Patent ID: 8049647
Filing Date: 2011-11-01
Classification: H03K

Abstract:
1. A capacitive keyboard device for integration to an electronic unit, which comprising: a capacitive keystroke-sensing module having a capacitive element, which is capable of responding to a user-initiated keystroke event by generating a capacitive frequency signal; a keystroke mode detection module, which is capable of processing the capacitive frequency signal extracted from the capacitive keystroke-sensing module to thereby produce a keystroke mode description signal which includes a falling-edge portion, a valley portion, and a rising-edge portion; a signal differentiation module, which is capable of performing a differentiation operation on the keystroke mode description signal generated by the keystroke mode detection module to thereby produce a differential signal whose waveform includes an upward-going pulse corresponding to the falling-edge portion of the keystroke mode description signal, a substantially flat portion corresponding to the valley portion of the keystroke mode description signal, and a downward-going pulse corresponding to the rising-edge portion of the keystroke mode description signal; a negative-slope detection module, which is capable of performing a negative-slope detection operation on the output differential signal of the signal differentiation module to thereby determine the minimum compressed capacitance corresponding to the maximum amplitude of the differential signal; a triggering threshold setting module, which is capable of setting a triggering threshold for the capacitive keyboard device, where the triggering threshold is a predetermined level between the rated capacitance of the capacitive element and the minimum compressed capacitance determined by the negative-slope detection module; and a key strobe signal generation module, which is capable of operating after the triggering threshold is set by comparing each subsequent capacitive frequency signal generated by the capacitive keystroke-sensing module against the triggering threshold, in such a manner that a key strobe signal is issued if the resultant compressed capacitance reaches below the triggering threshold; and otherwise, no key strobe signal is issued.