Coordinate inputting apparatus and signal transmitting system thereof

Abstract: A coordinate inputting apparatus has a separating circuit (1), a cable (2) and a position indicating pen (3). The separating circuit (1) has a low pass filter (4) for removing an alternating current component from a signal transmitted to a signal line (2a) and a band pass filter (5) for passing only a position information signal in a predetermined frequency band with respect to the signal transmitted to the signal line (2a). The cable (2) is constructed by the signal line (2a), a switching signal line (SW) and a ground line (GND). The signal line (2a) is used to supply power to the position indicating pen (3) and transmit a detecting signal from the position indicating pen (3) to each of an X-coordinate detecting circuit (30) and a Y-coordinate detecting circuit (31). The position indicating pen (3) has a low pass filter (7) and a band pass filter (8). A signal transmitting system of this coordinate inputting apparatus and other coordinate inputting apparatuses are also shown.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pen inputting apparatus for inputting handwritten characters and figures to a tablet arranged on a display screen of a display unit as inputting means of a personal computer, a word processor, etc. Fig. 1 is a block diagram showing one example of the circuit construction of a general pen inputting apparatus. Fig. 1 shows a circuit construction for detecting a detecting mode signal in the display integral type tablet described in Japanese Patent Application Laying Open (KOKAI) No. 05-265650. A liquid crystal panel 121 is constructed by a liquid crystal and an electrode functioning as a display electrode for operating this liquid crystal and a position detecting electrode of the electrostatic induction type tablet. A detecting pen 122 has an end tip electrode electrostatically coupled to the electrode of the liquid crystal panel. The detecting pen 122 detects an induced voltage induced at each of rising and falling times of an inverting signal for operating the liquid crystal when the detecting pen 122 approaches the liquid crystal panel 121. A preamplifier 123 amplifies the induced voltage induced in the end tip electrode of the detecting pen 122 in voltage and/or electric current. An inverting signal generating circuit 124 generates an inverting signal for operating the liquid crystal of the liquid crystal panel 121 and setting an inverting time point of applying directions of a voltage applied to the liquid crystal. A gate signal generating circuit 125 generates a first gate signal synchronized with rise and/or fall of the inverting signal and a second gate signal provided except for a transmitting time of this first gate signal. A first analog gate circuit 126 samples the induced voltage amplified in voltage and/or electric current by the first gate signal. A second analog gate circuit 127 samples the induced voltage amplified in voltage and/or electric current by the second gate signal. A first processing circuit 128 is constructed by a full wave rectifying circuit 128a for making a full wave rectification with respect to the induced voltage sampled by the first gate signal. The first processing circuit 128 is also constructed by an integrating circuit 128b for converting the rectified induced voltage to a direct current voltage. A second processing circuit 129 is constructed by a full wave rectifying circuit 129a for making a full wave rectification with respect to the induced voltage sampled by the second gate signal. The second processing circuit 129 is also constructed by an integrating circuit 129b for converting the rectified induced voltage to a direct current voltage. A comparing circuit 130 compares a level of the direct current voltage converted by the first processing circuit 128 with a level of the direct current voltage converted by the second processing circuit 129. The comparing circuit 130 judges by this comparison whether or not an end tip of the detecting pen approaches the display screen of the liquid crystal panel 121. The comparing circuit 130 outputs a detecting mode/nondetecting mode signal at a high or low voltage level by this comparison. Fig. 2 is a circuit diagram showing one example of the general circuit construction of the pen inputting apparatus. As shown in Fig. 2, the pen inputting apparatus has the first analog gate circuit 126 and the second analog gate circuit 127 each constructed by an analog switch (for example, a FET), the full wave rectifying circuits 128a and 129a each constructed by a diode bridge, etc., the integrating circuits 128b and 129b each constructed by an operational amplifier, etc. and the comparing circuit 130. Fig.3 is a timing chart showing each of waveforms of signals in the circuit construction shown in Fig.1 and timings of these signals. These signals shown in Fig. 3 will next be explained. An inverting signal "as" of (A) is generated from the inverting signal generating circuit 124. This inverting signal "as" is used to periodically invert applying directions of a voltage applied to the liquid crystal so as to prevent the liquid crystal of the liquid crystal panel from being deteriorated by electrolysis. At this time, the voltages of driving signals applied to the electrode of the liquid crystal panel are simultaneously changed. A first gate signal g1 of (B) and a second gate signal g2 of (C) are generated from the gate signal generating circuit 125 and are respectively transmitted to the first analog gate circuit 126 and the second analog gate circuit 127. A duty ratio (tg1:tg2) of the first and second gate signals is set in advance at a designing time point of the pen inputting apparatus. An induced voltage sk of (D) is obtained by inducing an electrostatic induced voltage having a spike shape and depending on a distance between the end tip electrode of the detecting pen 122 and the electrode of the liquid crystal panel 121 every time the applying directions of the voltage applied to the liquid crystal are inverted by the inverting