Patent Publication Number: US-7592974-B2

Title: Display device

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique for controlling a light-emission luminance of an image to be displayed on a display device such as a plasma display. 
     2. Description of the Related Art 
     A plasma display has a plurality of discharge cells arranged in a matrix form, and emits light through production of gas discharges in selected discharge cells to generate ultraviolet rays which excite fluorescent materials within the selected discharge cells. An image can be displayed at luminance levels or gradation levels of halftone by controlling the number of occurrences of the discharge per unit time in the discharge cells, i.e., the number of times a discharge sustain pulse is supplied to the discharge cells. According to a sub-field method commonly used for driving a plasma display, one field corresponding to one image is divided into a plurality of sub-fields, and ratios of sustain periods for light emission in the respective sub-fields are set to a power of two. Various combinations of the sub-fields make grayscale display. For example, when ratios of sustain periods for light emission in eight sub-fields are set to 2 0 :2 1 :2 2 :2 3 :2 4 :2 5 :2 6 :2 7 , i.e., 1:2:4:8:16:32:64:128, 256 gradation levels can be implemented by combining the sub-fields. Techniques related to the sub-field method are disclosed, for example, in Japanese Patent Kokai No. 2004-4606. 
     An existing plasma display has an ABL (Automatically Brightness Limit) function which variably sets the number of discharge sustain pulses in each sub-field in accordance with an average peak level (APL) of an input image signal in order to mainly reduce power consumption. The plasma display having the ABL function stores a characteristic curve indicative of the relationship of the number of discharge sustain pulses to an average peak level in a memory, and determines the number of discharge sustain pulses in accordance with a detected average peak level with reference to this characteristic curve. With this ABL function, the plasma display can reduce brightness or luminance over an entire screen by reducing the number of discharge sustain pulses in each sub-field when a high average peak level is detected, and increases brightness or luminance over the entire screen by increasing the number of discharge sustain pulses in each sub-field when a low average peak level is detected. For example, Japanese Patent Kokai No. 2003-29698 discloses an ABL function for a plasma display. The plasma display described in Japanese Patent Kokai No. 2003-29698 stores a plurality of kinds of characteristic curves, for example, a characteristic curve for standard use, a characteristic curve for burn-in prevention, a characteristic curve for power saving, and the like in a memory. A user can arbitrarily select a curve from among these characteristic curves, depending on the situation. 
     As described above, the ABL function mainly aims at power saving for the plasma display, but even if the ABL function is performed using the characteristic curve for power saving, the user cannot realize an actual amount of power consumption, and has no awareness of actively selecting the characteristic curve for power consumption. Also, even the characteristic curve for power saving is selected, the plasma display is not always operating with a small amount of power consumption as expected by the user. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide a display device capable of operating with the amount of power consumption desired by the user, and configured for user-friendly operation. 
     According to one aspect of the present invention, a display device is provided. The display device comprises: a characteristic acquisition unit for obtaining a characteristic indicative of a correspondence relationship between an average peak level and the number of display pulses corresponding to a target power consumption; an average peak level detector for detecting an average peak level of an input image signal; a driving control unit for determining the number of display pulses corresponding to the detected average peak level with reference to the characteristic; a driver for generating a display pulse a number of times equal to the number of display pulses determined by the driving control unit; and a display panel for receiving the display pulses from the driver to emit light at a luminance depending on the number of display pulses. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram schematically showing a configuration of a plasma display which is an embodiment of the present invention; 
         FIG. 2  is a plan view showing a partial region of a display panel; 
         FIG. 3  is a cross-sectional view taken along a V 1 -V 1  line of the display panel shown in  FIG. 2 ; 
         FIG. 4  is a diagram showing an example of a driving sequence for light emission used by a plasma display; 
         FIG. 5  is a timing chart schematically showing waveforms of pulses supplied to the display panel; 
         FIG. 6  is a diagram showing a relationship between gradation levels and sub-fields; 
         FIG. 7  is a diagram showing lookup tables corresponding to the respective sub-fields; 
         FIG. 8  is a graph showing an example of a relationship (ABL characteristic) between an average peak level and the number of discharge sustain pulses; 
         FIG. 9  is a graph showing another example of a relationship (ABL characteristic) between the average peak level and the number of discharge sustain pulses; 
         FIG. 10  is a diagram showing an example of displaying a target power consumption; 
         FIG. 11  is a diagram showing an example of displaying a target power consumption; 
         FIG. 12  is a diagram showing an example of displaying a target power consumption; 
         FIG. 13  is a diagram showing an example of displaying a target power consumption; 
         FIG. 14A  is a diagram showing an example of displaying a power consumption for one month; 
         FIG. 14B  is a diagram showing an example of displaying a power consumption for one year; 
         FIG. 14C  is a diagram showing an example of presenting a simultaneous display of a current power consumption and a power consumption for one month; and 
         FIG. 14D  is a diagram showing an example of presenting a simultaneous display of a current power consumption, a power consumption for one month and the electric rate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following, various embodiments of the present invention will be described with reference to the drawings. 
