JP2009063654A - Display device and drive method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a drive method of a display device using a spontaneous light emitting element performing satisfactory display by suppressing a variation in luminance during flash drive. <P>SOLUTION: In the display device performing the periodic flash drive, the flash period is matched with nearly l/n times a vertical blanking period, and nearly 1/m times (n is a 1 or more natural number) by which the periodic continuity in the position and time of the flash drive is maintained, and the fluctuation in the light emission area of the display region is suppressed and the variation in the total amount of the current flowing to the display region can be suppressed and therefore, the power supply variation due to the existence of a power supply impedance can be suppressed without depending on the magnitude of the power supply impedance, and the degradation in sharpness to be induced by the power supply variation is suppressed. <P>COPYRIGHT: (C)2009,JPO&INPIT

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. In the future, they will be applied to medium and large displays such as monitors for PCs (personal computers) and televisions. Applications are being considered. Mobile devices can be easily carried both indoors and outdoors. Therefore, it is necessary to realize an optimal display image in various usage environments from a dark place such as in a room to a bright place 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, 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 rewritten at 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. Therefore, even if the refresh rate of the image to be displayed is displayed at 60 Hz, flickering of the display screen occurs depending on the light emission frequency and the ratio of light emission time to non-light emission time (duty ratio) in one frame. The display quality will deteriorate.

  Also, 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. Patent Document 1 proposes 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.
JP 2006-30516 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 in the display region varies with time, and this current variation is a power source impedance having a finite value. It affects the power supply and causes power fluctuation. 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 the description of the present invention, one field period is a period from when data necessary to display one image is input to a pixel until the next image data is input. A period from the end of the row scanning period to the end of one field period in one field period is defined as a vertical blanking period.

  FIG. 9 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 to 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. Since the TS signal is scanned in the row direction, the light emission pattern in FIG. 9 represents the blinking timing in a plurality of rows at equal intervals in the display area. FIG. 9C shows a light emission pattern in the first row of the display area, showing light emission that matches the TS signal. (D)-(g) shows the light emission pattern of each row spaced apart from it by a certain distance. In each row, the light emission start is delayed by the scanning time of the interval. (J) indicated by a broken line at the bottom of FIG. 9 represents a blinking signal of a virtual scanning line 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. 9B, ΣI varies with time. Hereinafter, the fluctuation of ΣI will be described in detail.

  FIG. 12 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. In FIG. 9, light emission is performed once in one field period, but FIG. 12 shows a case where light emission is performed four times 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. 9 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, four 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. Since this period 106 is a period in which four bands of unlit rows move from the top to the bottom of the display area, 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 changes, the power supply drops according to the product of the power supply impedance and ΣI, resulting in a power supply voltage fluctuation.

  When the power supply voltage drops, the luminance changes. One of the causes is current-voltage characteristics of the organic EL element. FIG. 10 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.

  Another cause of the luminance change is a voltage-current characteristic of the TFT. FIG. 11 shows the source-drain voltage (Vds) -drain current (Ids) characteristics of a TFT (Thin Film Transistor). When the TFT saturation region is used for driving the light emitting element, the voltage drop is caused by the early characteristics. Causes current reduction. As a result, the current flowing into the self-luminous element is 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.

  The lower side of the light emission pattern 101 in FIG. 12 shows how the luminance change at that time looks on the display device.

  Since the total amount of current is large during the period 105 and the power supply voltage is decreasing, the luminance at the position where light is emitted during this period is decreasing. Further, since the total current amount is small and the power supply voltage does not drop during the period 106, the luminance at the position where light is emitted during this period is brighter than the other positions. 104 is obtained by integrating these fluctuations in luminance for one field period.

  As indicated by the integrated luminance 104, the luminance increases at a specific position and decreases at a position in between. The place where the luminance is small is where the period in which ΣI takes a large value coincides with the light emission period. Further, the place where the luminance is maximized is where the period in which ΣI takes a small value coincides with the light emission period. A large luminance difference is created between them.

