Hover Sensor Parasitic Capacitance Cancellation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Capacitive hover sensors face a degraded signal-to-noise ratio due to parasitic capacitance, which reduces the accuracy of hover sensing, and existing solutions like increasing electrode spacing or adding guard electrodes either increase costs or degrade display performance.

Innovation Solution

A hover sensor design featuring an electrode array with a first and second electrode subset, where each electrode in the first subset is coupled to a corresponding electrode in the second subset at a node, separated by a gap corresponding to a human hand size range, and charged substantially oppositely about a reference voltage, allowing for the cancellation of parasitic capacitance and enhancement of signal capacitance detection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If traditional capacitive hover sensing is used, then the sensing function is provided, but the signal-to-noise ratio is degraded due to parasitic capacitance

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidparasitic capacitance

Core Design Contradiction:

Measurement precisionVSObject-affected harmful factors

Solution Approach 1:

The electrode array is segmented into first and second electrode subsets, where each subset is charged to opposite polarities. This segmentation allows the system to differentiate between parasitic capacitance (which affects both subsets equally) and signal capacitance (which causes differential charge changes), thereby improving the signal-to-noise ratio.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent converts the harmful effect of parasitic capacitance into a beneficial reference. By charging opposite electrodes to opposite polarities and measuring differential charges, the system uses parasitic capacitance as a common-mode signal that can be subtracted out, transforming it from a noise source into a reference for cancellation.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

2Object-affected harmful factors

If electrode spacing is increased to reduce parasitic capacitance, then parasitic capacitance is reduced, but the sensing area is reduced

Engineering Contradiction:

Improveparasitic capacitanceVSAvoidsensing area

Core Design Contradiction:

Object-affected harmful factorsVSArea of stationary object

Solution Approach 1:

Instead of increasing spacing between all electrodes, the patent segments electrodes into opposite-polarity subsets. This allows electrodes to be placed closer together (maintaining larger sensing area) while still reducing parasitic capacitance effects through differential measurement and cancellation of common-mode signals.

Inventive Principle:

Principle #1Segmentation

3Object-affected harmful factors

If guard electrodes are added to reduce parasitic capacitance, then parasitic capacitance is reduced, but device complexity and cost increase

Engineering Contradiction:

Improveparasitic capacitanceVSAvoidcircuit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The patent makes the existing electrode array serve multiple functions: sensing hover objects and providing parasitic capacitance reference signals. By charging opposite electrodes to opposite polarities, the system uses the same electrodes for both sensing and parasitic capacitance cancellation, eliminating the need for separate guard electrodes and reducing overall device complexity.

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 significantly improves the signal-to-noise ratio and sensing accuracy by canceling common parasitic charges, reducing the need for multiple capacitance readout circuits and minimizing cost and complexity, while maintaining effective hover object detection.

Implementation Method 1

Methodology Applied

Scientific EffectParasitic capacitance cancellation: Capacitance

Implementation Method 2

an integration circuit configured to, for each respective node, store a net charge on a capacitor and provide an output voltage based on the net charge stored on the capacitor

Methodology Applied

Scientific EffectCapacitive charge storage: Capacitance

Data Source

PatentUS10120512B2Hover sensor

Publication Date: 2018.11.06 MICROSOFT TECHNOLOGY LICENSING LLC

AI summary

Examples are disclosed herein that relate to hover sensing. One example provides a hover sensor comprising an electrode array including a first electrode subset and a second electrode subset, each electrode in the first electrode subset coupled to a corresponding electrode in the second electrode subset at a respective node and separated from the corresponding electrode by a gap, a charge circuit configured to charge the first electrode subset substantially oppositely about a reference voltage to the second electrode subset, an integration circuit configured to, for each respective node, store a net charge on a capacitor and provide an output voltage based on the net charge stored on the capacitor, and a controller. The controller is configured to indicate a presence of a hover object responsive to identifying at least a threshold voltage change based on a sample of the output voltage.