       FIG. 1  is a block diagram schematically illustrating a configuration of a plasma display (display device) which is an embodiment of the present invention. This plasma display  1  comprises a display panel (plasma display panel)  2 , and an address electrode driver  16  and sustain electrode drivers  17 A,  17 B for driving the display panel  2 . The address electrode driver  16  and sustain electrode drivers  17 A,  17 B make up a driver of the present invention. The plasma display  1  further comprises an A/D converter (ADC)  10 ; a signal processor  11 ; an SF data generator  13 ; a frame memory circuit  14 ; an APL detector (average peak level detector)  20 ; a controller  21 ; and a power supply circuit  28 . 
     The power supply circuit  28  generates operating voltages using externally supplied power and supplies the operating voltages to all processing blocks of the plasma display  1 . The power supply circuit  28  incorporates a power consumption detector  29  for detecting the power consumption of the plasma display  1 . The power consumption detector  29  supplies the detected power consumption to the controller  21 . 
     An input image signal is composed of R (red), G (green), B (blue) analog signals. The A/D converter  10  samples and quantizes the R, G, B analog signals, respectively, to generate 8-bit R, G, B digital image signals which are output to the signal processor  11 . The signal processor  11  performs error diffusion processing and dither processing on the digital image signals from the A/D converter  10  to generate an image signal PD which is supplied to a multiplexer  12 , controller  21 , and APL detector  20 . The signal processor  11  performs the error diffusion processing for diffusing the low two bits of an 8-bit image signal to the high six bits of each surrounding pixel to generate a 6-bit signal. The signal processor  11  further adds an element of a dither matrix to the 6-bit signal resulting from the error diffusion processing, generates a 4-bit image signal PD by bit-shifting the resultant signal, and supplies the 4-bit image signal. 
     The multiplexer  12  superimposes display data from the controller  21  onto the image signal PD supplied from the signal processor  11  to generate a multiplexed image signal PDs which is output to the SF data generator  13 . The SF data generator  13  generates SF data (sub-field data) GD based on the multiplexed image signal PDs according to the sub-field method, and outputs the SF data GD to the frame memory circuit  14 . The frame memory circuit  14  temporarily stores the input SF data in an internal buffer memory (not shown), and reads SF data stored in the buffer memory and supplies the read SF data to the address electrode driver  16 . The address electrode driver  16  generates address pulses based on the SF data input thereto, and supplies the address pulses to address electrodes D 1 -D m  at a predetermined timing. 
     The display panel  2  comprises: a plurality of discharge cells CL arranged in a matrix form; m (m is an integer equal to or larger than two) address electrodes D 1 , . . . , D m  extending in a Y-direction from the address electrode driver  16 ; (n+1) (n is an integer equal to or larger than two) sustain electrodes L 1 , . . . , L n+1  extending in an X-direction perpendicular to the Y-direction from the first sustain electrode driver  17 A; and n sustain electrodes S 1 , . . . S n  extending in a −X direction from the second sustain electrode driver  17 B. The discharge cells CL are formed in respective regions near intersections of the address electrodes D 1 -D m  with the sustain electrodes L 1 -L n+1 , S 1 -S n . 
