Coordinate input apparatus

摘要

A coordinate input apparatus according to the present invention eliminates distortion caused by interference of a asymmetrical plate wave with an asymmetrical plate wave from the vibrations which are detected after they have been propagated in a vibration transmitting member and performs a highly accurate position coordinate detection. The vibrations of a pen which is brought into contact with the vibration transmitting member are detected by sensors provided on both the front and rear surfaces of the vibration transmitting member to determine a coordinate of a position where the vibrating pen has been brought into contact. At that time, the vibration sensors mounted on the front and rear of the vibration transmitting member in an opposed relation detect vibrations on the two surfaces of the transmitting member. The signals which are detected by each pair of front and rear sensors represent vibrations in which the asymmetrical plate waves having the same phase and the 180 DEG out-of-phase asymmetrical plate waves are superimposed on top of one another. The signals of the two sensors are input to a differential circuit. A resultant differential signal is input to a signal waveform detecting circuit. Since the differential signal is a signal in which the asymmetrical waves are cancelled with each other and in which the asymmetrical waves are amplified by twice, reduction in the vibration detection accuracy which is caused by distortion of waveforms can be prevented.