PURPOSE: To obtain both a differential sense coil and a differential amplifier without increasing the number of switches by closing two adjacent switches to select the switches of selection switch groups of row and column directions.
CONSTITUTION: For switch groups 15 and 18, the adjacent two switches are successively selected and closed. That is, switches 151 and 152, 152 and 153, 153 and 154 and so on are successively closed with the group 15. In this case, the coils consisting of parallel conductors with one turn respectively are defined as sense coils SC1, SC2 and so on. When the tip of an electromagnetic pen 9 is put close to those coils SC, a magnetic flux generated from a pan coil 10 interlinks the coils SC to induce voltage. This voltage is detected by a differential amplifier 21 and processed by a signal processing circuit 24.
SAKAI ICHIROU
KAWAKITA TATSUJIROU
