1. Field of the Invention
The present invention relates to a method for driving a plasma display panel.
2. Description of the Related Art
Currently, an AC (discharge)-type plasma display panel (PDP) is commercially available as a thin display device. In a PDP, two substrates (i.e., a front transparent substrate and a rear substrate) are disposed opposite each other with a predetermined interval therebetween. Pairs of row electrodes extending in a horizontal direction of the screen are formed on an inner surface of the front transparent substrate as a display surface. The inner surface of the front transparent substrate faces the rear substrate. A dielectric layer is formed on the inner surface of the front transparent substrate such that the dielectric layer covers the pairs of row electrodes. Column electrodes extending in a vertical direction of the screen are formed on the rear substrate such that the column electrodes cross the pairs of row electrodes. When viewed from the front (i.e., from the display surface side), discharge cells, which serve as pixels, are formed at intersections of the row electrode pairs and the column electrodes.
Grayscale driving is performed on such a PDP using a subfield scheme to achieve halftone display luminance faithful to an input image signal.
In such a grayscale drive method based on the subfield scheme, each field (unit display period) is divided into a plurality of subfields and a certain number of times (or a period during which) light emission is to be performed is allocated to each subfield. Display driving of an image signal for one field is performed on the subfield basis. An addressing process and a sustain process are sequentially performed in each subfield. In the addressing process, an addressing discharge is selectively generated between a row electrode and a column electrode in each discharge cell on the basis of an input image signal. A certain amount of wall charges are generated (or erased) in those discharge cells in which the addressing discharge has been generated. In other discharge cells in which no addressing discharge has been generated, the state of wall charges is maintained unchanged from the immediately previous state. Discharge cells having a specific amount of wall charges are set to an emission mode and other discharge cells having no specific amount of wall charges are set to a non-emission mode. In the sustain process, a discharge is repeatedly generated a number of times corresponding to a luminance weight value allocated to the subfield in those discharge cells that are in the emission mode, thereby maintaining light emission through the discharge. In the first subfield, an initialization process is performed prior to the addressing process. In the initialization process, a reset pulse is simultaneously applied to every discharge cell, thereby causing a reset discharge between row electrodes in every discharge cell. This initializes the amount of wall charges remaining in every discharge cell.
Since the reset discharge is a relatively strong discharge and contributes nothing to the contents of an image to be displayed, light emission caused by this discharge leads to a reduction in image contrast, especially a reduction in dark contrast when an entirely dark image is displayed.
In one suggested drive method, the dark contrast is increased by decreasing the peak potential of the reset pulse to weaken the reset discharge as the darkness of an image to be displayed increases (i.e., as the number of those discharge cells that are in a non-emission mode in one screen increases). See FIG. 8 of Japanese Patent Application Kokai (Publication) No. 2006-243002.
However, reducing the peak potential of the reset pulse may lead to generation of an insufficient amount of wall charges due to weakening of the reset discharge. In this case, erroneous discharges occur in the subsequent sustain process.
One object of the present invention is to provide a method for driving a plasma display panel (PDP) that can increase dark contrast without causing erroneous discharges.
According to a first aspect of the present invention, there is provided a method for driving a plasma display panel based on pixel data of pixels derived from an image signal. The plasma display panel includes a first substrate, a second substrate, a plurality of row electrode pairs disposed on the first substrate and a plurality of column electrodes disposed on the second substrate. The first substrate may be spaced from the second substrate to define discharge spaces therebetween. Discharge gases may be sealed in the discharge spaces. Discharge cells are formed respectively at intersections of the row electrode pairs with the column electrodes. A unit display period is divided into a plurality of subfields. The method includes an addressing process, in which each of the discharge cells is set to either an emission mode or a non-emission mode, in each subfield. The method also includes a sustain process for applying a sustain pulse in each subfield. In the sustain process, the sustain discharge may be repeatedly generated a number of times, corresponding to a number of times a sustain pulse is applied, in each subfield. The sustain discharge may be generated in those discharge cells which are in the emission mode. The method also includes a reset process, in which a reset pulse is applied to one of two row electrodes in each row electrode pair prior to the addressing process so as to initialize each of the discharge cells. The reset pulse takes place in one of the subfields in the unit display period. A peak potential of the reset pulse is altered based on a number of those discharge cells which are maintained in the non-emission mode during the unit display period and/or the number of times the sustain pulse is to be applied in the sustain process in said one subfield.