     A plan view of a partial region of the display panel  2  is shown in  FIG. 2 .  FIG. 3  is a cross-sectional view taken along a V 1 -V 1  line of the display panel  2  shown in  FIG. 2 . Referring to  FIG. 2 , each of the sustain electrodes S j , S j+1  (j is an integer from one to n−1) is composed of a flat bar-shaped bus electrode Sb extending in the −X direction, and a flat bar-shaped transparent electrodes Sa connected to the bus electrode Sb and extending in the Y-direction. The transparent electrode Sa, which is made of a electrically conductive transparent material such as ITO (indium tin oxide), has T-shaped ends. The bus electrode Sb is made of a black or a dark metal film. Each of the sustain electrodes L j , L j+1  is composed of a flat bar-shaped bus electrode Lb extending in the X-direction and made of a black or a dark metal film, and a flat bar-shaped transparent electrodes La connected to the bus electrode Lb and extending in the Y-direction. The transparent electrode La, which is made of a electrically conductive transparent material such as ITO, has a T-shaped leading end opposing one leading end of the transparent electrode Sa across a discharge gap G 1 . As shown in  FIG. 3 , these sustain electrodes S j , S j+1 , L j , L j+1  are formed on the back of a transparent front substrate  42 , and a front dielectric layer  43  is deposited to cover the sustain electrode S j , S j+1 , L j , L j+1 . On the front dielectric layer  43 , light-absorbent dielectric layers (black stripes)  40  containing a black or a dark pigment, extend in the X-direction in strip form. A protection film (not shown) made of MgO (magnesium oxide) is formed on the back of the front dielectric layer  43  and black stripes  40 . 
     On the other hand, on a back substrate  46  opposing the front substrate  42 , flat bar-shaped address electrodes D k−1 , D k , D k+1  (k is an integer from one to m−1) are deposited, extending in the Y-direction. As shown in  FIG. 2 , each of the address electrodes D k−1 , D k , D k+1  is arranged to oppose a pair of transparent electrodes Sa, La in the Z-direction (depth direction of the front substrate  42 ). Referring to  FIG. 3 , a back dielectric layer (protection layer)  45  is formed to cover these address electrodes D k−1 , D k , D k+1  for protection, and partitions (ribs)  41 A,  41 B,  41 C, continuous over an X-Y plane, are disposed on the back dielectric layer  45 . First partitions  41 A are disposed in a stripe form along the X-direction beneath the bus electrodes Lb, respectively, while second partitions  41 B are disposed in a stripe form along the X-direction beneath the bus electrodes Sb, respectively. A dielectric material  44  is stacked between the first partitions  41 A and the black stripes  40 . Third partitions  41 C are disposed to define respective spaces above the address electrodes on the back dielectric layer  45  in the X-direction. As shown in  FIG. 3 , the partitions (ribs)  41 A,  41 B,  41 C form a main discharge space  60  between a pair of transparent electrodes La, Sa and the address electrode D k , and form a sub-discharge space  61  between the leading end of the transparent electrode Sa and the address electrode D k . The main discharge space  60  and the sub-discharge space  61  are in communication with each other through a gap G 2  between the black stripe  40  and the second partition  41 B. Also, the main discharge space  60  and sub-discharge space  61  are filled with a discharge gas made of Xe (xenon) or the like which generates ultraviolet rays through a discharge. 
     An electron emission layer  47  made of a secondary electron emission material having a relatively low work function, for example, MgO (magnesium oxide), BaO (barium oxide) or the like is formed on an inner wall exposed to the sub-discharge space  61 . A fluorescent layer  48  is coated on an inner wall exposed to the main discharge space  60  for emitting red (R), green (G), or blue (B) light when it absorbs ultraviolet rays generated through a gas discharge. The discharge cell CL shown in  FIG. 1  corresponds to an area defined by the first partitions  41 A,  41 A and third partitions  41 C,  41 C, and each discharge cell CL has one main discharge space  60  and one sub-discharge space  61 . The foregoing description has been made of a structure of the display panel  2 . 
