This application claims the benefit of Korean Patent Application No. 10-2007-0102169 filed on Oct. 10, 2008, which is incorporated herein by reference for all purposes as if fully set forth herein.
1. Field
An exemplary embodiment of the invention relates to a plasma display apparatus and a method of driving the same.
2. Description of the Background Art
A plasma display apparatus includes a plasma display panel and a driver for driving the plasma display panel.
The plasma display panel has the structure in which barrier ribs formed between a front panel and a rear panel forms unit discharge cell or a plurality of discharge cells. Each discharge cell is filled with an inert gas containing a main discharge gas such as neon (Ne), helium (He) or a mixture of Ne and He, and a small amount of xenon (Xe). The plurality of discharge cells form one pixel. For example, a red discharge cell, a green discharge cell, and a blue discharge cell form one pixel. When the plasma display panel is discharged by applying a high frequency voltage to the discharge cell, the inert gas generates vacuum ultraviolet rays, which thereby cause phosphors formed between the barrier ribs to emit light, thus displaying an image. Since the plasma display apparatus can be manufactured to be thin and light, it has attracted attention as a next generation display device.
An exemplary embodiment of the invention provides a plasma display apparatus and a method of driving the same capable of improving the discharge efficiency by adjusting a maintenance period of a reset signal supplied to a plasma display panel depending on a gray level of an image.
Additional features and advantages of the exemplary embodiments of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the exemplary embodiments of the invention. The objectives and other advantages of the exemplary embodiments of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
In one aspect, a plasma display apparatus driven in a frame comprised of a plurality of subfields comprises a plasma display panel including a scan electrode and a sustain electrode, and a driver supplying a first signal, that rises from, a first voltage to a second voltage, is maintained at the second voltage during a predetermined period of time, and falls from the second voltage to a third voltage smaller than the first voltage with a slope, to the scan electrode, wherein the predetermined period of time is set at different values in at least two subfields.
In another aspect, a method of driving a plasma display apparatus, including a scan electrode and a sustain electrode, driven in a frame comprised of a plurality of subfields comprises supplying a first signal, that rises from a first voltage to a second voltage, is maintained at the second voltage during a predetermined period of time, and falls from the second voltage to a third voltage smaller than the first voltage with a slope, to the scan electrode, and setting the predetermined period of time at different values in at least two subfields.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of embodiments of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention. In the drawings:
Preferred exemplary embodiments of the invention will be described in a more detailed manner with reference to the drawings.
As shown in
The plasma display panel 100 includes a front panel (not shown) and a rear panel (not shown) which coalesce with each other at a given distance therebetween. The plasma display panel 100 includes scan electrodes Y1 to Yn, sustain electrodes Z1 to Zn, and address electrodes X1 to Ym.
The scan driver 200 supplies first falling signals to the scan electrodes Y1 to Yn during a pre-reset period prior to a reset period to thereby stably form wall charges on the electrodes. The scan driver 200 supplies reset signals to the scan electrodes Y1 to Yn during the reset period to thereby uniformly form wall charges inside discharge cells.
The reset signal includes a reset rising signal gradually rising to a highest voltage of the reset signal and a reset falling signal gradually falling to a lowest voltage of the reset signal.
The scan driver 200 supplies scan signals to the scan electrodes Y1 to Yn during an address period to thereby select discharge cells to be turned on. The scan driver 200 supplies sustain signals to the scan electrodes Y1 to Yn during a sustain period to thereby generate a sustain discharge inside the discharge cells selected during the address period.
The sustain driver 300 supplies first rising signals to the sustain electrodes Z1 to Zn during the pre-reset period, supplies a sustain bias voltage to the sustain electrodes Z1 to Zn during a set-down period and the address period, and supplies sustain signals to the sustain electrodes Z1 to Zn during the sustain period.
The data driver 400 receives data rapped for each subfield by a subfield mapping circuit (not shown) after being inverse-gamma corrected and error-diffused through an inverse gamma correction circuit (not shown) and an error diffusion circuit (not shown), or the like.
The data driver 400 supplies data signals corresponding to the scan signals to the address electrodes X1 to Xn in response to a data timing control signal received from a timing controller (not shown) during the address period.
As shown in
The scan electrode 112 and the sustain electrode 113 generate a mutual discharge therebetween in a discharge cell and maintain a discharge of the discharge cell.
