Capacitive Touch Force Sensing via Electrode Self-Capacitance
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Solution Overview
Problem
Existing touch-sensitive input devices in computing devices face challenges in accurately measuring force applied by users, particularly in compact devices like mobile phones and tablets, where integrating force sensors is difficult due to size and thickness limitations.
Innovation Solution
A touch-sensitive input device that includes a glass-plus-sensor module with a cover glass and electrodes, where the self-capacitance changes based on applied force, allowing for force estimation without additional components by measuring changes in self-capacitance and mutual capacitance between electrodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional force sensors are integrated into touch-sensitive input devices, then force measurement capability is improved, but device thickness and complexity increase
Solution Approach 1:
The existing capacitive touch sensor electrodes are made to serve dual functions: detecting touch location and measuring applied force. By analyzing capacitance changes (both self-capacitance and mutual capacitance) from the same electrode structure, the system eliminates the need for separate force sensors while adding force measurement capability to the existing touch interface.
Solution Approach 2:
The touch sensor system measures its own state changes to determine force magnitude. The electrodes inherently experience capacitance changes when force is applied, and the system utilizes these self-generated signals without requiring external sensing elements. The structure serves itself by converting mechanical deformation into measurable electrical parameter changes.
2Measurement precision
If additional force sensors are added to achieve accurate force measurement, then measurement precision is improved, but device size increases
Solution Approach 1:
The force sensing functionality is merged with the existing touch sensor structure. The same electrode layers and capacitor structures that detect touch presence are also used to measure force magnitude through capacitance change analysis. This consolidation eliminates additional sensor layers and maintains the original device thickness profile.
Solution Approach 2:
The capacitive sensor structure performs multiple measurement functions simultaneously - touch detection, touch location, and force measurement - all using the same physical components. This multi-functionality approach avoids adding dedicated force sensing elements that would increase device volume.
3Measurement precision
If self-capacitance and mutual capacitance measurements are used together, then force measurement accuracy is improved, but calculation complexity increases
Solution Approach 1:
The system uses feedback from multiple capacitance measurement channels (self-capacitance and mutual capacitance) to cross-validate and refine force measurements. By comparing and combining information from different electrode interactions, the system improves measurement reliability and compensates for variations in touch conditions through iterative calculation processes.
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
Enables accurate force measurement on touch-sensitive surfaces, such as touchpads and touchscreen displays, without the need for additional force sensors, enhancing user interaction and input precision in computing devices.
Implementation Method 1
calculating a change in a mutual capacitance between a first electrode and a second electrode included in a sensor module disposed below the surface of the touch-sensitive input device
Data Source
AI summary
In one general aspect, a method can include identifying contact with a surface of a touch-sensitive input device, identifying a location of the contact on the surface of the touch-sensitive input device, and calculating a change in a mutual capacitance between a first electrode and a second electrode included in a sensor module disposed below the surface of the touch-sensitive input device. The first electrode can be adjacent to the second electrode. The first electrode and the second electrode can be located approximate to the identified location of the contact on the surface of the touch-sensitive input device. The method can include estimating a contact-coupled capacitance based on the calculated change in a mutual capacitance between the first electrode and the second electrode, and calculating a force applied to the surface of the touch-sensitive input device at the identified location.