| 摘要 |
<p>PURPOSE:To enable accurate coordinate detection by setting a comparison level so that variation in the detection timing of a transmission time due to the variation of an electric signal generated by converting the vibration of a coordinate indicator is minimized. CONSTITUTION:A vibration wave signal detected by a vibration sensor 101 passes through an analog switch 103, is processed by the absolute value conversion of an absolute value circuit 104, and passes through an LPF 105 to detect its envelope signal. The transmission time is detected in the vicinity of the inflection point of an envelope signal corresponding to the zero-cross point of the signal generated by differentiating the envelope signal twice by a differentiation circuit 106. For the accurate determination of this detection timing, the comparison level of a comparison level setting circuit 110 is varied to decides the comparison level, with which the variation width of the transmission time with the signal level becomes minimum, as the best value. Consequently, variation in the transmission time with the vibration wave signal level at the time of coordinate input can be suppressed with the simple constitution and the accurate coordinate detection is attained.</p> |
