Switching Capacitance Circuits for Isolating Mutual and Self Capacitance
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Solution Overview
Problem
Capacitive touch sensors face challenges in accurately measuring self and mutual capacitance, which affects their operation and can lead to decreased measurement accuracy, especially in multi-touch applications where sensitivity and resolution are crucial.
Innovation Solution
The development of capacitance measurement circuits that allow for separate measurement of mutual and self capacitance using a switching capacitor technique, with specific circuit configurations and switching sequences to convert capacitance to current, enabling accurate detection in both single and multi-touch systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional capacitance measurement circuits are used, then the circuit structure is simple, but the measurement precision of mutual and self capacitance deteriorates
Solution Approach 1:
The measurement process is segmented into distinct phases: a first measurement phase that captures both mutual and self capacitance effects, and a second measurement phase that captures only self capacitance. By separating these measurements temporally and using differential calculation, the circuit achieves high measurement precision without requiring complex hardware structures.
Solution Approach 2:
A compensation electrode is introduced as an intermediary element that mirrors the self capacitance of the sensing electrode. This compensation electrode allows the circuit to measure and subtract self capacitance effects from the total measurement, thereby isolating the mutual capacitance component and improving measurement accuracy.
2Measurement precision
If self-capacitance influence is not compensated, then the circuit operation is simple, but the measurement precision of mutual capacitance deteriorates
Solution Approach 1:
The self capacitance component is extracted from the total capacitance measurement through a dedicated compensation measurement phase. By measuring self capacitance separately and subtracting it from the combined measurement, the circuit isolates the mutual capacitance signal, achieving high precision without adding significant operational complexity.
Solution Approach 2:
The circuit uses feedback by measuring self capacitance in one phase and using that information to compensate for self capacitance effects in the mutual capacitance measurement. This feedback mechanism allows the system to dynamically adjust for parasitic capacitance variations, improving measurement 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
These circuits enhance the accuracy and sensitivity of capacitance measurement, improving the reliability of capacitive touch sensors in various applications, including multi-touch touchpads and touchscreens by minimizing the influence of self-capacitance on mutual capacitance measurement.
Implementation Method 1
capacitance measurement circuits that allow for separate measurement of mutual and self capacitance using a switching capacitor technique
Implementation Method 2
switching sequences to convert capacitance to current
Data Source
AI summary
An embodiment of a capacitance measurement circuit may include multiple switches, a first node coupled with a first electrode and coupled with at least a first switch of the multiple switches, and a second node coupled with a second electrode and coupled with at least a second switch of the multiple switches, where the multiple switches are configured to reduce an influence of a self-capacitance of the first electrode and a self-capacitance of the second electrode on an output signal during measurement of a mutual capacitance between the first electrode and the second electrode, and where the multiple switches are configured to reduce an influence of the mutual capacitance on the output signal during measurement of at least one of the self-capacitance of the first electrode and the self-capacitance of the second electrode.