KR20170025106A - Touch detecting apparatus comprising flexible touch screen and method - Google Patents

Abstract

The present invention relates to a touch detection apparatus including a flexible touch screen and a method thereof, and more particularly, to a touch detection apparatus including a flexible touch screen and a method thereof, in which influence due to a parasitic capacitance is minimized while ensuring linearity. According to one embodiment of the present invention, a touch detection apparatus performing touch detection and including a flexible touch screen, and a method of driving the touch detection apparatus are provided. According to one embodiment of the present invention, the touch detection apparatus includes: a sensor pad for forming a touch capacitance in relation to a touch input tool; an operational amplifier having a first input terminal connected to an output of the sensor pad and a second input terminal for receiving a reference voltage, for outputting mutually different signals according to whether touch is performed or not; a first switch for controlling a potential across a driving capacitance connected between the first input terminal and an output terminal of the operational amplifier; a second switch maintained in an OFF state during a charging period, and switching connection between the output of the sensor pad and the first input terminal of the operational amplifier; and a parasitic capacitance compensation circuit for charging at least a part of the touch capacitance or a parasitic capacitance connected to the sensor pad when the second switch is in an ON state.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a touch sensing apparatus and method including a flexible touch screen,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0002] The present invention relates to a touch detection apparatus and method including a flexible touch screen, and more particularly, to a touch detection apparatus and method with minimized influence on parasitic capacitance while ensuring linearity.

The touch screen panel is a device for inputting a command of a user by touching a character or a figure displayed on the screen of the image display device with a finger or other contact means of a person, and is attached and used on the image display device. The touch screen panel converts a contact position that is touched by a human finger or the like into an electrical signal. The electrical signal is used as an input signal.

1 is an exploded top view of an example of a conventional capacitive touch screen panel.

1, a touch screen panel 10 includes a transparent substrate 12 and a first sensor pattern layer 13, a first insulating layer 14, and a second sensor pattern layer (not shown) sequentially formed on a transparent substrate 12 15, a second insulating film layer 16, and a metal wiring 17.

The first sensor pattern layer 13 may be connected on the transparent substrate 12 along the lateral direction and connected to the metal wiring 17 on a row-by-row basis.

The second sensor pattern layer 15 may be connected to the first insulating layer 14 along the column direction and alternately arranged with the first sensor pattern layer 13 so as not to overlap the first sensor pattern layer 13 . In addition, the second sensor pattern layer 15 is connected to the metal wiring 17 on a row basis.

When a human finger or a contact means is brought into contact with the touch screen panel 10, a change in capacitance according to the contact position is transmitted to the drive circuit side through the first and second sensor pattern layers 13 and 15 and the metal wiring 17 do. Then, the contact position is determined as the change in capacitance transferred is converted into an electrical signal.

However, the touch screen panel 10 must have a separate pattern of transparent conductive material such as indium tin oxide (ITO) on each of the sensor pattern layers 13 and 15, The insulating layer 14 must be provided to increase the thickness.

In addition, since the touch detection can be performed by accumulating the changes of capacitance slightly generated by the touch several times, it is necessary to detect the capacitance change at a high frequency. In order to sufficiently accumulate the capacitance change within a predetermined time, a metal wiring is required to maintain a low resistance, which thickens the bezel at the edge of the touch screen and generates an additional mask process.

To solve this problem, a touch detection apparatus as shown in Fig. 2 has been proposed.

2 includes a touch panel 20, a driving device 30, and a circuit board 40 connecting the two.

The touch panel 20 includes a plurality of sensor pads 22 formed on a substrate 21 and arranged in the form of a polygonal matrix and a plurality of signal wirings 23 connected to the sensor pads 22.

Each signal wiring 23 has one end connected to the sensor pad 22 and the other end extending to the lower edge of the substrate 21. The sensor pad 22 and the signal wiring 23 can be patterned on the cover glass 50. [

The driving device 30 sequentially selects a plurality of sensor pads 22 one by one to measure the electrostatic capacitance of the corresponding sensor pad 22, thereby detecting whether or not a touch is generated.

FIG. 3 is an equivalent circuit diagram for explaining an operation of performing touch detection when a touch occurs in the touch detection apparatus of FIG. 2. FIG.

