Abstract:
A drive system for an alternating current (AC) driven type gas discharge panel in which either one of the electrode pitches of X and Y electrodes is made smaller than the other. A positive pulse voltage is applied to the electrodes of the smaller electrode pitch and a negative pulse voltage is applied to the electrodes of the larger electrode pitch, thereby to write information in a selected discharge point. The AC driven type gas discharge panel of an electrode arrangement of an asymmetrical electrode pitch is driven with a maximum write margin which does not cause half select misfire.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a gas discharge panel drive system, and more particularly to a drive system for an alternating AC current driven type gas discharge panel which is capable of high resolution display. 
     2. Description of the Prior Art 
     A gas discharge panel, in which electrodes covered with dielectric layers are disposed opposite to each other across a space having sealed therein a discharge gas, is known under the name of a plasma display panel. In such a gas discharge panel heretofore employed, X-direction electrodes (hereinafter referred to as X electrodes) xi (i = 1, 2, 3, . . .) and Y-direction electrodes (hereinafter referred to as the Y electrodes) yj (J = 1, 2, 3, . . .) are disposed to intersect each other at right angles, and electrode pitches px and py are equal to each other, as shown, for example, in FIG. 1, which is a diagrammatic representation of the electrode arrangement in a conventional or &#34;prior art&#34; gas discharge panel. A sustain pulse is applied to each electrode and, in the case of a write operation, a write pulse is applied to each of selected ones of the X and Y electrodes. Letting a firing voltage and a minimum sustain pulse voltage (of a discharge point C ij  at the intersection of the electrodes xi and  yj) be represented with V f  and V sm , respectively, a pulse voltage V s  is selected to bear a relationship, V sm  &lt; V s  &lt; V f , and a write pulse voltage V w  to the selected discharge point is selected to have a relationship, V f  &lt; V w . 
     FIG. 2 shows an example of a driving waveform. Reference characters V xa  and V ya  indicate voltages applied to selected ones of the X and Y electrodes, respectively; V xb  and B yb  designate voltages applied to unselected X and Y electrodes, respectively; V a  identifies a voltage applid to a selected discharge point; PS denotes a sustain pulse of the voltage V s  ; PWX represents a positive half selection write pulse of a voltage V xw  ; PWY shows a negative half selection write pulse of a voltage V yw  ; and PW refers to a write pulse of a voltage V xw  + V yw  = V w . For example, in the case of writing information in a discharge point C33 at the intersection of the electrodes x3 and y3 in the panel shown in FIG. 1, a pulse train identified by the waveform V xa  and a pulse train indicated by the waveform V ya  are applied to the electrodes x3 and y3, respectively, and pulse trains identified by waveforms V xb  and V yb , respectively, are applied to the other unselected electrodes, by which the write pulse of the composite write pulse voltage V w  = V xw  + V yw  is applied to the discharge point C33 at the timing of write. Since the write pulse voltage V w  is higher than the firing voltage V f , a discharge spot is produced at the discharge point C33. 
     FIG. 3 is a graph showing the write characteristic of the conventional gas discharge panel described above, the ordinate representing the sustain pulse voltage V s  and the abscissa representing the composite write pulse voltage V w , and the hatched range being a normal operation region. For example, where the sustain pulse voltage V s  has a value V sl , the lowest composite write pulse voltage is V wl , above which write is possible. As the voltage V w  gradually rises, the intensity of a write discharge due to a charge coupling effect increases, resulting in an erroneous discharge or misfire of the neighboring discharge points owing to half selection. The range in which such misfire is not caused is defined as the write operation margin, and the composite write pulse voltage V w  must be set in such a range. 
     The present inventors have discovered polarity dependency of the write pulse in the phenomenon of causing such misfire at the neighboring discharge points. That is, when the composite write pulse voltage of the positive and negative write pulses PWX and PWY (FIG. 2) applied to the electrodes x3 and y3, respectively, is V whl , misfire is produced at the neighboring discharge points C32 and C34 along the electrode x3 supplied with the positive half selection write pulse PWX, but no misfire is caused at the neighboring discharge points C23 and C43 along the electrode y3 supplied with the negative half selection write pulse PWY, even if the voltages V xw  and V yw  of the half selection write pulses PWX and PWY, respectively, are equal to each other. When the composite write pulse voltage further increases to a value V wh2 , misfire is also produced at the abovesaid discharge points C23 and C43. That is, the neighboring discharge points in the X- and Y-directions, in which misfire is caused by half selection, differ with the polarity of the write pulse. 
     SUMMARY OF THE INVENTION 
     An object of this invention is to provide an AC driven type gas discharge panel drive system which is capable of high resolution display. 
     Another object of this invention is to provide an AC driven type gas discharge panel drive system which is capable of high resolution display and which has a simple construction, utilizing the fact that the generation of misfire at the neighboring discharge points is dependent upon the polarity of the write pulse applied to a selected discharge point. 
