JP2017129878A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress motion image blur even when screen brightness is high.SOLUTION: A liquid crystal display device 200 comprises a liquid crystal panel 220, backlights 211a-211c that are turned on by drive signals, and a backlight drive circuit 100 that outputs drive signals. Drive signals are generated such that a rate of change in duty cycle of a drive signal for a backlight unit 211a-211c with a predetermined brightness or less is smaller than a rate of change in duty cycle of a drive signal for a backlight 211a-211c with brightness greater than the predetermined brightness.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a backlight driving circuit connected to a liquid crystal panel including a group of liquid crystal pixels arranged in a matrix and a plurality of backlights each provided corresponding to a plurality of rows of the liquid crystal pixel group.

  Conventionally, the size of liquid crystal display devices such as liquid crystal televisions has been increasing. However, with the increase in size, there is a problem that blurring of an image when displaying a moving image (hereinafter, referred to as “moving image blur”) is conspicuous.

  Therefore, a method of performing a backlight scan in a liquid crystal display device is known in order to suppress moving image blur. The backlight scan is to sequentially turn on and off a plurality of backlights provided in a row direction in the liquid crystal pixel group of the display panel.

  As a method of such backlight scanning, when the screen moves fast, the moving image blur is suppressed by reducing the lighting duty ratio, which is the ratio of the lighting period in the backlight blinking cycle, while the screen When the movement of the motor is slow, there is a method of suppressing power consumption by maintaining the lighting duty ratio and suppressing the peak current (see, for example, Patent Document 1).

  As a result, it is possible to achieve both suppression of moving image blur and reduction of power consumption.

JP 2011-232535 A

  In such a backlight scanning method, it is necessary to increase the lighting duty ratio when the screen brightness is increased, that is, when the backlight brightness is increased.

  However, in the method disclosed in Patent Document 1, when the screen moves quickly, the lighting duty ratio is reduced, so that the brightness of the screen cannot be increased. In other words, there is a problem that blurring of moving images cannot be suppressed when the brightness of the screen is high.

  The present invention has been made to solve the above-described problem, and an object of the present invention is to provide a display device that can suppress blurring of a moving image even when the luminance of a screen is high.

  In order to achieve the above object, a display device according to one embodiment of the present invention includes a display unit, a light source that is turned on by a drive signal, and a control unit that outputs the drive signal, and the drive signal is a predetermined signal. The change rate of the duty ratio of the drive signal with respect to the luminance of the light source equal to or lower than the luminance is smaller than the change rate of the duty ratio of the drive signal with respect to the luminance of the light source higher than the predetermined luminance. In addition, the level of the driving signal at a luminance equal to or lower than the predetermined luminance may be higher than the level of the driving signal at a luminance higher than the predetermined luminance.

  That is, a display device according to one embodiment of the present invention includes a display portion including liquid crystal pixel groups arranged in a matrix, a plurality of light sources provided corresponding to a plurality of rows of the liquid crystal pixel group, and the plurality of light sources. A light source drive unit that supplies a drive signal to the light source, and the light source drive unit has a lighting duty ratio that is a ratio of a lighting period in a blinking cycle of each light source as an adjustment value indicating the luminance of the light source is higher. The driving signal is supplied so as to increase, and the liquid crystal pixel group transmits light from a light source corresponding to the liquid crystal pixel at a transmittance according to a signal voltage written to each liquid crystal pixel, and drives the light source. The unit turns off the light source before the signal voltage is written to the liquid crystal pixel group in the row corresponding to each light source, the duty ratio characteristic indicating the lighting duty ratio with respect to the luminance, and the driving with respect to the luminance. The amplitude characteristic indicating the amplitude of the signal has a first region in which the luminance is equal to or lower than a predetermined luminance and a second region in which the luminance is higher than the predetermined luminance, and the lighting duty ratio with respect to the luminance in the first region is The rate of change is smaller than the rate of change of the lighting duty ratio with respect to the luminance in the second region, and the current value of each drive signal in the lighting period in the first region is the value in each of the lighting periods in the second region. It is higher than the current value of the drive signal.

  Thereby, even if it is a case where the brightness | luminance of a screen is high, a moving image blur can be suppressed. Further, by turning off the corresponding light source before the signal voltage is written, the double image can be suppressed.

  In addition, a display device according to another aspect of the present invention includes a display unit, a light source, and a light source driving unit that outputs a driving signal of the light source according to a duty ratio characteristic and an amplitude characteristic according to the luminance of the light source. The duty ratio characteristic and the amplitude characteristic have a first area below the predetermined luminance and a second area higher than the predetermined luminance with reference to the predetermined luminance of the light source, The change rate of the duty ratio of the drive signal with respect to the luminance of the light source is smaller than the change rate of the duty ratio of the drive signal with respect to the luminance of the light source in the second region, and the amplitude of the drive signal in the first region is The amplitude of the drive signal in the second region is larger.

