JP2011113188A - Signal processing circuit for capacitance type touch panel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To normally perform touch position detection even if a finger intending a data input and a finger not intending the data input simultaneously touch a touch panel, in a differential input type touch sensor. <P>SOLUTION: In a step S1, by a calibration circuit 19, the offset adjustment of an output voltage Vout of a sensor circuit is performed. In the next step S2, by a differential input type sense circuit, a touch position is detected. In the next step S3, based on the output voltage Vout (preferably, an A/D-converted value) of the sensor circuit, it is decided whether or not a touch detection time ts is not shorter than a prescribed time t0. When the touch detection time ts is not shorter than the prescribed time t0 (ts>t0), a calibration circuit 19 operates, and the offset adjustment of the output voltage Vout of the sensor circuit is newly performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a signal processing circuit for a capacitive touch panel.

  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.

  Capacitive touch sensors include a differential input type and a single input type. The differential input type touch sensor detects a touch position by differentially amplifying signals from a pair of sense lines formed on the touch panel. On the other hand, the single input type detects a touch position based on a signal from one sense line formed on the touch sensor.

  In the differential input type touch sensor, noise applied to the touch panel is canceled by the pair of sense lines, and thus, the S / N ratio is superior to the single input type touch sensor.

Japanese Patent Laid-Open No. 2005-190050

  However, the differential input type touch sensor has a problem that it is difficult to detect two points on the touch panel, that is, to detect multi-touch. For this reason, when a finger not intended for data input and a finger intended for data input touch the touch panel simultaneously on the touch panel, there is a problem that the position detection of the finger intended for data input cannot be performed normally.

  For example, as shown in FIG. 9, when data is input using the right hand finger 51 while holding the touch panel 50 with the left hand, first, the left hand finger 52 not intended for data input touches the detection surface of the touch panel 50. Then, with the left hand finger 52 touched, the right hand finger 51 touches another position on the detection surface of the touch panel 50. In this case, the left finger 52 usually touches the touch panel 50 continuously for a longer time than the right hand finger 51 performing the data input operation.

  Then, in the differential input type touch sensor, due to the influence of the touch of the left hand finger 52, the touch position detection of the right hand finger 51 to be originally detected cannot be normally performed.

  A capacitive touch panel signal processing circuit comprising a plurality of sense lines and a drive line to which an AC drive signal is applied, wherein the first and second sense lines are selected from the plurality of sense lines. A second capacitance formed between the second sense line and the drive line, and a capacitance value of a first capacitance formed between the first sense line and the drive line. A sensor circuit that detects a capacitance difference with a capacitance value of capacitance and outputs an output voltage corresponding to the capacitance difference, a calibration circuit that adjusts an offset of the output voltage of the sensor circuit, and an output of the sensor circuit A control circuit that performs control so as to adjust the offset of the output voltage of the sensor circuit by operating the calibration circuit when a touch detection time determined based on the voltage becomes equal to or longer than a predetermined time. With features That.

  The signal processing circuit of the capacitive touch panel according to the present invention is configured such that when the touch detection time of the sense circuit (the time during which a touch position is detected by the sense circuit) exceeds a predetermined time, the output voltage of the sense circuit Offset adjustment is performed. That is, when the touch detection time exceeds a predetermined time, it is determined that the touch is not intended for data input, and offset adjustment is performed. Thereby, the influence of the touch of the finger not intended for data input can be canceled, and the touch position detection of the finger intended for data input can be performed normally.

It is a figure which shows the structure of the touch sensor containing an electrostatic capacitance type touch panel and a signal processing circuit. It is a figure which shows the structure of the signal processing circuit of the electrostatic capacitance type touch panel of this invention. It is a figure which shows the structure of a differential input type sensor circuit. It is a figure which shows the structure of the variable capacity | capacitance for calibration. It is a figure explaining operation | movement of a differential input type sensor circuit. It is a figure which shows the output waveform of a differential input type sensor circuit. It is an operation | movement timing diagram of the signal processing circuit of an electrostatic capacitance type touch panel. It is a flowchart explaining operation | movement of the signal processing circuit of the electrostatic capacitance type touch panel of this invention. It is a figure explaining the usage method of a touch panel.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the capacitive touch sensor 100 includes a touch panel 1, signal processing circuits 2 </ b> X and 2 </ b> Y, and a microcomputer 3.