     Briefly stated, in accordance with this invention, the electrode pitch of either one of the X and Y electrodes is selected larger than the electrode pitch of the other, and a write voltage is applied to the selected discharge point by applying a positive write pulse to the electrode of the smaller electrode pitch and a negative write pulse to the electrode of the larger electrode pitch. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a diagram explanatory of the electrode arrangement in a conventional gas discharge panel; 
     FIG. 2 is a waveform diagram showing driving waveforms used for the conventional gas discharge panel; 
     FIG. 3 is a graph showing the write operation characteristic of the conventional gas discharge panel; 
     FIG. 4 is a diagram explanatory of the electrode arrangement in a gas discharge panel embodying this invention; 
     FIG. 5 is a sectional view illustrating the principal part of the gas discharge panel of this invention; 
     FIG. 6 is a graph showing the write operation characteristic of the gas discharge panel of this invention; 
     FIG. 7 is a drive circuit for use in the embodiment of this invention; and 
     FIG. 8 is a waveform diagram showing driving waveforms employed in the embodiment of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 4 is explanatory of the electrode arrangement adopted in an embodiment of this invention, in which the pitch px of the electrodes xi (i = 1, 2, . . ., 10) is selected smaller than the pitch py of the electrodes yj (j = 1, 2, . . ., 5). In this case, the driving waveforms may be such, for instance, as shown in FIG. 2, and the write pulse PWX to the electrode xi is positive and the write pulse to the electrode yj is negative. That is, the electrode pitch of the electrodes supplied with the positive write pulse is selected smaller than the electrode pitch of the electrodes supplid with the negative write pulse. 
     FIG. 5 shows in section the principal part of the gas discharge panel, which is constructed to include a pair of substrates 1 and 2, as of glass, disposed opposite to each other. The substrate 1 carries on its inside a plurality of Y electrodes 3 arranged in a horizontal direction and covered with a dielectric layer 4, as of a low-melting-point glass. The other substrate 2 also carries on its inside X electrodes 5 disposed in a direction to intersect the abovesaid Y electrodes at right angles thereto and covered with a dielectric layer 6 as of a low-melting-point glass. 
     Prior to the assembly of such a gas discharge panel, glass spacers 7 are fixed to the dielectric layer 4 by an adhesive which is decomposed by heating, after firing of the dielectric layer 4. Then, the assembly including the substrate 1 is heated. By this heat treatment, the adhesive is decomposed or evaporated and, at the same time, the glass spacers 7 are fused with the dielectric layer 4 of the low-melting-point glass. Thereafter, a protective layer 8 of magnesium oxide (MgO) is formed on the surface of the dielectric layer 4 including the glass spacers 7. A similar protective layer 9 is also formed on the other dielectric layer 6. 
     The two substrates thus prepared are disposed opposite to each other, with the X and Y electrodes 5 and 3 crossing each other, and the periphery of the assembly is sealed with a sealing member 10. Next, a space 11 defined by the spacers 7 is evacuated, and then a mixed gas for discharge is sealed into the space 11, thus providing a gas discharge panel. 
     The operation characteristic of such a gas discharge panel is shown in FIG. 6, in which the hatched range is the normal operation region of the panel, which is substantially similar to the operation region of the conventional discharge panel as such operation region is depicted in FIG. 3. In the present invention, however, referring to FIGS. 4 and 6 the pitch of the electrodes xi is reduced as compared with that of the electrodes yj as described above. As a result of this, for instance, in the case of writing information in the discharge point C33, when the composite write pulse voltage is V whl , a faulty discharge is produced at the neighboring discharge points C32 and C34 along the electrode x3, and when the abovesaid composite voltage is V wh2 , a faulty discharge is similarly caused at the neighboring discharge points C23 and C43 along the electrode y3. A comparison of the characteristic shown in FIG. 6 with that of FIG. 3 reveals that V wh2  &gt; V wh2&#39;  and that V whl  &lt; V wh2&#39; . Consequently, even if the pitch of the electrodes xi is decreased, the normal operation range is not reduced. 
     Thus, since the decreased pitch of the electrodes xi does not lead to the reduction of the normal operation region, a stable and high resolution display can be provided. The pitch px (FIG. 4) of the electrodes xi may be reduced to about 1/2 of the pitch py of the other electrodes yj. Further, in the case where the pitch of the Y electrodes is smaller than that of the X electrodes, write can be accomplished by applying a negative pulse voltage to the X electrode and a positive pulse voltage to the Y electrode. That is, the present invention utilizes the phenomenon that the coupling effect of the neighboring discharge points in the direction (the X-direction) of the electrodes, supplied with the positive write pulse voltage is larger than in the direction (Y-direction) of the electrodes supplied with the negative write pulse voltage, and the invention achieves the high resolution display by reducing one of the electrode pitches without decreasing the write margin. 
