Touch Sensing Circuit Noise Suppression via Display Sync Switching

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Solution Overview

Problem

In modern touch-sensitive devices with compact designs, parasitic capacitance between the touch panel and display panel causes electrical noise interference, affecting touch sensing accuracy.

Innovation Solution

Incorporating switching units in the sensing control circuit that are controlled by synchronization signals from the display panel to prevent noise interference, and suspending operations of components like the analog-to-digital converter during refresh operations to minimize noise collection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If the distance between the touch panel and display panel is reduced to achieve compact design, then the device size is reduced, but the parasitic capacitance between the panels increases causing electrical noise interference

Engineering Contradiction:

Improvedevice sizeVSAvoidelectrical noise interference

Core Design Contradiction:

Volume of moving objectVSObject-affected harmful factors

Solution Approach 1:

A switching unit is introduced as an intermediary component between the sensing electrode and the sensing control circuit. This switching unit acts as a gate that can be opened or closed based on synchronization signals from the display panel, preventing noise from reaching the sensing circuit during display refresh operations while allowing normal touch sensing to proceed

Inventive Principle:

Principle #24Intermediary (Mediator)

2Object-affected harmful factors

If the switching unit is controlled by synchronization signals to prevent noise collection, then the electrical noise interference is reduced, but the device complexity increases

Engineering Contradiction:

Improveelectrical noise interferenceVSAvoidsensing control circuit complexity

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The switching unit is designed to serve multiple functions: it acts as a noise filter during display refresh operations, maintains normal touch sensing operation during non-refresh periods, and can be controlled by synchronization signals from the display panel. This multi-functionality reduces the need for separate dedicated noise filtering circuits

Inventive Principle:

Principle #6Universality (Multi-functionality)

3Productivity

If the analog-to-digital converter operates continuously, then the productivity is maintained, but the electrical noise from display refresh operations is collected affecting measurement precision

Engineering Contradiction:

Improvetouch sensing operation continuityVSAvoidtouch event detection accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

The switching unit operates periodically, opening during display refresh operations to block noise from reaching the sensing control circuit, and closing during non-refresh periods to allow normal touch sensing. This periodic operation pattern allows the system to maintain both continuous productivity and high measurement precision by timing the noise blocking appropriately

Inventive Principle:

Principle #19Periodic action

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

Effectively suppresses electrical noise from the display panel, enhancing the accuracy and reliability of touch sensing operations by isolating noise during synchronization and refresh cycles.

Implementation Method 1

The touch panel is formed by conductive electrodes that are arranged in two mutually perpendicular directions. There will be capacitances between intersections of the electrodes.

Methodology Applied

Scientific EffectCapacitance: Capacitance

Implementation Method 2

The first switching unit is coupled to a first end of the at least one sensing electrode, and arranged to selectively couple the first end of the at least one sensing electrode to a reference voltage level according to a first mask signal.

Methodology Applied

Scientific EffectElectrical Conductivity: Conduction (electrical)

Implementation Method 3

as the touch panel is also disposed close to the display panel, there will be parasitic capacitances between the touch panel and the display panel

Methodology Applied

Scientific EffectParasitic Capacitance: Parasitic Capacitance

Data Source

PatentUS11327604B2Touch sensing circuit that selectively couples a sensing electrode to a reference voltage in response to an assertion of a synchronization signal and touch sensitive device

Publication Date: 2022.05.10 HIMAX TECH LTD

AI summary

A touch sensing circuit for use in a touch sensitive device includes: an integrator, a first switching unit and a control signal generator. The integrator, coupled to at least one sensing electrode of a touch panel in the touch sensitive device, and arranged to collect charges on the at least one sensing electrode and accordingly generate an output sensed signal. The first switching unit is arranged to selectively couple a first end of the at least one sensing electrode to a reference voltage level according to a first mask signal. The control signal generator is arranged to generate the first mask signal according to a synchronization signal of a display panel in the touch sensitive device, wherein the first switching unit couples the first end of the at least one sensing electrode to the reference voltage level when the synchronization signal is asserted.