  The touch panel 1 includes X sense lines XL1 to XL4 and an X drive line DRXL extending in the X direction on the glass substrate 200. The X drive line DRXL is arranged adjacent to both sides of each X sense line XL1 to XL4. The touch panel 1 further includes Y sense lines YL1 to YL4 and a Y drive line DRYL that extend in the Y direction on the glass substrate and intersect the X sense lines XL1 to XL4. The Y drive line DRYL is disposed adjacent to both sides of each Y sense line YL1 to YL4. The X sense lines XL1 to XL4, the X drive line DRXL, the Y sense lines YL1 to YL4, and the Y drive line DRYL are electrically insulated from each other by a dielectric layer or the like.

  The signal processing circuits 2X and 2Y are arranged adjacent to the touch panel 1 on the glass substrate 200. The signal processing circuit 2X includes first to fourth input terminals CIN1 to CIN4 and a drive terminal CDRV that outputs an AC drive signal. The first input terminal CIN1 is connected to the X sense line XL1, and the second The input terminal CIN2 is connected to the X sense line XL3, the third input terminal CIN3 is connected to the X sense line XL2, and the fourth input terminal CIN4 is connected to the X sense line XL4. The drive terminal CDRV is connected to the X drive line DRXL.

  Similarly, the signal processing circuit 2Y includes first to fourth input terminals CIN1 to CIN4 and a drive terminal CDRV that outputs an AC drive signal (amplitude voltage Vref), and the first input terminal CIN1 is Y-sense. Connected to the line YL1, the second input terminal CIN2 is connected to the Y sense line YL3, the third input terminal CIN3 is connected to the Y sense line YL2, and the fourth input terminal CIN4 is connected to the Y sense line YL4. The The drive terminal CDRV is connected to the Y drive line DRYL.

Further, the signal processing circuits 2X and 2Y have a serial clock terminal SCL and a serial data terminal SDA, respectively. The serial clock terminal SCL is commonly connected to the serial clock line 4, and the serial data terminal SDA is commonly connected to the serial data line 5. In this case, the serial clock line 4 and the serial data line 5 form an I ² C bus.

  On the PCB substrate (not shown) outside the glass substrate 200, the microcomputer 3 as a master device is provided. The serial clock line 4 and serial data line 5 are connected to the microcomputer 3 via an FPC or the like. Thus, data communication is possible between the microcomputer 3 and the signal processing circuits 2X and 2Y. In this example, a microcomputer is used as the master device, but a DSP or a logic circuit may be used other than the microcomputer.

[Detailed configuration of signal processing circuit]
Hereinafter, a detailed configuration of the signal processing circuits 2X and 2Y of the capacitive touch panel will be described with reference to FIG. In this case, since the signal processing circuits 2X and 2Y have the same configuration, the signal processing circuit 2Y will be described.

As illustrated, the signal processing circuit 2Y includes a selection circuit 10, a control circuit 11, a drive circuit 12 that generates an AC drive signal, an inverter 13, a third capacitance C3, a fourth capacitance C4, and a differential. The amplifier 14 includes a first feedback capacitor 15, a second feedback capacitor 16, an AD converter 17, an I ² C bus interface circuit 18, a calibration circuit 19, and an EEPROM 20. The control circuit 11 is a circuit that controls the overall operation of the signal processing circuit 2Y.

  The selection circuit 10 has a first phase and a second phase. In the first phase, the selection circuit 10 selects signals from the first input terminal CIN1 and the second input terminal CIN2. That is, the first input terminal CIN 1 is connected to the non-inverting input terminal (+) of the differential amplifier 14 via the wiring 22, and the second input terminal CIN 2 is connected to the inverting input of the differential amplifier 14 via the wiring 23. Connected to terminal (-).

