Ghost Key Detection Circuit Using Return-Line Voltage Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional keyboards with key matrix structures face the 'ghost key' phenomenon, leading to manufacturing cost increases when attempting to mitigate this issue through enlarged matrices or separate keys with diodes.
Innovation Solution
A ghost key detecting circuit with a double cross structure of scan and return lines, coupled to switch elements and a level detecting circuit, which uses resistance and voltage measurements to accurately determine key states, preventing erroneous key registrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a key matrix structure is used to reduce manufacturing costs, then manufacturing cost decreases, but ghost key phenomenon occurs causing erroneous detection
Solution Approach 1:
The patent introduces a level detecting circuit as an intermediary component that measures voltage values at return lines and compares them against reference values. This mediator distinguishes between genuine key presses and ghost key events by detecting voltage level changes, thereby resolving the contradiction between using a simple matrix structure and achieving reliable detection without adding complex hardware like diodes.
Solution Approach 2:
The patent changes the detection parameter from simple presence/absence detection to voltage level measurement. By measuring and comparing voltage values at return lines against reference values, the system can identify ghost key events through abnormal voltage patterns, thus improving detection accuracy while maintaining the simple matrix structure and low manufacturing cost.
2Reliability
If diodes are added to separate each key to prevent ghost key, then detection accuracy improves, but manufacturing cost increases significantly
Solution Approach 1:
The patent extracts the ghost key prevention function from the physical structure (diodes) and implements it through a software-based voltage measurement and comparison mechanism. By removing the need for additional physical components like diodes and instead using the level detecting circuit to analyze voltage patterns, the solution maintains detection accuracy while significantly reducing manufacturing complexity and cost.
3Reliability
If the key matrix size is increased to avoid ghost key, then detection accuracy improves, but device complexity and cost increase
Solution Approach 1:
The patent replaces the mechanical/physical approach of increasing matrix size or adding diodes with an electrical measurement approach. By substituting physical structural modifications with electrical voltage measurement and comparison, the system achieves ghost key prevention without increasing matrix complexity or physical dimensions.
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 design effectively reduces manufacturing costs by accurately distinguishing actual key presses, eliminating the ghost key phenomenon without increasing costs, ensuring reliable key detection.
Implementation Method 1
performing level detection upon measured voltage values at the set of return lines
Implementation Method 2
a plurality of switch elements each having a predetermined resistance
Data Source
AI summary
A ghost key detecting circuit includes at least first and second scan lines, at least first and second return lines, a plurality of switch elements, and a level detecting circuit. The level detecting circuit is used for performing level detection upon measured voltage values at the first and second return lines. When a measured voltage value at a return line is greater than or equal to a reference voltage value, the level detecting circuit generates a logic signal for indicating that a switch element corresponding to the return line at a current scan line is turned off. When the measured voltage value is smaller than the reference voltage value, the level detecting circuit generates a logic signal for indicating that the switch element is turned on.