Computer graphics processing and selective visual display system – Display peripheral interface input device – Touch panel
Reexamination Certificate
1998-11-10
2001-05-08
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Display peripheral interface input device
Touch panel
C178S018010
Reexamination Certificate
active
06229528
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a coordinate data output equipment and a liquid crystal tablet equipment mounted on an electronic organizer, a personal digital assistant (PDA) or the like, for allowing input operation by a pen touch or finger touch, for example. More specifically, the present invention relates to a coordinate data output equipment and a liquid crystal tablet equipment having high coordinate measuring accuracy.
2. Description of the Background Art
A liquid crystal tablet equipment (coordinate data output equipment) includes a liquid crystal display and a tablet as a coordinate reading equipment stacked on the liquid crystal display, so as to attain matching between an input through the tablet and a display output on the liquid crystal display.
When a display signal is to be applied to a liquid crystal dot, a DC component is applied to the liquid crystal dot, which shortens service life of liquid crystal. Therefore, generally, polarity of a voltage applied to the liquid crystal dot is inverted at every prescribed time period to obtain an ac signal. More specifically, a liquid crystal driver generates an ac converting signal (polarity inverting signal) which is a square wave repeatedly rises and falls at every prescribed time period. The liquid crystal driver inverts the display signal at a timing of an edge of the AC converting signal, and the display signal is applied to the liquid crystal display device.
The tablet includes two transparent conductive films having uniform resistance distribution, opposed to each other with a small distance therebetween. One conductive film includes electrodes on upper and lower sides. The other conductive film includes electrodes on left and right sides. By applying voltage to the electrodes at different timings, a prescribed current is caused to flow through respective conductive films, whereby voltage gradients are generated in X and Y directions. When the tablet is pressed by a pen, for example, two conductive films are brought into contact at the pressed designated point. First, a voltage gradient is generated in the X direction and the voltage value at the contact point is read, which value provides a signal on the X coordinate. Thereafter, a voltage gradient is generated in the Y direction and voltage value at the contact point is read, which provides a signal on the Y coordinate. These X and Y coordinate signals, which are analog signals, are converted to digital signals by A/D conversion, and input to a CPU.
When the display signal to be applied to the liquid crystal dot has its polarity inverted in accordance with the ac inverting signal in the liquid crystal display, an electromagnetic wave in the form of a strong impulse is generated, which electromagnetic wave is superposed as a noise on the coordinate signals of the tablet stacked on the liquid crystal display, possibly degrading accuracy in coordinate measurement. More specifically, the timing of polarity inversion of the display signals in accordance with the ac converting signal is not synchronized with the timing of tablet detection, and therefore it may be possible that these timings happen to match each other. In that case, noise is superposed on the coordinate signals.
Japanese Patent Laying-Open No. 6-161658 discloses a liquid crystal tablet equipment which is proposed as a solution of the above described problem. In the equipment, a delay circuit for delaying, by a prescribed time period, the ac signal is provided, the delayed signal is passed to a tablet driving circuit as a tablet detection timing signal, and A/D converting operation of an A/D converter in a tablet driving circuit is started at an edge of the tablet detection timing signal. In this manner, it is possible to offset the timing of A/D conversion of the coordinate signals from the edge of the ac converting signal, that is, from the timing of polarity inversion of the display signals. Accordingly, the coordinate signals can be subjected to A/D conversion at a timing not causing any superposition of noise.
However, the ac converting signal has small frequency and long period. Therefore, the tablet detection timing signal obtained by delaying this signal also has long period, wait time until the start of A/D conversion of the coordinate signal becomes considerably long, and therefore it takes much time to measure the input coordinate point on the tablet.
Further, there is another more fundamental problem. The noise caused by the electromagnetic wave from the liquid crystal display to the tablet is generated not only at the timing of the edge of the ac converting signal. It is possible that an electromagnetic wave in the form of a strong impulse is generated when a line pulse (gate pulse signal) applied to liquid crystal dot array of the liquid crystal display attains active, which electromagnetic wave may possibly be superposed as noise on the coordinate signal of the tablet. The prior art described in the aforementioned laid-open application cannot remove the influence of the noise caused by the line pulse.
Further, when the timing of the edge of the ac converting signal and the timing of activation of the line pulse coincide in time, the noise superposed on the coordinate signal would be far greater. In that case, if the tablet detection timing signal is output after a delay of a prescribed time period provided by the delay circuit, A/D converting operation of the coordinate signal starts before sufficient attenuation of the noise, degrading accuracy in coordinate measurement.
SUMMARY OF THE INVENTION
The present invention was made to solve the above described problems and its object is to provide a coordinate data output equipment and a liquid crystal tablet equipment which allows improvement in coordinate measurement accuracy by removing undesirable influence of noise caused by a line pulse signal applied to the liquid crystal display and allowing coordinate measurement in short period of time.
Another object of the present invention is to provide a coordinate data output equipment and a liquid crystal tablet equipment which allows improvement in coordinate measurement accuracy by removing undesirable influence of noise caused by a line pulse signal applied to the liquid crystal display, allows coordinate measurement in short time period and consumes less power.
A still further object of the present invention is to provide a coordinate data output equipment and a liquid crystal tablet equipment which allows improvement in coordinate measurement accuracy by removing undesirable influence of noise caused by a line pulse signal and an ac converting signal applied to the liquid crystal display, and allows coordinate measurement in a short period of time.
A still further object of the present invention is to provide a general purpose coordinate data output equipment and a liquid crystal tablet equipment which allows improvement in coordinate measurement accuracy by removing undesirable influence of noise caused by a line pulse signal applied to the liquid crystal display, allows coordinate measurement in short period of time and consumes less power.
The liquid crystal tablet equipment in accordance with an aspect of the present invention includes: a liquid crystal display
15
; a liquid crystal display control circuit
14
for applying line pulse signals at a prescribed interval to an array of pixels constituting the liquid crystal display
15
; a tablet
17
stacked on the liquid crystal display
15
; an A/D converter
18
receiving a coordinate signal output from the tablet
17
; a tablet control circuit
16
for calculating coordinate data from a digital signal output from the A/D converter; and a CPU
11
for letting A/D converter
18
to output the digital signal after the lapse of a prescribed time period from the timing at which the line pulse signal is rendered active.
After the lapse of a prescribed time period from the timing of activation of the line pulse signal generated by the liquid crystal display control circuit
14
, the A
Masuda Akihiro
Okajima Yoshio
Bell Paul A.
Nixon & Vanderhye P.C.
Saras Steven
Sharp Kabushiki Kaisha
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