signal "as" when the detecting pen 122 approaches the display screen of the liquid crystal panel 121. A waveform of a sampling signal sp1 of (E) is obtained by sampling the induced voltage sk by the first gate signal g1 using the first analog gate circuit 126 and making a full wave rectification of this induced voltage sk by the full wave rectifying circuit 128a. A waveform of a sampling signal sp2 of (F) is obtained by sampling the induced voltage sk by the second gate signal g2 using the second analog gate circuit 127 and making a full wave rectification of this induced voltage sk by the full wave rectifying circuit 129a. A waveform of a signal dv1 of (G) is obtained by converting the full wave rectified sampling signal sp1 to a direct current voltage by the integrating circuit 128b. A waveform of a signal dv2 of (H) is obtained by converting the full wave rectified sampling signal sp2 to a direct current voltage by the integrating circuit 129b. An output signal pm1 of (I) is obtained by comparing levels of the direct current voltages dv1 and dv2 with each other by the comparing circuit 130. The level of the direct current voltage dv1 is greater than the level of the direct current voltage dv2 so that a high ("H") voltage signal is outputted as a detecting mode signal. At this time, it can be judged that the detecting pen 122 approaches the liquid crystal panel 121. For example, a noise signal ns of (J) shows a high frequency induced voltage. This noise signal ns shows one example of a signal waveform induced when the detecting pen 122 is separated from the display screen of the liquid crystal panel 121. A waveform of a sampling signal sp3 of (K) is obtained by sampling the noise signal ns by the first gate signal g1 using the first analog gate circuit 126 and making a full wave rectification with respect to this noise signal by the full wave rectifying circuit 128a. A waveform of a sampling signal sp4 of (L) is obtained by sampling the noise signal ns by the second gate signal g2 using the second analog gate circuit 127 and making a full wave rectification with respect to this noise signal by the full wave rectifying circuit 129a. A waveform of a direct current voltage signal dv3 of (M) is obtained by converting the full wave rectified sampling signal sp3 to a direct current voltage by the integrating circuit 128b. A waveform of a direct current voltage signal dv4 of (N) is obtained by converting the full wave rectified sampling signal sp4 to a direct current voltage by the integrating circuit 129b. A detecting mode signal pm2 of (O) is an output signal obtained by comparing levels of the direct current voltages dv1 and dv2 with each other by the comparing circuit 130. The level of the direct current voltage dv1 is lower than the level of the direct current voltage dv2 so that a low ("L") voltage signal is outputted as a nondetecting mode signal. At this time, it can be judged that the detecting pen 122 is separated from the liquid crystal panel 121. Accordingly, the detecting pen 122 can correctly extract the detecting mode signal pm by removing the noise signal ns therefrom even when the detecting pen 122 is separated from the liquid crystal panel 121 and the noise signal ns is induced. When the detecting pen 122 approaches the liquid crystal panel 121 in detection of the detecting mode signal pm, a high ("H") voltage signal is outputted as a detecting mode signal ns from the induced voltage sk having a spike shape. Conversely, when the detecting pen 122 is separated from the liquid crystal panel 121, no high ("H") voltage signal is outputted even when the noise signal ns is induced. A duty ratio (showing distribution of a sampling time) of the first gate signal g1 and the second gate signal g2 outputted from the gate signal generating circuit 125 is set in advance such that the high voltage signal is outputted when the detecting pen 122 approaches the liquid crystal panel 121 and no high voltage signal is outputted when the detecting pen 122 is separated from the liquid crystal panel 121 as mentioned above. Namely, an S/N ratio is improved by setting a time interval (tg1) of the first gate signal g1 to be equal to or greater than three times a discharging time constant of the spike-shaped induced voltage sk so as to reliably detect that the detecting pen 122 approaches the liquid crystal panel 121. The S/N ratio is further improved by greatly setting a time interval (tg2) of the second gate signal g2 in comparison with the time interval (tg1) of the first gate signal g1 so as to reliably detect that the detecting pen 122 is separated from the liquid crystal panel 121. Accordingly, the duty ratio of the gate signals is determined at a designing time point of electric circuits of the pen inputting apparatus such that the duty ratio becomes a suitable numeric value from various conditions and the above relation of the S/N ratio. These conditions include an electrostatic capacity (shown by a detected waveform of the spike-shaped induced voltage) between the electrode of the liquid crystal panel and the end tip electrode of the detecting pen, an amplifying degree of the preamplifier 123, time constants of capacitors C1, C2, resistors R1, R2 of the integrating circuits 128b, 129b as shown in Fig. 2, etc. The duty ratio of the gate signals is set at the designing time point of these electric circuits in consideration of dispersion in accuracy of parts. However, an unexpectable dispersion in accuracy of parts is caused every lot when the number of produced pen inputting apparatuses is increased. Therefore, there is a possibility that no pen inputting apparatus is normally operated by reducing the S/N ratio in detection of the above detecting mode/nondetecting mode signal. Further, when parts having high accuracy are used to reduce the dispersion in accuracy of parts, cost of the pen inputting apparatus is increased and the number of compensating parts is increased. SUMMARY OF THE INVENTION An object of the present invention is to provide a pen inputting apparatus having means for controlling a