JP5207685B2 - Display device and driving method thereof - Google Patents

Description

  The present invention relates to a display device in which self-emitting elements are arranged in a matrix and a driving method thereof. In particular, the present invention relates to an active matrix display device that performs display using a self-luminous element such as an EL (electroluminescence) element that blinks and an electric circuit that arbitrarily controls a light emission period, and a driving method thereof. About.

  In recent years, thin display devices using organic EL have attracted attention as self-luminous high-luminance displays. Since it is self-luminous, unlike a liquid crystal display device, a backlight is unnecessary. In addition, since the entire display panel can be thinned to about 1 to 2 mm, the size and weight can be reduced. Furthermore, there are no restrictions on viewing angle, fast response speed, high brightness, high contrast, and low power consumption. Therefore, it is regarded as a promising candidate for the next generation display. Organic EL displays are currently being applied to small displays for mobile devices (portable information devices) such as digital cameras and mobile phones. Furthermore, in the future, it is considered to be applied to medium- and large-sized displays such as PC monitors and televisions. Since mobile devices can be easily carried both indoors and outdoors, it is necessary to realize optimal display images in various usage environments from dark places such as in rooms to bright places such as outdoors in the sun. Further, since the PC monitor and the television are used under various environments by the user, it is necessary to realize an optimal display image.

  In a display device such as a CRT, a liquid crystal display, or an organic EL display, a refresh operation is performed to rewrite a video frame to be displayed several tens of times per second, and the rewrite frequency of this frame is called a refresh rate. Flickers occur when the refresh rate is low. Therefore, the refresh rate of these display devices is normally set to a frequency (60 Hz) at which no flicker occurs. By the way, the liquid crystal display device inverts the polarity of the voltage applied to the pixel electrode for each frame with respect to the reference voltage, inverts the polarity for each horizontal pixel line, or inverts the polarity for each display pixel. Flicker is suppressed by the driving method.

  On the other hand, an organic EL display device uses a self-luminous display element for each pixel, and emits light by displaying a current by passing a current through each light-emitting element. The brightness of the display screen can be set according to the light emission time and light emission intensity occupying one frame. Depending on the frequency of light emission and the ratio of light emission time to non-light emission time in one frame (duty ratio), a person visually recognizes the difference between light emission (bright part) and non-light emission (dark part), which is the flicker ( It is recognized as flicker). Therefore, even if the refresh rate of the image to be displayed is displayed at 60 Hz, the display screen flickers depending on the duty ratio, and the display quality deteriorates.

  Therefore, flicker does not occur by increasing the refresh rate of the video to be displayed. However, the operation speed of the drive circuit has to be increased, power consumption is increased, and the use member (such as an electronic component) and the drive circuit are significantly changed accordingly.

  For this reason, Patent Document 1 discloses a driving method that suppresses flicker without increasing the refresh rate, although it is a duty driving method that controls the brightness of the display screen by the duty ratio of the light emission time. This driving method is a driving method that suppresses flicker by dividing one frame into a plurality of subframes by light emission control and emitting light for each light emission period corresponding to the duty ratio in each subframe.

  Further, as a driving method for performing gradation display by the same blinking driving, there is a subfield method. In this method, one field corresponding to one image is divided into a plurality of subfields. Then, the ratio of the light emission sustain period in each subfield is set to a power of 2, and multi-gradation display is performed by a combination of these subfields. If the ratio of the light emission sustaining periods of the eight subfields SF1, SF2,..., SF8 is set to 1: 2: 4: 8: 16: 32: 64: 128, 256 gradations are realized by combining the subfields. Is possible. A technique related to the subfield method is disclosed in Patent Document 2, for example.

In this driving method, for the purpose of obtaining a good gradation display, the light emission period is divided into a plurality of periods, and the length of each light emission period is changed to a specific length (generally 2 to the power of n). However, this driving method is not related to the problems and objects of the present invention. Further, this driving method is a technique that is not related to the present invention because the gradation display means is different in that gradation display is controlled by the light emission period.
JP 2006-30516 A JP 2001-222257 A

  However, when the display device driving method described in Patent Document 1 is driven to blink at a certain duty ratio, the total amount of current flowing through the display region varies with time, and this current variation affects a power source impedance having a finite value. Cause power fluctuations. When one frame (or one field) is divided into a plurality of subframes (or subfields) and the light emission period is divided, the power supply fluctuation and the light emission period are synchronized, and luminance fluctuation occurs in the display area. As a result, the image quality is degraded.

  In addition, the subfield driving method of the display device described in Patent Document 2 divides the light emission period into a plurality of parts for the purpose of obtaining good gradation display, and sets the length of each light emission period to a specific length (generally, However, there is a problem that the gradation and the overall luminance cannot be set independently.

