JP2011039663A - Signal processing circuit for capacitance type touch sensor - Google Patents

Abstract

A signal processing circuit for a capacitive touch sensor capable of improving noise resistance and detecting a touch position of a fingertip or the like with high accuracy is provided.
A signal processing circuit includes a first adjustment capacitor CA1, a second adjustment capacitor CA2, a charge amplifier 12, and an AD converter 13. The first adjustment capacitor CA1 is connected in series with the first capacitor C1 via the first output terminal CO1. The second adjustment capacitor CA2 is connected in series with the second capacitor C2 via the second output terminal CO2. The charge amplifier 12 combines a first capacitor Ctot1 formed by combining the first capacitor C1 and the first adjustment capacitor CA1, and a second capacitor C2 combined with the second adjustment capacitor CA2. 2 outputs an output voltage Vout corresponding to a capacitance difference ΔC with respect to the combined capacitance Ctot2.
[Selection] Figure 1

Description

  The present invention relates to a signal processing circuit for a capacitive touch sensor, and more particularly to a signal processing circuit for a capacitive touch sensor that detects a touch position of a human fingertip or a pen tip by utilizing a change in capacitance. About.

  2. Description of the Related Art Conventionally, a capacitive touch sensor is known as a data input device for various electronic devices such as a mobile phone, a mobile audio device, a mobile game device, a television, and a personal computer.

  A signal processing circuit of a conventional capacitive touch sensor will be described with reference to FIGS. As shown in FIG. 10, a touch pad 61 is formed on the PCB substrate 60, and a capacitance 62 (capacitance value C) is formed between the touch pad 61 and the PCB substrate 60. The touch pad 61 is connected to the non-inverting input terminal (+) of the comparator 63 via the wiring 64. A reference voltage Vref is applied to the inverting input terminal (−) of the comparator 63. A constant current source 65 is connected to the wiring 64 that connects the touch pad 61 and the non-inverting input terminal (+) of the comparator 63.

  The operation of the signal processing circuit of this capacitive touch sensor will be described with reference to FIG. First, when the human finger 66 is far away from the touch pad 61, the capacitance value in the touch pad 61 is C. In this case, the capacitance 62 of the touch pad 61 is charged by the constant current from the constant current source 65, so that the voltage of the touch pad 61 increases from 0 V in the reset state and reaches the reference voltage Vref. The output voltage is inverted. The time from this reset until the comparator 63 is inverted is assumed to be t1.

  On the other hand, when the human fingertip 66 is brought close to the touch pad 61, the capacitance value of the touch pad 61 increases or decreases to C + C ′. This change C ′ is a capacitance value formed between the human finger and the touch pad 61. Then, the time until the voltage of the touch pad 61 reaches the reference voltage Vref from 0V is t2 (t2> t1). That is, it is possible to detect whether or not the human fingertip 66 touches the touch pad 61 based on the time difference (t2−t1) from the reset until the comparator 63 is inverted. In other words, the touch pad 61 can function as an ON / OFF switch for data input.

Japanese Patent Laid-Open No. 2005-190050

  However, in the signal processing circuit of the conventional capacitive touch sensor, there is a problem that when noise is applied to the touch pad 61, the voltage of the touch pad 61 changes and the circuit malfunctions. Further, when the touch pad 61 functions as a two-state switch of ON / OFF, the data input amount is limited.

The signal processing circuit for a touch sensor according to the present invention includes a first capacitor formed between the first touch pad and the common potential line, and a second capacitor disposed adjacent to the first touch pad. A signal processing circuit for a capacitive touch sensor that detects a touch position based on a capacitance difference of a second capacitor formed between a touch pad and the common potential line,
A first adjustment capacitor connected in series with the first capacitor; a second adjustment capacitor connected in series with the second capacitor; the first capacitor; and the first adjustment capacitor. A charge amplifier that outputs an output voltage corresponding to a capacitance difference between a first combined capacitor formed by combining the second combined capacitor formed by combining the second capacitor and the second adjustment capacitor; It is characterized by providing.

  According to the signal processing circuit for the capacitive touch sensor of the present invention, noise tolerance can be improved by adopting the differential capacitance detection method. Further, according to the signal processing circuit for the capacitive touch sensor of the present invention, the touch position of the fingertip or the like can be detected with high accuracy, and the data input amount can be increased.

  In particular, according to the signal processing circuit for the capacitive touch sensor of the present invention, since the adjustment capacitor is provided, the signal from the touch sensor side is attenuated so as to be adapted to the dynamic range of the charge amplifier. The amplifier can be operated appropriately.

