Field of the Invention
The present invention relates to a touch panel, a display device and a method of driving the same, and more particularly, to a display device, in which a touch panel is provided in a panel, and a method of driving the same.
Discussion of the Related Art
Touch panels are a type of input device that is included in display devices such as liquid crystal display (LCD) devices, plasma display panels (PDPs), organic light emitting display device (OLED), and electrophoretic display devices (EPDs), and enables a user to input information by directly touching a screen with a finger, a pen or the like while looking at the screen of the display device.
A method of manufacturing LCD devices may include an add-on type, in which a panel displaying an image and a touch panel sensing a touch are manufactured independently from each other and then are attached to each other, and an in-cell type, in which the touch panel is built into the panel.
The demand for display devices with in-cell type touch panel for slimming portable terminals such as smart phones and tablet Personal Computers (PCs), is recently increasing.
In an in-cell type display device, as disclosed in U.S. Pat. No. 7,859,521, a plurality of common electrodes for display are segmented into a plurality of touch driving areas and touch sensing areas. An in-cell type display device allows a mutual capacitance to be generated between the touch driving area and the touch sensing area, and thus, measures the change in a mutual capacitance that occurs in touch to determines whether there is a touch.
In other words, the related art in-cell type display device simultaneously performs a display function and a touch function. To this end, in the related art in-cell type display device, during an image display period, a common voltage is supplied to common electrodes, and during a touch sensing period, a touch driving signal is supplied to the common electrodes.
In a related art in-cell type mutual capacitive display device using the common electrode, the common electrode is used as a driving electrode and a receiving electrode that are necessary for touch sensing, and an image display period and a touch sensing period are temporally divided.
Therefore, in the image display period, a driving electrode and a receiving electrode function as a common electrode. In the touch sensing period, a periodic driving pulse is applied to the driving electrode, and a touch driver determines whether there is a touch by using a sensing signal that is received through the receiving electrode.
FIG. 1 is an exemplary waveform diagram showing an image display period and a touch sensing period in a related art in-cell type display device.
In the related art in-cell type display device, as described above and as shown in FIG. 1, a period (hereinafter simply referred to as one frame period) corresponding to one frame is divided into an image display period (Display) and a touch sensing period (Touch).
A touch panel applied to the related art in-cell type display device includes a driving electrode, to which a common voltage is supplied during the image display period and a driving voltage is supplied during the touch sensing period, and a receiving electrode, to which a common voltage is supplied during the image display period and a reference voltage is supplied during the touch sensing period.
During the image display period, the common voltage is supplied to the driving electrode and the receiving electrode.
During the touch sensing period, a touch driving signal having a pulse shape is supplied to the driving electrode and a reference voltage is supplied to the receiving electrode.
In this case, when one frame period starts, the image display period is performed, and after the image display period, the touch sensing period is performed.
FIG. 2 is an exemplary diagram illustrating a configuration of a related art touch panel using a capacitance type, and particularly, a configuration of a mutual type touch panel.
The touch panel using the capacitance type includes driving electrodes (TX1 to TX6), to which a common voltage is supplied during the image display period and a touch driving signal is supplied during the touch sensing period, and receiving electrodes (RX1 to RX4), to which a common voltage is supplied during the image display period and a reference voltage is supplied during the touch sensing period. The number of the driving electrodes and the number of the receiving electrodes may be variously changed depending on a size and a shape of the touch panel.
For example, if the touch driving signal is sequentially supplied to the driving electrodes (TX1 to TX6), sensing signals are received through the receiving electrodes (RX1 to RX4). In this case, in order to increase an accuracy of detection of sensing signals, the touch driver respectively supplies a plurality of touch driving signals to the driving electrodes in a repeating manner, and accumulates the sensing signals corresponding to the touch driving signals, to determine whether the touch panel is touched.
The above-described display devices of the related art may have the following problems.
First, as a size of a display device comprising a touch panel increases, the number of driving electrodes provided in the touch panel increases, and for this reason, time taken in supplying the touch driving signal to the driving electrodes increases. Therefore, as a size of the touch panel increases, the time for sensing a touch decreases. For example, when it is assumed that one second is required for touch driving signals are sequentially supplied to ten driving electrodes, two seconds are required for touch driving signals are sequentially supplied to twenty driving electrodes when a touch panel having an increased size. Therefore, as a size of a touch panel increases, the frequency for determining a touch for one minute decreases, and thus, a touch sensing performance is decreased. This may identically occur in an add-on type display device in addition to an in-cell type display device.
Second, particularly, the in-cell type display device, one frame period is divided into the touch sensing period and the image display period, and a ratio of the touch sensing period and the image display period is set. Therefore, when it is assumed that the touch sensing period is determined and a touch panel having an increased size, a time for which a touch driving signal is supplied to each of driving electrodes has to be decreased In other words, the number of the touch driving signals supplied to each of the driving electrodes has to be decreased. Therefore, an in-cell type display device's touch sensitivity is decreased more than an add-on type display device.
Third, furthermore, in the in-cell type display device, various common noises are easily inputted to the driving electrode and the receiving electrode, and thus, the touch sensitivity can be further decreased. A common noise is similarly inputted into a driving electrode and a receiving electrode of a touch panel. Examples of common noise include noise caused by static electricity, noise generated when battery charger is connected to the display device for battery charging, noise generated by a display signal for a display device, and noise generated by a driving signal for a backlight of an LCD device, or the like.
Fourth, the noise has a specific frequency or a specific waveform, or may have a white noise characteristic. Therefore, to solve the common noise, various types of and difficult-to-implement noise signal processing filters need to be added, and thus, the processor's computation may increase.
Fifth, if a voltage of a touch driving signal is increased for enhancing a touch sensitivity, a power consumption may increase.