Sigma-Delta ADC Temperature Sensor Curvature Correction
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Solution Overview
Problem
Current digital temperature sensors face limitations in accuracy due to non-linear temperature dependence, particularly 'curvature' in reference voltage, which affects the linearity of ADC output signals, and are sensitive to non-idealities like offset and mismatch.
Innovation Solution
A temperature sensor system that integrates curvature correction within the ADC converter, using a combination of PTAT and CTAT voltages to generate a temperature-independent reference voltage, reducing temperature errors and insensitivity to non-idealities through a sigma-delta analog-to-digital conversion process.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a typical bandgap reference voltage circuit is used to provide VREF, then the reference voltage is approximately constant across temperature range, but non-linear temperature dependence (curvature) remains which limits temperature sensor accuracy
Solution Approach 1:
The reference voltage generation is segmented into multiple independent voltage sources (first voltage source providing PTAT voltage, second voltage source providing CTAT voltage, third voltage source providing temperature-independent voltage) that are combined in specific ratios to achieve both stability and linearity. This segmentation allows independent optimization of each voltage source's characteristics.
Solution Approach 2:
The invention changes the parameters of the reference voltage by introducing multiple voltage sources with different temperature coefficients (PTAT, CTAT, and temperature-independent) and combining them in specific ratios. This parameter transformation converts a single unstable reference voltage into a composite reference voltage that is both stable and linear across temperature range.
2Measurement precision
If curvature correction techniques are applied to improve linearity, then temperature accuracy is improved, but device complexity increases due to additional circuitry and trimming requirements
Solution Approach 1:
The invention merges the curvature correction function directly into the reference voltage generation circuitry by combining multiple voltage sources (PTAT, CTAT, and temperature-independent) in a unified structure. This integration eliminates the need for separate curvature correction circuits and trimming mechanisms, achieving high accuracy while maintaining simplicity.
Solution Approach 2:
The reference voltage generation circuit is designed to perform multiple functions simultaneously: providing temperature stability, correcting curvature non-linearity, and serving as the reference for ADC conversion. This multi-functionality is achieved through the composite structure combining PTAT, CTAT, and temperature-independent voltage sources.
3Measurement precision
If ratiometric curvature correction is applied, then temperature error better than 0.2°C is achieved, but time multiplexing and doubling of ADC converter are required
Solution Approach 1:
The invention performs curvature correction in advance during the reference voltage generation stage by combining PTAT, CTAT, and temperature-independent voltages in specific ratios. This preliminary correction ensures that the reference voltage itself is linear across temperature, eliminating the need for subsequent time multiplexing or doubled ADC converters.
4Measurement precision
If digital domain curvature correction is applied, then non-linearity is corrected, but both analogic and digital circuitry modifications are required
Solution Approach 1:
The invention extracts the curvature correction function from the digital domain and implements it in the analog reference voltage generation domain. By taking out the correction requirement from the digital signal processing stage and addressing it at the analog reference voltage stage, the invention avoids the need for complex digital circuitry modifications while achieving the same linearity improvement.
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 provides a robust and simple design for high-accuracy temperature sensors with reduced temperature errors and improved linearity, independent of non-idealities such as offset and mismatch, without requiring high-order ratiometric corrections or digital/system-level curvature correction techniques.
Implementation Method 1
a first current source configured to produce a first current through a first diode-connected transistor having a first voltage drop across the first diode-connected transistor, the first current proportional to absolute temperature
Implementation Method 2
a second current source configured to produce a second current through a second diode-connected transistor having a second voltage drop across the second diode-connected transistor, the second current proportional to absolute temperature
Implementation Method 3
a third current source configured to produce a third, temperature-independent, current through a third diode-connected transistor having a third voltage drop across the third diode-connected transistor
Implementation Method 4
a processing network coupled to the first diode-connected transistor, the second diode-connected transistor and the third diode-connected transistor, the processing network sensitive to: a) a difference of the voltage drops across the first diode-connected transistor and the second diode-connected transistor, b) a difference of the voltage drops across the second diode-connected transistor and the third diode-connected transistor and c) the voltage drop across the second diode-connected transistor
Data Source
AI summary
A circuit includes a first current source configured to produce a first current in a first current line through a first diode-connected transistor having a voltage drop across the first diode-connected transistor, the first current being proportional to an absolute temperature via a first proportionality factor; a second current source configured to produce a second current in a second current line through a second diode-connected transistor having a voltage drop across the second diode-connected transistor, the second current being proportional to the absolute temperature via a second proportionality factor; a third current source configured to produce a third current in a third current line through a third diode-connected transistor having a voltage drop across the third diode-connected transistor; and a processing network including a sigma-delta analog-to-digital converter, the processing network being coupled to the, the second, and the third diode-connected transistors.