1 is a circuit diagram of a signal processing circuit for a capacitive touch sensor according to a first embodiment of the present invention. FIG. It is a specific circuit diagram of the signal processing circuit for the capacitive touch sensor according to the first embodiment of the present invention. It is a figure explaining operation | movement of the signal processing circuit for electrostatic capacitance type touch sensors which concerns on the 1st Embodiment of this invention. It is a figure which shows the input / output characteristic of a charge amplifier. It is a circuit diagram of a signal processing circuit for a capacitive touch sensor according to a second embodiment of the present invention. It is a top view which shows the structural example 1 of an electrostatic capacitance type touch sensor. It is the elements on larger scale of FIG. It is a figure which shows the input / output characteristic of the signal processing circuit which concerns on the 2nd Embodiment of this invention. It is a top view which shows the structural example 2 of an electrostatic capacitance type touch sensor. It is a figure which shows the structure of the conventional electrostatic capacitance type input device. It is a figure explaining operation | movement of the conventional electrostatic capacitance type input device.

[First Embodiment]
A signal processing circuit for a capacitive touch sensor according to a first embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the capacitive touch sensor side (touch panel) is disposed on an insulating substrate 10 such as a PCB substrate, and includes first and second touch pads 1 and 2 made of a conductive material, a common potential line. 6 is comprised. The common potential line 6 is formed adjacent to or surrounding the first and second touch pads 1 and 2. An AC common potential generated from an AC power supply 7 is applied to the common potential line 6.

  Between the first and second touch pads 1 and 2 and the common potential line 6, first and second capacitors C1 and C2 are formed, respectively. The first and second touch pads 1 and 2 are connected to first and second output terminals CO1 and CO2, respectively. When the human fingertip or the like is close to the first touch pad 1, the human fingertip or the like functions as an electrode, so that the capacitance value of the first capacitor C1 changes with respect to the capacitance value of the second capacitor C2. Therefore, by detecting this change in capacitance, it is possible to detect a touch position such as a human fingertip.

  In order to enable such detection, the signal processing circuit includes a first adjustment capacitor CA1, a second adjustment capacitor CA2, a charge amplifier 12, and an AD converter 13. The first adjustment capacitor CA1 is connected in series with the first capacitor C1 via the first output terminal CO1. The second adjustment capacitor CA2 is connected in series with the second capacitor C2 via the second output terminal CO2. In this case, one end of the first adjustment capacitor CA1 is connected to the first touch pad 1, and the other end is connected to the non-inverting input terminal (+) of the charge amplifier 12. In addition, one end of the second adjustment capacitor CA2 is connected to the second touch pad 2, and the other end is connected to the inverting input terminal (−) of the charge amplifier 12.

  The charge amplifier 12 combines a first capacitor Ctot1 formed by combining the first capacitor C1 and the first adjustment capacitor CA1, and a second capacitor C2 combined with the second adjustment capacitor CA2. 2 outputs an output voltage Vout corresponding to a capacitance difference ΔC with respect to the combined capacitance Ctot2.

  Then, the first combined capacitance Ctot1 = C1 · CA1 / (C1 + CA1) and the second combined capacitance Ctot2 = C2 / CA2 / (C2 + CA2). That is, by providing the first adjustment capacitor CA1, the first combined capacitor Ctot1 is adjusted to be smaller than the first capacitor C1 on the capacitive touch sensor side by a factor of CA1 / (C1 + CA1). Is done. The same applies to the second adjustment capacitor CA2.

As a result, the output voltage Vout of the charge amplifier 12 is attenuated.
Can be operated normally. That is, when the first and second adjustment capacitors CA1 and CA2 are not provided, there is a risk that the output voltage Vout exceeds the output dynamic range of the charge amplifier 12 and the output voltage Vout of the charge amplifier 12 is clipped. However, according to the present embodiment, such a problem can be solved. As a result, the output voltage Vout of the charge amplifier 12 changes smoothly following the capacitance difference ΔC (that is, the linearity is improved), and the touch position detection accuracy is improved.

  The AD converter 13 is provided to convert the output voltage Vout, which is an analog value of the charge amplifier 12, into a digital value. Thereby, the touch position can be obtained by digital calculation.

[Specific configuration example of signal processing circuit]
Next, a specific configuration example and operation of the signal processing circuit will be described with reference to FIGS. As shown in FIG. 2, as shown in FIG. 2, a portion surrounded by a broken line is an insulating substrate 10, and the above-described first capacitor C <b> 1 and second capacitor C <b> 2 are formed.

  The AC power supply 7 is formed of switches SW1 and SW2 that are alternately switched. The AC power supply 7 outputs a ground voltage (0 V) when the switch SW1 is closed and the switch SW2 is opened, and outputs a reference voltage Vref (plus voltage) when the switch SW1 is opened and the switch SW2 is closed. In this case, the AC voltage of the AC power supply 7 is a clock signal voltage that alternately repeats the reference voltage Vref (H level) and 0 V (L level).

