JP5293564B2 - Liquid crystal display device with touch panel and driving method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device with a touch panel for reliably removing an adverse influence of noise generated from a liquid crystal display device on the position detection of a capacitive touch panel, and for detecting an accurate touch position at any time. <P>SOLUTION: A mask signal generation circuit 51 generates a mask signal voltage Vmsk to generate a pulse according to the polarity inversion cycle of a common signal voltage Vcom transmitted from a display driving control circuit 2 of a liquid crystal display panel, and outputs it to a driving control circuit 56 of a touch panel. The driving control circuit 56 opens first to third switches SW1 to SW3 in synchronization with the pulse of an input mask signal voltage Vmsk, and interrupts measurement of the charging and discharging time of the synthetic capacitance of a capacitance Cp formed by each touch position detection electrode and a base capacitor Csum for scanning, and removes the adverse influence of noise generated in the polarity inversion timing of the common signal voltage Vcom on the measurement of a synthetic capacitance (Cp+Csum). <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a liquid crystal display device provided with a capacitive touch panel and a driving method thereof.

  In recent years, mobile devices equipped with a liquid crystal panel or the like as a display monitor are increasingly equipped with a touch panel as an input device on the display surface of the display monitor in order to meet the demand for a reduction in size and thickness.

  There are various types of touch panels such as a capacitive method, a resistive film method, and an electromagnetic induction method. Among them, the capacitive touch panel has an advantage that the touch surface has excellent durability. Therefore, as disclosed in Patent Document 1, it is often used as an input device of a liquid crystal display device as a display monitor of a mobile device.

JP 2009-86184 A

  In a liquid crystal display device, normally, as a countermeasure for preventing flicker or image sticking, the polarity of a drive signal acting on the liquid crystal is inverted every frame period or every line scanning period. In this case, the polarity of the common voltage set to a constant voltage value is often reversed every cycle. Harmful noise radio waves are generated at the timing of reversing the polarity of the common voltage.

  On the other hand, the capacitance type touch panel uses the fact that the capacitance at the position touched by the finger increases by the amount of the finger (human body), so that the time required for charging to a predetermined potential is utilized. Is counted for each sensor line, and the touch position is specified.

  Therefore, noise generated by the polarity inversion drive of the liquid crystal display device induces a voltage on the touch panel and unexpectedly charges, thereby adversely affecting the charge time count on the capacitive touch panel and causing an error in the count time. As a result, the accuracy of touch position detection is reduced.

  An object of the present invention is to provide a liquid crystal display device with a touch panel and a driving method thereof that reliably prevent the adverse effect of noise generated from the liquid crystal display device on the position detection of the capacitive touch panel and can always detect the touch position accurately. Is to provide.

  In the liquid crystal display device with a touch panel according to the first aspect of the present invention, a pair of substrates are joined with a liquid crystal layer sandwiched therebetween, and a plurality of pixel electrodes and these pixels are provided on respective opposing surfaces of the pair of substrates. A liquid crystal display panel in which a common electrode facing the electrode is disposed; and a liquid crystal that supplies a display signal voltage to the pixel electrode and a common signal voltage with periodic inversion of polarity to the common electrode Display panel driving means, a pair of substrates disposed on the viewing side of the display of the liquid crystal display panel, facing each other, and a plurality of transparent touch position detection electrodes respectively disposed on each facing surface of the pair of substrates A touch position based on a capacitance formed between the touch position detection electrode and the touch conductor corresponding to the touch position by driving the touch position detection electrode and the touch position detection electrode. Touch panel driving means for detecting is provided, and the touch panel driving means charges a capacitance formed by the touch position detection electrode by supplying a constant current to each of the touch position detection electrodes by a constant current circuit for charging, and compares The discharge circuit compares the output voltage from the charged capacitance with a reference voltage and outputs a comparison signal when a predetermined potential difference is reached, and discharges the accumulated charge in the capacitance according to the comparison signal. Furthermore, the liquid crystal display device with a touch panel determines a touch position from the charging time of the capacitance measured by the charging time measuring circuit based on the comparison signal, and is synchronized with the polarity inversion period of the common signal voltage A mask signal generating circuit for generating a mask signal composed of pulses, and charging the electrostatic capacitance in synchronization with a rising edge of the mask signal and the charging The measurement of the charging time by the inter-measuring circuit is stopped together, and the charging to the capacitance and the measurement of the charging time by the charging time measuring circuit are started in synchronization with the falling of the mask signal, and the charging time And a drive control circuit for specifying a touch position based on measurement data from the measurement circuit.

