| 摘要 |
<p>PURPOSE:To prevent erroneous detection of contact position coordinates due to noise by increasing the time constant of an integrator in a variable oscillator and stopping counting for impedance measurement for a time longer than the time when the output voltage of the integrator is unstable. CONSTITUTION:A timing generator 35 generates a trigger pulse (b) synchonously with a switch element driving pulse (a), and this pulse (b) is inputted to a monostable multivibrator MM 44 to output a pulse (c) in the high level for a certain time Tw, and an oscillation pulse (d) from a variable oscillator 20 is inputted to a counter 46 through an AND circuit 45 for the time TW and is counted. Consequently, a terminal L1 of a touch panel 21 and a terminal R1 are connected to the input terminal and the output terminal of a voltage follower 43 respectively by the first pulse (a), and in this state, the counted value of pulses (d) obtained by the counter 46 is taken into a microcomputer by the rise of the pulse (b). Terminal L2 to Ln are successively connected to terminals of the voltage follower 43 in the same manner to obtain the counted value and an impedance calculated value based on the counted value. The counter 46 stops counting when the pulse (c) is in the low level.</p> |
