Electrostatic capacity type touch sensor for detecting a large number of touch positions with a small number of detection electrodes

There is offered an electrostatic capacity type touch sensor capable of detecting a large number of touch positions with high accuracy. The electrostatic capacity type touch sensor is composed of a touch panel and a signal processing circuit. The touch panel is structured to include first through fourth detection electrodes, first and second common electric potential lines, a common electric potential wiring, a common electric potential terminal and first through fourth output terminals disposed on an insulating substrate. The signal processing circuit is structured to include a clock generator, a selection circuit, a charge amplifier, an A/D converter and an arithmetic unit. The charge amplifier detects a change in capacitance induced by that a finger of an operator touches the first through fourth detection electrodes.

CROSS-REFERENCE OF THE INVENTION

This application claims priority from Japanese Patent Application No. 2010-151093, the content of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electrostatic capacity type touch sensor.

2. Description of the Related Art

The electrostatic capacity type touch sensor has been known as an input device to various kinds of equipment. A conventional electrostatic capacity type touch sensor is provided with a touch panel having a display panel that shows an input content to be data-inputted and a detection unit to detect that the input content shown on the display panel is designated by an operator. The detection unit recognizes the input content designated by the operator by detecting a change in electrostatic capacitance induced by that a finger of the operator approaches a detection electrode formed on an insulative circuit board.

Technologies mentioned above are disclosed in Japanese Patent Application Publication No. 2005-190950, for example.

With the conventional electrostatic capacity type touch sensor, however, there is a limit for detecting a large number of touch positions on the touch panel, that is, for increasing a quantity of data input.

This invention is directed to offering an electrostatic capacity type touch sensor capable of detecting a large number of touch positions using a small number of detection electrodes.

This invention is also directed to offering an electrostatic capacity type touch sensor improved in linearity of correlation between an output of the sensor and the touch position, as well as in detection accuracy of the touch position.

SUMMARY OF THE INVENTION

This invention provides an electrostatic capacity type touch sensor having a substrate, a first common electric potential line disposed on the substrate, a second common electric potential line disposed on the substrate so as to surround the first common electric potential line, first and second detection electrodes disposed in a region interposed between the first and second common electric potential lines and being axisymmetrical with respect to a Y axis that intersects a common center of the first and second common electric potential lines, third and fourth detection electrodes disposed in the region and being axisymmetrical with respect to an X axis that intersects the common center and is orthogonal to the Y axis, and a charge amplifier generating a first output voltage that is proportional to a capacitance difference between a capacitance of a first capacitor formed between the first detection electrode and the first and second common electric potential lines and a capacitance of a second capacitor formed between the second detection electrode and the first and second common electric potential lines and a second output voltage that is proportional to a capacitance difference between a capacitance of a third capacitor formed between the third detection electrode and the first and second common electric potential lines and a capacitance of a fourth capacitor formed between the fourth detection electrode and the first and second common electric potential lines.

DETAILED DESCRIPTION OF THE INVENTION

First Embodiment

FIG. 1shows a structure of an electrostatic capacity type touch sensor according to a first embodiment of this invention.FIG. 2shows a structure of a touch panel in the electrostatic capacity type touch sensor shown inFIG. 1.FIG. 3is a cross-sectional view showing a section A-A inFIG. 1.

The electrostatic capacity type touch sensor is composed of a touch panel and a signal processing circuit. The touch panel is structured to include an insulating substrate10such as a PCB substrate, and first through fourth detection electrodes11,12,13and14, first and second common electric potential lines15and16, a common electric potential wiring17, a common electric potential terminal COM and first through fourth output terminals CO1, CO2, CO3and CO4disposed on the insulating substrate10.

The signal processing circuit is structured to include a clock generator18, a selection circuit19, a charge amplifier20, an A/D converter21and an arithmetic unit30.

