Abstract:
A display drive device includes a low-voltage circuit section driven by a first power supply potential and a high-voltage circuit section driven by a second power supply potential higher than the first power supply potential. The display drive device further includes a voltage supply circuit for supplying a third power supply potential different from the first and second power supply potentials, a common power supply line for connecting the third power supply potential to each of a plurality of output terminals, an output selection switch circuit for temporarily switching between display data output via the high-voltage circuit section to each output terminal, and the common power supply line, during a predetermined period, and a display data determining circuit for generating a control signal for controlling the output selection switch circuit. Thereby, the common power supply line is temporarily selected and controlled without signal collision when display data is switched.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a display drive device for driving a display panel. 
     2. Description of the Related Art 
     In recent years, plasma display panels (PDPs) that have a thin thickness, a large screen, and high definition, have attracted attention. The PDP comprises a plurality of discharge cells (pixels) arranged in a matrix. An image is displayed on the PDP by utilizing light emission when discharge occurs in the discharge cells. 
     A typical AC PDP has a plurality of display electrodes arranged in parallel and a plurality of data electrodes arranged orthogonal to these display electrodes. A display drive device drives these data electrodes, and therefore, can be considered to drive capacitive load. 
     As the screen size, definition and luminance of PDPs have been more and more increased, display drive devices for driving the PDPs increasingly require a larger number of outputs and a higher voltage. Therefore, it is important to suppress power consumption and heat generation when the data electrode is driven. 
     When different potentials are applied to two data electrodes, a space between the electrodes functions as a capacitor. In other words, capacitive load is generated. When the capacitive load is driven, a large amount of power is consumed. As a conventional technique of reducing power consumption, the followings are known. 
     U.S. Pat. No. 7,116,137 discloses a display drive device that converts display data into a predetermined voltage level and outputs the resultant data to data electrodes. In the display drive device, a common floating potential line in a floating state is provided that is normally connected via selection switches to all output terminals in a wired OR manner. When a change in data level is detected on an output terminal at a timing of switching display data (i.e., between before and after display data is switched), the output terminal is controlled so that the output terminal temporarily goes to a high impedance (Hi-Z) at a predetermined timing (within a period when display data is switched and panel display is not performed). At the same time, the corresponding selection switch is controlled so that the output terminal is connected via the selection switch to the wired OR-connected floating potential line. By this control, display output is temporarily interrupted at output terminals at which data is changed by switching display data, so that all the output terminals are connected to the common floating potential line. In this case, the output terminals having a change in level are short-circuited, so that capacitance charges accumulated by displaying are transferred between terminals that have immediately previously output an H (=High) level and terminals that have immediately previously output an L (=Low) level. Therefore, the common floating potential line in the floating state is settled at a potential that is determined, depending on the number of H-level output terminals and the number of L-level output terminals. For example, when, of the terminals having a change in data, the number of H-output terminals is the same as the number of L-output terminals, the potential of the common floating potential line is ideally VDD/2 (VDD is the H-level potential of a display output). Therefore, the next drive operation only needs to be performed from VDD/2 to GND or VDD, whereby drive power can be reduced. Thus, this is a two-step drive technique. 
     U.S. Pat. No. 7,319,347 discloses another two-step drive technique in which panel electrodes and a capacitor having a load capacitance sufficiently larger than that accumulated between each panel electrode are connected to a common line corresponding to the floating potential line of U.S. Pat. No. 7,116,137 described above. The capacitance potential of the capacitor is previously set to be VDD/2. Charge and discharge are performed between the capacitor capacitance and an output terminal that has a change in data level between before and after display data is switched, so as to transfer accumulated charges so that the output terminal has the potential VDD/2, which is advantageous to the next drive operation. 