  As described above, since the time variation of ΣI due to the light emission pattern and the movement of the light emission pattern are synchronized, the luminance is lowered at a specific position parallel to the row, and a bright and dark pattern appears on the display screen. This pattern appears in a fixed position. 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.

  Therefore, 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 time controlled in units of rows, such as a vertical scanning period, a blanking period, a lighting period, an extinguishing period, and a blinking period, are all expressed in units of a scanning period of 1 row (referred to as 1H). To do. Therefore they are all integers.

  Also, it is expressed that “the cycle is approximately 1 / M of the vertical blanking period (M is a natural number)” or “the light emission pattern is approximately 1 / N (N is a natural number) of one field period”. When that time produces a fraction less than one line scan period, it means rounding to a whole number by rounding, rounding up or down. Even in the expression without “substantially”, it means not only an exact value but also a value in a range including a fraction less than 1H before and after that.

  According to a first aspect of the present invention, there is provided a driving method of a display device in which a light emitting element emits light while shifting time in the order of scanning lines, and the cycle is approximately 1 / M (M is a natural number) of a vertical blanking period. There is provided a driving method characterized by driving a light emitting element of each scanning line with a light emitting pattern.

  In the above driving method, when the field period is an integral multiple of the vertical blanking period, the light emission pattern may be set to approximately 1 / N (N is a natural number) of one field period. .

  According to a second aspect of the present invention, there is provided a driving method of a display device in which a light emitting element emits light while shifting time in order of scanning lines, and when the field period is not an integral multiple of the vertical blanking period, A period emission pattern obtained by rounding up or rounding off the period obtained by dividing the field period by the integer obtained by rounding off the quotient obtained by dividing by the vertical blanking period, and the field A light emitting element for each scanning line in combination with a pattern of a B cycle that is equal to or longer than a cycle obtained by subtracting a remainder obtained by dividing the period by the A cycle from the A cycle and less than the A cycle There is provided a driving method characterized by driving the motor.

  In the driving method according to the second aspect of the present invention, a period of 1 / integer of the A period is applied instead of the A period, and a period of 1 / integer of the B period is applied instead of the B period. It may be.

  In the driving method according to the first or second aspect of the present invention, the duty ratio of the light emission pattern may be approximately 50%.

  The present invention relates to a display device that performs periodic blinking driving in order to suppress flicker while performing duty driving. Then, by determining the blinking period based on the field period and the row scanning period, fluctuations in ΣI (the total amount of current flowing to the display area) can be suppressed. Therefore, power supply fluctuation due to the presence of power supply impedance can be suppressed. As a result, it is possible to perform a good display while suppressing a decrease in image quality due to a luminance change caused by power supply fluctuation.

  Hereinafter, the best mode for carrying out a display device according to the present invention will be specifically described in Embodiments 1 to 3 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.

  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 gradation display data Vdata is output from each output terminal. The gradation display data Vdata 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. Gradation display data Vdata 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 of 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. M3 is in an OFF state. In this state, V (i−1) corresponding to the gradation display data Vdata of the previous row is not input to the pixel circuits 2 in the target row m.

  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 gradation display data Vdata 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 luminance 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 the time related to the scanning of one row during the period of the high level signal, and this is called the scanning period of one row, or 1H. In addition, a blinking cycle is defined as a sum period of one set of a period in which P2 is low level and a period in which high level is 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 2, but the configuration 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. The gradation display data Vdata is input to the pixel circuit 2 during this High level period.

  The light emission period control signal P2 becomes a low level period after the gradation display data Vdata is input, and enters a light emission state. Thereafter, a High level period is entered, and a non-light emitting state is entered. During one field period, light emission / non-light emission is repeated.

  In this embodiment, the blinking cycle is set to 1 / N of one field period (N is a natural number) and equal to the vertical blanking period.

  When one field period is not an integral multiple of the vertical blanking period, one field period is not an integral multiple of the blinking period. At that time, as described below, two different blinking periods may be combined to fit in one field period.

