METHOD FOR DRIVING LIQUID CRYSTAL DISPLAY DEVICE

• US 20110148826A1
• Filed: 12/15/2010
• Published: 06/23/2011
• Est. Priority Date: 12/18/2009
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: MIYAKE, Hiroyuki, KOYAMA, Jun
• Granted Patent: US 8,599,177 B2
• Time in Patent Office: Days
• US Class Current: 345/204
• CPC Class Codes: G02F 1/1345 Conductors connecting electrodes to cell terminals
• CPC Class Codes: G06F 3/0421 by interrupting or reflecting a light beam, e.g. optical touch-screen
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2310/04 Partial updating of the display screen
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2320/0209 Crosstalk reduction, i.e. to reduce direct or indirect influences of signals directed to a certain pixel of the displayed image on other pixels of said image, inclusive of influences affecting pixels in different frames or fields or sub-images which constitute a same image, e.g. left and right images of a stereoscopic display
• CPC Class Codes: G09G 2320/0219 Reducing feedthrough effects in active matrix panels, i.e. voltage changes on the scan electrode influencing the pixel voltage due to capacitive coupling
• CPC Class Codes: G09G 2320/10 Special adaptations of display systems for operation with variable images
• CPC Class Codes: G09G 2320/103 Detection of image changes, e.g. determination of an index representative of the image change
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 2340/0435 Change or adaptation of the frame rate of the video stream
• CPC Class Codes: G09G 2340/16 Determination of a pixel data signal depending on the signal applied in the previous frame
• CPC Class Codes: G09G 2354/00 Aspects of interface with display user
• CPC Class Codes: G09G 3/3618 with automatic refresh of the display panel using sense/write circuits
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence
• CPC Class Codes: G09G 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

The liquid crystal display device includes a first substrate provided with a terminal portion, a switching transistor, a driver circuit portion, and a pixel circuit portion including a pixel transistor and a plurality of pixels, a second substrate provided with a common electrode electrically connected to the terminal portion through the switching transistor, and liquid crystal between a pixel electrode and the common electrode. In a period during which a still image is switched to a moving image, the following steps are sequentially performed: a first step of supplying the common potential to the common electrode; a second step of supplying a power supply voltage to the driver circuit portion; a third step of supplying a clock signal to the driver circuit portion; and a fourth step of supplying a start pulse signal to the driver circuit portion.

Claims

1. A method for driving a liquid crystal display device comprising:

in a period during which a moving image is displayed,

turning on a pixel transistor including an oxide semiconductor layer which is electrically connected to a driver circuit portion formed over a first substrate, so that an image signal is supplied to a pixel electrode; and

turning on a switching transistor including an oxide semiconductor layer which is electrically connected to a terminal portion formed over the first substrate, so that a common potential is supplied to a common electrode which is electrically connected to the terminal portion through the switching transistor and which is formed over a second substrate;

in a period during which a still image is displayed,

turning off the pixel transistor so that the pixel electrode is in an electrically floating state; and

turning off the switching transistor so that the common electrode is in an electrically floating state; and

in a period during which a still image is switched to a moving image,

a first step of supplying the common potential to the common electrode;

a second step of supplying a power supply voltage to the driver circuit portion;

a third step of supplying a clock signal to the driver circuit portion; and

a fourth step of supplying a start pulse signal to the driver circuit portion.

2. A method for driving a liquid crystal display device comprising:

in a period during which a moving image is displayed,

turning on a pixel transistor including an oxide semiconductor layer which is electrically connected to a driver circuit portion formed over a first substrate, so that an image signal is supplied to a pixel electrode; and

turning on a switching transistor including an oxide semiconductor layer which is electrically connected to a terminal portion formed over the first substrate, so that a common potential is supplied to a common electrode which is electrically connected to the terminal portion through the switching transistor and which is formed over a second substrate;

in a period during which a still image is displayed,

turning off the pixel transistor so that the pixel electrode is in an electrically floating state; and

turning off the switching transistor so that the common electrode is in an electrically floating state; and

in a period during which a moving image is switched to a still image,

a first step of stopping supply of a start pulse signal to the driver circuit portion;

a second step of stopping supply of a clock signal to the driver circuit portion;

a third step of stopping supply of a power supply voltage to the driver circuit portion; and

a fourth step of stopping supply of the common potential to the common electrode.

3. The method for driving a liquid crystal display device, according to claim 2,

wherein the liquid crystal display device comprises:

a memory circuit which stores the image signals;

a comparator circuit which compares the image signals in each of pixels and calculates a difference; and

a display control circuit which controls the driver circuit and reads out the image signals, and

wherein in the comparator circuit, the image signals stored in the memory circuit in successive frame periods are read out and compared in each of the pixels to compare a difference, so that whether a moving image or a still image is displayed is determined.

4. The method for driving a liquid crystal display device, according to claim 3,

wherein a conduction state or a non-conduction state between the common electrode and the terminal portion to which the common potential is supplied is controlled by the switching transistor in accordance with a signal supplied from the display control circuit to a gate terminal of the switching transistor.

5. The driving method of a liquid crystal display device according to claim 3,

wherein the switching transistor has an off current per micrometer in channel width of 10 zA/μ

m or less at room temperature, and

wherein a conduction state or a non-conduction state between the common electrode and the terminal portion to which the common potential is supplied is controlled by the switching transistor.

6. A method for driving a liquid crystal display device including a pixel transistor which is electrically connected to a driving circuit portion, a pixel electrode which is electrically connected to the pixel transistor and a common electrode which is disposed to facing the pixel electrode, comprising step of;

a first step of starting supply of the common potential to the common electrode;

a second step of starting supply of a power supply voltage to the driver circuit portion;

a third step of starting supply of a clock signal to the driver circuit portion; and

a fourth step of starting supply of a start pulse signal to the driver circuit portion.

7. The driving method of a liquid crystal display device according to claim 6,

wherein the common electrode is formed over a first substrate, and

wherein the pixel electrode is formed over a second substrate.

8. A method for driving a liquid crystal display device including a pixel transistor which is electrically connected to a driving circuit portion, a pixel electrode which is electrically connected to the pixel transistor and a common electrode which is disposed to facing the pixel electrode, comprising step of;

a first step of stopping supply of a start pulse signal to the driver circuit portion;

a second step of stopping supply of a clock signal to the driver circuit portion;

a third step of stopping supply of a power supply voltage to the driver circuit portion; and

a fourth step of stopping supply of the common potential to the common electrode.

9. The driving method of a liquid crystal display device according to claim 8,

wherein the common electrode is formed over a first substrate, and

wherein the pixel electrode is formed over a second substrate.