     SUMMARY OF THE INVENTION 
     In the display drive device of U.S. Pat. No. 7,116,137 described above, the common floating potential line varies for each piece of display data. For example, when display data is switched, then if all output terminals go from the H level to the L level, the advantageous effect is not obtained for such display data. Thus, there is a pattern dependence, so that power consumption cannot be sufficiently reduced. Also, a tri-state output and the common floating potential line are connected in a wired OR manner. Therefore, if the timing of the selection switch varies depending on the wiring path or the like, both the tri-state output and the common floating potential line may be selected, resulting in signal collision. 
     If signal collision occurs, any display data output has an influence on the common floating potential line, the potential of the common floating potential line is likely to change, i.e., vary for each piece of display data. 
     In the display drive device of U.S. Pat. No. 7,319,347 described above, the potential VDD/2 is initially applied to the capacitor by any means, and thereafter, electronic charges are not additionally supplied to the capacitor from the outside, for example. If electronic charges are even once lost during an operation when a change occurs in a characteristic (e.g., small leakage occurs, power supply leakage occurs, etc.), the output terminal cannot be restored to the original potential VDD/2, for example. 
     To solve these problems, a display drive device according to the present invention includes a low-voltage circuit section driven by a first power supply potential, a high-voltage circuit section driven by a second power supply potential higher than the first power supply potential, a voltage supply circuit for supplying a third power supply potential higher than or equal to the first power supply potential and different from the second power supply potential, a common power supply line for connecting the third power supply potential to each of a plurality of output terminals, an output selection switch circuit for temporarily switching between display data output via the high-voltage circuit section to each output terminal, and the common power supply line, during a predetermined period, and a display data determining circuit for generating a control signal for controlling the output selection switch circuit. 
     The display data determining circuit has a function of, when one piece of display data is switched to another piece of display data, determining a change in level of display data in the same column of a display panel from both the pieces of display data, a function of determining how electric charges accumulated between each output terminal due to a display operation are changed due to the next display operation, and a function of generating a control signal to be supplied to the output selection switch circuit based on these determination results. When it is determined in the display data determining circuit that there is a change in display data level between before and after display data is switched, display data output to each output terminal having a change and the common power supply line are temporarily switched for a predetermined period, based on the control signal of the display data determining circuit, so that the display data is caused to be temporarily at the third power supply potential. Thereby, there is not pattern dependence of display data, and in addition, the voltage of the voltage supply circuit is invariably supplied to the common power supply line, resulting in an invariably stable voltage. Therefore, power consumption of a display drive operation can be optimally reduced. Also, heat generation by a display drive operation can be reduced in an amount corresponding to the reduction of power consumption. 
     According to the present invention, the potential of an output terminal having a change in data output between before and after display data is switched is forcedly caused to go to the third power supply potential before driving data to be next displayed. Therefore, a change in potential of the output terminal during a drive operation can be reduced, thereby making it possible to suppress power consumption and heat generation of the display drive device. Also, there is not data dependence of display data, and in addition, the common power supply line can be invariably stably maintained at the third power supply potential. 
     Moreover, by performing a drive operation in a stepwise manner, a peak current during output transition of display data can be reduced, so that EMI occurring in the display drive device can also be reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary configuration of a display drive device according to the present invention. 
         FIG. 2  is a diagram showing another exemplary configuration of the display drive device of the present invention. 
         FIG. 3  is a diagram showing still another exemplary configuration of the display drive device of the present invention. 
         FIG. 4  is a timing chart showing an operation of the display drive device of  FIG. 3 . 
         FIG. 5  is a diagram showing still another exemplary configuration of the display drive device of the present invention. 
         FIG. 6  is a timing chart showing an operation of the display drive device of  FIG. 5 . 
         FIG. 7  is a diagram showing still another exemplary configuration of the display drive device of the present invention. 
         FIG. 8  is a circuit diagram showing a specific example of an output selection switch circuit of  FIG. 7 . 
         FIG. 9  is a diagram showing still another exemplary configuration of the display drive device of the present invention. 
         FIG. 10  is a circuit diagram showing a specific example of a signal voltage converting section including an output selection switch circuit of  FIG. 9 . 