For example, when ΔN = field period / vertical blanking period, ΔN ′ is obtained by rounding off the decimal point of ΔN. When TSx = field period / ΔN ′, the fractional part of TSx is rounded down or the rounded up value is set as TSx ′ (first blinking period). Any light emission pattern that is expressed by a combination of a blinking cycle (second blinking cycle) within a range of × M and TSx ′ may be used. Here, M is an integer having the field period −TSx ′ × M as a minimum value of zero or more.

  That is, when the field period is not an integral multiple of the vertical blanking period, the following may be performed. That is, the field period is divided by an integer obtained by rounding off the quotient obtained by dividing the field period by the vertical blanking period. A cycle obtained by rounding up or rounding down the cycle obtained by this division is defined as A cycle. A period that is equal to or greater than the period obtained by subtracting the remainder obtained by dividing the field period by the A period from the A period and less than the A period is defined as the B period. Then, the light emitting elements of each scanning line may be driven by a combination of the A cycle pattern and the B cycle pattern.

  In any case, the duty ratio of the light emission pattern is 50%.

  Further, the A cycle may be divided into a plurality of pieces, or the B cycle may be divided into a plurality of pieces.

  FIG. 5 is a diagram showing how the total current fluctuation in the display area depending on the light emission timing and the luminance change at that time appear on the display device in this embodiment.

  In the pattern 11, the horizontal direction represents the position in the row scanning direction, the vertical direction represents time, the white portion means light emission, and the black portion means non-light emission. The TS signal is represented by a monochrome pattern at the left end of 11. 13 is a vertical blanking period. Looking at the left end of the blanking period, it can be seen that the blinking cycle of the white part and the black part coincides with the blanking period.

  The total current amount at a certain moment is represented by the total amount of white portions at a certain position in the horizontal direction, and the magnitude thereof is indicated by reference numeral 12. 11 means that the total amount of the white portion is equal at any time within 11, that is, the total amount of current is always constant.

  Since there is no current fluctuation, power supply fluctuation does not occur, and the light emission luminance is constant at any position and at any time. A line indicated by reference numeral 14 is obtained by integrating the light emission amount over one field period. As is clear from this, there is no change in luminance at the position in the row scanning direction, and good image quality can be obtained.

  Assume that an image signal is generated from an NTSC signal. In this case, one field period can be a 262 or 263 scanning period. At this time, if the display area is 240 rows, the vertical blanking period is 22 or 23 scanning periods.

  At this time, since it is desired to set the blinking period to be approximately equal to the vertical blanking period and to approximately 1 / N of one field period, N is first calculated when one field is defined as 262 scanning periods.

N = 262/22 = 11.9≈12
Using this value to determine the blinking cycle,
262/12 = 21.8≈22
In the 262 scanning period, the blinking cycle close to 262 / N when N = 12 is 22 scanning periods. At this time,
22 × 12 = 264
And the field period will be exceeded,
22 scanning periods × 11 times + 20 scanning periods × 1 time or
Adjustment may be performed within a range in which the blinking cycle hardly changes as 22 scanning periods × 10 times + 21 scanning periods × 2.

If one field is a 263 scanning period,
N = 263/23 = 11.4≈11, 263/11 = 23.9≈24
In the 263 scanning period, the blinking cycle close to 263 / N when N = 11 is 24 scanning periods. At this time,
24 × 11 = 264
And the field period will be exceeded,
24 scanning periods × 10 times + 22 scanning periods × 1 time or
The adjustment may be performed in this manner, 24 scanning periods × 9 times + 23 scanning periods × 2 times.

  Therefore, a mode in which the blinking period is set to approximately 22 or 24 scanning periods is one form in which the effect of the present invention can be obtained.

In another display device, for example, if one field period is 262 scanning periods and the display area is 200 rows,
N = 262/62 = 4.23≈4, 262/4 = 65.5≈66
The blinking cycle closest to 262 / N in this display device is 66 scanning periods. At this time,
4 × 66 = 264
And the field period will be exceeded,
66 scanning periods x 3 times + 64 scanning periods x 1 time or
Adjustments may be made in this way, 66 scanning periods × 2 times + 65 scanning periods × 2 times.

