Capacitive Keyboard Matrix Layout for Low-Pin-Count Input
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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 is used to detect the presence of a conductive object, reducing the pin count and allowing for a full keyboard implementation in a smaller area, with keys assigned to pre-defined areas on the sensor matrix, enabling efficient detection of key presses and position determination.
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 multiple keyboard rows into a single shared row line and multiple keyboard columns into a single shared column line. This merging approach allows the keyboard matrix to be scanned using fewer pins than the total number of rows and columns, directly resolving the contradiction between achieving full keyboard functionality and minimizing pin count.
Solution Approach 2:
The shared row line and shared column line serve multiple functions: they act as both input and output lines for different keys at different times during the scanning process. This multi-functionality allows the same physical pins to control and detect multiple keys, reducing the overall pin count while maintaining complete keyboard functionality.
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:
By merging multiple row lines into a single shared row line and multiple column lines into a single shared column line, the physical space required for trace routing on the die is significantly reduced. This consolidation directly addresses the contradiction between providing full keyboard functionality and minimizing die area.
3Ease of operation
If mechanical buttons are used for each keyboard key, then keyboard functionality is achieved, but the total keyboard area increases
Solution Approach 1:
The patent replaces mechanical buttons with a capacitive sensing system that detects key presses through changes in capacitance. This substitution eliminates the need for physical mechanical buttons, allowing the keyboard to be implemented in a much smaller area while maintaining full functionality. The capacitive sensors can be integrated into the same die area as the scanning circuitry.
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 decreases the pin count, reduces manufacturing costs, and allows for a full keyboard to be integrated into small devices without sacrificing display space, while also enabling single-chip control of keyboards and cursor positioning devices.
Implementation Method 1
A capacitance sensing matrix is used to detect the presence of a conductive object
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.