Touch Keypad Scanning With N-1 Averaging for False Trigger Suppression
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Solution Overview
Problem
Touch-on-metal (ToM) devices face challenges in accurately detecting key presses due to human body capacitance and adjacent metal deflection, leading to false triggers and unreliable key-press detection.
Innovation Solution
Implementing N-1 key scan averaging with baseline drift compensation, where the key matrix is continuously scanned at different bandwidths to determine baseline values and average signals from other keys, allowing for accurate key-press detection by comparing the touch-key sense signal to a threshold value generated from the average of other keys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional touch sensing is used in ToM devices, then key-press detection can be implemented, but false triggers occur due to human body capacitance and adjacent metal deflection
Solution Approach 1:
The patent introduces N-1 key scan averaging as an intermediary processing step between raw touch sensing and key-press determination. By averaging the sense signals from N-1 adjacent keys and comparing against the Nth key signal, the system creates a reference mechanism that filters out common-mode noise from human body capacitance and adjacent metal deflection, thereby resolving false triggers while maintaining detection reliability
Solution Approach 2:
The patent implements a feedback mechanism where the averaged baseline signal from N-1 keys continuously updates the threshold for detecting key-presses on the Nth key. This dynamic threshold adjustment provides feedback that adapts to changing environmental conditions and user interactions, eliminating false triggers while preserving reliable detection of actual key presses
2Measurement precision
If continuous scanning at high bandwidth is used to improve detection accuracy, then signal-to-noise ratio improves, but processing complexity and computational load increase
Solution Approach 1:
The patent segments the key matrix scanning process into two distinct phases: baseline scanning at a first bandwidth and key-press detection scanning at a second bandwidth. This segmentation allows the system to use lower bandwidth for routine baseline updates, reducing processing complexity, while switching to higher bandwidth only when key-press detection is needed, thereby maintaining measurement precision without continuously incurring high computational costs
Solution Approach 2:
The patent employs periodic action by continuously updating the baseline signal through periodic scanning of all keys and using this updated baseline for subsequent key-press detection. This periodic refresh of reference data maintains measurement precision over time while allowing the system to operate at optimized bandwidth levels during non-detection periods, balancing accuracy with processing efficiency
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 method effectively suppresses noise from human body capacitance and temperature drift, reducing false key-press conditions and improving the signal-to-noise ratio, thereby enhancing the reliability of key-press detection in ToM devices.
Implementation Method 1
touch sense can be based on inductive or capacitive sensing, implemented by a corresponding touch/key sense circuit
Data Source
AI summary
Touch/key sensing with N-1 key scan averaging, for use with an N-key touch input apparatus, including a key matrix of N touch-key sense circuits, including: (a) continuously scanning the key matrix at a first bandwidth to determine a respective touch-key baseline sense signal, independent of a key-press condition, and a related touch-key baseline value based on successive baseline sense signals; and (b) during successive key-scan periods, scanning the key matrix at a second bandwidth greater than the first bandwidth, and for each touch key N, determining a touch-key sense signal, generating an N-1 key-scan average value by averaging the touch-key baseline values for the other N-1 touch keys, comparing the Nth touch-key sense signal to a key-press threshold based on the N-1 key-scan average value; and (c) signaling a key-press condition if the touch-key sense signal is greater in magnitude than the N-1 key-scan average value by the key-press threshold.