BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a touch screen, and more particularly to an in-cell touch screen.
2. Description of Related Art
A touch screen is an input/output device that combines touch technology and display technology to enable users to directly interact with what is displayed. A capacitor-based touch panel is a commonly used touch panel that utilizes capacitive coupling effect to detect touch position. Specifically, capacitance corresponding to the touch position changes and is thus detected, when a finger touches a surface of the touch panel.
In order to produce thinner touch screens, in-cell technology has been adopted that eliminates one or more layers by building capacitors inside the display. Conventional in-cell touch screens, however, possesses substantive parasitic capacitors that form a large load, thereby affecting sensitivity of the touch screen. Accordingly, a need has arisen to propose a novel scheme for driving an in-cell touch screen with enhanced touch sensitivity.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the embodiment of the present invention to provide a method of driving an in-cell touch screen in order to reduce capacitance of the parasitic capacitors, or to reduce power consumption.
According to one embodiment, a touch screen has a common voltage (VCOM) layer divided into VCOM electrodes which act as sensing points in a touch sensing mode. In one embodiment, adjacent VCOM electrodes abutting a current VCOM electrode, a source line underlying the current VCOM electrode, and/or a gate line underlying the current VCOM electrode is set high-impedance in the touch sensing mode, such that an equivalent capacitor is not possessed by the current VCOM electrode, thereby substantially reducing a load at the sensing point. In another embodiment, a gate line underlying a current VCOM electrode is set high-impedance in the touch sensing mode. A voltage waveform of the current VCOM electrode is applied to adjacent VCOM electrodes abutting the current VCOM electrode and/or to a source line underlying the current VCOM electrode, such that an equivalent capacitor has no effect on the current VCOM electrode, thereby substantially reducing a load at the sensing point.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 schematically shows a perspective view of a capacitive in-cell touch screen according to an embodiment of the present invention;
FIG. 2 shows the VCOM layer of FIG. 1;
FIG. 3 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines of FIG. 1;
FIG. 4 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines according to a first embodiment of the present invention;
FIG. 5 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines according to a second embodiment of the present invention;
FIG. 6 shows voltage waveforms of a current VCOM electrode and the underlying source line according to a third embodiment of the present invention;
FIG. 7 shows voltage waveforms of a current VCOM electrode and the underlying source line according to a fourth embodiment of the present invention;
FIG. 8 shows voltage waveforms of a current VCOM electrode and the underlying source line according to a fifth embodiment of the present invention;
FIG. 9 shows voltage waveforms of a current VCOM electrode and the underlying source line according to a sixth embodiment of the present invention;
FIG. 10 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines of FIG. 1;
FIG. 11 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes, the source lines and the gate lines according to a seventh embodiment of the present invention; and
FIG. 12A, FIG. 12B and FIG. 12C show voltage waveforms of VCOM electrodes, the underlying source line and the underlying gate line.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 schematically shows a perspective view of a capacitive in-cell touch screen 100 according to an embodiment of the present invention. The self-capacitance in-cell touch screen (hereinafter touch screen) 100 primarily includes, from bottom up, gate (G) lines 11, source (S) lines 13 and a common voltage (VCOM) layer 15, which are isolated from each other. For brevity, some components of the touch screen 100 are not shown. For example, a liquid crystal layer may be disposed above the VCOM layer 15.
Specifically, gate lines 11 are disposed latitudinally or in rows, and source lines 13 are disposed longitudinally or in columns. The VCOM layer 15 is divided into VCOM electrodes 151 as exemplified in FIG. 2, which act as sensing points (or receiving (RX) electrodes) in a touch sensing mode, and the VCOM electrodes 151 are connected to a common voltage, e.g., a direct-current (DC) voltage, in a display mode.
As the VCOM electrodes 151, the source lines 13 and the gate lines 11 are close to each other for a compact touch screen 100, parasitic capacitors are possessed by the touch screen 100. FIG. 3 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes 151, the source lines 13 and the gate lines 11. VCOM1, VCOM2 and VCOM3 represent three adjacent VCOM electrodes 151. CC1 and CC2 represent equivalent capacitors between the VCOM electrodes 151. CS1, CS2 and CS3 represent equivalent capacitors between the VCOM electrodes 151 (i.e., VCOM1, VCOM2 and VCOM3) and underlying source lines 13, respectively. CG1, CG2 and CG3 represent equivalent capacitors between the VCOM electrodes 151 (i.e., VCOM1, VCOM2 and VCOM3) and underlying gate lines 11, respectively. Each sensing point (or VCOM electrodes 151) possesses a total capacitance of (CCX+CSX+CGX) (where X is 1, 2, or 3), which results in a load that affects sensitivity of the touch screen 100. In order to reduce capacitance of the parasitic capacitors, some embodiments are thus proposed.
