Interdigitated Touch Pad Electrode Design for Noise Reduction
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Solution Overview
Problem
Conventional capacitive touch sensor panels suffer from excessive noise and thermal drift, and do not provide a linear response as a finger moves across the touch-sensitive surface.
Innovation Solution
A multi-touch sensor panel design featuring a substrate with interdigitated conductive traces forming a rectilinear pattern, where rows and columns of traces are formed on either side of the substrate, allowing for improved connectivity and reduced noise through the use of flex circuits and a double-sided ITO substrate, and a novel fabrication process that minimizes the area needed for connectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If conventional transparent traces (ITO or ATO) are used on glass layers, then the touch panel maintains transparency and allows display visibility, but the panel exhibits excessive noise and thermal drift with non-linear response
Solution Approach 1:
The patent changes the material parameter from transparent conductive oxide (ITO/ATO) to opaque conductor (copper), and changes the trace geometry from conventional patterns to interdigitated comb patterns. This parameter change eliminates noise and thermal drift while maintaining the essential function of electrical conduction, though it sacrifices transparency for touch pad applications where display visibility is not required.
2Reliability
If conventional row and column trace patterns are used, then the sensor panel can detect touch events, but the response is non-linear as a finger moves across the surface
Solution Approach 1:
The patent employs asymmetric interdigitated comb patterns where alternate traces are driven with opposite phase signals. This asymmetric configuration creates a linear gradient in the electric field across the touch surface, enabling linear response as a finger moves across the panel while maintaining reliable touch detection capability.
3Measurement precision
If larger sensor panel areas are used to improve signal strength, then touch detection sensitivity increases, but the device size and complexity increase
Solution Approach 1:
The patent uses dynamic alternating phase driving signals applied to interdigitated traces, creating time-varying electric fields that enhance signal detection. This dynamic approach allows smaller panel areas to achieve the same sensitivity as larger conventional panels by optimizing the temporal characteristics of the detection signal.
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 design reduces noise and thermal drift, provides a linear response across the touch-sensitive surface, and allows for smaller sensor panel sizes while maintaining effective touch detection and tracking capabilities.
Implementation Method 1
At the 'intersections' of the traces, where the traces pass above and below each other ( but do not make direct electrical contact with each other), the traces essentially form two electrodes.
Implementation Method 2
The top and bottom glass layers are separated by a clear polymer spacer that acts as a dielectric between the row and column traces.
Data Source
AI summary
A multi-touch capacitive touch sensor panel can be created using a substrate with column and row traces formed on separate layers of the substrate. The column and row traces can include sections extending from a central trace and forming a rectilinear trace pattern with sections of the columns and rows interdigitated with one another. The trace pattern can comprise a plurality of pixels arranged continuously across the sensor panel. In this manner, the sensor panel can provide a linear or near linear response to touches across the touch sensor panel.