Sigma-Delta Capacitance Sensing for In-Phase and Quadrature Accuracy
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Solution Overview
Problem
Proximity sensor devices face challenges in accurately determining both the in-phase and quadrature components of interference at various frequencies, which affects their ability to effectively detect and process input signals from capacitive sensor electrodes.
Innovation Solution
The implementation of a clocked comparator and demodulator configuration within an input device, which actively drives a capacitive sensor electrode with a periodic reference signal and provides negative feedback to produce a digital representation of the sensing current, allowing for demodulation and obtaining digital measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional analog-to-digital conversion method is used for capacitive sensing, then the device structure is simpler, but the measurement precision of in-phase and quadrature components deteriorates
Solution Approach 1:
The patent segments the capacitive sensing measurement into two separate sigma-delta modulator channels: one dedicated to measuring the in-phase component and another dedicated to measuring the quadrature component. Each modulator processes its specific component independently, allowing for precise measurement of both components simultaneously without interference, thereby resolving the technical contradiction between measurement precision and device complexity.
2Measurement precision
If interference at various frequencies is not properly filtered, then the signal processing is faster, but the measurement precision deteriorates
Solution Approach 1:
The patent employs periodic reference signals at specific frequencies (e.g., 100 kHz for in-phase, 120 kHz for quadrature) that are modulated by the capacitive sensor electrode. This periodic action allows the sigma-delta modulators to selectively respond to their designated frequency components while automatically rejecting other frequency interference, thus maintaining measurement precision without requiring additional filtering stages that would slow down signal processing.
3Measurement precision
If multiple frequency components are measured simultaneously without separate modulators, then the device complexity is reduced, but the measurement precision of individual frequency components deteriorates
Solution Approach 1:
The patent segments the measurement function by allocating separate sigma-delta modulators to different frequency components. The first modulator is dedicated to measuring the in-phase component at one frequency, while the second modulator measures the quadrature component at another frequency. This segmentation ensures that each frequency component is measured with high precision without cross-interference, while the overall device complexity remains manageable through modular architecture.
Solution Approach 2:
Each sigma-delta modulator is designed as a universal building block that can be configured for different frequency measurements. The modulators share common circuitry and design principles, allowing them to perform multiple functions (measuring different frequency components) while maintaining a relatively simple overall device structure, thus resolving the contradiction between measurement precision and device complexity.
Data Source
AI summary
An input device includes a clocked comparator configured to actively drive a capacitive sensor electrode at a signal input of the clocked comparator with a first periodic reference voltage, and provide a digital representation of a sensing current resulting from driving the capacitive sensor electrode with the first periodic reference signal. The clocked comparator produces the digital representation of the sensing current based on a comparison of the signal input of the clocked generator with the first periodic reference signal. A feedback path provides negative feedback of the digital representation of the sensing current to the signal input of the clocked comparator. The input device further includes a demodulator configured to demodulate the digital representation of the sensing current using the first periodic reference signal to obtain a first digital measurement.