| 摘要 |
<p>PURPOSE:To take out a phase error due to only the change of the capacitance by inputting the prescribed phase error detecting output to a phase error detecting circuit as the correction value. CONSTITUTION:A capacitor is charged and discharged when an induction coil contained in a light pen, etc., having a contact with a coordinate input detecting plate 3 responds to the output of a transmission circuit 4 of a transmission loop including an oscillation circuit 11. The discharge of the capacitor is received by a reception circuit 5 of a reception loop. A phase detecting circuit 28 detects the phase error between the reception output of a clock counter circuit 9 and the reference output received from the circuit 11. The output of the circuit 28 is processed by a CPU 16, and the coordinate position of a light pen is decided by reference to a built-in ROM. At the same time, both circuits 4 and 5 are short-circuited with each other via a switch identification temperature compensating circuit 32. Then the detected value of the output phase difference between the circuits 4 and 5 detected by the circuit 28 is supplied to the circuit 28 as the correction value. The same phase difference caused by the switch output produced when the capacitance is changed in response to the input mode is detected, and the phase error due to only the change of the capacitance is taken out. Thus the selected mode is accurately identified.</p> |
