JP2006023460A - Electro-optic apparatus, its drive method and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the degradation in image quality such as a so-called false contour is caused in a system of dividing a light emitting period,. <P>SOLUTION: A first period T1 corresponds to high luminance while a second period T2 corresponds to low luminance. In a first writing period T1wrt, a set current corresponding to the high luminance is written, and an OLED (organic light emitting diode) element is forced to emit light in a first light emitting period T1el. In a second writing period T2wrt, a set current corresponding to the low luminance is written, and the OLED element is forced to emit light in a second light emitting period T2el. The first light emitting period T1el and the second light emitting period T2el are set to be adjacent to each other. Thereby, distributions of visual stimulation are approximated to each other to prevent generation of a false contour. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to, for example, an electro-optical device including an element whose light emission intensity is adjusted according to an electric current, a driving method thereof, and an electronic apparatus.

In recent years, organic light emitting diodes (hereinafter referred to as “OLED elements”) elements called organic electroluminescence elements and light emitting polymer elements have attracted attention as next-generation light-emitting devices that replace liquid crystal elements. Since this OLED element is a self-luminous type, it has less viewing angle dependence, and since it does not require a backlight or reflected light, it is suitable for low power consumption and thinning. It has characteristics.
Here, the OLED element is a current-type driven element that does not have voltage holdability like a liquid crystal element and cannot maintain a light emitting state when current is interrupted. For this reason, when the OLED element is driven by the active matrix method, a current corresponding to the gradation of the pixel is supplied to the pixel circuit in the writing period, and a voltage corresponding to the magnitude of the current is written to the gate of the driving transistor. Therefore, it is general that the voltage is held by a gate capacitance or the like, and the drive transistor continues to flow a current corresponding to the gate voltage to the OLED element.

In such a current programming method, the brightness of the OLED element can be accurately controlled. However, since the data line has a stray capacitance, there may be a case where a sufficient current cannot be supplied to the pixel depending on the magnitude of the gradation current. . Therefore, a technique is known in which one frame is divided, high luminance image data is written in the first half period, and low luminance image data is written in the second half period. According to this technique, it is possible to eliminate the shortage of writing of gradation current by individually setting the light emission period of the first half period and the light emission period of the second half period (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2003-15605 (see drawing)

By the way, in the method of dividing the light emission period, image quality degradation such as a so-called false contour becomes a problem (refer to the Journal of the Institute of Image Information and Television Engineers, Vol.58, No.4, pp.466-468). The principle is that when the line of sight moves within the screen, an afterimage remains on the retina and blurring occurs due to the effect. In particular, when the light emission period is far away, the image quality deterioration becomes remarkable.
In the conventional technique described above, the light emission period is arranged immediately after the high luminance writing period, and the light emission period is arranged immediately after the low luminance writing period. That is, the high-luminance light emission period and the low-luminance light emission period are separated in time. For this reason, in the prior art, image quality degradation due to false contours becomes a problem.
In addition, the above-described conventional technique only divides the light emission period at high luminance and low luminance, and the dynamic range of the current in the high luminance light emission period and the low luminance light emission period has not been studied. Furthermore, since the OLED element emits light in different processes during the high-luminance light emission period and the low-luminance light emission period, it is difficult to accurately maintain gradation continuity due to variations in the components of the drive circuit. It was.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide an electro-optical device that improves false contour, a driving method thereof, and an electronic apparatus. In addition, another object of the present invention is to provide an electro-optical device, a driving method thereof, and an electronic apparatus that make the current dynamic range close in a light emission period with high luminance and a light emission period with low luminance. In addition, another object of the present invention is to provide an electro-optical device, a driving method thereof, and an electronic apparatus that make gradation steps inconspicuous.

In order to solve the above problems, a driving method of an electro-optical device according to the present invention is provided corresponding to a plurality of scanning lines, a plurality of data lines, and an intersection of the scanning lines and the data lines. A pixel circuit, the pixel circuit flowing between the electro-optic element whose luminance is adjusted according to a supplied current, the data line and the pixel circuit, and corresponding to image data indicating gradation And a storage unit that stores a set current as a current to be supplied to the electro-optical element. The method includes: a first period; a second period; The period includes a first writing period and a first light emitting period. In the first writing period, a set current corresponding to high gradation image data is written to the storage means, and in the first light emitting period, the memory is stored. Setting the size stored in the means The second period includes a second writing period and a second light emitting period, and a set current corresponding to low gradation image data is supplied in the second writing period. In the second light emission period, a setting current having a magnitude stored in the storage means is supplied to the electro-optical element, and the first light emission period and the second light emission period are on the time axis. It is characterized by being adjacent to each other.
According to the present invention, since the writing of the setting current is divided into the first writing period corresponding to high luminance and the second writing period corresponding to low luminance according to the gradation indicated by the image data, The range can be narrowed. In addition, since the first light emission period and the second light emission period are adjacent to each other on the time axis, it is possible to effectively prevent the occurrence of false contours. Here, as an aspect adjacent on the time axis, when the first light emission period and the second light emission period are adjacent via the second writing period, and via the first writing period Includes adjacent cases.

