Delta-Sigma Modulator Feedback for Linear Capacitance Sensing
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Solution Overview
Problem
Conventional delta/sigma modulators face challenges in achieving linear input/output characteristics, which is crucial for accurate capacitance detection in applications like pressure sensors.
Innovation Solution
The delta/sigma modulator design incorporates a first multiplier based on a reference capacitor and a first variable capacitor, with a second multiplier in the feedback path using equal variable capacitances, allowing for linear input/output characteristics by varying the capacitance in proportion to the distance between electrodes, thereby achieving accurate pressure sensing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional delta/sigma modulator is used, then the device complexity is reduced, but the measurement precision and linearity of input/output characteristics deteriorate
Solution Approach 1:
The patent changes the capacitance values of capacitors in the feedback path to specific relationships (Cs2 = Cs3 = 2 × Cs1) to achieve linear input/output characteristics. This parameter optimization resolves the contradiction by tuning component values to eliminate non-linearity while maintaining the conventional modulator structure.
Solution Approach 2:
The patent introduces a feedback path with specifically configured capacitors (Cs2 and Cs3) that feed back a portion of the output to the input. This feedback mechanism with optimized capacitance ratios corrects non-linearity and improves measurement precision without requiring a complete redesign of the modulator architecture.
2Measurement precision
If the capacitance varies in proportion to the distance between electrodes, then the measurement precision improves, but the device complexity increases due to multiple variable capacitors
Solution Approach 1:
The patent makes multiple capacitors (Cs1, Cs2, Cs3) variable with the same control mechanism, allowing them to serve multiple functions: Cs1 provides the primary sensing function while Cs2 and Cs3 provide feedback and linearity correction. This multi-functionality approach improves pressure sensing accuracy without proportionally increasing device complexity.
Solution Approach 2:
The patent optimizes the capacitance ratios between multiple variable capacitors (setting Cs2 = Cs3 = 2 × Cs1) to achieve linear input/output characteristics. This parameter optimization allows the system to handle multiple capacitors efficiently by establishing simple proportional relationships rather than independent control.
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 configuration enables a highly accurate delta/sigma modulator with linear input/output characteristics, facilitating the development of precise analog-to-digital converters and pressure sensors.
Implementation Method 1
a capacitive sensor comprising a variable capacitor whose capacitance varies according to the distance between electrodes
Data Source
AI summary
According to one embodiment, a delta/sigma modulator includes a first multiplier based on a reference capacitor having capacitance CR and a first variable capacitor having capacitance CS1 according to a distance between electrodes thereof, the first multiplier being defined by a first multiplier factor given by CR/CS1 and being supplied with a reference voltage, a second multiplier based on a second variable capacitor having capacitance CS2 and a third variable capacitor having capacitance CS3, the second multiplier being defined by a second multiplier factor given by CS3/CS2 and being provided in a feedback path, and an adder configured to add an output of the first multiplier and an output of the second multiplier, wherein CS1, CS2 and CS3 are the same.