LCD Ground Noise Filtering Circuit for In-Cell Touch Panels
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Solution Overview
Problem
Display devices using in-cell touch panel LCDs suffer from malfunctions due to ground noise generated by radio waves, which cause significant voltage differences between common and pixel electrodes, leading to display errors.
Innovation Solution
The display device incorporates capacitors and impedance devices with specific impedance characteristics to block DC components and reduce impedance in frequency bands where ground noise is generated, using a series LC circuit to filter out noise at resonant frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the ground line is connected to both the battery and vehicle body ground, then the display device can be grounded properly, but ground noise from radio waves propagates through the ground line causing malfunction
Solution Approach 1:
The patent introduces a capacitor as an intermediary component between the ground line and the display device ground. This capacitor blocks the propagation of ground noise from the vehicle body ground to the display device while maintaining the grounding function, thus resolving the contradiction between grounding reliability and ground noise suppression
Solution Approach 2:
The patent changes the electrical parameters of the grounding path by introducing capacitive coupling. The capacitor's impedance characteristics allow it to block low-frequency ground noise while maintaining DC grounding, effectively changing the frequency response of the ground path to suppress harmful noise frequencies
2Ease of operation
If the ground line length is at least 1m between the display device and battery, then the display device can be connected to the battery ground, but the ground line forms an antenna that generates and propagates ground noise
Solution Approach 1:
The capacitor acts as a mediator that breaks the continuous conductive path of the ground line, preventing the formation of an effective antenna. By introducing this intermediary component, the ground line cannot function as a resonant antenna even when it has significant length, thus eliminating the antenna effect while maintaining grounding capability
3Reliability
If ground noise propagates to the display device, then the display device can operate, but voltage differences between common and pixel electrodes cause display errors
Solution Approach 1:
The capacitor serves as a mediator that isolates the display device's internal ground from external ground noise. This intermediary component prevents voltage fluctuations caused by ground noise from appearing on the pixel and common electrodes, thereby maintaining both operational reliability and display accuracy
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 effectively suppresses ground noise, minimizing voltage differences between common and pixel electrodes, thereby reducing display errors and ensuring stable operation.
Implementation Method 1
a capacitor having one end connected to wiring of the power source between the power source section and the display device, and an impedance device disposed between the other end of the capacitor and the ground of the display device. Here, the capacitor and the impedance device have such impedance characteristics that a DC component is blocked and impedance in a predetermined frequency band set as a frequency band in which ground noise is generated is reduced
Implementation Method 2
the capacitor and the impedance device have such impedance characteristics that a DC component is blocked and impedance in a predetermined frequency band set as a frequency band in which ground noise is generated is reduced
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 3A~3C
AI summary
A metal housing includes a printed circuit board, a display panel with an LCD panel, and an FPC that connects the printed circuit board and the LCD panel. An EH power source and an EL power source on the printed circuit board are used to drive pixel electrodes on the LCD panel. A series LC circuit and capacitors are disposed on the printed circuit board, and one end of the series LC circuit is connected to the ground and the other end is connected to power source wiring via the capacitors. The impedance characteristics of the series LC circuit and the capacitors C4 and C5 are set such that the impedance is sufficiently small in a frequency band of predicted ground noise and large in other frequency bands.