  In the present embodiment, the display device having the configuration of FIG. 1 is illustrated, but the present invention is not limited thereto, and any configuration that can implement the driving method of FIG.

  As described above, according to the present embodiment, the blinking period is set to be approximately 1 / N times the field period and substantially equal to the vertical blanking period. Accordingly, the last blinking cycle end timing of the field period in each row and the blinking cycle start timing of the next field period are almost continuous. Furthermore, the blinking cycle of the last line in the display area and the blinking period of the first line in the display area, which should normally be discontinuous due to the presence of the vertical blanking period, are substantially continuous. Accordingly, the light emitting areas in the display area are always equal, and the amount of current flowing into the display area can be stabilized. Thus, power supply fluctuation due to power supply impedance can be suppressed, and a change in luminance in the display area can be suppressed and a good display can be obtained.

  The overall 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. 6 is a timing chart illustrating an example of another driving method of the display device according to the present invention.

  In FIG. 6, 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 blinking cycle of the light emission period control signal P2.

  In the light emission period control signal P2 in this embodiment, the blinking period is set to approximately 1 / n times the vertical blanking period (n is a natural number). The timing chart of FIG. 5 represents the case where n = 2.

  FIG. 7 is a graph in which the rate of change of ΣI (= (maximum value of ΣI−minimum value of ΣI) / ΣI average value) when the blinking period is changed is an example of this embodiment. FIG. 7 shows the result of full-field display in one field period with 262 scanning periods, 240 display rows, and a duty ratio of 50%. At this time, as a general blinking cycle, the change rate of ΣI in the drive that blinks once in one field period is ΔΣI1. Further, the change rate of ΣI in the drive that blinks N times in one field period is assumed to be ΔΣIN.

  If the blinking period is set so that ΔΣIN is less than half of ΔΣI1, the sufficient effect of the present invention can be obtained.

  Reference numeral 21 in FIG. 8 represents a simulation of the time change of ΣI in the drive that blinks once in one field period. Reference numeral 22 is a simulation of the time change of ΣI of the drive with a blinking period of ΔΣIN which is less than half of ΔΣI1. Furthermore, 23 is a simulation of the time change of ΣI when the blinking period and the vertical blanking period are substantially equal. Even if it is not the blinking cycle that completely eliminates the time change of ΣI from this figure, the effect of the present invention can be sufficiently obtained by selecting the blinking cycle that makes the time change of ΣI less than half like 22. Is possible.

  More preferably, in FIG. 7, there are the following blinking cycles in which the rate of change in ΣI is smaller than the surrounding blinking cycle. That is, the flashing cycle is in a range where the value of (1 field period) / (flashing cycle) is almost an integer, and the flashing cycle is approximately 1 / n times the vertical blanking period (n is a natural number). A certain blinking period is such. In addition, the blinking cycle at which the rate of change in ΣI is small does not need to coincide with 1 / n times the vertical blanking period, and the amount of change in current can be sufficiently suppressed if it is approximately close. The effect of the present invention can be obtained more sufficiently.

  As a more preferable example, FIG. 7 shows a blinking cycle in which n = 1 and n = 2 as an example in which the blinking cycle is approximately 1 / n times the vertical blanking period. The change rate of ΣI is smaller than other blinking cycles, and the effect of the present invention can be obtained even when such blinking cycle is selected.

  As described above, according to the present embodiment, even if the blinking period is 1 / N times the field period and does not coincide with the vertical blanking period, if the change in ΣI becomes small, power supply fluctuation is suppressed, It is possible to suppress the luminance variation of the self-light emitting element and obtain a good display.

  In the first and second embodiments described above, the fluctuation itself of ΣI is eliminated by setting the blinking cycle to be close to a natural number of the vertical blanking period.

  In addition to this, as a method of eliminating the fluctuation of ΣI, the power supply voltage is changed to increase the power supply voltage during a period when the number of light emitting rows is larger than that of the non-lighted rows. In addition, there is a method of reducing the power supply voltage. That is, the power supply voltage is varied in synchronization with the light emission pattern, and as a result, control is performed so as to be a constant ΣI.