  A first reference capacitor CX1 is connected in series to the first adjustment capacitor CA1, and a second reference capacitor CX2 is connected in series to the second capacitor C2. Here, the capacitance values of CX1 and CX2 are set to be equal in the initial state, and are preferably approximately the same as the capacitance values of C1 + CA1 and C2 + CA2.

  An AC power supply 15 similar to the AC power supply 7 is connected to a common connection point of the first and second reference capacitors CX1 and CX2. The AC power supply 15 is formed of switches SW3 and SW4 that are alternately switched. The AC power supply 15 outputs a ground voltage (0 V) when the switch SW3 is closed and the switch SW4 is opened, and outputs a reference voltage Vref (plus voltage) when the switch SW3 is opened and the switch SW4 is closed. The AC power supply 7 and the AC power supply 15 are configured to output clock signal voltages having opposite phases.

  Reference numeral 16 denotes a general differential amplifier. A non-inverting input terminal (+) is connected to a wiring drawn from a connection point between the first adjustment capacitor CA1 and the first reference capacitor CX1, and its inverting input terminal ( −) Is connected to the wiring drawn from the connection point of the second adjustment capacitor CA2 and the second reference capacitor CX2.

  Further, a feedback capacitor Cf is connected between the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 16, and the non-inverting output terminal (+) and the inverting input terminal (−) of the differential amplifier 16. Are connected to the same feedback capacitor Cf. The capacitance value of the feedback capacitor Cf is Cf.

  Further, the switch SW5 is connected between the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 16, and the switch SW6 is connected to the non-inverting output terminal (+) and the inverting input terminal ( -) Connected between. The switches SW5 and SW6 are switched simultaneously. That is, when the switches SW5 and SW6 are closed, the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 16 are short-circuited, and the inverting output terminal (+) of the differential amplifier 16 is inverted. The input terminal (−) is short-circuited.

  The output voltage from the inverting output terminal (−) of the differential amplifier 16 is Vom, the output voltage from the non-inverting output terminal (+) of the differential amplifier 16 is Vop, and the difference voltage between them is Vout (= Vop−Vom). ).

  Next, the operation of the circuit having the above configuration will be described with reference to FIG. This circuit has two phases, a first phase (charge accumulation mode) and a second phase (charge transfer mode), and these two phases are alternately repeated many times.

  First, in the case of the first phase in FIG. 3A, the reference voltage Vref is applied to the first and second capacitors C1 and C2 by opening SW1 of the AC power supply 7 and closing SW2. Further, when SW4 of the AC power supply 15 is opened and SW3 is closed, the ground voltage (0 V) is applied to the first and second reference capacitors CX1 and CX2.

  Further, SW5 and SW6 are closed. Thereby, the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 16 are short-circuited, and the non-inverting output terminal (+) and the inverting input terminal (−) are short-circuited. As a result, the node N1 (wiring node connected to the inverting input terminal (−)), the node N2 (wiring node connected to the non-inverting input terminal (+)), the inverting output terminal (−), and the non-inverting output terminal ( The voltage of (+) becomes 1/2 · Vref. However, the common mode voltage of the differential amplifier 16 is ½ · Vref, which is ½ of the reference voltage.

  Next, in the case of the second phase in FIG. 3B, the ground voltage (0 V) is applied to the first and second capacitors C1 and C2 by closing SW1 of the AC power supply 7 and opening SW2. Further, when SW4 of AC power supply 15 is closed and SW3 is opened, reference voltage Vref is applied to first and second reference capacitors CX1 and CX2. In addition, SW5 and SW6 are opened.

Then, it returns to the state of the 1st phase of Drawing 3 (a), and shifts to the 2nd phase. In this case, CX1 = CX2 = C, and C is the initial capacitance value of C1 and C2. The capacitance values of the first and second adjustment capacitors CA1 and CA2 are CA. Furthermore, ΔC is a capacity difference between C1 and C2 when a human fingertip or the like approaches the touch pad.
That is, CA1 = CA2 = CA and C1-C2 = ΔC.
Then, C1 = C + 1/2 · ΔC and C2 = C−1 / 2 · ΔC are established.

Further, the first combined capacitance Ctot1 = C1 · CA / (C1 + CA) = α · (C + 1/2 · ΔC)
Here, α is expressed by the following equation.
α = CA / (CA + C1) = CA / (CA + C + 1/2 · ΔC)
Second combined capacitance Ctot2 = C2 · CA / (C2 + CA) = β · (C−1 / 2 · ΔC)
Here, β is expressed by the following equation.
β = CA / (CA + C2) = CA / (CA + C−1 / 2 · ΔC)

ここで、α・（Ｃ−１／２・ΔＣ）・（−１／２Ｖｒｅｆ）はＣ２の電荷量であり、Ｃ・（１／２Ｖｒｅｆ）はＣＸ２の電荷量、Ｃｆ・０（＝０）はＣｆの電荷量である。 When the charge conservation law is applied to the node N1, it is as follows.
In the first phase,

Here, α · (C−1 / 2 · ΔC) · (−1 / 2Vref) is the charge amount of C2, C · (1 / 2Vref) is the charge amount of CX2, and Cf · 0 (= 0) is This is the charge amount of Cf.

