Capacitive Sensor Electrode Selection for Accurate Touch Detection

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current capacitive sensing devices face limitations in accurately detecting touch inputs due to difficulties in controlling voltage on external objects and the inability to demodulate electret capacitive measurements, which are fundamentally DC and not suitable for touch input devices.

Innovation Solution

The capacitive sensor device employs a configuration with two pluralities of sensor electrodes arranged in an x/y grid, using a processing system to drive sensor electrodes with voltage and measure resulting charge or voltage, enabling both absolute and transcapacitive sensing, and disambiguating configurations through transcapacitive sensing methods.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If electret capacitive measurements are used, then the device can detect external objects, but the measurements are fundamentally DC and cannot be demodulated for touch input detection

Engineering Contradiction:

Improvedetection capabilityVSAvoidsignal demodulation

Core Design Contradiction:

ReliabilityVSEase of operation

Solution Approach 1:

The patent inverts the conventional capacitive sensing approach by using a guarded electrode configuration where the guard electrode is driven at a different potential than the sensing electrode. This inversion allows the system to measure AC capacitive coupling signals rather than DC electret measurements, enabling signal demodulation for touch input detection.

Inventive Principle:

Principle #13The other way round (Inversion)

2Measurement precision

If voltage control on external objects is attempted, then measurement accuracy may improve, but it is fundamentally difficult to control voltage on external objects

Engineering Contradiction:

Improvetouch input detection accuracyVSAvoidvoltage control

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The patent introduces a guarded electrode as an intermediary between the sensing electrode and the external object. The guard electrode is driven at a controlled potential to shield the sensing electrode from external voltage variations, allowing accurate capacitive measurements without requiring direct voltage control of external objects.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If multiple sensor electrodes are used to improve positioning accuracy, then positional information can be determined, but the device complexity increases

Engineering Contradiction:

Improvepositional information accuracyVSAvoidsensor electrode configuration

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent segments the sensor into multiple electrodes with specific functions: sensing electrodes for detecting capacitive coupling and guard electrodes for shielding. This segmentation allows the system to determine positional information through capacitive images while managing complexity through functional specialization of electrode groups.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent makes the sensor electrodes multi-functional by allowing them to serve both as sensing elements and as part of the guarded configuration. The same electrode structure performs both capacitive measurement and electrical shielding functions, reducing overall device complexity compared to separate sensing and shielding systems.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 allows for effective detection of touch inputs by capturing capacitive images and determining positional information, size, and type of input objects, improving the accuracy and functionality of capacitive sensing devices.

Implementation Method 1

a capacitive measurer measures capacitances using the received signals

Methodology Applied

Scientific EffectCapacitive coupling: Capacitance

Implementation Method 2

a processing system drives sensor electrodes with voltage and measure resulting charge or voltage

Methodology Applied

Scientific EffectElectrical signal driving: Conduction (electrical)

Data Source

PatentUS8896328B2Capacitive sensor device

Publication Date: 2014.11.25 SYNAPTICS INC

AI summary

A processing system for a capacitive sensor device comprises circuitry and logic; and the capacitive sensor device comprises a first plurality of sensor electrodes and a second plurality of sensor electrodes. The processing system is configured to acquire a first plurality of capacitive measurements by emitting and receiving first electrical signals with the first plurality of sensor electrodes of the capacitive sensor device. The processing system is also configured to select a first set of the first plurality of sensor electrodes based on the first plurality of capacitive measurements. The processing system is further configured to acquire a second plurality of capacitive measurements by emitting second electrical signals with the first set of the first plurality of sensor electrodes and receiving the second electrical signals with the second plurality of sensor electrodes.