duty ratio of gate signals for determining two sampling times as a setting condition for detecting a detecting mode signal so that dispersion in accuracy of parts is absorbed and an optimum duty ratio is determined with respect to each of manufactured products, and a stable detecting mode/nondetecting mode signal can be detected and a function for automatically setting the duty ratio is also provided. The above object can be achieved by a pen inputting apparatus comprising: a liquid crystal panel constructed by a liquid crystal and an electrode for operating this liquid crystal; a detecting pen having an end tip electrode electrostatically coupled to the electrode of the liquid crystal panel and detecting an induced voltage induced at each of rising and falling times of a signal for operating the liquid crystal; inverting signal generating means for operating the liquid crystal of the liquid crystal panel and generating an inverting signal for inverting applying directions of a voltage applied to the liquid crystal; gate signal generating means for generating a first gate signal synchronized with each of rise and fall of the inverting signal and a second gate signal provided except for a transmitting time of this first gate signal; first sampling processing means for sampling the induced voltage induced in the end tip electrode of the detecting pen by the first gate signal and converting this induced voltage to a direct current voltage when the rise and fall of the inverting signal are changed; second sampling processing means for sampling an induced voltage induced after the sampling of the first sampling processing means by the second gate signal; the second sampling processing means converting this induced voltage to a direct current voltage; and judging means for judging whether or not an end tip of the detecting pen approaches a display screen of the liquid crystal panel on the basis of comparison of levels of the direct current voltages converted by the first and second sampling processing means; the judging means outputting results of this judgment as a detecting mode/nondetecting mode signal; characterized in that said pen inputting apparatus comprises duty ratio control means for controlling a duty ratio of the first and second gate signals generated by the gate signal generating means; wherein the pen inputting apparatus being constructed such that the duty ratio control means controls sampling times of the gate signals supplied to the first and second sampling processing means by controlling the duty ratio of the first and second gate signals, and adjusts the levels of the direct current voltages converted by the first and second sampling processing means so that the judging means stably judges the detecting mode/nondetecting mode signal. In this pen inputting apparatus, the duty ratio control means preferably has duty ratio setting means for setting the duty ratio by numeric value data. The pen inputting apparatus further preferably comprises an automatic setting functional key for indicating an automatic setting function of the duty ratio. The duty ratio control means controls an operation of the gate signal generating means such that the duty ratio of the gate signals is sequentially changed from predetermined numeric value data when the automatic setting function is indicated by the automatic setting functional key and the detecting pen approaches a predetermined region on the display screen of the liquid crystal panel. The duty ratio control means also detects the duty ratio of the gate signals when the judging means outputs the detecting mode signal. The duty ratio control means further controls the gate signals with numeric value data of this detected duty ratio as initial set data. This pen inputting apparatus has means for controlling the duty ratio of the gate signals for determining two sampling times as a setting condition for detecting the detecting mode signal. Accordingly, dispersion in accuracy of parts is absorbed and an optimum duty ratio is determined with respect to each of manufactured products. Further, a stable detecting mode/nondetecting mode signal can be detected and a function for automatically setting the duty ratio is also provided. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram showing one example of the circuit construction of a general pen inputting apparatus; Fig. 2 is a circuit diagram showing one example of the circuit construction of the general pen inputting apparatus; Fig. 3 is a timing chart showing each of waveforms of signals in the circuit construction shown in Fig. 1 and timings of these signals; Fig. 4 is a block diagram showing the basic construction of a pen inputting apparatus in the present invention; Fig. 5 is a block diagram showing the circuit construction of a pen inputting apparatus in accordance with one embodiment of the present invention; Fig. 6 is a timing chart showing each of waveforms of signals in the circuit construction of the pen inputting apparatus shown in Fig. 5 and timings of these signals; Fig. 7 is a flow chart showing processing for automatically setting a duty ratio; Fig. 8 is a flow chart showing processing for automatically setting a duty ratio. Fig. 4 is a block diagram showing the basic construction of a pen inputting apparatus in the present invention. In Fig. 4, the pen inputting apparatus in the present invention comprises: a liquid crystal panel 201 constructed by a liquid crystal and an electrode for operating this liquid crystal; a detecting pen 202 having an end tip electrode electrostatically coupled to the electrode of the liquid crystal panel 201 and detecting an induced voltage induced at each of rising and falling times of a signal for operating the liquid crystal; inverting signal generating means 203 for operating the liquid crystal of the liquid crystal panel 201 and generating an inverting signal for inverting applying directions of a voltage applied to the liquid crystal; gate signal generating means 204 for generating a first gate signal synchronized with each of rise and fall of the