Active matrix display device

• US 20020167477A1
• Filed: 04/29/2002
• Published: 11/14/2002
• Est. Priority Date: 04/27/2001
• Status: Active Grant

• Current Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Sanyo Electric Company Limited (Panasonic Holdings Corporation)
• Inventors: Senda, Michiru, Yokoyama, Ryoichi, Tsutsui, Yusuke
• Granted Patent: US 6,956,553 B2
• Time in Patent Office: Days
• US Class Current: 345/89
• CPC Class Codes: G09G 2300/0443 with several sub-pixels for the same colour in a pixel, not specifically used to display gradations G09G3/364 takes precedence
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 3/2074 using sub-pixels
• CPC Class Codes: G09G 3/3648 using an active matrix G09G3/367 - G09G3/3696 take precedence

Abstract

In the active matrix display device with a DRAM as the retaining circuit, the voltage retained in the retaining circuit is set in the brightness saturation region, which is outside the region of the voltage used in the moving picture display mode. With the voltage in this region, the difference in the brightness will not be recognized even if the voltage decreases before the refreshing operation. This prevents flickering and improves the display quality.

Claims

1. An active matrix display device comprising:

a plurality of pixel elements;

a plurality of pixel element electrodes disposed corresponding to the pixel elements; and

a plurality of retaining circuits disposed corresponding to the pixel elements, each of the retaining circuits retaining a voltage, the voltages retained by the retaining circuits being supplied to the corresponding pixel element electrodes to form an image,

wherein the voltages retained by the retaining circuits are in a brightness saturation region of the display device in which a change in the voltages retained by the retaining circuits does not substantially change a brightness of the image.

3. The active matrix display device of claims 1 or 2, wherein a refreshing operation for refreshing the voltages retained by the retaining circuit is performed at a predetermined interval, the voltages retained by the retaining circuits decrease by an amount in the interval, and the voltages retained by the retaining circuits are higher than the boundary voltage by at least that amount.

6. The active matrix display device of any of claims 1-5, wherein each of the pixel element electrodes comprises a plurality of sub-pixel element electrodes, each having different surface areas.

7. The active matrix display device of any of claims 1-5, wherein each of the retaining circuits comprises a capacitance element retaining the voltage retained by the retaining circuit.

2. An active matrix display device comprising:

a first substrate and a second substrate;

a liquid crystal disposed between the first substrate and the second substrate;

a plurality of pixel element electrodes disposed on the first substrate;

a plurality of retaining circuits disposed on the first substrate, the retaining circuits corresponding to the pixel element electrodes, each of the retaining circuits retaining a voltage, the voltages retained by the retaining circuits being supplied to the corresponding pixel element electrodes to form an image; and

a common electrode disposed on the second substrate, the common electrode facing the pixel element electrodes,

wherein the voltages retained by the retaining circuits are in a brightness saturation region of the display device, the brightness saturation region being defined by a boundary voltage beyond which any change in a voltage applied between the common electrode and one of the pixel element electrodes does not substantially change an optical transmittance of the liquid crystal.

4. An active matrix display device comprising:

a first substrate and a second substrate;

a liquid crystal disposed between the first substrate and the second substrate;

a plurality of pixel element electrodes disposed on the first substrate;

a plurality of retaining circuits disposed on the first substrate, the retaining circuits corresponding to the pixel element electrodes, each of the retaining circuits retaining a voltage, the voltages retained by the retaining circuits being supplied to the corresponding pixel element electrodes to form an image; and

a common electrode disposed on the second substrate, the common electrode facing the pixel element electrodes,

wherein the voltages retained by the retaining circuits are sufficient to provide about 90% or more of an optical transmittance of a brightness saturation region of the display device, or enough to provide about 10% or less of the optical transmittance of the brightness saturation region, the brightness saturation region being defined by a boundary voltage beyond which any change in a voltage applied between the common electrode and one of the pixel element electrodes does not substantially change an optical transmittance of the liquid crystal.

