JP6532582B2 - Liquid crystal monitor, electronic device, control method, and program - Google Patents

Description

  The present invention relates to a liquid crystal monitor, an electronic device, a control method, and a program.

  A liquid crystal monitor with a touch panel is used as a display monitor for a mobile communication terminal such as a smartphone or a digital camera. For example, many capacitive touch panels are mounted to cope with multi-touch and gesture operations. In a liquid crystal monitor with a touch panel, the touch panel is disposed on the display surface side of the liquid crystal monitor as shown in FIG. In FIG. 6, reference numeral 601 denotes a touch panel, 602 denotes a TFT panel of a liquid crystal monitor (display), and 603 denotes a backlight of the liquid crystal monitor.

  Because of the structure in which the touch panel is disposed on the liquid crystal monitor, the touch panel is affected by the noise generated by the driving of the liquid crystal and the driving of the backlight. In particular, in the in-cell type or the on-cell type, it is known that the influence is remarkable due to the structure in which the touch panel is disposed on the liquid crystal electrode or the color filter without sandwiching the glass or the film.

  A white light emitting diode is mainly used for the backlight of the liquid crystal monitor, and the light emission luminance is determined by the current value flowing to the white light emitting diode. As the current control of the light emitting diode, a method of controlling the current value by direct current, and a method called pulse width modulation control (PWM control) which is a method of controlling the timing of flowing current while fixing the direct current value by pulse width There are two control methods. Since the color of the white light emitting diode changes depending on the current value when DC control is performed, PWM control is used to prevent the color from changing with the brightness of a monitor such as a digital camera for checking the captured image on a monitor. I often use

  However, in the PWM control, switching on and off of the backlight current is repeated to generate noise due to the switching, and the noise is received by the touch panel. When the capacitance detection frequency of the touch panel for detecting an operation on the touch panel and the PWM drive frequency of the backlight current coincide with each other, the influence of noise becomes large, and the output signal of the touch panel fluctuates, which causes erroneous detection of the operation.

  For example, Patent Document 1 discloses a technique for reducing noise due to driving of the backlight by synchronizing touch detection of the touch panel and driving of the backlight.

JP, 2013-235197, A

  However, in the technology disclosed in Patent Document 1, it is necessary to arrange the backlights in parallel along the area where touch detection of the touch panel is performed. Moreover, since it is necessary to perform control for synchronizing touch detection of the touch panel and driving of the backlight to each of the backlights connected in parallel, touch detection of the touch panel and control of the backlight become complicated. An object of the present invention is to provide an electronic device capable of suppressing the influence of noise generated by driving a backlight and preventing erroneous detection of an operation on a touch panel.

The liquid crystal monitor according to the present invention is a liquid crystal monitor with a capacitive touch panel, and is arranged in a second direction intersecting the first direction with a plurality of first electrodes arranged in a first direction. The backlight, and output means for outputting a detection signal corresponding to a change in mutual capacitance between the first electrode and the second electrode; and the backlight The present invention is characterized in that PWM control is possible at a PWM frequency different from a natural number multiple of the frequency at which the detection signal is output.
An electronic device according to the present invention is characterized by including the liquid crystal monitor described above, and a backlight control unit that performs PWM control of the backlight at the PWM frequency.

  According to the present invention, the drive control of the backlight is performed at a frequency different from the frequency at which the signal is detected from the touch panel, so that the influence of noise generated by the drive of the backlight can be suppressed. Detection can be prevented.

It is a figure which shows the structural example of the electronic device in embodiment of this invention. It is a figure for demonstrating the touch panel in this embodiment. It is a figure which shows the example of the detection timing of the touch panel in this embodiment. It is a figure which shows the example of the detection timing of the touch panel in this embodiment, and the drive timing of a backlight. It is a figure which shows the example of a setting of the current drive frequency of the backlight in this embodiment. It is a sectional view showing the composition of the liquid crystal monitor with a touch panel.

  Hereinafter, embodiments of the present invention will be described based on the drawings.

  FIG. 1 is a block diagram showing an example of the configuration of an electronic device 1 according to an embodiment of the present invention. A CPU (Central Processing Unit) 11 is a microcomputer that controls the system of the electronic device 1. The CPU 11 as a control unit performs control related to each functional unit of the electronic device 1 by developing the program stored in the non-volatile memory 12 in the main memory 13 and executing the program. For example, the CPU 11 controls the current drive frequency of the backlight 23 according to the capacitance detection frequency of the touch panel 19 for detecting a touch operation on the touch panel 19 as described later.