3, when a touch occurs, a touch capacitance Ct is formed between a touch generating tool (for example, a finger) and the sensor pad 22, and a common capacitance Ct is formed between the sensor pad 22 and the common electrode. A capacitance Cvcom is formed. An unknown parasitic capacitance Cp is formed in the sensor pad 22 and a driving capacitance Cdrv is formed between the sensor pad 22 and the alternate voltage Vdrv supply path.

The touch detection method of the touch detection device will be described as follows.

First, the sensor pad 22 is charged by the charging signal Vb. Thereafter, when the supply of the charging signal Vb is interrupted by the transistor, the charges charged in the touch capacitance Ct, the parasitic capacitance Cp, the driving capacitance Cdrv and the common voltage capacitance Cvcom are isolated do. This charge isolated state is referred to as a floating state. At this time, when the alternating voltage Vdrv is applied, the output voltage Vo of the sensor pad 22 changes in accordance with the alternating voltage Vdrv. In this case, the rise and fall of the output voltage Vo have different values depending on the connected capacitances. The phenomenon that the rising or falling value of the voltage level changes depending on the connected capacitance is called a " kick-back " .

The voltage variation (? Vo) of the output voltage (Vo) of the sensor pad (22) when a touch occurs in the touch detection apparatus can be expressed by the following Equation (1).

Here, VdrvH and VdrvL are the high level voltage and the low level voltage of the alternating voltage Vdrv, respectively.

Since the touch capacitance Ct is located in the denominator in Equation 1, the output voltage variation? Vo (level shift) before and after the touch does not have a linear relationship with the touch capacitance Ct.

Since the level shift? Vo before and after the touch corresponds to the touch area related to the touch capacitance Ct, if the linearity between the level shift? Vo and the touch capacitance Ct is secured, Can be obtained.

Therefore, there is a need for a technique capable of ensuring linearity between the level shift before and after the touch and the touch capacitance. Further, there is a need for a touch detection device that ensures such linearity and minimizes the influence of parasitic capacitance between the respective parts constituting the touch panel.

In recent years, a flexible image display device has been developed. In this case, the touch screen panel applied to the flexible image display device is also required to have a flexible characteristic.

Therefore, development of a technique capable of securing the linearity between the level shift and the touch capacitance before and after the touch, reducing the influence of the parasitic capacitance existing in the touch detection device, and simultaneously imparting the flexible characteristic to the touch detection device need.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a touch detection apparatus and method which can minimize the influence of parasitic capacitance while maintaining linearity between a level shift value and a touch capacitance.

According to an aspect of the present invention, there is provided a touch pad device including: a sensor pad for forming a touch capacitance in relation to a touch input tool; An operational amplifier having a first input terminal connected to an output of the sensor pad and a second input terminal receiving a reference voltage and outputting different signals according to whether the touch is made; A first switch for controlling a potential at both ends of a driving capacitance connected between a first input terminal and an output terminal of the operational amplifier; A second switch that is maintained in an off state during the charging interval and switches connection between an output of the sensor pad and a first input of the operational amplifier; And a parasitic capacitance compensation circuit that charges at least a part of the parasitic capacitance or the touch capacitance connected to the sensor pad when the second switch is in the ON state.

The amount of charge supplied by the parasitic capacitance compensating circuit when the second switch is in an ON state may be the same amount as the amount of charge charged in the parasitic capacitance.

The parasitic capacitance compensation circuit may include a feedback capacitance whose one end is connected to the sensor pad when the second switch is on and the feedback voltage is supplied to the other end.

The potential at both ends of the feedback capacitance can be controlled by a switch synchronized with the first switch.

The magnitude of the feedback capacitance may be set such that a change in the output terminal voltage of the operational amplifier does not occur when the first switch is in the ON state and when the second switch is in the ON state in the absence of the touch capacitance.

The touch detection apparatus may further include a parasitic capacitance elimination circuit for applying a voltage equal to an output voltage of the sensor pad to another sensor pad.

The parasitic capacitance elimination circuit may apply a ground voltage to the other sensor pad when the first switch is in the on state and a voltage of the same magnitude as the reference voltage when the second switch is in the on state.

The touch detection apparatus may further include a level shift detection section for detecting whether or not the touch is based on a voltage variation at the output terminal of the operational amplifier.

