In-Cell Touch Panel Common-Electrode Level Shifting for Audible Noise
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Solution Overview
Problem
In in-cell type display touch modules, the time-sharing action between display driving and touch detection generates audible noise due to low-frequency signal components applied to common electrodes, causing parasitic capacitance and physical vibrations that can be perceived as sound, especially during the guarding action in self-capacitive touch detection.
Innovation Solution
A semiconductor device with a DC level shift circuit that adjusts the DC level of toggle signals to match the reference voltage for display, minimizing signal fluctuations and reducing audible noise by controlling the supply of reference voltages and detection signals through a timing control circuit, and utilizing a power source select circuit to manage voltage levels for efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If common electrodes are driven by toggle signals during touch detection period, then touch detection function is enabled, but audible noise is generated due to low-frequency signal components causing parasitic capacitance and physical vibrations
Solution Approach 1:
The patent changes the DC level parameter of the toggle signal to match the reference voltage during display drive period and to ground potential during touch detection period. This parameter change eliminates low-frequency signal components that cause parasitic capacitance and physical vibrations, thereby suppressing audible noise while maintaining touch detection functionality.
Solution Approach 2:
The patent implements periodic switching between display drive mode and touch detection mode. During display drive period, common electrodes receive reference voltage; during touch detection period, they receive toggle signals with adjusted DC level. This periodic action allows the system to alternate between display and touch functions while controlling noise generation through proper signal level management.
2Device complexity
If common electrodes are used for both display driving and touch detection, then device integration is improved, but signal level fluctuations cause audible noise during time-sharing operation
Solution Approach 1:
The patent dynamically changes the DC level parameter of signals applied to common electrodes based on the operational mode. By adjusting the signal level to match reference voltage during display drive and to ground potential during touch detection, the patent eliminates signal level fluctuations that would otherwise cause audible noise, enabling integrated display and touch functions to coexist without noise interference.
Solution Approach 2:
The patent introduces a level shift circuit as an intermediary component between the toggle signal source and the common electrodes. This intermediary circuit adjusts the DC level of toggle signals to appropriate values based on operational mode, mediating between the conflicting requirements of display driving and touch detection while preventing audible noise generation.
Data Source
AI summary
The semiconductor device is intended for connection with an in-cell type display touch panel having a plurality of common electrodes, a reference voltage for display is applied to the common electrodes in a display drive period, and the common electrodes serve as sensor electrodes in a touch detection period. The semiconductor device includes a DC level shift circuit operable to shift the DC level of a toggle signal output by a toggle drive circuit to the reference voltage. The semiconductor device supplies the reference voltage to the common electrodes of the display touch panel in the display drive period, and performs a guarding action in which at least a part of the plurality of common electrodes is supplied with a toggle signal shifted in DC level in the touch detection period.