Mutual Capacitance Touch Panel Phase Shift Mitigation
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Solution Overview
Problem
Large mutual capacitance touch screen panels face performance issues due to excessive phase shifts, which are not effectively handled by existing technologies, leading to increased power consumption and silicon die area, especially when a 90-degree panel rotation is required to mitigate phase shift, resulting in higher costs and inefficiencies.
Innovation Solution
The implementation of an orthogonal-based digital signal processing methodology using a Hadamard matrix or its modified version, with cyclical extensions and region-specific phase shifts, allows for effective phase shift mitigation without the need for 90-degree rotation, thereby reducing power consumption and silicon die area while maintaining orthogonality of row drive signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the panel is rotated 90 degrees to reduce column length and phase shift, then phase shift is reduced, but the number of columns exceeds rows requiring more A/Ds and LNAs, increasing power consumption and silicon die area
Solution Approach 1:
The patent changes the excitation matrix from conventional non-orthogonal designs to orthogonal matrices (Hadamard or Walsh matrices), fundamentally altering the signal processing parameters. This enables accurate capacitance decoding without panel rotation, maintaining the preferred configuration with fewer columns than rows while eliminating excessive phase shift issues through mathematical orthogonality properties
2Reliability
If the panel is rotated 90 degrees to reduce column length and phase shift, then phase shift is reduced, but silicon die area increases due to more A/Ds and LNAs
Solution Approach 1:
The patent transforms the signal processing approach by implementing orthogonal excitation matrices, which fundamentally changes the system parameters to eliminate phase shift sensitivity. This allows maintaining the cost-effective panel configuration with fewer columns requiring fewer A/D converters and LNA amplifiers, thereby reducing silicon die area while achieving reliable phase shift mitigation
3Device complexity
If conventional excitation matrices are used, then device complexity is lower, but condition number is high causing error amplification and poor signal-to-noise ratio
Solution Approach 1:
The patent changes the fundamental parameter of the excitation matrix from conventional designs to orthogonal matrices with perfect orthogonality properties. This parameter change results in a condition number of 1, which eliminates error amplification during inversion and provides optimal signal-to-noise ratio, dramatically improving capacitance measurement precision despite increased computational structure
Data Source
AI summary
A method of mitigating a phase shift in a mutual capacitance touch screen panel having a plurality of row conductors intersecting with a plurality of column conductors to form a matrix of pixels, the method comprising: driving the row conductors with row drive signals formed from an excitation matrix, wherein each row in the excitation matrix is orthogonal to every other row in the excitation matrix, and the excitation matrix has a dimension larger than the matrix of pixels; sensing signals from the column conductors; and determining the mutual capacitance of the pixels using the sensed signals and an inverse of the excitation matrix. The excitation matrix can be a Hadamard matrix or a modified Hadamard matrix and can comprise a cyclic extension at the end of each row. A different region-specific phase shift can be applied to different clusters of signals.