  In the second phase, the selection circuit 10 selects signals from the third input terminal CIN3 and the fourth input terminal CIN4. That is, the third input terminal CIN3 is connected to the non-inverting input terminal (+) of the differential amplifier 14 via the wiring 22, and the fourth input terminal CIN4 is connected to the inverting input of the differential amplifier 14 via the wiring 23. Connected to terminal (-).

  One terminal of the third capacitance C3 is connected to the wiring 22, and one terminal of the fourth capacitance C4 is connected to the wiring 23. The other terminals of the third and fourth capacitors are connected in common, and an inverted AC drive signal obtained by inverting the AC drive signal SCDRV from the drive circuit 12 via the inverter 13 is connected to the other terminal. * SCDRV is applied.

  Thereby, as shown in FIG. 3, a differential input type sensor circuit is formed. FIG. 3 shows a configuration when the selection circuit 10 selects signals from the first input terminal CIN1 and the second input terminal CIN2 (first phase). In this case, as shown in FIG. 1, a first capacitance C1 is formed between the Y sense line YL1 connected to the first input terminal CIN1 and the Y drive line DRYL, and the second input terminal CIN2 A second capacitance C2 is formed between the Y sense line YL3 and the Y drive line DRYL connected to.

  Then, as shown in FIG. 3, the first capacitance C1 is connected in series to the third capacitance C3, and the second capacitance C2 is connected in series to the fourth capacitance C4. The The AC drive signal SCDRV from the drive circuit 12 is applied to the common connection node of the first capacitance C1, that is, the Y drive line DRYL.

  The connection node N2 between the first capacitance C1 and the third capacitance C3 is connected to the non-inverting input terminal (+) of the differential amplifier 14. The connection node N1 between the second capacitance C2 and the fourth capacitance C4 is connected to the inverting input terminal (−) of the differential amplifier 14.

  The first feedback capacitor 15 and the switch SW1 are connected between the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 14, and the non-inverting output terminal (+) and the inverting input of the differential amplifier 14 are connected. The second feedback capacitor 16 and the switch SW2 are connected between the terminals (−).

  The switches SW1 and SW2 are preferably CMOS analog switches in order to improve the linearity of the signal transfer characteristics. Further, the capacitance values of the first and second feedback capacitors 15 and 16 are preferably the same Cf.

  This differential input type sensor circuit outputs an output voltage Vout corresponding to the difference between the capacitance value of the first capacitance C1 and the capacitance value of the second capacitance C2. The detailed operation will be described later.

Since the output voltage Vout of the sensor circuit described above is an analog signal, digital signal processing cannot be performed as it is. Therefore, the AD converter 17 converts the output voltage Vout into a digital signal. The output of the AD converter 17 is converted into serial data of a predetermined format by the I ² C bus interface circuit 18 and transmitted to the microcomputer 3 via the serial clock terminal SCL and the serial data terminal SDA. The microcomputer 3 performs arithmetic processing on the received serial data and determines a touch position on the touch panel 1.

[Calibration configuration]
The calibration configuration of the sensor circuit described above will be described with reference to FIGS.

  The sensor circuit has an unbalance between the capacitance values of the first capacitance C1 and the second capacitance C2 in an initial state (a state where the human finger or the like is not far from the touch panel 1). If there is a difference between both capacitance values, an offset of the output voltage Vout occurs. When the offset occurs, the detection accuracy of the touch sensor deteriorates.

  Further, as described above, when a finger not intended for data input and a finger intended for data input touch the touch panel at the same time on the touch panel 1, the position detection of the finger intended for data input cannot be performed normally.

  Therefore, the third and fourth electrostatic capacitances C3 and C4 are configured by variable capacitances so that the offset of the output voltage Vout can be adjusted.

  That is, the calibration circuit 19 is based on the output voltage Vout of the sensor circuit (preferably a digital value after AD conversion) so that the offset becomes a desired value, preferably a minimum value. The capacitance values of the capacitances C3 and C4 are adjusted.

  For the calibration shown in FIG. 3 for the sensor circuit, in the initial state, the capacitance values of the first to fourth capacitances C1 to C4 are preferably equal to each other (C1 = C2 = C3 = C4 = C).