A light transmittance and an electrical conductivity of the scan electrode 112 and the sustain electrode 113 need to be considered so as to emit light generated inside the discharge cells to the outside and to secure the driving efficiency. Accordingly, the scan electrode 112 and the sustain electrode 113 each include transparent electrodes 112a and 113a made of a transparent material, e.g., indium-tin-oxide (ITO) and bus electrodes 112b and 113b made of a metal material such as silver (Ag).
An upper dielectric layer 114 covering the scan electrode 112 and the sustain electrode 113 is formed on the front substrate 111 on which the scan electrode 112 and the sustain electrode 113 are formed. The upper dielectric layer 114 limits discharge currents of the scan electrode 112 and the sustain electrode 113 and provides electrical insulation between the scan electrode 112 and the sustain electrode 113.
A protective layer 115 is formed on an upper surface of the upper dielectric layer 114 to facilitate discharge conditions. The protective layer 115 may be formed of a material with a high secondary electron Emission coefficient, for example, magnesium oxide (MgO).
The address electrode 123 formed on the rear substrate 121 applies a data signal to the discharge cell.
A lower dielectric layer 125 covering the address electrode 123 is formed on the rear substrate 121 on which the address electrode 123 is formed.
Barrier ribs 122 are formed on the lower dielectric layer 125 to partition the discharge cells. A phosphor layer 124 emitting visible light for an image display during an address discharge is formed inside the discharge cells partitioned by the barrier ribs 122. The phosphor layer 124 may include a red phosphor layer R, a green phosphor layer G, and a blue phosphor layer B.
Driving signals are applied to the scan electrode 112, the sustain electrode 113, and the address electrode 123 to generate a discharge inside the discharge cells of the plasma display panel. Hence, an image is displayed on the plasma display panel.
As shown in
Each subfields may be subdivided into a reset period for initializing all the discharge cells, an address period for selecting cells to be discharged, and a sustain period for representing a gray level in accordance with the number of discharges.
For instance, if an image with 256 gray levels is to be displayed, a frame period (i.e., 16.67 ms) corresponding to 1/60 second, as shown in
The number of sustain signals supplied during a sustain period of a subfield determines a weight value of the subfield. In other words, a predetermined weight value may be assigned to each subfield using a sustain period of each subfield. For instance, in such a method of setting a weight value of a first subfield at 20 and a weight value of a second subfield at 21, a weight value of each subfield can be set so that weight values of subfields increase in a ratio of 2n (where, n=0, 1, 2, 3, 4, 5, 6, 7). An image with various gray values can be displayed by controlling the number of sustain signals supplied during a sustain period of each subfield depending on a weight value of each subfield.
The plasma display apparatus uses a plurality of frames to display an image for 1 second. For instance, 60 frames are used to display an image for 1 second.
While one frame includes 8 subfields in
The image quality in the plasma display apparatus depends on the number of subfields constituting a frame. For instance, when 12 subfields constitute a frame, the number of representable weight values of an image may be 212. When 10 subfields constitute a frame, the number of representable weight values of an image may be 210.
Further, while the subfields are arranged in increasing order of weight values in
The scan driver 200, the sustain driver 300, and the data driver 400 of
As shown in
Although
The sustain driver 300 may supply a first rising signal Vz, whose a polarity is opposite to a polarity of the first falling signal Pre-Ramp, to the sustain electrode Z during the supply of the first falling signal Pre-Ramp.
A voltage of the first rising signal Vz is substantially equal to at least one of a sustain bias voltage Vzb or a sustain voltage Vs corresponding to a highest voltage of a sustain signal SUS. Hence, the first rising signal Vz may be supplied using a sustain bias voltage source or a sustain voltage source.
The first rising signal Vz may depend on the temperature of the plasma display panel, the surroundings of the plasma display panel, or the first falling signal Pre-Ramp corresponding to the first rising signal Vz.
As above, wall charges with a predetermined polarity are accumulated on the scan electrode Y, and wall charges with a polarity opposite the polarity of the wall charges accumulated on the scan electrode Y are accumulated on the sustain electrode Z by supplying the first falling signal Pre-Ramp and the first rising signal Vz to the scan electrode Y and the sustain electrode Z during the pre-reset period, respectively.
Because the frame includes the pre-reset period, a magnitude of a highest voltage of a reset signal can be reduced. Hence the amount of light generated during the reset period can be reduced, and a contrast characteristic can be improved.
The scan driver 200 supplies a reset signal including a reset rising signal Ramp-up and a reset falling signal Ramp-down to the scan electrode Y during the reset period.