According to a second aspect of the present invention, there is provided another method for driving a plasma display panel based on pixel data of pixels derived from an image signal. The plasma display panel includes first and second substrates disposed opposite each other. Discharge spaces may be formed between the first and second substrates. Discharge gases may be sealed in the discharge spaces. The plasma display panel also includes a plurality of row electrode pairs provided on the first substrate and a plurality of column electrodes provided on the second substrate. Discharge cells are formed respectively at intersections of the row electrode pairs with the column electrodes. A unit display period is divided into a plurality of subfields. The method includes an addressing process for setting each of the discharge cells to an emission mode or a non-emission mode in each subfield. In the addressing process, an addressing discharge may be generated in each of the discharge cells. The method also includes a sustain process for applying a sustain pulse in each subfield. In the sustain process, a sustain discharge may be repeatedly generated a number of times, corresponding to a number of times a sustain pulse is applied, in those discharge cells that are in the emission mode. The method also includes a reset process, in which a reset pulse is applied to one of two row electrodes in each row electrode pair prior to the addressing process to initialize each of the discharge cells. The reset process takes place in one of the subfields in the unit display period. A peak potential of the reset pulse is changed based on the number of times the sustain pulse is to be applied in the sustain process in said one subfield.
According to a third aspect of the present invention, there is provided still another method for driving a plasma display panel based on pixel data of pixels derived from an image signal. The plasma display panel includes first and second substrates disposed opposite each other. Discharge spaces may be formed between the first and second substrates. The plasma display panel also includes a plurality of row electrode pairs on the first substrate and a plurality of column electrodes on the second substrate. Discharge gases may be sealed in the discharge spaces. Discharge cells are formed respectively at intersections of the row electrode pairs with the column electrodes. A unit display period is divided into a plurality of subfields. The method includes an addressing process in each subfield. In the addressing process, each of the discharge cells is set to one of an emission mode and a non-emission mode. The method also includes a sustain process for applying a sustain pulse in each subfield. In the sustain process, a sustain discharge may be repeatedly generated a number of times, corresponding to a number of times a sustain pulse is applied, in those discharge cells that are in the emission mode. The method also includes a reset process, in which a reset pulse is applied to one of two row electrodes in each row electrode pair prior to the addressing process to initialize each of the discharge cells. The reset process takes place in one of the subfields in the unit display period. The reset process includes a front half process in which a first reset pulse having a positive peak potential is applied to said one of the two row electrodes and a rear half process in which a second reset pulse having a negative peak potential is applied to the same one of the two row electrodes subsequently to the front half process. The negative peak potential of the second reset pulse is changed based on a number of those discharge cells that are maintained in the non-emission mode during a unit display period in which the second reset pulse is applied.
The reset process and sustain process are performed in one subfield of the unit display period. In the reset process, a reset pulse is applied to row electrodes of the plasma display panel to initialize each discharge cell to either an emission mode or a non-emission mode. In the sustain process, a sustain discharge is repeatedly generated a number of times, corresponding to the number of times a sustain pulse is to be applied, in those discharge cells that are in the emission mode. A peak potential of the reset pulse is adjusted in accordance with the number of discharge cells that are maintained in the non-emission mode during the unit display period and the number of times the sustain pulse is to be applied in the sustain process in said one subfield.
The absolute value of the peak potential of the reset pulse decreases as the number of discharge cells that are maintained in the non-emission mode during the unit display period increases (i.e., as the overall darkness of an image to be displayed increases). As a result, the luminance of light emitted through the reset discharge drops, thereby achieving an increase in the dark contrast. When the number of times the sustain pulse is to be applied in the sustain process is less than a predetermined number, the absolute value of the peak potential of the reset pulse is set to be smaller than when the number of times the sustain pulse is to be applied is equal to or greater than the predetermined number. According to this drive method, when the number of times the sustain pulse is applied is large, a strong(er) reset discharge is generated, compared to when the number of times the sustain pulse is applied is small, thereby making it possible to initialize the amount of wall charges generated in the discharge cells to a desired amount. Consequently, an erroneous sustain discharge can be prevented even if the number of sustain pulse applications is large, while improving (enhancing) a dark contrast.
