1. Field of the Invention
The present disclosure relates to a liquid crystal display (LCD) device, and particularly, to an in-cell touch type LCD device and a method for driving the same, the method capable of preventing deterioration of picture quality and enhancing touch sensitivity, by dividing a touch block in a spatial manner, not in a time manner.
2. Background of the Invention
A liquid crystal display (LCD) device includes a display panel for displaying images by driving switching devices formed at intersections between a plurality of data lines and gate lines, driving ICs for controlling the display panel, and an additional optical source such as a backlight unit.
Especially, an LCD device applied to a mobile device is provided with a touch panel for touching a screen using a finger or a stylus pen, etc. rather than a general interface device such as a keyboard and a remote controller, so as to select a specific object or region on the screen.
Such touch panel has a structure where a touch panel additionally fabricated from a display panel is attached to an LCD panel, an in-cell touch structure where a touch electrode and lines are directly formed on a substrate of an LCD panel thus to implement a single panel, etc. An in-cell touch type LCD device is being spotlighted due to high sensitivity, simplified fabrication processes, etc.
The in-cell touch type LCD device should include a plurality of touch blocks for sensing a touch input, and sensing lines electrically connected to the touch blocks, as well as gate lines and data lines.
FIG. 1 is a view of the conventional in-cell touch type liquid crystal display (LCD) device.
The in-cell touch type LCD device includes gate lines (GL) and data lines (DL) which define a plurality of pixels on a substrate 10 by crossing each other, and common lines (CL) for applying common voltages (Vcom) to pixels. A driver 20 electrically connected to the respective lines is mounted to one side of the substrate. And, sensing lines (not shown) formed of low-resistance metallic material are formed on layers different from layers where the gate lines (GL) and the data lines (DL) are formed. The sensing lines are configured to transmit information on a touched position to a touch sensing circuit. The touched position is represented as coordinates values of X and Y axes. Therefore, the sensing lines include X-sensing lines extending in an X-direction, and Y-sensing lines extending in a Y-direction.
A touch block (TB) is formed on an entire display region of the substrate 10. The touch block senses a minute capacitance change occurring when a user touches the substrate using a touch pen or a finger, and converts the sensed capacitance change into a current. Then, the touch block transmits the current to the touch sensing circuit through the aforementioned sensing lines. A single touch block (TB) occupies an area corresponding to 40 gate lines, and the touch blocks (TB) may be formed in about 20 in number {TB0˜TBn(n=19)}.
A terminal portion 30 is implemented as a flexible substrate, and transmitting and receiving each type of signals by being electrically connected to an external system, is provided at one side end of the LCD panel 10.
Under such structure, once the touch block (TB) is touched, a capacitance change generated from a pixel electrode and a common electrode is transmitted to the touch sensing circuit through the sensing lines. As a result, a touched position is sensed. To this end, a common voltage (Vcom) should be applied to the common electrode. Here, the common voltage (Vcom) alternatively implements a direct current (DC) waveform having a fixed potential in correspondence to a pixel voltage, and a sensing waveform configured to sense a touch input and performing a swing operation at prescribed time intervals.
If the sensing waveform common voltage and the pixel voltage are simultaneously applied to the common electrode and the pixel electrode, respectively, the two voltages simultaneously change, thereby causing a difficulty in sensing a touch input.
For instance, if a user touches a region on an LCD panel corresponding to a first touch block (TB0), and if gate driving signals are applied to gate lines (GL) of the first touch block (TB0), a potential of the pixel voltage greatly changes. At the same time, if the sensing waveform common voltage (Vcom) is applied to the first touch block (TB0), the corresponding sensing lines cannot precisely sense a touch input. Therefore, the conventional in-cell touch type LCD device is driven as the touch block is time-divided into a touch time period and a display time period.
FIG. 2 is a view showing signal waveforms implemented when driving the conventional in-cell touch type LCD device.
Referring to FIG. 2, the in-cell touch type LCD device is operated as the touch block is time-divided into a touch time period and a display time period, for a single time period of a horizontal synchronization signal (Hsync) which defines a single horizontal time period (1H). That is, for the single horizontal time period (1H), a sensing waveform common voltage (Vcom) which swings in an alternating current (AC) waveform is firstly allocated to the LCD device, and then a high-potential gate driving signal (VG) is allocated to the LCD device. At the same time, the common voltage (Vcom) is converted into a direct current (DC) waveform. Therefore, the high-potential gate driving signal (VG) and the touch waveform common voltage (Vcom) do not overlap each other.
However, the conventional in-cell touch type LCD device may have the following problems.
Firstly, as the two signals are applied to the LCD device in a time-division manner for the limited single horizontal time period, the time period for which the signals are applied is reduced to about the half. As an example, in case of an LCD device having a single horizontal time period (1H) of 20 us, a touch time period is 8 us, and a display time period is 12 us. Accordingly, the display time period is reduced by about 40% when compared with that of the existing LCD device. This may cause a difficult in obtaining a sufficient time to charge a pixel voltage, thereby resulting in deterioration such as cross-talk.
Secondly, touch sensitivity may be lowered due to a short touch time period.
Thirdly, since the touch time period and the display time period are alternately allocated per horizontal line, a gate overlap driving method for overlapping gate driving signals between neighboring gate lines so as to obtain a sufficient time to charge a pixel voltage, cannot be applied to the LCD device.