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

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

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.

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.

FIG. 1 shows a structure of an electrostatic capacity type touch sensor according to a first embodiment of this invention.

FIG. 2 shows a structure of a touch panel in the electrostatic capacity type touch sensor shown in FIG. 1 .

FIG. 3 is a cross-sectional view showing a section A-A in FIG. 1 .

FIG. 4 shows a correlation between each of capacitance changes ΔC 1 and ΔC 2 of detection electrodes and a rotation angle of a sector form.

FIG. 5 shows a correlation between tan −1 (ΔC 1 /ΔC 2 ) and the rotation angle of the sector form.

FIG. 6 is a circuit diagram of a charge amplifier.

FIGS. 7A and 7B are to explain operations of the charge amplifier.

FIG. 8 shows a structure of an electrostatic capacity type touch sensor according to a second embodiment of this invention.

FIG. 9 shows a structure of an electrostatic capacity type touch sensor according to a third embodiment of this invention.

FIG. 10 shows a structure of an electrostatic capacity type touch sensor according to a fourth embodiment of this invention.

FIG. 11 shows a structure of an electrostatic capacity type touch sensor according to a fifth embodiment of this invention.

First Embodiment

FIG. 1 shows a structure of an electrostatic capacity type touch sensor according to a first embodiment of this invention. FIG. 2 shows a structure of a touch panel in the electrostatic capacity type touch sensor shown in FIG. 1 . FIG. 3 is a cross-sectional view showing a section A-A in FIG. 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 substrate 10 such as a PCB substrate, and first through fourth detection electrodes 11 , 12 , 13 and 14 , first and second common electric potential lines 15 and 16 , a common electric potential wiring 17 , a common electric potential terminal COM and first through fourth output terminals CO 1 , CO 2 , CO 3 and CO 4 disposed on the insulating substrate 10 .

The signal processing circuit is structured to include a clock generator 18 , a selection circuit 19 , a charge amplifier 20 , an A/D converter 21 and an arithmetic unit 30 .

The first common electric potential line 15 is 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 line 16 is 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 line 15 and the second common electric potential line 16 are 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 lines 15 and 16 is about 0.5 mm, for example.

The first common electric potential line 15 is electrically connected with the second common electric potential line 16 through the common electric potential wiring 17 . The common electric potential wiring 17 is 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 CO 1 -CO 4 , and is electrically isolated from the first through fourth output terminals CO 1 -CO 4 . The common electric potential wiring 17 is connected to the common electric potential terminal COM. A clock alternating between an H level and an L level is applied from the clock generator 18 to the common electric potential terminal COM. As a result, the clock is applied to the first and second common electric potential lines 15 and 16 .

The first through fourth detection electrodes 11 - 14 are disposed in a ring region RE having a width W and interposed between the first and second common electric potential lines 15 and 16 . The first and second detection electrodes 11 and 12 are shaped and disposed axisymmetrical with respect to a Y axis that intersects the center O. The third and fourth detection electrodes 13 and 14 are 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 electrodes 11 and 12 are shaped and disposed point-symmetrical with respect to the center O, while the third and fourth detection electrodes 13 and 14 are shaped and disposed point-symmetrical with respect to the center O. The first and second detection electrodes 11 and 12 are shaped in a pair of crescents congruent with each other, while the third and fourth detection electrodes 13 and 14 are shaped in a pair of crescents congruent with each other. A width of each of the first and second detection electrodes 11 and 12 takes a maximum value at Y=0, while a width of each of the third and fourth detection electrodes 13 and 14 takes a maximum value at X=0. The maximum value is about 4 mm, for example.

A right edge of the first detection electrode 11 faces a right half of the second common electric potential line 16 with a short separation (about 0.5 mm), while a left edge of the second detection electrode 12 faces a left half of the second common electric potential line 16 with a short separation (about 0.5 mm). A lower edge of the third detection electrode 13 faces an upper half of the first common electric potential line 15 with a short separation (about 0.5 mm), while an upper edge of the fourth detection electrode 14 faces a lower half of the first common electric potential line 15 with a short separation (about 0.5 mm).