FIG. 4 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes 151, the source lines 13 and the gate lines 11 according to a first embodiment of the present invention. In the embodiment, VCOM1, VCOM2 and VCOM3 are under touch sensing in turn. When a current VCOM electrode 151 (e.g., VCOM2) is currently under touch sensing, adjacent VCOM electrodes 151 (e.g., VCOM1 and VCOM3) are set high-impedance (Hi-Z) or floating, for example, by a high-impedance unit 21 shown in FIG. 2. Further, the source line 13 (e.g., S2) underlying the current VCOM electrode 151 and the gate line 11 (e.g., G2) underlying the current VCOM electrode 151 are set high-impedance (Hi-Z) or floating. Accordingly, the equivalent capacitors CC1, CC2, CS2 and CG2 are no longer possessed by the current VCOM electrode 151 (or the sensing point), thereby substantially reducing the load at the sensing point.
FIG. 5 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes 151, the source lines 13 and the gate lines 11 according to a second embodiment of the present invention. In the embodiment, VCOM1, VCOM2 and VCOM3 are under touch sensing in turn. When a current VCOM electrode 151 (e.g., VCOM2) is currently under touch sensing, a voltage waveform at the current VCOM electrode 151 is applied to adjacent VCOM electrodes 151 (e.g., VCOM1 and VCOM3), for example, by a VCOM unit 22 shown in FIG. 2. Accordingly, the adjacent VCOM electrodes 151 and the current VCOM electrode 151 operate simultaneously. The voltage waveform at the current VCOM electrode 151 is also applied to the source line 13 (e.g., S2) underlying the current VCOM electrode 151. Accordingly, the current VCOM electrode 151 and the underlying source line 13 operate simultaneously. As two ends of an equivalent capacitor (e.g., CC1, CC2 or CS2) have the same voltage waveform or operates simultaneously, the equivalent capacitor therefore has no effect on the current VCOM electrode 151 (or the sensing point). Further, the gate line 11 (e.g., G2) underlying the current VCOM electrode 151 is set high-impedance (Hi-Z) or floating. Accordingly, the equivalent capacitor CG2 is no longer possessed by the current VCOM electrode 151 (or the sensing point), thereby substantially reducing the load at the sensing point.
FIG. 6 shows voltage waveforms of a current VCOM electrode 151 and the underlying source line 13 according to a third embodiment of the present invention. In this embodiment, the voltage waveform of the current VCOM electrode 151 is applied to the underlying source line 13 during a conversion phase and a pre-charge phase, which compose a sensing period.
In practice, the equivalent capacitor due to the source line 13 has effect on touch sensing result only in the conversion, but has no effect on the touch sensing result in the pre-charge phase. Accordingly, as shown in FIG. 7, a fourth embodiment of the present invention, the voltage waveform of the current VCOM electrode 151 is applied to the underlying source line 13 only during a conversion phase.
FIG. 8 shows voltage waveforms of a current VCOM electrode 151 and the underlying source line 13 according to a fifth embodiment of the present invention. In the embodiment, the voltage waveform of the current VCOM electrode 151 is applied to the underlying source line 13 only when the voltage waveform becomes stable in the conversion phase and the pre-charge phase. During sub-periods when the voltage waveform is not stable or sub-periods of transition (from high level to low level or from low level to high level), the source line 13 (e.g., S2) underlying the current VCOM electrode 151 is set high-impedance (Hi-Z) or floating, thereby reducing power consumption. It is noted that, during the sub-periods of transition, the voltage at the source line 13 may be pulled up or down via the equivalent capacitor (e.g., CS2).
As described above that the equivalent capacitor due to the source line 13 has effect on touch sensing result only in the conversion, the voltage waveform of the current VCOM electrode 151 is applied to the underlying source line 13 only when the voltage waveform becomes stable in the conversion phase, as shown in FIG. 9, a sixth embodiment of the present invention. During sub-periods when the voltage waveform is not stable or sub-periods of transition, the source line 13 (e.g., S2) underlying the current VCOM electrode 151 is set high-impedance (Hi-Z) or floating, thereby reducing power consumption. Similar to the fifth embodiment (FIG. 8), during the sub-periods of transition, the voltage at the source line 13 may be pulled up via the equivalent capacitor (e.g., CS2).