  However, for example, when the capacitance value C1 of the first capacitance C1 is larger than the capacitance value C2 of the second capacitance C2 by ΔC (C2 = C + ΔC, C1 = C), an offset of the output voltage Vout occurs. . Therefore, the offset value can be set to the minimum value (zero) by adjusting the capacitance value C3 of the third capacitance C3 to be larger by ΔC than the capacitance value C4 of the fourth capacitance C4. . (C4 = C + ΔC, C3 = C)

  Conversely, when the capacitance value C1 of the first capacitance C1 is smaller than the capacitance value C2 of the second capacitance C2 by ΔC (C2 = C−ΔC, C1 = C), the third capacitance The capacitance value C3 of C3 is adjusted to be smaller than the capacitance value C4 of the fourth electrostatic capacitance C4 by ΔC. (C4 = C−ΔC, C3 = C)

In this case, as a configuration example of the third capacitance C3, as shown in FIG. 4, the third capacitance C3 includes m capacitances C31 to C3m and switches S31 to S3m. The The capacitance values of the capacitances C31 to C3m are preferably weighted in order to finely change the capacitance value of the third capacitance C3. For example, if the capacitance value of C31 is C0, C32 = 1/2 · C0, C33 = 1/4 · C0, C34 = 1/8 · C0,... C3m = 1/2 ^m−1 · C0. . Each switch S31 to S3m is controlled to be turned on / off by a corresponding m-bit adjustment signal from the calibration circuit 19. The same applies to the fourth capacitance C4.

  According to such a configuration, the capacitance values of the third and fourth capacitances C3 and C4 can be adjusted by the corresponding 2m-bit adjustment signal from the calibration circuit 19. Based on the output voltage Vout, the calibration circuit 19 can determine a 2 m-bit adjustment signal whose offset is a desired value, preferably a minimum value. The determined adjustment signal is written and held in an electrically writable and erasable nonvolatile memory such as the EEPROM 20.

[Operation of sensor circuit]
Next, the operation of the differential input type sensor circuit described above with reference to FIG. 3 will be described with reference to FIGS. In this case, the AC drive signal is a clock signal that alternately repeats a high level (= Vref) and a low level (ground voltage = 0 V). The output voltage from the inverting output terminal (−) of the differential amplifier 14 is Vom, the output voltage from the non-inverting output terminal (+) of the differential amplifier 14 is Vop, and the difference voltage between them is the output voltage Vout ( = Vop-Vom).

  The first sensor circuit has two modes of a charge accumulation mode and a charge transfer mode, and these two modes are alternately repeated.

  First, in the charge accumulation mode of FIG. 5A, Vref is applied to the first and second capacitances C1 and C2. A ground voltage (0 V) is applied to the third and fourth capacitances C3 and C4.

  Further, the switches SW1 and SW2 are turned on. As a result, the inverting output terminal (−) and the non-inverting input terminal (+) of the differential amplifier 14 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 (+) is set to ½ Vref. In this case, the common mode voltage of the differential amplifier 22 is set to ½ Vref.

  Next, in the charge transfer mode of FIG. 5B, a ground voltage (0 V) is applied to the first and second capacitances C1 and C2 in contrast to the charge accumulation mode. Further, Vref is applied to the third and fourth capacitances C3 and C4. The switches SW1 and SW2 are turned off.

  The capacitance values of the respective electrostatic capacitors in the initial state are assumed to be equal to each other. (C1 = C2 = C3 = C4 = C) Further, a capacitance difference between C1 and C2 when a human finger approaches the touch pad is represented by ΔC. (C1-C2 = ΔC) In this case, C1 = C + 1 / 2ΔC and C2 = C−1 / 2ΔC.

ここで、（Ｃ−１／２ΔＣ）・（−１／２Ｖｒｅｆ）はＣ２の電荷量であり、Ｃ・（１／２Ｖｒｅｆ）はＣ４の電荷量、Ｃｆ・０（＝０）はＣｆの電荷量である。 In the charge accumulation mode of FIG. 5A, the amount of charge at the node N1 is given by the following equation.

Here, (C−1 / 2ΔC) · (−1 / 2Vref) is the charge amount of C2, C · (1 / 2Vref) is the charge amount of C4, and Cf · 0 (= 0) is the charge amount of Cf. It is.