  If it is to be executed, it is necessary to divide the light emission period further and control it. This is not preferable because high-speed operation is essential for driving. For example, when displaying 256 gradations, at least the field period is divided into 1/256, but if the overall luminance is further changed to 10 levels, it is necessary to divide at least the field period into 1 / (256 × 10). There is. Moreover, it is not related to the problems and objects of the present invention, and is a technique different from the present invention.

  In the description of the present invention, the field period is defined as a minimum unit period until data necessary for displaying one image is input to a pixel to emit light and the next image data is input. In the field period, a period from the end of the row scanning period to the end of the field period is defined as a vertical blanking period.

  FIG. 13 illustrates the variation in the total amount of current flowing in the display area during duty driving. The TS signal is a light emission control signal for the first row of the display area. If Hi, light is emitted, and if Low, no light is emitted.

  In the display area, pixels are arranged in a two-dimensional form of m rows × n columns. Here, m and n are natural numbers. Data is line-sequentially written into the pixels, a signal for selecting a row to be written is scanned by m rows, and the TS signal is also scanned by each row sequentially.

  The light emission pattern of FIG. 13 represents the blinking timing in a plurality of rows at equal intervals in the display area. The top row of the display area has the same light emission pattern as the TS signal shown at the top of FIG. Further, the start of light emission is delayed for each row at a constant interval by the scanning time of that interval.

  The non-display area indicated by the broken line at the bottom in FIG. 13 represents a virtual scanning blinking signal during the vertical blanking period, and there is no row that is actually scanned and emits light at this timing.

  ΣI represents the sum of currents flowing through the light emitting elements emitting light in each row at each timing, that is, the total amount of current flowing through the display area (referred to as ΣI).

  As shown in FIG. 13, ΣI varies with time. Hereinafter, the fluctuation of ΣI will be described in detail.

  FIG. 16 shows the time change of blinking, the time change of ΣI, and the luminance distribution when the light emitting area moves from the top to the bottom of the display area. FIG. 13 shows a case where light emission is performed once in one field period, but FIG. 16 shows a case where light emission is performed twice in one field period.

  In the pattern 101, the horizontal direction represents the position in the row scanning direction (vertical direction of the display area), and the vertical direction represents time. The white part means light emission, and the black part means non-light emission. The TS signal in FIG. 13 corresponds to the black and white pattern at the left end of 101.

  A time change 102 of the total current ΣI is shown on the right side of the light emission pattern 101. The vertical axis represents time, which coincides with the time in the light emission pattern 101 in the display area. ΣI alternately repeats a period 105 in which the value is large and a period 106 in which the value is small. Reference numeral 103 denotes a vertical blanking period.

  For a while after the first line of the display area (the left end of 101) turns from lighting to extinction, the number of lit lines and the number of unlit lines are constant along the vertical direction (the horizontal axis of 101) in the display area. Takes a constant value. During this period 105, two illuminated rows move from the top to the bottom of the display area. The number of lit rows is greater than the number of unlit rows, and the difference is equal to the number of virtual scans during the vertical blanking period.

  After that, when the first row in the display area is turned off and the last row is turned on from turning off, the number of lit rows is reduced and the number of turned off rows is increased. For this reason, ΣI decreases. Since the decrease in the lit row and the increase in the unlit row are changes at a constant rate with time, ΣI shows a linear change with respect to time.

  When the first row enters the lighting period, the number of lit rows and unlit rows becomes constant again. This period 106 is a period in which two bands of unlit rows move from the top to the bottom of the display area. Therefore, the number of lit rows is small and the number of unlit rows is large compared to the period 105. (The difference is also equal to the number of virtual scans during the vertical blanking period.) Therefore, the value of ΣI is smaller than the period of 105.

  Thereafter, while the first row of the display area is kept lit, when the last row turns off, the number of lit rows increases and the number of unlit rows decreases thereafter. For this reason, ΣI increases.

  The above is one cycle of time variation of ΣI. Thus, when there is a vertical blanking period, the difference between the lit row and the unlit row in the display area changes. This is the cause of the fluctuation of ΣI.

  Since the power supply has a power supply impedance peculiar to the apparatus, when ΣI fluctuates, the power supply voltage drops according to the product of the power supply impedance and ΣI, resulting in power supply fluctuation.

  When the power supply voltage drops, the luminance changes. One of the causes is the current-voltage characteristic of the drive transistor. FIG. 14 shows Vds-Ids characteristics of a driving TFT (Thin Film Transistor). When the TFT saturation region is used to drive the light emitting element, a voltage drop causes a decrease in current due to Early characteristics. As a result, the current flowing into the self-luminous element is reduced, causing a reduction in luminance.

