Common Electrode Touch Detection Slew Rate Control
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Solution Overview
Problem
Existing touch screens require separate touch sensing layers, which can complicate integration with display functions and increase complexity, whereas integrating touch detection into display infrastructure without impacting display performance is desirable.
Innovation Solution
Configuring common electrodes in a display pixel array to function as capacitive sense elements for touch detection during allocated time durations, while providing bias or reference voltages during display operations, and using a predetermined slew rate to minimize parasitic capacitance effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If separate touch sensing layers are used for capacitive sense arrays, then touch detection capability is achieved, but device complexity and integration difficulty increase
Solution Approach 1:
The patent merges the touch sensing function with the display common electrode layer by configuring the common electrodes to operate in both display mode and touch sensing mode. This integration eliminates the need for separate touch sensing layers, directly resolving the contradiction between achieving touch detection capability and reducing device complexity.
Solution Approach 2:
The common electrodes are designed to serve dual functions: providing bias/reference voltages during display operations and acting as capacitive sense elements during touch detection. This multi-functionality allows a single component to fulfill both display and touch sensing roles, thereby reducing overall device complexity while maintaining reliable touch detection.
2Device complexity
If common electrodes are used for both display and touch sensing, then device complexity is reduced, but parasitic capacitance effects increase
Solution Approach 1:
The patent applies preliminary anti-action by driving the common electrodes with a controlled slew rate that is predetermined to prevent capacitive sense signal overshoot. This pre-established constraint on voltage change rate counteracts the harmful parasitic capacitance effects before they can cause current saturation, allowing the integrated design to function reliably.
Solution Approach 2:
The patent changes the operating parameters of the common electrodes by controlling the slew rate of the integration voltage to be less than a predetermined threshold. This parameter adjustment optimizes the balance between achieving adequate touch sensing performance and minimizing parasitic capacitance effects, enabling the common electrodes to serve both functions effectively.
3Speed
If integration voltage varies at high slew rate, then touch detection response speed improves, but current saturation occurs in capacitance sense circuit
Solution Approach 1:
The patent optimizes the slew rate parameter of the integration voltage to fall within a specific range that is sufficient for adequate touch detection response while remaining below the threshold that would cause capacitive sense signal overshoot and current saturation. This careful parameter selection resolves the contradiction between response speed and circuit reliability.
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
Enables effective touch detection within existing display infrastructure without compromising display functions, reducing the need for separate touch sensing layers and enhancing user experience and efficiency.
Implementation Method 1
reducing the impact of parasitic capacitance between the one or more electrical nodes and the set of driven common electrodes on touch detection implemented via the set of common electrodes
Implementation Method 2
Capacitances of these capacitive sense elements vary when an object (e.g., a finger, a hand, a stylus, or another object) comes into contact with or hovers above the touch sensing surface
Data Source
AI summary
This application is directed to detecting touch events using a display pixel array. The display pixel array includes display pixels each of which is disposed between a display electrode and a common electrode. For touch sensing, a processing device drives the subset of common electrodes with an integration voltage that varies by a voltage variation at a predetermined slew rate. The processing device also drives a subset of display electrodes corresponding to the subset of common electrodes in a synchronous manner, thereby reducing an impact of parasitic capacitance associated with the subset of common electrodes. Each of the subset of display electrodes is driven with an adjusted display voltage that varies by the voltage variation at the predetermined slew rate. While driving the subsets of common and display electrodes, a capacitive sense signal associated with the subset of common electrodes is measured at an output of a capacitance sense circuit.