  Further, another driving method of the electro-optical device according to the invention includes a plurality of scanning lines, a plurality of data lines, and a pixel circuit provided corresponding to the intersection of the scanning lines and the data lines. The pixel circuit includes an electro-optic element whose luminance is adjusted according to a supplied current, and a current that flows between the data line and the pixel circuit, and a set current according to image data indicating gradation. A method of driving the electro-optical device, the storage unit storing the current supplied to the electro-optical element, wherein one frame includes a first period and a second period. In the first writing period, a set current corresponding to high gradation image data is written in the storage means, and is stored in the storage means in the first light emission period. A set current of a magnitude The second period includes a second writing period and a second light emitting period. In the second writing period, a setting current corresponding to low gradation image data is written to the storage unit. In the second light emission period, a setting current having a magnitude stored in the storage means is supplied to the electro-optic element, and a minimum value of the setting current written in the first writing period is a first minimum value, and its maximum When the value is the first maximum value, the minimum value of the setting current to be written in the second writing period is the second minimum value, and the maximum value is the second maximum value, the first light emission period and the second light emission period Is set to be equal to the ratio between the first maximum value and the first minimum value and equal to the ratio between the second maximum value and the second minimum value.

  According to this invention, the dynamic range of the set current in the first period is a range from the first minimum value to the first maximum value, and the dynamic range of the set current in the second period is from the second minimum value to the second maximum value. The range is up to the value. Here, if the ratio between the first light emission period and the second light emission period is K, the ratio between the first maximum value and the first minimum value is S1, and the ratio between the second maximum value and the second minimum value is S2, then K Since S1 = S2, the dynamic ranges of the first period and the second period can be matched. As a result, the insufficient writing of the set current is resolved, and accurate gradation display is possible. Note that “equal ratio” includes not only the case where they completely match, but also those within the range of product variation. In short, it should be judged from the viewpoint of bringing the dynamic range of the set current closer.

  In the above-described driving method of the electro-optical device, the ratio between the first light emission period and the second light emission period is set to be equal to the square root of the ratio between the maximum value and the minimum value of the gradation to be displayed. It is preferable to do. Also in this case, the dynamic ranges of the first period and the second period can be matched, so that insufficient writing of the set current can be solved and accurate gradation display can be performed.

  In the above-described driving method of the electro-optical device, the gradation range to be displayed in the first period and the gradation range to be displayed in the second period are set to partially overlap, When the range is the overlapping range, it is determined whether or not the gradation to be displayed is in the overlapping range. If the gradation to be displayed is in the overlapping range, the first period or the second period It is preferable that the electro-optic element is driven by selecting at random. In this case, when the gradation to be displayed is in the overlapping range, the driving in the first period and the driving in the second period are selected at random, so that the gradation step due to the variation can be made inconspicuous.

  In the above-described driving method of the electro-optical device, the first range of gradations to be displayed in the first period and the second range of gradations to be displayed in the second period are set to overlap with the boundary value. It is determined whether the gradation to be displayed is within a predetermined range including the boundary value. If the gradation to be displayed is within the overlapping range, the gradation to be displayed is random. The tone values are combined, it is determined whether the combined gradation value belongs to the first range or the second range, the first period or the second period is selected according to the determination result, and the It is preferable to drive the electro-optic element. In this case, when gradations to be displayed are within a predetermined range, random gradation values are synthesized, so that gradation steps due to variations can be made inconspicuous.

  Next, an electro-optical device according to the present invention includes a plurality of scanning lines, a plurality of data lines, and a pixel circuit provided corresponding to an intersection of the scanning lines and the data lines, and the pixels The circuit flows between the electro-optical element whose luminance is adjusted according to a supplied current and the data line and the pixel circuit, and a set current according to image data indicating a gradation is supplied to the electro-optical element. Storage means for storing current to be supplied, and one frame includes a first period including a first writing period and a first light emitting period, and a second writing period and a second light emitting period. Divided into a second period, in the first writing period and the second writing period, the scanning line is selected and the magnitude of the set current supplied to the data line is written to the storage means And controlling the pixel circuit in the first light emission period. And the second light emission period is adjacent on the time axis, and the pixel circuit is controlled to supply the set current having the magnitude stored in the storage means to the electro-optical element during these periods. A driving unit for supplying a set current corresponding to high gradation image data to the data line in the first writing period, and a setting current corresponding to low gradation image data in the second writing period; Second driving means for supplying to the data line.

  According to the present invention, since the writing of the setting current is divided into the first writing period corresponding to high luminance and the second writing period corresponding to low luminance according to the gradation indicated by the image data, The range can be narrowed. In addition, since the first light emission period and the second light emission period are adjacent to each other on the time axis, it is possible to effectively prevent the occurrence of false contours. Here, as an aspect adjacent on the time axis, when the first light emission period and the second light emission period are adjacent via the second writing period, and via the first writing period Includes adjacent cases.

  Another electro-optical device according to the invention includes a plurality of scanning lines, a plurality of data lines, and a pixel circuit provided corresponding to the intersection of the scanning lines and the data lines, The pixel circuit has an electro-optical element whose luminance is adjusted according to a supplied current, and a current that flows between the data line and the pixel circuit, and a set current corresponding to image data indicating a gradation. Storage means for storing current to be supplied to a first frame, a first period including a first writing period and a first light emitting period, a second writing period and a second light emitting period. Divided into a second period, and in the first writing period and the second writing period, the scanning line is selected and the magnitude of the set current supplied to the data line is written in the storage means. The pixel circuit to control the first light emission First driving means for controlling the pixel circuit so as to supply the set current having a magnitude stored in the storage means to the electro-optic element during the second light emission period, and in the first writing period. A set current corresponding to high gradation image data is supplied to the data line, and a set current corresponding to low gradation image data is supplied to the data line in the second writing period. The minimum value of the set current written during the writing period is the first minimum value, the maximum value is the first maximum value, the minimum value of the setting current written during the second writing period is the second minimum value, and the maximum value is the first value. When the maximum value is two, the ratio between the first maximum value and the first minimum value and the ratio between the second maximum value and the second minimum value are the first light emission period and the second light emission period. Second driving means that is set to be equal to the ratio of Obtain. According to the present invention, the dynamic ranges of the first period and the second period can be matched. As a result, the insufficient writing of the set current is resolved, and accurate gradation display is possible.