  Another cause of the luminance change is the current-voltage characteristic of the self-luminous element. FIG. 15 shows voltage-current characteristics of a typical organic EL element. When the voltage applied to a light emitting element such as an organic EL is reduced, the current is also reduced, causing a reduction in luminance.

  Depending on the configuration of the pixel circuit, when the power source drops, the current flowing into the self-light-emitting element may increase and the luminance may increase. In the following, a circuit configuration in which the luminance decreases as the power source decreases is considered.

  Below the light emission pattern 101 in FIG. 16 is a diagram showing how the luminance change looks on the display device.

  Since the total amount of current is large during the period 105 and the power supply is lowered, the luminance at the position where light is emitted during this period is lowered. Further, since the total amount of current is small during the period 106 and the power supply is not lowered, the luminance at the position where light is emitted during this period is brighter than the other positions. A result obtained by integrating these luminance fluctuations in the field period is 104. Since the time variation of ΣI due to the light emission pattern and the movement of the light emission pattern are synchronized, the luminance decreases at a specific position in the row scanning direction, and it appears as a light and dark pattern whose position is fixed on the display screen. Such brightness non-uniformity causes image quality degradation.

  The magnitude of this luminance change is determined by integrating a plurality of factors such as the magnitude of the power supply impedance, the sensitivity to the voltage drop of the pixel circuit, the influence of the TFT characteristics, and the efficiency of the self-light emitting element.

  FIG. 17 shows a temporal change in ΣI and the light emission luminance at each position (1)-(4) in the light emission pattern of FIG. That is, FIG. 17 shows the light emission control signal TS, the total amount of current ΣI flowing into the display area depending on the light emission timing, the light emission timing of the positions (1) to (4) of a certain row in the display area, and the luminance at that time. The time change of is shown. Regarding the light emission timing and luminance, the Low side is extinguished, the Hi side emits light, the middle means light is emitted slightly darker, and the slanted line is an explanatory diagram in which the luminance gradually changes.

  The position (1) represents the state of light emission in the first row of the display area, and has the same light emission pattern as the TS signal. Each of (2) to (4) is a state of light emission at a position shifted downward by 1/4 in the vertical direction of the display area from (1), and when a row is shifted by row scanning, the time Thus, the light emission start of the TS signal is delayed, and the light emission timing changes depending on the row as shown in the figure. Focusing on the fluctuation of ΣI, the period 106 with a small ΣI in FIG. 16 corresponds to the periods P1, P2, P1 ′, and P2 ′ in FIG.

  At position (1), light emission starts immediately after the start of the field period, and as shown in FIG. 16, the first half of the light emission period (period P1) is a period during which ΣI is small and constant and the power supply voltage is kept high. Therefore, it emits light with high luminance. However, since the power supply voltage decreases with the increase of ΣI from the middle, the light emission luminance also decreases. The second light emission also has a similar light emission pattern.

  At position (2), light emission starts at a position where ΣI is high, so light is emitted at a slightly lower luminance. Thereafter, the luminance slightly increases as ΣI decreases. The second light emission also has a similar light emission pattern.

  In the positions (3) and (4), the light emission start timing is delayed by 1/2 field period with respect to the positions (1) and (2), respectively, but the light emission patterns are exactly the same.

  At position (2) and position (4), the fluctuation in which ΣI is rising and the light emission period are synchronized, and there is almost no bright light emission period. As a result, a large difference occurs in the amount of light emission in each row integrated in a certain time (for example, one field period), and a luminance change occurs in the row direction in the display area as indicated by 104 in FIG. Is causing.

  The present invention relates to a display device that performs periodic blinking driving, and an object thereof is to provide a driving method of a display device that performs good display while suppressing deterioration in image quality caused by power supply fluctuations.

  In this specification, the “light emission cycle” refers to one continuous period including one lighting period and one light-off period. The lengths of the turn-on and turn-off periods in one light emission cycle are not necessarily the same. The ratio of the lighting period in one light emission cycle is called a lighting duty.

  Further, in this specification, the “light emission pattern” refers to a section division method and switching timing when one field period is divided into several sections and light emission and extinction are switched alternately. The light emission period and the light extinction period in this case do not depend on the display signal of each pixel, but are a section in which light emission can be controlled in units of rows and a section in which light emission is prohibited. The light emission pattern is such that one field is divided in half, the first half is turned on, the second half is turned off.

The display device driving method according to the present invention includes an image display unit in which pixels including light emitting elements are two-dimensionally arranged in a row direction and a column direction, and sequentially shifts time from the pixels in the first row. A driving method of a display device that emits light from the light emitting element included in the pixel,
The light emission luminance of the light emitting element is determined by an image signal,
In one field, the light emitting element is caused to emit light by a first light emission period and a second light emission period, and the length of the first light emission period and the length of the second light emission period, and the first At least one of the duty ratio of the light emission period and the duty ratio of the second light emission period is different from each other.