  A device may be devised to compensate for the luminance distribution due to the fluctuation of ΣI itself. The place where the luminance is low due to the fluctuation of ΣI is determined by the blinking period and the blanking period, and is fixed at a specific place in the display area. The luminance distribution can be compensated by disposing an element having higher current-luminance characteristics than the surroundings, that is, an element that emits light brighter with respect to the same current at that position. The luminance distribution due to the characteristics of the light emitting element cancels out the luminance distribution formed by synchronizing the fluctuation of ΣI and the light emission pattern, thereby producing uniform luminance.

  Also, the luminance distribution can be compensated by converting image data that emits light in a low-luminance place into image data that emits lighter.

  The power supply voltage is supplied to each pixel circuit through a Vcc wiring line provided in the row direction as shown in FIG. If the impedance of the wiring is adjusted for each row and the power supply voltage supplied to the pixels is distributed, a luminance distribution parallel to the row can be created. This is also one of the methods for compensating the luminance distribution due to the ΣI fluctuation.

  In this way, a uniform display device can be obtained by compensating for the fluctuation of ΣI with the power supply voltage fluctuation or the luminance distribution prepared in advance in the panel.

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

  FIG. 13 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. 13, a video captured by the imaging unit 51 or a 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 can be used for a display device in which self-emitting elements are arranged in a matrix and a driving method thereof. In particular, 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 method for driving these active matrix display devices. Can do.

  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. 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 an example of the range which can apply the drive method which concerns on this invention. It is a figure which shows an example of the effect of the drive method which concerns on this invention. 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 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 Light emission pattern 12 Total current amount change to display area 13 Vertical blanking period 14 Luminance change in position in row scanning direction 21 Time variation of ΣI in the drive in which the blinking cycle blinks once in one field period 22 Time change in ΣI driven in the blinking cycle of ΔΣIN which is less than half of ΔΣI1 Change in time of ΣI with period 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 (7)

A driving method of a display device that causes a light emitting element to blink at a period of time shifted for each scanning line,
A driving method characterized in that a blinking cycle of the light emitting element is set to 1 / M (M is a natural number) of a vertical blanking period. The driving method according to claim 1,
The field period is an integer multiple of the vertical blanking period,
The driving method is characterized in that the blinking cycle of the light emitting element is 1 / N (N is a natural number) of one field period. A driving method of a display device that causes a light emitting element to blink at a period of time shifted for each scanning line,
Using the scanning period of one row as a unit
The field period is not an integer multiple of the vertical blanking period,
During the field period, as the blinking cycle of the light emitting element,
A first blinking period which is converted to an integer by rounding up or rounding down the period obtained by dividing the field period by an integer obtained by rounding off the quotient obtained by dividing the field period by the vertical blanking period; ,
A second blinking that is equal to or greater than the period obtained by subtracting the remainder obtained by dividing the field period by the first blinking period from the first blinking period and less than the first blinking period. A driving method characterized by mixing a period. The driving method according to any one of claims 1 to 3,
A driving method, wherein a duty ratio of a light emission period with respect to a blinking cycle of the light emitting element is set to 50%. A display device in which a light emitting element blinks with a period shifted for each scanning line,
A display device, wherein a blinking cycle of the light emitting element is 1 / M (M is a natural number) of a vertical blanking period. The display device according to claim 5,
The field period is an integer multiple of the vertical blanking period,
The display device is characterized in that the blinking cycle of the light emitting element is 1 / N (N is a natural number) of one field period. A display device in which a light emitting element blinks with a period shifted for each scanning line,
Using the scanning period of one row as a unit
The field period is not an integer multiple of the vertical blanking period,
During the field period, as the blinking cycle of the light emitting element,
A first blinking period which is converted to an integer by rounding up or rounding down the period obtained by dividing the field period by an integer obtained by rounding off the quotient obtained by dividing the field period by the vertical blanking period; ,
A second blinking that is equal to or greater than the period obtained by subtracting the remainder obtained by dividing the field period by the first blinking period from the first blinking period and less than the first blinking period. A display device characterized by a mixture of periods.