  The non-volatile memory 12 is a storage unit that stores various programs for the CPU 11 to operate. The main memory 13 is made of, for example, a random access memory (RAM). For example, the CPU 11 controls each part of the electronic device 1 according to a program stored in the non-volatile memory 12 using the main memory 13 as a work memory. In addition, when the electronic device 1 has a camera function such as an imaging device or a lens (not shown), the main memory 13 is also used as a memory for storing captured still images and moving images, and a predetermined number of still images are stored. And a storage capacity sufficient to store moving images for a predetermined time.

  The power switch (SW) 14 is a switch that controls the on / off of the electronic device 1. The power supply circuit 15 is a circuit for supplying power to each part in the electronic device 1, and supplies power to each part in the electronic device 1 when the power switch 14 is turned on. Further, the power supply circuit 15 is controlled in operation by receiving a signal from the CPU 11 to shift to or return from the power saving mode. The battery 16 is a power supply of the electronic device 1. In addition, not only the battery 16 but an AC adapter may be used. The recording medium 17 is a recording medium that can be inserted into and removed from the electronic device 1. The external connection interface (I / F) 18 is an interface that enables connection with an external device such as USB (Universal Serial Bus) or HDMI (High-Definition Multimedia Interface).

  The touch panel (touch sensor) 19 is, for example, a capacitive touch panel, and generates a capacitance between the touch operation and a conductive object such as a finger. The touch panel 19 is installed in a two-dimensional plane, for example, on the display surface side of the display 21 as a display unit. The touch panel control unit 20 is a controller circuit that controls the touch panel 19. The touch panel control unit 20 transmits a capacitance detection signal to the touch panel 19, calculates coordinates and areas in which a touch operation is detected based on the detection signal from the touch panel 19, and transmits the calculated operation to the CPU 11 to detect operation on the touch panel 19. to enable.

  The display 21 as a display unit is, for example, a display monitor including a liquid crystal panel. The display control unit 22 is a controller circuit that receives a control signal of display data from the CPU 11, processes the received control signal, and outputs a display signal for displaying an image on the display 21.

  The backlight 23 is a backlight of the display 21. The backlight 23 is made of, for example, a white light emitting diode. The backlight control unit 24 is a controller circuit for controlling the luminance of the backlight 23 and controls driving of the backlight 23. The backlight control unit 24 controls the current supplied to the backlight 23 by pulse width modulation driving (PWM driving), and the backlight 23 is subjected to PWM control. The imaging device 25 is an optical sensor that converts an optical image formed as a subject through a lens (not shown) into an electrical signal.

  FIG. 2 is a view showing a configuration example of the touch panel 19 and the touch panel control unit 20. The touch panel 19 is, for example, a capacitive touch panel. The touch panel 19 has a plurality of column electrodes 205 arranged in a column and a plurality of row electrodes 206 arranged in a row, and the row electrodes 206 of the electrodes arranged to be orthogonal to each other are used as scanning lines. Is used as a read line.

  FIG.2 (b) is an enlarged view of the intersection part of the electrode shown by the frame A shown to Fig.2 (a). The column electrode 205 is fixed at a predetermined potential, and the row electrode 206 is connected to a constant current circuit 208. When a weak current is caused to flow by the constant current circuit 208, charges are accumulated in mutual capacitance 207 generated between the column electrode 205 and the row electrode 206. In order to obtain a signal of a sufficient level as a detection signal per crossing point at which one column electrode 205 and one row electrode 206 cross, the effect of noise is exerted because the accumulation time becomes long with only one accumulation. It is likely to be received.

  Therefore, a sub-scan is performed in which accumulation is performed a plurality of times in a short time per intersection, and integration is performed in the integration circuit 209. The result of the measurement of one intersection (one scan) is converted by the A / D converter 210 into a digital signal. By measuring the amount of change in the signal value of the detection signal output from the A / D converter 210 as the amount of change in electrostatic capacitance, it is possible to determine the presence or absence of a touch operation on the touch panel 19. The integration circuit 209 and the A / D converter 210 are provided, for example, in the detection signal processing circuit 203.

  In FIG. 2A, the control circuit 201 has a PLL (Phase Locked Loop) circuit for generating a clock signal using an external clock input or an internal oscillation circuit as a source oscillation. The PLL circuit of the control circuit 201 can change the period of one scan or the period of one sub scan. The scanning line drive circuit 202 and the detection signal processing circuit 203 are driven by a clock signal supplied by the control circuit 201.