The first common electric potential line15is disposed on a circumference of a circle having a radius R and a center point located at a center O. The second common electric potential line16is disposed on a circumference of a circle having a radius (R+W) and a center point located at the center O. That is, the first common electric potential line15and the second common electric potential line16are disposed on the circumferences of the two concentric circles, respectively. In this case, it is preferable that R is 12.5 mm, W is 5 mm and a width of each of the first and second common electric potential lines15and16is about 0.5 mm, for example.

The first common electric potential line15is electrically connected with the second common electric potential line16through the common electric potential wiring17. The common electric potential wiring17is made of an upper wiring layer or a lower wiring layer that is different from a wiring layer forming the first through fourth output terminals CO1-CO4, and is electrically isolated from the first through fourth output terminals CO1-CO4. The common electric potential wiring17is connected to the common electric potential terminal COM. A clock alternating between an H level and an L level is applied from the clock generator18to the common electric potential terminal COM. As a result, the clock is applied to the first and second common electric potential lines15and16.

The first through fourth detection electrodes11-14are disposed in a ring region RE having a width W and interposed between the first and second common electric potential lines15and16. The first and second detection electrodes11and12are shaped and disposed axisymmetrical with respect to a Y axis that intersects the center O. The third and fourth detection electrodes13and14are shaped and disposed axisymmetrical with respect to an X axis that intersects the center O. The X axis and the Y axis intersect orthogonally.

In other words, the first and second detection electrodes11and12are shaped and disposed point-symmetrical with respect to the center O, while the third and fourth detection electrodes13and14are shaped and disposed point-symmetrical with respect to the center O. The first and second detection electrodes11and12are shaped in a pair of crescents congruent with each other, while the third and fourth detection electrodes13and14are shaped in a pair of crescents congruent with each other. A width of each of the first and second detection electrodes11and12takes a maximum value at Y=0, while a width of each of the third and fourth detection electrodes13and14takes a maximum value at X=0. The maximum value is about 4 mm, for example.

A right edge of the first detection electrode11faces a right half of the second common electric potential line16with a short separation (about 0.5 mm), while a left edge of the second detection electrode12faces a left half of the second common electric potential line16with a short separation (about 0.5 mm). A lower edge of the third detection electrode13faces an upper half of the first common electric potential line15with a short separation (about 0.5 mm), while an upper edge of the fourth detection electrode14faces a lower half of the first common electric potential line15with a short separation (about 0.5 mm).

The first detection electrode11and the third detection electrode13are separated from each other by a narrow boundary region BL1in a first quadrant of an X-Y coordinate system defined by the X axis and the Y axis. The cross-sectional view of the section A-A inFIG. 3shows that an insulating film22covers the first detection electrode11, the third detection electrode13and the first and second common electric potential lines15and16, which are disposed on the insulating substrate10.

The second detection electrode12and the third detection electrode13are separated from each other by a narrow boundary region BL2in a second quadrant of the X-Y coordinate system. Similarly, the second detection electrode12and the fourth detection electrode14are separated from each other by a narrow boundary region BL3in a third quadrant of the X-Y coordinate system. Similarly, the first detection electrode11and the fourth detection electrode14are separated from each other by a narrow boundary region BL4in a fourth quadrant of the X-Y coordinate system. The boundary regions BL1and BL2are axisymmetrical with respect to the Y axis, while the boundary regions BL3and BL4are axisymmetrical with respect to the Y axis. A width of each of the boundary regions BL1-BL4is about 0.5 mm.

The first and second common electric potential lines15and16, and the first through fourth detection electrodes11-14can be formed using transparent conductive material such as ITO (Indium Tin Oxide) or metal such as aluminum.