The display device according to the present invention includes an image display unit in which pixels including a light emitting element and a pixel circuit that drives the light emitting element are two-dimensionally arranged in the row and column directions;
A scanning line and a light emission period control line provided in common for pixels included in the same row;
A row control circuit connected to the scan line and the light emission period control line;
A data line provided in common for pixels included in the same column;
A column control circuit connected to the data line;
A display device comprising:
The column control circuit outputs gradation signal data corresponding to the light emission luminance of the light emitting element to the data line,
The row control circuit outputs, to the scanning lines, scanning signals for causing the light emitting elements included in the pixels of each row to emit light in order from the pixels in the first row while shifting the time. Light is emitted in one light emission cycle and a second light emission cycle, and the length of the first light emission cycle, the length of the second light emission cycle, the duty ratio of the first light emission cycle, and the second light emission. A light emission period control signal for making at least one of the duty ratios of the periods different from each other is output to the light emission period control line.

  In the present invention, in order to suppress flicker while performing duty driving, a light emitting period and a light emission start timing are determined with respect to a display device that performs blinking driving by shifting the phases of the light emission period and the power supply fluctuation period. As a result, it is possible to suppress the self-light emitting element from emitting light only at the timing when the power source is lowered or from emitting light only when the power source is high. That is, light emission is performed at the timing when the power source is lowered and when the power source is not lowered within the field period, and the luminance uniformity in the display region is improved, so that a good display can be performed.

  Hereinafter, the best mode for carrying out a display device according to the present invention will be specifically described in Embodiments 1 to 5 with reference to the drawings. This embodiment is a driving method that is applied to an active matrix display device using an EL element, and that can display favorable while performing blinking driving. In each example, an organic EL display device using an EL element will be described as an example. However, the display device of the present invention is not limited to this, and an apparatus that can control light emission of a self-light emitting element. If so, it is preferably applied. In the display device according to the present invention, the light emission intensity of the EL element which is a light emitting element is determined by the image signal.

  FIG. 1 shows the overall configuration of a display device according to this embodiment.

  In FIG. 1, the image display unit includes a pixel 1 including an EL element having the number of RGB primary colors and a pixel circuit 2 (see FIG. 2) that includes a TFT for controlling a current input to the EL element. Then, they are arranged two-dimensionally in m rows × n columns. Here, m and n are natural numbers. A row control circuit 3 and a column control circuit 4 are provided around the display area. Scan signals P1 (1) to P1 (m) and light emission period control signals P2 (1) to P2 (m) are output from the output terminals of the row control circuit 3. The scanning signal is input to the pixel circuits 2 in each row via the scanning line 5. The light emission period control signal is input to the pixel circuits 2 in each row via the light emission period control line 6. A video signal is input to the column control circuit 4, and a voltage signal Vdata that is gradation display data is output from each output terminal. The voltage signal Vdata which is gradation display data is input to the pixel circuits in each column via the data line 7.

  FIG. 2 shows a configuration example of the pixel circuit 2 including the EL element of this embodiment.

  In FIG. 2, P1 is a scanning signal, and P2 is a light emission period control signal. A voltage signal Vdata which is gradation display data is input as a data signal. The anode (anode) of the EL element is connected to the drain terminal of the TFT (M3), and the cathode (cathode) is connected to the ground potential CGND. M2 and M3 are P-type TFTs, and M1 is an N-type TFT.

  FIG. 3 is a timing chart for explaining a driving method of the pixel circuit 2.

  In FIG. 3, V (i−1), V (i), and V (i + 1) are i−1 line (1 line before), i line (target line), and i + 1 line (1 line after) in the field unit. The voltage data Vdata input to the pixel circuit 2 in the target column is shown.

  First, at a time point before time t0, a low level signal is input to the pixel circuit 2 in the target row and a high level signal is input to the light emission period control signal P2, and the transistor M1 is turned off and M3 Is in an OFF state. In this state, V (i−1) corresponding to the voltage signal Vdata, which is the gradation display data of the previous row, is not input to the pixel circuits 2 in the target row.

  Next, at time t0, a high level signal is input to P1, a high level signal is input to P2, and the transistor M1 is turned ON and M3 is turned OFF. In this state, V (i) corresponding to the voltage signal Vdata which is the gradation display data of the corresponding row is input to the pixel circuit 2 of the m row. The input voltage Vdata is charged into the capacitor C1 disposed between the gate terminal of M2 and the power supply potential VCC.

  Next, at time t1, a low level signal is input to P1, a low level signal is input to P2, and M1 is OFF and M3 is ON. In this state, since M3 is in a conductive state, a current corresponding to the current driving capability of M2 is supplied to the EL element by the voltage charged in C1. As a result, the EL element emits light with a pattern as shown in FIG. 3D at a luminance of gradation corresponding to the supplied current.

