| 摘要 |
<p>PURPOSE:To prevent the generation of malfunction or the drop of position detecting accuracy on the tablet side by allowing the generation timing of display data latch pulses of a display device to coincide with the transmission period of radio waves from the tablet of a coordinate input device. CONSTITUTION:A reference clock (b) is converted into a sine wave, the sine wave is transmitted to a duplexer circuit 3, connection is switched to a PLL circuit 4 or a voltage detecting circuit 7 by a switching signal (d), and a signal (f) to be applied to a selection circuit 2 is intermitted at time T. A loop coil of a position detecting part 1 generates a radio wave based upon the signal (f). When an input pen 9 is held on the detecting part 1 through a liquid crystal display panel 10, a tuning circuit 16 in the pen 9 generates an induction voltage (g). An induction voltage is generated in the circuit 7 by the radio wave generated by the voltage (g) and a DC signal (i) is sent to a processor 8. The processor 8 converts the voltage of the signal (i) into a digital value in each loop coil and computes the digital value to find out a position specified by the pen 9. When an image is displayed on the panel 10, noise (j) is generated synchronously with a display data latch pulse (a), but the noise (j) is not mixed with a receiving signal (h) during the generation of radio waves and no bad influence is generated.</p> |
