Switched Charge Transfer Capacitance Sensing Without Active Analog Circuits
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Solution Overview
Problem
Current capacitance sensors face challenges in simplifying design, achieving versatility, and maintaining cost-effectiveness while providing accurate capacitance sensing across various applications, often requiring complex and costly active analog components.
Innovation Solution
The use of switched charge transfer techniques with passive electrical networks and standard microcontrollers to detect capacitance, allowing charge sharing between measurable and filter capacitances through passive impedance, enabling accurate capacitance measurement without external active components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitance sensing techniques are used, then accurate capacitance detection can be achieved, but the design complexity increases and cost increases due to requiring active analog components
Solution Approach 1:
The patent replaces active analog components with a digital-based charge transfer technique. A microcontroller digitally switches charge between capacitances through controlled voltage application and charge sharing cycles, eliminating the need for complex analog circuitry while maintaining measurement accuracy.
Solution Approach 2:
The patent introduces a digital-to-analog converter (DAC) as an intermediary component that bridges the digital microcontroller and the analog capacitance measurement system. The DAC converts digital control signals to analog voltages needed for charge transfer, simplifying the overall design by using readily available mixed-signal components rather than complex pure analog circuitry.
2Measurement precision
If traditional capacitance sensing techniques are used, then accurate capacitance detection can be achieved, but the cost increases due to requiring external active components
Solution Approach 1:
The patent substitutes expensive active analog components with a microcontroller-based digital system. The charge transfer technique uses digital switching and counting to measure capacitance, eliminating the need for precision analog amplifiers, filters, and other costly active components, thereby reducing manufacturing costs.
Solution Approach 2:
The system uses the microcontroller's built-in digital I/O pins and timing capabilities to perform the capacitance measurement function. The microcontroller itself generates the switching signals, measures the charge transfer timing, and processes the results, eliminating the need for separate dedicated analog measurement circuits and reducing component count and cost.
3Device complexity
If switched charge transfer techniques are used, then design complexity is reduced and cost is reduced, but the requirement for external active components is eliminated which may impact measurement capability
Solution Approach 1:
The DAC serves as an intermediary that enables the digital microcontroller to control the analog charge transfer process accurately. This ensures that the simplified digital-based design maintains measurement reliability by providing precise voltage control during charge transfer operations.
Solution Approach 2:
The patent replaces active analog measurement components with a digital timing-based measurement approach. The microcontroller measures capacitance by timing the duration of charge transfer operations or counting clock cycles during charge sharing, providing reliable digital measurements without requiring analog measurement circuitry.
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 allows for efficient and cost-effective capacitance detection in a wide range of applications, including user input devices, by utilizing readily available components and reducing complexity, thus enhancing sensor design flexibility and accuracy.
Implementation Method 1
allowing the measurable capacitance to share charge with a filter capacitance through a passive impedance
Data Source
AI summary
Methods, systems and devices are described for detecting a measurable capacitance using charge transfer techniques. According to various embodiments, a charge transfer process is performed for two or more times. During the charge transfer process, a pre-determined voltage is applied to the measurable capacitance, and the measurable capacitance is then allowed to share charge with a filter capacitance through a passive impedance that remains coupled to both the measurable capacitance and to the filter capacitance throughout the charge transfer process. The value of the measurable capacitance can then be determined as a function of a representation of a charge on the filter capacitance and the number of times that the charge transfer process was performed. 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 an input sensor.