  Further, the control circuit 201 sequentially detects whether the signal value of the detection signal at the intersection of each electrode output from the detection signal processing circuit 203 exceeds an arbitrary touch determination threshold. The control circuit 201 sets a touch detection flag and transfers data to the memory 204 if the signal value of the detection signal exceeds the threshold for touch determination. When scanning of all intersections of the electrodes on the touch panel 19 is completed, the control circuit 201 groups the touch detection area and calculates the center of gravity of the touch position from detection data of one frame stored in the memory 204. I do. Thus, the control circuit 201 calculates the touch detection number and the touch detection coordinates.

  The scanning line drive circuit 202 outputs scan pulses Y0 to Y8 to sequentially select and drive the row electrodes 206 (Y0 to Y8) as scanning lines. A weak current is supplied to the selected row electrode 206 by the constant current circuit 208. The number of sub-scans per scanning line can be arbitrarily changed by an instruction from the CPU 11 to the control circuit 201. The detection signal processing circuit 203 sequentially selects the column electrodes 205 as read lines and reads out the detection signals X0 to X8.

  FIG. 3 is a diagram illustrating an example of the capacitance detection timing of the touch panel 19 performed by the touch panel control unit 20. In FIG. 3, VSYNC is a vertical synchronization signal indicating display of one frame of the display 21, and HSYNC is a horizontal synchronization signal indicating drawing of one line of the display 21.

  In order to detect the touch operation on the touch panel 19 in accordance with the display on the display 21, the capacitance at the intersection of all the electrodes of the touch panel 19 is detected within one frame (1 VSYNC) period, and the number of touch detections and touch detection coordinates Needs to be calculated. As described above, in order to carry out sub-scans to carry out multiple accumulations per intersection and to carry out capacitance detection and operation processing of all points within one frame, the frame rate must be at least as long as the number of column electrodes and the number of sub-scans. The sub-scan is performed once in a cycle TTC divided by.

  In the example shown in FIG. 3, when the scan pulses Y1 to Y8 are at high level (on), sub scan, that is, capacitance detection is performed. Further, when the scan pulses Y1 to Y8 are at low level (off), arithmetic processing for generating a detection signal is performed via the integration circuit 209 and the A / D converter 210 shown in FIG. 2B.

  For example, since the touch panel 19 is also affected by the noise due to the gate drive of the TFT pixels of the display (liquid crystal monitor) 21, the capacitance detection of the touch panel 19 is performed during the blanking period of horizontal synchronization or at the timing when the gate voltage is stable. There are many things. In particular, in the in-cell or on-cell touch panel, the sub-scan frequency of the touch panel 19 is synchronized with the horizontal synchronization frequency HSYNC because the electrode of the TFT doubles as the electrode of the touch panel.

  FIG. 4 is a diagram illustrating an example of the capacitance detection timing of the touch panel 19 and the drive timing of the backlight 23 performed by the touch panel control unit 20. In the example shown in FIG. 4A, the cycle (period for performing sub-scan) TTC in which the touch panel control unit 20 controls the touch panel 19 and the current drive cycle TBL1 of the backlight 23 are synchronized. At this time, there occurs a case where the switching timing of the current of the backlight 23 and the timing TSC of the sub scan (capacitance detection) on the touch panel 19 always coincide with each other.

  Since the timing always matches, the touch panel 19 is affected by the noise generated by the switching of the current of the backlight 23, and the detection signal from the touch panel 19 fluctuates. Fluctuation in the detection signal from the touch panel 19 leads to an erroneous detection such as detection as a touch operation even if the touch operation is not performed or detection as a touch operation even though the touch operation is not performed .

  In the example illustrated in FIG. 4B, the cycle TTC in which the touch panel control unit 20 controls the touch panel 19 and the current drive cycle TBL2 of the backlight 23 are set to frequencies different in cycle. It can be seen that, by setting the frequency to be different, the number of times the switching timing of the current of the backlight 23 coincides with the timing TSC of the sub scan (capacitance detection) on the touch panel 19 is reduced. Therefore, the influence of the noise generated by the switching of the current of the backlight 23 can be suppressed, and the erroneous detection of the touch operation on the touch panel 19 can be prevented.

  Therefore, in the present embodiment, the cycle TTC and the current drive cycle TBL2 of the backlight 23 are different as shown in FIG. 4B according to the cycle TTC in which the touch panel control unit 20 controls the touch panel 19. Set the frequency of the cycle. More specifically, the current drive cycle TBL2 of the backlight 23 is set so as to have a frequency different from a frequency that is a natural number multiple of the frequency of the cycle TTC in which the touch panel 19 is controlled. For example, the CPU 11 acquires a cycle TTC in which the touch panel control unit 20 controls the touch panel 19. Then, the CPU 11 sets the current drive cycle TBL2 when the backlight 23 is PWM-driven in the backlight control unit 24 so as to have a cycle different from the obtained cycle TTC (and the cycle multiplied).

