Patent Publication Number: US-6215463-B1

Title: Driving system for a display panel

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a driving system of a matrix display system used as a display for an information terminal device, personal computer, and television receiver, and having such a display panel as an alternative current plasma display panel (ACPDP), electroluminescence (EL) panel, and liquid crystal panel wherein capacitive load is generated, and more particularly to a system wherein power for applying pixel data pulses to capacitive column electrodes is effectively reduced. 
     Recently, as a display device becomes large in size, thickness of the display device is desired to be thin. Therefore, various types of display devices of thin thickness are provided. As one of the display devices, an ACPDP is known. 
     A conventional ACPDP comprises a plurality of column electrodes and a plurality of row electrodes formed in pairs and disposed to intersect the column electrodes. A pair of row electrodes form one row (one scanning line) of an image. The column electrodes and the row electrodes are covered by dielectric layers respectively, at a discharge space. At the intersection of each of the column electrodes and each pair of row electrodes, a discharge cell (pixel) is formed. 
     FIG. 4 shows a timing chart of drive signals for driving the conventional ACPDP. 
     A reset pulse RPx of negative polarity is applied to each of the row electrodes X 1 -Xn. At the same time, a reset pulse RPy of positive polarity is applied to each of the row electrodes Y 1 -Yn. Thus, all of the row electrodes in pairs in the PDP are excited so that discharge occurs in each discharge cell, thereby producing charged particles in the discharge cell. Thereafter, when the discharge is finished, wall charge is formed and accumulated on the discharge cell (A reset all at once period). 
     Then, pixel data pulses AP 1 -APn corresponding to the pixel data for every row are applied to the column electrodes A 1 -Am in order in accordance with display data. At that time, scanning pulses (selecting and erasing pulses) SP are applied to the row electrodes Y 1 -Yn in order in synchronism with the timings of the data pulse AP 1 -APn. 
     At the time, only in the discharge cell (non-lighting pixel) to which the scanning pulse SP and the pixel data pulse AP are simultaneously applied, the discharge occurs, so that the wall charge produced at the reset all at once period is erased. 
     On the other hand, in the discharge cell to which only the scanning pulse SP is applied, the discharge does not occur. Thus, the wall charge produced at the reset all at once period is held. Namely, a predetermined amount of the wall charge is selectively erased in accordance with the pixel data (An address period). 
     Next, a discharge sustaining pulse IPx of negative polarity is applied to the row electrodes X 1 -Xn, and a discharge sustaining pulse IPy of negative polarity is applied to the row electrodes Y 1 -Yn at offset timing from the discharge row pulses IPx. 
     During the discharge sustaining pulses are continuously applied, the discharge cell which holds the a wall charge sustains the discharge and emission of light (A discharge sustaining period). On the other hand, a discharge cell in which the wall charge is erased does not emit. 
     Then, wall charge erasing pulses EP are applied to the row electrodes Y 1 -Yn for erasing the wall charges formed in all discharge cells. 
     By repeating the cycle comprising the reset all at once period, address period, discharge sustaining period, and wall charge erasing period, the pixel display is performed. 
     In such a driving system, there may be generated a potential difference between a column electrode to which a pixel data pulse is applied and an adjacent column electrode to which no pixel data pulse is applied during the address period. Therefore, a parasitic capacity between the adjacent column electrodes must be charged and discharged every time the pixel data is written on the scanning line. As a result, reactive power generates. In the case where only a single color, namely, red, green or blue is shown on the display, the reactive power is increased so that a large power for writing pixel data is required in addition to the power necessary for displaying. Hence the power consumption is increased. 
     In order to decrease the parasitic capacitance, which causes the increase in power consumption as described above, it is necessary to increase the distance between column electrodes, which renders it difficult to produce a extremely fine display panel. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a driving system for a display panel wherein the power consumption is reduced and the fine the display panel is still achieved. 
