Capacitive Touch Sensor Noise Reduction via Timing Control

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Solution Overview

Problem

Capacitive touch-sensor arrays are susceptible to noise interference from display panels, such as LCDs, which can affect capacitance measurements and degrade the signal-to-noise ratio (SNR), leading to inaccurate detection of touch events.

Innovation Solution

A touch-screen system that includes a sequencer state machine to control the timing of capacitance measurements based on detected noise signals, generating sensitivity windows to ignore insignificant noise events and synchronize conversions with noise patterns, thereby improving the SNR and reducing noise interference.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Speed

If capacitance measurements are performed continuously to detect touch events, then detection speed is improved, but noise interference from display panels increases and measurement accuracy deteriorates

Engineering Contradiction:

Improvetouch event detection speedVSAvoidcapacitance measurement accuracy

Core Design Contradiction:

SpeedVSMeasurement precision

Solution Approach 1:

The patent implements periodic capacitance measurements synchronized with the display panel's noise pattern. The sequencer state machine controls conversions to occur during specific time windows when noise levels are lower, creating a periodic measurement rhythm that balances detection speed with measurement accuracy by avoiding continuous measurement during high-noise periods

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system performs preliminary noise characterization by detecting and storing the display panel's noise pattern during initialization or calibration phases. This preliminary action enables the sequencer to pre-determine optimal measurement timing windows, allowing the system to proactively schedule capacitance measurements during low-noise periods rather than reactively filtering noise after measurement

Inventive Principle:

Principle #10Preliminary action

2Productivity

If the sensing frequency is increased to improve response time, then productivity is improved, but the system becomes more susceptible to noise interference from display panels

Engineering Contradiction:

Improvetouch detection response timeVSAvoidnoise susceptibility

Core Design Contradiction:

ProductivityVSObject-affected harmful factors

Solution Approach 1:

The patent dynamically adjusts the sensing frequency and measurement timing based on the detected noise characteristics. The sequencer state machine modifies conversion rates and timing windows in real-time according to the display panel's operating state, allowing the system to maintain high productivity during low-noise periods while reducing susceptibility during high-noise periods such as when the display is actively refreshing

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system continuously monitors the output of capacitance measurements for noise indicators and uses this feedback to adjust subsequent measurement timing. When noise is detected in measurement results, the sequencer modifies future conversion timing to avoid noisy periods, creating a closed-loop system that adapts sensing frequency and timing to maintain optimal signal-to-noise ratio while preserving response time

Inventive Principle:

Principle #23Feedback

Data Source

PatentUS9170322B1Method and apparatus for automating noise reduction tuning in real time

Publication Date: 2015.10.27 PARADE TECHNOLOGIES LTD

AI summary

An embodiment of a method for detecting noise for a capacitance sensing panel may comprise generating an input signal based on a noise signal, performing a series of measurements for measuring capacitances from a capacitive sensor sensitive to the noise signal, and controlling timing for at least one of the subconversions based on the input signal.