More specifically, the scan driver 200 supplies the reset rising signal Ramp-up to the scan electrode Y during a setup period of the reset period. The reset rising signal Ramp-up generates a weak dark discharge inside the discharge cells of the whole screen. Hence, wall charges of a positive polarity are accumulated on the sustain electrode Z and the address electrode X, and wall charges of a negative polarity are accumulated on the scan electrode Y.
The scan driver 200 supplies the reset falling signal Ramp-down, which falls from a positive voltage level lower than a highest voltage of the reset rising signal Ramp-up to a given voltage level lower than the ground level voltage GND, to the scan electrode Y during a set-down period of the reset period, thereby generating a weak erase discharge inside the discharge cells. Hence, wall charges excessively accumulated inside the discharge cells are erased, and the remaining wall charges are uniformly distributed inside the discharge cells to the extent that an address discharge can stably occur.
The reset rising signal Ramp-up and the reset falling signal Ramp-down are supplied in a first subfield of a frame. The first subfield means a first arranged subfield of a plurality of subfields constituting the frame. During reset periods of the remaining subfields except the first subfield, the scan driver 200 may supply a first signal to the scan electrode Y. The first signal rises from a first voltage to a second voltage larger than the first voltage, is maintained at the second voltage during a predetermined period of time, and falls from the second voltage to a third voltage smaller than the first voltage with a slope.
The sustain driver 300 supplies a sustain bias voltage Vzb to the sustain electrode Z during the set-down period and an address period. The sustain bias voltage Vzb reduces a voltage difference between the scan electrode Y and the sustain electrode Z, and thus can prevent the generation of an erroneous discharge between the scan electrode Y and the sustain electrode Z.
The scan driver 200 supplies a scan signal Scan, which falls from a scan bias voltage Vsc to a voltage −Vy, to the scan electrode Y during the address period. The scan bias voltage Vsc may be smaller than the ground level voltage GND. The data driver 400 supplies a data signal Dp corresponding to the scan signal Scan to the address electrode X.
As a voltage difference between the scan signal Scan and the data signal Dp is added to a wall voltage by wall charges produced during the reset period, an address discharge occurs inside the discharge cells, to which the data signal Dp is supplied. Wall charge are formed inside the discharge cells selected by generating the address discharge to the extent that a discharge can occur when the sustain voltage Vs is supplied.
During a sustain period, the scan driver 200 and the sustain driver 300 supply sustain signals sus to the scan electrode Y and the sustain electrode Z, respectively. As a wall voltage inside the discharge cells selected by generating the address discharge is added to the sustain signal sus, every time the sustain signal sus is applied, a sustain discharge occurs between the scan electrode Y and the sustain electrode Z.
The sustain signal sus is a signal swing between the first voltage and the second voltage. The first voltage may be substantially equal to the ground level voltage GND, and the second voltage may be substantially equal to the sustain voltage Vs of the sustain signal sus.
After a last sustain signal is supplied during a sustain period of a last subfield of the plurality of subfields, the scan driver 200 may supply an erase signal.
As shown in
During a reset period of a first subfield SF1 of a frame, a reset signal including a reset rising signal Ramp-up and a reset falling signal Ramp-down is supplied to the scan electrode Y. During reset periods of the remaining subfields SF2 to SF10 except the first subfield SF1, a reset signal including only the reset falling signal Ramp-down is supplied to the scan electrode Y.
The first signal and a second signal may include a reset falling signal. The reset falling signal rises from the first voltage to the second voltage, is maintained at the second voltage during a first period W1 or a second period W2, and falls from the second voltage to the third voltage with a slope.
The first signal and the second signal are supplied during the reset periods of the remaining subfields SF2 to SF10 except the first subfield SF1. The first period W1 of the first signal, whose a voltage level is maintained at the second voltage, may be different from the second period W2 of the second signal, whose a voltage level is maintained at the second voltage.
The first signal is supplied earlier than the second signal during the reset periods of the remaining subfields SF2 to SF10 except the first subfield SF1. A length of the first period W1 of the first signal is shorter than a length of the second period W2 of the second signal.
For example, if one frame includes 10 subfields SF1 to SF10, a length of a first period W1 of the first signal supplied during reset periods of the 2nd to 7th subfields SF2 to SF7 is shorter than a length of a second period W2 of the second signal supplied during reset periods of the 8th to 10th subfields SF8 to SF10.
A reason why the length of the first period W1 is shorter than the length of the second period W2 is to prevent the center of light from moving to the first subfield. In other words, the center of light can move to the intermediately arranged subfield of the plurality of subfields of one frame.