Focusing on the boundary region BL1between the first detection electrode11and the third detection electrode13in the first quadrant, coordinates (X, Y) of a point A on a center line (indicated by a chain double-dashed line inFIG. 1and inFIG. 2) of the boundary region BL1are represented by following equations.
X=(R+W×n/90°)×cos(π×n/180°)  (1)
Y=(R+W×n/90°)×sin(π×n/180°)  (2)

Here, n is 0°-90°. When n=0°, there is derived (X, Y)=(R, 0), that is, the point A is located on the circumference of the circle representing the first common electric potential line15. When n=90°, there is derived (X, Y)=(0, R+W), that is, the point A is located on the circumference of the circle representing the second common electric potential line16.

There is considered a sector form with a center angle δ (10°, for example) regarding the circle representing the second common electric potential line16, as shown inFIG. 2. An overlapping region (shaded region inFIG. 2) between the sector form and the ring region RE interposed between the first and second common electric potential lines15and16can be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode11included in the touch region is denoted as S1, and an area of the third detection electrode13included in the touch region is denoted as S2. Suppose the sector form rotates counterclockwise around the center O in the first quadrant of the X-Y coordinate system. It corresponds to that a touch position of the finger of the operator to the touch panel rotates counterclockwise in the ring region RE. A state shown inFIG. 2corresponds to the case in which a rotation angle of the sector form is 0°. When the rotation angle reaches 80° as it increases from 0°, an edge B of the sector form reaches the Y axis.

FIG. 4shows a correlation between a change in each of the areas S1and S2and the rotation angle of the sector form (center angle δ=10′). That is, as the rotation angle increases, the area S1decreases linearly and the area S2increases linearly. S1+S2remains constant. A scale of a vertical axis inFIG. 4is a relative scale, and is set so that S1+S2=50.

When looked from the viewpoint of capacitances and their changes, a first capacitor C1is formed between the first detection electrode11and the first and second common electric potential lines15and16, while a second capacitor C2is formed between the second detection electrode12and the first and second common electric potential lines15and16. When the finger of the operator is far away from the touch panel, a capacitance of the first capacitor C1is equal to a capacitance of the second capacitor C2. When the finger of the operator touches the ring region RE, the capacitance of the first capacitor C1increases in proportion to the area S1. That is because the number of electric lines of force between the first detection electrode11and the first and second common electric potential lines15and16increases by the number of electric lines of force passing through the finger of the operator when a dielectric model in which the finger of the operator is regarded as a dielectric material is applied. Therefore, a capacitance difference ΔC1between the capacitance of the first capacitor C1and the capacitance of the second capacitor C2varies in proportion to the area S1. However, in the case where an electric field shielding model in which the finger of the operator is grounded and works to shield the electric field is applied, the capacitance of the first capacitor C1decreases in proportion to the area S1. Following explanations are based on the dielectric model.

Similarly, a third capacitor C3is formed between the third detection electrode13and the first and second common electric potential lines15and16, while a fourth capacitor C4is formed between the fourth detection electrode14and the first and second common electric potential lines15and16. When the finger of the operator is far away from the touch panel, a capacitance of the third capacitor C3is equal to a capacitance of the fourth capacitor C4. When the finger of the operator touches the ring region RE, the capacitance of the third capacitor C3increases in proportion to the area S2. Therefore, a capacitance difference ΔC2between the capacitance of the third capacitor C3and the capacitance of the fourth capacitor C4varies in proportion to the area S2.

Thus, as the rotation angle of the sector form increases, the capacitance difference ΔC1decreases linearly and the capacitance difference ΔC2increases linearly against the increase in the rotation angle of the sector form, as shown inFIG. 4.

FIG. 5is derived from calculation of the angle based on an equation A TAN 2 (ΔC1, ΔC2)=tan−1(ΔC1/ΔC2). Here, tan−1is an inverse function of tan. A horizontal axis inFIG. 5represents the rotation angle of the sector form. A vertical axis inFIG. 5represents tan−1(ΔC1/ΔC2), and its unit is radian. A curve inFIG. 5representing a correlation between tan−1(ΔC1/ΔC2) and the rotation angle is substantially a straight line with a deviation from an ideal linear correlation (indicated by a chain line inFIG. 5) being less than 1%. Therefore, the rotation angle of the sector form, that is, the touch position of the finger of the operator can be determined with high accuracy from the capacitance differences ΔC1and ΔC2electrically obtained by the signal processing circuit and through the calculation based on the equation described above.