     According to the present invention, there is provided a driving system for a display panel having a plurality of row electrodes, a plurality of column electrodes intersecting with the row electrodes, comprising, a data voltage source circuit having a voltage source for supplying a voltage of about one half of a maximum voltage for driving the column electrode, a diode provided between the voltage source and an output terminal, a first switch connected to the voltage source at an end thereof, a second switch connected to another end of the first switch at an end thereof, and to a ground at the other end, and a voltage adding capacitor provided between a junction of the first and second switches and the output terminal, a column driver for driving the column electrodes, the column driver having an input terminal connected to the output terminal of the data voltage source circuit, a plurality of output terminals connected to the column electrodes, a third switch provided between the input terminal and each of the output terminals, a fourth switch provided between each of the output terminals and a ground, control circuit means for producing control signals for controlling the first to fourth switches. 
     These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a schematic perspective view showing a plasma display panel driven by the present invention; 
     FIG. 2 is a diagram showing a circuitry of a system for driving the display panel; 
     FIG. 3 is time charts explaining the operation of the driving system of FIG. 2; and 
     FIG. 4 is time charts showing drive signals for a conventional plasma display panel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows an ACPDP  10  of a reflection type to which the present invention is applied. The ACPDP  10  comprises a pair of glass substrates  11  and  12  disposed opposite to each other, interposing a discharge space  17  therebetween. The glass substrate  11  as a display portion has row electrodes (sustain electrodes) X and Y which are alternately disposed in pairs to be parallel with each other at the inside portion thereof. The row electrodes X and Y are covered by a dielectric layer  15  for producing wall charge. A protection layer  16  made of MgO is coated on the dielectric layer  15 . 
     Each of the row electrodes X and Y comprises a transparent electrode  14  formed by a transparent conductive film having a large width and a bus electrode (metallic electrode)  13  formed by a metallic film having a small width and layered on the transparent electrode  14 . 
     On the glass substrate  12  as a rear member, a plurality of elongated barriers  19  are provided at the inside portion thereof for defining the discharge space  17 . The barrier  19  extends in the direction perpendicular to the row electrodes X, Y. Between the barriers  19 , column electrodes (address electrodes) A are formed to intersect the row electrodes X and Y of the glass substrate  11 . A phosphor layer  18  having a predetermined luminous color R, G or B covers each of the column electrodes D and opposite side portions of the barrier  19 . The discharge space  17  is filled with discharge gas which is a mixture of neon and a small quantity of xenon. Thus, a pixel (including a discharge cell) is formed at the intersection of the row electrodes X and Y on the glass substrate  11  and the column electrode A on the glass substrate  12 . Since the ACPDP having a plurality of pixels is formed, it is possible to display images. 
     Referring to FIG. 2, an embodiment of a driving system for driving the PDP shown in FIG. 1 comprises a driver IC  1  for driving the column electrodes, data voltage source circuit  2  for driving the driving IC, and a control circuit  3  for controlling the operation of the driver IC  1  and the data voltage source circuit  2 . 
     The data voltage source circuit  2  has a constant voltage source Vd for supplying a constant voltage which corresponds to about one half of the maximum voltage V of the pixel data pulses AP. The data voltage source circuit  2  further comprises a p-channel field-effect transistor (FET) Q 1  as a first switching means, n-channel FET Q 2  as a second switching means, and a diode D 1 . One terminal of the p-channel FET Q 1  is connected to the constant voltage source Vd while the other terminal is connected to an output terminal OUT through a capacitor C 1  for adding voltages. One terminal of the n-channel FET Q 2  is also connected to the output terminal OUT through the capacitor C 1  while the other terminal is grounded. The power from the source Vd is applied to an input terminal P 1  of the driver IC  1  through the diode D 1  and the output terminal OUT. 
     The driver IC  1  has the input terminal P 1  connected to the output terminal OUT of data voltage source circuit  2 , a plurality of output terminals PZ 1  to PZn, each of which is connected to one of the column electrodes of the PDP, and a ground terminal P 2 . 
     The input terminal P 1  is connected to a plurality of high-voltage resistive p-channel MOSFETs QP 1  to QPn provided as a third switching means. The other terminals of the MOSFETs QP 1  to QPn are connected to respective output terminals PZ 1  to PZn. A plurality of high-voltage resistive n-channel MOSFTs QN 1  to QNn are provided between the corresponding output terminals PZ 1  to PZn and the ground terminal P 2  as a fourth switching means. 