Because the reset rising signal Ramp-up and the reset falling signal Ramp-Down are supplied in only the first subfield SF1, the wall charges may be unstably distributed inside the discharge cells in the subfields following the first subfield SF1. Therefore, the wall charges can be stably distributed by the second signal having the second period W2 longer than the first period W1.
A last sustain signal SUS_last of sustain signals Sus supplied to the scan electrode during a sustain period of a last subfield SF10 of a frame may be an erase signal. Hence, the last sustain signal SUS_last erases the most of non-uniformly distributed wall charges, and thus the remaining wall charges can be uniformly distributed inside the discharge cells.
Because a waveform and a function of the last sustain signal SUS_last may be substantially equal to waveforms and functions of the first and second signals, the last sustain signal SUS_last corresponding to the erase signal may be the first and second signals.
A length of the first period W1, a length of the second period W2, or the last sustain signal SUS_last may change depending on a gray level of an image.
When a gray level of an image is smaller than 51% of a highest gray level of the image, the image gray level is referred to as a first gray level. When a gray level of an image is equal to or larger than 51% of a highest gray level of the image, the image gray level is referred to as a second gray level. The scan driver supplies the first signal in the first gray level and supplies the second signal in the second gray level.
If the highest gray level is 256 gray levels, a gray level corresponding to 51% of the highest gray level is 131 gray levels.
For example, an image capable of being displayed through 131 gray levels may be a dark image, an image whose a movement is small, an image in which changes in the screen being the entire background are small in as a nature documentary. These images can be sufficiently displayed through a low gray level.
Various values of a gray level are required to display an image on the plasma display panel. The image quality may depend on how many gray values are used to display an image. If many gray values are used so as to improve the image quality, power consumption may increase due to an excessive driving voltage. Therefore, it is advantageous that the number of gray values is used to display the image to the extent that the image quality is not reduced.
The length of the second period of the second signal supplied to the scan electrode in case of the second gray level is longer than the length of the first period of the first signal supplied to the scan electrode in case of the first gray level.
As above, because the first signal is supplied in the first gray level and the second signal is supplied in the second gray level, a reduction in the image quality can be prevented while the power consumption does not increase.
The second period W2 of the second signal is 3 to 5 times the first period W1 of the first signal. In other words, the second period W2 of the second signal may be 240 μs to 300 μs, and the first period W1 of the first signal may be 60 μs to 80 μs.
If the length of the first period W1 is substantially equal to the length of the second period W2, the center of light cannot be prevented from moving to the first subfield SF1 of the plurality of subfields constituting one frame. Further, because the reset rising signal Ramp-up and the reset falling signal Ramp-down are supplied in only the first subfield SF1 and only the reset falling signal Ramp-down is supplied in the subfields following the first subfield SF1, the wall charges may be unstably distributed inside the discharge cells.
If the length of the first period W1 is excessively shorter than the length of the second period W2, the center of light may move to the 8th to 10th subfields SF8 to SF10 of the plurality of subfields constituting one frame.
Accordingly, the second period W2 of the second signal may be 3 to 5 times the first period W1 of the first signal so as to uniformly distribute the wall charges inside the discharge cells while the center of light is maintained in one frame. In other words, the second period W2 of the second signal may be 240 μs to 300 μs, and the first period W1 of the first signal may be 60 μs to 80 μs.
In
In
Because the waveform of the first signal is substantially the same as the waveform of the second signal except that a period of the first signal whose the voltage level is maintained at the second voltage is different from a period of the second signal whose the voltage level is maintained at the second voltage, a description of the waveform of the second signal is omitted.
Accordingly, the first signal and the second signal can be supplied using the same voltage source, and thus the manufacturing cost can be reduced.
As shown in
The predetermined period of tire may be adjusted depending on a gray level of an image displayed on the screen. Therefore, the predetermined period of time may change depending on image gray level in each of a plurality of subfields constituting one frame.
In other words, the predetermined period of time of the first signal may be adjusted depending on the image gray level in each of the remaining subfields except a first subfield of one frame. In
In
In (a) of
As shown in
The second voltage is supplied during a first period in an n-th subfield of the 1st frame in case of the first gray level, and the second voltage is supplied during a second period in an n-th subfield of the 2nd frame in case of the second gray level.
In
In (a) of
As above, because the second period of the second voltage in the second frame following the first frame is longer than the first period of the second voltage in the first frame, the light center can move to the intermediately arranged subfield of each frame. Hence, the wall charges can be uniformly distributed inside the discharge cells
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
Number | Date | Country | Kind |
---|---|---|---|
10-2007-0102169 | Oct 2007 | KR | national |