Keyboard Matrix Layout to Eliminate Ghost Keys Without Diodes
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Solution Overview
Problem
Conventional keyboard control circuits suffer from ghost key issues, which are not acceptable in gaming applications, and the use of diodes to prevent them increases the size, complexity, and cost of the array module.
Innovation Solution
A keyboard control circuit with a key matrix of scan lines and return lines where ghost key positions are defined in relation to safe key positions, allowing key switches only at safe positions to control conduction, eliminating the need for diodes and preventing ghost keys.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diodes are disposed at each intersection to prevent ghost keys, then ghost key prevention is achieved, but the array module has relatively large size, complicated wiring, and high cost
Solution Approach 1:
The patent segments the key matrix into safe key positions and ghost key positions based on the scanning sequence. By identifying and designating specific positions as safe (where keys are actually placed) and others as ghost positions (where no keys are placed), the system prevents ghost key errors without requiring additional hardware components at each intersection.
Solution Approach 2:
The patent applies local quality by treating different positions in the key matrix differently. Safe key positions are configured to receive key switches and generate valid signals, while ghost key positions are deliberately left without key switches. This localized differentiation allows the system to prevent ghost keys only where necessary without adding complexity throughout the entire matrix.
2Reliability
If diodes are disposed at each intersection to prevent ghost keys, then ghost key prevention is achieved, but the array module has relatively large size
Solution Approach 1:
The patent extracts and removes the unnecessary diode components from the key matrix intersections. By recognizing that ghost key prevention can be achieved through software/scanning sequence control rather than hardware diodes, the design eliminates the diodes entirely, thereby reducing the array module size and simplifying the structure.
3Reliability
If diodes are disposed at each intersection to prevent ghost keys, then ghost key prevention is achieved, but the array module has high cost
Solution Approach 1:
The patent replaces expensive passive components (diodes) with a software-based scanning sequence approach. The scanning sequence method uses control logic and timing to prevent ghost keys, eliminating the need for additional expensive hardware components at each matrix intersection, thereby reducing manufacturing cost.
Data Source
AI summary
A keyboard control circuit for a keyboard having P keys includes an array module that includes P key switches, and a key-matrix having N scan lines that intersect M return lines to form N×M intersections, where P<N×M. The intersections include ghost key positions free of the key switches, and safe key positions being of a number at least equal to P. Each key switch is disposed at a corresponding safe key position. Each ghost key position cooperates with a corresponding group of first, second and third ones of the safe key positions to constitute four corners of a rectangle in the key matrix. A processing unit provides a scan signal to each scan line during a scan period, receives at least one scan line from the return lines in response to operation of at least one key switch, and outputs an input signal corresponding to operation of the at least one key switch.