A structure of the signal processing circuit is hereafter explained in detail. Each of the first through fourth detection electrodes11-14is connected to each of the first through fourth output terminals CO1-CO4disposed on the insulating substrate10, respectively. Each of the first through fourth output terminals CO1-CO4is connected to corresponding each of input terminals of the selection circuit19. The selection circuit19selects the first and second output terminals CO1and CO2in a first phase, and selects the third and fourth output terminals CO3and CO4in a second phase.

Each of the first and second output terminals CO1and CO2selected in the first phase is respectively connected to a non-inverting input terminal (+) and an inverting input terminal (−) of the charge amplifier20. Each of the third and fourth output terminals CO3and CO4selected in the second phase is respectively connected to the non-inverting input terminal (+) and the inverting input terminal (−) of the charge amplifier20.

The charge amplifier20is structured so as to output in the first phase a first output voltage V1(Vout=V1) that is proportional to the capacitance difference ΔC1between the capacitance of the first capacitor C1and the capacitance of the second capacitor C2and to output in the second phase a second output voltage V2(Vout=V2) that is proportional to the capacitance difference ΔC2between the capacitance of the third capacitor C3and the capacitance of the fourth capacitor C4. Then, following equations hold:
V1/V2=ΔC1/ΔC2
tan−1(ΔC1/ΔC2)=tan−1(V1/V2)

The A/D converter21converts the first and second output voltages V1and V2of the charge amplifier20into digital signals. The arithmetic unit30is made of a microcomputer, for example, and calculates tan−1(V1/V2) using the first and second output voltages V1and V2converted into the digital signals so that the rotation angle of the sector form, that is, the touch position of the finger of the operator is determined based on the correlation between tan−1(V1/V2) and the rotation angle of the sector form.

In this case, a correlation curve between tan−1(V1/V2) and the rotation angle is the same as the correlation curve between tan−1(ΔC1/ΔC2) and the rotation angle, and is almost a straight line. Therefore, the rotation angle of the sector form, that is, the touch position of the finger of the operator can be accurately determined based on the calculation of tan−1(V1/V2). The electrostatic capacity type touch sensor according to the first embodiment of this invention has excellent noise immunity, since it detects the change in the capacitance induced by the finger touch of the operator by a differential method. A data input device can be formed by assigning the touch position to an input content to be data-inputted.

The detection of the touch position in the first quadrant of the X-Y coordinate system is explained as described above. The same applies to the detection of the touch position in each of the second, third and fourth quadrants.

[Example Structure of Charge Amplifier]

An example of a concrete structure of the charge amplifier20is described hereafter referring toFIGS. 6,7A and7B. The charge amplifier20is structured to include clock generators18and25, capacitors CX1and CX2, a differential amplifier26, switches SW5and SW6and first and second feedback capacitors Cf1and Cf2.

FIG. 6shows a case in which the first and second output terminals CO1and CO2are selected by the selection circuit19, a signal from the first output terminal CO1is applied to the non-inverting input terminal (+) of the charge amplifier20, and a signal from the second output terminal CO2is applied to the inverting input terminal (−) of the charge amplifier20. The first capacitor C1and the second capacitor C2are formed on the insulative substrate10that is depicted as a portion encircled by a dashed line inFIG. 6.

The clock generator18forms a part of the charge amplifier20, and is composed of switches SW1and SW2that are turned on and off alternately. The clock generator18outputs a ground voltage (0 V) when the switch SW1is turned on and the switch SW2is turned off, and outputs a reference voltage Vref (positive voltage) when the switch SW1is turned off and the switch SW2is turned on. That is, the clock generator18outputs a clock alternating between the reference voltage Vref (H level) and 0 V (L level).