  Preferably, the first driving unit is set so that a ratio between the first light emission period and the second light emission period is equal to a square root of a ratio between a maximum value and a minimum value of gradations to be displayed. Also in this case, the dynamic ranges of the first period and the second period can be matched, so that insufficient writing of the set current can be solved and accurate gradation display can be performed.

  Further, the second driving means sets the overlapping range so that the gradation range to be displayed in the first period and the gradation range to be displayed in the second period partially overlap; When the determination unit determines whether the gradation to be displayed is in the overlapping range, and the determination unit determines that the gradation to be displayed is in the overlapping range, the first period or the It is preferable to include a current supply unit that randomly selects a second period and supplies the set current to the data line. In this case, when the gradation to be displayed is in the overlapping range, the driving in the first period and the driving in the second period are selected at random, so that the gradation step due to the variation can be made inconspicuous.

  The second driving means is a setting means for setting the first range of gradations to be displayed in the first period and the second range of gradations to be displayed in the second period so as to overlap with a boundary value. Determining means for determining whether or not the gradation to be displayed is within a predetermined range including the boundary value, and when the determination means determines that the gradation to be displayed is within the predetermined range, Combining means for synthesizing random gradation values to gradations to be displayed, and when the combined gradation values belong to the first range, the set current is supplied to the data lines in the first period to synthesize It is preferable that the apparatus further comprises current supply means for supplying the set current to the data line in the second period when the gradation value belongs to the second range. In this case, when gradations to be displayed are within a predetermined range, random gradation values are synthesized, so that gradation steps due to variations can be made inconspicuous.

  Next, an electronic apparatus according to the present invention includes the above-described electro-optical device, and corresponds to, for example, a personal computer, a mobile phone, and a portable information terminal.

<1. First Embodiment>
FIG. 1 is a block diagram showing an electrical configuration of the electro-optical device according to the first embodiment of the present invention. As shown in FIG. 1, the electro-optical device 10 includes a display area A. In the display area A, a plurality of scanning lines 101 and a plurality of light emission control lines 102 extend in the horizontal direction (X direction), while a plurality of data lines 103 extend in the vertical direction (Y direction) in the drawing. Has been. Pixel circuits 400 are provided so as to correspond to the intersections of the scanning lines 101 and the data lines 103, respectively.
Here, for convenience of explanation, in the present embodiment, the number of scanning lines 101 (number of rows) is m, the number of data lines (number of columns) is n, and the pixel circuit 400 is a matrix of vertical m rows × horizontal n columns. Assuming a configuration arranged in a shape.

The Y driver 100 selects the scanning line 101 row by row, and supplies H level scanning signals G _{WRT1 to} G _WRTm to the selected scanning line 101. Further, the light emission control signals G _{EL1 to} G _ELm are supplied to the light emission control line 102. That is, the Y driver 100 _supplies the scanning signals G _{WRT1 to} G _WRTm and the light emission control signals G _{EL1 to} G _ELm to the scanning line 101 and the light emission control line 102 for each row.
The X driver 200 includes a current DA converter and the like corresponding to each data line 103, and is a pixel circuit for one row corresponding to the scanning line 101 selected by the Y driver 100, that is, one located in the selected row. The gradation signals X1 to Xn are supplied to the pixel circuits 400 in the ˜n columns via the data lines 103 in the 1st to nth columns, respectively. The power supply circuit 360 generates a power supply voltage Vdd and a precharge voltage Vpre. The power supply voltage Vdd is supplied to each pixel circuit 400 via the current supply line 104, and the precharge voltage Vpre is supplied to the precharge circuit 220.

The timing control circuit 340 generates various timing signals, supplies them to the Y driver 100 and the X driver 200, and supplies a precharge control signal Gpre to the precharge circuit 220. The precharge circuit 220 includes transistors connected to the n data lines 103, respectively. When the precharge control signal Gpre becomes active (H level), each transistor is turned on and the precharge voltage Vpre is supplied to the data line 103.
The interface circuit 320 performs image processing such as gamma correction on input image data Din supplied from an external device, and supplies the input image data Din to the frame memory 300 as output image data Dout. The frame memory 300 stores output image data Dout for one frame and sequentially supplies it to the X driver 200.

FIG. 2 is a circuit diagram illustrating a configuration of the pixel circuit 400. The pixel circuit 400 of this example is arranged in the first row and the first column shown in FIG. 1, and is supplied with the scanning signal G _WRT1 and the light emission control signal G _EL1 . The other pixel circuits 400 are similarly configured. The pixel circuit 400 includes a drive transistor TR1, a program transistor TR2, a switching transistor TR3, an EL transistor TR4, a storage capacitor C, and an OLED element 420. The cathode of the OLED element 420 is grounded (GND). The driving transistor TR1 is composed of a P-channel TFT, and the other transistors are composed of N-channel TFTs. A power supply voltage Vdd is supplied through the current supply line 104. Note that the drive transistor TR1 may be configured by an N-channel TFT, the other transistors may be configured by P-channel TFTs, and the polarity of the OLED element 420 may be inverted.

The switching transistor TR3 functions as switching means for switching the connection state between the data line 103 and the pixel circuit 400. The switching transistor TR3 is turned on when the scanning signal G _WRT1 supplied via the scanning line 101 is active (high level), and connects the data line 103 and the pixel circuit 400, while the scanning signal G _WRT1 is inactive ( (Low level), the data line 103 and the pixel circuit 400 are separated from each other.

