Delay-Based Capacitive Touch Matrix Sensing for Noise-Robust Multi-Touch
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Solution Overview
Problem
Capacitive touch sensors are prone to noise, environmental variations, and device lot variations, which affect their accuracy and reliability, especially in multi-touch applications, requiring robust noise filtering and calibration systems to mitigate these issues.
Innovation Solution
The capacitive touch sensor system employs a spread spectrum signal generator, median filtering, and averaging techniques, combined with a high-speed delay-based capacitance measurement front-end and adaptive calibration algorithms to reduce noise and account for environmental and device variations, enabling accurate multi-touch detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If capacitive touch sensors are used for multi-touch detection, then touch detection capability is improved, but noise susceptibility and environmental variation increase
Solution Approach 1:
The sensor system divides the sensing array into multiple independent sensing elements arranged in rows and columns, allowing individual measurement of cross-capacitance for each element. This segmentation enables precise localization of multiple touch points while isolating noise effects to specific elements that can be individually filtered.
Solution Approach 2:
The patent introduces reference capacitance measurements and calibration routines as intermediary processes that mediate between the raw sensor signals and the final touch detection. These intermediary measurements capture environmental variations and device-specific characteristics, which are then used to compensate and correct the actual touch measurements.
2Measurement precision
If noise filtering techniques are applied, then measurement accuracy is improved, but system complexity increases
Solution Approach 1:
The system employs periodic calibration routines and repeated measurements at different time instances. By performing measurements multiple times and applying temporal filtering, the system achieves noise reduction through averaging while maintaining a relatively simple filter structure that processes signals in regular intervals.
Solution Approach 2:
The patent implements feedback mechanisms where calibration data from reference measurements is fed back into the measurement process to adjust and compensate for environmental variations. This feedback loop continuously refines the measurement accuracy without requiring complex real-time filtering algorithms.
3Reliability
If calibration systems are implemented to offset variations, then device reliability is improved, but manufacturing complexity increases
Solution Approach 1:
The system performs calibration measurements and environmental characterization during the manufacturing process or initial setup phase. By capturing device-specific characteristics and environmental baselines in advance, the calibration data is stored and applied during normal operation, eliminating the need for complex real-time adjustment mechanisms and simplifying manufacturing.
Data Source
AI summary
A method of matrix sensing using delay-based capacitance sensing, including using X-axis lines as active lines for capacitance measurements and using Y-axis lines as a disturbance to identify the location of a touch in a key matrix is disclosed. A sensing signal is applied to the X-axis lines, and a disturbance signal is applied to the Y-axis lines. If a location is touched, cross-capacitance is reduced, which is measured by sweeping data along the X-axis lines.