JP2019021328A - Liquid crystal monitor, electronic device, control method, and program - Google Patents

Abstract

An electronic apparatus is provided that suppresses the influence of noise generated by driving a backlight and prevents erroneous detection of an operation on a touch panel. A display, a touch panel provided on a display surface side of the display capable of detecting a touch operation, a backlight of the display, and a backlight control means for controlling the backlight current by pulse width modulation driving. The CPU controls the backlight control means to drive the backlight at a current drive frequency different from the sub-scan frequency of the touch panel, thereby suppressing the influence of noise generated by driving the backlight and touching the touch panel. To prevent false detections. [Selection] Figure 4

Description

  The present invention relates to an electronic device, a control method for the electronic device, a program, and a storage medium.

  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 installed to support 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 liquid crystal monitor (display) TFT panel, and 603 denotes a liquid crystal monitor backlight.

  Since the touch panel is arranged on the liquid crystal monitor, the touch panel is affected by noise generated by driving the liquid crystal or the backlight. In particular, it has been found that in-cell type and on-cell type systems have a significant influence due to the structure in which the touch panel is disposed on the liquid crystal electrode or the color filter without sandwiching glass or 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 a current value flowing through the white light emitting diode. As the current control of the light emitting diode, there are a method of controlling the current value with a direct current and a method called pulse width modulation control (PWM control) for controlling the timing of current flow with a fixed direct current value with the pulse width. There are two control methods. When DC control is performed, the color of the white light-emitting diode changes depending on the current value. For monitors such as digital cameras that check captured images on the monitor, PWM control is used to prevent the color from changing with luminance. Is often used.

  However, in PWM control, switching of the backlight current is repeatedly switched on and off, so that noise due to switching occurs and the touch panel receives the noise. If 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 increases, and the output signal of the touch panel fluctuates, causing an operation to be erroneously detected.

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

JP 2013-235197 A

  However, in the technique disclosed in Patent Document 1, it is necessary to arrange backlights in parallel along a region where touch detection of the touch panel is performed. Further, since it is necessary to perform control for synchronizing the touch detection of the touch panel and the driving of the backlight for each of the backlights connected in parallel, the touch detection of the touch panel and the 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 operations on the touch panel.

  An electronic apparatus according to the present invention includes a display unit, a touch panel provided on the display surface side of the display unit, wherein the plurality of column electrodes and the plurality of row electrodes for detecting a touch operation are arranged to be orthogonal to each other. A backlight for controlling the luminance of the display means, a backlight control means for controlling the backlight current by pulse width modulation driving, and the column electrodes and the row electrodes that change in response to a touch operation from the touch panel. Control means for causing the backlight control means to drive and control the backlight at a second frequency different from a frequency that is a natural number multiple of the first frequency for detecting a signal at an intersection with the backlight. .

  According to the present invention, by controlling driving of the backlight at a frequency different from the frequency at which the signal is detected from the touch panel, it is possible to suppress the influence of noise generated by the driving of the backlight. 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 touchscreen in this embodiment. It is a figure which shows the example of the detection timing of the touchscreen in this embodiment. It is a figure which shows the example of the detection timing of a touchscreen 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 sectional drawing which shows the structure of the liquid crystal monitor with a touch panel.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating a configuration example 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 serving as a control unit performs control related to each functional unit of the electronic device 1 by expanding and executing a program stored in the nonvolatile memory 12 in the main memory 13. For example, the CPU 11 controls the current drive frequency of the backlight 23 according to the capacity detection frequency of the touch panel 19 for detecting a touch operation on the touch panel 19 as described later.

  The nonvolatile memory 12 is a storage unit that stores various programs for the CPU 11 to operate. The main memory 13 is composed of, for example, a RAM (Random Access Memory). For example, the CPU 11 controls each unit of the electronic device 1 using the main memory 13 as a work memory in accordance with a program stored in the nonvolatile memory 12. When the electronic device 1 has a camera function such as an image sensor 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. Or a storage capacity sufficient to store a moving image for a predetermined time.