  According to a second aspect of the present invention, in the liquid crystal display device with a touch panel according to the first aspect, a charging time at the time of non-touch is provided in parallel with the capacitance formed between the touch position detection electrode and the touch conductor. A base capacitor is provided as an electrostatic capacity for setting the value to a predetermined value.

  According to a third aspect of the present invention, in the liquid crystal display device with a touch panel according to the first or second aspect, a drive control circuit of the touch position detecting means is a first opening / closing circuit interposed in the charging constant current circuit. A switch, a second opening / closing switch interposed in the energization circuit to the touch position detection electrode, and a third opening / closing switch provided in the charging time measurement circuit, and synchronized with the rising edge of the mask signal Then, the first open / close switch and the second open / close switch are opened to suspend charging, and the third open / close switch is opened to suspend charging time measurement, in synchronization with the falling edge of the mask signal. The first open / close switch and the second open / close switch are closed to restart charging, and the third open / close switch is closed to restart charging time measurement.

  According to a fourth aspect of the present invention, in the liquid crystal display device with a touch panel according to the second aspect, the second open / close switch simultaneously opens and closes the touch position detection electrode and the base capacitor from the comparison discharge circuit. It is characterized by being formed.

  According to a fifth aspect of the present invention, in the liquid crystal display device with a touch panel according to any one of the first to fourth aspects, the polarity of the common signal voltage is inverted at the rising timing of the mask signal. The timing of falling before the timing is after the timing of inverting the polarity of the common signal voltage.

  According to a sixth aspect of the present invention, there is provided a driving method for a liquid crystal display device with a touch panel, wherein a pair of substrates are joined with a liquid crystal layer sandwiched therebetween, and a plurality of pixel electrodes and A liquid crystal display panel in which a common electrode facing each pixel electrode is disposed, and a display signal voltage is supplied to the pixel electrode and a common signal voltage with periodic inversion of polarity is supplied to the common electrode. Liquid crystal display panel driving means, a pair of substrates disposed on the viewing side of the display of the liquid crystal display panel and opposed to each other, and a plurality of transparent touch position detections respectively disposed on the opposing surfaces of the pair of substrates An electrostatic capacitance type touch panel comprising electrodes and the touch position detection electrode are driven, and the touch is detected based on the capacitance formed between the touch position detection electrode corresponding to the touch position and the touch conductor. A method of driving a liquid crystal display device with a touch panel configured with touch panel driving means for detecting a position, wherein a mask signal composed of a pulse synchronized with a polarity inversion period of the common signal voltage is generated, and each touch position detection A constant current is supplied to each electrode to charge the capacitance formed by each touch position detection electrode, and in this charging process, the charging is interrupted in synchronization with the rising edge of the mask signal and in synchronization with the falling edge. The charging is resumed, a comparison signal is output by comparing the output voltage from the charged capacitance and a reference voltage, and the accumulated charge of the capacitance is discharged in accordance with the comparison signal, and the comparison Based on the signal, the charging time of the capacitance is measured, and in the measurement process, the measurement is interrupted in synchronization with the rising edge of the mask signal and the falling edge The measurement is restarted, the touch position detection electrode related to the touch position is selected from the charging time for each touch position detection electrode, the touch position is specified, and the touch position information is transmitted to the display driving means of the liquid crystal display panel. Output.

  According to the present invention, the adverse effect of noise generated from the liquid crystal display device on the detection of the position of the capacitive touch panel is reliably removed, and the touch position is always detected accurately.

