LOW-PASS FILTER OF GRAPHICAL TABLET HAS CUT-OFF FREQUENCY LOWER THAN SAMPLING FREQUENCY

摘要

A graphical tablet includes a pair of parts to be brought into electrical contact with one another under user-interaction. Electrical signals are generated indicative of X and Y coordinates of the contact. The signals are filtered by low-pass filter means. The filtered X and Y signals are sampled with a particular sampling frequency and are held in separate X and Y holding means. The cut-off frequency of the filter means is at least part of the time substantially lower than the sampling frequency, as each holding means has to settle for only increments and decrements relative to its stored sample value. Thus the spectrum of noise rejection is widened with respect to the prior art.