         FIG. 11  is a diagram showing still another exemplary configuration of the display drive device of the present invention. 
         FIG. 12  is a timing chart showing an operation of the display drive device of  FIG. 11 . 
         FIG. 13  is a diagram showing still another exemplary configuration of the display drive device of the present invention. 
         FIG. 14  is a timing chart showing an operation of the display drive device of  FIG. 13 . 
         FIG. 15  is a plan view of a module package including the display drive device of the present invention. 
         FIG. 16  is a plan view of a panel module employing the module package of  FIG. 15 . 
         FIG. 17  is a circuit block diagram showing a television set employing the panel module of  FIG. 16 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
       FIG. 1  shows an exemplary configuration of a display drive device according to the present invention. In  FIG. 1 , the display drive device comprises a low-voltage circuit section  1 , a high-voltage circuit section  2 , a voltage supply circuit  3 , a common power supply line  4 , output terminals  5 , display data determining circuits  10 , signal voltage converting sections  11 , and output selection switch circuits  20  each including a selector  21  having two inputs and one output. For example, a first power supply potential for driving the low-voltage circuit section  1  is 3.3 to 5 V, a second power supply potential for driving the high-voltage circuit section  2  is about 80 V, a third power supply potential that the voltage supply circuit  3  supplies to the common power supply line  4  is about 40 V. 
     The output selection switch circuit  20  forcedly causes the potential of an output terminal  5  to be equal to the third power supply potential if the data output of the output terminal  5  changes between before and after display data is switched, thereby making it possible to reduce a change in potential of the output terminal  5  during a drive operation. In addition, since the third power supply potential is applied from the voltage supply circuit  3  to the common power supply line  4 , the potential of the common power supply line  4  is invariably stable, so that a spike does not occur during a switching operation. 
     With the configuration of  FIG. 1 , signal collision can be advantageously avoided by using the two-input one-output selector  21 . In addition, since the Hi-Z state does not exist inside the display drive device, the display drive device is not likely to suffer from an influence of noise. Moreover, even when there are variations in switch timing among the output terminals  5 , other terminals are not affected, since the power supply signal has a higher intensity. 
     Note that the voltage supply circuit  3  is desirably a charge pump circuit, which does not consume power very much. The display data determining circuit  10  preferably compares pieces of data held by two latches. 
     Also, as the voltage supply circuit  3 , a circuit equipped with a smoothing capacitor is desirably provided so as to supply a stabler potential. 
       FIG. 2  shows another exemplary configuration of the display drive device of the present invention. In  FIG. 2 , an output connection/disconnection switch  22  for selecting an open or closed state is provided between the output of a selector  21  having two inputs and one output included in an output selection switch circuit  20 , and an output terminal  5 . 
     When the output selection switch circuit  20  is used to switch a path from display data to the power supply potential of the voltage supply circuit  3 , the output connection/disconnection switch  22  is initially opened, then the two-input one-output selector  21  is switched to the power supply potential of the voltage supply circuit  3 , and then after a lapse of a time enough for all the output terminals  5  to go to the stationary state, the output connection/disconnection switch  22  is closed. Conversely, when a path is switched from the power supply potential of the voltage supply circuit  3  to display data, the output connection/disconnection switch  22  is initially opened, then the two-input one-output selector  21  is switched to the display data, and after a lapse of a time enough for all the output terminals  5  to go to the stationary state, the output connection/disconnection switch  22  is closed. 
     As described above, with the configuration of  FIG. 2 , the two-input one-output selector  21  and the output connection/disconnection switch  22  are controlled in accordance with a switching sequence, thereby making it possible to reliably eliminate signal collision at each output terminal  5  and an influence of timing variations. 
       FIG. 3  shows still another exemplary configuration of the display drive device of the present invention.  FIG. 4  shows an operation of the display drive device of  FIG. 3 . Each output selection switch circuit  20  of  FIG. 3  comprises a display data output selection switch  23  and a potential output selection switch  24 . 