Program transistor TR2, in the writing period of the pixel circuit 400 the scanning signal _{G WRT1} becomes active, whereas in the ON state, the OFF state in the period where the scanning signal _{G WRT1} becomes inactive. When the program transistor TR2 and the switching transistor TR3 are turned on, as shown in FIG. 3, the gradation signal X1 flows through the drive transistor TR1 as the set current idata. At this time, the storage capacitor C is charged so that the set current idata can flow, and the source potential corresponding to the amount of the set current idata is supplied to the source of the drive transistor TR1. When the scanning signal _GWRT1 becomes inactive, the program transistor TR2 is turned off.

  Since the gate of the driving transistor TR1 has high impedance, the charge charged in the storage capacitor C is held and the gate potential is kept constant. That is, the potential corresponding to the set current idata is programmed in the storage capacitor C. Accordingly, the program transistor TR2, the drive transistor TR1, and the storage capacitor C function as a storage unit that stores the current amount of the set current idata.

On the other hand, in the light emission period, the program transistor TR2 and the switching transistor TR3 are turned off, and the light emission control signal _GEL becomes active (high level). Then, the EL transistor TR4 is turned on, and the set current idata programmed in the writing period flows through the OLED element 420 as shown in FIG. Thereby, a predetermined gradation can be displayed.

  FIG. 5 shows a timing chart for explaining operations of the Y driver 100 and the X driver 200. Focusing on the first row, one frame includes a first period T1 (first half frame) corresponding to high-luminance output image data Dout and a second period T2 (first half) corresponding to low-luminance output image data Dout. ½ frame). The first period T1 includes a first writing period T1wrt and a first light emission period T1el. The second period T2 includes a second writing period T2wrt and a second light emission period T2el. In the first writing period T1wrt, the setting current idata corresponding to the high-luminance output image data Dout is supplied to the data line 103. In the second writing period T2wrt, the setting current idata corresponding to the low-luminance output image data Dout is supplied to the data line 103. The first light emission period T1el is set to be longer than the second light emission period T2el. These points are the same in the second to m-th rows.

  In the present embodiment, the first light emission period T1el and the second light emission period T2el are adjacent to each other via the second writing period T2wrt. The reason why the first light emission period T1el and the second light emission period T2el are brought close to each other is to improve image quality degradation due to false contours. This point will be specifically described. First, as shown in FIG. 6, it is assumed that a person's line of sight moves from left to right on a screen in which the left half is slightly bright and the right half is slightly dark. In this case, the locus of light emission on the retina is as shown in FIG. 7A, and the stimulus distribution on the retina is as shown in FIG. As shown in the figure, a region Q that is slightly disturbed at the boundary portion of the screen is generated in the visually recognized stimulus.

Here, assuming that the first light emission period T1el and the second light emission period T2el having low luminance are separated as shown in FIG. 8, the locus of light emission on the retina is as shown in FIG. The upper stimulus distribution is as shown in FIG. As shown in the figure, the stimulus P that is visually recognized has a region P that is greatly disturbed at the boundary of the screen. This is a cause of image quality degradation, and a shift in the light emission period due to a change in gradation results in spatial nonuniformity on the retina, resulting in a false contour.
As described above, in the present embodiment, since the first light emission period T1el and the second light emission period T2el are adjacent to each other, the region Q is extremely small. As a result, the occurrence of false contours can be prevented and image quality degradation can be greatly improved. In the timing chart shown in FIG. 5, the second period T2 may be arranged in the first half of one frame and the first period T1 may be arranged in the latter half. In this case, the first light emission period T1el and the second light emission period T2el are adjacent to each other via the first writing period T1wrt.

In this embodiment, various conditions are set so that the dynamic range of the set current idata corresponding to high luminance is equal to the dynamic range of the set current idata corresponding to low luminance. As a result, it is possible to solve the shortage of writing with low luminance.
FIG. 10 shows the relationship between the gradation value and the first light emission period T1el and the second light emission period T2el. First, the minimum value of the set current idata corresponding to high luminance is set as a first minimum current value Iamin, and the maximum value is set as a first maximum current value Iamax. In addition, the minimum value of the setting current idata corresponding to the low luminance is a second minimum current value Ibmin, and the maximum value is a second maximum current value Ibmax. Further, in the first period T1 corresponding to high luminance, the intermediate gradation Nmid is displayed from the maximum gradation Nmax, and in the second period T2 corresponding to low luminance, the minimum gradation Nmin is displayed from the intermediate gradation Nmid. . The intermediate gradation Nmid is a boundary value between them. Note that the minimum gradation Nmin does not include a black level that does not cause the OLED to emit light at all.

Here, it is assumed that the intermediate gradation Nmid is displayed. The light emission amount of the OLED element 420 is proportional to the set current idata. When the intermediate gradation Nmid is displayed using the first period T1, the light emission amount is Iamin · T1el, and when the intermediate gradation Nmid is displayed using the second period T2, the light emission amount is Ibmax · T2el. . From this, the following formula (1) is established.
Iamin · T1el = Ibmax · T2el
T1el / T2el = Iamin / Ibmax
Here, since T1el / T2el = K,
Ibmax / Iamin = K (1)

Next, when Nmax / Nmid = S1 and Nmid / Nmin = S2 and Expression (1) is applied, the dynamic range of the set current idata in the first period T1 and the second period T2 is as follows.
1) Second period T2 corresponding to low luminance
Minimum current (displays minimum gradation Nmin): Ibmin = Ibmax / S2 = K · Iamin / S2
Maximum current (displaying intermediate gradation Nmid): Ibmax = K · Iamin
2) First period T1 corresponding to high luminance
Minimum current (displays midtone Nmid): Iamin
Maximum current (displays maximum gradation Nmax): Iamax = S1 · Iamin