  The power switch (SW) 14 is a switch that controls 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 supply SW 14 is turned on. The operation of the power supply circuit 15 is controlled in response to a signal from the CPU 11 for shifting to a power saving mode, a return signal, or the like. The battery 16 is a power source for 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 apparatus 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 (registered trademark) (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 capacity detection signal to the touch panel 19, calculates coordinates and a region where the touch operation is detected based on the detection signal from the touch panel 19, and transmits to the CPU 11, thereby detecting operation on the touch panel 19. to enable.

  The display 21 as a display unit is a display monitor composed of a liquid crystal panel, for example. The display control unit 22 is a controller circuit that receives a display data control signal 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 drives and controls the backlight 23. The backlight control unit 24 controls the current flowing through the backlight 23 by pulse width modulation driving (PWM driving), and the backlight 23 is PWM-controlled. The image sensor 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 diagram illustrating 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 includes a plurality of column electrodes 205 arranged in a column and a plurality of row electrodes 206 arranged in a row. The row electrodes 206 of the electrodes arranged so as to be orthogonal to each other serve as scanning lines. Are used as readout lines.

  FIG. 2B is an enlarged view of the intersection of the electrodes shown in the frame A shown in FIG. The column electrode 205 is fixed at a predetermined potential, and the row electrode 206 is connected to the constant current circuit 208. When a weak current is caused to flow by the constant current circuit 208, electric charge is accumulated in the mutual capacitance 207 generated between the column electrode 205 and the row electrode 206. In order to obtain a signal having a sufficient level as a detection signal per intersection where one column electrode 205 and one row electrode 206 intersect, the accumulation time becomes longer with only one accumulation, and therefore the influence of noise is reduced. There is a high possibility of receiving.

  Therefore, a sub-scan for performing accumulation for a plurality of times in a short time per intersection is performed, and integration is performed by the integration circuit 209. The result of measurement at one intersection (one scan) is converted into a digital signal by the A / D converter 210. By measuring the change amount of the signal value of the detection signal output from the A / D converter 210 as the capacitance change amount, it is possible to determine whether or not there is a touch operation on the touch panel 19. The integration circuit 209 and the A / D converter 210 are provided in the detection signal processing circuit 203, for example.

  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. With the PLL circuit of the control circuit 201, it is possible to change the cycle of one scan or the cycle of one sub-scan. The scanning line driving circuit 202 and the detection signal processing circuit 203 are driven by a clock signal supplied from the control circuit 201.

  The control circuit 201 sequentially detects whether or not 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 value. If the signal value of the detection signal exceeds the threshold value for touch determination, the control circuit 201 attaches a touch detection flag and transfers the data to the memory 204. When the control circuit 201 completes scanning of all the intersections of the electrodes in the touch panel 19 for one frame, the touch detection area grouping and the centroid calculation of the touch position are performed from the detection data of one frame stored in the memory 204. I do. Thereby, the control circuit 201 calculates the number of touch detections and touch detection coordinates.

  The scanning line driving circuit 202 outputs scan pulses Y0 to Y8, and sequentially selects and drives the row electrodes 206 (Y0 to Y8) as scanning lines. A weak current is passed through the selected row electrode 206 by the constant current circuit 208. The number of sub-scans per scanning line can be arbitrarily changed by a command from the CPU 11 to the control circuit 201. The detection signal processing circuit 203 sequentially selects the column electrodes 205 as readout lines and reads the detection signals X0 to X8.

  FIG. 3 is a diagram illustrating an example of the capacity 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 one frame display on the display 21, and HSYNC is a horizontal synchronization signal indicating one line drawing on 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 capacitances at the intersections of all the electrodes of the touch panel 19 are detected within one frame (1 VSYNC) period, and the number of touch detections and the touch detection coordinates are detected. Need to be calculated. As described above, in order to perform sub-scanning that performs accumulation a plurality of times per intersection and to perform capacitance detection and calculation processing for all points within one frame, the frame rate is determined by the number of column electrodes and the number of sub-scans at the longest. One sub-scan is performed at a period TTC divided by.

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

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

  FIG. 4 is a diagram illustrating an example of the capacitance detection timing of the touch panel 19 and the driving timing of the backlight 23 performed by the touch panel control unit 20. In the example illustrated in FIG. 4A, the period (the sub-scanning period) TTC in which the touch panel control unit 20 controls the touch panel 19 and the current driving period TBL <b> 1 of the backlight 23 are synchronized. At this time, a case where the current switching timing of the backlight 23 and the sub-scan (capacity detection) timing TSC on the touch panel 19 always coincide with each other occurs.