The capacitor CX1is connected in series to the first capacitor C1, while the capacitor CX2is connected in series to the second capacitor C2. The clock generator25, that is similar to the clock generator18, is connected to a connecting node between the capacitors CX1and CX2. The clock generator25is composed of switches SW3and SW4that are turned on and off alternately. The clock generator25outputs the ground voltage (0 V) when the switch SW3is turned on and the switch SW4is turned off, and outputs the reference voltage Vref (positive voltage) when the switch SW3is turned off and the switch SW4is turned on. The clock generators18and25are structured so as to output the clocks that are opposite in phase to each other.

A wiring drawn out from a connecting node N2between the first capacitor C1and the capacitor CX1is connected to a non-inverting input terminal (+) of the differential amplifier26that is an ordinary differential amplifier, while a wiring drawn out from a connecting node N1between the second capacitor C2and the capacitor CX2is connected to its inverting input terminal (−).

The first feedback capacitor Cf1is connected between an inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier26, while the second feedback capacitor Cf2is connected between a non-inverting output terminal (+) and the inverting input terminal (−) of the differential amplifier26. Each of the first and second feedback capacitors Cf1and Cf2has a capacitance CfA.

The switch SW5is connected between the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier26, while the switch SW6is connected between the non-inverting output terminal (+) and the inverting input terminal (−) of the differential amplifier26. The switches SW5and SW6are turned on and off simultaneously. That is, when the switches SW5and SW6are turned on, the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier26are short-circuited, and the non-inverting output terminal (+) and the inverting input terminal (−) of the differential amplifier26are short-circuited.

A voltage difference between an output voltage Vom from the inverting output terminal (−) of the differential amplifier26and an output voltage Vop from the non-inverting output terminal (+) of the differential amplifier26is represented by Vout (=Vop−Vom).

Next, operations of the charge amplifier20structured as described above are explained referring toFIGS. 7A and 7B. The charge amplifier20has a charge accumulation mode and a charge transfer mode that alternate between each other.

In the charge accumulation mode that is shown inFIG. 7A, the reference voltage Vref is applied to the first and second capacitors C1and C2by turning off the switch SW1and turning on the switch SW2of the clock generator18. Also, the ground voltage (0 V) is applied to the capacitors CX1and CX2by turning off the switch SW4and turning on the switch SW3of the clock generator25.

Also, the switches SW5and SW6are turned on. With this, the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier26are short-circuited, while the non-inverting output terminal (+) and the inverting input terminal (−) are short-circuited. As a result, a voltage at the node N1, a voltage at the node N2, a voltage at the inverting output terminal (−) and a voltage at the non-inverting output terminal (+) become ½ Vref. Here, a common mode voltage of the differential amplifier26is ½ Vref, which is a half of the reference voltage Vref.

Next, in the charge transfer mode that is shown inFIG. 7B, the ground voltage (0 V) is applied to the first and second capacitors C1and C2by turning on the switch SW1and turning off the switch SW2of the clock generator18. Also, the reference voltage Vref is applied to the capacitors CX1and CX2by turning on the switch SW4and turning off the switch SW3of the clock generator25. Also, SW5and SW6are turned off. After that, the operation returns to the charge accumulation mode shown inFIG. 7A, and then turns to the charge transfer mode shown inFIG. 7Bagain.

It is assumed that a capacitance CX1A of the capacitor CX1is equal to a capacitance CX2A of the capacitor CX2. That is, CX1A=CX2A. The capacitance of the first capacitor C1is denoted as C1A, and the capacitance of the second capacitor C2is denoted as C2A. Each of the capacitances C1A and C2A in an initial state in which the finger of the operator is far away from the touch panel is denoted as C. The capacitance difference ΔC1represents a difference between the capacitance C1A of the first capacitor C1and the capacitance C2A of the second capacitor C2in the case where the finger of the operator touches the first detection electrode11. That is, C1A−C2A=ΔC1. Then, following equations hold.
C1A=C+ΔC1
C2A=C

Now, the law of conservation of electric charge is applied regarding the node N2.

