Display panel and driving method therefor

Abstract: The present invention is concerned with a display panel having display cells, each of which is discharged to glow by means of paired cell-by-cell common electrodes and a discrete electrode, set in array, and a driving method for the display panel. An object of the present invention is to decrease the number of discrete contacts linked to the discrete electrodes so that the display cells can be driven discretely. Another object thereof is to define time domains, during which a plurality of common electrodes is controlled, within the period of a unit sequence so that the display cells can be driven discretely. A display panel has common electrodes, a plurality of cell-by-cell common electrodes, and discrete electrodes. The common electrodes are extending in columns on a transparent substrate. The cell-by-cell common electrodes are extending in rows from the common electrodes. The discrete electrodes are located among the adjoining cell-by-cell common electrodes on the transparent substrate. Display cells each of which is discharged to glow by means of paired cell-by-cell common electrodes and a discrete electrode are arranged in the display panel. According to a driving method for the display panel, the cell-by-cell common electrodes are interposed between the plurality of adjoining common electrodes. The discrete electrodes are located successively over display cells adjoining in rows. Time domains are determined during which display pulses are applied sequentially to the plurality of common electrodes. A unit sequence is completed over the time domains. Discharge control pulses are applied to the discrete electrodes. Thus, the display cells are lit or unlit.

Description: BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to a display panel for displaying pictures or the like, and a driving method for such a display panel. 2. Description of the Related Art In the past, a display panel for displaying pictures by utilizing gas discharge has been described in, for example, "Plasma Display" written by Ohwaki and Yoshida (November of 1983). In the display panel, comb electrodes coated with an insulating material such as glass are opposed to each other in the form of a matrix with a discharge space between them. Display cells arranged in the form of a matrix are driven concurrently by a single comb electrode. Moreover, for controlling display on the conventional display panel, the comb electrodes arranged in the form of a matrix are used to successively drive the electrodes of the comb electrode juxtaposed coincidentally with scanning lines. Microscopic discharge is induced in display cells formed between the selected electrodes of the comb electrode and electrodes of the other comb electrode opposed in the form of a matrix. This is a writing operation. The display cells in which microscopic discharge has been induced by the writing operation are selectively caused to glow. Nevertheless, the whole display screen is caused to glow. This is a sustaining operation. Broadly, display is achieved by performing these two operations. The conventional display panel has the foregoing structure. The electrodes arranged in the form of a matrix concurrently drive a plurality of display cells numbering 100 or more. Wall charges or space charges on the electrodes affect the other cells on the same electrodes. Consequently, a large difference in performance between one product and another is created in the process of manufacturing. Display cannot therefore help being controlled depending on the properties of display cells to be discharged. A control margin is therefore not large enough to stabilize display. Moreover, this poses a problem in that the yield of manufacturing the display panel is lowered duly. Moreover, according to a conventional driving method for display panels, a luminance must be controlled for each display cell in order to display a picture. Since display electrodes are in charge of numerous display cells, a special procedure must be adopted for visualizing gradation. Furthermore, according to a conventional gradation control mode for display panels, luminance cannot be varied continuously. Points exhibiting discontinuous gradation, which result in a so-called pseudo contour, are visualized. This leads to greatly degraded quality of picture display. SUMMARY OF THE INVENTION The present invention attempts to solve the foregoing problems. Discrete contacts are led out from display cells so that the display cells can be driven discretely. The same number of bits as the number of cells is needed in terms of circuitry. This leads to an increase in number of ICs employed and an increase in number of discrete contacts. In consideration of this situation, an object of the present invention is to provide a display panel having a simple configuration that includes a reduced number of discrete contacts. In the display panel, cell-by-cell common electrodes included in the display cells are connected to a plurality of common electrodes. Discrete electrodes included in the display cells are extending successively between the plurality of common electrodes. The object of the present invention is to also provide a driving method for the display panel enabling discrete driving of each display cell. According to the driving method, time domains during which the