Partial Mutual Capacitive Touch Sensing for Reduced Lag
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Solution Overview
Problem
Capacitive touch screens face challenges in simultaneously achieving high sensitivity for detecting user hovers and accurately distinguishing between multiple touch/hover instances, as existing self and mutual capacitance sensing modes have weaknesses such as ghosting and low sensitivity for hovers.
Innovation Solution
A method that operates a touch screen controller to switch between self and mutual capacitance sensing modes, focusing mutual capacitance sensing on only those force lines or columns with strength values above a threshold, reducing unnecessary sensing and thereby minimizing lag and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If mutual capacitance sensing is performed on all force lines, then touch detection accuracy is improved, but sensing time increases causing lag
Solution Approach 1:
Self capacitance sensing is performed first on all force lines to identify potential touch locations. Based on these preliminary results, mutual capacitance sensing is then selectively performed only on force lines that show potential touch activity, avoiding unnecessary sensing on inactive lines and reducing overall sensing time while maintaining detection accuracy
Solution Approach 2:
The sensing process is divided into two stages: a first stage performing self capacitance sensing on all force lines to identify potential touches, and a second stage performing mutual capacitance sensing only on selected force lines. This segmentation allows the system to focus computational resources where needed, reducing total sensing time while maintaining accuracy
2Speed
If self capacitance sensing is used, then sensing speed is improved, but ghosting occurs reducing touch distinction accuracy
Solution Approach 1:
The sensing process is segmented into two modes: self capacitance sensing performed on all force lines to maintain speed, followed by selective mutual capacitance sensing on identified touch lines to eliminate ghosting. This combination allows the system to benefit from the speed of self capacitance sensing while using mutual capacitance sensing to verify and clarify actual touch locations
Solution Approach 2:
Self capacitance sensing acts as an intermediary step that identifies potential touch locations, which then guides the subsequent mutual capacitance sensing process. This intermediary step allows the system to use the faster self capacitance method for initial detection while using mutual capacitance sensing as a verification mechanism to eliminate ghosting artifacts
3Measurement precision
If mutual capacitance sensing is performed on all force lines, then ghosting is reduced, but processing time increases
Solution Approach 1:
Self capacitance sensing is performed as a preliminary action to identify which force lines actually have touch activity. This preliminary information is then used to guide the mutual capacitance sensing process, ensuring that processing resources are applied only where necessary to reduce ghosting, thereby maintaining high processing throughput
Solution Approach 2:
Instead of performing mutual capacitance sensing on all force lines (excessive action), the system performs it only on the subset of force lines that show potential touch activity in the self capacitance stage (partial action). This partial application of mutual capacitance sensing is sufficient to reduce ghosting while avoiding the performance penalty of applying it universally
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 reduces the time required for mutual capacitance sensing, allowing for timely coordinate reporting within a frame rate, thereby reducing lag and enhancing the signal-to-noise ratio, effectively addressing the sensitivity and ghosting issues in capacitive touch screens.
Implementation Method 1
In mutual capacitance sensing, the capacitance between each row and column of the matrix may be sensed. A change in the sensed capacitance between a row and a column may indicate that an object, such as a finger, is touching the screen or is in proximity to the screen near the region of intersection of the row and column.
Implementation Method 2
Mutual capacitance sensing circuits employ a 'forcing' signal applied to a column conductor of the capacitive touch matrix and sensing of the coupled signal on respective row conductors (or vice-versa).
Data Source
AI summary
Disclosed herein is a method of operating a touch screen controller in a device with a touch screen having force lines and sense lines. The method includes receiving touch data from the touch screen, and operating the touch screen in a self capacitance sensing mode. In the self capacitance sensing mode, which force lines have strength values indicating a potential touch to the touch screen are determined. The method also includes operating the touch screen in a mutual capacitance sensing mode, and in the mutual capacitance sensing mode, performing mutual capacitance sensing on only a subset of the force lines, with the subset of the force lines including at least those force lines indicating the potential touch to the touch screen.