ここで、α・（Ｃ−１／２・ΔＣ）・（１／２・Ｖｒｅｆ）はＣ２の電荷量、Ｃ・（−１／２・Ｖｒｅｆ）はＣ４の電荷量、Ｃｆ・（Ｖｏｐ−１／２・Ｖｒｅｆ）はＣｆの電荷量である。
第１相と第２相においてノードＮ１の電荷量は等しいから、数１＝数２である。 In the second phase,

Here, α · (C−1 / 2 · ΔC) · (1/2 · Vref) is the charge amount of C2, C · (−1 / 2 · Vref) is the charge amount of C4, and Cf · (Vop−1). / 2 · Vref) is the charge amount of Cf.
Since the charge amount of the node N1 is the same in the first phase and the second phase, Equation 1 = Equation 2.

Solving this equation for Vop yields:

数３、数４から、Ｖｏｕｔを求める。

Similarly, when the law of conservation of charge is applied to the node N2 and the equation is solved for Vom, the following equation is obtained.

From equations 3 and 4, Vout is obtained.

  That is, the charge amplifier 12 can obtain the output voltage Vout in the charge transfer mode of FIG. On the other hand, when the first and second adjustment capacitors CA1 and CA2 are not provided, since α = β = 1, Vout = ΔC / Cf · Vref. Therefore, by providing the first and second adjustment capacitors CA1 and CA2, the output voltage Vout is attenuated by (α + β) / 2. As shown in FIG. 4, it can be seen that the output voltage Vout (= V1) of the charge amplifier 12 changes in proportion to the capacitance difference ΔC between the first and second capacitors C1 and C2.

  That is, by providing the first and second adjustment capacitors CA1 and CA2, the first and second combined capacitors Ctot1 and Ctot2 are reduced, and the capacitance difference ΔC is also reduced at a ratio of (α + β) / 2. Become. The nodes N1 and N2 are fixed to ½ · Vref in the charge accumulation mode with the first and second combined capacitances Ctot1 and Ctot2 decreased. Thereafter, the mode shifts to the charge transfer mode, and capacitance-voltage conversion is performed. At this time, since the capacitance difference ΔC is small, the output voltage Vout also decreases. In this case, since the input dynamic range of the charge amplifier 12 is designed to be, for example, 400 fF at the maximum, it is necessary to suppress the capacitance difference ΔC to 400 fF. The first and second adjustment capacitors CA1 and CA2 are determined so as to suppress the capacitance difference ΔC to 400 fF.

[Second Embodiment]
In the first embodiment, the first and second touch pads 1 and 2 are provided on the capacitive touch sensor side (touch panel), and a signal processing circuit that processes signals from these touch pads is shown. In the present embodiment, in addition to the first and second touch pads 1 and 2 on the capacitive touch sensor side (touch panel), signal processing corresponding to the case where the third and fourth touch pads 3 and 4 are provided. Circuit.

  That is, as shown in FIG. 5, the capacitive touch sensor side (touch panel) is disposed on an insulating substrate 10 such as a PCB substrate, and is common to first to fourth touch pads 1 to 4 made of a conductive material. It is configured including the potential line 6. The common potential line 6 is formed adjacent to or surrounding the first to fourth touch pads 1 to 4.

  A first capacitor C 1 is formed between the first touch pad 1 and the common potential line 6, and a second capacitor C 2 is formed between the second touch pad 2 and the common potential line 6. Similarly, a third capacitor C 3 is formed between the third touch pad 3 and the common potential line 6, and a fourth capacitor C 4 is formed between the fourth touch pad 4 and the common potential line 6. The That is, a wide range of touch positions can be detected using the first to fourth touch pads 1 to 4 as compared to the first embodiment.

  In order to enable such detection, the signal processing circuit includes first to fourth adjustment capacitors CA1 to CA4, a selection circuit 11, a charge amplifier 12, and an AD converter 13. The first to fourth adjustment capacitors CA1 to CA4 are connected in series with the first to fourth capacitors C1 to C4 via the first to fourth output terminals CO1 to CO4, respectively.

  The selection circuit 11 first selects a pair of first and second output terminals CO1 and CO2, and then selects a pair of third and fourth output terminals CO3 and CO4. The selected pair is connected to the non-inverting input terminal (+) and the inverting input terminal (−) of the charge amplifier 12, respectively.