plurality of common electrodes is controlled respectively are determined within the period of a unit sequence. A display panel according to the present invention is defined by claim 1. A method for driving such a display is defined by claim 4. Preferred embodiments are set out in the dependent claims. BRIEF DISCRIPTION OF THE DRAWINGS Fig. 1 is a plan view showing the structure of a display panel in accordance with the first embodiment including electrodes. Fig. 2 shows a sequence of applications of pulses for driving the display panel in accordance with the first embodiment; Fig. 3 is a plan view showing the structure of a display panel in accordance with the third embodiment including electrodes; Fig. 4 is a plan view showing the structure of the display panel in accordance with the third embodiment including electrodes. DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment A description will be made of the structure of a display panel in accordance with the first embodiment. Paired cell-by-cell common electrodes and discrete electrodes are arranged on a front glass substrate. The front glass substrate is coated with an insulating material layer. Concave parts are cut in coincident areas on an opposed back glass substrate, whereby discharge spaces of display cells are created. A large number of display cells is arranged. Phosphor layers of three primary colors of red, green, and blue are applied orderly to the bottom of each concave part. When a predetermined voltage is applied to the paired cell-by-cell common electrodes and discrete electrode, plasma is generated in the discharge space of the concave part opposed to the paired cell-by-cell common electrodes and discrete electrode. Ultraviolet rays are absorbed by the phosphor layers. Consequently, a glow of a predetermined color emanates from the concave part through the front glass substrate. Fig. 1 is a plan view showing the cell-by-cell common electrodes and discrete electrodes in the display panel of the first embodiment. In Fig. 1, reference numerals 1 and 2 denote common electrodes extending in columns. The common electrodes 1 and 2 are connected to common contacts 3 and 4 respectively. The common contacts 3 and 4 are connected to external drive circuits that are not shown. Reference numerals 5 and 6 denote a plurality of cell-by-cell common electrodes extending in rows from the common electrodes 1 and 2 between the common electrodes 1 and 2. Reference numerals 7 and 8 denote discrete electrodes located successively among the adjoining cell-by-cell common electrodes 5 or 6. Reference numerals a1 to a6 denotes display cells each composed of paired cell-by-cell common electrodes 6 and a discrete electrode 7. Reference numeral 9 denotes a discrete contact located at the center node of the discrete electrodes 7 and 8. The discrete contacts 9 are, as shown in Fig. 1, juxtaposed in a row linearly and led out externally. Second Embodiment A driving method for a display panel in accordance with the second embodiment will be described in conjunction with Fig. 2. Fig. 2 shows a sequence of applications of pulses required for driving the display panel shown in Fig. 1. As shown in Fig. 2, a time domain 11 and a time domain 13 are defined within the period of a unit sequence. During the time domain 11, a plurality of display pulses 10 is applied to the common contact 3. During the time domain 13, a plurality of display pulses 12 is applied to the common contact 4. The numbers of display pulses applied during the time domains 11 and 13 are determined according to the number of display cells a1 to a6 and the number of display cells b1 to b6. When the plurality of display pulses 10 is applied to the common contact 3, the plurality of display pulses 10 is applied to the plurality of cell-by-cell common electrodes 5 by way of the common electrode 1 due to the structure shown in Fig. 1. Likewise, when the plurality of display pulses 12 is applied to the common contact 4, the plurality of display pulses 12 is applied to the plurality of cell-by-cell common electrodes 6 by way of the common electrode 2. The display pulses 10 and 12 to be applied to the common electrodes 1 and 2 respectively are, as shown in Fig. 2, composite voltage pulses. The composite voltage pulses each have a second voltage pulse 15 superposed on a first voltage pulse 14 during the duration of the first voltage pulse. The first and second voltage pulses 14 and 15 both exhibit, for example, 160 V. However, the first and second voltage pulses 14 and 15 may exhibit a voltage equal to or higher than a discharge sustaining voltage (130 V or higher) and equal to or lower than a discharge start voltage (220 V). On the other hand, discharge control pulses 16 and 17 like the ones shown in Fig. 2 are applied to the discrete electrodes 7 and 8 through the discrete contacts 9. The discharge control pulses 16 and 17 exhibit a discharge sustaining voltage of, for example, 0 V or a discharge suppressing voltage of, for example, 100 V. For lit cells whose discharge and glow should be sustained, the voltage (0 V) needed for sustaining discharge is applied to the discrete contacts 9. For unlit cells whose discharge and glow should be suppressed, the voltage (100 V) within a discharge suppression domain is applied to the individual contacts 9. Referring to Fig. 2, the display pulses 10 are applied