Patent Application
20110279407
1. Field of the Invention
The present invention relates to a technology for processing a touch line signal of a touch screen, and more particularly, to a circuit for processing a touch line signal of a touch screen, which can reduce the number of elements of a sensing read circuit by processing a touch line signal using a charge sharing scheme.
2. Description of the Related Art
Recently, touch screens are frequently used as a user interface device. Touch screens are divided into a resistive film type, a capacitance type, an infrared type and an ultrasonic type, depending upon a panel type. A touch screen of the capacitance type has advantages in terms of high transmittance, durability and price, and thus, is widely used in a mobile phone, a portable terminal such as a personal digital assistant (PDA), a monitor, and a variety of electric appliances. Hereafter, the touch screen of the capacitance type will be described.
A user can issue a desired command by touching an optional point on a touch screen display device using a stylus pen or a finger. To this end, the touch screen display device includes, in addition to a plurality of pixels for displaying an image, a plurality of touch sensing elements for sensing the point which is touched by the user.
A gate signal and a data signal are applied to each pixel, and each touch sensing element senses a touch made by the user and outputs a resultant sensing signal. To this end, the touch screen display device a gate driving unit and a data driving unit for applying the gate signal and the data signal, and a touch line signal processing circuit for processing the output signal of each touch sensing element, which is to be outputted to a touch line.
Referring to
Parasitic capacitors CP1, CP2, . . . exist between peripheral pads of the sensor capacitors CS1, CS2, . . . , and ground terminals, respectively.
Among the plurality of sensing read circuits 110_1 to 110_N, the sensing read circuit 110_1 includes a sensing read-out unit 111_1 for reading a voltage charged in the first sensor capacitor CS1 formed on the touch screen panel 300, and an integrator 112_1 for generating a touch detection output voltage Vo1 by integrating the charged voltage of the first sensor capacitor CS1, which is transmitted from the sensing read-out unit 111_1.
The operation of the conventional circuit 100 for processing the touch line signal of the touch screen will be described below. First, a precharge switch SWPC is turned on for a predetermined time in a precharge mode so that a supply voltage VDD is precharged in the first sensor capacitor CS1 through the precharge switch SWPC.
Then, a read-out switch SWRO is turned on for a predetermined time in a read-out mode so that a voltage charged in the first sensor capacitor CS1 is transmitted to the integrator 112_1 through the read-out switch SWRO.
At this time, when the first sensor capacitor CS1 is touched on the touch screen panel 300 by a user, the distance between the electrode plates of the first sensor capacitor CS1 is reduced, resulting in a change in the capacitance thereof. Therefore, the voltage transmitted from the first sensor capacitor CS1 to the integrator 112_1 changes (e.g., drops).
The integrator 112_1 integrates the voltage input through the read-out switch SWRO to generate the touch detection output voltage Vo1. The touch detection output voltage Vo1 of the integrator 112_1 corresponds to a value obtained by dividing the amount of input charge by a capacitance value of an integrator capacitor Ci. That is, an integration value of a touch line current is the amount of output charge.
As described above, the conventional circuit for processing the touch line signal of the touch screen uses an absolute value comparison scheme in which the voltage of the first sensor capacitor CS1 connected to one touch line is compared with a reference voltage Vref by an operational amplifier OP of the integrator 112_1, and the touch detection output voltage Vo1 is determined according to the comparison result.
The touch detection output voltage Vo1 for one touch line is generated by the one sensing read circuit 110_1 through the above-described process, and touch detection output voltages Vo2-VoN for the other touch lines are generated by the sensing read circuits 110_2 to 110_N in the same manner.
The switch unit 120 includes N switches SW1 to SWN corresponding to the number of the sensing read circuits 110_1 to 110_N, and sequentially turns on the switches SW1 to SWN to sequentially transmit the touch detection output voltages Vo1-VoN, which are output from the sensing read circuits 110_1 to 110_N, to the A/D converter 130.
The A/D converter 130 converts the analog touch detection output voltages Vo1-VoN, which are input through the above-described process, into digital signals, and output the digital signals.
In the case of the conventional circuit for processing the touch line signal of the touch screen as described above, many integrators are necessary because the sensor capacitors are connected to the integrators in a one-to-one fashion, so that a large installation space is necessary, resulting in a significant increase in power consumption.
In addition, it may be difficult to measure the absolute value of capacitance and the sensor output voltages of the integrators may be changed by the parasitic capacitors.
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a circuit for processing a touch line signal of a touch screen, in which sensing read circuits are formed in a differential structure and a charge sharing scheme is applied, so that one sensing read circuit can process a plurality of touch line signals.