According to another embodiment of the present invention, there is provided a touch input device including a sensor pad for forming a touch capacitance and a drive capacitance for supplying a reference voltage to the touch pad, Charging the parasitic capacitance connected to the sensor pad and the touch capacitance through the reference voltage and the parasitic capacitance compensation circuit; And detecting whether or not the touch is detected based on the other end voltage variation of the drive capacitance.

The amount of charge supplied by the parasitic capacitance compensation circuit may be the same amount as the amount of charge to be charged into the parasitic capacitance.

The parasitic capacitance compensation circuit may perform charging through a feedback capacitance whose one end is connected to the sensor pad and a feedback voltage is supplied to the other end.

The initializing step may include applying a ground voltage to a sensor pad other than the sensor pad, and the charging step may include applying the reference voltage to the another sensor pad.

According to the embodiment of the present invention, since the level shift value serving as a basis of touch detection and the touch capacitance have linearity, an advantage of being able to easily obtain an output value in a linear relationship can be obtained. On the other hand, The charging of the capacitance is performed by the parasitic capacitance compensation circuit, so that the influence of the parasitic capacitance on the touch detection can be minimized.

1 is an exploded top view of a conventional touch screen panel.
2 is an exploded top view of a conventional touch detection device.
FIG. 3 is an equivalent circuit diagram for explaining an operation of performing touch detection when a touch occurs in the touch detection apparatus of FIG. 2. FIG.
4 is a circuit diagram illustrating a touch detection apparatus according to an embodiment.
5 is a circuit diagram illustrating a touch detection apparatus according to an embodiment of the present invention.
6 is a circuit diagram illustrating a touch detection apparatus according to another embodiment of the present invention.

The terms used in this specification will be briefly described and the present invention will be described in detail.

While the present invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. Also, in certain cases, there may be a term selected arbitrarily by the applicant, in which case the meaning thereof will be described in detail in the description of the corresponding invention. Therefore, the term used in the present invention should be defined based on the meaning of the term, not on the name of a simple term, but on the entire contents of the present invention.

When an element is referred to as "including" an element throughout the specification, it is to be understood that the element may include other elements as well, without departing from the spirit or scope of the present invention. Also, the terms "part," " module, "and the like described in the specification mean units for processing at least one function or operation, which may be implemented in hardware or software or a combination of hardware and software . When a part is "connected" to another part, it includes not only a direct connection but also a connection with another system in the middle.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In order to clearly illustrate the present invention, parts not related to the description are omitted, and similar parts are denoted by like reference characters throughout the specification.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 is a circuit diagram illustrating a touch detection apparatus according to an embodiment.

4, the touch sensing device 400 includes a sensor pad 410, a touch capacitance Ct, a parasitic capacitance Cp, a driving capacitance Cdrv, an operational amplifier OP-amp, Digital converter (ADC).

The sensor pad 410 forms a touch capacitance Ct with the touch input tool as a patterned electrode on the substrate for touch input detection. The sensor pads 410 may be formed in a plurality of independent polygons, and may be formed of a transparent conductive material. For example, the sensor pad 410 may be formed of a transparent conductive material such as indium tin oxide (ITO), antimony tin oxide (ATO), indium zinc-oxide (IZO), carbon nanotube (CNT), or graphene ≪ / RTI >

The parasitic capacitance Cp and the driving capacitance Cdrv can be grouped into one each for the sensor pad 410 and the signal wiring (not shown) connected thereto. The sensor pad 410, the signal wiring, the parasitic capacitance Cp and the driving capacitance Cdrv are collectively referred to as a " touch sensing unit ". This touch sensing unit is a concept that includes the case where each component is electrically connected by a multiplexer.

The parasitic capacitance Cp means a capacitance attached to the sensor pad 410 and is a kind of parasitic capacitance formed by the sensor pad 410 or signal wiring. The parasitic capacitance Cp may be a concept including capacitance formed between the touch sensing device 400 and the common electrode of the display device when the touch sensing device 400 is mounted on a display device such as an LCD.

The driving capacitance Cdrv is a capacitance formed in a path that supplies a driving voltage Vdrv alternating at a predetermined frequency to the sensor pad 410. [ The driving voltage Vdrv applied to the driving capacitor Cdrv is preferably a square wave signal. The driving voltage Vdrv may be a clock signal having the same duty ratio, but may have a different duty ratio.