  Next, at time t2, a high-level signal is input to P2, M3 is turned off, current supply to the EL element is stopped, and a non-light-emitting state is entered. The light emission period is controlled by changing the period when P2 is at the low level and the time when the P2 is at the low level.

  Next, at time t3, a low level signal is input to P2, M3 is turned on, a current is supplied to the EL element, and a light emission state is obtained. The non-light emission period is controlled by changing the period during which P2 is at a high level.

  The period P1 from time t0 to time t1 is a period related to scanning of one row, and this period is called one scanning period. Further, a light emission cycle is a sum period of a set of continuous periods of P2 being low level and high level specified from time t1 to time t3.

  In the present embodiment, the configuration of FIG. 2 is given as an example of the pixel circuit, but is not limited thereto.

  FIG. 4 is an example of a timing chart illustrating a method for driving a display device according to the present invention.

  In FIG. 4, P1 (1) to P1 (m) indicate scanning signals P1 corresponding to the first to mth rows, respectively. P2 (1) to P2 (m) indicate light emission period control signals P2 corresponding to the first to mth rows, respectively.

  In the row scanning period, the scanning signals P1 (1), P1 (2), P1 (3),..., P1 (m) of the first row, the second row, the third row,. Are sequentially set to the high level for each scanning period. During this High level period, the voltage signal Vdata which is gradation display data is input to the pixel circuit 2.

  The light emission period control signal P2 is in a low level period after the voltage signal Vdata which is gradation display data is input, and enters a light emission state. Thereafter, a High level period is entered, and a non-light emitting state is entered. The sum of one light emission period and non-light emission period is the light emission period, and light emission and non-light emission are repeated during the field period.

  In the example of FIG. 4, after the light emission cycle having the length of the light emission cycle A (first light emission cycle) is repeated once or a plurality of times, the last light emission cycle of the field period is shorter than the others, and the light emission cycle B ( The second light emission period) is set.

  That is, this embodiment is characterized in that the field period is composed of a plurality of light emission periods having different lengths.

  FIG. 5 shows, as one example of this embodiment, a case where there is one light emission period A and one light emission period B shorter than that in the field period. That is, FIG. 5 shows the light emission control signal TS and the total current amount ΣI flowing into the display area. Further, FIG. 5 shows the light emission timing of the positions (1) to (4) of a certain row in the display area, the luminance at that time, and the respective time changes.

  Position (1) represents the state of light emission in the first row of the display area, and has the same light emission pattern as the TS signal. Each of (2) to (4) shows the state of light emission at a position shifted down by m / 4 rows. When a row is shifted by row scanning, the light emission start of the TS signal is delayed by that time. As shown in FIG. 5, the light emission timing changes depending on the row.

  At position (1), light emission starts immediately after the start of the field period, and the period when ΣI is Q1 is a period during which the power supply fluctuation is small, so light is emitted with high luminance. However, as ΣI increases from the middle, the power supply drops, and the light emission luminance also decreases. After that, the light emission period B is short and the light emission period B is short, but light is emitted in the same light emission pattern. At position (2), light emission starts at the end of Q1 and emits light with high brightness. However, as ΣI rises, brightness immediately decreases, and when ΣI is stable at a high position, it is stable at slightly lower brightness. Emits light. Then, most of the second light emission corresponding to the pulse of the light emission period B is light emission in the Q1 'period of the next field, and light is emitted brightly. The positions (3) and (4) also emit light while the luminance changes according to the fluctuation of ΣI.

  In the driving method with the same light emission period, the period in which ΣI takes a large value coincides with the light emission period at a specific position as in position (2) or position (4) in FIG. As in (3), the period in which ΣI takes a small value coincides with the light emission period at another specific position, and a large luminance difference occurs between them. By changing the length of the light-emission period and driving without shifting the phase of the ΣI and the phase of the light-emission pattern to synchronize, it is possible for any row to have a bright light-emission period for at least some period Become. As a result, it is possible to suppress a difference in light emission amount in each row integrated in a certain time (for example, one field period), to suppress a luminance change in the display region, and to obtain a good image quality.

  FIG. 6 illustrates changes in luminance in the row direction within the display area including the positions (1) to (4). 10 is the luminance variation of this embodiment, and 11 is the luminance variation when the light emission periods in FIG. 13 are equal. It can be seen from FIG. 6 that fluctuations in luminance are suppressed in this embodiment.

  In the present embodiment, the display device having the configuration shown in FIG. 1 is illustrated. However, the present invention is not limited to this, and a driving method in which light emission periods having different lengths exist in the field period as shown in FIG. 4 or FIG. Any configuration can be used.