The first detection electrode 11 and the third detection electrode 13 are separated from each other by a narrow boundary region BL 1 in 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 in FIG. 3 shows that an insulating film 22 covers the first detection electrode 11 , the third detection electrode 13 and the first and second common electric potential lines 15 and 16 , which are disposed on the insulating substrate 10 .

The second detection electrode 12 and the third detection electrode 13 are separated from each other by a narrow boundary region BL 2 in a second quadrant of the X-Y coordinate system. Similarly, the second detection electrode 12 and the fourth detection electrode 14 are separated from each other by a narrow boundary region BL 3 in a third quadrant of the X-Y coordinate system. Similarly, the first detection electrode 11 and the fourth detection electrode 14 are separated from each other by a narrow boundary region BL 4 in a fourth quadrant of the X-Y coordinate system. The boundary regions BL 1 and BL 2 are axisymmetrical with respect to the Y axis, while the boundary regions BL 3 and BL 4 are axisymmetrical with respect to the Y axis. A width of each of the boundary regions BL 1 -BL 4 is about 0.5 mm.

The first and second common electric potential lines 15 and 16 , and the first through fourth detection electrodes 11 - 14 can be formed using transparent conductive material such as ITO (Indium Tin Oxide) or metal such as aluminum.

Focusing on the boundary region BL 1 between the first detection electrode 11 and the third detection electrode 13 in the first quadrant, coordinates (X, Y) of a point A on a center line (indicated by a chain double-dashed line in FIG. 1 and in FIG. 2 ) of the boundary region BL 1 are 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 line 15 . 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 line 16 .

There is considered a sector form with a center angle δ (10°, for example) regarding the circle representing the second common electric potential line 16 , as shown in FIG. 2 . An overlapping region (shaded region in FIG. 2 ) between the sector form and the ring region RE interposed between the first and second common electric potential lines 15 and 16 can be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode 11 included in the touch region is denoted as S 1 , and an area of the third detection electrode 13 included in the touch region is denoted as S 2 . 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 in FIG. 2 corresponds 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. 4 shows a correlation between a change in each of the areas S 1 and S 2 and the rotation angle of the sector form (center angle δ=10′). That is, as the rotation angle increases, the area S 1 decreases linearly and the area S 2 increases linearly. S 1 +S 2 remains constant. A scale of a vertical axis in FIG. 4 is a relative scale, and is set so that S 1 +S 2 =50.

When looked from the viewpoint of capacitances and their changes, a first capacitor C 1 is formed between the first detection electrode 11 and the first and second common electric potential lines 15 and 16 , while a second capacitor C 2 is formed between the second detection electrode 12 and the first and second common electric potential lines 15 and 16 . When the finger of the operator is far away from the touch panel, a capacitance of the first capacitor C 1 is equal to a capacitance of the second capacitor C 2 . When the finger of the operator touches the ring region RE, the capacitance of the first capacitor C 1 increases in proportion to the area S 1 . That is because the number of electric lines of force between the first detection electrode 11 and the first and second common electric potential lines 15 and 16 increases 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 ΔC 1 between the capacitance of the first capacitor C 1 and the capacitance of the second capacitor C 2 varies in proportion to the area S 1 . 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 C 1 decreases in proportion to the area S 1 . Following explanations are based on the dielectric model.

Similarly, a third capacitor C 3 is formed between the third detection electrode 13 and the first and second common electric potential lines 15 and 16 , while a fourth capacitor C 4 is formed between the fourth detection electrode 14 and the first and second common electric potential lines 15 and 16 . When the finger of the operator is far away from the touch panel, a capacitance of the third capacitor C 3 is equal to a capacitance of the fourth capacitor C 4 . When the finger of the operator touches the ring region RE, the capacitance of the third capacitor C 3 increases in proportion to the area S 2 . Therefore, a capacitance difference ΔC 2 between the capacitance of the third capacitor C 3 and the capacitance of the fourth capacitor C 4 varies in proportion to the area S 2 .