The first input terminal of the operational amplifier OP-amp is connected to the output of the sensor pad 410, and the reference voltage Vref is applied to the second input terminal. A driving capacitance Cdrv is connected between the first input terminal and the output terminal of the operational amplifier OP-amp and the potential across the driving capacitance Cdrv is controlled by the first switch SW1. The second switch SW2 is connected between the first input terminal of the operational amplifier OP-amp and the output terminal of the sensor pad 410. [ The output terminal of the operational amplifier OP-amp is connected to the level shift detection section. The level shift detection unit may include an analog-to-digital converter (ADC) or the like, and detects whether or not it is touched based on the voltage variation at the output terminal of the operational amplifier (OP-amp).

In the touch sensing apparatus 400 shown in Fig. 4, the first switch SW1 and the second switch SW2 are alternately turned on / off.

When the first switch SW1 is turned on, the touch capacitance Ct is connected to the ground potential, and both ends of the parasitic capacitance Cp are also connected to the ground potential. At this time, the sensor pad 410 is initialized. Further, the driving electrostatic capacity Cdrv is also initialized. 4, when the first switch SW1 is connected between both ends of the driving capacitance Cdrv and the first switch SW1 is turned on, the voltage across the driving capacitance Cdrv is 0V. However, The driving electrostatic capacitance Cdrv is connected to a predetermined charging voltage so that the initial voltage may be charged when the first switch SW1 is turned on. Hereinafter, an example shown in FIG. 4 will be described.

4, no charge is charged in the touch capacitance Ct, parasitic capacitance Cp, and drive capacitance Cdrv while the first switch SW1 is turned on. On the other hand, the both-end potential of the driving capacitance Cdrv connected between the first input terminal and the output terminal of the operational amplifier OP-amp is the same as the reference voltage Vref input to the second input terminal of the operational amplifier OP-amp Loses.

When the first switch SW1 is turned off and the second switch SW2 is turned on, the potential difference across the both ends of the second switch SW2 becomes equal to the reference voltage Vref. When the steady state is reached, both the touch capacitance Ct and the parasitic capacitance Cp are charged to the reference voltage Vref. The operational amplifier OP-amp charges the driving capacitance Cdrv with the same amount of charge as the charges charged in the touch capacitance Ct and the parasitic capacitance Cp.

The sum (Q ₁ ) of the charges charged in the touch capacitance Ct and the parasitic capacitance Cp is as follows. Here, we use the formula of Q = CV.

On the other hand, the potential difference Vdrv across the driving capacitance Cdrv becomes as follows. Here, Q ₂ is the amount of charge charged in the drive electrostatic capacity Cdrv when the second switch SW2 is turned on and then reaches the steady state.

As described above, since Q ₁ and Q ₂ are equal to each other by the operational amplifier OP-amp, the potential difference Vdrv at both ends of the driving capacitance Cdrv can be calculated by the following equations (2) and It develops together.

The potential difference across the driving capacitance Cdrv is 0 V before the second switch SW2 is turned on and the potential of the node to which the first input terminal of the operational amplifier OP- The change amount? Vo of the output terminal voltage of the pre-touch operational amplifier OP-amp is equal to the voltage Vdrv across the drive capacitance Cdrv after the second switch SW2 is turned on Loses.

Since the driving electrostatic capacitance Cdrv and the reference voltage Vref have a constant value, the variation? Vo of the output voltage of the operational amplifier OP-amp becomes proportional to the touch capacitance Ct. Accordingly, a relationship can be established in which the operational amplifier (OP-amp) output terminal voltage level difference before and after the touch, that is, the level shift? Vo, is proportional to the touch capacitance Ct. Also, the output value of the analog-to-digital converter (ADC), which receives the level shift? Vo, is also linearly proportional to the touch capacitance Ct, thereby securing the linearity.

However, as can be seen from Equation (4), the level shift? Vo value is affected not only by the touch capacitance Ct to be grasped for detection but also by the parasitic capacitance Cp. Which in turn reduces the accuracy of the touch detection.

In the present invention, a circuit is proposed which minimizes the influence of the parasitic capacitance Cp while securing the linearity between the level shift (? Vo) value and the touch capacitance (Ct).

5 is a circuit diagram illustrating a touch detection apparatus according to an embodiment of the present invention.

Referring to FIG. 5, it can be seen that parasitic capacitance compensation circuit 500 is added to the circuit diagram described with reference to FIG.