ここで、（Ｃ−１／２ΔＣ）・（１／２Ｖｒｅｆ）はＣ２の電荷量、Ｃ・（−１／２Ｖｒｅｆ）はＣ４の電荷量、Ｃｆ・（Ｖｏｐ−１／２Ｖｒｅｆ）はＣｆの電荷量である。 In the charge transfer mode of FIG. 5B, the amount of charge at the node N1 is given by the following equation.

Here, (C−1 / 2ΔC) · (1 / 2Vref) is the charge amount of C2, C · (−1 / 2Vref) is the charge amount of C4, and Cf · (Vop−1 / 2Vref) is the charge amount of Cf. It is.

According to the law of conservation of charge, the amount of charge of the node N1 in the charge accumulation mode and the charge transfer mode is equal to each other, and therefore, Equation 1 = Equation 2.
Solving this equation for Vop yields:

Similarly, when the charge amount in the charge accumulation mode and the charge transfer mode is obtained for the node N2, the charge conservation law is applied, and the equation is solved for Vom, the following expression is obtained.

即ち、差動入力型の第１のセンス回路の出力電圧Ｖｏｕｔは、第１の静電容量Ｃ１と第２の静電容量Ｃ２の容量値の差ΔＣに比例して変化することがわかる。 From equations 3 and 4, Vout is obtained.

That is, it can be seen that the output voltage Vout of the differential input type first sense circuit changes in proportion to the difference ΔC between the capacitance values of the first capacitance C1 and the second capacitance C2.

  The above calculation is based on the premise that C1 = C2 = C3 = C4 = C. However, if there is a capacity difference between C1 and C2 in the initial state, C3 and C4 also have the same capacity difference. In addition, the offset of the output voltage Vout can be set to a predetermined value or a minimum value by adjusting C3 and C4 using the calibration circuit 19 or the like.

  Next, touch sensor characteristics of the output voltage Vout of the first sense circuit will be described with reference to Table 1 and FIG. As described above, the selection circuit 10 has a first phase and a second phase. In the first phase, the selection circuit 10 selects signals from the first input terminal CIN1 and the second input terminal CIN2, and in the second phase. Selects signals from the third input terminal CIN3 and the fourth input terminal CIN4.

  Assume that the output voltage of the first sense circuit in the first phase is V1, and the output voltage of the second sense circuit in the second phase is V2. In this case, the output voltage V1 is a voltage proportional to the difference between the capacitance values of the capacitance between the Y sense line YL1 and the Y drive line DRYL and the capacitance between the Y sense line YL3 and the Y drive line DRYL.

  The output voltage V2 is a voltage proportional to the difference between the capacitance values of the capacitance between the Y sense line YL2 and the Y drive line DRYL and the capacitance between the Y sense line YL4 and the Y drive line DRYL. Then, it is assumed that a human finger or the like touches the touch panel 1 in a range from the Y sense line YL1 to the Y sense line YL4 by a single touch.

先ず、人の指等がＹセンス線ＹＬ１にタッチした場合、第１相の第１の出力電圧Ｖ１は、プラス（＋）の値になる。これは、Ｙセンス線ＹＬ１とＹ駆動線ＤＲＹＬとの間の容量の容量値がＹセンス線ＹＬ３とＹ駆動線ＤＲＹＬとの間の容量の容量値より大きくなるからである。また、第２相の第２の出力電圧Ｖ２は０Ｖになる。これは、人の指等がＹセンス線ＹＬ１にだけタッチしているので、Ｙセンス線ＹＬ２，ＹＬ４に係る容量値の変化はないからである。

First, when a human finger or the like touches the Y sense line YL1, the first phase first output voltage V1 becomes a plus (+) value. This is because the capacitance value of the capacitance between the Y sense line YL1 and the Y drive line DRYL is larger than the capacitance value of the capacitance between the Y sense line YL3 and the Y drive line DRYL. The second phase second output voltage V2 is 0V. This is because a capacitance of the Y sense lines YL2 and YL4 does not change because a human finger or the like touches only the Y sense line YL1.