     Referring next to  FIG. 1 , the APL detector  20  detects an average peak level (APL) of an image signal transmitted from the signal processor  11  every field period or at intervals of a predetermined number of field periods, and supplies the detected average peak level to the controller  21 . The detected average peak level is used for obtaining characteristic curve and ABL processing, as described later. 
     The controller  21  comprises a driving control unit  22 , a characteristic acquisition unit  24 , a database  25 , a power setting unit  26 , and a power measuring unit  27 , and is connected to an input device  30 , an output interface unit (I/F)  31 , and a wireless interface unit (wireless I/F)  32 . Though not explicitly shown in the figure, the controller  21  can control the A/D converter  10 , signal processor  11 , multiplexer  12 , SF data generator  13 , frame memory circuit  14 , and address electrode driver  16 . 
     The input device  30  comprises a key input device, a pointing device or the like, and can be used by a user to enter data such as numerical values. The input device  30  supplies to the controller  21  an input value from the user or a command corresponding to the input value. The output interface unit  31  is connected to an external device such as a media receiver, a set top box or the like, and has a function of outputting data supplied from the controller  21  to an external device connected thereto. The wireless interface unit  32  has a function of making a short-distance wireless communication with an external device, for example, a remote operation device such as a remote controller, via an infrared link. 
     The driving control unit  22  controls the SF data generator  13 , frame memory circuit  14 , address electrode driver  16 , first sustain electrode driver  17 A, and second sustain electrode driver  17 B in accordance with the image signal PD input from the signal processor  11  and the value of the detected average peak level supplied from the APL detector  20 . The following description will be made of a gradation driving method implemented by the driving control unit  22 . 
       FIG. 4  illustrates an example of a driving sequence for light emission. One field is divided into N (N is an integer equal to or larger than one) sub-fields SF 1  to SF N , each of which has an addressing period Tw and a light emission sustain period Ti. Only the first sub-field SF 1  has a reset period Tr immediately before the addressing period Tw, while only the last sub-field SF N  has an erase period Te immediately after the light emission sustain period Ti. 
       FIG. 5  is a timing chart schematically showing waveforms of pulses supplied to the display panel  2  in the reset period Tr, addressing period Tw, and light emission sustain period Ti. Referring to  FIG. 5 , first, in the reset period Tr of the first sub-field SF 1 , the first sustain electrode driver  17 A supplies reset pulses RP L  of positive polarity to the sustain electrodes L 1 , . . . , L n+1 , respectively, the second sustain electrode driver  17 B supplies reset pulses RP S  of negative polarity to the sustain electrodes S 1 , . . . , S n , respectively, and the address electrode driver  16  supplies reset pulses RP D  of positive polarity to the address electrodes D 1 , . . . , D m , respectively. In this reset period Tr, a gas discharge (reset discharge) occurs in the discharge spaces  60 ,  61  between the transparent electrode Sa and the address electrode D k  Of the display panel  2  shown in  FIG. 3 , causing charges to be generated in the sub-discharge space  61 . The charges move into the main discharge space  60  through the gap G 2 . As a result, a wall charge is accumulated on the surface of the fluorescent layer  48  of the main discharge space  60  in each of all the discharge cells CL. 
     In the next addressing period Tw, an erase addressing discharge is produced selectively in discharge cells CL to be turned off, to extinguish the wall charges. Specifically, as shown in  FIG. 5 , the second sustain electrode driver  17 B sequentially supplies a scanning pulse SP of positive polarity to the address electrodes D 1 , . . . , D m . In this event, the address electrode driver  16  sequentially supplies address pulses DP 1 , . . . , DP n  synchronized to the timing at which each scanning pulse SP is applied. Specifically, the address electrode driver  16  supplies to the address electrodes D 1 -D m  the address pulses DP 1  synchronized to the scanning pulse SP supplied to the sustain electrode S 1  on a first line, and then supplies the address electrodes D 1 -D m  with the address pulses DP 2  synchronized to the scanning pulse SP supplied to the sustain electrode S 2  on a second line. The address electrode driver  16  repeatedly performs the foregoing processing until it supplies the address pulses DP n  synchronized to the scanning pulse SP supplied to the sustain electrode S n  on the last line. In this addressing period Tw, a gas discharge (erase addressing discharge) occurs in the space between the address electrode D k  and the transparent electrode Sa shown in  FIG. 3  in each of those discharge cells CL to be turned on. As a result, the wall charges accumulated in the discharge cells CL are extinguished. 
