JP2008268262A - Driving method of electro-optical device - Google Patents

Abstract

When an electro-optical device is driven using a time-division gradation method, flicker is sufficiently suppressed.
An electro-optical device driving method for expressing a plurality of gradations by dividing one frame period into a plurality of sub-frame periods having different periods and causing an electro-optical element to emit light in each sub-frame period. When the electro-optic element emits light during the longest subframe period among the subframe periods, the longest subframe period is divided into the length of the shortest subframe period and is discontinuously dispersed during one frame period. To emit light.
[Selection] Figure 3

Description

  The present invention relates to a driving method for an electro-optical device.

  In recent years, electro-optical devices using organic EL elements or liquid crystal elements have attracted attention as electro-optical devices. As a method for expressing the gradation of such an electro-optical device, for example, a time division gradation method is known in which gradation is expressed by controlling the light emission time in one frame of the organic EL element. In the time division gradation method, a plurality of subframes having different lengths are set in one frame. In general, each subframe corresponds to a different luminance, and gradation is expressed by causing an organic EL element to emit light during a predetermined subframe.

In the case of time division gradation, flicker may occur when the light emission / non-light emission of the element is switched. In particular, flicker is conspicuous when a subframe having a relatively long period is selected. For example, when the frame frequency is 30 frames, the flicker is not noticeable up to the luminance of 25%, but the flicker becomes noticeable at the luminance of 50%. For example, Japanese Patent Application Laid-Open No. H10-133707 discloses a technique for dealing with the flicker problem in such time-division gradation.
JP 2004-151644 A

  An object of the present invention is to sufficiently suppress flicker when an electro-optical device is driven using a time division gradation method.

  The driving method of the electro-optical device according to the present invention includes pixels including an electro-optical element, and one frame period is divided into a plurality of sub-frame periods having different periods, and the pixels are turned on in each sub-frame period. A method for driving an electro-optical device that expresses a plurality of gradations, wherein when the pixel is lit for the longest subframe period among the subframe periods, the longest subframe period is the shortest subframe. It is divided into lengths of periods, and is lit in a discontinuous manner during one frame period.

Even if the lighting time of a pixel is divided into short times and lighted discontinuously, the same gradation can be expressed as long as the total lighting time during one frame period is the same. Therefore, according to the present invention, flicker can be suppressed by shortening the lighting time while maintaining the gradation. Since flicker occurs mainly when the longest subframe period is lit, dividing the longest subframe period can prevent flicker without increasing the burden of driving processing.
As the electro-optical element, for example, an organic EL element or a liquid crystal element can be used.

In the electro-optical device driving method according to the present invention, when the electro-optical element is turned on in each sub-frame period, each sub-frame period is divided into the length of the shortest sub-frame period. Alternatively, the light may be emitted discontinuously.
Accordingly, flicker can be more reliably suppressed while maintaining the gradation.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Embodiment 1 FIG.
FIG. 1 is a diagram showing a circuit configuration of an organic EL device (electro-optical device) 100 which is an example of an electro-optical device of the present invention. The organic EL device 100 includes a plurality of scanning lines 101, a plurality of signal lines 102 arranged orthogonal to the scanning lines 101, a plurality of power supply lines 103 extending in parallel to the signal lines 102, each scanning line 101, and each And a plurality of pixel portions A provided in the vicinity of the intersection with the signal line 102. That is, the organic EL device 100 of this example is an active matrix display device that includes a plurality of pixel portions A and in which the pixel portions are arranged in a matrix.

  Each scanning line 101 is connected to a scanning line driving circuit 105 including a shift register and a level shifter. Each signal line 102 is connected to a data line driving circuit 104 including a shift register, a level shifter, a video line, and an analog switch. Each pixel unit A includes a switching transistor 112 to which a scanning signal is supplied to the gate via the scanning line 101, a capacitor 111 for holding a pixel signal supplied from the signal line 102 via the switching transistor 112, and A driving transistor 113 to which the pixel signal held by the capacitor 111 is supplied to the gate, and a pixel into which a driving current flows from the power supply line 103 when the pixel signal is electrically connected to the power supply line 103 via the driving transistor 113 A light emitting functional layer sandwiched between an electrode (anode) and a counter electrode (cathode) facing the pixel electrode is provided. An organic EL element (light emitting element) 300 is configured by these pixel electrodes, the counter electrode, and the light emitting functional layer. The light emitting functional layer includes a hole transport layer, a light emitting layer, and an electron injection layer.

  In the organic EL device 100, when the scanning line 101 is driven and the switching transistor 112 is turned on, the potential of the signal line 102 at that time is held in the capacitor 111, and the driving transistor is changed according to the state of the capacitor 111. The on / off state of 113 is determined. Then, a current flows from the power supply line 103 to the pixel electrode through the channel of the driving transistor 113, and a current flows to the cathode through the light emitting functional layer. The light emitting functional layer emits light according to this flowing current amount. A desired image display can be performed by controlling the light emission state of each light emitting functional layer.