In order to achieve the above object, according to one aspect of the present invention, there is provided a circuit for processing a touch line signal of a touch screen includes: a plurality of sensing read circuits including sensing read-out units, which are configured to precharge a first sensor capacitor and a second sensor capacitor formed on a touch screen panel with a ground voltage and a supply voltage, allow charges charged in the first sensor capacitor and the second sensor capacitor to be shared, and read-out a charge sharing result obtained by allowing the charges of the first sensor capacitor and the second sensor capacitor to be shared, and integrators configured to integrate output voltages of the sensing read-out units; and a switch unit configured to sequentially connect output terminals of the plurality of sensing read circuits to an input terminal of an analog-to-digital converter.
The above objects, and other features and advantages of the present invention will become more apparent after a reading of the following detailed description taken in conjunction with the drawings, in which:
Reference will now be made in greater detail to a preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings. Wherever possible, the same reference numerals will be used throughout the drawings and the description to refer to the same or like parts.
Referring to
Among the plurality of sensing read circuits 210_1 to 210_N/2, the sensing read circuit 210_1 includes a sensing read-out unit 211_1 and an integrator 212_1 to generate a touch detection output voltage Vo1 by detecting a change in the capacitance of the first sensor capacitor CS1 and the second sensor capacitor CSK.
That is, the sensing read circuits 210_1 to 210_N/2 are formed in a differential structure and the one sensing read circuit 210_1 processes two pieces of touch data through the first sensor capacitor CS1 and the second sensor capacitor CSK, so that the number of the sensing read circuits 210_1 to 210_N/2 is reduced to ½ of the number N of the conventional sensing read circuits.
When the first sensor capacitor CS1 is formed on one of a plurality of touch lines arranged on the touch screen panel 300 in a vertical or horizontal direction, the second sensor capacitor CSK is preferably positioned adjacent to the touch line on which the first sensor capacitor CS1 is formed.
The sensing read-out unit 211_1 includes a first precharge switch SWPC1, a second precharge switch SWPC2, a charge sharing switch SWCS, and a read-out switch SWRO.
The first precharge switch SWPC1 has a first terminal connected to a ground voltage GND and a second terminal connected to one terminal of the first sensor capacitor CS1, and precharges the first sensor capacitor CS1 with the ground voltage GND.
The second precharge switch SWPC2 has a first terminal connected to a supply voltage VDD and a second terminal connected to one terminal of the second sensor capacitor CSK, and precharges the second sensor capacitor CSK with the supply voltage VDD.
The charge sharing switch SWCS has a first terminal connected to the second terminal of the first precharge switch SWPC1 and a second terminal connected to the second terminal of the second precharge switch SWPC2, and allows charges of the precharged first sensor capacitor CS1 and the precharged second sensor capacitor CSK to be shared.
The read-out switch SWRO has a first terminal connected to a common node between the first sensor capacitor CS1 and the second sensor capacitor CSK and a second terminal connected to an input terminal of the integrator 212_1, and reads out a result, which is obtained by allowing the charges of the first sensor capacitor CS1 and the second sensor capacitor CSK to be shared, to transmit the result to the integrator 212_1.
The integrator 212_1 integrates the charge sharing result transmitted from the sensing read-out unit 211_1 to generate the touch detection output voltage Vo1.
The integrator 212_1 includes an operational amplifier OP, an integrator capacitor Ci, and a reset switch SWRE. The operational amplifier OP has an inverted input terminal (−) to which the charge sharing result transmitted from the sensing read-out unit 211_1 is input, and a non-inverted input terminal (+) to which a reference voltage Vref is input. The integrator capacitor Ci has a first terminal connected to an output terminal of the operational amplifier OP and a second terminal connected to the non-inverted input terminal (+). The reset switch SWRE is connected in parallel to the integrator capacitor Ci to reset the integrator capacitor Ci.
The switch unit 220 includes a plurality of switches SW1 to SWN/2. The plurality of switches SW1 to SWN/2 have first terminals connected to the output terminals of the plurality of the sensing read circuits 210_1 to 210_N/2, respectively, and second terminals connected to the input terminal of the AD converter 230.
Hereinafter, the operation of the circuit for processing the touch line signal of the touch screen in accordance with the embodiment of the present invention will be described with referenced to
First, in a precharge mode, as illustrated in (a) of
Thus, one terminal of the first sensor capacitor CS1 is connected to the ground terminal, so that the first sensor capacitor CS1 is precharged with the ground voltage. At this time, a first parasitic capacitor CP1, which exists between a connection pad of the first sensor capacitor CS1 and the ground, is also precharged with the ground voltage.
Simultaneously to this, the second sensor capacitor CSK is connected to the power terminal and precharged with the supply voltage. At this time, a second parasitic capacitor CPK, which exists between a connection pad of the second sensor capacitor CSK and the ground, is also precharged with the supply voltage.
Next, in a charge sharing mode, as illustrated in (b) of
Q
T1=(CSK+CPK)·VDD+(CS1+CP1)·0 Equation 1
Then, in a read-out mode, as illustrated in (c) of
Q
Ci=[(CSK−CS1)+(CPK−CP1)]·VDD/2 Equation 2
As expressed by Equation 2, since charges charged in the first and second parasitic capacitor CP1 and CPK are offset, if they have charge values similar to each other, it is possible to ignore the influence by them.