It is a typical sectional view showing a liquid crystal display with a touch panel as one embodiment of the present invention. It is explanatory drawing which shows the structure of the touch position detection electrode of the touchscreen in the said liquid crystal display device with a touchscreen, (a) is arrangement | positioning of the electrode of one board | substrate side, (b) is arrangement | positioning of the electrode of the other board | substrate side, c) shows the arrangement of both electrodes in a state where both substrates are joined. It is a block diagram explaining the structure concerning the drive method and drive of the said liquid crystal display device with a touch panel. It is a timing chart which shows the relationship between the charging / discharging characteristic curve of the electrostatic capacitance for every touch position detection electrode in the said touch panel, a charge time measurement pulse, a mask signal, and the common signal voltage of a liquid crystal display panel. FIG. 4 is a graph showing the relationship between the charge / discharge characteristic curve of capacitance for each touch position detection electrode and the charge time measurement pulse in the capacitive touch panel, where (a) is a non-touched state, and (b) is a touch. Each state is shown. It is a timing chart which shows the relationship between the mask signal in the said touch panel, and each opening / closing operation | movement of the 1st-4th opening / closing switch.

  First, the overall configuration of a liquid crystal display device with a touch panel as one embodiment of the present invention will be described with reference to FIG.

  The liquid crystal display panel 1 in the present embodiment is an active matrix type liquid crystal display panel, and a pair of first and second glass substrates 11 and 12 having a rectangular shape face each other with a predetermined gap and are joined by a sealing material 13. A plurality of pixel electrodes 14 are arranged in a matrix arrangement on the facing surface of one glass substrate 11, and a common electrode 15 facing all the pixel electrodes 14 arranged in a matrix on the facing surface of the second glass substrate 12. Is installed. Between the first and second glass substrates 11 and 12, for example, twisted nematic liquid crystal is sealed.

  In the liquid crystal display panel 1, the source signal voltage applied to each pixel electrode 14 from the display drive control circuit 2 and the gate electrode of the TFT switch for turning on / off the application of the source signal voltage to each pixel electrode 14 are provided for each row. A gate signal voltage for scanning the gate line connected to the common electrode 15 and a common signal voltage applied to the common electrode 15 are supplied. Here, the polarity of the common signal voltage is inverted every one gate line scan.

  On the second glass substrate 12 on the display viewing side of the liquid crystal display panel 1, a capacitive touch panel 3 is installed via an adhesive layer 4 made of a transparent resin. The capacitive touch panel 3 according to the present embodiment is a projection capacitive touch panel, and a pair of first and second glass substrates 31 and 32 having a rectangular shape are arranged to face each other with a predetermined gap. First and second touch position detection electrodes 34 made of a transparent conductive film such as ITO (indium tin oxide) are respectively bonded to the first and second glass substrates 31 and 32 by a spacer 33. , 35 are installed.

  As shown in FIGS. 2A and 2B, the first and second touch position detection electrodes 34 and 35 are linearly connected to each other by inclining a plurality of square electrode pads 341 and 351 by 45 °. The six first touch position detection electrodes 34x1 to 34x6 have a predetermined pitch along the longitudinal direction (hereinafter referred to as the X direction) on the opposing surface of the first glass substrate 31. 10 second touch position detection electrodes 35y1 to 35y10 are arranged at the same pitch p along the short direction (hereinafter referred to as the Y direction) on the opposing surface of the second glass substrate 32. They are arranged in parallel.

  In the state where the first and second glass substrates 31 and 32 are joined, as shown in FIG. 2C, the first and second touch position detection electrodes 34-x1 to 34-x6, 35y1 to 35y10 are used. Are orthogonal to each other, and the electrode pads 341 and 351 are projected so as not to overlap each other.

  Lead wires are led out from the first and second touch position detection electrodes 34-x1 to 34-x6 and 35-y1 to 35-y10, respectively, and are arranged in parallel with the substrate edges on the same side of the glass substrates 31 and 32, respectively. The first and second connection terminals 342 and 352 are provided. And these 1st, 2nd connection terminals 342 and 352 are each connected to the touch panel drive means 5 (refer FIG. 1).