Here, the condition that the dynamic ranges of the set current idata in the first period T1 and the second period T2 match each other is that the minimum current and the maximum current in each period match each other. Therefore, in order to satisfy this condition, it is necessary to satisfy the following expressions (2) and (3).
K · Iamin / S2 = Iamin → K = S2 (2)
K · Iamin = S1 · Iamin → K = S1 (3)
Therefore, the ratio K between the first light emission period T1el and the second light emission period T2el is equal to the ratio S1 between the first maximum current value Iamax and the first minimum current value Iamin, and the second maximum current value Ibmax and the second minimum current value. When the ratio is equal to the ratio S2 of Ibmin, the set current idata in the first period T1 and the second period T2 coincide. In this embodiment, it is set as such.

Further, the display gradations from the minimum gradation Nmin to the maximum gradation Nmax are equally divided, and if the number of gradations is Z, the condition that the set current idata in the first period T1 and the second period T2 matches is as follows. It is given by the following formula (4).
Z = Nmax / Nmin = (Iamax · T1el) / (Ibmin · T2el)
= K · Iamax / Ibmin
= K ² (4)
Therefore, when the ratio K between the first light emission period T1el and the second light emission period T2el is equal to the square root of the ratio Z between the maximum gradation Nmax and the minimum gradation Nmin, the set current of the first period T1 and the second period T2 idata matches. In this embodiment, it is set as such.

  As described above, in the present embodiment, the dynamic range of the set current idata in the first writing period T1wrt corresponding to high luminance is made equal to the dynamic range of the set current idata in the second writing period T2wrt corresponding to low luminance. be able to. When the writing period is divided into low luminance and high luminance, it is important to sufficiently write the set current idata in both writing periods in terms of accurately displaying gradation. On the other hand, since the data line 103 has a stray capacitance, the set current idata is written according to a predetermined time constant that takes into account the value of the stray capacitance. In this case, if the dynamic range is wide or narrow, writing in a wide dynamic range takes time compared to writing in a narrow dynamic range, and the set current idata may not be sufficiently written. In the present embodiment, since the dynamic ranges of the first writing period T1wrt and the second writing period T2wrt match, there is no advantageous / disadvantageous relationship regarding the writing of the set current idata. Also, by matching the two, the dynamic range can be narrowed compared to the case where they do not match, and the set current idata can be easily written. As a result, it is possible to solve the insufficient writing of the set current idata and display an accurate gradation.

<2. Second Embodiment>
Next, a second embodiment of the present invention will be described. The electro-optical device 10 according to the second embodiment is the same as the electro-optical device according to the first embodiment except for the relationship between the gradation range displayed using the first period T1 and the gradation range displayed using the second period T2. It is the same as the device 10.
FIG. 11 shows the relationship between the gradation value according to the second embodiment and the first light emission period T1el and the second light emission period T2el. As shown in the figure, in the first period T1 corresponding to high luminance, the first intermediate gradation Nmid1 is displayed from the maximum gradation Nmax, and in the second period T2 corresponding to low luminance, the second intermediate gradation Nmid2 is displayed from the minimum gradation. The key Nmin is displayed. The first intermediate gradation Nmid1 and the second intermediate gradation Nmid2 are set to Nmid1 <Nmid2. Therefore, the gradation range handled in the first period T1 and the gradation range handled in the second period T2 overlap in the range from the first intermediate gradation Nmid1 to the second intermediate gradation Nmid2. Regarding the value of the gradation current idata in the first writing period T1wrt, the first maximum current value Iamax corresponds to the maximum gradation Nmax, and the first minimum current value Iamin corresponds to the first intermediate gradation Nmid1. Further, regarding the value of the gradation current idata in the second writing period T2wrt, the second maximum current value Ibmax corresponds to the second intermediate gradation Nmid2, and the second minimum current value Ibmin corresponds to the minimum gradation Nmin. In addition, the value of the gradation current idata in the second writing period T2wrt corresponding to the first intermediate gradation Nmid1 is Ibmid1, and the gradation current idata in the first writing period T1wrt corresponding to the second intermediate gradation Nmid2. The value of is Iamid2.

  In the present embodiment, when the gradation to be displayed is in the overlapping range from the first intermediate gradation Nmid1 to the second intermediate gradation Nmid2, the display is performed using the first period T1 or the second period T2 is set. Randomly select whether to use or display. The reason why the overlapping range is set and selected at random is as follows. That is, when divided into the first period T1 corresponding to high luminance and the second period T2 corresponding to low luminance, the OLED element 420 is caused to emit light in different processes. . That is, there is a step in the gradation that is actually displayed at the boundary between the gradation range handled by the first period T1 and the gradation range of the second period T2. In particular, when an image in which the gradient changes gently is displayed, the gradation difference is noticeable. Therefore, the gradation range is made inconspicuous by setting the overlapping range and switching it at random.

  FIG. 12 shows a detailed configuration of the X driver 200 according to the second embodiment. As shown in this figure, the X driver 200 includes a gradation value determination circuit 201, a gain adjustment circuit 202, a serial / parallel conversion circuit 203, and a current conversion unit 204. The gradation value determination circuit 201 determines which range the gradation indicated by the output image data Dout supplied from the frame memory 300 belongs to, and generates a control signal W based on the determination result. The gain adjustment circuit 202 generates gradation data D ′ according to the control signal W.

