Abstract: A keyboard apparatus including a key module and a detection circuit is provided. The key module includes a plurality of keys, a plurality of scan lines and a plurality of return lines. The scan lines and the return lines are crossed to each other and respectively coupled to the keys. The detection circuit detects a plurality of return voltages of the return lines and generates a plurality of detection signals accordingly so as to indicate that a switch of each of the keys is at an on state or at an off state. The detection circuit includes a plurality of P-type transistors. A first terminal of each P-type transistor is coupled to a ground terminal, a control terminal of each P-type transistor is directly coupled to a corresponding one of the return lines, and a second terminal of each P-type transistor generates and outputs one of the detection signals.

Abstract: 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.

Abstract: 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.