  Returning to FIG. 1, the front cover 6 made of a transparent glass plate or a plastic plate such as polyethylene terephthalate (PET) is transparent on the touch side of the touch panel 3 (the observation side of the liquid crystal display device with the touch panel). It is fixed via a resin adhesive layer 7. When operating the liquid crystal display device with a touch panel, the touch position information is transferred from the touch panel driving means 5 to the liquid crystal display panel 1 by touching a necessary pressing position from the entire cover 6 while visually recognizing the display of the liquid crystal display panel 1. To the display drive control circuit 2.

  Next, the configuration of the touch panel driving means 5 in the present embodiment will be described with reference to FIG.

  The touch panel driving means 5 is generally composed of a mask signal generation circuit 51, a selector circuit 52, a charging constant current circuit 53, a comparison discharge circuit 54, a charging time measurement circuit 55, and a drive control circuit 56.

  The mask signal generation circuit 51 generates a mask signal voltage Vmsk according to the common signal voltage Vcom sent from the display drive control circuit 2 of the liquid crystal display panel 1 and outputs it to the drive control circuit 56. As shown in FIG. 4, the mask signal voltage Vmsk has a pulse that rises a predetermined time (1 μsec) before the rising timing of the common signal voltage Vcom whose polarity is line-inverted, and falls after the same time, and then the common signal voltage Vcom. Pulse signal voltage generated at each polarity inversion timing.

  In response to an instruction from the drive control circuit 56, the selector circuit 52 includes six first touch position detection electrodes 34-x1 to 34-x6 extending in the X-axis direction and ten second touches extending in the Y-axis direction shown in FIG. This is a circuit that sequentially selects and scans a total of 16 touch position detection electrodes 35-y1 to 35-y10.

  The charging constant current circuit 53 converts the current supplied from the power supply VDD into a constant current via the constant current device 531, and outputs the current to the touch position detection electrode selected by the selector circuit 52.

  The comparison discharge circuit 54 includes a low-pass filter (LPF) 541, a comparator 542, and a resistor R. The capacitance Cp formed by the selected touch position detection electrode and an external base capacitor connected in parallel to the capacitance Cp. A circuit in which an output circuit of capacitance synthesized with Csum is connected to one input terminal of a comparator 542 after passing through a low-pass filter (LPF) 541, and a ground discharge circuit in which a resistor R is interposed It is branched to. The comparator 542 compares the voltage input to the one terminal with the reference voltage Vth, and outputs the comparison result as a binary digital signal. On the ground side of the resistor R in the ground discharge circuit, a fourth open / close switch SW4 that is opened / closed according to the output signal of the comparator 542 is interposed. The low-pass filter 541 is interposed for removing high frequency noise.

  The charging time measuring circuit 55 includes a 16-bit counter 551 and an oscillator 552. The counter 551 measures a clock pulse supplied from the oscillator 552 according to an output signal from the comparator 542. That is, for example, the voltage input to the one terminal is compared with the reference voltage Vth, and when the voltage input to the one terminal is lower than the reference voltage Vth, the output signal from the comparator 542 is “0”. During this period, clock pulses are counted, and when the voltage input to the one terminal reaches the reference voltage Vth, the output signal changes to “1”, and at this time, the count is stopped. The counter 551 outputs the count value to the drive control circuit 56. A third open / close switch SW3 is interposed between the counter 551 and the oscillator 552.

  The drive control circuit 56 outputs a scanning signal to the selector circuit 52 to sequentially scan the first and second touch position detection electrodes 34-x1 to 34-x6 and 35-y1 to 35-y10, and generates the mask signal. According to the mask signal output from the circuit 51, the opening / closing of the first, third, and fourth open / close switches SW1, SW3, SW4 is controlled. As a result, the first and second touches output from the counter 551 are controlled. The touch position is determined from the charging time count value for each of the position detection electrodes 34-x1 to 34-x6 and 35-y1 to 35-y10, and the touch position information is output to the display drive control circuit 2.