More specifically, when the gradation indicated by the output image data Dout is G, the following control is executed.
(1) Nmin ≦ G <Nmid1
In this case, the OLED element 420 is caused to emit light using the second period T2. For this reason, the gradation value determination circuit 201 controls the gain adjustment circuit 202 so as to generate gradation data D ′ by adjusting the gain of the output image data Dout as follows. That is, the gradation data D ′ is generated so that the gradation range Nmin to Nmid1 of the output image data Dout corresponds to Ibmin to Ibmid1, and the gradation data D ′ is output in the second writing period T2wrt. To do.

(2) Nmid1 ≦ G ≦ Nmid2
In this case, the OLED element 420 is caused to emit light using the first period T1 or the second period T2. The gradation value determination circuit 201 controls the gain adjustment circuit 202 so as to generate gradation data D ′ by adjusting the gain of the output image data Dout as follows. That is, one of the first period T1 and the second period T2 is selected at random. When the first period T1 is selected, the gradation data D ′ is generated so that the gradation range Nmid1 to Nmid2 of the output image data Dout corresponds to Iamin to Iamid2, and the first writing period T1wrt. Is used to output gradation data D ′. On the other hand, when the second period T2 is selected, the gradation data D ′ is generated so that the gradation range Nmid1 to Nmid2 of the output image data Dout corresponds to Ibmid1 to Ibmax, and the second writing is performed. The gradation data D ′ is output using the period T2wrt.

(3) Nmid2 <G ≦ Nmax
In this case, the OLED element 420 is caused to emit light using the first period T1. For this reason, the gradation value determination circuit 201 controls the gain adjustment circuit 202 so as to generate gradation data D ′ by adjusting the gain of the output image data Dout as follows. That is, the gradation data D ′ is generated so that the gradation range Nmid2 to Nmax of the output image data Dout corresponds to Iamid2 to Iamax, and the gradation data D ′ is output in the first writing period T1wrt. To do.

The generated gradation data D ′ is converted from serial gradation data D ′ to parallel gradation data d 1, d 2,. The current conversion unit 204 includes n current DA converters, which convert the gradation data d1, d2,... Dn into data signals X1, X2,.
As described above, in the present embodiment, since the overlapping range is provided and the first period T1 and the second period T2 are randomly selected when the gradation to be displayed is in the overlapping range, the discontinuity of the gradation is conspicuous. It becomes possible to eliminate.

<3. Third Embodiment>
Next, a third embodiment of the present invention will be described. The electro-optical device 10 according to the third embodiment is the same as that of the first embodiment except for processing when the gradation to be displayed is in a predetermined range including the intermediate gradation Nmid (hereinafter referred to as the intermediate range ΔNmid). The same as the electro-optical device 10.
FIG. 13 shows a detailed configuration of the X driver 200 according to the third embodiment. As shown in this figure, the X driver 200 is obtained by adding an intermediate range determination circuit 205, a random data generation circuit 206, and an addition circuit 207 to the configuration of the second embodiment described above (see FIG. 12). . The intermediate range determination circuit 205 determines whether or not the gradation of the output image data Dout belongs to the intermediate range ΔNmid, and if so, controls the random data generation circuit 206 to generate random data Dr. Here, the intermediate range ΔNmid is a range of ± ΔN centering on the intermediate gradation Nmid as shown in FIG.

  The random data Dr generated by the random data generation circuit 206 takes a random value in the range from gradation -ΔN to gradation + ΔN. Further, when the gradation of the output image data Dout does not belong to the intermediate range ΔNmid, the random data generation circuit 206 does not generate random data Dr. Therefore, the adding circuit 207 adds the random data Dout to the output image data Dout only when the gradation of the output image data Dout belongs to the intermediate range ΔNmid, and when it does not belong to the intermediate range ΔNmid, the output image data Dout is left as it is. Output.

  The gradation value determination circuit 201 determines whether the gradation of the output data from the addition circuit 207 is equal to or higher than the intermediate gradation Nmid, and controls the gain adjustment circuit 202 based on the determination result. Specifically, when the gray level is equal to or higher than the intermediate gray level Nmid, the gray level data D ′ is generated so that the gray level range Nmid to Nmax corresponds to Iamin to Iamax, and the first writing period is set. The gradation data D ′ is output at T1wrt. On the other hand, if it is less than the intermediate gradation Nmid, gradation data D ′ is generated so that the gradation range Nmin to Nmid corresponds to Ibmin to Ibmax, and the gradation data D ′ is generated in the second writing period T2wrt. The key data D ′ is output.

  As described above, in the present embodiment, random gradations are synthesized when gradations to be displayed within a predetermined range from the boundary of the gradation range that each of the first period T1 and the second period T2 is responsible for. . When driving by dividing into a first period T1 corresponding to high luminance and a second period T2 corresponding to low luminance, even if the gradation becomes discontinuous due to variations, the gradation to be actually displayed in the intermediate range ΔNmid Is randomized, so that gradation steps can be made inconspicuous.