  Further, FIG. 5 shows an example in which the duty ratio is approximately 50%. However, if there are those with different light emission periods in the field period, the ratio (duty ratio) of the light emission period in each light emission period. Can be any ratio.

  Moreover, if the duty ratio of each light emission period is the same, even if the light emission period is changed, the sum of the light emission periods is maintained, so that the luminance hardly changes. Therefore, it is more preferable that the luminance other than the gradation can be easily changed by setting the duty ratio. However, when the present embodiment is implemented with a logic circuit, it is necessary to adjust the light emission period so that the count value of the light emission period becomes an integer, such as when the count value of the light emission period calculated from the duty ratio is not an integer. . Therefore, even if the duty ratios are not completely the same, the above convenience is not impaired.

  As described above, according to the present embodiment, the light emission control signal is provided so that there are those having different light emission periods in the field period. Therefore, it is possible to suppress the light emission timing in each row from synchronizing with ΣI, and to reduce the rows that emit light only with low luminance in most light emission periods. In other words, it is possible to disperse the timing at which bright lines shine in almost all rows in the display area. In this way, it is possible to obtain a good display by suppressing the luminance difference in each row and suppressing the luminance change in the display area.

  The entire configuration of the display device in this embodiment is the same as that in FIG. 1, and the pixel circuit 2 and the driving method thereof are also the same as those in FIGS.

  FIG. 7 is a timing chart illustrating an example of another driving method of the display device according to the present invention.

  In FIG. 7, P1 (1) to P1 (m) indicate scanning signals P1 corresponding to the first to mth rows, respectively. P2 (1) to P2 (m) indicate light emission period control signals P2 corresponding to the first to mth rows, respectively. What is different from the driving method described in the timing chart of FIG. 4 is the waveform of the light emission period control signal P2.

  The light emission period control signal P2 in this embodiment is set to a waveform that is driven with a light emission pattern in which at least one light emission period is different from other light emission periods. Alternatively, the light emission period control signal P2 is set to a waveform that is driven with a light emission pattern in which at least one extinction is different from other extinction periods.

  In FIG. 7, as an example, the light emission periods A and A ′ have the same length, and the light emission period of the light emission period A ′ within the field period is set longer than the other. As another example, the light emission periods A and A ′ may have different lengths.

  FIG. 8 shows another example of the light emission period control signal P2 as another example of this embodiment. FIG. 8A shows a waveform that forms a periodic light emission pattern, which is a conventional driving method.

  On the other hand, FIG. 8B is an example of a waveform in which the light emission end timing is changed within the hatched area in the figure while the light emission start timing in the light emission period 2 is maintained and the light emission end timing is varied. . The length of the light emission period 2 may be changed as long as the non-light emission period 2 is not lost. FIG. 8C shows an example of a waveform in which both the second light emission start timing and the light emission end timing are varied within the shaded area in the figure and the length of the light emission period is changed. FIG. 8D shows a waveform in which the second light extinction start timing is maintained and the light emission start timing is varied within the hatched range in the figure, and the length of the first light extinction period is changed. The length of the extinguishing period 1 may be changed as long as the light emitting period 2 is not lost. FIG. 8E shows an example of a waveform in which both the end timing of the first light emission period and the start timing of the second light emission period are varied within the hatched range in the figure, and the length of the first light extinction period is changed. is there.

  Although FIG. 8 illustrates an example in which the light emission period is only twice in the field period, the light emission period and the light-off period may be N times (N is a natural number). Further, the light emission period or the light extinction period for changing the length or timing may be any light emission period or light extinction period in the field period, and the length or timing of the N-1 light emission periods may be changed individually. Further, the length and timing of the maximum N−1 extinguishing periods may be individually changed. Further, the length and timing of the maximum N-1 light emission periods and the maximum N-1 extinguishing periods may be individually changed.

  In addition, when the length of the light emission period or the light extinction period is changed, the luminance is also changed by the change of the light emission time. Therefore, when light is emitted at a desired duty ratio using the driving method of this embodiment, a pattern of a light emission period control signal corresponding to the desired duty ratio is recorded in advance in a storage element or the like, and the duty ratio is set at the time of light emission. The light emission period control signal may be output using a corresponding pattern.

  As described above, according to the present embodiment, the light emission period control signal P2 is driven with a light emission pattern in which at least one of at least one light emission period or at least one extinction period is different from the other periods. Set to waveform. Thereby, the time change of ΣI, that is, the synchronization between the power supply fluctuation and the light emission pattern can be suppressed. In addition, the timing of bright emission can be distributed to each row in the display area. Therefore, it is possible to suppress the luminance difference between the rows and obtain a good display.