FIG. 10 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes 151, the source lines 13 and the gate lines 11. VCOM1, VCOM2 and VCOM3 represent three adjacent VCOM electrodes 151. CC1 and CC2 represent equivalent capacitors between the VCOM electrodes 151. CS1, CS2 and CS3 represent equivalent capacitors between the VCOM electrodes 151 (i.e., VCOM1, VCOM2 and VCOM3) and underlying source lines 13, respectively. CG1, CG2 and CG3 represent equivalent capacitors between the VCOM electrodes 151 (i.e., VCOM1, VCOM2 and VCOM3) and underlying gate lines 11, respectively. CP1, CP2 and CP3 represent equivalent capacitors pertaining to the VCOM electrodes 151 (i.e., VCOM1, VCOM2 and VCOM3) caused by other than the source lines 13 and the gate lines 11. Each sensing point (or VCOM electrodes 151) possesses a total capacitance of (CCX+CSX+CGX+CPX) (where X is 1, 2, or 3), which results in a load that affects sensitivity of the touch screen 100. In order to reduce capacitance of the parasitic capacitors, further embodiments are thus proposed.
FIG. 11 shows a circuit diagram illustrating equivalent capacitors among the VCOM electrodes 151, the source lines 13 and the gate lines 11 according to a seventh embodiment of the present invention. In the embodiment, VCOM1, VCOM2 and VCOM3 are under touch sensing in turn. When a current VCOM electrode 151 (e.g., VCOM2) is currently under touch sensing having a voltage waveform with a first amplitude VB, the same voltage waveform with a second amplitude VA is applied to adjacent VCOM electrodes 151 (e.g., VCOM1 and VCOM3), for example, by a VCOM unit 22 shown in FIG. 2. The same voltage waveform with the second amplitude VA is also applied to the source line 13 (e.g., S2) and the gate line 11 (e.g., G2) underlying the current VCOM electrode 151.
Let QC1 represents the charge contributed to the VCOM electrode 151 by the equivalent capacitor CC1, QC2 represents the charge contributed to the VCOM electrode 151 by the equivalent capacitor CC2, QS2 represents the charge contributed to the VCOM electrode 151 by the equivalent capacitor CS2, QG2 represents the charge contributed to the VCOM electrode 151 by the equivalent capacitor CG2, QP2 represents the charge contributed to the VCOM electrode 151 by the equivalent capacitor CP2, and Qtotal total represents the charge contributed to the VCOM electrode 151 by the total capacitance (CC1+CC2+CS2+CG2+CP2):
Q
C1=(VB−VA)*CC1
Q
C2=(VB−VA)*CC2
Q
S2=(VB−VA)*CS2
QG2=(VB−VA)*CG2
QP2=VB*CP2
Q
total
=Q
C1
+Q
C2
+Q
S2
+Q
G2
+Q
P2
It is noted that, if the second amplitude VA is greater than the first amplitude VB (i.e., VA>VB), the charges QC1, QC2, QS2 and QG2 are inverse to the charge QP2, thereby compensating for the effects caused by QP2.
The present embodiment is more useable when multiple channels are sensed concurrently, in that case the equivalent capacitor CP2 (that is, the equivalent capacitors pertaining to the VCOM electrodes 151 caused other than the source lines 13 and the gate lines 11) predominates with greater effects on the touch sensitivity.
FIG. 12A, FIG. 12B and FIG. 12C show voltage waveforms of VCOM electrodes 151, the underlying source line 13 (e.g., S2) and the underlying gate line 11 (e.g., G2). It is observed in FIG. 12A that the voltage waveform applied to the underlying source line 13 (e.g., S2), the underlying gate line 11 (e.g., G2) and the adjacent
VCOM electrodes 151 (e.g., VCOM1 and VCOM3) has a fixed amplitude (i.e., the second amplitude VA) during a conversion phase. However, in FIG. 12B, the applied voltage waveform overdrives before settling on the second amplitude VA in the conversion phase and the pre-charge phase. Alternatively, in FIG.
12C, the applied voltage waveform underdrives before settling on the second amplitude VA in the conversion phase and the pre-charge phase.
Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.
Patent Application
20160334916
