Capacitance Sensing Apparatus Noise Removal via Segmented Integration
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Solution Overview
Problem
Capacitive touchscreens face challenges in accurately sensing touch inputs due to electrical noise from wireless communications and display modules, and require precise offset value settings, which can be disrupted by foreign objects or unintended user interactions.
Innovation Solution
A capacitance sensing apparatus that integrates capacitance changes in both positive and negative directions during a driving signal period, followed by differential amplification of integrated output voltages to generate offset information, ensuring accurate touch input detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If capacitance changes are sensed directly without integration, then the sensing response is fast, but common noise from wireless communications and display modules cannot be effectively removed
Solution Approach 1:
The sensing period is divided into multiple sub-periods (first period, second period, third period) with different operations. The integration is performed in stages rather than continuously, allowing noise removal while maintaining manageable circuit complexity. Each segment handles specific tasks: charging, integrating, and resetting.
Solution Approach 2:
The circuit performs periodic integration operations synchronized with the driving signal period. By integrating during specific periods and resetting at others, the system achieves noise removal through periodic sampling and averaging, converting continuous noise into removable periodic components.
2Measurement precision
If offset values are set continuously to adapt to operational environment changes, then the touch input detection accuracy is improved, but false touch recognition occurs due to foreign objects and unintended user interactions
Solution Approach 1:
Offset values are determined in advance during a reset period before actual touch sensing begins. This preliminary offset determination captures environmental conditions without being influenced by foreign objects or unintended touches that may occur during active sensing, thereby improving reliability.
Solution Approach 2:
The system performs preliminary offset calibration that anticipates and compensates for environmental noise and foreign object effects before they can interfere with actual touch detection. By establishing the baseline in advance, the system prevents false readings rather than reacting to them.
3Reliability
If the integration period is extended to improve noise filtering, then common noise removal is enhanced, but the response time for touch input detection increases
Solution Approach 1:
The integration process is segmented into discrete phases within each driving period, allowing the system to achieve effective noise filtering through multiple integration cycles while maintaining a predictable and bounded response time. The segmentation prevents indefinite integration delays.
Solution Approach 2:
Integration is performed periodically at specific intervals rather than continuously, creating a rhythm of sensing and resetting that balances noise filtering with response speed. The periodic nature ensures that touch events are detected within known time windows.
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 removes common noise and allows for precise setting of offset values, enhancing the accuracy of touch input recognition and reducing errors caused by noise or foreign objects.
Implementation Method 1
a first integrating circuit unit integrating a voltage charged in the node capacitor to generate an output voltage of which a voltage level is changed twice during a second period, different from the first period
Implementation Method 2
a second integrating circuit unit integrating a voltage charged in the buffer capacitor to generate an output voltage of which a voltage level is changed twice during the first period
Implementation Method 3
an amplifying unit differentially amplifying a non-inverted output voltage and an inverted output voltage of the second integrating circuit unit
Data Source
AI summary
A capacitance sensing apparatus includes: a driving circuit unit applying a driving signal of a first period to a node capacitor; a first integrating circuit unit integrating voltage charged in the node capacitor to generate output voltage of which a voltage level is changed twice during a second period; a buffer capacitor charged or discharged by the output voltage of the first integrating circuit unit; a second integrating circuit unit integrating voltage charged in the buffer capacitor to generate output voltage of which a voltage level is changed twice during the first period; and an amplifying unit differentially amplifying non-inverted output voltage and inverted output voltage of the second integrating circuit unit, wherein the amplifying unit amplifies voltage corresponding to a difference between the non-inverted output voltage and the inverted output voltage during a reset section of the second integrating circuit unit to generate offset information.