The above and other objects, aspects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Referring to
As shown in
The PDP 50 includes a front substrate (not shown) serving as a display surface and a rear substrate (not shown) that is disposed opposite the front substrate with discharge gases being sealed in a discharge space defined between the front and rear substrates. Row electrodes X1 to Xn and row electrodes Y1 to Yn are alternately arranged in parallel to each other on the front substrate. Column electrodes D1 to Dm are arranged, crossing the row electrodes, on the rear substrate. A row electrode Xi and a neighboring electrode Yi make a pair to serve as a display line so that n pairs of row electrodes (X1 and Y1, X2 and Y2, . . . and Xn and Yn) serve as 1st to nth display lines of the PDP 50, respectively. Discharge cells (or display cells) PC, each serving as a pixel, are formed in respective intersection portions (each having a discharge space) between the pairs of row electrodes and the column electrodes. That is, n×m discharge cells PC1,1 to PCn,m are arranged in a matrix in a screen of the PDP 50.
An A/D converter 1 converts a luminance level of each discharge cell PC of an input image signal into pixel data PD, for example represented in 8 bits, and supplies the 8-bit pixel data PD to a black display cell counter 2, a sustain pulse count setting unit 3, and a subfield (SF) data generator 4.
Based on an input image signal, the black display cell counter 2 counts the number of those discharge cells PC that are maintained in a black display state (i.e., a luminance level of 0) over a display period of each frame (or field). In the following description, the display period of each frame is referred to as a unit display period. The black display cell counter 2 supplies a black display cell count signal BN indicating the counted number of discharge cells PC that are maintained in a black display state to a peak potential setting unit 5.
Based on an input image signal, the sustain pulse count setting unit 3 determines the number of sustain pulses to be allocated to each of subfields SF1 to SF14, as shown in
An accumulated running time counter 6 measures the sum of periods (i.e., an accumulated running time) during which power has been supplied to the plasma display device since the plasma display device has been shipped from a manufacturer (factory) and supplies an accumulated running time signal RT indicating the accumulated running time to the peak potential setting unit 5.
The peak potential setting unit 5 determines a negative peak potential PV, which will be used as a negative peak potential of a reset pulse RP2Y2 (described below), based on the accumulated running time signal RT, the sustain pulse count signal SN, and a black display cell count signal BN, and supplies a peak potential setting signal RPS indicating the negative peak potential PV to a Y electrode driver 53. The peak potential setting unit 5 uses a sustain pulse count signal SN and a black display cell count signal BN of the same frame (field) when determining the negative peak potential PV.
The subfield data generator 4 applies a grayscale conversion process including an error diffusion process and/or a dithering process on each pixel data PD of each discharge cell PC received from the A/D converter 1 to convert the pixel data into 4-bit grayscale pixel data PDs which represents an entire luminance range of the input image signal in 16 gray levels (first to sixteenth gray levels) as shown in
The drive controller 56 supplies various control signals to the X electrode driver 51, the Y electrode driver 53, and the addressing driver 55. The X electrode driver 51, the Y electrode driver 53, and the addressing driver 55 are collectively referred to as a panel driver. The control signals are used to drive the PDP 50 according to a light emission drive sequence as shown in
In the sustain process I of each subfield SF, the drive controller 56 provides the panel driver with a control signal for causing the panel driver to repeatedly apply a sustain pulse IP (described below) the same number of times as the number of sustain pulses indicated by the sustain pulse count signal SN.
