Capacitive Touch Input Device Stray Capacitance Compensation Circuit

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Solution Overview

Problem

Capacitive type touch input devices face challenges in detecting touch inputs due to large reference capacitance values, which include unintended stray capacitance, making it difficult to differentiate variations in capacitance caused by touch inputs.

Innovation Solution

A compensator circuit is connected to the touch input detector to adjust the equivalent capacitance value, allowing for a smaller or larger capacitance value to be viewed from the input, thereby enhancing or reducing the sensitivity of the touch input detection by synchronizing the direction changes of currents through the touch input detector and the compensator.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Stability of the object's composition

If the reference capacitance is increased to ensure stable baseline, then the stability of capacitance measurement is improved, but the sensitivity to touch input detection deteriorates

Engineering Contradiction:

Improvestability of capacitance measurementVSAvoidsensitivity to touch input detection

Core Design Contradiction:

Stability of the object's compositionVSMeasurement precision

Solution Approach 1:

The patent divides the capacitance measurement system into separate functional components: a touch input detector for measuring capacitance variations and a compensator for managing stray capacitance. This segmentation allows each component to be optimized independently - the detector maintains high sensitivity while the compensator ensures measurement stability by accounting for stray capacitance effects.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The compensator acts as an intermediary element between the touch input detector and the stray capacitance. It introduces a controlled capacitance value that offsets the unwanted stray capacitance, thereby stabilizing the reference capacitance without compromising the detector's ability to sense touch-induced capacitance changes.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Measurement precision

If the reference capacitance is decreased to enhance touch input sensitivity, then the sensitivity to touch input detection is improved, but the stability of capacitance measurement deteriorates

Engineering Contradiction:

Improvesensitivity to touch input detectionVSAvoidstability of capacitance measurement

Core Design Contradiction:

Measurement precisionVSStability of the object's composition

Solution Approach 1:

The compensator implements a feedback mechanism by continuously monitoring and adjusting the reference capacitance to account for stray capacitance variations. This feedback loop maintains stable baseline capacitance while preserving the detector's sensitivity to touch inputs, as the compensator dynamically balances the capacitance components.

Inventive Principle:

Principle #23Feedback

3Ease of manufacture

If stray capacitance is present in the reference capacitance, then the ease of manufacture is improved, but the measurement precision deteriorates

Engineering Contradiction:

Improveease of manufactureVSAvoidmeasurement precision

Core Design Contradiction:

Ease of manufactureVSMeasurement precision

Solution Approach 1:

The patent converts the harmful effect of stray capacitance into a beneficial control parameter. Instead of trying to eliminate stray capacitance (which would complicate manufacturing), the compensator measures and compensates for its effects, transforming the manufacturing simplicity of including stray capacitance into a precise measurement capability through software-based compensation.

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 configuration allows for more sensitive detection of capacitance variations when a touch input is applied, either by decreasing or increasing the equivalent capacitance value, thus improving the accuracy of touch input detection.

Implementation Method 1

capacitive capacitance is formed between the conductor and the finger. The capacitive capacitance may provide a current path between the conductor and the finger. The size of the capacitive capacitance may vary according to the distance between the conductor and the finger.

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

the reference capacitance may include unintended stray capacitance, there is a limitation in that the reference capacitance may be larger than design intention

Methodology Applied

Scientific EffectStray capacitance: Parasitic Capacitance

Data Source

PatentUS9904426B2Capacitive type touch input device with compensation circuit for stray capacitance

Publication Date: 2018.02.27 ZINITIX CO LTD

AI summary

Provided is a touch chip including a touch input detector and a compensator, wherein an input terminal of the touch input detector and an output terminal of the compensator are together connected to a touch input sensing electrode, and a direction change of a first current flowing through the input terminal of the touch input detector and a direction change of a second current flowing through the output terminal of the compensator are performed through synchronization.