inverting signal and a second gate signal provided except for a transmitting time of this first gate signal; first sampling processing means 205 for sampling the induced voltage induced in the end tip electrode of the detecting pen 202 by the first gate signal and converting this induced voltage to a direct current voltage when the rise and fall of the inverting signal are changed; second sampling processing means 206 for sampling an induced voltage induced after the sampling of the first sampling processing means 205 by the second gate signal; the second sampling processing means 206 converting this induced voltage to a direct current voltage; judging means 207 for judging whether or not an end tip of the detecting pen 202 approaches a display screen of the liquid crystal panel 201 on the basis of comparison of levels of the direct current voltages converted by the first and second sampling processing means 205 and 206; the judging means 207 outputting results of this judgment as a detecting mode/nondetecting mode signal; and duty ratio control means 208 for controlling a duty ratio of the first and second gate signals generated by the gate signal generating means 204. In this pen inputting apparatus, the duty ratio control means 208 controls sampling times of the gate signals supplied to the first and second sampling processing means 205 and 206 on the basis of a set duty ratio, and adjusts the levels of the direct current voltages converted by the first and second sampling processing means 205 and 206 so that the judging means 207 stably judges the detecting mode/nondetecting mode signal. In accordance with the above construction, voltages for operating the liquid crystal are simultaneously changed by supplying an inverting signal for periodically inverting the applying directions of a voltage applied to the liquid crystal. When the detecting pen approaches a surface of the liquid crystal panel 201, a spike-shaped induced voltage is induced and this voltage depends on a distance between the end tip electrode of the detecting pen 202 and the electrode of the liquid crystal panel 201. It is possible to set and change a duty ratio of a sampling time for sampling the induced voltage induced in the end tip electrode of the detecting pen 202 by the first gate signal and a sampling time for sampling the induced voltage by the second gate signal. Accordingly, it is possible to accurately judge times at which an end tip of the detecting pen 202 approaches the liquid crystal panel 201 and does not approach this liquid crystal panel 201 with respect to each of manufactured products having dispersion in accuracy of parts. Therefore, a stable detecting mode/nondetecting mode signal can be detected. The duty ratio control means 208 preferably has duty ratio setting means 209 for setting the duty ratio by numeric value data. The duty ratio setting means 209 is constructed by a setting key 209a, etc. Accordingly, the duty ratio of the first and second gate signals can be set and changed by numeric value data from the setting key 209a externally arranged so that a detecting mode/nondetecting mode signal suitable for each of manufactured products can be stably detected. The duty ratio setting means 209 further preferably comprises an automatic setting functional key 209b for indicating an automatic setting function of the duty ratio. The duty ratio control means 208 preferably controls an operation of the gate signal generating means 204 such that the duty ratio of the gate signals is sequentially changed from predetermined numeric value data when the automatic setting function is indicated by the automatic setting functional key 209b and the detecting pen 202 approaches a predetermined region on the display screen of the liquid crystal panel 201. The duty ratio control means 208 also preferably detects the duty ratio of the gate signals when the judging means 207 outputs the detecting mode signal. The duty ratio control means 208 further preferably controls the gate signals by initializing numeric value data of this detected duty ratio. Accordingly, the detecting mode signal is automatically detected and a duty ratio having high accuracy is set by only indicating the automatic setting function by the automatic setting functional key 209b and making the detecting pen 202 approach a predetermined region on the display screen of the liquid crystal panel 201. Further, the pen inputting apparatus preferably has memory means 210 for storing the duty ratio by numeric value data. Accordingly, the duty ratio setting means 209 can easily set and change the duty ratio by storing the duty ratio set from the setting key 209a externally arranged. A time interval of the first gate signal generated by the above gate signal generating means 204 includes changing time points of rise and fall of the above inverting signal and is shorter than a half period of the inverting signal. A time interval of the second gate signal generated by the gate signal generating means 204 can be set to a time interval started after termination of the generation of the first gate signal and terminated until the inverting signal is changed. Accordingly, an induced voltage caused by inverting the applying directions of a voltage applied to the liquid crystal can be sampled by the first gate signal. Further, an induced voltage caused by noises can be sampled by the second gate signal. Accordingly, it can be correctly judged whether an end tip of the detecting pen approaches the display screen of the liquid crystal panel or not. Each of the inverting signal and the gate signals is preferably constructed by a clock signal forming a signal for operating the liquid crystal and is also preferably formed as a signal integer times this clock signal. Accordingly, numeric value data of the duty ratio and the number of clock signals can be controlled in a state in which the numeric value data correspond to the number of clock signals. It is preferable to further arrange a preamplifier 211 for amplifying the induced voltage induced in the end tip electrode of the