Upon receiving the control signals from the drive controller 56, the panel driver, which includes the X electrode driver 51, the Y electrode driver 53, and the addressing driver 55, applies various drive pulses to the column electrodes D and the row electrodes X and Y of the PDP 50, for example according to a first pulse sequence shown in
The manner in which drive pulses are applied in the first pulse sequence shown in
First, in a front side of a first reset process R1 of a subfield SF1, the Y electrode driver 53 applies a positive reset pulse RP1Y1, to all the row electrodes Y1 to Yn. The reset pulse RP1Y1 has a pulse waveform that slowly changes in potential in a leading edge portion thereof, as compared with a sustain pulse IP (described below). During this pulse application, the addressing driver 55 sets the column electrodes D1 to Dm to ground potential (i.e., 0V). Upon application of the reset pulse RP1Y1 to the row electrodes Y1 to Yn, a first reset discharge occurs between the row electrode Y and column electrode D of every the discharge cell PC. That is, in the front side of the first reset process R1, predetermined voltages are applied between the row and column electrodes Y and D to bring the row electrodes Y and the column electrodes D into positive and negative potentials, respectively, thereby reducing a particular discharge (first reset discharge). This first reset discharge causes a current to flow from the row electrodes Y to the column electrodes D and is hereinafter referred to as a “column-side negative (cathode) discharge”. The first reset discharge occurring in this manner generates negative wall charges near the row electrodes Y and positive wall charges near the column electrodes D in all the discharge cells PC. In addition, in the front side of the first reset process R1, the X electrode driver 51 applies a reset pulse RP1x to each of the row electrodes X1 to Xn. The reset pulse RP1x has the same polarity (positive polarity) as that of the reset pulse RP1Y1. The reset pulse RP1X has a peak potential that can prevent surface discharge, which would otherwise occur between the row electrodes X and Y upon application of the reset pulse RP1Y1.
Subsequently, in the rear side of the first reset process R1 of the subfield SF1, the Y electrode driver 53 generates a reset pulse RP1Y2, which has a pulse waveform that slowly decreases down to a negative peak potential as shown in
The second reset discharge occurring in the rear side of the first reset process R1 erases wall charges that have been generated near each of the row electrodes X and Y in each discharge cell PC, thereby initializing every discharge cell PC to a non-emission mode. As the reset pulse RP1Y2 is applied, a weak discharge also occurs between the row electrodes Y and the column electrodes D in all the discharge cells PC. This weak discharge erases some of positive wall charges generated near the column electrodes D, thereby adjusting the amount of the positive wall charges to a level that can guarantee a selective write addressing discharge in the first selective write addressing process W1W.
Subsequently, in the first selective write addressing process W1W of the subfield SF1, the Y electrode driver 53 simultaneously applies a base pulse BP− having a specific negative potential to the row electrodes Y1 to Yn while sequentially applying a write scan pulse SPW having a negative peak potential to each of the row electrodes Y1 to Yn as shown in
In the weak light emission process LL of the subfield SF1, the Y electrode driver 53 simultaneously applies a weak light emission pulse LP having a specific positive peak potential to the row electrodes Y1 to Yn as shown in
The potential change rate in a rising edge portion of the weak light emission pulse LP is faster than that in a rising edge portion of each of the reset pulses RP1Y1 and RP2Y1. That is, the potential change rate of a leading edge portion of the weak light emission pulse LP is faster than the potential change rate of a leading edge portion of the reset pulse, so that the intensity of a discharge that occurs in the weak light emission process LL is greater than the first reset discharge that occurs in the first reset process R1. The luminance of light emitted through such a discharge is lower than that of the sustain discharge that occurs between the row electrodes X and Y since the discharge is the above-described column-side negative (cathode) discharge and is caused by a weak light emission pulse LP having a lower peak potential than that of the sustain pulse IP. That is, in the weak light emission process LL, a discharge that is accompanied by light emission at a luminance level higher than the first reset discharge and lower than the sustain discharge (i.e., a discharge that is accompanied by weak light emission at a luminance level usable for display) occurs as a weak light emission discharge. In the first selective write addressing process W1W performed immediately before the weak light emission process LL, a selective write addressing discharge occurs between the column and row electrodes D and Y in the discharge cells PC. Accordingly, in the subfield SF1, luminance of a gray level corresponding to a luminance level that is one level higher than a luminance level of “0” is expressed due to both light emission that is caused by the selective write addressing discharge and light emission that is caused by the weak light emission discharge.
