Differential Sensing for Touch Sensors Parasitic Capacitance

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Capacitive touch sensors face challenges in accurately detecting the location and proximity of objects due to parasitic capacitance effects and limited sensitivity, especially in self-capacitance implementations, which can lead to reduced accuracy and increased noise in measurements.

Innovation Solution

The implementation of differential sensing techniques, where two electrode tracks are driven to the same voltage and their output currents are measured differentially, reduces parasitic capacitance effects and increases sensitivity by enabling the detection of smaller capacitance changes, thereby improving the accuracy of object location determination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If self-capacitance sensing is used, then device complexity is reduced, but measurement precision deteriorates due to parasitic capacitance effects

Engineering Contradiction:

Improvesensing circuit complexityVSAvoidcapacitance detection accuracy

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent introduces a compensating capacitor connected in parallel with the parasitic capacitance to serve as an intermediary element. This compensating capacitor allows the system to measure and cancel out the parasitic capacitance effects, thereby improving measurement precision while maintaining the simplicity of self-capacitance sensing architecture

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent dynamically adjusts the capacitance value of the compensating capacitor to match the parasitic capacitance value. By changing the parameter (capacitance value) of the compensating capacitor, the system can adaptively compensate for parasitic effects across different operating conditions, improving measurement accuracy without adding complex circuitry

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If traditional single-ended sensing is used, then device complexity is low, but sensitivity deteriorates due to inability to detect smaller capacitance changes

Engineering Contradiction:

Improvesensing architectureVSAvoidsensitivity to capacitance changes

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The patent segments the sensing measurement into two components: the parasitic capacitance component and the touch-induced capacitance component. By using a compensating capacitor to represent and isolate the parasitic component, the system can separately measure and subtract this baseline, thereby enhancing sensitivity to smaller touch-induced capacitance changes

Inventive Principle:

Principle #1Segmentation

3Measurement precision

If noise reduction techniques are applied, then measurement precision improves, but device complexity increases

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidsignal processing circuitry

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent converts the harmful parasitic capacitance into a beneficial measurement reference by using the compensating capacitor to model and measure the parasitic capacitance value. This approach transforms the noise source into a useful calibration reference, improving signal-to-noise ratio without requiring complex filtering or shielding techniques

Inventive Principle:

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

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 and accuracy of touch sensor systems by reducing noise and allowing for the detection of smaller capacitance changes, while also enabling higher gains in amplifiers without exceeding measurement limits, thus providing improved signal-to-noise ratios and precise object location detection.

Implementation Method 1

When an object touches or comes within proximity of the surface of the capacitive touch screen, a change in capacitance may occur within the touch screen at the location of the touch or proximity

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

Capacitive touch sensors face challenges in accurately detecting the location and proximity of objects due to parasitic capacitance effects

Methodology Applied

Scientific EffectParasitic capacitance: Parasitic Capacitance

Data Source

PatentUS10955973B2Differential sensing for touch sensors

Publication Date: 2021.03.23 ATMEL CORP

AI summary

In one embodiment, a method includes outputting a first current associated with a first electrode track of a self-capacitance touch sensor. The method also includes outputting a second current associated with a second electrode track of the self-capacitance touch sensor. The method also includes measuring a voltage associated with a difference between the first and second currents and determining a position of an object relative to the self-capacitance touch sensor based on the voltage.