Capacitive Touch Screen Spread Spectrum Signal Processing
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Solution Overview
Problem
Capacitive touch screens face challenges in improving sensitivity to detect inputs from conductive pens with smaller contact areas, as existing methods amplify noise along with signals, leading to increased malfunctions due to inadequate signal-to-noise ratio.
Innovation Solution
The implementation of a capacitive touch screen apparatus that generates and processes spread spectrum signals to enhance signal restoration and noise reduction, using electrode layers aligned in different directions, and employing signal restoration units to synchronize and filter signals, thereby improving sensitivity and reducing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the threshold level is decreased to improve sensitivity for detecting conductive pen inputs, then sensitivity is improved, but the probability of generating malfunctions increases due to inadequate signal-to-noise ratio
Solution Approach 1:
A noise filter is introduced as an intermediary component between the signal detection unit and the threshold comparison process. The noise filter processes the detected signal to remove noise components before the signal is compared to the threshold, allowing the threshold to remain at a safe level while still achieving high sensitivity through improved signal quality.
Solution Approach 2:
Noise filtering is performed in advance before the threshold comparison and decision-making processes. By pre-processing the signal to remove noise, the system prepares a cleaner signal that can be reliably compared against the threshold, preventing malfunctions while maintaining sensitivity.
2Measurement precision
If signal amplification is applied to enhance weak touch signals, then signal detection capability is improved, but noise is simultaneously amplified leading to degraded signal-to-noise ratio
Solution Approach 1:
The noise filter serves as an intermediary that selectively processes signal components. It allows weak touch signals to pass through while attenuating noise components, enabling signal enhancement without proportional noise amplification. This resolves the contradiction by introducing frequency-selective or amplitude-selective filtering between the detection and amplification stages.
Solution Approach 2:
The filtering operation applies different quality characteristics to different parts of the signal spectrum. Rather than uniformly amplifying all signal components, the system applies selective amplification to signal frequencies while suppressing noise frequencies, achieving local quality enhancement that improves signal-to-noise ratio.
3Reliability
If a large contact area is used to increase capacitance change for reliable detection, then detection reliability is improved, but the ability to detect small contact inputs like conductive pens is reduced
Solution Approach 1:
The system changes the detection parameter from relying solely on capacitance change magnitude to using noise-filtered signal characteristics. By processing the signal through a noise filter, the system can detect subtle capacitance changes from small contacts with the same reliability as larger contacts, because the filtering enhances the signal-to-noise ratio for all contact sizes equally.
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 effectively identifies touch coordinates with improved sensitivity and reduced noise, enhancing the accuracy of touch input detection on capacitive touch screens, particularly for conductive pens, while maintaining a stable signal-to-noise ratio.
Implementation Method 1
an electric field is generated between the first electrode layer 11 and the second electrode layer 13. The predetermined signal applied to the first electrode layer 11 is transferred to the second electrode layer 13 through the electric field
Implementation Method 2
When the predetermined signal is applied to the first electrode layer 11 from the first circuit, an electric field is generated between the first electrode layer 11 and the second electrode layer 13
Implementation Method 3
A spread spectrum signal is generated, and the spread spectrum signal is applied to the first electrode layer
Implementation Method 4
a band restoration is processed for a signal input from the second electrode layer
Data Source
AI summary
Methods and apparatus are provided for identifying coordinates of a touch area on a touch screen panel based on a capacitive scheme. The touch screen panel has a first electrode layer having first electrode lines aligned in a first direction and a second electrode layer having second electrode lines aligned in a second direction. A signal generation unit generates a spread spectrum signal and supplies the spread spectrum signal to the first electrode layer. A signal restoration unit processes a band restoration for a signal input from the second electrode layer. A touch area coordinate identification unit identifies the coordinates of the touch area on the touch screen panel from a signal input from the signal restoration unit.