     In the next light emission sustain period Ti, the first sustain electrode driver  17 A repeatedly supplies discharge sustain pulses IP L  of negative polarity to the sustain electrodes L 1 , . . . , L n+1 , respectively, the number of times assigned thereto, while the second sustain electrode driver  17 B repeatedly supplies discharge sustain pulses IPS of negative polarity to the sustain electrodes S 1 , . . . , S n , respectively, the number of times assigned thereto. The amplitude of the last discharge sustain pulses IP E  supplied to the sustain electrodes S 1 -S n  is set to be slightly larger than that of the previous discharge sustain pulse IP S . As a result, in the discharge cells CL in which the wall charge is formed, a gas discharge (sustain discharge) occurs near a pair of transparent electrodes Sa, La in the main discharge space  60  shown in  FIG. 3 . The fluorescent layer  48  absorbs ultraviolet rays generated through this discharge, and excites to emit light in one of R, G, B. 
     In the addressing period Tw in the next sub-field SF 2 , as described above, the erase addressing discharge is produced in the discharge cells CL to be turned off, to extinguish the wall charges. In the next light emission sustain period Ti, the sustain electrode drivers  17 A,  17 B repeatedly supply the discharge sustain pulses IP L , IP S  as described above numbers of times assigned thereto. Subsequently, the processing is performed in the sub-fields SF 3 -SF N  as shown in  FIG. 4 , and in the last erase period Te, the wall charges are extinguished by simultaneously producing erase discharges in all the discharge cells CL. 
       FIG. 6  illustrates a relationship between gradation levels of image data PD S  and the sub-fields SF 1 -SF 15 . The SF data generator  13  converts 4-bits of image data PDs supplied from the multiplexer  12  to 15-bits of SF data GD in accordance with a conversion table shown in  FIG. 6 , and outputs the SF data GD to the frame memory circuit  14 . Specifically, when the gradation level of the input data PDs is “0,” the least significant bit (LSB) of the SF data GD is set to “1,” and each of the remaining bits is set to “0.” When the gradation level of the input data PDs is “k” (k is an integer from one to 14), a (k+1)-th bit of the SF data GD is set to “1,” and all the remaining bits are set to “0.” When the gradation level of the input data PDs is “15,” all the bits from the least significant bit to the most significant bit (MSB) of the SF data are set to “0.” 
     The address electrode driver  16  receives the SF data GD from the frame memory  14 , samples and latches the SF data GD for one horizontal line, then generates an address pulse corresponding to the value of each bit of the image data GD, and supplies the address pulses to the address electrodes D 1 -D m . Referring to  FIG. 6 , when the LSB of the SF data GD has the value “1,” an erase addressing discharge occurs to extinguish the wall charges in those discharge cells CL to be turned off, in the addressing period Tw of the first sub-field SF 1 . When a k-th bit (k is an integer from one to 14) of the SF data GD has the value “1,” a sustain discharge occurs in those discharge cells CL which have the wall charges, in each light emission sustain period Ti of the first to (k−1)-th sub-fields SF 1 -SF k−1 , and an erase addressing discharge occurs in the addressing period Tw of the k-th sub-field SF k . When all the bits from the LSB to the MSB of the SF data GD have the value “0,” a sustain discharge occurs in those discharge cells CL which have the wall charges, in each light emission sustain period Ti of all the sub-fields SF 1 -SF 15 , and no erase addressing discharge occurs in the addressing period Tw. 