Thus, as the rotation angle of the sector form increases, the capacitance difference ΔC 1 decreases linearly and the capacitance difference ΔC 2 increases linearly against the increase in the rotation angle of the sector form, as shown in FIG. 4 .

FIG. 5 is derived from calculation of the angle based on an equation A TAN 2 (ΔC 1 , ΔC 2 )=tan −1 (ΔC 1 /ΔC 2 ). Here, tan −1 is an inverse function of tan. A horizontal axis in FIG. 5 represents the rotation angle of the sector form. A vertical axis in FIG. 5 represents tan −1 (ΔC 1 /ΔC 2 ), and its unit is radian. A curve in FIG. 5 representing a correlation between tan −1 (ΔC 1 /ΔC 2 ) and the rotation angle is substantially a straight line with a deviation from an ideal linear correlation (indicated by a chain line in FIG. 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 ΔC 1 and ΔC 2 electrically 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 electrodes 11 - 14 is connected to each of the first through fourth output terminals CO 1 -CO 4 disposed on the insulating substrate 10 , respectively. Each of the first through fourth output terminals CO 1 -CO 4 is connected to corresponding each of input terminals of the selection circuit 19 . The selection circuit 19 selects the first and second output terminals CO 1 and CO 2 in a first phase, and selects the third and fourth output terminals CO 3 and CO 4 in a second phase.

Each of the first and second output terminals CO 1 and CO 2 selected in the first phase is respectively connected to a non-inverting input terminal (+) and an inverting input terminal (−) of the charge amplifier 20 . Each of the third and fourth output terminals CO 3 and CO 4 selected in the second phase is respectively connected to the non-inverting input terminal (+) and the inverting input terminal (−) of the charge amplifier 20 .

The charge amplifier 20 is structured so as to output in the first phase a first output voltage V 1 (Vout=V 1 ) that is proportional to the capacitance difference ΔC 1 between the capacitance of the first capacitor C 1 and the capacitance of the second capacitor C 2 and to output in the second phase a second output voltage V 2 (Vout=V 2 ) that is proportional to the capacitance difference ΔC 2 between the capacitance of the third capacitor C 3 and the capacitance of the fourth capacitor C 4 . Then, following equations hold:

V 1 /V 2 =ΔC 1 /ΔC 2

tan −1 (Δ C 1 /ΔC 2)=tan −1 ( V 1 /V 2)

The A/D converter 21 converts the first and second output voltages V 1 and V 2 of the charge amplifier 20 into digital signals. The arithmetic unit 30 is made of a microcomputer, for example, and calculates tan −1 (V 1 /V 2 ) using the first and second output voltages V 1 and V 2 converted 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 (V 1 /V 2 ) and the rotation angle of the sector form.

In this case, a correlation curve between tan −1 (V 1 /V 2 ) and the rotation angle is the same as the correlation curve between tan −1 (ΔC 1 /ΔC 2 ) 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 (V 1 /V 2 ). 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 amplifier 20 is described hereafter referring to FIGS. 6 , 7 A and 7 B. The charge amplifier 20 is structured to include clock generators 18 and 25 , capacitors CX 1 and CX 2 , a differential amplifier 26 , switches SW 5 and SW 6 and first and second feedback capacitors Cf 1 and Cf 2 .

FIG. 6 shows a case in which the first and second output terminals CO 1 and CO 2 are selected by the selection circuit 19 , a signal from the first output terminal CO 1 is applied to the non-inverting input terminal (+) of the charge amplifier 20 , and a signal from the second output terminal CO 2 is applied to the inverting input terminal (−) of the charge amplifier 20 . The first capacitor C 1 and the second capacitor C 2 are formed on the insulative substrate 10 that is depicted as a portion encircled by a dashed line in FIG. 6 .

The clock generator 18 forms a part of the charge amplifier 20 , and is composed of switches SW 1 and SW 2 that are turned on and off alternately. The clock generator 18 outputs a ground voltage (0 V) when the switch SW 1 is turned on and the switch SW 2 is turned off, and outputs a reference voltage Vref (positive voltage) when the switch SW 1 is turned off and the switch SW 2 is turned on. That is, the clock generator 18 outputs a clock alternating between the reference voltage Vref (H level) and 0 V (L level).

