Switching Capacitor Circuits for Accurate Self and Mutual Capacitance
Find Innovative SolutionsGenerate Solutions
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 detection systems where sensitivity to sensor self-capacitance is high.
Innovation Solution
The development of capacitance measurement circuits that allow for separate measurement of mutual and self-capacitance using a switching capacitor technique, with circuits configured as current sinks or sources, and the use of integration capacitors coupled to ground or high voltage supply potentials, enabling precise capacitance-to-current conversion and digital value conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional capacitance measurement circuits are used, then the circuit structure is simple, but the measurement precision deteriorates due to high sensitivity to sensor self-capacitance
Solution Approach 1:
The measurement process is divided into separate phases: a first phase where the sensing electrode is connected to a first potential, and a second phase where it is connected to a second potential. This temporal segmentation allows independent measurement of mutual capacitance and self-capacitance, resolving the interference issue while maintaining reasonable circuit complexity.
Solution Approach 2:
The circuit employs periodic switching between different potential connections during measurement cycles. By alternately connecting the sensing electrode to different potentials in a periodic manner, the system can differentiate between mutual capacitance signals and self-capacitance effects, improving measurement precision without requiring overly complex circuitry.
2Measurement precision
If separate measurement of mutual and self-capacitance is implemented, then measurement precision improves, but the loss of time increases due to multiple measurement phases
Solution Approach 1:
The measurement system uses periodic switching between measurement phases, allowing both mutual and self-capacitance to be measured in alternating cycles. This approach achieves separate measurement capability while keeping the time penalty manageable through efficient phase alternation rather than sequential measurement.
Solution Approach 2:
The measurement process maintains continuous operation by alternating between different measurement modes without idle periods. While one capacitance type is being measured, the system is actively measuring the other, ensuring that useful measurement action continues throughout the entire cycle and minimizing overall measurement time.
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 of capacitance measurement, minimizing the influence of self-capacitance on mutual capacitance measurement and allowing for reliable operation in single and multi-touch detection systems, including touchscreens and touchpads, by linearizing the relationship between capacitance and integration capacitor voltage.
Implementation Method 1
an integration capacitor in a capacitance-to-current converter
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.