<4. Electronic equipment>
Next, an electronic apparatus to which the electro-optical device 10 according to the first to third embodiments described above is applied will be described. FIG. 15 shows a configuration of a mobile personal computer to which the electro-optical device 10 is applied. The personal computer 2000 includes an electro-optical device 10 as a display unit and a main body 2010. The main body 2010 is provided with a power switch 2001 and a keyboard 2002. Since the electro-optical device 10 uses the OLED element 420, it is possible to display an easy-to-see screen with a wide viewing angle.
FIG. 16 shows a configuration of a mobile phone to which the electro-optical device 10 is applied. A cellular phone 3000, a plurality of operation buttons 3001, scroll buttons 3002, and the electro-optical device 10 as a display unit are provided. By operating the scroll button 3002, the screen displayed on the electro-optical device 10 is scrolled.
FIG. 17 shows a configuration of a portable information terminal (PDA: Personal Digital Assistants) to which the electro-optical device 10 is applied. The information portable terminal 4000 includes a plurality of operation buttons 4001, a power switch 4002, and the electro-optical device 10 as a display unit. When the power switch 4002 is operated, various types of information such as an address book and a schedule book are displayed on the electro-optical device 10.
In addition, as an electronic device to which the electro-optical device 10 is applied, in addition to those shown in FIGS. 15 to 17, a digital still camera, a liquid crystal television, a viewfinder type, a monitor direct view type video tape recorder, a car navigation device, a pager, Examples include electronic notebooks, calculators, word processors, workstations, videophones, POS terminals, and devices equipped with touch panels. The electro-optical device 10 described above can be applied as a display unit of these various electronic devices. In addition, it is not limited to a display unit of an electronic device that directly displays an image or a character, but is applied as a light source of a printing device that is used to indirectly form an image or a character by irradiating light to the photosensitive member. Also good.

1 is a block diagram illustrating an overall configuration of an electro-optical device according to a first embodiment of the invention. FIG. 2 is a circuit diagram of a pixel circuit 400 of the same device. FIG. It is explanatory drawing which shows the electric current path in the writing period. It is explanatory drawing which shows the current pathway in the light emission period. 2 is a timing chart for explaining operations of a Y driver 100 and an X driver 200 used in the apparatus. It is explanatory drawing which shows the relationship of a movement of a gaze and a screen. It is explanatory drawing which shows the relationship between the locus | trajectory of the light emission on a retina, and the stimulus distribution on a retina in the drive method of the apparatus. It is explanatory drawing which shows an example in case a 1st light emission period and a 2nd light emission period leave | separate. It is explanatory drawing which shows the relationship between the locus | trajectory of the light emission on a retina at the time of employ | adopting the timing shown in FIG. 8, and the stimulus distribution on a retina. It is explanatory drawing which shows the relationship between the gradation value which concerns on 1st Embodiment, 1st writing period T1el, and 2nd writing period T2el. It is explanatory drawing which shows the relationship between the gradation value which concerns on 2nd Embodiment, 1st writing period T1el, and 2nd writing period T2el. It is a block diagram which shows the detailed structure of the X driver 200 which concerns on 2nd Embodiment. It is a block diagram which shows the detailed structure of the X driver 200 which concerns on 3rd Embodiment. It is explanatory drawing which shows intermediate range (DELTA) Nmid. 1 is a perspective view showing a configuration of a personal computer as an example of an electronic apparatus to which an electro-optical device is applied. It is a perspective view which shows the structure of the mobile telephone which is an example of the electronic device to which the electro-optical apparatus is applied. It is a perspective view which shows the structure of the portable information terminal which is an example of the electronic device to which the electro-optical device is applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Scanning line, 102 ... Light emission control line, 103 ... Data line, 400 ... Pixel circuit, 420 ... OLED element (electro-optical element), 100 ... Y driver (first drive means), 200 ... X driver (second drive) Means), idata ... set current, T1 ... first period, T2 ... second period, T1el ... first light emission period, T2el ... second light emission period, Iamin ... first minimum current value, Iamax ... first maximum current value, Ibmin: second minimum current value, Ibmax: second maximum current value, Nmax: maximum gradation, Nmid: intermediate gradation, Nmin: minimum gradation, ΔNmid: intermediate range.

Claims (15)