  Next, the touch position detection operation by the touch panel drive unit 5 of the present embodiment will be described with reference to FIGS.

  First, as a comparative example, a charging time measurement operation when a noise radio wave is not generated from a liquid crystal display panel and a mask signal is not output will be described. The first and second switches SW1, SW2 are closed (turned on), and a current is supplied to, for example, the first touch position detection electrode 34-x1 and the base capacitor Csum selected by the selector circuit 52, and the first touch position detection electrode The capacitance Cp1 formed by 34-x1 and the base capacitor Csum are both charged, and the output voltage Vc of the capacitance obtained by combining them rises with time as shown in FIG. While the combined capacitance is charged, the clock pulse CLK is constantly supplied from the oscillator 552 to the counter 551. When the output voltage Vc of the combined capacitance reaches the reference voltage Vth due to continued charging, the fourth open / close switch SW2 is closed (turned on) as shown in FIG. Discharging starts. At the same time, the first, second, and third open / close switches SW1, SW2, and SW3 are opened, and the charging of the combined capacitance and the supply of clock pulses are stopped.

  Here, if the portion facing the first touch position detection electrode 34-x1 on the front cover 6 is not touched, the capacitance Cp1 formed by the first touch position detection electrode 34-x1 is substantially zero. As shown in FIG. 5A, the charging time t1 is only the charging time of the base capacitor Csum.

  On the other hand, when the portion facing the first touch position detection electrode 34-x1 is touched with a finger, a certain capacitance Cp1 is provided between the first touch position detection electrode 34-x1 and the finger. Is formed, and the capacitance obtained by combining the base capacitor Csum and the capacitance Cp1 is charged. Therefore, as shown in FIG. 5B, when the charging time t1 is not touched (FIG. 5 ( It becomes longer than a) reference). This charging time t1 is output from the counter 551 to the drive control circuit 56 as the count value of the clock pulse CLK.

  When the combined capacitance of the base capacitor Csum and the touch electrode capacitance Cp1 is discharged and the output voltage becomes substantially zero, the drive control circuit 56 passes the selector circuit 52 through the first touch position detection electrode 34 in the next order. -Energize x2. Each of the first and second touch position detection electrodes 34-x1 to 34-x6 and 35-y1 to 35-y10 is scanned once for a period of time from the end of energization to the measurement of the charging time to the end of discharging. In this embodiment, the charging time t1 when not touched is set to 700 μs, and the total time with the discharging time t2, that is, one scan time (t1 + t2) is set to 1250 μs.

  The one scan operation is sequentially performed on the 16 first and second touch position detection electrodes 34-x1 to 34-x6 and 35-y1 to 35-y10, and the six first touch position detection electrodes (X-axis) Electrode) The charging time of 34-x1 to 34-x6 is longer than the others and the charging time of 10 second touch position detection electrodes (Y-axis electrodes) 35-y1 to 35-y10 is longer than the others. The crossing position with the long electrode is specified as the touch position. Information on the specified touch position is output to the display drive control circuit 2 of the liquid crystal display panel 1.

  For example, in FIG. 2C, when the charging time of the first touch position detection electrode 34-x3 in the third row and the second touch position detection electrode 35-y6 in the sixth column is relatively longer than others, Positions corresponding to the four electrode pads (341-x3) a, (341-x3) b, (351-y6) a, (351-y6) b where the electrodes 34-x3, 35-y6 intersect Is the touch position.

  In the liquid crystal display device with a touch panel according to the present embodiment, as described above, the polarity of the common signal voltage Vcom of the liquid crystal display panel 1 is inverted for each line scan, and the timing at which the polarity of the common signal voltage Vcom is inverted. Generates noise radio waves. This noise radio wave induces a voltage on the touch panel 3, affects the charging time of the combined capacitance (Csum + Cp) and the count of the clock pulse CLK, and causes variation in the charging time. The accuracy of detection will be reduced.