  The overall configuration of the display device in this embodiment is the same as that in FIG. 1, the pixel circuit 2 and its driving method are the same as those in FIGS. 2 and 3, and an example of a timing chart for explaining the driving method is the same as that in FIG. Therefore, the description and drawings are omitted.

  In FIG. 9, there are a plurality of light emission periods within the field period, and while maintaining the duty ratio, one light emission period (light emission period C) is short for (A) to (E), and conversely, (F) is long. It is the waveform of the changed light emission period control signal P2. The lengths of the other light emission periods are changed by changing the length of the light emission period C. In FIG. 9A, the light emission periods are all equal. In FIG. 9C, the light emission period C is approximately half the length of the other light emission periods. In FIG. 9E, there is no light emission period C and all other light emission periods are equal. In FIG. 9F, the light emission period C is approximately twice as long as the other light emission periods.

  FIG. 10 is a graph obtained by calculating the in-plane luminance difference of the display area when the driving of FIG. 9 is performed. The horizontal axis represents the length of the light emission cycle C, and the vertical axis represents the in-plane luminance difference of the display area. Plotting is performed while changing the length of the light emission period C, and FIGS. 10A to 10F correspond to the case of driving with the waveforms of FIGS. 9A to 9F. It can be seen that the in-plane luminance difference varies depending on the drive pattern.

  As shown in FIG. 10, in order to suppress the in-plane luminance difference, the light emission periods in the field period are not all equal as shown in FIGS. 9A and 9E, and the length is longer than other light emission periods. However, it suffices if there are different light emission periods.

  Further, as shown in FIG. 9C and FIG. 9F, if at least one light emission period is nearly twice as long as the other light emission periods in the field period, the other driving is performed. The in-plane luminance difference can be suppressed more than the pattern, which is preferable.

  However, the present invention does not require that one light emission period be exactly twice the other light emission period. The gist of the present invention is to make the in-plane luminance difference smaller than the in-plane luminance difference of (E) and (A) in which the light emission periods are all equal.

  For this purpose, the effect of the present invention can be obtained if the in-plane luminance difference can be suppressed to an intermediate level of (A) and (C), or (E) and (C), or (A) and (F). It is possible to get enough. From the simulation result of FIG. 10, it is lower than the intermediate value (B) from the relationship between (A) and (C), and is the intermediate value from the relationship between (E) and (C) (D A method for setting such a light emission period lower than () is expressed as follows.

When there is at least one light emission period A and at least one light emission period B within the field period,
Light emission cycle A × 1/4 ≦ Light emission cycle B ≦ Light emission cycle A × 3/4
By driving with a light emission period control signal having a light emission period that satisfies this relationship, the in-plane luminance difference can be suppressed and a good display can be obtained.

  As described above, according to this embodiment, the effect of the present invention can be sufficiently obtained if a certain light emission period is different in length from other light emission periods. In addition, when one light emission period is approximately twice as long as another light emission period, a more preferable effect of the present invention is obtained, and it is possible to suppress a luminance difference in the light emission region and obtain a good display.

  The overall configuration of the display device in this embodiment is the same as that in FIG. 1, the pixel circuit 2 and its driving method are the same as those in FIGS. Therefore, the description and drawings are omitted.

  FIGS. 11A and 11B are the same as FIGS. 8A and 8C. (G) and (H) are examples of the waveform of the light emission period control signal P2 in which there are a plurality of light emission periods in the field period and the light emission period is changed while maintaining the duty ratio. (G) has three types of light emission periods (a first light emission period, a second light emission period, and a third light emission period).

  This embodiment is an example of a driving method in which a plurality of light emission periods are changed.

  12A to 12F indicate the same positions as in the case of driving with the waveforms of FIGS. 9A to 9F. For FIGS. 12G and 12H, the horizontal axis has no meaning and is plotted on the same graph for comparison with (A) to (F). 12G and 12H, the in-plane luminance difference is smaller than that of FIGS. In (A) to (F), only one of the plurality of light emission periods in the field period is changed, but (G) and (H) change the length of more light emission periods. The light emission period control signal P2 is set so that the in-plane luminance difference is small.

  You may drive the light emitting element of each scanning line with the waveform of a random pattern like M series.

  As described above, according to this embodiment, a certain light emission period is different in length from other light emission periods, and even when there are a plurality of light emission periods having different lengths, the present invention is more preferable. An effect is obtained, and it is possible to suppress a luminance difference in the light emitting region and obtain a good display.

  The present embodiment is an example in which each of the above-described embodiments is used in an electronic device.

  FIG. 18 is a block diagram of an example of the digital still camera system of the present embodiment. In the figure, 50 is a digital still camera system, 51 is a photographing unit, 52 is a video signal processing circuit, 53 is a display panel, 54 is a memory, 55 is a CPU, and 56 is an operation unit.