5. An active matrix display device comprising:

a first substrate and a second substrate;

a liquid crystal disposed between the first substrate and the second substrate;

a plurality of pixel element electrodes disposed on the first substrate;

a plurality of retaining circuits disposed on the first substrate, the retaining circuits corresponding to the pixel element electrodes, each of the retaining circuits retaining a voltage, the voltages retained by the retaining circuits being supplied to the corresponding pixel element electrodes to form an image; and

a common electrode disposed on the second substrate, the common electrode facing the pixel element electrodes, wherein

the display device operates in a moving picture display mode and a still image display mode, the moving picture display mode using an image signal to display an analog image, the still picture display mode using the voltages retained by the retaining circuits to display a digital image, and

the voltages retained by the retaining circuits are outside of a range of voltages applied to the pixel element electrodes in the moving picture display mode.

8. An active matrix display device comprising:

a pixel element;

a pixel element electrode disposed for the pixel element;

a plurality of sub-pixel element electrodes disposed for the pixel element electrode, each of the sub-pixel element electrodes having a different surface area; and

a plurality of retaining circuits disposed for the pixel element electrode, each of the retaining circuits corresponding to one of the sub-pixel element electrodes, retaining a voltage, and supplying the voltage to the corresponding sub-pixel element electrode,

wherein the sub-pixel element electrodes are symmetrically disposed with respect to a first line of symmetry passing substantially through a center of the pixel element, with respect to a second line of symmetry passing substantially through the center of the pixel element, or with respect to both the first line and the second line, the first line and the second line being substantially orthogonal to each other.

9. The active matrix display device of claim 8, wherein a smallest sub-pixel element electrode among the sub-pixel element electrodes is disposed substantially in the center of the pixel element, and the sub-pixel element electrodes with larger surface areas surround the sub-pixel element electrodes with smaller surface areas, respectively.

10. The active matrix display device of claim 9, wherein the smallest sub-pixel element electrode has a rectangular shape and the sub-pixel element electrodes larger than the smallest sub-pixel element electrode have a rectangular shape with a rectangular opening in a center thereof.

11. An active matrix display device comprising:

a first substrate and a second substrate;

a liquid crystal disposed between the first substrate and the second substrate;

a plurality of pixel element electrodes disposed on the first substrate;

a plurality of retaining circuits disposed on the first substrate, the retaining circuits corresponding to the pixel element electrodes, each of the retaining circuits retaining a voltage, the voltages retained by the retaining circuits being supplied to the corresponding pixel element electrodes to form an image; and

a common electrode disposed on the second substrate, the common electrode facing the pixel element electrodes,

wherein a refreshing operation for refreshing the voltages retained by the retaining circuits is performed with a first cycle, and an inverting operation for inverting the voltages retained by the retaining circuits, so that a direction of an electric field applied to the liquid crystal is inverted, is performed with a second cycle, the inverting operation coinciding with one of the refreshing operations.

12. The active matrix display device of claim 11, wherein the second cycle is a multiple of the first cycle.

13. The active matrix display device of claim 11, wherein the first cycle and the second cycle are equal.

16. The active matrix display device of claim 15, further comprising a plurality of pixel element selection transistors, each of the pixel element selection transistors connecting one of the image signal lines and the corresponding retaining circuit, wherein all of the pixel element selection transistors corresponding to one of the pixel element electrodes turn on or off simultaneously.

17. The active matrix display device of claim 15, wherein each of the retaining circuits comprises a capacitance element, and the capacitance elements function as supplemental storage capacitance elements in the moving picture display mode.

18. The active matrix display device of claim 15, wherein the sub-pixel element electrodes corresponding to one of the pixel element electrodes each have different surface areas.

14. An active matrix display device comprising:

a first substrate and a second substrate;

a liquid crystal disposed between the first substrate and the second substrate;

a plurality of pixel element electrodes disposed on the first substrate;

a plurality of retaining circuits disposed on the first substrate, the retaining circuits corresponding to the pixel element electrodes, each of the retaining circuits retaining a voltage, the voltages retained by the retaining circuits being supplied to the corresponding pixel element electrodes to form an image and decrease after being retained by the retaining circuits; and

a common electrode disposed on the second substrate, the common electrode facing the pixel element electrodes, wherein

the display device has a brightness saturation region being defined by a boundary voltage beyond which any change in a voltage applied between the common electrode and one of the pixel element electrodes does not substantially change an optical transmittance of the liquid crystal, the voltages retained by the retaining circuits being in the brightness saturation region, and

the voltages retained by the retaining circuits are inverted in a cycle having a period shorter than a period necessary for the retained voltage to decrease below the boundary voltage.

