| 摘要 |
<p>PURPOSE:To reduce the effects of external noises by providing the detecting electrodes at four sides of an input screen having a planar resistance and setting the current of the detecting electrode at a fixed level with impression of a constant current source. CONSTITUTION:Constant current sources 8a and 8b are connected between the detecting electrodes 5a and 5b and the earth terminals via switches 7a and 7c. While the detecting electrodes 5c and 5d are grounded at other sides via switches 7b and 7d and the sources 8a and 8b. The operational amplifiers 9a and 9b are connected between electrodes 5c and 5d and 5a and 5b respectively. Then the potential difference output between both amplifiers is sent to sample and hold circuits 10a and 10b in the form of the X and Y coordinates of an input position. A detection control circuit 11 is actuated synchronously with a holding circuit 10 through the alternate open/close operations between switches 7a/7b and 7c/7d. Thus a constant current flows between the electrode 5 and the input position with impression of the voltage of a power supply 4 for impression of drive voltage. Then the voltage is produced according to the place of the constant current. Thus the X and Y coordinates are detected.</p> |