to the common electrode 1 during the time domain 11. In cells not having the discharge control pulse 16 applied to the discrete electrodes 9 therein (discharge sustaining voltage 0V), the composite voltage pulses are applied to the cell-by-cell common electrodes 5 and discrete electrodes 7. The composite voltage pulses exceed the discharge start voltage. This results in discharge. On the other hand, in display cells having the discharge control pulse 16 applied to the discrete electrodes 7 therein, the potentials at the discrete electrodes 7 rise. A voltage high enough for discharge is not applied to the discrete electrodes 7 and cell-by-cell common electrodes 5. Consequently, discharge is suppressed. The same applied to the time domain 13. During the time domain 11, the display pulses 10 are applied to the cell-by-cell common electrodes 5, and the discharge control pulse 16 is applied to the discrete electrodes 7. Control is thus given to sustain or suppress glow of the display cells a1 to b6. At this time, the display pulses 12 are not applied to the cell-by-cell common electrodes 6. Even if the discharge control pulse 16 is applied to the discrete electrodes 8, a voltage (100 V) lower than the discharge start voltage and discharge sustaining voltage is applied to the cell-by-cell common electrodes 6. The display cells b1 to b6 are therefore not discharged to glow. Glows of the display cells a1 to a6 and the display cells b1 to b6 exhibit the waveform shown in Fig. 2. As apparent from Fig. 2, when control is given to change the pulse widths of the discharge control pulses 16 and 17 to be applied to the discrete contacts 9, it is controlled whether the display cells should be lit or unlit, that it, glow of the display cells should be sustained or suppressed. As mentioned above, in the display panel shown in Fig. 1, the time domains 11 and 13 are defined within the period of a unit sequence. So-called two systems including the common electrodes 1 and 2 respectively are actuated during the time domains 11 and 13. Consequently, the display cells a1 to a6 and the display cells b1 to b6 can all be driven and controlled discretely. Third Embodiment The structure of a display panel in accordance with the third embodiment and a driving method for the display panel will be described below. Fig. 3 is a plan view showing the structure of a display panel in which numerous cells are arranged in rows and columns in the form of a matrix. In Fig. 3, reference numerals 18 and 19 denote common electrode portions extending in rows along both columnar edges of the display panel. Reference numeral 20 denotes a plurality of common electrodes extending in columns from the common electrode portion 18. Reference numeral 21 denotes a plurality of common electrodes extending in columns from the common electrode portion 19. The pluralities of common electrodes 20 and 21 are juxtaposed alternately in rows. Reference numerals 22 and 23 denote numerous cell-by-cell common electrodes extending in rows among the common electrodes 20 and 21. Cell-by-cell common electrodes are extending successively from the common electrodes 21, which extend among the common electrodes 20, on both sides of the common electrodes 20. Reference numeral 24 denotes numerous discrete electrodes extending successively among the cell-by-cell common electrodes 22 and the cell-by-cell common electrodes 23. Reference numeral 25 denotes discrete contacts arranged in columns linearly in the center nodes of the discrete electrodes 24. A cell-by-cell common electrode 22 or 23 and an adjoining discrete electrode 24 constitute each display cell. A driving method for the display panel shown in Fig. 3 is a method utilizing so-called two systems including the common electrodes 20 and 21 respectively that are linked to the common electrode portions 18 and 19. Similarly to the second embodiment, time domains during which the two systems are actuated separately are defined within the period of a unit sequence. The display cells are thus driven discretely. In practice, the display panel of the third embodiment visualizes display pixels of, for example, 5 by 5 mm 2 in size, and has cells of 1.5 by 4 mm 2 in size. In the display panel, the gap between the cell-by-cell common electrodes 22 and 23 and discrete electrode 24 is 70 µm. Discharge gas (5 %-diluted Ne-Xe) of 500 torr is sealed in a discharge space of about 500 µm high. Fig. 4 is a plan view showing the structure of an actually manufactured display panel including the common electrodes 20 and 21 and discrete electrodes 24. The encircled portion of the structure in Fig. 3 is shown in enlargement. In Fig. 4, reference numerals 20 and 21 denote common electrodes. Reference numerals 22 and 23 denote cell-by-cell common electrodes. Reference numeral 24 denotes discrete electrodes mounted on a glass substrate (transparent substrate) 26. The cell-by-cell common electrodes 22 and 23 and the discrete electrodes 24 are realized with transparent electrodes. Reference numeral 25 denotes discrete contacts communicating with the discrete electrodes 24 on both sides thereof. The discrete contacts 25 are realized with pins projecting to the back surface of the display panel. One display cell is composed of a wide cell-by-cell common electrode 22 and discrete electrode 24 or of a cell-by-cell common electrode 23 and discrete