Equation (3) shown below holds in the charge accumulation mode.
Electric Charges atN2=(C+ΔC1)×(−½Vref)+C×(½Vref)  (3)

Here, (C+ΔC1)×(−½Vref) represents an amount of electric charges stored in the first capacitor C1, and C×(½Vref) represents an amount of electric charges stored in the capacitor CX1.

Equation (4) shown below holds in the charge transfer mode:
Electric Charges atN2=(C+ΔC1)×(½Vref)+C×(−½Vref)+CfA×(Vom−½Vref)  (4)

Here, (C+ΔC1)×(½Vref) represents an amount of electric charges stored in the first capacitor C1, C×(−½Vref) represents an amount of electric charges stored in the capacitor CX1and CfA×(Vom−½Vref) represents an amount of electric charges stored in the first feedback capacitor Cf1.

Since the amount of electric charges at the node N2in the charge accumulation mode is equal to that in the charge transfer mode, Equation (3)=Equation (4) holds.

Following equation is derived by solving Equation (3)=Equation (4) for Vom:
Vom=½Vref×(1−2ΔC1/CfA)  (5)

Similarly, the law of conservation of electric charge is applied regarding the node N1.

Equation (6) shown below holds in the charge accumulation mode.
Electric Charges atN1=C×(−½Vref)+C×(½Vref)=0  (6)

Equation (7) shown below holds in the charge transfer mode.
Electric Charges at N1=C×(½Vref)+C×(−½Vref)+CfA×(Vop−½Vref)  (7)

Since the amount of electric charges at the node N1in the charge accumulation mode is equal to that in the charge transfer mode, Equation (6)=Equation (7) holds.

Following equation is derived by solving Equation (6)=Equation (7) for Vop:
Vop=½Vref  (8)

Following equation is derived from equations (5) and (8):
Vout=Vop−Vom=Vref×ΔC1/CfA(9)

It is understood that the output voltage Vout (=V1) of the charge amplifier20varies in proportion to the capacitance difference ΔC1between the capacitances of the first and second capacitors C1and C2.

The case in which the first and second output terminals CO1and CO2are selected by the selection circuit19is explained above. Similar explanation applies to the case in which the third and fourth output terminals CO3and CO4are selected by the selection circuit19, and a signal from the third output terminal CO3is applied to the no-inversion input terminal (+) of the charge amplifier20and the signal from the fourth output terminal CO4is applied to the inverting input terminal (−) of the charge amplifier20. That is, the output voltage Vout (=V2) of the charge amplifier20varies in proportion to the capacitance difference ΔC2between the capacitances of the third and fourth capacitors C3and C4in this case.

Second Embodiment

FIG. 8shows a structure of an electrostatic capacity type touch sensor according to a second embodiment of this invention. Difference from the electrostatic capacity type touch sensor according to the first embodiment is in the structure of the touch panel. That is, a first common electric potential line15ais disposed on a circumference of a first ellipse having a center O. A second common electric potential line16ais disposed on a circumference of a second ellipse that shares the center O with the first ellipse. The second ellipse is larger than the first ellipse.

First through fourth detection electrodes11a-14aare disposed in a ring region REa interposed between the first and second common electric potential lines15aand16a. The first and second detection electrodes11aand12aare shaped and disposed axisymmetrical with respect to a Y axis that intersects the center O. The third and fourth detection electrodes13aand14aare shaped and disposed axisymmetrical with respect to an X axis that intersects the center O. The X axis and the Y axis intersect orthogonally. Note that boundary regions corresponding to the boundary regions BL1-BL4shown inFIG. 1are omitted inFIG. 8.

