Input device

1. An input device comprising:

a plurality of input keys arranged in a matrix of three or more rows and three or more columns;

electrodes facing some or all of surfaces of the input keys that surround intersections of rows and columns formed by the arrangement of the input keys; and

an input key detecting unit that identifies operated input keys among the plurality of input keys depending on combinations of the electrodes having a change in electrostatic capacitance.

2. The input device according to claim 1 ,

wherein the input key detecting unit includes a clock signal generating unit that generates clock signals; a delay unit that performs delay processing on the clock signals according to the electrostatic capacitance of the electrodes when a human body approaches or contacts the input keys; a logical conjunction unit that inputs delayed clock signals and non-delayed clock signals and outputs output signals according to a delayed amount of the delayed clock signals; a smoothing unit that smoothes the output signals of the logical conjunction unit such that the output signals become analog signals; an A/D conversion unit that converts the analog signals to digital signals; and a controller that identifies the input keys, which human body approaches or contacts, by combinations of the digital signals.

3. The input device according to claim 1 ,

wherein the electrodes have non-touch sensitive parts, which do not respond to operation of the input keys, in positions not facing the input keys.