Capacitance Sensing Keyboard Matrix With Reduced Pin Count
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Solution Overview
Problem
Conventional resistance scan matrix keyboards have a large pin count, which increases the die area and reduces robustness, making them unsuitable for small form factor devices and limiting additional functionality, and virtual keyboards occupy valuable display space.
Innovation Solution
A capacitance sensor matrix with a reduced pin count is used to detect the presence of a conductive object, allowing for a smaller keyboard form factor and integration on devices like mobile handsets without sacrificing display real estate, by assigning keyboard keys to pre-defined areas and measuring capacitance variations to determine key positions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional resistance scan matrix keyboard is used, then keyboard functionality is achieved, but the pin count increases and die area increases
Solution Approach 1:
The patent combines row and column scanning functions into a single scan line by time-multiplexing the scanning process. The scan line sequentially activates rows and columns at different time intervals, allowing a single pin to perform both row scanning and column scanning functions that traditionally required separate pins. This merging reduces the pin count from M+N pins to just 2 pins while maintaining full keyboard functionality.
Solution Approach 2:
The patent implements dynamic time-multiplexed scanning where the scan line alternates between row scanning mode and column scanning mode. During row scanning, the scan line activates different rows sequentially; during column scanning, it activates different columns sequentially. This dynamic switching allows the system to encode key press information in the timing and sequence of detected signals, reducing the need for multiple static connection pins.
2Ease of operation
If a conventional resistance scan matrix keyboard is used, then keyboard functionality is achieved, but the die area increases
Solution Approach 1:
The patent merges multiple scanning functions into a single integrated scanning circuit that uses time-multiplexing. Instead of requiring separate hardware circuits for row scanning and column scanning, the invention uses one scanning circuit to perform both functions by switching between modes temporally. This consolidation dramatically reduces the circuit area on the die while preserving complete keyboard functionality.
Solution Approach 2:
The scan line is designed to serve multiple functions: it acts as both a row activation line and a column activation line at different times. The single scanning circuit performs multiple tasks including row scanning, column scanning, and key detection, making it a universal component that replaces what would traditionally require multiple specialized circuits, thereby reducing overall die area.
3Ease of operation
If mechanical buttons are used for each keyboard key, then keyboard functionality is achieved, but the keyboard area increases
Solution Approach 1:
The patent replaces the mechanical button system with a capacitive sensing system. Instead of requiring physical buttons with mechanical switches, the invention uses capacitive sensors that detect changes in capacitance caused by finger proximity or contact. This substitution eliminates the need for mechanical components, allowing for a much more compact keyboard layout while maintaining tactile feedback and input functionality.
Solution Approach 2:
The patent changes the detection parameter from mechanical switch closure to capacitance change. By measuring capacitance variations at different sensor locations, the system can identify which key is pressed without requiring physical buttons. This parameter change enables a compact membrane or flat keyboard design where sensors are embedded in a thin structure, dramatically reducing the overall keyboard area compared to mechanical button assemblies.
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 solution reduces manufacturing costs, enables a full-size keyboard on smaller devices, and allows for a single chip to control both keyboard and cursor positioning functions, enhancing user input capabilities without increasing pin count.
Implementation Method 1
A capacitance sensor matrix with a reduced pin count is used to detect the presence of a conductive object, allowing for a smaller keyboard form factor and integration on devices like mobile handsets
Data Source
AI summary
An apparatus and method for selecting a keyboard key based on a position of a presence of a conductive object on a sensing device and a pre-defined area of the keyboard key. The apparatus may include a sensing device and a processing device. The sensing device may include a plurality of sensor elements to detect a presence of a conductive object on the sensing device. Multiple keyboard keys are assigned to pre-defined areas of the sensing device. The processing device is coupled to the sensing device using capacitance sensing pins, and may be operable to determine a position of the presence of the conductive object, and to select a keyboard key based on the position of the conductive object and the pre-defined areas of the sensing device.