Next, in a front side of a second reset process R2 of the subfield SF2, the Y electrode driver 53 applies a positive reset pulse RP2Y1, which has a pulse waveform that slowly changes in potential in a leading edge portion thereof, if compared with the sustain pulse IP, to all the row electrodes Y1 to Yn. During this process, the addressing driver 55 sets the column electrodes D1 to Dm to ground (i.e., 0V) and the X electrode driver 51 applies a reset pulse RP2x having a positive peak potential to each of the row electrodes X1 to Xn. The reset pulse RP2x can prevent surface discharge that would otherwise occur between the row electrodes X and Y upon application of the reset pulse RP2Y1. Although the positive peak potential of the reset pulse RP2X is lower than the positive peak potential of the sustain pulse IP, the X electrode driver 51 may set all the row electrodes X1 to Xn to ground (i.e., 0V), instead of applying the reset pulse RP2x to the row electrodes X1 to Xn, if setting to ground does not cause a surface discharge between the row electrodes X and Y. As the reset pulse RP2Y1 is applied to the row electrodes Y1 to Yn, a first reset discharge, which is weaker than the column-side negative (cathode) discharge in the weak light emission process LL, occurs between the row and column electrodes Y and D in those discharge cells PC in which column-side negative (cathode) discharge did not occur in the weak light emission process LL.
That is, in the front side of the second reset process R2, specific voltages are applied between the row and column electrodes Y and D to bring the row electrodes Y and the column electrodes D into positive and negative potentials, respectively, thereby inducing a column-side negative (cathode) discharge with current flowing from the row electrodes Y to the column electrodes D as the first reset discharge. On the other hand, even though the reset pulse RP2Y1 is applied, no discharge occurs in those discharge cells PC in which the weak light emission discharge takes place in the weak light emission process LL. Accordingly, immediately after the front side of the second reset process R2 is finished, all the discharge cells PC are in a state in which negative wall charges are generated near the row electrodes Y and positive wall charges are generated near the column electrodes D.
In the rear side of the second reset process R2 of the subfield SF2, the Y electrode driver 53 applies a reset pulse RP2Y2 to all the row electrodes Y1 to Yn. The reset pulse RP2Y2 has a pulse waveform that slowly decreases down to a negative peak potential PV indicated by the peak potential setting signal RPS as shown in
In the second selective write addressing process W2W of the subfield SF2, the Y electrode driver 53 simultaneously applies a base pulse BP− having a specific negative potential to the row electrodes Y1 to Yn while sequentially applying a write scan pulse SPW having a negative peak potential to each of the row electrodes Y1 to Yn as shown in
In the sustain process I of each of the subfields SF2 to SF14, the X electrode driver 51 and the Y electrode driver 53 repeatedly and alternately apply a sustain pulse IP having a positive peak potential to the group of row electrodes X1 to Xn and the group of row electrodes Y1 to Yn. The number of sustain pulses IP repeatedly applied in the sustain process I of each of the subfields SF2 to SF14 is decided based on the number of sustain pulses of each subfield SF indicated by the sustain pulse count signal SN. For example, when the number of sustain pulses of the subfield SF2 indicated by the sustain pulse count signal SN is “1,” only the Y electrode driver 53 among the X and Y electrode drivers 51 and 53 applies only one sustain pulse IP to the Y row electrode group in the sustain process I of the subfield SF2 as shown in
In the sustain process I, a sustain discharge occurs between row electrodes X and Y in those discharge cells PC that have been set to an emission mode each time the sustain pulse IP is applied. As the sustain discharge occurs, a fluorescent layer 17 emits light, which is then emitted from the PDP 50 through the front transparent substrate 10. Accordingly, the luminance of light viewed is determined according to the number to times the sustain discharge is repeated. As the sustain pulse IP is applied, a discharge also occurs between row electrodes Y and column electrodes D of those discharge cells PC that have been set to an emission mode. As this discharge and the sustain discharge occur, negative wall charges are generated near the row electrodes Y in the discharge cells PC and positive wall charges are generated near the row electrodes X and the column electrodes D in the discharge cells PC.
