Coordinate input apparatus

摘要

This invention has as its object to provide a coordinate input apparatus which can attain an accurate coordinate input operation. When a vibration is input, the input vibration is detected by a sensor (6). The vibration is amplified, and an envelope detection circuit (52) generates the envelope of the amplified vibration. A gate signal generation circuit (58) receives the envelope and a second-order differential signal of the envelope generated by an inflection point detection circuit (53). The gate signal generation circuit (58) attenuates the envelope and adds a predetermined offset to the attenuated envelope. The gate signal generation circuit (58) compares the sum signal with the second-order differential signal to generate a gate signal. In the duration of the gate signal, a tg comparator (54) detects, as a group delay time, a time up to the zero cross point of the second-order differential signal, and a tp comparator (57) detects, as a phase delay time, a time up to the zero cross point in a predetermined order of a phase signal. An arithmetic control circuit (1) calculates the coordinate position of a vibration input source on the basis of these delay times. <MATH>