Capacitive Touch Sensing During Liquid Crystal Data Writing
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Solution Overview
Problem
Capacitive touch panels in display devices face challenges in accurately detecting contact positions due to radiation noise from liquid crystal panels, leading to decreased signal-to-noise ratio and increased detection errors, especially when data is being written to the liquid crystal panel.
Innovation Solution
A display device configuration that includes a position detecting section with a code sequence signal supplying circuit and a control circuit, allowing signals to be applied to position detecting elements during a period when noise from the display section is minimal, enabling accurate position detection by reconstructing signals and increasing the number of sensing events within a frame period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the touch panel operates continuously during liquid crystal panel data writing, then productivity is maintained, but measurement precision deteriorates due to radiation noise
Solution Approach 1:
The patent implements periodic sensing operations during vertical blanking periods when the liquid crystal panel is not writing data. The touch panel performs capacitance measurements only during these noise-free intervals, creating a periodic detection pattern that avoids radiation noise while maintaining continuous display operation. This resolves the contradiction by scheduling measurements when conditions are favorable rather than attempting continuous operation.
Solution Approach 2:
The patent applies code sequence signals to drive lines before the sensing period begins, allowing the system to prepare the electrical environment in advance. This preliminary signaling ensures that when the actual capacitance measurement occurs during the vertical blanking period, the drive lines are already properly conditioned, enabling accurate detection without interference from ongoing data writing operations.
2Measurement precision
If the sensing period is extended to improve signal-to-noise ratio, then measurement precision improves, but productivity decreases due to reduced display update frequency
Solution Approach 1:
The patent utilizes vertical blanking periods - brief intervals between field updates in interlaced display systems - to perform touch sensing operations. These periodic intervals provide sufficient time for capacitance measurements without extending into the active display periods, thereby maintaining the display update frequency while achieving adequate signal-to-noise ratio during the noise-free blanking periods.
Solution Approach 2:
The patent maintains continuous display operation by overlapping the touch sensing operations with the vertical blanking periods of the display refresh cycle. Rather than interrupting display updates for sensing, the system continuously performs both functions in parallel - display updating during active periods and touch sensing during blanking periods - ensuring neither function compromises the other's productivity.
3Productivity
If code sequence signals are applied to multiple drive lines simultaneously, then productivity increases by reducing sensing time, but device complexity increases
Solution Approach 1:
The patent divides the touch sensing operation into segmented phases corresponding to different vertical blanking periods and field intervals. By segmenting the sensing operation to match the display's field structure, the system can apply code sequences to multiple drive lines in parallel during each segment without creating signal conflicts. This segmentation approach enables faster sensing while keeping signal management complexity manageable through structured temporal division.
Solution Approach 2:
The patent applies code sequence signals to drive lines in advance of the actual capacitance measurement, during the early portion of the vertical blanking period. This preliminary application of signals allows multiple drive lines to be conditioned simultaneously without interfering with each other, as the signals are established before the critical measurement phase begins. This preliminary action reduces the time required for actual sensing while avoiding the complexity of coordinating simultaneous signal applications during the measurement itself.
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 configuration improves the signal-to-noise ratio and enables high-accuracy position detection by reducing the time required for sensing and increasing the number of sensing events, even during periods when data is being written to the liquid crystal panel.
Implementation Method 1
the capacitive touch panel is configured to detect the contact position of a detection target such as a finger by sensing a change in capacitance
Implementation Method 2
the radiation noise is being generated in the liquid crystal panel 51 while display data is being written
Data Source
AI summary
A sense line drive circuit (24) (i) receives signals passing through capacitances and outputted via sense lines (SeL1, SeL2 . . . and SeLn) during a period other than a period during which image data is sequentially written to a plurality of pixels in a liquid crystal panel and (ii) detects where, in a plurality of portions where the sense lines (SeL1, SeL2 . . . and SeLn) and drive lines (DL2, DL2 . . . and DLn) are close to each other, a detection target is present.