Guarded Power Domain for Touch Sensing Accuracy
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Solution Overview
Problem
Capacitive touch sensor panels in touch screens often experience errors due to parasitic or stray capacitances between touch node electrodes and other components, which can affect the accuracy of touch detection.
Innovation Solution
Operating the touch and display circuitry in a different power domain than the rest of the system, using a guarded power domain for touch operations and a system power domain for display operations, and employing a guard buffer to differentiate the chassis ground from the battery ground, thereby reducing or eliminating stray capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If touch and display circuitry operate in the same power domain as the rest of the system, then device complexity is reduced, but parasitic capacitances between touch electrodes and chassis ground increase causing touch detection errors
Solution Approach 1:
The system is divided into separate power domains: a guarded power domain for touch circuitry and a system power domain for display and other circuitry. This segmentation isolates the touch electrodes from parasitic capacitances to chassis ground, improving touch detection accuracy while managing the complexity through structured domain separation.
Solution Approach 2:
A guard buffer acts as an intermediary component between the guarded power domain and the system power domain. It differentiates between chassis ground and battery ground, providing a reference voltage that eliminates the effect of parasitic capacitances on touch electrode measurements, thereby resolving the contradiction between reliability and complexity.
2Measurement precision
If touch operations use a guarded power domain, then stray capacitances are reduced improving measurement precision, but device complexity increases due to multiple power domains
Solution Approach 1:
The guarded power domain provides a specialized local environment for touch circuitry with distinct electrical characteristics (guarded reference voltage) compared to the system power domain. This local quality optimization ensures high measurement precision for touch sensing without requiring the entire device to adopt complex guarded architecture.
Solution Approach 2:
The guard buffer serves as a mediator that translates between the guarded reference voltage domain and the system ground domain. It enables precise touch measurements by maintaining the guarded reference voltage while interfacing with standard system components, thus improving measurement precision without proportionally increasing overall device complexity.
3Use of energy by moving object
If touch and display operations are time-multiplexed, then power efficiency is improved, but operational speed decreases due to sequential operation
Solution Approach 1:
The system dynamically switches between time-multiplexed operation (for power efficiency) and concurrent operation (for speed requirements). During idle periods, touch and display operations are time-multiplexed to save power. When responsiveness is critical, the system enables concurrent operation in the guarded power domain, providing adaptive performance optimization.
Solution Approach 2:
The system employs periodic time-multiplexed operation where touch sensing and display refreshing are alternated in periodic time slots. This periodic action reduces average power consumption while maintaining acceptable responsiveness. The periodic structure allows the system to switch to concurrent operation during critical periods when speed is prioritized over power savings.
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 improves the accuracy of touch detection by minimizing the impact of stray capacitances, enhancing the signal-to-noise ratio and dynamic range, and allowing for concurrent touch and display operations while maintaining power efficiency.
Implementation Method 1
parasitic or stray capacitances can exist between the touch node electrodes used for sensing touch on the touch sensor panels, and other components of the devices in which the touch sensor panels are included
Data Source
AI summary
An electronic device can include an integrated touch and display chip that can operate in multiple power domains. For example, the integrated touch and display chip can operate in a guarded power domain during the touch operation and can operate in a system power domain during non-guarded display operations. In some examples, two power domains can include a guarded power domain and a system power domain, whose grounds can be differentiated by a guard buffer signal. In some examples, the guard buffer can be disposed between the integrated touch and display chip and a battery of the device. In some examples, the guard buffer can be disposed between the battery of the device and the chassis of the device.