Capacitive Touch Noise Compensation Using Impedance Dividers
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
As touch sensitive displays in handheld devices become thinner, they experience increased parasitic capacitances that couple display noise to the sensing layer, degrading touch sensing accuracy due to uneven noise amplitudes across sense lines.
Innovation Solution
A common voltage layer is used to capacitively couple display noise to sense lines via different parasitic impedances, with compensation impedances of varying values to equalize noise amplitudes at each sense line, and a sense block performs differential sensing to reject noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If touch sensitive displays are made thinner to meet consumer desires, then device thickness is reduced, but parasitic capacitances increase causing display noise to couple through to the sensing layer
Solution Approach 1:
The patent applies local quality by providing different compensation impedance values to different sense lines based on their specific locations. Sense lines closer to display noise sources receive different compensation than those farther away, creating location-specific noise cancellation that addresses the uneven noise distribution caused by thin display construction.
Solution Approach 2:
The patent changes the impedance parameter of compensation elements coupled to each sense line to equalize noise amplitudes. By adjusting compensation impedance values based on measured or simulated noise levels at each sense line location, the system compensates for position-dependent noise coupling in thin displays.
2Object-affected harmful factors
If display noise coupling is reduced through conventional methods, then some noise rejection is achieved, but undesirable amounts of display noise remain coupled through to the sensing layer
Solution Approach 1:
The patent implements feedback by measuring or simulating the actual noise amplitude at each sense line location, then using this information to determine appropriate compensation impedance values. This closed-loop approach ensures that the compensation is precisely tailored to the actual noise conditions, achieving superior noise rejection and maintaining touch sensing accuracy.
Solution Approach 2:
The patent applies preliminary action by pre-calculating or pre-measuring the noise coupling characteristics for each sense line location before operation. Compensation impedance values are determined in advance based on these characteristics, allowing the system to proactively cancel noise rather than reactively correcting it during operation.
3Measurement precision
If different noise amplitudes are present at different sense lines, then noise rejection becomes difficult, but uniform compensation may not be effective due to location-dependent noise levels
Solution Approach 1:
The patent addresses location-dependent noise by implementing local quality through position-specific compensation impedance values. Each sense line receives compensation tailored to its specific location and noise characteristics, achieving uniform noise amplitudes across all sense lines while accounting for the spatial variation in noise coupling.
Solution Approach 2:
The patent applies segmentation by dividing the sensing layer into multiple zones based on sense line locations relative to display noise sources. Each zone receives appropriate compensation through individually configured compensation elements, allowing the system to manage complexity by organizing compensation on a per-zone basis rather than requiring a completely different approach for each sense line.
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 solution effectively reduces display noise interference, enhancing the accuracy and reliability of touch sensing by equalizing noise amplitudes across sense lines and using differential sensing to reject noise, thereby improving the performance of touch sensitive displays.
Implementation Method 1
The common voltage layer capacitively coupling the display noise from the display layer to the each of the plurality of sense lines of the sensing layer via a different parasitic impedance
Implementation Method 2
Each of the plurality of compensation impedances forms an impedance divider with the parasitic impedance of its respective sense line
Implementation Method 3
The sense block rejects the display noise by performing differential sensing of the plurality of sense lines
Data Source
AI summary
An electronic device disclosed herein includes a display layer generating display noise based on scanning thereof, and a sensing layer including a plurality of sense lines. A common voltage layer is coupled to the display layer and the sensing layer, with the common voltage layer capacitively coupling the display noise from the display layer to the each of the plurality of sense lines of the sensing layer via a different parasitic impedance. An amplitude of the display noise seen at an input to each sense line is a function of a location of that sense line. The electronic device includes a plurality of compensation impedances, with each compensation impedance coupled to a different one of the plurality of sense lines. Each of the plurality of compensation impedances has an impedance value such that an amplitude of the display noise at an output of each sense line is substantially equal.