Immediately after the final sustain pulse IP is applied in the sustain process I of each of the subfields SF2 to SF14, the Y electrode driver 53 applies a wall charge adjustment pulse CP to the row electrodes Y1 to Yn. The wall charge adjustment pulse CP has a pulse waveform that slowly decreases down to a negative peak potential in a leading edge portion thereof as shown in
In a selective erasure addressing process WD of each of the subfields SF3 to SF14, the Y electrode driver 53 applies a base pulse BP+ having a specific positive potential to each of the row electrodes Y1 to Yn while sequentially applying an erase scan pulse SPD having a negative peak potential to each of the row electrodes Y1 to Yn as shown in
In the erasure process E of the last subfield SF14, the Y electrode driver 53 applies an erasure pulse EP having a negative peak potential to all the row electrodes Y1 to Yn. Upon application of the erasure pulse EP, an erasure discharge occurs only in those discharge cells PC that are in an emission mode. This erasure discharge switches these emission-mode discharge cells PC to a non-emission mode.
The above-described drive is performed based on 16 subfield data GD of 1st to 16th gray levels as shown in
In the case of the second gray level representing luminance that is one level higher than that of the first gray level representing black (luminance level “0”), the panel driver induces a selective write addressing discharge for setting the discharge cell PC to an emission mode only in the subfield SF1 among the subfields SF1 to SF14 as shown in
In the case of the second gray level representing luminance that is one level higher than that of the second gray level, the panel driver induces a selective write addressing discharge for setting the discharge cell PC to an emission mode only in the subfield SF2 among the subfields SF1 to SF14 as shown in
In the case of the fourth gray level representing luminance that is one level higher than that of the second gray level, first, the panel driver causes a selective write addressing discharge for setting the discharge cell PC to an emission mode in the subfield SF1 and causes a weak light emission discharge in the discharge cell PC set to an emission mode (as denoted by “□”). In the case of the fourth gray level, the panel driver causes a selective write addressing discharge for setting the discharge cell PC to an emission mode only in the subfield SF2 among the subfields SF1 to SF14 (as denoted by “⊚”) and causes a selective erasure addressing discharge for switching the discharge cell PC to a non-emission mode in the next subfield SF3 (as denoted by “●”). Accordingly, the fourth gray level represents luminance corresponding to a luminance level of a “α+1” since light of a luminance level of “α” is emitted in the subfield SF1 and one sustain discharge, which entails light emission of a luminance level of “1,” also occurs in the subfield SF2.
In the case of each of the fifth to sixteenth gray levels, first, the panel driver causes a selective write addressing discharge for setting the discharge cell PC to an emission mode in the subfield SF1 and causes a weak light emission discharge in the emission-mode discharge cell PC (as denoted by “□”). The panel driver also induces a selective erasure addressing discharge for switching the discharge cell PC to a non-emission mode in only one subfield SF corresponding to that gray level (as denoted by “●”). Accordingly, in the case of each of the fifth to sixteenth gray levels, the panel driver causes the weak light emission discharge in the subfield SF1 and causes one sustain discharge in the subfield SF2. Thereafter, in each of continuous subfields corresponding to the gray level (as denoted by “◯”), the panel driver causes a sustain discharge a number of times allocated to the subfield concerned. Thus, luminance corresponding to the sum of the luminance level “α” and the total number of sustain discharges occurring in a one-field (or one-frame) display period is viewed in each of the fifth to sixteenth gray levels. As a result, according to the above-described drive method, a range of luminance levels of “0” to “255+α” can be represented using the first to sixteenth gray levels as shown in
In the above-described drive method, a weak light emission discharge rather than a sustain discharge is generated, as a discharge that contributes to a display image, in the subfield SF1 that has the smallest luminance weight. Since the weak light emission discharge occurs between column electrodes D and row electrodes Y, the level of luminance of light emitted through the weak light emission discharge is lower than that of the sustain discharge that occurs between row electrodes X and Y. Thus, the luminance difference between the first gray level (black: luminance level “0”) and the second gray level (one level higher than black) is less when the luminance at the second gray level is represented through the weak light emission discharge, than when the second gray level is represented through the sustain discharge. This increases (enhances) the capability of representing gray levels of low luminance images. In the case of the second gray level, no reset discharge occurs in the second reset process R2 of the subfield SF2 subsequent to the subfield SF1, and therefore a reduction in the dark contrast due to the reset discharge is suppressed.
