Sigma-Delta Capacitance Detection Using Passive Networks
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Solution Overview
Problem
Current capacitance sensors face challenges in simplifying design while maintaining accuracy and cost-effectiveness, particularly in requiring external active analog components, which increases complexity and cost.
Innovation Solution
The implementation of sigma-delta measurement techniques using passive networks and standard microcontrollers, eliminating the need for external active analog components by applying a voltage to measurable capacitance, allowing charge sharing with a passive network, and adjusting charge based on threshold values to quantify capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If external active analog components are used in capacitance sensors, then measurement precision is improved, but device complexity and cost increase
Solution Approach 1:
The patent replaces active analog components (electronic circuitry) with passive components (capacitors, resistors, switches) and digital signal processing. The measurement system uses a passive RC network combined with a sigma-delta modulator implemented in digital logic or microcontroller, eliminating the need for operational amplifiers, voltage followers, and other active analog components while maintaining measurement precision through digital filtering and processing of the quantized charge signals.
Solution Approach 2:
The patent introduces a passive RC network as an intermediary between the capacitance sensor and the digital processing stage. This passive network converts the capacitive charge into a voltage signal that can be processed by digital logic through the sigma-delta modulator, serving as a bridge between the analog sensor output and digital processing without requiring active analog components.
2Measurement precision
If external active analog components are used in capacitance sensors, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive active analog components with inexpensive passive components and standard digital logic or microcontroller units. The passive RC network uses simple capacitors and resistors that are cheap to manufacture, and the sigma-delta modulator can be implemented using standard digital logic families or integrated into a microcontroller, significantly reducing bill of materials cost while maintaining measurement precision through digital processing.
Solution Approach 2:
The patent enables the system to perform its own signal conditioning and processing functions using passive components and digital logic that are already present in the system. The RC network naturally performs charge-to-voltage conversion, and the sigma-delta modulator uses the system's existing digital processing capabilities, eliminating the need for additional expensive active components and reducing overall manufacturing cost.
3Device complexity
If passive networks and sigma-delta techniques are used, then device complexity is reduced, but measurement precision may worsen
Solution Approach 1:
The patent employs periodic charging and discharging cycles in the RC network, where the capacitor is repeatedly charged to a reference voltage and then discharged through the RC time constant. This periodic action generates a train of quantized pulses that represent the input capacitance value. The periodic nature allows the use of simple digital counting and averaging to achieve high measurement precision without complex circuitry.
Solution Approach 2:
The patent implements a feedback mechanism in the sigma-delta modulator where the quantized output is fed back through the RC network to adjust the charging process. This feedback ensures that the average output voltage accurately represents the input capacitance value, compensating for non-linearities and improving measurement precision. The feedback loop operates digitally, maintaining simplicity while enhancing accuracy.
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 approach enables efficient and accurate capacitance detection with reduced complexity and cost, suitable for various applications, including position sensing of fingers or objects, using readily available components.
Implementation Method 1
The measurable capacitance is allowed to share charge with a passive network
Data Source
AI summary
Methods, systems and devices are described for detecting a measurable capacitance using sigma-delta measurement techniques. According to various embodiments, a voltage is applied to the measurable capacitance using a first switch. The measurable capacitance is allowed to share charge with a passive network. If the charge on the passive network is past a threshold value, then the charge on the passive network is changed by a known amount for a sufficient number of repetitions until the measurable capacitance can be detected. Such a detection scheme may be readily implemented using conventional components, and can be particularly useful in sensing the position of a finger, stylus or other object with respect to a button, slider, touchpad or other input sensor.