     Diodes DP 1  to DPn are provided as parasitic diodes for the p-channel MOSFETs and diodes DN 1  to DNn are provided as parasitic diodes for the n-channel MOSFETs. The output terminals PZ 1  to PZn are connected to column electrodes to which data are to be applied. 
     The control circuit  3  applies control signals to the p-channel FET Q 1  and the n-channel FET Q 2  of the data voltage source circuit  2 , p-channel MOSFETs QP 1  to QPn and n-channel MOSFETs QN 1  to QNn, thereby to control the operation of the switching means comprising the FETs. 
     The operation of the driving system will be described hereinafter with reference to FIG. 3 in which voltage levels in the devices of FIG. 2 are shown. 
     When the FET Q 1  in the data voltage source circuit  2  is rendered OFF and the FET Q 2  ON, a predetermined electric charge from the constant voltage source Vd is applied to the capacitor C 1  through the diode D 1 , thereby storing the charge in the capacitor C 1 . Hence the capacitor C 1  is charged with the constant voltage which is one half (V/2) of the maximum voltage V of the pixel data pulse AP. 
     While the FET Q 1  is and the FET Q 2  is ON, the voltage level at the input terminal P 1  of the driving IC  1  is at V/2, namely at about one half of the maximum voltage V of the pixel data pulse AP. The control circuit  3  applies control signals to render ON p-channel MOSFETs QPi, wherein i represents integers from 1 to n, selected from the MOSFETs QP 1  to QPn. At the same time, corresponding n-channel MOSFETs QNi are rendered OFF. Accordingly, the voltage level at each of the respective output terminals PZi rises from zero (first voltage level) to V/2 (second voltage level). Hence the column electrodes to which the data are to be applied are charged through the diode D 1  of the data voltage source circuit  2  and the respective MOSFETs QPi. 
     When the FET Q 1  is rendered ON and the FET Q 2  OFF in response to the control signals from the control circuit  3 , the voltage V/2 stored in the capacitor C 1  is added to the voltage V/2 applied to the input terminal P 1  through the diode D 1 . As a result, the voltage level at the input terminal P 1  becomes the maximum voltage V (third voltage level), thereby raising the voltage level at each of the output terminal PZi to the voltage V. 
     When the FET Q 1  of the data voltage source circuit  2  is rendered OFF and the FET Q 2  ON in response to the control signals from the control circuit  3 , the capacitor C 1  is applied with the predetermined charge from the constant voltage source Vd through the diode D 1  to be charged with the voltage V/2. At that time, the voltage level at the input terminal P 1  is decreased to the voltage V/2, thereby lowering the voltage level at each of the output terminal PZi to V/2. 
     With further operations of the MOSFETs QPi and Qpn, namely, rendering the MOSFETs QPi OFF and MOSFETs QNi ON, the voltage level at each output terminal PZi is further decreased from V/2 to zero. 
     The pixel data pulses AP are thus generated as shown by the waveform in FIG. 3 in accordance with the operations of the FETs Q 1  and Q 2  and MOSFETs QPi and QNi. Since the current (AP) is one half of that of the conventional system, the power consumption is decreased to one half of that of the conventional driving system. In addition, since the peak current flowing through the output terminal PZi is divided into two, unwanted radiation (electromagnetic wave of high frequency as noises) can be restrained. 
     In accordance with the present invention, the driving system is provided with the capacitor for storing voltage, so that the voltage applied through the switching means to the driving IC for generating the pixel data pulses can be selectively changed between the constant voltage supplied from the constant voltage source and the double of the constant voltage by adding the voltage charged in the capacitor. Hence the power for driving the capacitive column electrodes when applying pixel data thereto can be effectively reduced. 
     While the invention has been described in conjunction with preferred specific embodiment thereof, it will be understood that this description is intended to illustrate and not limit the scope of the invention, which is defined by the following claims.