  The cycle TTC in which the touch panel control unit 20 controls the touch panel 19 is set in advance, information on the cycle TTC is stored in the non-volatile memory 12, and the cycle TTC is acquired by the CPU 11 reading the information. You may In addition, since the number of times of switching of the current of the backlight 23 is smaller than the number of times of capacitance detection on the touch panel 19 when the current drive cycle of the backlight 23 is slower than the cycle of controlling the touch panel 19, noise is further affected. It can be reduced.

  FIG. 5 is a diagram for explaining the setting region of the current drive frequency of the backlight 23 in the present embodiment. 20 KHz or less hits general human hearing range. In an electronic device such as a digital camera equipped with a moving image recording function, the backlight control unit 24 performs switching control of current drive of the backlight 23. Here, when the backlight control unit 24 performs switching control at 20 KHz or less, the vibration of peripheral parts such as a capacitor is transmitted to a microphone (not shown) inside the electronic device 1 and a frequency range that can be heard by human beings It is recorded as voice noise.

  Therefore, in the electronic device having the moving image recording function, it is necessary to set the current drive frequency of the backlight 23 to 20 KHz or more. By setting the current drive frequency of the backlight 23 as follows, in an electronic device such as a digital camera having a moving image recording function, it is prevented that audible audio noise is recorded by switching control of the backlight 23 Can.

5A shows the setting of the current drive frequency FBL (= 1 / period TBL2) of the backlight 23 when the sub-scan frequency FTC (= 1 / period TTC) of the touch panel 19 becomes the same frequency as the horizontal synchronization frequency. It is a figure showing a frequency band. For example, in consideration of noise due to gate driving of the TFT pixels of the liquid crystal monitor, the sub scan frequency FTC is set to the same frequency as the horizontal synchronization frequency. In that case, for example, the current drive frequency FBL is set to satisfy the following equation at a frequency later than the frequency band of the hatched portion where the sub scan time TSC is added to the period TTC of the sub scan frequency FTC.
20 KHz <FBL <1 / (TTC + TSC)

FIG. 5B is a diagram showing a set frequency band of the current drive frequency FBL of the backlight 23 when the sub-scan frequency FTC of the touch panel 19 is 20 KHz or less in the audible range. In that case, it is necessary to avoid the current drive frequency FBL from being synchronized with the frequency of multiplication of the sub-scan frequency FTC. At this time, for example, the current drive frequency FBL is higher than the frequency band of the hatched portion in which the sub scan time TSC is added to the period TTC / 2 of the multiplication frequency of the sub scan frequency FTC (double in this example) exceeding the audible range 20 KHz. Set to satisfy the following equation at a slow frequency.
20 KHz <FBL <1 / (TTC / 2 + TSC)

FIG. 5C is a diagram showing a set frequency band of the current drive frequency FBL of the backlight 23 when the sub-scan frequency FTC of the touch panel 19 is sufficiently higher than the audible range of 20 KHz. In that case, it is necessary to avoid the current drive frequency FBL from being synchronized with the frequency which is a division of the sub scan frequency FTC. At this time, for example, the current drive frequency FBL is the hatched frequency obtained by adding the sub-scan time TSC to the period 2 × TTC of the divided frequency of the sub-scan frequency FTC (1/2 in this example) exceeding the audible range 20 KHz. Set to satisfy the following formula at a frequency slower than the band.
20 KHz <FBL <1 / (2 x TTC + TSC)

  According to the present embodiment, the influence of the switching noise of the current of the backlight 23 on the detection of the capacitance on the touch panel 19 can be obtained only by setting the drive frequency of the backlight 23 according to the frequency of the cycle for controlling the touch panel 19. It can be easily suppressed. As a result, it is possible to prevent erroneous detection of the touch operation on the touch panel 19, and to improve the operability of the touch panel 19.

  In FIGS. 3 and 5A, the sub-scan frequency FTC of the touch panel 19 is set to the same frequency as the horizontal synchronization frequency, but any frequency exceeding an audible range of 20 KHz may be used. Also, although the current drive frequency FBL of the backlight 23 is fixed, the current drive frequency FBL of the backlight 23 is set so as to satisfy the conditions of FIGS. 5 (a), (b) and (c). For example, it is optional to be dynamically changed according to the duty ratio and each operation condition.

  Further, in the present embodiment, the touch panel is a capacitive type, but the present invention can be applied regardless of the type as long as the touch panel has a type in which a sensor is sequentially driven by a scanning line. Further, the present invention is not limited to the number of electrodes, the configuration of the electrodes, and the method of touch operation detection described in the present embodiment. For example, the configuration of the A / D converter and the integration circuit, the order of data conversion, and the presence or absence of data conversion are not limited. In the present embodiment, a configuration called an in-cell touch panel is appropriately shown as an example, but the present invention is also applicable to touch panels of other types.