  When the timing always matches, the detection signal from the touch panel 19 fluctuates due to the influence of noise generated by the touch panel 19 due to the switching of the current of the backlight 23. When the detection signal from the touch panel 19 fluctuates, it causes a false detection factor such that the touch operation is not detected as a touch operation, or the touch operation is detected even though the touch operation is not performed. .

  In the example illustrated in FIG. 4B, the touch panel control unit 20 sets a frequency with a period different from the period TTC for controlling the touch panel 19 and the current driving period TBL <b> 2 of the backlight 23. It can be seen that the frequency of switching the current of the backlight 23 and the sub-scan (capacitance detection) timing TSC on the touch panel 19 are reduced by using different frequencies. Therefore, the influence of noise generated by switching the current of the backlight 23 can be suppressed, and erroneous detection of a touch operation on the touch panel 19 can be prevented.

  Therefore, in the present embodiment, according to the cycle TTC in which the touch panel control unit 20 controls the touch panel 19, the cycle TTC and the current driving cycle TBL2 of the backlight 23 are different as shown in FIG. 4B. Set to the frequency of the cycle. More specifically, the current driving cycle TBL2 of the backlight 23 is set to be a frequency different from a frequency that is a natural number multiple of the frequency of the cycle TTC for controlling the touch panel 19. 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 driving cycle TBL2 when the backlight 23 is PWM-driven in the backlight control unit 24 so as to be different from the acquired cycle TTC (and the multiplied cycle).

  The touch panel control unit 20 sets a cycle TTC for controlling the touch panel 19 in advance, stores information on the cycle TTC in the nonvolatile memory 12, and the CPU 11 reads the information to obtain the cycle TTC. Anyway. Further, if the current driving cycle of the backlight 23 is made slower than the cycle for controlling the touch panel 19, the number of times of switching the current of the backlight 23 is smaller than the number of times the capacity of the touch panel 19 is detected. Less.

  FIG. 5 is a diagram for explaining a current drive frequency setting region of the backlight 23 in the present embodiment. The frequency below 20 KHz corresponds to a general human audible range. In an electronic device such as a digital camera equipped with a moving image recording function, the backlight control unit 24 performs current-driven switching control of the backlight 23. Here, when the backlight control unit 24 performs switching control at 20 KHz or less, vibrations of peripheral components such as a capacitor are transmitted to a microphone (not shown) inside the electronic device 1, and a frequency region in which humans can hear it. Recorded as audio noise.

  Therefore, in an electronic device having a moving image recording function, it is necessary to set the current drive frequency of the backlight 23 to 20 KHz or higher. 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, audible audio noise is prevented from being recorded by switching control of the backlight 23. Can do.

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

FIG. 5B is a diagram illustrating 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 that case, it is necessary to avoid that the current drive frequency FBL is synchronized with the frequency multiplied by the sub-scan frequency FTC. At this time, for example, the current drive frequency FBL exceeds the audible range of 20 KHz than the frequency band in the hatched portion obtained by adding the sub-scan time TSC to the cycle TTC / 2 of the frequency multiplied by the sub-scan frequency FTC (twice in this example). Set to satisfy the following formula at a slow frequency.
20KHz <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 that the current drive frequency FBL is synchronized with a frequency that is a frequency division of the sub-scan frequency FTC. At this time, for example, the current drive frequency FBL exceeds the audible range of 20 KHz, and the frequency of the hatched portion obtained by adding the sub-scan time TSC to the period 2 × TTC of the divided frequency of the sub-scan frequency FTC (in this example, 1/2 times) Set to satisfy the following formula at a frequency slower than the band.
20KHz <FBL <1 / (2 × TTC + TSC)

  According to the present embodiment, the influence of the switching noise of the current of the backlight 23 in the capacitance detection on the touch panel 19 can be reduced by simply 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. Thereby, erroneous detection of the touch operation on the touch panel 19 can be prevented, and the operability of the touch panel 19 can be improved.

