Sigma-Delta Capacitance Converter for Continuous Dynamic Sensing
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Solution Overview
Problem
Conventional capacitance sensing methods, such as charge-accumulation circuits, face limitations in tracking dynamic capacitance changes and require multiple stages (reset, integrate, measure) which reduces accuracy and flexibility, and are not suitable for single-wire configurations or dynamic full-scale range adjustments.
Innovation Solution
A sigma-delta modulator-based system that continuously measures capacitance using a switching capacitor in a feedback loop, allowing adjustments to conversion time and resolution, and operates in a one-wire configuration without an operational amplifier or separate comparator, enabling tracking of fast capacitance changes and simultaneous output to different digital filters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional charge-accumulation circuits are used for capacitance measurement, then the measurement process is structured with multiple stages (reset, integrate, measure), but this reduces measurement accuracy and flexibility
Solution Approach 1:
The patent merges the reset, integrate, and measure stages into a single continuous measurement process using a sigma-delta modulator. The modulator continuously compares the sensor capacitance with a reference capacitance and generates a digital output stream, eliminating the need for separate staged operations while improving measurement accuracy through continuous feedback.
Solution Approach 2:
The sigma-delta modulator implements continuous capacitance measurement by constantly switching between the sensor capacitance and reference capacitance. This continuous action allows for dynamic tracking of capacitance changes and provides higher resolution measurements compared to discrete staged approaches.
2Adaptability or versatility
If conventional capacitance sensing methods are used, then the system structure is well-defined, but it is not suitable for single-wire configurations or dynamic full-scale range adjustments
Solution Approach 1:
The sigma-delta modulator circuit is designed to handle multiple measurement modes and configurations through a single unified structure. The same circuit can operate with single-wire or multi-wire configurations and adapt to different full-scale ranges by adjusting the reference capacitance value, providing universal applicability without requiring separate dedicated circuits for each mode.
3Speed
If conventional methods are used, then the measurement process is discrete, but this reduces the ability to track dynamic capacitance changes
Solution Approach 1:
The sigma-delta modulator provides continuous measurement by constantly switching between capacitors and integrating the difference over time. This continuous process enables the system to track rapid capacitance changes while maintaining high resolution through the accumulation of measurement data over multiple switching cycles.
Solution Approach 2:
The modulator uses periodic switching between the sensor capacitance and reference capacitance at a high frequency. This periodic action, combined with digital filtering of the output stream, enables both fast tracking of dynamic changes and high measurement precision through averaging effects.
Data Source
AI summary
Apparatuses and methods of converting a capacitance measured on a sense element to a digital value are described. One apparatus includes a modulator having a modulator capacitor, a sense element selectively coupled in a feedback loop of the modulator to operate as a switching capacitor. The apparatus also includes a first switch coupled between a voltage source and a first node of the switching capacitor and a second switch coupled between the first node of the switching capacitor and a first node of the modulator capacitor. The switching capacitor provides a charge current to the modulator capacitor via the second switch. The modulator measures a capacitance of the sense element and converts the measured capacitance to a digital code representing the capacitance.