Patent Application
20080123011
The present invention relates to liquid crystal display (LCD) devices, particularly to an LCD device having a stable actual common voltage.
Because LCD devices have the advantages of portability, low power consumption, and low radiation, they have been widely used in various portable information products such as notebooks, personal digital assistants (PDAs), video cameras, and the like. Furthermore, LCD devices are considered by many to have the potential to completely replace CRT (cathode ray tube) monitors and televisions.
A common electrode layer 14 is formed on the first substrate 11, adjacent to the liquid crystal layer 15. The common electrode layer 14 covers substantially an entire surface of the first substrate 11, and generally is a transparent conducting layer.
The second substrate 13 includes a plurality of gate lines 16 that are parallel to each other, a plurality of data lines 18 that are parallel to each other and perpendicular to the gate lines 16, and a plurality of pixel electrodes 17. The gate lines 16 intersect with but are insulated from the data lines 18. Each of the pixel electrodes 17 is formed in an area enclosed by two adjacent gate lines 16 and two adjacent data lines 18. The gate lines 16 and the data lines 18 generally face toward the common electrode layer 14. Thus each gate line 16 and the common electrode layer 14 constitute a coupling capacitor, and each data line 18 and the common electrode layer 14 constitute a coupling capacitor.
When the LCD device 10 displays images, a predetermined common voltage is applied to the common electrode layer 14, and a gray scale voltage is applied to each of the pixel electrodes 17. Thus, an electric field is generated in the liquid crystal layer 15. A transmittance of light passing through the liquid crystal layer 15 is adjusted by controlling the strength of the electric field, thereby obtaining desired images.
The voltages of the gates line 16 and the data lines 18 are quickly changed, and the actual common voltage may be rippled because of the coupling effects of the coupling capacitors. That is, desired voltage-transmittance characteristics of the liquid crystal layer 15 are shifted, and this typically leads to a deterioration in the quality of images displayed.
What is needed, therefore, is an LCD device that can overcome the above-described deficiencies.
In one preferred embodiment, a liquid crystal display device includes a first substrate, a second substrate parallel to the first substrate, and a liquid crystal layer between the first substrate and the second substrate. The first substrate includes a common electrode adjacent to the liquid crystal layer. The second substrate includes a plurality of gate lines, a plurality of data lines perpendicular to the gate lines, a plurality of first decouple layers formed on the gate lines and a plurality of second decouple layers formed on the data lines. The first and second decouple layers are connected to ground.
Other aspects, novel features and advantages will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. In the drawings, all the views are schematic.
The first substrate 21 includes a common electrode layer 24. The common electrode 24 is formed on the first substrate 21, adjacent to the liquid crystal layer 25. The common electrode layer 24 covers substantially an entire surface of the first substrate 21. The common electrode 24 is a generally transparent conducting layer, and is typically made from indium tin oxide (ITO) or indium zinc oxide (IZO). The common electrode 24 has a predetermined common voltage applied thereto.
The second substrate 23 includes a plurality of gate lines 26 that are parallel to each other, a plurality of data lines 28 that are parallel to each other and perpendicular to the gate lines 26, a plurality of first decouple layers 261, a plurality of second decouple layers 281, a plurality of thin film transistors (TFTs) 22, and a plurality of pixel electrodes 27. The gate lines 26 intersect with the data lines 28, thereby defining a plurality of pixel units (not labeled). Each pixel unit includes a TFT 22 and a pixel electrode 27. Each TFT 22 includes a gate electrode (not labeled) connected to a gate line 26, a source electrode (not labeled) connected to a data line 28, and a drain electrode (not labeled) connected to a pixel electrode 27. Each TFT 22 serves as a switching element. The data lines 28 can be made from a refractory metal, such as chromium (Cr), titanium (Ti), or an alloy having either or both of these metals. The gate lines 26 can be made from a low resistance metal such as aluminum (Al) or an aluminum alloy.
Referring to
When the LCD device 20 displays images, a plurality of gate-on voltages are applied in sequence to the gate lines 26. A plurality of gray scale voltages are applied to the data lines 28, and thus to the corresponding TFTs 22.
Each TFT 22 is turned on when a corresponding gate-on voltage is applied to the gate electrode thereof. Then, a corresponding gray scale voltage is applied to the drain electrode of the TFT 22 through the source electrode of the TFT 22. Consequentially, the gray scale voltage is applied to the corresponding pixel electrode 27. Thus, an electric field is generated due to a voltage difference between the pixel electrode 27 and the common electrode 24. Generally, if an electric field with the same direction is continuously applied to the liquid crystal of the liquid crystal layer 25, the liquid crystal is liable to be degraded. For this reason, the gray scale voltages are changed alternately between positive and negative values relative to the common voltage. Thereby, degradation of the liquid crystal is avoided.
Thus, variable voltages are continuously applied to the gate lines 26 and data lines 28. Because each of the first decouple layers 261 and the respective gate line 26 constitute a coupling capacitor, the variations of the voltage applied to the gate line 26 only have effect on the first decouple layer 261. The first decouple layer 261 is connected to ground, therefore the coupling effect is greatly reduced. The second decouple layers 281 have substantially the same function as the first decouple layers 261. Thus the actual common voltage can remain undisturbed and stable. As a result, the quality of images displayed by the LCD device 20 remains unimpaired.
Further or alternative embodiments may include the following. The first and second decouple layers 261, 281 can have an invariable voltage applied thereto. In such case, the first and second decouple layers 261, 281 can also prevent variations in the common voltage.
It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200620016001.6 | Nov 2006 | CN | national |