  That is, when a pair of the first and second output terminals CO1 and CO2 is selected, a signal from the first output terminal CO1 is transmitted to the non-inverting input terminal of the charge amplifier 12 via the first adjustment capacitor CA1. Applied to (+). The signal from the second output terminal CO2 is applied to the inverting input terminal (−) of the charge amplifier 12 via the second adjustment capacitor CA2.

  Then, as in the first embodiment, the charge amplifier 12 includes, as the output voltage Vout, the first combined capacitor Ctot1 formed by combining the first capacitor C1 and the first adjustment capacitor CA1, and the first The output voltage V1 corresponding to the capacitance difference ΔC between the second combined capacitor Ctot2 formed by combining the second capacitor C2 and the second adjustment capacitor CA2 is output.

  Next, when the pair of the third and fourth output terminals CO3 and CO4 is selected, the signal from the third output terminal CO3 is input to the non-inverting input of the charge amplifier 12 via the third adjustment capacitor CA3. Applied to terminal (+). The signal from the fourth output terminal CO4 is applied to the inverting input terminal (−) of the charge amplifier 12 via the fourth adjustment capacitor CA4.

  Then, the charge amplifier 12 uses the third combined capacitor Ctot3 formed by combining the third capacitor C3 and the third adjustment capacitor CA3 as the output voltage Vout, and the fourth capacitor C4 and the fourth adjustment capacitor. An output voltage V2 corresponding to a capacitance difference ΔC with a fourth combined capacitor Ctot4 obtained by combining CA4 is output.

  Although the touch position can be detected based on the output voltages V1 and V2 of the charge amplifier 12, an AD converter 13 for converting the output voltages V1 and V2 into digital values is provided in order to obtain the touch position by digital calculation. ing.

  Note that the selection circuit 11 is deleted, and two charge amplifiers 12 are provided corresponding to the pair of the first and second output terminals CO1 and CO2 and the pair of the third and fourth output terminals CO3 and CO4. May be.

[Configuration Example 1 of Capacitive Touch Sensor]
Next, a configuration example on the capacitive touch sensor side (touch panel) will be described. FIG. 6 is a plan view of this capacitive touch sensor. FIG. 7 is an enlarged view of the first touch pad 1 and the third touch pad 3 of FIG.

  This capacitive touch sensor (touch panel) includes first to fifth touch pads 1 to 5 arranged on an insulating substrate 10 such as a PCB substrate, a common potential line 6, and an AC power source 7 that generates a common potential VCOM. It is comprised including.

  In FIG. 6, the leftmost first touch pad 1 includes first to fifth sub touch pads 1a to 1e arranged in a line in the X direction, and the first to fifth sub touch pads 1a to 1e. 1e are electrically connected to each other by adjacent wiring.

  The common potential line 6 is disposed so as to surround the first to fifth sub-touch pads 1a to 1e, respectively, so that an AC common potential VCOM from the AC power source 7 is applied thereto. The common potential line 6 forms a diamond-shaped cell surrounding each sub-touch pad, and the aggregate of cells has a honeycomb structure as a whole. Further, the common potential line 6 is electrically insulated from the adjacent wiring connecting the first to fifth sub touch pads 1a to 1e. An insulator (not shown) is interposed between the first to fifth sub-touch pads 1a to 1e and the common potential line 6, so that the first to fifth sub-touch pads 1a to 1e are It is capacitively coupled to the common potential line 6. The first touch pad 1 is connected to the first output terminal CO1 via a wiring.

  In this case, among the sub touch pads 1a to 1e, the area S1 of the first sub touch pad 1a arranged in the center is the largest, and the second sub touch pad arranged on the left side of the first sub touch pad 1a. The area S2 of the touch pad 1b is smaller than the area S1 of the first sub touch pad 1a. The area S3 of the third sub touch pad 1c arranged on the left side of the second sub touch pad 1b is smaller than the area S2 of the second sub touch pad 1b. That is, the area of the sub-touch pad that satisfies the relationship of S1> S2> S3 and is closer to the end portion is smaller.

  The fourth sub touch pad 1d is arranged symmetrically with the second sub touch pad 1b with the first sub touch pad 1a as the center, and the fifth sub touch pad 1e is the first sub touch pad. Arranged symmetrically with the third sub-touch pad 1c around 1a.

  Specifically, as shown in FIG. 7, the first sub-touch pad 1a has a diamond shape. The second sub touch pad 1b has a triangular shape left by cutting out the lower half of the rhombus of the first sub touch pad 1a. The third sub touch pad 1c has a shape in which a notch K is formed in the triangle of the second sub touch pad 1b.