     FIG. 7 illustrates the principal part of the construction of a drive circuit for use in the embodiment of the abovesaid drive system. A gas discharge panel PDP is shown to have a 5 × 7 dot matrix for a character display, and the Y electrode pitch is larger than the X electrode pitch. 
     Y electrode groups, each composed of seven electrodes y11 to y17 and y21 to y27 of large pitch, for defining respective character rows, are connected to pairs of &#34;up sustain&#34; transistors QYU1 and QYU2 and &#34;down sustain&#34; transistors OYD1 and QYD2 through two groups of diode arrays DYU1, DYU2 and DYD1, DYD2, respectively. The electrodes of the respective electrode groups are respectively connected through resistor arrays RY11 to RY17 and RY21 to RY27 to address switching transistors QYA1 and QYA2 connected to a negative power source -V yw . Further, corresponding ones of electrodes of the Y electrode groups are respectively connected to address clamping transistors QYC1 to QYC7 through diode arrays DYA1 and DYA2. Thus, the Y electrodes are selectively supplied with the negative write pulse PWY by the address switching transistors and the address clamping transistors of the resistor-diode matrix structure. 
     On the other hand, X electrode groups, each composed of five electrodes x11 to x15 and x21 to x25 of small pitch, for defining respective character columns, are connected to pairs of &#34;up sustain&#34; transistors QXU1 and QXU2 and &#34;down sustain&#34; transistors QXD1 and QXD2 through two groups of diode arrays DXU1, DXU2 and DXD1, DXD2, respectively. Further, corresponding ones of the electrodes of the respective X electrode groups are respectively connected to address switching transistors QXA1 to QXA5 through resistor arrays RX11 to RX15 and RX21 to RX25. The address switching transistors QXA1 to QXA5 are respectively connected to a positive power source +V xw  and, by their selective switching operation, the X electrodes of the respective X electrode groups are selectively supplied with the positive write pulse PWX. In this case, the selection of the respective X electrode groups is accomplished by the &#34;down sustain&#34; transistors QXD1 and QXD2 in such a manner that unselected ones of electrodes are clamped at the ground potential. Reference character +V 3  indicates a sustain voltage. By the operation of the &#34;up sustain&#34; transistors and &#34;down sustain&#34; transistors on both sides of the X and Y electrode groups, the sustain pulse is applied to each electrode. 
     In the abovesaid drive circuit, write pulses corresponding to character pattern information are sequentially applied to selected ones of the X electrodes for each character block in the so-called line in a timed manner, by which a desired character can be written for a display. In this case, since the pitch of the X electrodes extending in a vertical direction is smaller than the pitch of the Y electrodes, the displayed character is easy to interpret and, further, driving can be effected with a large operation margin. 
     FIG. 8 shows driving waveforms used in the embodiment of this invention. Reference characters V xa  and V ya  indicate pulse waveforms which are applied to selected ones of the X and Y electrodes, respectively; V xb  and V yb  designate pulse waveforms applied to unselected X and Y electrodes, respectively; V a  identifies a pulse waveform applied to a selected discharge point; PS denotes a sustain pulse of a voltage V s  ; PWX represents a positive half selection write pulse of a voltage V xw  ; PWY shows a negative half selection write pulse of a voltage V yw  ; and PW refers to a write pulse of a voltage V xw  + V yw  = V w . Following the write pulse PW, the sustain pulse PS is applied to stabilize a discharge produced at the selected discharge point. 
     The voltage V xw  of the half selection write pulse PWX can be made equal to the voltage V s  of the sustain pulse PS. In such a case, the power source for producing the voltage V s  = V xw  can also be used for the generation of the write pulse PWX and the sustain pulse PS. 
     Further, a voltage V xw , may also be superimposed on the sustain pulse PS to obtain the half selection write pulse PWX and, in this case, by this write pulse PWX and the half selection write pulse PWY, of the voltage V yw , the write pulse PW of the voltage V s  + V xw&#39;  + V yw&#39;  = V w  can be applied to the selected discharge point. 
     In short, it is sufficient only to apply pulses to selected ones of the X and Y electrodes so that the potential difference between the opposing electrodes forming the selected discharge point may provide a voltage high enough to produce a discharge. Accordingly, in this invention, the negative write pulse, which is applied to the electrodes of the larger pitch, does not imply that it is absolutely negative (as viewed from the ground potential) but implies that it has a polarity which is negative relative to the potential of the electrode of the smaller pitch. 
     As has been described in the foregoing, in the present invention, either one of the electrode pitches of the X and Y electrodes is selected to be smaller than the other so as to enable a high resolution display, and by applying a positive write pulse to the electrodes of the smaller electrode pitch and a negative write pulse to the electrodes of the larger electrode pitch, a composite write pulse is applied to a selected discharge point to perform the same normal operation as in the prior art panel. Accordingly, this invention has the advantage of ensuring that the gas discharge panel is capable of providing a stable, high resolution display. 
     It will be apparent that many modifications and variations may be effected without departing from the scope of novel concepts of this invention.