electrode 24 which are enclosed with a wavy line in Fig. 4. In the display panel shown in Fig. 4, display cells for rendering 16 dots in width and 16 dots in length are created in a panel of 8 cm wide and long. Each dot is rendered by three adjoining display cells responsible for three primary colors of red (R), green (G), and blue (B). The total number of display cells is 768 and the number of discrete contacts 25 is a half of the number of display cells or 384. Fourth Embodiment Next, a description will be made of a method of visualizing gradation in the display panel of the third embodiment shown in Fig. 4. A plurality of display pulses, that is, composite voltage pulses is applied to the common electrodes 20 and 21 (18 and 19) during the associated time domains. The number of display pulses needed for discharge and display can be changed by changing the pulse width of a discharge control pulse to be applied to the discrete electrodes 24. The luminance of a glow is proportional to the number of times of discharge and glow. Luminance and gradation can be visualized according to the number of display pulses applied during a discharge sustaining period which is dependent on the pulse width of a discharge control pulse. In practice, a predetermined number of display pulses, that is, 255 pulses are applied during each time domain. When the discharge control pulse is applied to the discrete electrodes 24 at the rate of one discharge control pulse per 0 to 255 display pulses, the number of times of glow ranges 255 to 0. Gradation of 256 levels can be visualized by changing the number of times of glow. However, display pulses are applied alternately to the common electrodes 20 and 21 during the associated time domains. During a time domain during which the display pulses are applied to the common electrodes 20, no display pulse is applied to the other common electrodes 21. By the way, a time band defined with several display pulses is created immediately after the transition from the time domain during which no pulse is applied to the time domain during which pulses are applied. During the time band, discharge may become unstable and the intensity of glow may be lowered. A plurality of display pulses is therefore applied to the common electrodes 20 and 21 during the time domains. Consequently, uncertainly in intensity of glow can be stabilized and the intensity of glow can be stabilized. In practice, application of five pulses or more has result in stable glow.

Claims: A display panel including common electrodes (1, 2) extending in columns on a transparent substrate (26), and a plurality of cell-by-cell common electrodes (5, 6) extending in rows from the common electrodes, the panel having display cells (a1 to a6, b1 to b6) set in an array, wherein the cell-by-cell common electrodes (5, 6) are interposed between the plurality of adjacent common electrodes (1, 2), characterized in that discrete electrodes (7, 8) are located between the adjacent cell-by-cell common electrodes (5, 6) on the transparent substrate (26), and in that the discrete electrodes (7, 8) are located over successive display cells (a1 to a6, b1 to b6) adjacent in rows, wherein each display cell (a1 to a6, b1 to b6) is discharged to glow by means of a pair of a cell-by-cell common electrode (5, 6) and a discrete electrode (7, 8). The display panel according to claim 1, wherein discrete contacts (9) are located in the centre nodes of the adjoining discrete electrodes (7, 8) and common contacts (3, 4) are linked to the common electrodes (1, 2). The display panel according to claim 1 or 2, wherein common electrode portions (18, 19) are extending in rows along both columnar edges of the transparent (26), and common electrodes (20, 21) are connected alternately to these common electrode portions (18, 19). A method for driving the display panel according to any of claims 1 to 3, characterized in that one time domain (11) and another time domain (13) during which display pulses (10, 12) are applied sequentially to the one common electrode (1) and the other common electrode (2) are determined in order to complete a unit sequence, discharge control pulses (16, 17) are applied to the discrete electrodes (7, 8), and the display cells (a1 to a6, b1 to b6) on the plurality of rows are thus lit or unlit. The method according to claim 4, wherein the display pulses (10, 12) are applied as composite voltage pulses reaching a first level equal to or lower than the discharge start voltage and subsequently rising to a second higher level superposed on the first level and higher than the discharge start voltage during the pulse duration of the respective voltage pulse and wherein the pulse widths of the discharge control pulses (16, 17) are controlled in order to control whether the display cells (a1 to a6, b1 to b6) should be unlit. The method according to claim 5, wherein a plurality of the display pulses (10, 12) is applied during each of the time domains during which the display pulses (10, 12) are applied to the one common electrode (1) or the other common electrode (2).

Inventors: ARIMOTO HIRONOBU, ITO ATSUSHI, ARIMOTO, HIRONOBU, ITO, ATSUSHI, ARIMOTO, HIRONOBU, C/O MITSUBISHI DENKI K.K., ITO, ATSUSHI, C/O MITSUBISHI DENKI K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1999
Main classification: H01J17
IPC codes: H01J17, H01J11, G09G3, G09F9