The parasitic capacitance compensation circuit 500 according to an embodiment includes a feedback capacitance Cfb, and the potential difference across the feedback capacitance Cfb is controlled by the first switch SW1. One end of the feedback capacitance Cfb is connected to or disconnected from the output of the sensor pad 410 by the second switch SW2 and the feedback voltage Vfb is applied to the other end.

When the first switch SW1 is turned on and the second switch SW2 is turned off as shown in Fig. 4, the potential difference between the touch capacitance Ct and the parasitic capacitance Cp is 0 V So that the charge is not charged. In addition, both the unit potential difference of the driving capacitance Cdrv and the potential difference across the feedback capacitance Cfb become 0V, so that no charge is charged in all the electrostatic capacitors. At this time, both potentials across the driving capacitance Cdrv become equal to the reference voltage Vref, and the both-end potentials of the feedback capacitance Cfb become equal to the feedback voltage Vfb.

When the first switch SW1 is turned off and the second switch SW2 is turned on, the potential of the node to which the output of the sensor pad 410 and the second switch SW2 are connected becomes equal to the reference voltage Vref. In this way, touch capacitance (Ct) and the parasitic capacitance (Cp) are both charged by the reference voltage (Vref), the sum (Q ₁₎ of the charge amount becomes equal to the equation (2).

On the other hand, if the feedback voltage Vfb is larger than the reference voltage Vref, a potential difference is generated across the feedback capacitance Cfb. Specifically, the potential at one end connected to the output of the sensor pad 410 at both ends of the feedback capacitance Cfb becomes lower than the potential at the other end to which the feedback voltage Vfb is applied, whereby the feedback capacitance Cfb is And serves to supply electric charges to the touch detection device.

The sum of the charge amount on the touch capacitance (Ct) and the parasitic capacitance (Cp) (Q ₁₎ is therefore equal to the driving capacitance (Cdrv) and feedback capacitance sum (Q ₂₎ of the charge amount of (Cfb) is supplied The following equation can be developed.

Here, it is assumed that the feedback voltage Vfb is twice the reference voltage Vref, and substituting it is as follows.

On the other hand, as described above, the amount of change in the output terminal voltage of the operational amplifier OP-amp before and after the touch operation, and the level shift? V0 value are set to the voltage Vdrv ), Substituting Vdrv by? Vo in Equation (6) results in the following.

If the feedback capacitance Cfb can be adjusted to the same value as the parasitic capacitance Cp in the above equation, the value of the level shift? Va before and after the touch can be a value independent of the parasitic capacitance Cp.

That is, a certain amount of charge is supplied from the parasitic capacitance compensation circuit 500 when the second switch SW2 is in an on state. If the magnitude of the feedback capacitance Cfb is properly adjusted, the parasitic capacitance compensation circuit 500, Serves to charge all the parasitic capacitance Cp other than the touch capacitance Ct. Therefore, since the charging by the driving electrostatic capacitance Cdrv only charges the touch capacitance Ct, the value of the level shift? Va before and after the touch is independent of the parasitic capacitance Cp and is only related to the touch capacitance Ct Is the value.

A process of optimizing the magnitude of the feedback capacitance Cfb will be described below. Assuming that the touch capacitance Ct is '0', if the parasitic capacitance Cp is completely removed, when the first switch SW1 and the second switch SW2 are turned on / off alternately , The output voltage of the operational amplifier (OP-amp) should be the reference voltage (Vref). This is because, in an ideal case, there should be no change in the amount of charge charged in the touch detection device, and the potential difference across the driving capacitance Cdrv must always be zero.

Therefore, if the output terminal voltage of the operational amplifier OP-amp or the output terminal voltage of the analog-digital converter ADC is checked while changing the feedback capacitance Cfb, the optimum feedback capacitance Cfb can be selected do. An optimum value can be found while changing only the feedback capacitance Cfb regardless of the parameter of another element, for example, the driving capacitance Cdrv, so that simple circuit calibration or optimization becomes possible.

6 is a circuit diagram illustrating a touch detection apparatus according to another embodiment of the present invention.

Referring to FIG. 6, the touch sensing apparatus of the present invention may further include a parasitic capacitance elimination circuit 600 together with a parasitic capacitance compensation circuit 500.

The configuration and function of the parasitic capacitance compensation circuit 500 are the same as those described with reference to Fig.

