Capacitance Sensing Matrix Keyboard Without Display Space Loss
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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 keys to pre-defined areas and measuring capacitance variations to determine key presses.
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 applies universality by using a single capacitive sensing pin to perform multiple key detection functions. Instead of requiring separate pins for each key or row/column combination, the system uses one pin that can sequentially sense capacitance changes across multiple keys through software-controlled scanning, allowing one pin to replace what would traditionally require many pins in a resistance matrix keyboard
Solution Approach 2:
The patent changes the detection parameter from resistance (in conventional keyboards) to capacitance. By measuring capacitance variations at a single pin location and using timing/frequency measurements of charge/discharge cycles, the system can distinguish between different key presses without requiring physical or electrical separation through multiple pins, thus reducing pin count while maintaining full 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:
The patent applies universality by using a single capacitive sensing pin to perform multiple key detection functions. Instead of requiring separate pins for each key or row/column combination, the system uses one pin that can sequentially sense capacitance changes across multiple keys through software-controlled scanning, allowing one pin to replace what would traditionally require many pins in a resistance matrix keyboard
Solution Approach 2:
The patent merges the functions of multiple pins into a single pin by combining capacitive sensing with software-based key identification. The physical sensing element is consolidated into one pin, while the logical separation of keys is achieved through software algorithms that analyze timing and capacitance patterns, thereby minimizing the physical die area required for the keyboard controller
3Area of stationary object
If a virtual keyboard is used, then display space is preserved, but valuable display real estate is occupied
Solution Approach 1:
The patent replaces the virtual display-based keyboard interface with a physical capacitive sensing array that can detect key presses without requiring visual display elements. This substitution allows the keyboard to function as a physical input device independent of the display, preserving display real estate while providing tactile feedback and eliminating the need to allocate screen space for virtual key representations
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 enables a full-size keyboard to be implemented on smaller devices with reduced manufacturing costs and without occupying touch-screen display space, while also supporting other user input devices with a single processing chip.
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
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.