There is considered a sector form with a center angle δ (10°, for example) regarding the ellipse representing the second common electric potential line16a. An overlapping region (shaded region inFIG. 8) between the sector form and the ring region REa interposed between the first and second common electric potential lines15aand16acan be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode11aincluded in the touch region is denoted as S1a, and an area of the third detection electrode13aincluded in the touch region is denoted as S2a. Suppose the sector form rotates counterclockwise around the center O in the first quadrant of the X-Y coordinate system. It corresponds to that a touch position of the finger of the operator to the touch panel rotates counterclockwise in the ring region REa. In the second embodiment also, the area S1adeceases and the area S2aincreases as the rotation angle of the sector form increases. Other structures are the same as those in the first embodiment.

The first output voltage V1and the second output voltage V2of the charge amplifier20are defined in the same way as in the first embodiment. The rotation angle of the sector form, that is, the touch position of the finger of the operator can be accurately determined based on the calculation of tan−1(V1/V2) with the electrostatic capacity type touch sensor according to the second embodiment, although the linearity of the correlation curve between tan−1(V1/V2) and the rotation angle is slightly poorer than that in the first embodiment.

Third Embodiment

FIG. 9shows a structure of an electrostatic capacity type touch sensor according to a third embodiment of this invention. Difference from the electrostatic capacity type touch sensor according to the first embodiment is in the structure of the touch panel. That is, a first common electric potential line15bis disposed on a perimeter of a first square having a center O. A second common electric potential line16bis disposed on a perimeter of a second square that shares the center O with the first square. The second square is larger than the first square.

First through fourth detection electrodes11b-14bare disposed in a ring region REb interposed between the first and second common electric potential lines15band16b. The first and second detection electrodes11band12bare shaped and disposed axisymmetrical with respect to a Y axis that intersects the center O. The third and fourth detection electrodes13band14bare shaped and disposed axisymmetrical with respect to an X axis that intersects the center O. The X axis and the Y axis intersect orthogonally. Note that boundary regions corresponding to the boundary regions BL1-BL4shown inFIG. 1are omitted inFIG. 9.

There is considered a sector form with a center angle δ (10°, for example) regarding the second square representing the second common electric potential line16b. An overlapping region (shaded region inFIG. 9) between the sector form and the ring region REb interposed between the first and second common electric potential lines15band16bcan be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode11bincluded in the touch region is denoted as S1b, and an area of the third detection electrode13bincluded in the touch region is denoted as S2b. Suppose the sector form rotates counterclockwise around the center O in the first quadrant of the X-Y coordinate system. It corresponds to that a touch position of the finger of the operator to the touch panel rotates counterclockwise in the ring region REb. In the third embodiment also, the area S1bdeceases and the area S2bincreases as the rotation angle of the sector form increases. Other structures are the same as those in the first embodiment.

The first output voltage V1and the second output voltage V2of the charge amplifier20are defined in the same way as in the first embodiment. The rotation angle of the sector form, that is, the touch position of the finger of the operator can be accurately determined based on the calculation of tan−1(V1/V2) with the electrostatic capacity type touch sensor according to the third embodiment, although the linearity of the correlation curve between tan−1(V1/V2) and the rotation angle is slightly poorer than that in the first embodiment. First and second rhombuses may be used instead of the first and second squares.

Fourth Embodiment

FIG. 10shows a structure of an electrostatic capacity type touch sensor according to a fourth embodiment of this invention. Difference from the electrostatic capacity type touch sensor according to the first embodiment is in the structure of the touch panel. That is, a first common electric potential line15cis disposed on a circumference of a first arc with a radius R having a center O. A second common electric potential line16cis disposed on a circumference of a second arc with a radius (R+W), which shares the center O with the first arc. Both ends of the first common electric potential line15care respectively connected to both ends of the second common electric potential line16cwith wirings to form a closed ring region REc.