The capacitor CX 1 is connected in series to the first capacitor C 1 , while the capacitor CX 2 is connected in series to the second capacitor C 2 . The clock generator 25 , that is similar to the clock generator 18 , is connected to a connecting node between the capacitors CX 1 and CX 2 . The clock generator 25 is composed of switches SW 3 and SW 4 that are turned on and off alternately. The clock generator 25 outputs the ground voltage (0 V) when the switch SW 3 is turned on and the switch SW 4 is turned off, and outputs the reference voltage Vref (positive voltage) when the switch SW 3 is turned off and the switch SW 4 is turned on. The clock generators 18 and 25 are structured so as to output the clocks that are opposite in phase to each other.

A wiring drawn out from a connecting node N 2 between the first capacitor C 1 and the capacitor CX 1 is connected to a non-inverting input terminal (+) of the differential amplifier 26 that is an ordinary differential amplifier, while a wiring drawn out from a connecting node N 1 between the second capacitor C 2 and the capacitor CX 2 is connected to its inverting input terminal (−).

The first feedback capacitor Cf 1 is connected between an inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 26 , while the second feedback capacitor Cf 2 is connected between a non-inverting output terminal (+) and the inverting input terminal (−) of the differential amplifier 26 . Each of the first and second feedback capacitors Cf 1 and Cf 2 has a capacitance CfA.

The switch SW 5 is connected between the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 26 , while the switch SW 6 is connected between the non-inverting output terminal (+) and the inverting input terminal (−) of the differential amplifier 26 . The switches SW 5 and SW 6 are turned on and off simultaneously. That is, when the switches SW 5 and SW 6 are turned on, the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 26 are short-circuited, and the non-inverting output terminal (+) and the inverting input terminal (−) of the differential amplifier 26 are short-circuited.

A voltage difference between an output voltage Vom from the inverting output terminal (−) of the differential amplifier 26 and an output voltage Vop from the non-inverting output terminal (+) of the differential amplifier 26 is represented by Vout (=Vop−Vom).

Next, operations of the charge amplifier 20 structured as described above are explained referring to FIGS. 7A and 7B . The charge amplifier 20 has a charge accumulation mode and a charge transfer mode that alternate between each other.

In the charge accumulation mode that is shown in FIG. 7A , the reference voltage Vref is applied to the first and second capacitors C 1 and C 2 by turning off the switch SW 1 and turning on the switch SW 2 of the clock generator 18 . Also, the ground voltage (0 V) is applied to the capacitors CX 1 and CX 2 by turning off the switch SW 4 and turning on the switch SW 3 of the clock generator 25 .

Also, the switches SW 5 and SW 6 are turned on. With this, the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 26 are short-circuited, while the non-inverting output terminal (+) and the inverting input terminal (−) are short-circuited. As a result, a voltage at the node N 1 , a voltage at the node N 2 , 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 amplifier 26 is ½ Vref, which is a half of the reference voltage Vref.

Next, in the charge transfer mode that is shown in FIG. 7B , the ground voltage (0 V) is applied to the first and second capacitors C 1 and C 2 by turning on the switch SW 1 and turning off the switch SW 2 of the clock generator 18 . Also, the reference voltage Vref is applied to the capacitors CX 1 and CX 2 by turning on the switch SW 4 and turning off the switch SW 3 of the clock generator 25 . Also, SW 5 and SW 6 are turned off. After that, the operation returns to the charge accumulation mode shown in FIG. 7A , and then turns to the charge transfer mode shown in FIG. 7B again.

It is assumed that a capacitance CX 1 A of the capacitor CX 1 is equal to a capacitance CX 2 A of the capacitor CX 2 . That is, CX 1 A=CX 2 A. The capacitance of the first capacitor C 1 is denoted as C 1 A, and the capacitance of the second capacitor C 2 is denoted as C 2 A. Each of the capacitances C 1 A and C 2 A 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 ΔC 1 represents a difference between the capacitance C 1 A of the first capacitor C 1 and the capacitance C 2 A of the second capacitor C 2 in the case where the finger of the operator touches the first detection electrode 11 . That is, C 1 A−C 2 A=ΔC 1 . Then, following equations hold.