  In FIG. 18, the video captured by the imaging unit 51 or the video recorded in the memory 54 can be signal-processed by the video signal processing circuit 52 and viewed on the display panel 53. The CPU 55 controls the photographing unit 51, the memory 54, the video signal processing circuit 52, and the like according to the input from the operation unit 56, and performs photographing, recording, reproduction, and display suitable for the situation. In addition, the display panel 53 can be used as a display unit of various electronic devices.

  The present invention relates to a display device in which self-emitting elements are arranged in a matrix and a driving method thereof. In particular, the present invention is applied to an active matrix display device that performs display using a self-luminous element such as an EL (electroluminescence) element that blinks and an electric circuit that arbitrarily controls a light emission period, and a driving method thereof. .

  For example, an information display device can be configured using this display device. This information display device takes the form of, for example, a mobile phone, a mobile computer, a still camera, or a video camera. Alternatively, it is a device that realizes a plurality of these functions. The information display device includes an information input unit. For example, in the case of a mobile phone, the information input unit includes an antenna. In the case of a PDA or a portable PC, the information input unit includes an interface unit for a network. In the case of a still camera or a movie camera, the information input unit includes a sensor unit such as a CCD or CMOS.

It is a figure which shows an example of the display apparatus which concerns on this invention. It is a figure which shows an example of the pixel circuit in the display apparatus which concerns on this invention. 3 is a timing chart for explaining the operation of the pixel circuit shown in FIG. 2. 3 is a timing chart for explaining the operation of the display device shown in FIG. 1. It is a figure which shows an example of the light emission pattern of the drive method which concerns on this invention, a power supply fluctuation | variation, and a luminance change. It is a figure which shows an example of the luminance change at the time of the drive shown in FIG. 6 is a timing chart illustrating another example of the operation of the display device illustrated in FIG. 1. It is a figure which shows the other example of the light emission pattern which concerns on the timing chart of FIG. It is a figure which shows the example of the light emission pattern of the drive method which concerns on this invention. It is a figure which shows an example of the effect of this invention in the drive of FIG. It is a figure which shows the example of the light emission pattern of the drive method which concerns on this invention. It is a figure which shows an example of the effect of this invention in the drive of FIG. It is a figure which shows an example of the drive method of the conventional display apparatus, and an electric current amount fluctuation | variation. It is a figure which shows the TFT characteristic which affects the image quality of a display apparatus. It is a figure which shows the EL characteristic which affects the image quality of a display apparatus. It is a figure which shows an example of the light emission pattern of a prior art example, a power supply fluctuation | variation, and a luminance change. It is a figure which shows an example of the light emission pattern of a prior art example, a power supply fluctuation | variation, and a luminance change. It is a block diagram which shows the whole structure of the digital still camera system using the display apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pixel 2 Pixel circuit 3 Row control circuit 4 Column control circuit 5 Scan line 6 Light emission period control line 7 Data line 11 Luminance change of the row scanning direction position at the time of the conventional drive 12 Luminance change of the row scan direction position at the time of the drive of this invention 50 Digital Still Camera System 51 Shooting Unit 52 Video Signal Processing Circuit 53 Display Panel 54 Memory 55 CPU
56 Operation unit 101 Light emission pattern 102 Total current amount change to display area 103 Vertical blanking period 104 Brightness change in row scanning direction position 105 Timing when luminance decreases 106 Timing when luminance increases

Claims (2)

A pixel including a light emitting element includes an image display unit arranged two-dimensionally in a row direction and a column direction,
An active matrix having a scanning line and a light emission period control line provided for each of a plurality of pixels included in the same row, and causing the light emitting elements included in the pixels of each row to emit light in order from the pixels of the first row while shifting time. A method for driving a display device of a type,
The light emission luminance of the light emitting element is determined by an image signal,
In one field, the light emitting element has a first light emission period, a second period that is twice the first light emission period, and a second duty ratio that is the same as the duty ratio of the first light emission period. And a light emitting period of the active matrix display device. An image display unit in which pixels including a light emitting element and a pixel circuit that drives the light emitting element are two-dimensionally arranged in the row and column directions;
A scanning line and a light emission period control line provided in common for pixels included in the same row;
A row control circuit connected to the scan line and the light emission period control line;
A data line provided in common for pixels included in the same column;
A column control circuit connected to the data line;
A display device comprising:
The column control circuit outputs gradation signal data corresponding to the light emission luminance of the light emitting element to the data line,
The row control circuit outputs, to the scanning lines, scanning signals for causing the light emitting elements included in the pixels of each row to emit light in order from the pixels in the first row while shifting the time. A light emission period control signal including a light emission period of 1 and a second light emission period having a cycle that is twice the first light emission period and having the same duty ratio as that of the first light emission period. A display device that outputs to the light emission period control line.