  The organic EL device 100 is driven by the time division gradation method and can express 64 gradations. The gradation can be expressed by controlling the length of time during which light is emitted within one frame period. FIG. 2 is a diagram for explaining gradation expression by the time division gradation method. As shown in the figure, one frame is divided into six subframes. Each sub-frame has a different period length, and each period corresponds to a light emission time in which each gradation can be expressed. In general, in the case of 64 gradations, one frame has six periods corresponding to gradations of “1”, “2”, “4”, “8”, “16”, and “32”, respectively. Consists of subframes.

  Of the six subframes SF1 to SF6, the subframe SF6 of the longest period (“32”) corresponds to the gradation of the luminance of the organic EL element of 50%, and the subframe SF5 of the next long period (“16”). Corresponds to a gradation with a luminance of 25%. The subframe SF1 of the shortest period (“1”) corresponds to the darkest gradation. As shown in FIG. 2, when the organic EL element emits light during the subframe SF6, the luminance is 50%, and when the organic EL element is emitted during the subframe SF5, the luminance is 25%.

FIG. 3 is a diagram illustrating a method for driving the organic EL device 100 according to the present invention.
Even if the light emission time of the organic EL element is divided into short time periods to emit light discontinuously in one frame, the same gradation can be expressed as long as the total light emission time is the same. In the first embodiment, by using this characteristic, the subframe to be the light emission period is divided into the shortest subframe SF1 as shown in FIG. 3A, and the light emission period and the non-light emission period are further divided. It is dispersed so that it repeats alternately. For example, when the frame frequency is 30 frames, it is blinked at a cycle of 529.1 μs. Thus, flicker can be suppressed by dispersing the light emission time in a very short period. Further, in the case of a moving image, afterimages are suppressed, and display accuracy is improved.

  FIG. 3B shows a driving method when the subframe is not divided. For example, when the frame frequency is 30 frames, light is emitted for 16.9 ms and turned off for 16.9 ms when the luminance is displayed at 50%. Under these conditions, flicker occurs. Therefore, as shown in FIG. 3A, flickering is prevented while maintaining the luminance by blinking at a cycle of 529.1 μs within one frame so that the total light emission time becomes 16.9 ms. can do.

  In the first embodiment, as shown in FIG. 3A, all the subframes are divided into the shortest subframe SF1 and dispersed so that the light emission period and the non-light emission period are alternately repeated. However, the subframe may be divided only by the longest subframe SF6, for example. Flicker occurs mainly when light is emitted during the longest subframe, so that even if the subframe SF6 is divided, a large effect can be obtained.

  Further, in Embodiment 1, the subframe is divided into the length of the shortest subframe SF1, but the division length is not limited to this. For example, in the case of the subframe SF6, it may be divided into two equal parts and divided into the same length as the subframe SF5 or may be further divided into shorter parts.

Electronic Device Next, a specific example of an electronic device including the organic EL device 100 described above will be described.
FIG. 4 is a perspective view illustrating a specific example of an electronic apparatus provided with the organic EL device 100. FIG. 4A is a perspective view illustrating a mobile phone which is an example of an electronic device. The cellular phone 1000 includes a display unit 1001 configured using the organic EL device 100 according to the present invention. FIG. 4B is a perspective view illustrating a wrist watch which is an example of an electronic apparatus. The wristwatch 1100 includes a display unit 1101 configured using the organic EL device 100 according to the present invention. FIG. 4C is a perspective view illustrating a portable information processing device 1200 which is an example of an electronic device. The portable information processing apparatus 1200 includes an input unit 1201 such as a keyboard, a main body unit 1202 in which arithmetic units and storage units are stored, and a display unit 1203 configured using the organic EL device 100 according to the present invention. ing.
In addition to the above, the organic EL device 100 can be used as a display unit of a device such as a display device, a television device, electronic paper, a clock, a calculator, or the like.

FIG. 1 is a diagram illustrating a circuit configuration of an organic EL device that is an example of the electro-optical device of the present invention. FIG. 2 is a diagram for explaining gradation expression by the time-division gradation method. FIG. 3 is a diagram illustrating a method for driving an organic EL device according to the present invention. FIG. 4 is a diagram illustrating an example of an electronic apparatus including the electro-optical device according to the invention.

Explanation of symbols

  100 organic EL device, 101 scanning line, 102 signal line, 103 power supply line, 104 data line driving circuit, 105 scanning line driving circuit, 111 capacitor, 112 switching transistor, 113 driving transistor, 115 ground line, 300 organic EL element

Claims (4)

An electro-optical device having a pixel including an electro-optical element, wherein one frame period is divided into a plurality of sub-frame periods each having a different period, and the pixel is turned on in each sub-frame period to express a plurality of gradations Driving method,
When the pixel is turned on for the longest subframe period among the subframe periods, the longest subframe period is divided into the length of the shortest subframe period, and is discontinuously distributed in one frame period. And driving the electro-optical device.   When the electro-optic element is turned on in each subframe period, each subframe period is divided into the length of the shortest subframe period, and light is emitted discontinuously in one frame period. The method of driving an electro-optical device according to claim 1.   The method of driving an electro-optical device according to claim 1, wherein the electro-optical element is an organic EL element.   The method of driving an electro-optical device according to claim 1, wherein the electro-optical element is a liquid crystal element.

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