detecting pen 202 in voltage and/or electric current. Accordingly, each of the first and second sampling processing means 205 and 206 can stably sample the induced voltage since the preamplifier 211 amplifies the induced voltage induced in the end tip electrode of the detecting pen 202 in voltage and/or electric current. The first sampling processing means 205 can be constructed by an analog gate circuit 205a for sampling the above induced voltage by the first gate signal, a full wave rectifying circuit 205b for making a full wave rectification of the sampled induced voltage, and an integrating circuit 205c for converting the full wave rectified induced voltage to a direct current voltage. The second sampling processing means 206 can be constructed by an analog gate circuit 206a for sampling the above induced voltage by the second gate signal, a full wave rectifying circuit 206b for making a full wave rectification of the sampled induced voltage, and an integrating circuit 206c for converting the full wave rectified induced voltage to a direct current voltage. Accordingly, when each of the analog gate circuits 205a and 206a samples the induced voltage by each of the first and second gate signals, each of the full wave rectifying circuits 205b and 206b makes the full wave rectification with respect to the sampled induced voltage. The rectified induced voltage is then converted to a direct current voltage by each of the integrating circuits 205c and 206c. In the present invention, the liquid crystal panel 201 has both a display electrode of the liquid crystal panel and a position detecting electrode of an electrostatic induction type tablet. The detecting pen 202 has an end tip electrode electrostatically coupled to the electrode of the liquid crystal panel and detecting an induced voltage induced at each of rising and falling times of a signal for operating the liquid crystal. Each of the inverting signal generating means 203, the gate signal generating means 204, the duty ratio control means 208 and the memory means 210 uses a microcomputer composed of a CPU, a ROM, a RAM and an I/O port. In particular, the memory means 210 uses a ROM (E 2 PROM) in these elements. The first sampling processing means 205 is constructed by the analog gate circuit 205a, the full wave rectifying circuit 205b and the integrating circuit 205c. The second sampling processing means 206 is constructed by the analog gate circuit 206a, the full wave rectifying circuit 206b and the integrating circuit 206c. The judging means 207 uses a comparing circuit constructed by an operational amplifier. The setting key 209a and the automatic setting functional key 209b of the setting means 209 use a keyboard. The preamplifier 211 uses an operational amplifier. The preferred embodiments of a pen inputting apparatus in the present invention will next be described in detail with reference to Figs. 5 to 8. The pen inputting apparatus in the present invention is not limited to these embodiments. The pen inputting apparatus in the present invention is suitably used as an apparatus for mainly inputting handwritten characters and figures to a tablet arranged on the display screen of a display unit of a personal computer, a word processor, etc. Each of constructional elements of the pen inputting apparatus constitutes a pen inputting apparatus capable of changing a setting condition for detecting a detecting mode signal in the present invention. Further, each of these constructional elements constitutes a pen inputting apparatus for obtaining a detecting mode signal (a pen input signal) which is not influenced by external noises. Fig. 5 is a block diagram showing a pen inputting apparatus in accordance with one embodiment of the present invention. In Fig. 5 a liquid crystal panel 101 is constructed by a liquid crystal and an electrode functioning as a display electrode for operating this liquid crystal and a position detecting electrode of an electrostatic induction type tablet. A detecting pen 102 has an end tip electrode electrostatically coupled to the electrode of the liquid crystal panel. The detecting pen 102 detects induced voltages induced at rising and falling times of a signal for operating the liquid crystal when the detecting pen 102 approaches the liquid crystal panel 101. A preamplifier 103 amplifies an induced voltage induced in the end tip electrode of the detecting pen 102 in voltage and/or electric current. An inverting signal generating circuit 104 generates an inverting signal for operating the liquid crystal of the liquid crystal panel 101 and setting an inverting time point of applying directions of a voltage applied to the liquid crystal. A gate signal generating circuit 105 generates a first gate signal synchronized with each of rise and fall of the inverting signal and a second gate signal provided except for a transmitting time of this first gate signal. A first analog gate circuit 106 samples the induced voltage amplified in voltage and/or electric current by the first gate signal. A second analog gate circuit 107 samples the induced voltage amplified in voltage and/or electric current by the second gate signal. For example, each of the first analog gate circuit 106 and the second analog gate circuit 107 is constructed by an analog switch (FET). A first processing circuit 108 is constructed by a full wave rectifying circuit 108a for making a full wave rectification with respect to the induced voltage sampled by the first gate signal. The first processing circuit 108 is also constructed by an integrating circuit 108b for converting the rectified induced voltage to a direct current voltage. A second processing circuit 109 is constructed by a full wave rectifying circuit 109a for making a full wave rectification with respect to the induced voltage sampled by the second gate signal. The second processing circuit 109 is also constructed by an integrating circuit 109b for converting the rectified induced voltage to a direct current voltage. Each of the full wave rectifying circuits 108a and 109a is constructed by a diode