Patent ID: 8264384

Claim:
A keyboard control circuit for a keyboard that has a number (P) of keys, said keyboard control circuit comprising: an array module including a key matrix having a number (N) of scan lines, and a number (M) of return lines that intersect the number (N) of the scan lines to form a number (N×M) of intersections, where P<(N×M), each of said intersections having a scan line coordinate (X i ), where i ranges from 1 to N, and a return line coordinate (Y j ) where j ranges from 1 to M, said intersections including safe key positions and ghost key positions, the safe key positions being of a number that is at least equal to P, wherein each of the ghost key positions corresponds to a group of first, second and third ones of the safe key positions, in which the first and second ones of the safe key positions have the same return line coordinate, in which the first and third ones of the safe key positions have the same scan line coordinate, in which a corresponding one of the ghost key positions and the second one of the safe key positions have the same scan line coordinate, and in which the corresponding one of the ghost key positions and the third one of the safe key positions have the same return line coordinate, and a number (P) of key switches, each of which is disposed at a corresponding one of the safe key positions in said key matrix and is operable to control conduction between a corresponding one of said scan lines and a corresponding one of said return lines intersecting each other at the corresponding one of the safe key positions in said key matrix, wherein the ghost key positions are free of said key switches; and a processing unit coupled to said scan lines and said return lines, providing a scan signal to each of said scan lines during a scan period, receiving at least one scan signal from said return lines in response to operation of at least one of said key switches, and outputting an input signal corresponding to operation of the at least one of said key switches.