Then, the integrator 212_1 integrates the voltage charged in the integrator capacitor Ci to output the output voltage Vo1, wherein the output voltage Vo1 is expressed by Equation 3 below. The reset switch SWRE in the integrator 212_1 is used to reset a previous voltage charged in the integrator capacitor Ci before the integration.
V
o1
=Q
Ci
/C
i Equation 3
As described above, the embodiment of the present invention uses a relative comparison scheme in which a voltage according to the amount of changed charges of the pair of the sensor capacitors CS1 and CSK connected to the touch lines adjacent to each other is compared with the reference voltage Vref by the operational amplifier OP of the integrator 212_1, and the touch detection output voltage Vo1 is determined according to the comparison result.
That is, according to the circuit for processing the touch line signal of the touch screen in accordance with the embodiment of the present invention, it is not necessary to detect an absolute value of capacitance, and the amount of charges varying depending on a change in the capacitance of the pair of the sensor capacitors CS1 and CSK is measured using a specific voltage, so that it is possible to detect whether the touch screen panel is touched.
For example, when the first sensor capacitor CS1 is touched by a user, the distance between the electrode plates of the first sensor capacitor CS1 is reduced, resulting in a change in the capacitance thereof. Therefore, a relatively low voltage is output from the sensing read out unit 211_1 through the above-described precharge, charge sharing and read-out processes, as compared with the case in which a touch is not performed. At this time, the operational amplifier OP of the integrator 212_1 compares the low voltage input through the inverted input terminal thereof with the reference voltage Vref and outputs the touch detection output voltage Vo1 at a ‘high’ level according to the comparison result.
In another example, when the second sensor capacitor CSK is touched by a user, the distance between the electrode plates of the second sensor capacitor CSK is reduced, resulting in a change in the capacitance thereof. Therefore, a relatively high voltage is output from the sensing read out unit 211_1 through the above-described precharge, charge sharing and read-out processes, as compared with the case in which a touch is not performed. At this time, the operational amplifier OP of the integrator 212_1 compares the high voltage input through the inverted input terminal thereof with the reference voltage Vref, and outputs the touch detection output voltage Vo1 at a ‘low’ level according to the comparison result.
However, when any one of the first and second sensor capacitors CS1 and CSK is not touched, the high or low voltage is not output from the sensing read out unit 211_1 through the above-described precharge, charge sharing and read-out processes. At this time, the operational amplifier OP of the integrator 212_1 compares the voltage input through the inverted input terminal thereof with the reference voltage Vref, and outputs a preset voltage, for example, a voltage having a level equal to the level of the reference voltage Vref, as the touch detection output voltage Vo1 according to the comparison result.
Meanwhile, in a switch enable mode, as illustrated in (d) to (f) of
The A/D converter 230 converts the analog touch detection output voltages Vo1 to VoN/2 input through the above-described process into digital signals, and outputs the digital signals.
The system controller (not shown) recognizes a vertical coordinate of a point touched on the touch screen panel based on the digital signals output from the A/D converter 230, and recognizes a horizontal coordinate based on signals detected through gate lines or separately installed horizontal lines, thereby determining vertical and horizontal touch coordinates.
For example, in the case in which 100 gate lines and 100 touch lines are provided on the touch screen panel, when a changed vertical coordinate signal is output from a sensing read circuit connected to a 30th touch line and a signal is applied to a 50th gate line, an X axis coordinate is 50 and a Y axis coordinate is 30. That is, a point at which the 50th gate line crosses the 30th touch line is determined as a touch area.
Since the first sensor capacitor CS1 and the second sensor capacitor CSK are connected to the touch lines adjacent to each other as described above, it is possible to obtain a more accurate touch sensing result when a K value for determining the distance therebetween is appropriately set.
This is because the adjacent touch lines may be simultaneously touched by a one-time touch operation when the K value is set to be very small, and a touch operation may not be detected when the K value is set to be very large.
In this regard, it is preferable to set the K value as an appropriate value through a sufficient experimental process when designing the touch screen panel.
As is apparent from the above description, in the circuit for processing the touch line signal of the touch screen in accordance with the embodiment of the present invention, sensing read circuits are formed in a differential structure and a charge sharing scheme is applied, so that one sensing read circuit can process two pieces of touch data, resulting in the reduction of power consumption and a chip area.
In addition, since the embodiment of the present invention uses a relative comparison scheme in which relative capacitance values of a pair of sensor capacitors are measured and compared with each other to detect whether a touch is performed, it is not insensitive to the absolute value of capacitance and it is possible to remove the influence by parasitic capacitors by allowing capacitance values by the parasitic capacitors to be offset.
Although a preferred embodiment of the present invention has been described for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and the spirit of the invention as disclosed in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2010-0044817 | May 2010 | KR | national |