     The foregoing driving method is different from the driving method which sets ratios (weights) of light emission sustain periods assigned to each sub-field to a power of two, as described in the aforementioned Japanese Patent Kokai No. 2004-4606. The driving method of this embodiment employs a selective erase addressing method which only requires one time for each of the reset period Tr and erase period Te in each of the discharge cells CL in each field period (display period). Therefore, after the wall charges have been accumulated in all the discharge cells CL of the display panel  2  at the beginning of each field, the discharge cells CL will continue to emit light until the wall charges are erased by the erase addressing discharge, thereby advantageously preventing a pseudo contour when a moving image is displayed. 
     The driving control unit  22  has the characteristic setting unit  23  which stores the characteristic representing a correspondence relationship between the average peak level (APL) and the number of occurrences of light emission (the number of times of supplying a discharge sustain pulse), i.e., a lookup table (characteristic table). The driving control unit  22  determines the number of discharge sustain pulses for each sub-field in accordance with the detected average peak level supplied from the APL detector  20  with reference to the lookup table set in the characteristic setting unit  23 , and assigns the determined numbers of discharge sustain pulses to the sub-fields SF 1 -SF N  ( FIG. 4 ), respectively. The numbers of discharge sustain pulses assigned to the respective sub-fields SF 1 -SF N  are stored in a register (not shown). The characteristic setting unit  23  stores lookup tables  50   1 , . . . ,  50   N  corresponding to the respective sub-fields SF 1 , . . . , SF N , as show in  FIG. 7 , so that the driving control unit  22  references a lookup table  50   i  corresponding to a sub-field SF i  (i is an integer from one to N) when determining the number of discharge sustain pulses to be assigned to the sub-field SF i . 
       FIGS. 8 and 9  show examples of the relationship (ABL characteristic) between the average peak level and the number of discharge sustain pulses in the lookup table as described above. In  FIGS. 8 and 9 , the horizontal axis of the graph corresponds to the average peak level (APL), while the left vertical axis of the graph corresponds to the number of discharge sustain pulses. A curve Pt is an ABL characteristic curve which represents the relationship between the APL and the number of discharge sustain pulses. It should be noted that the values of average peak levels in the graphs are normalized to have the value of “100” when all the discharge cells CL emit light at the highest gradation level, i.e., when the entire screen of the display panel  2  emits light at the highest peak luminance. Also, the right vertical axis of the graph corresponds to the power consumption (in Watts) of the plasma display  1 . A curve Ct is a power characteristic curve representing a relationship between the APL and the power consumption. 
       FIG. 8  illustrates an ABL characteristic when a target power consumption is set to 300 Watts (by default). The power characteristic curve Ct monotonously increases from an initial value Cmin to 300 Watts in an initial region of the APL value from zero to S 0  (=approximately 13), and levels at approximately 300 Watts in a region of the APL value from S 0  to 100. The ABL characteristic curve Pt takes a substantially constant upper limit value Pmax in a region of the APL value from zero to S 0 , and monotonously decreases in a region of the APL value from S 0  to 100. In the initial region, the number of discharge sustain pulses is fixed at the upper limit value Pmax, while the power characteristic curve Ct monotonously increases. On the other hand, in the region of the APL value from S 0  to 100, the power consumption (target power consumption) is fixed at 300 Watts, while the ABL characteristic curve Pt monotonously decreases under such limitations. The ABL characteristic curve in the default state has been previously measured and stored in a ROM or the like. 
       FIG. 9  illustrates an ABL characteristic when the target power consumption is set to 200 Watt. Referring to  FIG. 9 , in the region of the APL value from 0 to S 0 , the number of discharge sustain pulses of the ABL characteristic curve is fixed at the upper limit value Pmax, while the power characteristic curve Ct monotonously increases from the initial value Cmin to 200 Watts. In the region of the APL value from S 0  to 100, the power consumption (target power consumption) of the power characteristic curve Ct is fixed at 200 Watts, while the ABL characteristic curve Pt monotonously decreases under such limitations. 