  Therefore, in the liquid crystal display device with a touch panel according to the present invention, the mask signal voltage Vmsk is generated in correspondence with the polarity inversion timing of the common signal voltage Vcom, and the combined capacitance (Csum + Cp) is synchronized with the mask signal voltage Vmsk. Charging and charging time measurement were temporarily stopped to eliminate the influence of the noise radio wave.

  That is, as shown in FIG. 4, a mask signal Vmsk is generated which is a rectangular pulse signal that rises a predetermined time before the polarity inversion timing of the common signal voltage Vcom and falls after a predetermined time of the polarity inversion timing. Synchronously, the first, second, and third open / close switches SW1, SW2 are respectively scanned during the scanning of the first and second touch position detection electrodes 34-x1 to 34-x6, 35-y1 to 35-y10. , SW3 is opened (turned off), and the charging of the combined capacitance (Csum + Cp) and the counting of the charging time are interrupted. As a result, the charging time becomes longer than the uninterrupted charging time by the mask signal shown in FIG. 5 by the time corresponding to the interruption, and the interruption clock is missing as shown in FIG. The number of clocks is substantially constant at the time of touch and non-touch by eliminating the influence of noise radio waves. As a result, the touch position can always be accurately detected without being affected by noise due to the polarity inversion of the common signal voltage Vcom.

  As described above, in the liquid crystal display device with a touch panel of the present embodiment, the polarity of the common signal voltage Vcom that drives the liquid crystal display panel 1 is inverted, and the touch panel 3 is a projected capacitive touch panel. Corresponding to the polarity inversion timing of the voltage Vcom, the energization of the touch position detection electrode during scanning is interrupted to interrupt the charging of the combined capacitance (Csum + Cp), and the supply of the clock pulse to the counter 551 is interrupted. As a result, variations in charging time and measured values due to noise generated in synchronization with the polarity inversion timing of the common signal voltage Vcom are eliminated, and the touch position can always be detected accurately.

  In addition, this invention is not limited to said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, the polarity of the common signal voltage Vcom of the liquid crystal display panel 1 is line-inverted. However, the present invention is not limited to this, and the frame inversion type liquid crystal display panel in which the polarity of the common signal voltage Vcom is inverted every frame period. In this case, the present invention is effectively applied.

DESCRIPTION OF SYMBOLS 1 Liquid crystal display panel 11 1st glass substrate 12 2nd glass substrate 13 Sealing material 14 Pixel electrode 15 Common electrode 2 Display drive control circuit 3 Capacitive touch panel 31 1st glass substrate 32 2nd glass substrate 33 Frame-shaped spacer 34,
34-x1 to 34-x6 first touch position detection electrode 341 first electrode pad 342 first connection terminal 35
35-y1 to 35-y10 Second touch position detection electrode 351 Second electrode pad 352 Second connection terminals 4, 7 Adhesive layer 5 Touch panel driving means 51 Mask signal generation circuit 52 Selector circuit 53 Charging constant current circuit 54 Comparison discharge circuit 55 Charging time measurement circuit 56 Drive control circuit 6 Full cover

Claims (6)