A plurality of scanning lines; a plurality of data lines; and a pixel circuit provided corresponding to each intersection of the scanning lines and the data lines, wherein the pixel circuit has a luminance in accordance with a supplied current. An electro-optic element to be adjusted; and storage means for storing a set current that flows between the data line and the pixel circuit and that corresponds to image data indicating a gradation as a current that is supplied to the electro-optic element. A method for driving an electro-optical device, comprising:
One frame is composed of a first period and a second period.
The first period includes a first writing period and a first light emission period,
In the first writing period, a set current corresponding to high gradation image data is written to the storage means,
In the first light emission period, a set current having a magnitude stored in the storage unit is supplied to the electro-optic element,
The second period includes a second writing period and a second light emitting period,
In the second writing period, a setting current corresponding to low gradation image data is written to the storage means,
In the second light emission period, a set current having a magnitude stored in the storage means is supplied to the electro-optic element,
The method of driving an electro-optical device, wherein the first light emission period and the second light emission period are adjacent to each other on a time axis. 2. The electro-optical device driving method according to claim 1, wherein the first light emission period and the second light emission period are adjacent to each other via the second writing period. The method of driving an electro-optical device according to claim 1, wherein the first light emission period and the second light emission period are adjacent to each other via the first writing period. A plurality of scanning lines; a plurality of data lines; and a pixel circuit provided corresponding to each intersection of the scanning lines and the data lines, wherein the pixel circuit has a luminance in accordance with a supplied current. An electro-optic element to be adjusted; and storage means for storing a set current that flows between the data line and the pixel circuit and that corresponds to image data indicating a gradation as a current that is supplied to the electro-optic element. A method for driving an electro-optical device, comprising:
One frame is composed of a first period and a second period.
The first period includes a first writing period and a first light emission period,
In the first writing period, a set current corresponding to high gradation image data is written to the storage means,
In the first light emission period, a set current having a magnitude stored in the storage unit is supplied to the electro-optic element,
The second period includes a second writing period and a second light emitting period,
In the second writing period, a setting current corresponding to low gradation image data is written to the storage means,
In the second light emission period, a set current having a magnitude stored in the storage means is supplied to the electro-optic element,
The minimum value of the set current written in the first writing period is the first minimum value, the maximum value is the first maximum value, the minimum value of the setting current written in the second writing period is the second minimum value, and the maximum When the value is the second maximum value, a ratio between the first light emission period and the second light emission period is equal to a ratio between the first maximum value and the first minimum value, and the second maximum value and the second light emission period are equal to each other. A method of driving an electro-optical device, wherein the driving method is set to be equal to a ratio with the second minimum value. The ratio between the first light emission period and the second light emission period is set to be equal to a square root of a ratio between a maximum value and a minimum value of gradations to be displayed. Driving method of electro-optical device. The gradation range to be displayed in the first period and the gradation range to be displayed in the second period are set to partially overlap, and when the range is an overlapping range,
It is determined whether the gradation to be displayed is in the overlapping range,
5. The electro-optic according to claim 4, wherein when the gradation to be displayed is in the overlapping range, the electro-optic element is driven by randomly selecting the first period or the second period. Device driving method. The first range of gradations to be displayed in the first period and the second range of gradations to be displayed in the second period are set to overlap with a boundary value;
It is determined whether the gradation to be displayed is within a predetermined range including the boundary value,
When the gradation to be displayed is in the overlapping range, a random gradation value is synthesized with the gradation to be displayed,
Determining whether the combined tone value belongs to the first range or the second range;
The driving method of the electro-optical device according to claim 4, wherein the electro-optical element is driven by selecting the first period or the second period according to a determination result. A plurality of scanning lines; a plurality of data lines; and a pixel circuit provided corresponding to each intersection of the scanning lines and the data lines, wherein the pixel circuit has a luminance in accordance with a supplied current. An electro-optical element to be adjusted, and a storage unit that stores a set current according to image data indicating a gradation and flowing between the data line and the pixel circuit as a current to be supplied to the electro-optical element. An optical device,
One frame is divided into a first period including a first writing period and a first light emitting period, and a second period including a second writing period and a second light emitting period, and the first writing period and the In the second writing period, the pixel circuit is controlled to select the scanning line and write the magnitude of the set current supplied to the data line to the storage unit, and the first light emitting period and the first light emitting period First driving means for controlling the pixel circuit so that two light emission periods are adjacent to each other on the time axis and the set current having a magnitude stored in the storage means is supplied to the electro-optical element in these periods. ,
In the first writing period, a setting current corresponding to high gradation image data is supplied to the data line, and in the second writing period, a setting current corresponding to low gradation image data is supplied to the data line. Second driving means for supplying to
An electro-optical device. The electro-optical device according to claim 8, wherein the first driving unit makes the first light emission period and the second light emission period adjacent to each other through the second writing period. The electro-optical device according to claim 8, wherein the first driving unit makes the first light emission period and the second light emission period adjacent to each other through the first writing period. A plurality of scanning lines; a plurality of data lines; and a pixel circuit provided corresponding to each intersection of the scanning lines and the data lines, wherein the pixel circuit has a luminance in accordance with a supplied current. An electro-optic element to be adjusted; and storage means for storing a set current that flows between the data line and the pixel circuit and that corresponds to image data indicating a gradation as a current that is supplied to the electro-optic element. An electro-optic device,
One frame is divided into a first period including a first writing period and a first light emitting period, and a second period including a second writing period and a second light emitting period, and the first writing period and the In the second writing period, the pixel circuit is controlled to select the scanning line and write the magnitude of the set current supplied to the data line to the storage unit, and the first light emitting period and the first light emitting period First driving means for controlling the pixel circuit so as to supply the set current having a magnitude stored in the storage means to the electro-optic element in two light emission periods;
In the first writing period, a setting current corresponding to high gradation image data is supplied to the data line, and in the second writing period, a setting current corresponding to low gradation image data is supplied to the data line. And the minimum value of the set current to be written in the first writing period is the first minimum value, the maximum value is the first maximum value, and the minimum value of the setting current to be written in the second writing period is the second minimum When the value and the maximum value are the second maximum value, the ratio between the first maximum value and the first minimum value and the ratio between the second maximum value and the second minimum value are the first light emission period. And a second driving means that is set to be equal to a ratio of the second light emission period;
An electro-optical device. The first driving means is set so that a ratio between the first light emission period and the second light emission period is equal to a square root of a ratio between a maximum value and a minimum value of gradations to be displayed. The electro-optical device according to claim 11. The second driving means includes
Setting means for setting an overlapping range so that a gradation range to be displayed in the first period and a gradation range to be displayed in the second period partially overlap;
Determining means for determining whether or not a gradation to be displayed is in the overlapping range;
Current supply for randomly selecting the first period or the second period and supplying the set current to the data line when the determination unit determines that the gradation to be displayed is in the overlapping range. Means,
The electro-optical device according to claim 11, comprising: The second driving means includes
Setting means for setting the first range of gradations to be displayed in the first period and the second range of gradations to be displayed in the second period to overlap with a boundary value;
Determination means for determining whether or not a gradation to be displayed is in a predetermined range including the boundary value;
When the determination unit determines that the gradation to be displayed is within the predetermined range, a combining unit that combines a random gradation value with the gradation to be displayed;
When the combined gradation value belongs to the first range, the set current is supplied to the data line in the first period, and when the combined gradation value belongs to the second range, the second period. Current supply means for supplying the set current to the data line in FIG.
The electro-optical device according to claim 11, comprising: An electronic apparatus comprising the electro-optical device according to claim 8.

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