| 摘要 |
<p>PURPOSE:To delete noise by extracting the signal component of a fixed frequency out of the output of a detector serving as a stylus, detecting twice the time during which the signal component crosses a prescribed level in a short period and extracting the signal component as an output when the coincidence is obtained between both detection time. CONSTITUTION:The frequency component of about 280kHz of the output of a detector 30 is extracted through a BPF52 and supplied to a comparator 53 consisting of a zero cross detecting circuit to obtain a pulse output SZ. Then counters 61 and 62 detect the high level periods of a signal G1 which rises at the front edge of a signal DX1 or DY1 when a current flows to a conductor X1 or Y1 at the most edge side of a position detector plate 10 and falls with the rise of the signal SZ and a signal G2 which is obtained in the same way in the second drive period. Both signals G1 and G2 are supplied to a comparator 56 and compared with each other by a comparing signal SC. When the substantial coincidence is obtained between both signals, no noise component is mixed therewith. Thus a detection output is obtained.</p> |