As described above, the parasitic capacitance compensation circuit 500 compensates for the amount of charge charged in the parasitic capacitance other than the touch capacitance Ct, so that the amount of charge supplied by the drive capacitance Cdrv is smaller than the capacitance of the touch capacitance Ct To be equal to the change of the charged amount by the battery.

The parasitic capacitance elimination circuit 600 according to the embodiment of the present invention performs a function of minimizing the amount of charge introduced into the parasitic capacitance 600.

In the touch detection apparatus, the parasitic capacitance may be generated by another sensor pad 410-2 (Cp0) regardless of the sensor pad 410-1 which is the current touch detection target, (Cpt) due to the relationship between the sensor pad 410-1 and another adjacent sensor pad 410-2.

The touch detection apparatus shown in Fig. 6 detects the presence of parasitics generated between the sensor pads through the operation of matching the potential between the sensor pad 410-1, which is the current touch detection object, and the adjacent sensor pads 410-2, Minimize the capacitance (Cpt).

To this end, the parasitic capacitance elimination circuit 600 supplies a voltage equal to the output terminal voltage of the current sensor pad 410-1 to the other sensor pad 410-2.

As described above, the first switch SW1 and the second switch SW1 of the touch detection apparatus are alternately turned on / off. When the first switch SW1 is in the ON state, the sensor pad 410-1 are connected to the ground. Therefore, the potential at the output terminal N1 of the sensor pad 410-1 becomes equal to the ground voltage GND.

On the other hand, when the second switch SW2 is on, the output of the sensor pad 410-1, which is the current touch detection target, is connected to the first input terminal of the operational amplifier OP-amp. Since the reference voltage Vref is supplied to the second input terminal of the operational amplifier OP-amp, the potential at the output terminal N1 of the sensor pad 410-1 becomes equal to the reference voltage Vref.

Therefore, when the first switch SW1 is in the ON state, the ground potential GND is supplied to the sensor pad 410-2 other than the sensor pad 410-1 to be the touch detection object, and the second switch SW2 When the reference voltage Vref is supplied to the sensor pad 410-2 other than the sensor pad 410-1 to be the touch detection object, the potential difference between the adjacent sensor pads can be maintained at zero have.

If there are two conductors with a dielectric material between them, the amount of charge Q filled in the structure can be expressed as Q = CV. Where C is the capacitance value of the structure and V is the potential difference between both conductors.

In the above equation, when the potential difference (V) of both conductors is converged close to zero, the amount of charge Q drawn by the inter-conductor potential difference can also converge to zero. Since the electrostatic capacitance C is proportional to the charging ability of the electric charge, if the electric charge quantity Q to be charged becomes close to 0, the electrostatic capacity C formed by the inter-conductor relation also converges to zero.

Therefore, if the potential difference between the two sensor pads 410-1 and 410-2 is controlled to be always close to 0, the parasitic capacitance (hereinafter referred to as " parasitic capacitance " Cpt) can also be minimized.

The parasitic capacitance elimination circuit 600 for alternately supplying the ground potential GND and the reference voltage Vref to the sensor pad 410-2 other than the sensor pad 410-1 which is the current touch detection object, The input stage may include a feedback amplifier (OP-amp_fb) coupled to the output. A signal source SS for alternately supplying the ground potential GND and the reference voltage Vref may be connected to the second input terminal of the feedback amplifier OP-amp_fb.

The signal source SS may be a clock signal whose low signal is at the ground potential GND and whose hinging signal is equal to the reference voltage Vref. When the signal source SS is a clock signal, the frequency should be the same as the switching frequency of the first switch SW1 and the second switch SW2. When the first switch SW1 is in the ON state, (SW2) is in the ON state, a high signal should be output.

Also, as another example, the signal source SS may be implemented with a reference voltage (Vref) source and a switch (not shown). The reference voltage Vref is supplied to the second input terminal of the feedback amplifier OP-amp_fb, and the supply of the reference voltage Vref can be interrupted at predetermined intervals through the switch. The supply of the reference voltage Vref is cut off when the first switch SW1 is turned on and the supply of the reference voltage Vref is turned on when the second switch SW2 is turned on to perform the function of the signal source SS . In this case, the switch for connecting or disconnecting the second input terminal of the feedback amplifier OP-amp_fb and the reference voltage Vref may be turned on / off in synchronization with the second switch SW2.