bridge, etc. For example, each of the integrating circuits 108b and 109b is constructed by an operational amplifier. A comparing circuit 110 compares a level of the direct current voltage converted by the first processing circuit 108 with a level of the direct current voltage converted by the second processing circuit 109. The comparing circuit 110 also judges whether or not an end tip of the detecting pen 102 approaches the display screen of the liquid crystal panel 101. The comparing circuit 110 outputs a detecting mode/nondetecting mode signal pm at a high or low voltage level by this comparison. The comparing circuit 110 is constructed by an operational amplifier, but may be constructed by an A/D converting circuit and a microcomputer. A setting circuit 111 sets a duty ratio. A duty ratio control circuit 112 controls the duty ratio. A memory circuit 113 stores the set duty ratio. Each of the inverting signal generating circuit 104, the gate signal generating circuit 105, the setting circuit 111, the duty ratio control circuit 112 and the memory circuit 113 can be constructed by a microcomputer composed of a CPU, a ROM, a RAM, an I/O port, etc. The duty ratio of the memory circuit 113 can be rewritten and initialized from the exterior thereof by arranging a ROM such as a rewritable and non-volatile E 2 PROM in the memory circuit 113. A keyboard 114 includes a setting key 114a and an automatic setting functional key 114b. Fig. 6 is a timing chart showing each of waveforms of signals in the circuit construction of the pen inputting apparatus shown in Fig. 5 and timings of these signals. These signals shown in Fig. 6 will next be explained. An inverting signal "as" of (1) is generated from the inverting signal generating circuit 104. This inverting signal "as" is used to periodically invert applying directions of a voltage applied to the liquid crystal so as to prevent the liquid crystal of the liquid crystal panel from being deteriorated by electrolysis. At this time, the voltages of driving signals applied to the electrode of the liquid crystal panel are simultaneously changed. A first gate signal g1 of (2) and a second gate signal g2 of (3) are generated from the gate signal generating circuit 105 and are respectively transmitted to the first analog gate circuit 106 and the second analog gate circuit 107. A duty ratio (tg1:tg2) of the first and second gate signals can be reset by a time constant of an induced voltage. An induced voltage sk of (4) is obtained by inducing an induced voltage (an electrostatic induced voltage) having a spike shape and depending on a distance between the end tip electrode of the detecting pen 102 and the electrode of the liquid crystal panel 101 every time the applying directions of the voltage applied to the liquid crystal are inverted by the inverting signal "as" when the detecting pen 102 approaches the display screen of the liquid crystal panel 101. A waveform of a sampling signal sp1 of (5) is obtained by sampling the induced voltage sk by the first gate signal g1 using the first analog gate circuit 106 and making a full wave rectification of this induced voltage sk by the full wave rectifying circuit 108a. A waveform of a sampling signal sp2 of (6) is obtained by sampling the induced voltage sk by the second gate signal g2 using the second analog gate circuit 107 and making a full wave rectification of this induced voltage sk by the full wave rectifying circuit 109a. A waveform of a signal dv1 of (7) is obtained by converting the full wave rectified sampling signal sp1 to a direct current voltage by the integrating circuit 108b. A waveform of a signal dv2 of (8) is obtained by converting the full wave rectified sampling signal sp2 to a direct current voltage by the integrating circuit 109b. An output signal pm1 of (9) is a signal obtained by comparing levels of the direct current voltages dv1 and dv2 with each other by the comparing circuit 110. The level of the direct current voltage dv1 is greater than the level of the direct current voltage dv2 so that a high ("H") voltage signal is outputted as a detecting mode signal. At this time, it can be judged that the detecting pen 102 approaches the liquid crystal panel 101. For example, a noise signal ns of (10) shows a high frequency induced voltage. This noise signal ns shows one example of a signal waveform induced when the detecting pen 102 is separated from the display screen of the liquid crystal panel 101. A waveform of a sampling signal sp3 of (11) is obtained by sampling the noise signal ns by the first gate signal g1 using the first analog gate circuit 106 and making a full wave rectification with respect to this noise signal by the full wave rectifying circuit 108a. A waveform of a sampling signal sp4 of (12) is obtained by sampling the noise signal ns by the second gate signal g2 using the second analog gate circuit 107 and making a full wave rectification with respect to this noise signal by the full wave rectifying circuit 109a. A waveform of a direct current voltage signal dv3 of (13) is obtained by converting the full wave rectified sampling signal sp3 to a direct current voltage by the integrating circuit 108b. A waveform of a direct current voltage signal dv4 of (14) is obtained by converting the full wave rectified sampling signal sp4 to a direct current voltage by the integrating circuit 109b. A detecting mode signal pm2 of (15) is an output signal obtained by comparing the levels of the direct current voltages dv1 and dv2 with each other by the comparing circuit 110. The level of the direct current voltage dv1 is lower than the level of the direct current voltage dv2 so that a low ("L") voltage signal is outputted as a nondetecting mode signal. At this time, it can be judged that the detecting pen 102 is separated from the liquid crystal panel 101. Accordingly, the detecting pen 102 can correctly extract the detecting mode/nondetecting mode signal pm by removing the noise signal ns therefrom even when the detecting pen 102 is separated from the liquid crystal panel 101 and the noise signal ns