  In this case, it is preferable to provide the notch K on the side of the third sub-touch pad 1c that faces the common potential line 6 in order to improve the accuracy of touch position detection. This is because, according to the experimental results, the touch position detection accuracy depends not only on the area of the sub-touch pad but also on the distance between the sub-touch pad and the common potential line 6. The shapes of the second sub-touch pad 1b and the fourth sub-touch pad 1d are the same, and the shapes of the third sub-touch pad 1c and the fifth sub-touch pad 1e are the same.

  In FIG. 6, the first to fifth sub-touch pads 1a to 1e are shown, but the notch portions K of the third sub-touch pad 1c and the fifth sub-touch pad 1e are not shown. It is. Further, although the pitches in the X direction of the first to fifth sub-touch pads 1a to 1e are equal, the pitch is preferably set so that the two pitches are approximately the same as the width of the human fingertip. Furthermore, the first to fifth sub-touch pads 1a to 1e and the common potential line 6 may be formed using a transparent conductive material such as ITO, or may be formed using a metal material such as aluminum. good.

  The second touch pad 2 is disposed adjacent to the right side of the first touch pad 1 and has the same structure as the first touch pad 1. That is, the second touch pad 2 includes first to fifth sub touch pads 2a to 2e arranged in a line in the X direction, and the first to fifth sub touch pads 2a to 2e are connected to each other by adjacent wirings. Electrically connected. The common potential line 6 is disposed so as to surround the first to fifth sub-touch pads 2a to 2e, respectively. The second touch pad 2 is connected to the second output terminal CO2 via a wiring.

  The first and second touch pads 1 and 2 described above form a pair and contribute to the detection of the touch position. That is, based on the capacitance difference between the first capacitor C 1 generated between the first touch pad 1 and the common potential line 6 and the second capacitor C 2 generated between the second touch pad 2 and the common potential line 6. The touch position of a human fingertip or the like is detected. In this case, in an initial state where a human fingertip or the like is far from the first and second touch pads 1 and 2, the capacitance values of the first capacitor C1 and the second capacitor C2 are equal.

In order to detect the touch position with high accuracy in a wider range, a pair of third and fourth touch pads 3 and 4 is arranged in addition to the pair of first and second touch pads 1 and 2.
In addition to the capacitance difference between the pair of the first and second touch pads 1 and 2, the third capacitor C 3 and the fourth touch pad 4 generated between the third touch pad 3 and the common potential line 6 The touch position is detected based on the capacitance difference with the fourth capacitor C4 generated between the common potential lines 6. Also in this case, in the initial state where the human fingertip or the like is far away from the third and fourth touch pads 3 and 4, the capacitance values of the third capacitor C3 and the fourth capacitor C4 are equal.

  The third and fourth touch pads 3 and 4 have the same structure as the first and second touch pads 1 and 2. That is, the third touch pad 3 is arranged in a line between the first touch pad 1 and the second touch pad 2 and is electrically connected to each other, the first to fifth sub touch pads 3a to 3e. Consists of. In this case, as shown in FIG. 7, the second sub touch pad 3 b is an inverted triangle, and together with the fifth sub touch pad 1 e of the first touch pad 1, in one cell of the common potential line 6. Has been placed. Similarly, the third touch pad 3 c is an inverted triangle having a notch K, and together with the fourth sub-touch pad 1 d of the first touch pad 1, in another cell of the common potential line 6. Is arranged. The third touch pad 3 is connected to the third output terminal CO3 via a wiring.

  The fourth touch pad 4 is disposed adjacent to the right side of the second touch pad 2 and includes first to fifth sub touch pads 4a to 4e that are electrically connected to each other. Also in this case, the second sub-touch pad 4 b is an inverted triangle, and is disposed in one cell of the common potential line 6 together with the fifth sub-touch pad 2 e of the second touch pad 2. Similarly, the third sub-touch pad 4 c is an inverted triangle having a notch K, and together with the fourth sub-touch pad 2 d of the first touch pad 1, another cell of the common potential line 6. Is placed inside. The fourth touch pad 4 is connected to the fourth output terminal CO4 via a wiring.

  In order to further expand the detection range of the touch position, the fifth touch pad 5 including the first to fifth sub touch pads 5a to 5e electrically connected to each other is disposed. In this case, the first to third sub touch pads 5a to 5c of the fifth touch pad 5 are arranged in a row in the X direction adjacent to the right side of the first sub touch pad 4a of the fourth touch pad 4. The remaining fourth and fifth sub touch pads 5d and 5e are arranged in a row in the X direction adjacent to the left side of the first sub touch pad 1a of the first touch pad 1. . The fifth touch pad 5 is connected to the first output terminal CO1 via a wiring.

  And as shown in FIG. 6, the above-mentioned 1st-5th touchpads 1-5 are repeatedly arranged in the Y direction. In this example, 15 first sub-touch pads 1a at the center of the first touch pad 1 are arranged in the Y direction, and these are electrically connected to each other by adjacent wirings. The same applies to the first sub touch pads 2a to 5a at the center of the second to fifth touch pads 2 to 5.

