Trackpad Current Compensation for Metallic Finish Sensitivity Loss
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Solution Overview
Problem
Trackpads suffer from reduced sensitivity due to insulating metallic finishes and larger electrode sizes, which decrease the signal-to-noise ratio and hinder finger detection, limiting their precision and range of applications.
Innovation Solution
A current source is used to negatively compensate for the charging current of the trackpad's capacitors, increasing sensitivity by sinking a portion of the charging current and enhancing the charging current when a finger is present, thereby improving the detection of finger presence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a metallic finish is applied to the trackpad surface for aesthetics, then the appearance is enhanced, but the sensitivity of the trackpad decreases due to the insulating layer
Solution Approach 1:
A mylar label is introduced as an intermediary layer between the metallic finish and the electrode grid. This label has a capacitively-coupled region that allows electrical coupling through the insulating metallic layer, enabling the finger to capacitively couple to the electrode beneath the metallic finish while maintaining the aesthetic appearance.
2Area of stationary object
If electrodes with larger surface area are used, then the trackpad area increases, but the parasitic capacitance increases and sensitivity decreases
Solution Approach 1:
The mylar label with its capacitively-coupled region acts as a mediator that enhances the capacitive coupling between the finger and the electrode. This allows the use of larger electrode areas to increase trackpad size while the label's coupling region maintains sensitivity by reducing the effective parasitic capacitance impact.
3Illumination intensity
If the insulating layer thickness increases, then the aesthetic finish is improved, but the signal-to-noise ratio decreases by up to 60%
Solution Approach 1:
The mylar label with its capacitively-coupled region serves as a mediator that penetrates or bridges the insulating metallic finish. This coupled region provides a direct capacitive pathway that bypasses the insulating effect of the thick metallic layer, restoring the signal-to-noise ratio while allowing the use of thicker insulating layers for aesthetic purposes.
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 enhances the sensitivity of trackpads, allowing for more precise input and a wider range of applications by increasing the sensitivity to finger presence, even with insulating metallic finishes and larger electrodes.
Implementation Method 1
As a finger moves across the grid, the finger forms the second plate of a two-plate capacitor. The finger effectively capacitvely couples to the lower electrode, thus changing the capacitance of the electrode beneath the finger by some small amount.
Implementation Method 2
A current source is used to negatively compensate for the charging current of the trackpad's capacitors, increasing sensitivity by sinking a portion of the charging current and enhancing the charging current when a finger is present
Data Source
AI summary
A device compensating for a loss in sensitivity of a sensor, such as a trackpad. The device may be standalone, integrated with the trackpad itself, or within the associated integrated circuit designed to measure relative electrode capacitances. The embodiment generally employs a current source to negatively compensate for the current available to charge at least one capacitor (or other storage device) in the trackpad.