Capacitive Touch Panel Control Device with Impedance Compensation
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Solution Overview
Problem
Capacitive touch panels face coordinate calculation errors due to varying impedance values of users, especially when the impedance value is relatively small, leading to inaccuracies in determining the touched point's coordinates.
Innovation Solution
A control method and device that input AC signals to the corners of the top conductive layer, detect current values, compensate for detected currents based on bottom conductive layer currents, and calculate coordinates using compensated values to accurately determine the touched point on a capacitive touch panel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the impedance value of the user is relatively small, then more current flows to ground through the bottom conductive layer, but coordinate calculation errors occur because the total current absorbed by the human body cannot be regarded as the summation of all current variations
Solution Approach 1:
The patent segments the current detection into two parts: current variations at the top conductive layer corners (ΔI1, ΔI2, ΔI3, ΔI4) and current through the bottom conductive layer (Ib). By separately detecting and compensating these segmented current components, the system accurately calculates coordinates regardless of whether the user's impedance is large or small.
Solution Approach 2:
The patent implements a feedback mechanism where the detected bottom layer current (Ib) is used to compensate the top layer current variations. The controller calculates the relationship between Ib and the corner current variations, then uses this feedback to correct coordinate calculation errors, ensuring accuracy across different user impedance values.
2Device complexity
If the total current absorbed by human body is regarded as the summation of all current variations, then coordinate calculation is simplified, but coordinate calculation errors exist when impedance value is relatively small
Solution Approach 1:
The patent performs preliminary detection of the bottom conductive layer current (Ib) before coordinate calculation. This preliminary action allows the system to pre-determine the compensation value needed based on the user's impedance characteristics, then apply this compensation in the coordinate calculation process to eliminate errors.
Solution Approach 2:
The bottom conductive layer current (Ib) serves as an intermediary parameter that mediates between the top layer current variations and the final coordinate calculation. By introducing Ib as an intermediate compensation factor, the system bridges the gap between simplified current summation and accurate coordinate determination.
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
The solution effectively compensates for impedance-related errors, enabling precise calculation of coordinate data for the touched point, improving accuracy across different users.
Implementation Method 1
Because the top conductive layer (81) and the bottom conductive layer (82) are made of conductive material, a capacitor exists between the two conductive layers (81)(82). Therefore, the AC signal input to the top conductive layer (81) can be conducted to the ground through the capacitor.
Implementation Method 2
the coordinate information is obtained based on variations of electrical currents since a user's finger can absorb a minor current when touching the panel
Data Source
AI summary
A control device for a capacitive touch panel has multiple voltage driving/current detecting circuits respectively connected to four corners of a top conductive layer of the touch panel. An auxiliary voltage driving/current detecting circuit is connected to a bottom conductive layer of the touch panel. When the touch panel is pressed, all voltage driving/current detecting circuits detect first current values at four corners of the top conductive layer. The auxiliary voltage driving/current detecting circuit also detects a second current value from the bottom conductive layer. The second current value is used to compensate all first current values so that the coordinate information of the position being pressed can be exactly calculated.