  FIG. 8 is a characteristic diagram of the signal processing circuit described above. In this case, the output voltage V1 of the charge amplifier 12 of the signal processing circuit is between the first capacitor C1, the second touchpad 2, and the common potential line 6 generated between the first touchpad 1 and the common potential line 6. The second capacitor C2 is proportional to the capacitance difference ΔC = C1−C2. Similarly, the output voltage V2 of the charge amplifier 12 is configured to be proportional to the capacitance difference ΔC = C3−C4.

  The horizontal axis in FIG. 8 corresponds to the coordinates in the X direction of the touch panel in FIG. 1, and P1 to P5 are the center positions of the sub touchpads 1a to 5a at the center of the first to fifth touchpads 1 to 5, respectively. It corresponds to. When the parameter θ corresponds to the X coordinate, θ = 0 ° corresponds to P1, θ = 90 ° corresponds to P3, θ = 180 ° corresponds to P2, and θ = 270 ° corresponds to P4. Θ = 360 ° corresponds to P5.

  When the human fingertip or the like is moved in the X direction from the first touch pad 1 to the fifth touch pad 5, the output voltage V1 of the charge amplifier 12 can be approximated by V1 = cos θ. . (When 1/2 of the amplitude of V1 is normalized to “1”)

  This is because the areas of the first to fifth sub-touch pads 1a to 1e of the first touch pad 1 and the first to fifth sub-touch pads 2a to 2e of the second touch pad 2 are as described above. For example, when the area of the first sub-touch pads 1a and 2a is “2”, the area of the second and fourth sub-touch pads 1b, 2b, 1d and 2d is “1”. It has been experimentally confirmed that the area of the third and fifth sub-touch pads 1c, 2c, 1e, 2e can be approximated to the waveform of V1 = cos θ by setting “0.5”.

  To explain this point qualitatively, when the human fingertip is on the first sub-touchpad 1a (P1) of the first touchpad 1, in the model in which the human fingertip functions as a dielectric, Since the number of lines increases locally, the first capacitance C1 increases compared to the second capacitance C2. Then, when the human fingertip or the like moves from the first sub-touch pad 1a → the fourth sub-touch pad 1d → the fifth sub-touch pad 1e, the sub-touch pad area decreases and the human finger or the like Since the capacitive coupling with the touch pad is also reduced, the first capacitance C1 is also reduced.

  However, in the electric field shielding model in which a human fingertip is grounded to shield the electric field, the capacitance change is reversed. Reflecting this capacitance change, the output voltage V1 becomes the maximum value “1” on P1, and the fingertip of the person is the first sub touch pad 1a → the fourth sub touch pad 1d → the fifth sub touch pad. It decreases as it moves to 1e and becomes “0” on P3. Then, when a human finger or the like goes from P3 to P2, the polarity of the output voltage V1 is reversed and becomes the minimum value −1 at P2. Thereafter, when a human finger or the like moves from P4 to P5, the output voltage V1 starts to increase and becomes “0” again at P5.

  Similarly, when a human fingertip or the like is moved in the X direction from the first touch pad 1 to the fifth touch pad, the output voltage V2 of the charge amplifier 12 can be approximated by V2 = sin θ. . (When the half of the amplitude of V2 is normalized to “1”) This is because the third touch pad 3 and the fourth touch pad 4 are changed to the first touch pad 1 and the second touch pad 2, respectively. This is because the phase is shifted in the X direction by θ = 90 °.

  Therefore, the touch position θ can be calculated from the output voltages V1 and V2. In order to efficiently calculate the touch position θ, it is preferable to use the ratio of the output voltages V1 and V2, V2 / V1. V2 / V1 is approximated by tan θ. That is, V2 / V1 = tan θ. When arctan, which is an inverse function of tan, is used, the touch position angle θ is expressed by θ = arctan (V2 / V1).

  In addition, an ATRAN2 function (a function obtained by extending the input range of the ATAN function to 0 to 360 °) is created from the output voltages V1 (= cos θ) and V2 (= sin θ), and linear position information can be obtained by using this ATAN2. Obtainable. That is, θ = ATAN2 (cos θ, sin θ).

  The algorithm for calculating the touch position θ as described above is executed using an arithmetic unit such as a microcomputer after the output voltages V1 and V2 which are analog values of the charge amplifier 12 are converted into digital values by the AD converter 13. It is preferable to do.

[Configuration Example 2 of Capacitive Touch Sensor]
A configuration example 1 of the capacitive touch sensor will be described. FIG. 9 is a plan view of this capacitive touch sensor. This capacitive touch sensor enables detection of touch positions (X, Y coordinates) in the X direction and the Y direction.