C 1 A=C+ΔC 1

C 2 A=C

Now, the law of conservation of electric charge is applied regarding the node N 2 .

Equation (3) shown below holds in the charge accumulation mode.

Electric Charges at N 2=( C+ΔC 1)×(−½ V ref)+ C ×(½ V ref)  (3)

Here, (C+ΔC 1 )×(−½Vref) represents an amount of electric charges stored in the first capacitor C 1 , and C×(½Vref) represents an amount of electric charges stored in the capacitor CX 1 .

Equation (4) shown below holds in the charge transfer mode:

Electric Charges at N 2=( C+ΔC 1)×(½ V ref)+ C ×(−½ V ref)+ CfA ×( Vom− ½ V ref)  (4)

Here, (C+ΔC 1 )×(½Vref) represents an amount of electric charges stored in the first capacitor C 1 , C×(−½Vref) represents an amount of electric charges stored in the capacitor CX 1 and CfA×(Vom−½Vref) represents an amount of electric charges stored in the first feedback capacitor Cf 1 .

Since the amount of electric charges at the node N 2 in 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= ½ V ref×(1−2 ΔC 1 /CfA )  (5)

Similarly, the law of conservation of electric charge is applied regarding the node N 1 .

Equation (6) shown below holds in the charge accumulation mode.

Electric Charges at N 1 =C ×(−½ V ref)+ C ×(½ V ref)=0  (6)

Equation (7) shown below holds in the charge transfer mode.

Electric Charges at N1 =C ×(½ V ref)+ C ×(−½ V ref)+ CfA ×( Vop− ½ V ref)  (7)

Since the amount of electric charges at the node N 1 in 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= ½ V ref  (8)

Following equation is derived from equations (5) and (8):

V out= Vop−Vom=V ref×Δ C 1 /CfA   (9)

It is understood that the output voltage Vout (=V 1 ) of the charge amplifier 20 varies in proportion to the capacitance difference ΔC 1 between the capacitances of the first and second capacitors C 1 and C 2 .

The case in which the first and second output terminals CO 1 and CO 2 are selected by the selection circuit 19 is explained above. Similar explanation applies to the case in which the third and fourth output terminals CO 3 and CO 4 are selected by the selection circuit 19 , and a signal from the third output terminal CO 3 is applied to the no-inversion input terminal (+) of the charge amplifier 20 and the signal from the fourth output terminal CO 4 is applied to the inverting input terminal (−) of the charge amplifier 20 . That is, the output voltage Vout (=V 2 ) of the charge amplifier 20 varies in proportion to the capacitance difference ΔC 2 between the capacitances of the third and fourth capacitors C 3 and C 4 in this case.

Second Embodiment

FIG. 8 shows 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 line 15 a is disposed on a circumference of a first ellipse having a center O. A second common electric potential line 16 a is 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 electrodes 11 a - 14 a are disposed in a ring region REa interposed between the first and second common electric potential lines 15 a and 16 a . The first and second detection electrodes 11 a and 12 a are shaped and disposed axisymmetrical with respect to a Y axis that intersects the center O. The third and fourth detection electrodes 13 a and 14 a are 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 BL 1 -BL 4 shown in FIG. 1 are omitted in FIG. 8 .

There is considered a sector form with a center angle δ (10°, for example) regarding the ellipse representing the second common electric potential line 16 a . An overlapping region (shaded region in FIG. 8 ) between the sector form and the ring region REa interposed between the first and second common electric potential lines 15 a and 16 a can be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode 11 a included in the touch region is denoted as S 1 a , and an area of the third detection electrode 13 a included in the touch region is denoted as S 2 a . 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 S 1 a deceases and the area S 2 a increases as the rotation angle of the sector form increases. Other structures are the same as those in the first embodiment.

