Coordinate input apparatus

摘要

A coordinate input apparatus which can attain an accurate coordinate input operation, includes a sensor for detecting an input variation. The vibration is amplified, and an envelope detection circuit generates the envelope of the amplified vibration. A gate signal generation circuit receives the envelope and a second-order differential signal of the envelope generated by an inflection point detection circuit. The gate signal generation circuit attenuates the envelope and adds a predetermined offset to the attenuated envelope. The gate signal generation circuit 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 detects, as a group delay time, a time up to the zero cross point of the second-order differential signal, and a tp comparator 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 calculates the coordinate position of a vibration input source on the basis of these delay times.