  Next, when a human finger or the like touches the Y sense line YL2, the first output voltage V1 of the first phase becomes 0V. This is because there is no change in the capacitance values related to the Y sense lines YL1, YL3. On the other hand, the second-phase second output voltage V2 has a positive (+) value. This is because the capacitance value between the Y sense line YL2 and the Y drive line DRYL is larger than the capacitance value between the Y sense line YL4 and the Y drive line DRYL.

  Next, when a human finger or the like touches the Y sense line YL3, the first output voltage V1 of the first phase becomes a negative (−) value. This is because the capacitance value of the capacitance between the Y sense line YL3 and the Y drive line DRYL is larger than the capacitance value of the capacitance between the Y sense line YL1 and the Y drive line DRYL. On the other hand, the second output voltage V2 of the second phase is 0V. This is because a person's finger or the like touches only the Y sense line YL3, so that there is no change in the capacitance value related to the Y sense lines YL2, YL4.

  Finally, when a human finger or the like touches the Y sense line YL4, the first output voltage V1 of the first phase becomes 0V. This is because the capacitance values of the Y sense lines YL1 and YL3 are not changed. On the other hand, the second output voltage V2 of the second phase has a minus (−) value. This is because the capacitance value of the capacitance between the Y sense line YL4 and the Y drive line DRYL is larger than the capacitance value of the capacitance between the Y sense line YL2 and the Y drive line DRYL. In Table 1 and FIG. 7, the absolute values of the maximum values of the first and second output voltages V1, V2 are normalized to “1”.

  Further, as shown in FIG. 7, it can be seen that the first and second output voltages V1, V2 continuously change according to the touch position. That is, when the point on the Y sense line YL1 is the origin and the horizontal axis is the X coordinate axis, the first output voltage V1 is approximated by V1 = cosX, and the second output voltage V2 is approximated by V2 = sinX. The Therefore, the touch position (Y coordinate) can be detected based on the first and second output voltages V1 and V2.

As an example, since V2 / V1 = tanX holds, the relational expression of X = arctan (V2 / V1) and the polarities (+, −) of the first and second output voltages V1, V2 are used. The X coordinate of the touch position can be obtained. arctan is an inverse function of tan. In this case, as described above, the AD converter 17 converts the first and second output voltages V1 and V2 into digital values and transmits them to the microcomputer 3 via the I ² C bus interface circuit 18. Then, the microcomputer 3 can perform the above-described calculation to obtain the X coordinate of the touch position.

  Similarly, by operating the signal processing circuit 2X, it is possible to detect the Y coordinate of the touch position on the X sense lines XL1 to XL4 based on the first and second output voltages V1 and V2. In this case, as shown in FIG. 7, for example, the X and Y coordinates of the touch position can be obtained by operating the signal processing circuits 2X and 2Y in time series.

  In particular, the differential input type sense circuit has advantages of high sensitivity and high noise resistance. On the other hand, the first sense circuit may not be able to detect multi-touch. For example, this is a case where a human finger or the like touches the Y sense lines YL1 and YL3 at the same time. In this case, since there is no capacitance difference between the capacitance related to the Y sense line YL1 and the capacitance related to the Y sense line YL3, the first output voltage V1 becomes zero, which is indistinguishable from the initial state.

[Operation sequence of signal processing circuit]
The operation sequence of the signal processing circuits 2X and 2Y will be described based on the flowchart of FIG. The following operation sequence is controlled by the control circuit 11.

First, in the initial state (a state that is far from the touch panel 1 to the extent that a human finger or the like is not detected), the calibration circuit 19 performs the offset adjustment of the output voltage Vout of the sensor circuit as described above. (Step S1)
In the next step S2, the touch position is detected by the differential input type sensing circuit.

  In the next step S3, it is determined whether or not the touch detection time ts is equal to or longer than the predetermined time t0 based on the output voltage Vout (preferably AD converted value) of the sensor circuit. If the touch detection time ts is equal to or longer than the predetermined time t0 (ts> t0), the calibration circuit 19 operates and the offset adjustment of the output voltage Vout of the sensor circuit is performed again.

