JPS5614385A - Encoder unit - Google Patents

Abstract

PURPOSE: To improve the SN ratio to obtain a high-sensitivity encoder unit, by providing surface wave transducers on the surface and the reverse face in one end part of a glass substrate and by connecting their input ends to a common oscillator and by connecting a differential circuit to receiving output ends.

CONSTITUTION: When an arbitrary select position is pressed with finger 10, main reflection is obtained in contact face (f), however, reflection waves e' and e''' dependent upon end parts e and e" of transducers 12 and 14 and reflection waves c' and c''' dependent upon end parts c and c" of glass sybstrate 8 are generated also. Though e' and e", and c' and c''' out of these reflection waves are different from each other respectively by the surface and the reverse face, they have the same phase and the same amplitude because they are in the same distance from transducers; and therefore, when their difference is taken by a differential amplifier, they are cancelled by each other and only main reflection wave f' is left. Even if they are different in phase and amplitude, their difference is very little. Though wave c' becomes smaller than wave c''' on the reverse face of no main reflection due to the influence of wave f', waves c' and c''' are approximately equal to each other be cause reflection dependent upon the finger is small. Thus, only main reflection can be detected, and the SN ratio can be improved, and a high sensitivity can be obtained.

COPYRIGHT: (C)1981,JPO&Japio