6, the feedback amplifier OP-amp-fb includes the feedback amplifier OP-amp_fb in the parasitic capacitance elimination circuit 600. However, the feedback amplifier OP-amp-fb minimizes the distortion of the signal supplied to the second input terminal It is needless to say that the feedback amplifier OP-amp_fb is omitted and the signal source SS may be directly connected to the output of the sensor pad 410-2.

According to the embodiment shown in FIG. 6, the parasitic capacitance Cpt due to the relationship between the sensor pads is all eliminated in the ideal case, and only the parasitic capacitance Cp0 other than the parasitic capacitance Cp0 remains.

Since the feedback capacitance Cfb of the parasitic capacitance compensation circuit 500 functions to charge the parasitic capacitance, the parasitic capacitance Cpt due to the relationship between the sensor pads is removed by the parasitic capacitance elimination circuit 600 The size of the feedback capacitance Cfb may have a smaller value than in the embodiment described with reference to FIG. 5, thereby minimizing the area occupied by the feedback capacitance Cfb in the circuit configuration .

It will be understood by those skilled in the art that the foregoing description of the present invention is for illustrative purposes only and that those of ordinary skill in the art can readily understand that various changes and modifications may be made without departing from the spirit or essential characteristics of the present invention. will be. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be construed as being included within the scope of the present invention.

500: Parasitic capacitance compensation circuit
600: Parasitic capacitance elimination circuit

Claims (12)

A sensor pad forming a touch capacitance in relation to the touch input tool;
An operational amplifier having a first input terminal connected to an output of the sensor pad and a second input terminal receiving a reference voltage and outputting different signals according to whether the touch is made;
A first switch for controlling a potential at both ends of a driving capacitance connected between a first input terminal and an output terminal of the operational amplifier;
A second switch that is maintained in an off state during the charging interval and switches connection between an output of the sensor pad and a first input of the operational amplifier; And
And a parasitic capacitance compensation circuit which charges at least a part of the parasitic capacitance or the touch capacitance connected to the sensor pad when the second switch is in the ON state. The method according to claim 1,
Wherein the amount of charge supplied by said parasitic capacitance compensation circuit when said second switch is in an ON state is the same amount as the amount of charge charged into said parasitic capacitance. The method according to claim 1,
Wherein the parasitic capacitance compensation circuit comprises:
And a feedback capacitance whose one end is connected to the sensor pad and the other end is fed with a feedback voltage when the second switch is in the ON state. 3. The method of claim 2,
And the both-end potential of the feedback capacitance is controlled by a switch synchronized with the first switch. 3. The method of claim 2,
Wherein the magnitude of the feedback capacitance is set such that a change in the output terminal voltage of the operational amplifier does not occur when the first switch is in the ON state and when the second switch is in the ON state in the absence of the touch capacitance, Device. The method according to claim 1,
Further comprising a parasitic capacitance elimination circuit for applying a voltage equal to an output voltage of the sensor pad to another sensor pad. The method according to claim 6,
Wherein the parasitic capacitance elimination circuit comprises:
And applies a ground voltage to the other sensor pad when the first switch is in the on state and a voltage in the same magnitude as the reference voltage when the second switch is in the on state. The method according to claim 1,
Further comprising a level shift detection section for detecting whether or not a touch is made on the basis of a voltage variation at the output terminal of the operational amplifier. A step of initializing a sensor pad forming a touch capacitance and a drive capacitance supplied with a reference voltage at one end in relation to a touch input tool;
Charging the parasitic capacitance connected to the sensor pad and the touch capacitance through the reference voltage and the parasitic capacitance compensation circuit; And
Detecting whether or not the touch is detected based on the other-end voltage variation of the drive electrostatic capacitance. 10. The method of claim 9,
Wherein the amount of charge supplied by said parasitic capacitance compensation circuit is the same amount as the amount of charge charged into said parasitic capacitance. 10. The method of claim 9,
Wherein the parasitic capacitance compensation circuit comprises:
Wherein the charging is performed through a feedback capacitance whose one end is connected to the sensor pad and a feedback voltage is supplied to the other end. 10. The method of claim 9,
Wherein the initializing step includes applying a ground voltage to a sensor pad other than the sensor pad,
Wherein the charging step comprises applying the reference voltage to the other sensor pad.

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