  That is, in the X direction, the first to fifth touch pads 1A to 5A are arranged on the insulating substrate 10 as in the above-described configuration example 1, and the first and fifth touch pads 1A and 5A are Are connected to the first output terminal CO1A, and the second to fourth touch pads 2A to 4A are connected to the second to fourth output terminals CO2A to CO4A, respectively.

  On the other hand, in the Y direction, first to fifth touch pads 1B to 5B having the same configuration as the first to fifth touch pads 1A to 5A are arranged on the insulating substrate 10. In FIG. 9, the first to fifth touch pads 1B to 5B are shown in black.

  The first to fifth touch pads 1B to 5B are repeatedly arranged in the X direction. In this example, 14 sub-touch pads in the center of the first touch pad 1B are arranged in the X direction, and these are electrically connected to each other by adjacent wirings. The same applies to the sub touch pad at the center of the second to fifth touch pads 2 to 5.

  The first and fifth touch pads 1B and 5B are connected to the first output terminal CO1B, and the second to fourth touch pads 2B to 4B are connected to the second to fourth output terminals CO2B to CO4B, respectively. Has been.

  In this case, two signal processing circuits in FIG. 5 are provided corresponding to the first to fifth touch pads 1A to 5A and the first to fifth touch pads 1B to 5B.

DESCRIPTION OF SYMBOLS 1-5 1st-5th touchpad 1a-1e 1st-5th sub touchpad 6 Common electric potential line 7 AC power supply 10 Insulation board | substrate 11 Selection circuit 12 Charge amplifier 13 AD converter 15 AC power supply 16 Differential amplifier K notch part CO1-CO4 1st-4th output terminal CA1-CA4 1st-4th adjustment capacity | capacitance

Claims (5)

A first capacitor formed between the first touch pad and the common potential line, and formed between the second touch pad arranged adjacent to the first touch pad and the common potential line. A signal processing circuit for a capacitive touch sensor that detects a touch position based on a difference in capacitance between the second capacitors,
A first adjustment capacitor connected in series with the first capacitor;
A second adjustment capacitor connected in series with the second capacitor;
A first combined capacitor formed by combining the first capacitor and the first adjusted capacitor; and a second combined capacitor formed by combining the second capacitor and the second adjusted capacitor. And a charge amplifier that outputs an output voltage corresponding to a capacitance difference. A signal processing circuit for a capacitive touch sensor. The charge amplifier includes a first reference capacitor connected in series with the first adjustment capacitor;
A second reference capacitor connected in series with the second adjustment capacitor;
An AC power source that applies an AC potential opposite in phase to the common potential applied to the common potential line to the first and second reference capacitors;
A non-inverting input terminal is connected to a connection point between the first adjustment capacitor and the first reference capacitor, and an inverting input terminal is connected to a connection point between the second adjustment capacitor and the second reference capacitor. Differential amplifier,
A first feedback capacitor and a first switch connected between an inverting output terminal and a non-inverting input terminal of the differential amplifier;
The capacitive touch sensor according to claim 1, further comprising a second feedback capacitor and a second switch connected between a non-inverting output terminal and an inverting input terminal of the differential amplifier. Signal processing circuit. A first capacitor formed between the first touch pad and the common potential line, and formed between the second touch pad arranged adjacent to the first touch pad and the common potential line. A first capacitance difference between the second capacitance and a third capacitance formed between a third touch pad and the common potential line; and a third capacitance formed adjacent to the third touch pad. A signal processing circuit for a capacitive touch sensor that detects a touch position based on a second capacitance difference of a fourth capacitance formed between a fourth touch pad and the common potential line. And
A first adjustment capacitor connected in series with the first capacitor;
A second adjustment capacitor connected in series with the second capacitor;
A third adjustment capacitor connected in series with the third capacitor;
A fourth adjustment capacitor connected in series with the fourth capacitor;
A first combined capacitor formed by combining the first capacitor and the first adjusted capacitor; and a second combined capacitor formed by combining the second capacitor and the second adjusted capacitor. A third output capacitor that outputs a first output voltage corresponding to the capacitance difference, and that combines the third capacitor and the third adjustment capacitor; and the fourth capacitor and the fourth adjustment. A signal processing circuit for a capacitive touch sensor, comprising: a charge amplifier that outputs a second output voltage corresponding to a capacitance difference with a fourth combined capacitor formed by combining the capacitor.   Selection to select one of the first signal pair from the first combined capacitor and the second combined capacitor, and the second signal pair from the third combined capacitor and the fourth combined capacitor The signal processing circuit for a capacitive touch sensor according to claim 2, further comprising a circuit.   5. The signal processing circuit for a capacitive touch sensor according to claim 1, further comprising an AD converter that converts the output voltage of the charge amplifier into a digital value. 6.

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