Sharp Kabushiki Kaisha Corporation

Kazunari Okamura

Takao Tagawa

Noritoshi Kako

Kengo Takahama

Hitoshi Nohno

Kiyohiro Nozaki

A detection and hold circuit outputs a reference signal having a level proportional to an x-coordinate detection pulse input from an X-coordinate signal amplifier. A delay element delays the reference signal. An adder adds the x-coordinate detection pulse from the X-coordinate signal amplifier and a delayed signal from the delay element. Comparators obtain a coordinate detection pulse making a detection signal from another detection and hold circuit for an LCD voltage inversion pulse serve as a reference signal. Thus noise following the x-coordinate detection pulse is removed to generate a coordinate detection pulse with a reference value corresponding to the level of the LCD voltage inversion pulse to allow a stable coordinate detection to be achieved. A correction signal generation circuit reads out correction data stored in an internal memory and transmits the data as a correction signal to a correction voltage generation circuit in an x-coordinate detection period when the segment electrode placed in the lower position is scanned. The correction voltage generation circuit generates a correction voltage for canceling a voltage induced at the common electrode placed in the upper position based on the input correction signal and a bias power source input from a DC power supply circuit.

Display-integrated type tablet device

An induction voltage signal induced at a detection electrode of a detection pen is binarized by a slice voltage 'e.sub.s '. The number of pulses existing in the binary signal is counted by a counting device. The resulting count value obtained by the counting device and the number of times of electrode scanning in an x-coordinate detection period or a y-coordinate detection period are compared with each other by means of a comparator. When the number of pulses is greater, an error detection alarm signal is output by an alarm device. Thus the existence of the pulses based on the error detection signal is detected in the binary signal based on the induction voltage signal from the detection electrode to output the error detection alarm signal. The above arrangement allows the coordinates at the tip end of the detection pen to be detected in a stable and correct manner even when external noise is detected.

Growing community of inventors

Tenri, Japan

Kazunari Okamura