15. An active matrix display device comprising:

a plurality of gate signal lines disposed in a direction;

a plurality of image signal lines disposed in a direction different from the direction of the gate signal lines;

a plurality of pixel elements;

a plurality of pixel element electrodes disposed corresponding to the pixel elements, the image signal lines sending an image signal to the corresponding pixel element electrodes;

a plurality of sub-pixel element electrodes disposed for each of the pixel element electrodes and insulated from each other, each of the sub-pixel element electrodes being connected to the corresponding image signal line; and

a plurality of retaining circuits disposed for each of the pixel element electrodes, each of the retaining circuit corresponding to one of the sub-pixel element electrodes and retaining a voltage corresponding to the image signal, wherein

the display device has a still image display mode in which a still image is formed based on the voltages retained by the retaining circuits and a moving picture display mode in which a moving picture is formed based on voltages applied to the sub-pixel element electrodes according to the image signal, and

each of the sub-pixel element electrodes of one of the pixel element electrodes receives an equal voltage according to the image signal in the moving picture display mode.

19. An active matrix display device comprising;

a first substrate and a second substrate;

a liquid crystal disposed between the first substrate and the second substrate;

a plurality of pixel element electrodes disposed on the first substrate;

a plurality of sub-pixel element electrodes disposed for each of the pixel element electrodes and having different surface areas;

a plurality of retaining circuits disposed on the first substrate, each of the retaining circuits corresponding to one of the sub-pixel element electrodes and comprising a capacitance element retaining a voltage; and

a common electrode disposed on the second substrate, the common electrode facing the pixel element electrodes,

wherein each of the sub-pixel element electrodes corresponding to one of the pixel element electrodes possesses an equal capacitance, the capacitance being a sum of a capacitance of the corresponding capacitance element and a liquid crystal capacitance formed between the corresponding sub-pixel element electrode and the common electrode through the liquid crystal.

20. An active matrix display device comprising;

a first substrate and a second substrate;

a liquid crystal disposed between the first substrate and the second substrate;

a plurality of pixel element electrodes disposed on the first substrate;

a plurality of sub-pixel element electrodes disposed for each of the pixel element electrodes and having different surface areas;

a plurality of retaining circuits disposed on the first substrate, each of the retaining circuits corresponding to one of the sub-pixel element electrodes and comprising a capacitance element retaining a voltage; and

a common electrode disposed on the second substrate, the common electrode facing the pixel element electrodes,

wherein the sub-pixel element electrodes with smaller surface areas among the subs pixel element electrodes corresponding to one of the pixel element electrodes correspond to the retaining circuits with larger capacitance among the retaining circuits corresponding to said one of the pixel element electrodes.

21. An active matrix display device comprising;

a first substrate and a second substrate;

a liquid crystal disposed between the first substrate and the second substrate;

a plurality of pixel element electrodes disposed on the first substrate;

a plurality of sub-pixel element electrodes disposed for each of the pixel element electrodes and having different surface areas;

a plurality of retaining circuits disposed on the first substrate, each of the retaining circuits corresponding to one of the sub-pixel element electrodes and comprising a capacitance element retaining a voltage; and

a common electrode disposed on the second substrate, the common electrode facing the pixel element electrodes,

wherein a capacitance of one of the capacitance elements is larger than a liquid crystal capacitance formed between the common electrode and the corresponding sub-pixel element electrode through the liquid crystal.

22. An active matrix display device comprising;

a first substrate and a second substrate;

a liquid crystal disposed between the first substrate and the second substrate;

a plurality of pixel element electrodes disposed on the first substrate;

a plurality of sub-pixel element electrodes disposed for each of the pixel element electrodes and having different surface areas;

a plurality of pixel element selection transistors, each of the pixel element selection transistors corresponding to one of the sub-pixel element electrodes and selecting the corresponding sub-pixel element electrode;

a plurality of retaining circuits disposed on the first substrate, each of the retaining circuits corresponding to one of the sub-pixel element electrodes and comprising a capacitance element retaining a voltage; and

a common electrode disposed on the second substrate, the common electrode facing the pixel element electrodes,

wherein the surface area of one of the sub-pixel element electrodes determines a capacitance of the corresponding capacitance element and a channel width of the corresponding pixel element selection transistor.