Key Matrix Input Logic for Multi-Key Ghosting Prevention

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Solution Overview

Problem

Conventional key input devices with a key matrix structure fail to accurately detect simultaneous presses of three or more keys, leading to erroneous detection of unpressed keys, which hinders gaming and other complex input operations in mobile phones.

Innovation Solution

A key input device with a determination unit that analyzes detection information from the key matrix circuit to identify potential simultaneous presses and corrects for erroneous connections between signal lines, preventing unintended processing by blocking output when multiple keys are pressed simultaneously.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a conventional key matrix structure is used, then the device complexity is low and manufacturing is simple, but measurement precision deteriorates when three or more keys are pressed simultaneously causing erroneous detection

Engineering Contradiction:

Improvekey detection accuracyVSAvoidcircuit structure complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent applies preliminary action by performing detection logic analysis before final key press determination. The key scan circuit analyzes the detection information to identify patterns indicating simultaneous multi-key presses, and determines whether erroneous detection has occurred before outputting the final key press result. This preliminary analysis prevents the propagation of detection errors to the output stage.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent implements feedback by using the key scan circuit to analyze detection information from the key matrix and determine whether erroneous detection has occurred. The system feeds back this analysis result to control the output, blocking erroneous key press information from being transmitted to the external device. This feedback mechanism corrects detection errors without requiring additional hardware circuits.

Inventive Principle:

Principle #23Feedback

2Measurement precision

If rectifying circuits (diodes) are added to each key switch to prevent erroneous detection, then measurement precision improves, but device complexity increases and manufacturing becomes more difficult

Engineering Contradiction:

Improvekey detection accuracyVSAvoidmanufacturing simplicity

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

The patent replaces the mechanical/electrical rectifying circuit (diode) approach with a software/logic-based solution. Instead of adding physical diode components to each key switch to prevent reverse current flow, the key scan circuit uses detection logic to analyze the detection information, identify erroneous detection patterns, and block erroneous outputs. This substitution eliminates the need for additional rectifying components while achieving the same functional goal.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The patent introduces an intermediary layer between the key matrix circuit and the output stage. The key scan circuit acts as an intermediary that receives detection information from the key matrix, analyzes it to determine whether erroneous detection has occurred, and selectively blocks or transmits the information. This intermediary approach prevents erroneous key press information from reaching the output without requiring direct modification of each key switch with rectifying circuits.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If rectifying circuits are added to prevent erroneous detection, then reliability improves, but device complexity increases

Engineering Contradiction:

Improvedetection reliabilityVSAvoidcircuit complexity

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent replaces physical rectifying circuits with a logic-based detection and determination system. The key scan circuit uses detection logic to analyze detection information and identify patterns indicating simultaneous multi-key presses that cause erroneous detection. This substitution maintains detection reliability while avoiding the addition of complex rectifying circuitry to each key switch.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

Solution Approach 2:

The key scan circuit performs multiple functions: it scans the key matrix, detects key press states, analyzes detection information for erroneous patterns, determines whether simultaneous multi-key presses have occurred, and blocks erroneous outputs. This multi-functional approach consolidates what would otherwise require separate rectifying circuits for each key into a single universal scanning and analysis mechanism.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Data Source

PatentUS8947362B2Key input device and mobile communication terminal using the key input device

Publication Date: 2015.02.03 KYOCERA CORP

AI summary

First detection information related to electrical connection between each row signal line and each column signal line is received from a key matrix circuit (S101). Based on the first detection information, it is determined whether a possibility exists that a user has pressed at least three key switches simultaneously and electrical connection between signal lines for a key switch that has not been pressed has been erroneously detected (S108). Information in accordance with key switches pressed by the user is output based on the first detection information when the determination is negative (S109), whereas output of information based on the first detection information is blocked when the determination is positive.