  That is, when the touch detection time ts is equal to or longer than the predetermined time t0, the control circuit 11 determines that the touch is not intended for data input, and operates the calibration circuit 19 to perform offset adjustment. ing. That is, in this case, the sensor circuit is set to the same state as the offset adjustment state in step S1.

  Thereby, the touch position detection of the finger intended for data input can be performed normally, and the data input can be performed normally.

  If the touch detection time ts is less than the predetermined time t0 (ts <t0), the control circuit 11 determines that the touch is intended for data input, and operates the sensor circuit without operating the calibration circuit 19. Continue detection by.

  Specifically, the touch detection time ts is preferably defined as a time during which the output voltage Vout of the sensor circuit is within a certain range. If the output voltage Vout (V1, V2) of the sensor circuit is constant, the corresponding touch position is determined, but considering the error of the output voltage Vout (V1, V2) and some variation in the touch position, This is because, if the output voltage Vout (V1, V2) is in a certain range, it is preferable to perform offset adjustment assuming that a certain position is touched.

  Further, as described above, when data is input with the right hand finger 51 while holding the touch panel 50 with the left hand, usually, the left hand finger 52 not intended for data input first touches the detection surface of the touch panel 50. Then, with the left hand finger 52 touched, the right hand finger 51 touches another position on the detection surface of the touch panel 50. See FIG. 9. In such a case, the touch detection time of the right hand finger 51 for data input is often 1 second or less, and the left hand finger 52 is often several tens of seconds or more. Therefore, by setting the predetermined time to several seconds, for example, it is possible to correctly determine whether or not the touch is intended for data input.

  In the configuration of FIG. 1, the X drive line DRXL and the Y drive line DRYL are provided, and the AC drive signal is supplied from the drive terminals CDRV of the signal processing circuits 2X and 2Y to the X drive line DRXL and the Y drive line DRYL. X sense lines XL1 to XL4 and Y sense lines YL1 to YL4 can also be used as drive lines.

  In this case, when the signal processing circuit 2Y operates as a touch sensor, an AC drive signal is supplied from the signal processing circuit 2X to the X sense lines XL1 to XL4. On the other hand, when the signal processing circuit 2X operates as a touch sensor, an AC drive signal is supplied from the signal processing circuit 2Y to the Y sense lines YL1 to YL4. According to such a configuration, the X drive line DRXL, the Y drive line DRYL, and the like are not necessary.

1 Touch Panel 2X, 2Y Signal Processing Circuit 3 Microcomputer 4 Serial Clock Line 5 Serial Data Line 10 Selection Circuit 11 Control Circuit 12 Drive Circuit 13 Inverter 14 Differential Amplifier 15 First Feedback Capacitor 16 Second Feedback Capacitor 17 AD Converter 18 I ² C bus interface circuit 19 Calibration circuit 20 EEPROM 22, 23 Wiring

Claims (4)

A capacitive touch panel signal processing circuit comprising a plurality of sense lines and a drive line to which an AC drive signal is applied,
The first and second sense lines are selected from the plurality of sense lines, and the capacitance value of the first capacitance formed between the first sense line and the drive line and the second sense line are selected. A sensor circuit that detects a capacitance difference with a capacitance value of a second capacitance formed between the sense line and the drive line, and outputs an output voltage corresponding to the capacitance difference;
A calibration circuit for adjusting the offset of the output voltage of the sensor circuit;
A control circuit that performs control so as to adjust the offset of the output voltage of the sensor circuit by operating the calibration circuit based on the output voltage of the sensor circuit when the touch detection time exceeds a predetermined time; A signal processing circuit for a capacitive touch panel.   The calibration circuit includes a first variable capacitor connected in series to the first capacitance, and a second variable capacitor connected in series to the second capacitance, The signal processing circuit of the capacitive touch panel according to claim 1, wherein an adjustment signal for adjusting a capacitance value of the first or second variable capacitor is output.   The capacitive touch panel signal processing circuit according to claim 1, wherein the touch detection time is a time during which an output voltage of the sensor circuit is within a certain range.   4. The capacitive touch panel signal processing according to claim 1, wherein the calibration circuit adjusts an offset so that an offset of an output voltage of the sensor circuit becomes a minimum value. circuit.

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