Capacitance Touch Sensing with Asynchronous Display Timing
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Solution Overview
Problem
Capacitance-based touch-sensitive display devices face noise interference from display activity, leading to jitter issues that can corrupt capacitance measurements, making simultaneous touch detection and display operation challenging, especially in in-cell configurations where electrodes are used for both display and touch sensing.
Innovation Solution
Implementing a touch-sensing frame rate that is asynchronous with the video frame rate, allowing capacitance measurements to be performed on a fixed basis while allocating idle time for display-write operations, thereby minimizing jitter without modifying video display electronics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If capacitance measurements are performed simultaneously with display activity, then touch detection can occur in real-time, but noise interference from display activity corrupts capacitance measurements causing jitter
Solution Approach 1:
The patent segments the frame period into distinct capacitance-measurement intervals and display-write intervals, preventing simultaneous operation of touch sensing and display writing. This temporal segmentation eliminates noise interference from display activity during capacitance measurements while maintaining real-time touch detection capability through frequent measurement frames.
Solution Approach 2:
The patent implements periodic capacitance measurements at fixed frame rates (e.g., 60 Hz or higher) within dedicated capacitance-measurement intervals. This periodic action ensures consistent, jitter-free measurements while the display operates periodically in separate intervals, resolving the contradiction between real-time detection and measurement precision.
2Device complexity
If the touch-sensing frame rate is synchronized with the video frame rate, then coordination between touch and display is simplified, but jitter from video timing variations corrupts capacitance measurements
Solution Approach 1:
The patent extracts the touch-sensing frame rate from dependency on the video frame rate, establishing an independent, fixed touch-sensing frame rate (e.g., 60 Hz). This decoupling removes jitter from video timing variations that would otherwise corrupt capacitance measurements, while the controller independently coordinates both operations without complex synchronization.
3Measurement precision
If a fixed touch-sensing frame rate different from video frame rate is used, then jitter is minimized and measurement accuracy improves, but idle time must be allocated for display-write operations
Solution Approach 1:
The patent dynamically allocates idle time within the frame period based on the difference between the fixed touch-sensing frame rate and video frame rate. The controller flexibly schedules display-write operations during these idle intervals, ensuring that capacitance measurements occur without interference while display operations complete their required writes, optimizing both measurement precision and display performance.
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 noise interference and enables accurate touch detection, including from active styluses, by decoupling touch-sensing and display-write operations, improving the reliability of capacitance measurements and user input recognition.
Implementation Method 1
perform capacitance measurements on one or more electrodes of a capacitance-based touch sensor in capacitance-measurement intervals of a touch-sensing frame
Data Source
AI summary
A touch-sensitive display device includes a capacitance-based touch sensor including a plurality of electrodes, a display including a plurality of pixels, an image source configured to output image frames at a video frame rate, and a controller. The controller is configured to perform capacitance measurements on the capacitance-based touch sensor in capacitance-measurement intervals of a touch-sensing frame, and perform display-write operations on the display to write each image frame to the display in display-write intervals of the touch-sensing frame that do not temporally overlap with the capacitance-measurement intervals of the touch-sensing frame. The controller is configured repeat the touch-sensing frame at a fixed touch-sensing frame rate that is different than the video frame rate.