Although a weak light emission discharge, entailing light emission of a luminance level of “α,” is generated in the subfield SF1 in each of the fourth and subsequent gray levels in the drive method shown in
In the plasma display device shown in
More specifically, the peak potential setting unit 5 obtains the number of sustain pulses allocated to a subfield SF (i.e., the subfield SF2), which includes a sustain process I that is first performed after the second reset process R2 is performed, based on the sustain pulse count signal SN. Then, the peak potential setting unit 5 determines whether or not the number of sustain pulses allocated to the subfield SF2 is less than a predetermined number (for example, “3”). When the number of sustain pulses allocated to the subfield SF2 is equal to or higher than the predetermined number “3,” the peak potential setting unit 5 sets a potential of “−L5,” which is the negative of a specific potential of “L5,” as the negative peak potential PV of the reset pulse RP2Y2, regardless of the accumulated running time signal RT and the black display cell count signal BN.
On the other hand, when the number of sustain pulses allocated to the subfield SF2 is less than the predetermined number “3,” the peak potential setting unit 5 sets a potential, which is the negative of a potential of L1 to L5 (L1<L2<L3<L4<L5) that is determined based on the respective values of the accumulated running time signal RT and the black display cell count signal BN as shown in
More specifically, as shown in
When the number of black display cells BN is equal to or greater than a predetermined number “b,” the peak potential setting unit 5 sets a potential, which is the negative of a potential of “L” that decreases as the accumulated running time indicated by the accumulated running time signal RT decreases, as the negative peak potential PV of the reset pulse RP2Y2.
When the number of sustain pulses allocated to the subfield SF2 is less than a predetermined number of “3” as shown in
As described above, the peak potential setting unit 5 sets the negative peak potential PV of the reset pulse RP2Y2 such that the absolute value of the negative peak potential PV decreases (moves toward 0V) as the number of discharge cells in a black display state “BN” increases. Accordingly, a voltage applied between row electrodes Y and X upon application of the reset pulse RP2Y2 in the rear side of the second reset process R2 shown in
However, as the intensity of the reset discharge decreases (i.e., the reset discharge is weakened), it is difficult to fully erase wall charges in the second reset process R2 and thus the amount of remaining wall charges may become greater than a predetermined amount (expected amount). Then, discharge cells in which no write addressing discharge occurs in the second selective write addressing process W2W immediately after the second reset process R2 (i.e., discharge cells that should be in a non-emission mode) may undergo an erroneous sustain discharge in the sustain process I immediately after the second selective write addressing process W2W. Particularly, we found that the probability of occurrence of such an erroneous sustain discharge increases as the number of sustain pulses repeatedly applied in the sustain process I increases whereas it decreases as the number of applied sustain pulses decreases. We also found that, even though such an erroneous sustain discharge occurs, it is not visually perceived since luminance is not high when the number of sustain pulses is small (when the number of sustain pulses applied in the sustain process I is small).
Thus, when the number of sustain pulses “SN” allocated in the sustain process I is less than a predetermined number of “3,” the peak potential setting unit 5 sets the absolute value of the negative peak potential PV of the second reset pulse RP2Y2 to a lower value (one of L1 to L4) since an erroneous discharge hardly occurs or an erroneous discharge is not noticeable even if it occurs. Accordingly, the reset discharge is weakened to achieve an increase in the dark contrast. On the other hand, when the number of sustain pulses “SN” allocated in the sustain process I is equal to or greater than the predetermined number “3,” the peak potential setting unit 5 sets the absolute value of the negative peak potential PV of the reset pulse RP2Y2 to a higher value (L5) than when the number of sustain pulses “SN” is less than “3.” Accordingly, the intensity of the reset discharge is increased to the extent that the amount of wall charges remaining in all the discharge cells becomes less than a predetermined amount to prevent the occurrence of such an erroneous discharge.
In addition, plasma display panels have a tendency that sufficient discharges become difficult to occur after extensive accumulated running time.
Thus, as the accumulated running time signal RT increases, the peak potential setting unit 5 increases the absolute value of the negative peak potential PV of the reset pulse RP2Y2 to increase the intensity of the reset discharge, thereby preventing the occurrence of the erroneous discharge.