First through fourth detection electrodes11c-14care disposed in the ring region REc interposed between the first and second common electric potential lines15cand16c. Note that boundary regions corresponding to the boundary regions BL1-BL4shown inFIG. 1are omitted inFIG. 10.

There is considered a sector form with a center angle δ (10°, for example) regarding the second arc representing the second common electric potential line16c. An overlapping region (shaded region inFIG. 10) between the sector form and the ring region REc interposed between the first and second common electric potential lines15cand16ccan be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode11eincluded in the touch region is denoted as S1c, and an area of the third detection electrode13cincluded in the touch region is denoted as S2c. Suppose the sector form rotates counterclockwise around the center O. It corresponds to that a touch position of the finger of the operator to the touch panel rotates counterclockwise in the ring region REc. In the fourth embodiment also, the area S1cdeceases and the area S2cincreases as the rotation angle of the sector form increases. Other structures are the same as those in the first embodiment.

The first output voltage V1and the second output voltage V2of the charge amplifier20are defined in the same way as in the first embodiment. The rotation angle of the sector form, that is, the touch position of the finger of the operator can be accurately determined based on the calculation of tan−1(V1/V2) with the electrostatic capacity type touch sensor according to the fourth embodiment, although the linearity of the correlation curve between tan−1(V1/V2) and the rotation angle is slightly poorer than that in the first embodiment.

Fifth Embodiment

FIG. 11shows a structure of an electrostatic capacity type touch sensor according to a fifth embodiment of this invention. Difference from the electrostatic capacity type touch sensor according to the first embodiment is in the structure of the touch panel. That is, a first common electric potential line15dis disposed on a circumference of a first four-leaf clover shape having a center O. A second common electric potential line16dis disposed on a circumference of a second four-leaf clover shape that shares the center O with the first four-leaf clover shape. The second four-leaf clover shape is larger than the first four-leaf clover shape.

First through fourth detection electrodes11d-14dare disposed in the ring region REd interposed between the first and second common electric potential lines15dand16d. The first and second detection electrodes11dand12dare shaped and disposed axisymmetrical with respect to a Y axis that intersects the center O. The third and fourth detection electrodes13dand14dare shaped and disposed axisymmetrical with respect to an X axis that intersects the center O. The X axis and the Y axis intersect orthogonally. Note that boundary regions corresponding to the boundary regions BL1-BL4shown inFIG. 1are omitted inFIG. 11.

There is considered a sector form with a center angle δ (10°, for example) regarding the second four-leaf clover shape representing the second common electric potential line16d. An overlapping region (shaded region inFIG. 11) between the sector form and the ring region REd interposed between the first and second common electric potential lines15dand16dcan be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode11dincluded in the touch region is denoted as S1d, and an area of the third detection electrode13dincluded in the touch region is denoted as S2d. Suppose the sector form rotates counterclockwise around the center O in the first quadrant of the X-Y coordinate system. It corresponds to that a touch position of the finger of the operator to the touch panel rotates counterclockwise in the ring region REd. In the fifth embodiment also, the area S1ddeceases and the area S2dincreases as the rotation angle of the sector form increases. Other structures are the same as those in the first embodiment.

The first output voltage V1and the second output voltage V2of the charge amplifier20are defined in the same way as in the first embodiment. The rotation angle of the sector form, that is, the touch position of the finger of the operator can be accurately determined based on the calculation of tan−1(V1/V2) with the electrostatic capacity type touch sensor according to the fifth embodiment, although the linearity of the correlation curve between tan−1(V1/V2) and the rotation angle is slightly poorer than that in the first embodiment.

This invention provides the electrostatic capacity type touch sensor capable of detecting a large number of touch positions using the four detection electrodes. In addition, the accuracy in detecting the touch positions can be improved by improving the linearity of the correlation between the output of the sensor and the touch position.