is induced. When the detecting pen 102 approaches a surface of the liquid crystal panel 101 in inversion of the applying directions of the voltage applied to the liquid crystal as mentioned above, a voltage sk having a spike shape is induced and this voltage sk depends on a distance between the end tip electrode of the detecting pen 102 and the electrode of the liquid crystal panel. It is judged by using this spike-shaped induced voltage sk whether or not the detecting pen 102 approaches the liquid crystal panel 101. First, the spike-shaped induced voltage sk induced in the end tip electrode of the detecting pen 101 is sampled by each of the first and second gate signals g1 and g2 generated by the gate signal generating circuit 105 and each of the first and second analog gate circuits 106 and 107. Next, a full wave rectification of the spike-shaped induced voltage sk as a sampled signal is made by the full wave rectifying circuits 108a and 109a in the first processing circuit 108 and the second processing circuit 109, respectively. The rectified voltage is converted to each of direct current voltages dv1 and dv2 by each of the integrating circuits 108b and 109b. These direct current voltages are compared with each other by the comparator 110. When the voltage dv1 of the sampling signal sampled by the gate signal g1 is higher than the voltage dv2, a detecting mode signal pm becomes a high ("H") voltage signal. Accordingly, it can be judged that the detecting pen 102 sufficiently approaches the liquid crystal panel 101. In contrast to this, when the end tip electrode of the detecting pen 102 is separated from the liquid crystal panel 101 and a noise signal ns (as a noise of a high frequency induced voltage) is induced, the voltage dv2 of the sampling signal sampled by the second gate signal g2 is higher than the voltage dv1 so that the detecting mode signal pm does not become a high ("H") voltage signal, but becomes a low ("L") voltage signal. Accordingly, when the detecting mode signal pm is a high voltage signal, it is considered to be continuously effective that a coordinate signal is detected from the detecting pen 102. In contrast to this, when a nondetecting mode signal is a low voltage signal, detection of the coordinate signal is stopped so that only correct coordinates can be detected. Fig. 7 is a flow chart showing processing for manually setting a duty ratio. Fig.7 shows a method for directly inputting a set value of the duty ratio of the first and second gate signals for setting the detecting mode signal pm to a high voltage signal from the keyboard 114, etc. in a state in which an inputting operation of the detecting pen 102 is performed at a designating point on the display screen such as a central point of the display screen. In a step S401, the inputting operation of the detecting pen 102 is performed at a designating point on the display screen of the liquid crystal panel such as a center of the display screen. In a step S402, the duty ratio of the first and second gate signals is inputted to the pen inputting apparatus by numeric value data from the setting key 114a. In a step S403, it is checked whether the detecting mode signal pm becomes a high voltage signal or not. The set duty ratio is changed until a pen input signal becomes a high voltage signal. In a step S404, if the detecting mode signal pm becomes a high voltage signal, the setting operation of the duty ratio is completed so that numeric value data of this duty ratio are automatically stored to the memory circuit 113. Fig. 8 is a flow chart showing processing for automatically setting the duty ratio. Fig. 8 shows a method for automatically retrieving and storing a set value of the duty ratio of the first and second gate signals for setting the detecting mode signal pm to a high voltage signal in a state in which an inputting operation of the detecting pen 102 is performed at a designating point on the display screen such as a central point of the display screen. In a step S501, the inputting operation of the detecting pen 102 is performed at a designating point on the display screen of the liquid crystal panel. The inputting operation of an automatic setting functional key 114b is then performed. In a step S502, a sampling time (tg1) of the first gate signal g1 is set to be minimized. In a step S503, it is checked whether the detecting mode signal pm becomes a high voltage signal or not. In a step S504, the sampling time of the first gate signal g1 is gradually increased and the duty ratio is changed until the detecting mode signal pm becomes a high voltage signal. In a step S505, if the detecting mode signal becomes a high voltage signal, the sampling time of the first gate signal g1 is fixed and the duty ratio (tg1:tg2) is determined. Numeric value data of this duty ratio is stored to the memory circuit 113 so that an automatic setting operation of the duty ratio is completed. Accordingly, the duty ratio control circuit 112 adjusts the sampling times of the gate signals g1 and g2 supplied to the first and second analog gate circuits 106 and 107 by controlling an operation of the gate signal generating circuit 105 based on the set duty ratio so that levels of the direct current voltages dv1 and dv2 outputted from the first and second processing circuits 108 and 109 can be controlled. Further, it is possible to accurately judge times at which an end tip of the detecting pen 102 approaches the liquid crystal panel 101 and does not approach this liquid crystal panel 101 with respect to each of manufactured products having dispersion in accuracy of parts. Accordingly, a stable detecting mode signal can be obtained. The following effects can be obtained from the above-mentioned construction of the pen inputting apparatus in the present invention. (1) Voltages for operating a liquid crystal are simultaneously changed by supplying an inverting signal for periodically inverting applying directions of a voltage applied to the liquid crystal. When a detecting pen approaches the surface of a liquid crystal panel, a spike-shaped