltages rather than directly measuring currents, thereby eliminating the sensitivity to manufacturing process variations.
2Measurement precision
If voltage-based temperature sensing is implemented using bandgap reference, then manufacturing process variations are avoided, but the device complexity increases due to additional circuits
Solution Approach 1:
The voltage-equalizing circuit serves multiple functions: it equalizes voltages during the first time period to charge the sampling capacitor, and then isolates the capacitor during the second time period for measurement. This multi-functionality reduces the need for separate dedicated circuits, thereby managing complexity while achieving high measurement precision.
Solution Approach 2:
The circuit operates in periodic cycles, alternating between a voltage equalizing phase and a measurement phase. During the first time period, voltages are equalized; during the second time period, the sampling capacitor is isolated and the temperature is measured. This periodic operation allows the same circuit components to perform different functions at different times, reducing overall circuit complexity.
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 proposed circuit significantly improves temperature sensing accuracy by isolating from manufacturing process variations and channel length modulation, using a high accuracy clock signal to calculate precise temperature values.
Implementation Method 1
The sampling capacitor is configured to electrically isolate from the first terminal of the resistor after sampling a first voltage
Implementation Method 2
a first voltage, having a first negative temperature coefficient, of the first terminal of the resistor... and a second voltage, having a second negative temperature coefficient greater than the first negative temperature coefficient
Data Source
AI summary
A temperature sensing circuit includes a current source circuit, a resistor, a bandgap voltage generation circuit, a voltage-equalizing circuit and a temperature determining circuit. The current source circuit has a first current output terminal and a second current output terminal. The bandgap voltage generation circuit includes a pair of bipolar junction transistors. The voltage-equalizing circuit equalizes voltages of a first current output terminal and the second current output terminal. The temperature determining circuit includes a sampling capacitor and a calculation circuit. The sampling capacitor samples a first voltage of a first terminal of the resistor and a second voltage of a second terminal of the resistor. The calculation circuit generates a temperature value by calculating a voltage difference between the first voltage and the second voltage.