     When display data is switched to the power supply potential of a voltage supply circuit  3  in the output selection switch circuit  20 , a display data output selection switch  23  is initially opened while a potential output selection switch  24  is in the opened state (default). As a result, the display data output selection switch  23  and the potential output selection switch  24  are both opened. After a lapse of a time enough for all the output terminals  5  to go to the stationary state, the potential output selection switch  24  is closed. Note that the potential output selection switch  24  is opened at a predetermined time. 
     Conversely, when the power supply potential of the voltage supply circuit  3  is switched to display data, the potential output selection switch  24  is initially opened while the display data output selection switch  23  is in the opened state. As a result, the display data output selection switch  23  and the potential output selection switch  24  are both opened. After a lapse of a time enough for all the output terminals  5  to go to the stationary state, the display data output selection switch  23  is closed. 
     With the configuration of  FIG. 3 , by providing a period when both the switches  23  and  24  are simultaneously OFF, signal collision at the output terminal  5  can be prevented, and an influence of variations in operation timing of the selection switch can be eliminated. 
       FIG. 5  shows still another exemplary configuration of the display drive device of the present invention.  FIG. 6  shows an operation of the display drive device of  FIG. 5 . The configuration of  FIG. 5  is obtained by adding an output connection/disconnection switch  22  to the configuration of  FIG. 3 . Specifically, the output connection/disconnection switch  22  is provided between a wiring branching point of the display data output selection switch  23  and the potential output selection switch  24 , and the output terminal  5 . 
     With the configuration of  FIG. 5 , when the output connection/disconnection switch  22  is opened, a transient state occurring when the display data output selection switch  23  and the potential output selection switch  24  are switched can be prevented from propagating to the output terminal  5 . Therefore, the output connection/disconnection switch  22  may be closed after the output terminal  5  goes to the stationary state. In this case, selection can be switched irrespective of timings of switching the display data output selection switch  23  and the potential output selection switch  24 . In other words, if the output connection/disconnection switch  22  is in the OFF period, the timings of the display data output selection switch  23  and the potential output selection switch  24  may differ from each other to some extent. By performing a control in accordance with such a switching sequence, an influence of signal collision on the output terminal  5  and an influence of variations in timing of the display data output selection switch  23  or the potential output selection switch  24  at the output terminals  5  can be reliably eliminated. 
       FIG. 7  shows still another exemplary configuration of the display drive device of the present invention.  FIG. 8  shows a specific example of an output selection switch circuit  20  of  FIG. 7 . The output selection switch circuit  20  of  FIG. 7  comprises a display data output H selection switch  25 , a display data output L selection switch  26 , and a potential output selection switch  27 . As shown in  FIG. 8 , for example, the display data output H selection switch  25  can be implemented using a P-channel MOSFET, the display data output L selection switch  26  can be implemented using an N-channel MOSFET, and the potential output selection switch  27  can be implemented using a P-channel MOSFET. 
     The output selection switch circuit  20  of  FIG. 7  is configured to select one of the three switches  25  to  27 , and the output terminal  5  has a four-valued (H, L, a voltage supply circuit potential, and Hi-Z) output. Note that a potential output selection signal and the like in  FIG. 8  are generated based on a horizontal synchronization (HSYNC) signal or the like by the display data determining circuit  10 . 
     An exemplary switching sequence in  FIG. 7  will be described as follows. When display data is switched to the power supply potential of the voltage supply circuit  3 , the display data output H selection switch  25  and the display data output L selection switch  26  are both initially opened while the potential output selection switch  27  is in the opened state. Here, the level (H or L) of display data is not considered. Next, the potential output selection switch  27  is closed. Conversely, when the power supply potential of the voltage supply circuit  3  is switched to display data, the potential output selection switch  27  is initially opened while the display data output H selection switch  25  and the display data output L selection switch  26  are both in the opened state. Next, the display data output H selection switch  25  and the display data output L selection switch  26  are both released from the forcedly opened state, and are opened or closed, depending on the level (H or L) of display data. 