induced voltage is induced and this voltage depends on a distance between an end tip electrode of the detecting pen and an electrode of the liquid crystal panel. It is possible to change and control a duty ratio of a sampling time for sampling the induced voltage induced in the end tip electrode.of the detecting pen by a first gate signal and a sampling time for sampling this induced voltage by a second gate signal. Accordingly, it is possible to accurately judge times at which an end tip of the detecting pen approaches the liquid crystal panel and does not approach this liquid crystal panel with respect to each of manufactured products having dispersion in accuracy of parts. Therefore, a stable detecting mode/nondetecting mode signal can be detected. (2) If the duty ratio of the first and second gate signals is set and changed by numeric value data from a setting key externally arranged, a detecting mode/nondetecting mode signal suitable for each of manufactured products can be stably detected. (3) When an automatic setting functional key is arranged, a detecting mode signal is automatically detected and a duty ratio having high accuracy can be set by only indicating an automatic setting function and making the detecting pen approach a predetermined region on the display screen of the liquid crystal panel. (4) The duty ratio can be more easily set and changed if the duty ratio set from the setting key externally arranged is stored. (5) The induced voltage caused by inverting the applying directions of the voltage applied to the liquid crystal is sampled by the first gate signal. An induced voltage caused by noises is sampled by the second gate signal. Accordingly, it can be correctly judged whether the end tip of the detecting pen approaches the display screen of the liquid crystal panel or not. (6) A duty ratio having high accuracy can be set by controlling numeric value data of the duty ratio and the number of clock signals in a state in which the numeric value data correspond to the number of clock signals.

Claims: A pen inputting apparatus, comprising: a liquid crystal panel (101; 201) constructed by a liquid crystal and an electrode for operating this liquid crystal; a detecting pen (102; 202) having an end tip electrode electrostatically coupled to the electrode of said liquid crystal panel (101; 201) and detecting an induced voltage induced at each of rising and falling times of a signal for operating the liquid crystal; inverting signal generating means (104; 203) for operating the liquid crystal of said liquid crystal panel (101; 201) and generating an inverting signal for inverting applying directions of a voltage applied to the liquid crystal; gate signal generating means (105; 204) for generating a first signal synchronized with each of rise and fall of said inverting signal and a second gate signal provided except for a transmitting time of this first gate signal; first sampling processing means (108; 205) for sampling the induced voltage induced in the end tip electrode of said detecting pen (102; 202) by the first gate signal and converting this induced voltage to a direct current voltage when the rise and fall of said inverting signal are changed; second sampling processing means (109; 206) for sampling an induced voltage induced after the sampling of the first sampling processing means (102; 205) by the second gate signal; the second sampling processing means (109; 206) converting this induced voltage to a direct current voltage; and judging means (110; 207) for judging whether or not an end tip of said detecting pen (102; 202) approaches a display screen of said liquid crystal panel (101; 201) on the basis of comparison of levels of the direct current voltages converted by said first and second sampling processing means (108, 109; 205, 206); the judging means (110; 207) outputting results of this judgment as a detecting mode/-nondetecting mode signal; characterized in that said pen inputting apparatus further comprises: duty ratio control means (112; 208) for controlling a duty ratio of the first and second gate signals generated by said gate signal generating means (105; 204), wherein said duty ratio control means (112; 208) controls sampling times of the gate signals supplied to the first and second sampling processing means (108, 109; 205, 206) by controlling the duty ratio of the first and second gate signals, and adjusts the levels of the direct current voltages converted by the first and second sampling processing means (108, 109; 205, 206) so that the judging means (110; 207) stably judges the detecting mode/non-detecting mode signal. The pen inputting apparatus as claimed in claim 1, wherein the duty ratio control means (112; 208) has duty ratio setting means (111, 114; 209) for setting said duty ratio by numeric value data. The pen inputting apparatus as claimed in claims 1 or 2, wherein the pen inputting apparatus further comprises an automatic setting functional key (209b) for indicating an automatic setting function of said duty ratio; said duty ratio control means (112; 208) controls an operation of said gate signal generating means (105; 204) such that the duty ratio of said gate signals is sequentially changed from predetermined numeric value data when the automatic setting function is indicated by said automatic setting functional key (209b) and said detecting pen (102; 202) approaches a predetermined region on the display screen of said liquid crystal panel (101; 201); said duty ratio control means (112; 208) also detects the duty ratio of the gate signals when the judging means (110; 207) outputs the detecting mode signal; and said duty ratio control means (112; 208) further controls said gate signals with numeric value data of this detected duty ratio as initial set data.

Inventors: HIRANO KATSUMI, HIROMOTO KUNIO, IGUCHI SHIGEKI, NISHIMURA TOMOHIKO, NOMIYA KAZUYOSHI, HIRANO, KATSUMI, HIROMOTO, KUNIO, IGUCHI, SHIGEKI, NISHIMURA, TOMOHIKO, NOMIYA, KAZUYOSHI
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1995
Main classification: G06K11
IPC codes: G06F3