     The database  25  stores lookup tables provided for each power consumption, and the characteristic acquisition unit  24  has a function of retrieving lookup tables  50   1 , . . . ,  50   N  to be set in the characteristic setting unit  23  in accordance with the target power consumption specified by the power setting unit  26 . The database  25  can store, for example, lookup tables (ABL characteristics) corresponding to the power consumptions of 300 Watts, 200 Watts, and 100 Watts, respectively. When no lookup table corresponding to the target power consumption is stored in the database  25 , the characteristic acquisition unit  24  also has a function of calculating a lookup table corresponding to the target power consumption using lookup tables stored in the database  25  through interpolation. For example, when the target power consumption of 250 Watts is specified by the power setting unit  26 , the characteristic acquisition unit  24  can interpolate an ABL characteristic curve Pt for 250 Watts using the ABL characteristic curve Pt for 300 Watts shown in  FIG. 8  and the ABL characteristic curve Pt for 200 Watts shown in  FIG. 9 . Alternatively, the characteristic acquisition unit  24  can calculate the ABL characteristic curve Pt based on a basic function f(T;x) of the ABL characteristic which has been previously prepared and stored. The basic function f(T;x) relates to the target power consumption T and APL value x, and the functional shape of f(T;x) is uniquely determined by giving the target power consumption T. 
     As described above, the characteristic acquisition unit  24  obtains a lookup table, i.e., the ABL characteristic curve Pt in accordance with the target power consumption specified by the power setting unit  26 . For setting this ABL characteristic curve Pt in the characteristic setting unit  23 , the driving control unit  22  can assign the number of discharge sustain pulses for each of the sub-fields SF 1 -SF N  to adjust the power consumption of the plasma display  1  to the target power consumption. Since the lookup tables are updated each time the target power consumption is specified, the power consumption of the plasma display  1  can be meticulously controlled in accordance with the situation. 
     Next, the user can directly enter or specify the value of target power consumption, for example, 300, 200, 180 or the like by operating on the input device  30  such as an operation panel provided on the plasma display  1 . The input device  30  supplies these input values to the power setting unit  26  which sets the input value from the input device  30  as the target power consumption. Alternatively, the user can enter a value corresponding to the target power consumption instead of directly entering the value of the target power consumption by operating the input device  30 . For example, when the user depresses a button corresponding to the target power consumption of 300 Watts from among a plurality of buttons corresponding to 300 Watts, 250 Watts, and 180 Watts, respectively, the input device  30  supplies to the power setting unit  26  a command corresponding to the depressed button, so that the power setting unit  26  sets the target power consumption in accordance with the command communicated from the input device  30 . 
     Further, the user can enter a rate of change in the power consumption of the plasma display  1  by operating the input device  30 , for example, 50%, 40%, 33% or the like. The input device  30  supplies to the power setting unit  26  the value of the rate of change, or a command corresponding to the rate of change, and the power setting unit  26  calculates the target power consumption in accordance with the specified rate of change, and sets the calculated target power consumption. For example, when the rate of change (reduction rate) is specified to be 33%, the target power consumption of 33% is subtracted from the currently set target power consumption, and the resulting amount is set to a new target power consumption. The power supply circuit  28  comprises the power consumption detector  29  for detecting the amount of power consumed at each of the processing blocks in the plasma display  1 , and supplies detected data to the power measuring unit  27 . The power measuring unit  27  calculates the overall power consumption of the plasma display  1  based on the detected data supplied from the power consumption detector  29 , and supplies the overall power consumption to the power setting unit  26 . When the foregoing rate of change is specified, the power setting unit  26  can also subtract the rate of change in the power consumption from the power consumption of the plasma display  1  to set the resulting amount to the target power consumption. 
