| 摘要 |
<p>PROBLEM TO BE SOLVED: To improve coordinate detection accuracy and to suppress the lowering of the contrast ratio of a liquid crystal panel by roughly equalizing the frequency components of the pen detection signals of a row coordinate and a column coordinate and equalizing the pulse width of a row coordinate detection pulse signal and the width of the row coordinate detection pulse signal. SOLUTION: For a coordinate detection period, a coordinate detection pulse generation circuit 15 outputs coordinate detection pulse signals of almost the equal frequencies and pulse widths to a row driver 12 and a column driver 13A. The column driver 13A is made to simultaneously perform the scannings of the coordinate detection pulse signals corresponding to three columns for the column electrode on a color liquid crystal panel 11. Thus, because the detection signals of the same frequency component in the both of a row electrode and a column electrode in a pen 17 is detected by equalizing the frequency components of the coordinate detection pulse signals of a row and a column, the band of a band-pass filter 18 becomes possible to be narrowed and the noise entering from the pen 17 is reduced and coordinate detection accuracy is improved.</p> |