The first output voltage V 1 and the second output voltage V 2 of the charge amplifier 20 are 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 (V 1 /V 2 ) with the electrostatic capacity type touch sensor according to the second embodiment, although the linearity of the correlation curve between tan −1 (V 1 /V 2 ) and the rotation angle is slightly poorer than that in the first embodiment.

Third Embodiment

FIG. 9 shows 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 line 15 b is disposed on a perimeter of a first square having a center O. A second common electric potential line 16 b is 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 electrodes 11 b - 14 b are disposed in a ring region REb interposed between the first and second common electric potential lines 15 b and 16 b . The first and second detection electrodes 11 b and 12 b are shaped and disposed axisymmetrical with respect to a Y axis that intersects the center O. The third and fourth detection electrodes 13 b and 14 b are 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 BL 1 -BL 4 shown in FIG. 1 are omitted in FIG. 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 line 16 b . An overlapping region (shaded region in FIG. 9 ) between the sector form and the ring region REb interposed between the first and second common electric potential lines 15 b and 16 b can be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode 11 b included in the touch region is denoted as S 1 b , and an area of the third detection electrode 13 b included in the touch region is denoted as S 2 b . 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 S 1 b deceases and the area S 2 b increases as the rotation angle of the sector form increases. Other structures are the same as those in the first embodiment.

The first output voltage V 1 and the second output voltage V 2 of the charge amplifier 20 are 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 (V 1 /V 2 ) with the electrostatic capacity type touch sensor according to the third embodiment, although the linearity of the correlation curve between tan −1 (V 1 /V 2 ) 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. 10 shows 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 line 15 c is disposed on a circumference of a first arc with a radius R having a center O. A second common electric potential line 16 c is 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 line 15 c are respectively connected to both ends of the second common electric potential line 16 c with wirings to form a closed ring region REc.

First through fourth detection electrodes 11 c - 14 c are disposed in the ring region REc interposed between the first and second common electric potential lines 15 c and 16 c . Note that boundary regions corresponding to the boundary regions BL 1 -BL 4 shown in FIG. 1 are omitted in FIG. 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 line 16 c . An overlapping region (shaded region in FIG. 10 ) between the sector form and the ring region REc interposed between the first and second common electric potential lines 15 c and 16 c can be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode 11 e included in the touch region is denoted as S 1 c , and an area of the third detection electrode 13 c included in the touch region is denoted as S 2 c . 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 S 1 c deceases and the area S 2 c increases as the rotation angle of the sector form increases. Other structures are the same as those in the first embodiment.

The first output voltage V 1 and the second output voltage V 2 of the charge amplifier 20 are 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 (V 1 /V 2 ) with the electrostatic capacity type touch sensor according to the fourth embodiment, although the linearity of the correlation curve between tan −1 (V 1 /V 2 ) and the rotation angle is slightly poorer than that in the first embodiment.

Fifth Embodiment

FIG. 11 shows 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 line 15 d is disposed on a circumference of a first four-leaf clover shape having a center O. A second common electric potential line 16 d is 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 electrodes 11 d - 14 d are disposed in the ring region REd interposed between the first and second common electric potential lines 15 d and 16 d . The first and second detection electrodes 11 d and 12 d are shaped and disposed axisymmetrical with respect to a Y axis that intersects the center O. The third and fourth detection electrodes 13 d and 14 d are 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 BL 1 -BL 4 shown in FIG. 1 are omitted in FIG. 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 line 16 d . An overlapping region (shaded region in FIG. 11 ) between the sector form and the ring region REd interposed between the first and second common electric potential lines 15 d and 16 d can be considered as a touch region to which the finger of the operator touches.

An area of the first detection electrode 11 d included in the touch region is denoted as S 1 d , and an area of the third detection electrode 13 d included in the touch region is denoted as S 2 d . 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 S 1 d deceases and the area S 2 d increases as the rotation angle of the sector form increases. Other structures are the same as those in the first embodiment.

The first output voltage V 1 and the second output voltage V 2 of the charge amplifier 20 are 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 (V 1 /V 2 ) with the electrostatic capacity type touch sensor according to the fifth embodiment, although the linearity of the correlation curve between tan −1 (V 1 /V 2 ) 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.