  The control for setting the drive frequency of the backlight 23 to a frequency different from the sub-scan frequency FTC of the touch panel 19 may be performed by one hardware, or a plurality of hardware share processing. You may go.

  Further, although the present invention has been described in detail based on its preferred embodiments, the present invention is not limited to these specific embodiments, and various forms within the scope of the present invention are also included in the present invention. included. Furthermore, each embodiment mentioned above shows only one embodiment of the present invention, and it is also possible to combine each embodiment suitably.

  Moreover, although the case where this invention was applied to the electronic device was demonstrated to the example in the embodiment mentioned above as an example, this is not limited to this example, It is applicable if it is an apparatus which has a touch panel and a display part. That is, the present invention is applied to personal computers, PDAs, mobile communication terminals and digital cameras, mobile phone terminals and mobile image viewers, printer devices equipped with displays, digital photo frames, music players, game machines, electronic book readers, etc. It is possible.

(Other embodiments)
The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or storage medium, and one or more processors in a computer of the system or apparatus read and execute the program. Can also be realized. It can also be implemented by a circuit (eg, an ASIC) that implements one or more functions.

1: Electronic device 11: CPU 12: Non-volatile memory 13: Main memory 19: Touch panel 20: Touch panel control unit 21: Display 22: Display control unit 23: Back light 24: Back light control unit 25: Imaging device 201: Control circuit 202: scanning line drive circuit 203: detection signal processing circuit 204: memory 205: column electrode 206: row electrode 207: mutual capacitance 208: constant current circuit 209: integration circuit 210: A / D converter

Claims (16)

A liquid crystal monitor with a capacitive touch panel,
A plurality of first electrodes arranged in a first direction;
A plurality of second electrodes arranged in a second direction intersecting the first direction;
An output means for outputting a detection signal corresponding to a change in mutual capacitance between the first electrode and the second electrode;
With backlight,
The liquid crystal display monitor, wherein the backlight is configured to be able to perform PWM control at a PWM frequency different from a natural number multiple of the frequency at which the detection signal is output.   The liquid crystal monitor according to claim 1, wherein the touch panel is an in-cell or on-cell touch panel. Have a liquid crystal panel,
The liquid crystal monitor according to claim 2, wherein the electrode of the liquid crystal panel doubles as the electrode of the touch panel. A liquid crystal monitor according to any one of claims 1 to 3.
And a backlight control unit that performs PWM control of the backlight at the PWM frequency.   The electronic device according to claim 4, wherein the frequency is higher than the PWM frequency.   The electronic device according to claim 4, wherein the backlight control unit acquires information on the frequency, and performs PWM control of the backlight based on the acquired information. Storage means for storing the information;
7. The electronic device according to claim 6, wherein the backlight control unit acquires the information from the storage unit. An electronic device having a capacitive touch panel, a liquid crystal panel, and a backlight,
Touch panel control means for controlling timing of detecting a detection signal of the touch panel;
An electronic apparatus comprising: backlight control means for performing PWM control of the backlight at a PWM frequency different from a natural number multiple of a frequency for detecting the detection signal.   The electronic device according to claim 8, wherein the touch panel is an in-cell or on-cell touch panel.   The electronic device according to claim 9, wherein an electrode of the liquid crystal panel doubles as an electrode of the touch panel.   The electronic device according to any one of claims 8 to 10, wherein the frequency is higher than the PWM frequency.   The electronic device according to any one of claims 8 to 11, wherein the backlight control means acquires information on the frequency, and performs PWM control of the backlight based on the acquired information. Storage means for storing the information;
The electronic device according to claim 12, wherein the backlight control unit acquires the information from the storage unit. With electrostatic capacitive touch panel having a plurality of first electrodes arranged in a first direction, a plurality of second electrodes arranged in a second direction intersecting the first direction, and a backlight Control method of the liquid crystal monitor of
Outputting a detection signal corresponding to a change in mutual capacitance between the first electrode and the second electrode;
And PWM controlling the backlight with a PWM frequency different from a natural number multiple of the frequency at which the detection signal is output. A control method of an electronic device having a capacitive touch panel, a liquid crystal panel, and a backlight,
Controlling the timing of detecting the detection signal of the touch panel;
PWM controlling the backlight with a PWM frequency different from a natural number multiple of the frequency for detecting the detection signal.   A program for causing a computer to execute each step of the control method according to claim 14 or 15.

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