Common-Mode Hover Detection for Touch Sensors
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Solution Overview
Problem
Current touch sensors face challenges in accurately detecting the presence and location of touches or proximity inputs due to noise interference from display components, which affects the reliability of capacitance measurements.
Innovation Solution
The implementation of a mechanical stack with a conductive layer positioned between the touch sensor electrodes and the display, acting as a shield to reduce noise interference, combined with a touch-sensor controller that processes changes in capacitance to determine the position of touches or proximity inputs, using drive and sense electrodes capacitively coupled across a space without electrical contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a touch sensor is integrated with a display screen, then direct user interaction with displayed content is enabled, but noise interference from display components degrades capacitance measurement reliability
Solution Approach 1:
A common-mode sensor is introduced as an intermediary element between the touch sensor electrodes and the display components. This common-mode sensor detects noise signals generated by display components (such as backlight inductors) and enables the controller to subtract these noise signals from the capacitance measurements, thereby isolating the true touch signal from the harmful electromagnetic interference.
Solution Approach 2:
The system implements a feedback mechanism where the common-mode sensor continuously monitors noise levels and provides this information to the controller. The controller then uses this feedback to dynamically adjust and subtract the noise component from the touch sensor readings, creating a closed-loop system that actively compensates for interference.
2Device complexity
If touch sensor electrodes are positioned close to display components, then integration is achieved, but noise interference from display components increases
Solution Approach 1:
The common-mode sensor serves as a mediator that is strategically positioned between the touch sensor electrodes and the display components. This intermediary structure allows the system to maintain close integration while simultaneously providing a detection mechanism for noise signals, enabling the controller to distinguish between touch inputs and display-generated interference.
Solution Approach 2:
The system converts the harmful noise signals generated by display components into useful information by using the common-mode sensor to detect these same noise signals. The controller then uses this detected noise information to subtract the interference from the capacitance measurements, thereby transforming the harmful electromagnetic interference into a correctable parameter that improves overall measurement accuracy.
3Measurement precision
If capacitance measurement sensitivity is increased to detect lighter touches, then detection precision improves, but susceptibility to noise interference increases
Solution Approach 1:
The common-mode sensor provides continuous feedback about noise levels to the controller, enabling real-time adjustment of the measurement process. The controller uses this feedback to dynamically subtract noise components from the capacitance readings, allowing the system to maintain high sensitivity for detecting light touches while simultaneously compensating for noise interference through active signal processing.
Solution Approach 2:
By detecting noise signals through the common-mode sensor, the system converts what would otherwise be harmful interference into useful information. The controller uses this noise information to subtract the interference component from the capacitance measurements, thereby enabling high-sensitivity touch detection even in the presence of display-generated electromagnetic noise.
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 configuration enhances the accuracy and reliability of touch detection by effectively shielding noise from display components, improving the sensitivity and precision of capacitance measurements for touch sensors.
Implementation Method 1
a mechanical stack with a conductive layer positioned between the touch sensor electrodes and the display, acting as a shield to reduce noise interference
Implementation Method 2
drive and sense electrodes capacitively coupled across a space without electrical contact
Implementation Method 3
When an object touches or comes within proximity of the surface of the touch sensor, a change in capacitance may occur within the touch screen at the location of the touch or proximity
Data Source
AI summary
In one embodiment, a method includes substantially simultaneously applying a pre-determined voltage to a conductive layer and to one or more electrodes of a touch sensor. The conductive layer is spatially separated from the electrodes by at least a thickness of a substrate. The method also includes determining a difference between a measurement current of one or more of the electrodes and a reference value; and determining whether a proximity or touch input to the touch sensor has occurred based at least in part on the difference.