The Y electrode driver 53 includes a second reset pulse generation circuit as shown in
As shown in
According to a peak potential setting signal RPS received from the peak potential setting unit 5, the peak control circuit CNT supplies a switching signal SW1 to the switching element S1 to turn the switching element S1 on or off. When performing a peak potential control drive mode C (will be described below), the peak control circuit CNT supplies a power source voltage change signal PW1 to the DC power source B1 to change a potential PVMAX generated by the DC power source B1 to another negative potential according to the peak potential setting signal RPS. When performing a peak potential control drive mode D (will be described below), the peak control circuit CNT supplies a resistance change signal RC1 to the variable resistor VR1 to change resistance of the variable resistor VR1 according to the peak potential setting signal RPS.
When a switching signal SW1 (for example, a signal SW1 having a logic level of “1”) indicating an on state is supplied to the switching element S1, the switching element S1 is turned on to permit the negative potential PVMAX generated by the DC power source B1 to be applied to all the row electrodes Y through the variable resistor VR1. When a switching signal SW1 (for example, having a logic level of “0”) indicating an off state is provided to the switching element S1, the switching element S1 is turned off to set all the row electrodes Y to a high impedance state.
The peak control circuit CNT performs control based on one of the peak potential control drive modes A to D (will be described below) to generate, on row electrodes Y, a second reset pulse RP2Y2 having a negative peak potential PV indicated by the peak potential setting signal RPS.
In the peak potential control drive mode A, the peak control circuit CNT keeps the switching element S1 in the on condition during a period according to the peak potential setting signal RPS. For example, when the switching element S1 is set to the on condition during a period TQMAX as shown in
In the peak potential control drive mode A, flickering may occur since the pulse width of the second reset pulse RP2Y2 varies depending on the peak potential setting signal RPS. In this case, a period required for the addressing process (W1W, W2W, WD) in each of the subfields SF1 to SF14 is extended by a time by which the pulse width of the second reset pulse RP2Y2 has been reduced, so as to prevent such flickering.
In the peak potential control drive mode B, the peak control circuit CNT keeps the switching element S1 to the on condition during a period according to the peak potential setting signal RPS. For example when the switching element S1 is set to the on condition during a period TQMAX as shown in
In the peak potential control drive mode C, the peak control circuit CNT keeps the switching element S1 to the on condition during the period TQMAX and changes a negative potential PVMAX, which is to be generated by the DC power source B1, to another potential in response to (or based on) the peak potential setting signal RPS. Thus, when the negative potential PVMAX which is to be generated by the DC power source B1 is changed to a potential PV1 smaller than the potential PVMAX in the peak potential control drive mode C, a second reset pulse RP2Y2 having a waveform in which the potential of the row electrodes Y reaches the negative peak potential PV1 earlier than in the case of
In the peak potential control drive mode D, the peak control circuit CNT keeps the switching element S1 in the on condition during the period TQMAX and changes the resistance of the variable resistor VR1 in response to (or based on) the peak potential setting signal RPS. Thus, in the peak potential control drive mode D, as the resistance of the variable resistor VR1 increases, the potential change rate during the falling edge of the second reset pulse RP2Y2 drops so that a value that the negative peak potential finally reaches decreases correspondingly as shown in
Although the reset pulses RP1Y1 and RP2Y1 are applied to the row electrodes Y1 to Yn in the front sides of the reset processes R1 and R2 shown in
For example, the first reset process R1 shown in
Although the peak potential setting circuit 5 uses the accumulated running time signal RT, the sustain pulse count signal SN, and the black display cell count signal BN as parameters for generating the peak potential setting signal RPS in the above-described embodiments, the accumulated running time signal RT may be omitted from these parameters.
Although the number of sustain pulses that are to be applied in the sustain process I of the subfield SF2 is exemplified by “1” (in the example shown in
An external optical sensor (not shown) may be installed for detecting luminance of ambient regions around the screen of the PDP 50. When the luminance of ambient regions is higher than a predetermined level, the peak potential setting circuit 5 may fixedly set the negative peak potential of the second reset pulse RP2Y2 to a negative potential having a larger absolute value (for example, a potential L5 shown in
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various changes, modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
This application is based on Japanese Patent Application No. 2008-64243 filed on Mar. 13, 2008 and the entire disclosure thereof is incorporated herein by reference.
Number | Date | Country | Kind |
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2008-064243 | Mar 2008 | JP | national |
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