     The value of the target power consumption set by the power setting unit  26  can be displayed on the display panel  2  or on a separate display unit independent of the display panel. Specifically, the controller  21  outputs the value of the target power consumption set by the power setting unit  26 , included in display data DD, to the multiplexer  12 . The multiplexer  12  superimposes the display data DD onto an image signal PD input from the signal processor  11 , thus displaying the value of the target power consumption on the display panel  2 .  FIG. 10A  is a diagram showing an exemplary display of the value of the target power consumption. As shown in  FIG. 10A , the target power consumption “200 W” can be displayed in a lower region of the display panel  2  on the front surface of the display panel  1 . 
     The plasma display  1  also has an auxiliary display unit  51  disposed in the housing  3 , and can display the target power consumption on this auxiliary display unit  51 . The controller  21  outputs the value of the target power consumption set by the power setting unit  26  to the auxiliary display unit  51  through the output interface unit  31 , and can display the target power consumption “200 W” on the auxiliary display unit  51 , as shown in  FIG. 10B . 
     The controller  21  can further output the value of the target power consumption to an external device through the output interface unit  31  or wireless interface unit  32  to display the target power consumption on a display unit provided in the external device. For example, the target power consumption “200 W” can be displayed on a display unit  53  provided in a media receiver  52 , as shown in  FIG. 11 , the value of the target power consumption can be wirelessly transmitted to a remote controller  54  to display the target power consumption “200 W” on a display unit  55  of the remote controller  54 , as shown in  FIG. 12 , or the target power consumption “200 W” can be displayed on a display unit  57  provided in a power supply plug  56  connected to the power supply circuit  28  ( FIG. 1 ), as shown in  FIG. 13 . 
     The user can switch operating states of the display panel  2  and the display units  51 ,  53 ,  55 ,  57  from a target power consumption display state to a non-display state, and vice versa. 
     Alternatively, instead of displaying the target power consumption on the display panel  2  and display units  51 ,  53 ,  55 ,  57 , a message, a character string, or a pattern may be displayed to permit the user to recognize the target power consumption. 
     The power measuring unit  27  ( FIG. 1 ) has a function of calculating the current power consumption of the plasma display  1  based on detected data supplied from the power consumption detector  29 , and measuring the power consumption of the plasma display in units of predetermined periods, such as years, months, or days. Here, the power measuring unit  27  also measures the power consumption during a standby state (standby power) when the main power supply of the plasma display  1  is shut off. The power measuring unit  27  further has a function of calculating the electric rate or electricity charges corresponding to the measured power consumption and storing the calculated electric rate in a memory (not shown). 
     The controller  21  can display the power consumption measured on a periodic basis, and the electric rate corresponding thereto on the display panel  2  and display units  51 ,  52 ,  53 ,  55 ,  57 . For example, the controller  21  displays the power consumption “50 hWh/month” for one month as shown in  FIG. 14A ; the power consumption “400 kWh/year” for one year as shown in  FIG. 14B ; the current power consumption “200 W” in parallel with the power consumption “50 kWh/month” for one month as shown in  FIG. 14C ; or the current power consumption “200 W” in parallel with the power consumption “50 kWh/month” for one month and the corresponding electric rate “1,000 yens/month.” 
     The unit price used by the power measuring unit  27  for calculating the electric rate (for example, the electric rate per 1 kwh) can be set by the user. Also, the user can reset the power consumption measured on a periodic basis and can reset the electric rates to their initial values. 
     As described above, since the target power consumption as well as the power consumption measured on a periodic basis and the electric rate are displayed on the display panel  2  and the like, the user can readily view the target power consumption set by operating the input device  30 , and can therefore know the power consumption of the plasma display  1  in a simple manner. It is therefore possible to provide the plasma display  1  which can permit the user to realize a reduction in power consumption and can support the power saving in consideration of the earth environment. 
     It is understood that the foregoing description and accompanying drawings set forth the preferred embodiments of the invention at the present time. Various modifications, additions and alternatives will, of course, become apparent to those skilled in the art in light of the foregoing teachings without departing from the spirit and scope of the disclosed invention. Thus, it should be appreciated that the invention is not limited to the disclosed embodiments but may be practiced within the full scope of the appended claims. 
     This application is based on a Japanese Patent Application No. 2004-138403 which is hereby incorporated by reference.