  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 is arbitrary as long as the frequency exceeds the audible range of 20 KHz. Further, 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. 5A, 5B, and 5C. For example, it can be arbitrarily changed according to the duty ratio and each operating condition.

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

  Note that 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 may share the processing. You may go.

  Although the present invention has been described in detail based on the preferred embodiments thereof, the present invention is not limited to these specific embodiments, and various forms without departing from the gist of the present invention are also included in the present invention. included. Furthermore, each embodiment mentioned above shows only one embodiment of this invention, and it is also possible to combine each embodiment suitably.

  In the above-described embodiment, the case where the present invention is applied to an electronic device has been described as an example. However, this is not limited to this example, and any device having a touch panel and a display unit can be applied. That is, the present invention is applied to personal computers, PDAs, mobile communication terminals, digital cameras, mobile phone terminals, portable image viewers, printer devices with displays, digital photo frames, music players, game machines, electronic book readers, and the like. Is possible.

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

DESCRIPTION OF SYMBOLS 1: Electronic device 11: CPU 12: Non-volatile memory 13: Main memory 19: Touch panel 20: Touch panel control part 21: Display 22: Display control part 23: Backlight 24: Backlight control part 25: Imaging element 201: Control circuit 202: Scanning line driving 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

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

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 and a plurality of first electrodes arranged in the first direction. A plurality of second electrodes, output means for outputting a detection signal corresponding to a change in mutual capacitance between the first electrode and the second electrode, and a backlight, wherein the backlight is The PWM control can be performed at a PWM frequency different from a natural number multiple of the frequency at which the detection signal is output.
An electronic apparatus according to the present invention includes the above-described liquid crystal monitor and backlight control means for performing PWM control of the backlight at the PWM frequency.

Claims (9)

Display means;
A plurality of column electrodes for detecting a touch operation and a plurality of row electrodes are arranged so as to be orthogonal to each other, and a touch panel provided on the display surface side of the display means;
A backlight for controlling the luminance of the display means;
Backlight control means for controlling the current of the backlight by pulse width modulation driving; and
The backlight is lit at a second frequency different from a natural frequency multiple of the first frequency for detecting a signal at an intersection of the column electrode and the row electrode that changes in response to a touch operation from the touch panel. An electronic apparatus comprising: a control unit that causes the light control unit to drive-control.   The electronic device according to claim 1, wherein the control unit acquires the first frequency, and causes the backlight control unit to perform drive control according to the acquired second frequency.   The electronic device according to claim 1, wherein the second frequency is a frequency that is faster than an audible range and slower than the first frequency.   The second frequency is a frequency faster than an audible range and a frequency slower than a frequency closest to the audible range among a frequency multiplied or divided by the first frequency. The electronic device according to any one of the above. Storage means for storing information of the first frequency set in advance;
5. The electronic apparatus according to claim 1, wherein the control unit acquires information on the first frequency from the storage unit.   The electronic device according to claim 1, wherein the second frequency is a frequency slower than the first frequency. A display means, a plurality of column electrodes for detecting a touch operation, and a plurality of row electrodes are arranged so as to be orthogonal to each other, a touch panel provided on the display surface side of the display means, and the brightness of the display means are controlled. A control method of an electronic device having a backlight
The backlight control means of the electronic device controls the current of the backlight by pulse width modulation driving; and
The backlight is lit at a second frequency different from a natural frequency multiple of the first frequency for detecting a signal at an intersection of the column electrode and the row electrode that changes in response to a touch operation from the touch panel. And a step of causing the light control means to drive and control the electronic device. A display means, a plurality of column electrodes for detecting a touch operation, and a plurality of row electrodes are arranged so as to be orthogonal to each other, a touch panel provided on the display surface side of the display means, and the brightness of the display means are controlled. A program for causing a computer to execute a control method of an electronic device having a backlight,
Causing the backlight control means of the electronic device to control the current of the backlight by pulse width modulation driving; and
The backlight is lit at a second frequency different from a natural frequency multiple of the first frequency for detecting a signal at an intersection of the column electrode and the row electrode that changes in response to a touch operation from the touch panel. A program for causing a computer to execute the step of causing the light control means to drive-control.   A computer-readable storage medium having the program according to claim 8 recorded thereon.

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