A liquid crystal display panel in which a pair of substrates are joined with a liquid crystal layer sandwiched therebetween, and a plurality of pixel electrodes and a common electrode facing the pixel electrodes are respectively disposed on the opposing surfaces of the pair of substrates; Liquid crystal display panel driving means for supplying a display signal voltage to the pixel electrode and supplying a common signal voltage with a periodic reversal of polarity to the common electrode; and installed on the observation side of the display of the liquid crystal display panel; A capacitive touch panel composed of a pair of substrates arranged opposite to each other and a plurality of transparent touch position detection electrodes respectively disposed on the opposing surfaces of the pair of substrates, and driving the touch position detection electrodes, thereby touch positions Touch panel drive means for detecting a touch position based on a capacitance formed between the touch position detection electrode corresponding to the touch conductor and the touch conductor, the touch panel drive means, A constant current circuit for electricity supplies a constant current to each touch position detection electrode to charge a capacitance formed by the touch position detection electrode, and an output from the capacitance charged by a comparison discharge circuit Comparing the voltage with the reference voltage, a comparison signal is output when a predetermined potential difference is reached, and the accumulated charge in the capacitance is discharged in accordance with the comparison signal, and further, measured by a charging time measuring circuit based on the comparison signal A liquid crystal display device with a touch panel that determines a touch position from the charging time of the capacitance,
A mask signal generation circuit for generating a mask signal composed of pulses synchronized with the polarity inversion period of the common signal voltage;
Both the charging to the capacitance and the measurement of the charging time by the charging time measuring circuit are stopped in synchronization with the rising edge of the mask signal, and the charging to the capacitance is stopped in synchronization with the falling edge of the mask signal. Along with starting measurement of the charging time by the charging time measuring circuit, and a drive control circuit for specifying a touch position based on measurement data from the charging time measuring circuit,
A liquid crystal display device with a touch panel, comprising:   A base capacitor serving as a capacitance for setting the charging time at the time of non-touch to a predetermined value is provided in parallel with the capacitance formed between the touch position detection electrode and the touch conductor. The liquid crystal display device with a touch panel according to claim 1.   The drive control circuit of the touch position detecting means includes a first open / close switch interposed in the charging constant current circuit, and a second open / close switch interposed in an energization circuit to the touch position detection electrode, A third open / close switch provided in the charging time measuring circuit, and in synchronization with the rising of the mask signal, the first open / close switch and the second open / close switch are opened to stop charging and The third open / close switch is opened to interrupt the measurement of the charging time, and the first open / close switch and the second open / close switch are closed in synchronization with the falling edge of the mask signal, and charging is resumed. 3. The liquid crystal display device with a touch panel according to claim 1, wherein the open / close switch is closed and the measurement of the charging time is resumed. 4.   3. The liquid crystal display device with a touch panel according to claim 2, wherein the second opening / closing switch is formed at a position for simultaneously opening and closing the touch position detection electrode and the base capacitor from the comparison discharge circuit. .   The timing at which the mask signal rises is before the timing at which the polarity of the common signal voltage is inverted, and the timing at which the mask signal falls is after the timing at which the polarity of the common signal voltage is inverted. 4. A liquid crystal display device with a touch panel according to claim 4. A liquid crystal display panel in which a pair of substrates are joined with a liquid crystal layer sandwiched therebetween, and a plurality of pixel electrodes and a common electrode facing the pixel electrodes are respectively disposed on the opposing surfaces of the pair of substrates; Liquid crystal display panel driving means for supplying a display signal voltage to the pixel electrode and supplying a common signal voltage with a periodic reversal of polarity to the common electrode; and installed on the observation side of the display of the liquid crystal display panel; A capacitive touch panel composed of a pair of substrates arranged opposite to each other and a plurality of transparent touch position detection electrodes respectively disposed on the opposing surfaces of the pair of substrates, and driving the touch position detection electrodes, thereby touch positions A touch panel liquid crystal display comprising touch panel driving means for detecting a touch position based on a capacitance formed between the touch position detection electrode corresponding to the touch conductor and a touch conductor. A method of driving a device,
Generate a mask signal consisting of a pulse synchronized with the polarity inversion period of the common signal voltage,
A constant current is supplied to each touch position detection electrode to charge the capacitance formed by each touch position detection electrode, and in this charging process, the charging is interrupted in synchronization with the rising of the mask signal and Resume the charging in sync with the fall,
Comparing an output voltage from the charged capacitance and a reference voltage and outputting a comparison signal and discharging the accumulated charge of the capacitance according to the comparison signal,
Based on the comparison signal, the charging time of the capacitance is measured.In this measurement process, the measurement is interrupted in synchronization with the rising edge of the mask signal and the measurement is restarted in synchronization with the falling edge.
A touch panel characterized by selecting a touch position detection electrode related to the touch position from a charging time for each touch position detection electrode, specifying the touch position, and outputting the touch position information to the display driving means of the liquid crystal display panel. Driving method for a liquid crystal display device.

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