Touch Panel Drive Cycle Decoupling for LCD Noise Reduction
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Solution Overview
Problem
In liquid crystal display devices with touch panels, the drive frequency of the touch panel is synchronized with the horizontal synchronizing signal, leading to potential false detections due to noise or electromagnetic interference.
Innovation Solution
The touch panel is driven by a drive pulse with a cycle different from the display's horizontal synchronizing signal, using a drive pulse output unit that applies pulses at multiple timings within one horizontal synchronizing period, and a detection circuit that accumulates potential changes at both rising and falling edges of the drive pulses, while a detection switch is controlled to avoid noise interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the touch panel is driven at the same frequency as the horizontal synchronizing signal for display, then the scanning timing is synchronized with display, but false detections occur due to electromagnetic interference and noise at integral multiple frequencies
Solution Approach 1:
The patent applies periodic action by driving the touch panel at a frequency that is an integer multiple of the display horizontal synchronizing signal frequency. Specifically, the touch panel scanning is performed at frequencies such as 2 times, 3 times, or higher multiples of the horizontal synchronizing signal frequency. This periodic driving approach allows the system to perform multiple touch detection cycles within one display horizontal period, improving detection reliability while avoiding electromagnetic interference that occurs at the fundamental display frequency.
2Reliability
If the touch panel scanning is performed at integral multiple frequencies of the horizontal synchronizing signal, then touch detection reliability improves, but electromagnetic interference and noise at these frequencies may cause false detections
Solution Approach 1:
The patent introduces an intermediary approach by using a frequency multiplication relationship between the touch panel driving signal and the display horizontal synchronizing signal. Instead of directly driving at the display frequency (which causes interference) or at completely unrelated frequencies (which reduce efficiency), the system uses integer multiple frequencies as an intermediary that maintains synchronization benefits while avoiding the fundamental interference frequency. This intermediary frequency relationship allows the detection circuit to distinguish touch signals from interference through frequency discrimination.
3Device complexity
If the drive frequency of the touch panel is synchronized with the horizontal synchronizing signal, then the system operation is simplified, but noise at the drive frequency and its harmonics causes false detections
Solution Approach 1:
The patent applies universality by making the touch panel driving system multi-functional with respect to frequency relationships. The same horizontal synchronizing signal that controls display timing also serves as the basis for touch panel driving, but through frequency multiplication. This allows a single synchronizing signal source to control both display and touch operations, maintaining system simplicity while the frequency multiplication provides the functional differentiation needed to avoid interference and improve detection 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
This approach reduces false detections by decoupling the touch panel's drive cycle from the display's electromagnetic interference, allowing for accurate touch detection with reduced noise influence.
Implementation Method 1
devices that display an image by changing the orientation of a liquid crystal composition confined between two substrates, a thin film transistor substrate (hereinafter referred to as a 'TFT substrate') and a color filter substrate, through a change in an electric field to thereby control the degree of transmission of light transmitting through the liquid crystal composition
Implementation Method 2
an electrostatic capacitive coupling system that detects a change in capacitance
Data Source
AI summary
A liquid crystal display device with a touch panel includes: pixel electrodes as a plurality of electrodes to each of which a potential corresponding to a gray-scale value is applied; common electrodes as a plurality of electrodes that extend in one direction; detection electrodes as a plurality of electrodes that extend in a direction different from the one direction and detect a contact position on the panel; a liquid crystal layer that is formed of a liquid crystal composition; and a drive pulse output unit that sequentially applies a potential for detecting a touch to drive electrodes as a plurality of electrodes of a portion of the common electrodes, wherein the drive pulse output unit can output a drive pulse to the drive electrode at plural different timings within one horizontal synchronizing period for display.