       FIG. 9  shows still another exemplary configuration of the display drive device of the present invention.  FIG. 10  shows a specific example of a signal voltage converting section  11  including an output selection switch circuit  20  of  FIG. 9 . In  FIG. 10 ,  28  indicates a level shifter. In  FIGS. 9 and 10 , the output selection switch circuit  20  is provided inside the signal voltage converting section  11 . Thereby, layout efficiency can be improved as compared to  FIGS. 1 ,  2 ,  3  and  5 , so that the size of a chip can be suppressed. 
       FIG. 11  shows still another exemplary configuration of the display drive device of the present invention.  FIG. 12  shows an operation of the display drive device of  FIG. 11 . In  FIG. 11 , the display drive device comprises an output selection switch circuit  20  having any of the configurations described above, a voltage supply connection/disconnection switch control circuit  30 , a signal voltage converting section  31 , and a voltage supply connection/disconnection switch  40 . 
     With the configuration of  FIG. 11 , the voltage supply connection/disconnection switch  40  is provided between a voltage supply circuit  3  and a common power supply line  4 . The voltage supply connection/disconnection switch  40  is controlled at the following timings. The voltage supply connection/disconnection switch  40  is closed slightly before a display switching timing, display is switched, step drive is finished, and the voltage supply connection/disconnection switch  40  is opened for a display period or a period continuing slightly before the next display switching timing. The third power supply potential does not need to be invariably applied to the common power supply line  4  and the common power supply line  4  may be driven only for a required period. Therefore, power consumption in the voltage supply circuit  3  can be further reduced. 
     Note that the voltage supply connection/disconnection switch  40  may be a switch that can electrically interrupt a path and therefore may be controlled into a high impedance state. 
       FIG. 13  shows still another exemplary configuration of the display drive device of the present invention.  FIG. 14  shows an operation of the display drive device of  FIG. 13 . As shown in  FIGS. 13 and 14 , the power supply potential of the voltage supply circuit  3  may be the same as the first power supply potential that is used to drive the low-voltage circuit section  1 . Since the common power supply line  4  does not have an optimal potential, the efficiency decreases. However, an existing power supply can be advantageously employed. In addition, although a drive operation is only divided and performed in a stepwise manner, drive power can be expected to be reduced as compared to the case of non-step driving. 
     Note that a voltage supply circuit  3  equipped with a connection/disconnection switch may be added to  FIG. 13  and connected with the low-voltage power supply of  FIG. 13  in a wired OR manner. When not required, the common power supply line  4  may be caused to go to the floating potential. This is because, the common power supply line  4  is not perfectly interrupted, and when not required, 3.3 V is supplied to the common power supply line  4 , so that high impedance is avoided in the LSI, whereby noise on the common power supply line  4  is reduced, for example. 
       FIG. 15  is a plan view of a module package including the display drive device of the present invention. In  FIG. 15 , the module package  100  comprises a display input signal joint terminal portion  101 , an FPC  102 , a display output joint terminal portion  103 , and a data driver  104  (the display drive device of the present invention). 
       FIG. 16  is a plan view of a panel module employing the module package  100  of  FIG. 15 . In  FIG. 16 , the panel module  110  comprises a PDP panel  111 , a display input common circuit board  112 , and a signal processing control circuit  113 . One module package  100  is provided for each of a plurality of division columns of the PDP panel  111 . Reductions in power consumption of the data drivers  104  significantly contribute to a reduction in power consumption of the whole panel module  110 . 
       FIG. 17  is a circuit block diagram showing a television set employing the panel module  110  of  FIG. 16 . In  FIG. 17 , the television set  120  comprises a panel block  121 . 
     As described above, the present invention can suppress power consumption and heat generation and therefore is useful as a driver for a display panel having capacitive load, such as a PDP, an EL panel or the like.