  For example, the light source driving unit includes a timing instruction unit for instructing the timing of turning on and off the light source such that the higher the luminance is, the longer the lighting period is. When the luminance is higher than the predetermined luminance, the first voltage is set. A voltage generator that generates a second voltage higher than the first voltage when the luminance is less than or equal to the predetermined luminance, and a driver that is provided corresponding to each light source and supplies the drive signal to the corresponding light source The driver converts the first voltage generated by the voltage generation unit into a first current, converts the second voltage into a second current, and converts the converted current by the timing instruction unit. The drive signal may be supplied during a period in which lighting of the corresponding light source is instructed.

  As a result, the current can be switched between two stages with a simple configuration.

  The timing instruction unit generates a voltage switching signal indicating whether the luminance is higher than the predetermined luminance, and the voltage generation unit generates the voltage switching signal generated by the timing instruction unit. The first voltage may be generated when the value is higher than the predetermined luminance, and the second voltage may be generated when the luminance is equal to or lower than the predetermined luminance.

  In addition, the level of the drive signal at the first luminance below the predetermined luminance may be substantially equal to the level of the drive signal at the second luminance different from the first luminance below the predetermined luminance. Further, the level of the drive signal at the third luminance higher than the predetermined luminance may be substantially equal to the level of the drive signal at the fourth luminance different from the third luminance higher than the predetermined luminance. The drive signal during the lighting period of the light source may have a higher level as the luminance of the light source is lower. That is, each drive signal in the lighting period may have a higher current value as the luminance is lower.

  Thereby, flicker can be suppressed.

  A voltage generating unit configured to generate a first voltage when the luminance of the light source is higher than the predetermined luminance and generate a second voltage higher than the first voltage when the luminance of the light source is equal to or lower than the predetermined luminance; The control unit may output the drive signal based on the first voltage and the second voltage. In addition, the light source has a timing instruction unit for instructing the lighting and extinguishing timing so that the lighting period of the light source becomes longer as the luminance of the light source is higher, and the control unit is based on an instruction from the timing instruction unit, The drive signal may be output. That is, the light source drive unit includes a timing instruction unit that instructs lighting and extinguishing timing of each light source so that the lighting period becomes longer as the luminance is higher, and a voltage generation unit that generates a higher voltage as the luminance is lower. And a driver that is provided corresponding to each light source and supplies the driving signal to the corresponding light source, the driver converts the voltage generated by the voltage generation unit into a current, the converted current, You may supply as a said drive signal in the period when lighting of the corresponding light source is instruct | indicated by the said timing instruction | indication part.

  As a result, the current can be adjusted steplessly with a simple configuration.

  Further, the timing instruction unit generates a PWM (Pulse Width Modulation) signal having a smaller duty ratio as the luminance is lower, and the voltage generation unit performs DA (digital-analog) conversion of the duty ratio of the PWM signal. Thus, the smaller the duty of the PWM signal is, the smaller the duty of the PWM signal is, by inverting the voltage level of the DA converter that generates a lower analog voltage and the analog voltage generated by the DA converter as the duty of the PWM signal is smaller. And an inverting circuit for generating a high voltage.

  The DA converter is an integrator composed of a resistor and a capacitor, and the inverting circuit is configured such that an analog voltage generated by the DA converter is applied to a control terminal, and one of two output terminals. One of the transistors may have a grounded transistor.

  The luminance may be specified by a user operation. That is, the plurality of luminances may be designated by a user operation.

  According to the present invention, it is possible to realize a display device capable of suppressing moving image blur even when the screen has high brightness.

1 is a block diagram showing a configuration of a liquid crystal display device on which a backlight drive circuit according to Embodiment 1 is mounted. It is a block diagram which shows the detailed structure of a backlight drive circuit. It is a circuit diagram which shows an example of a detailed structure of a voltage switching circuit. 4 is a timing chart schematically showing an example of lighting and extinguishing timings of the backlight panel and signal voltage writing timings to the liquid crystal panel in the first embodiment. It is a graph which shows the drive current in the lighting period of a backlight with respect to an adjustment value. It is a graph which shows the lighting duty ratio of a backlight with respect to an adjustment value. 4 is a timing chart schematically showing the lighting and extinguishing timings of the backlight panel and the writing timing of the signal voltage to the liquid crystal panel in the comparative example of the first embodiment. 6 is a timing chart schematically showing another example of the lighting and extinguishing timing of the backlight panel and the timing of writing the signal voltage to the liquid crystal panel in the first embodiment. It is a table | surface which shows the lighting duty ratio, drive current, and light emission luminance of a backlight panel at the time of changing an adjustment value. 10 is a graph showing light emission luminance with respect to the adjustment value shown in FIG. 9. It is a graph which shows the chromaticity of a backlight panel at the time of changing an adjustment value. 6 is a block diagram showing a detailed configuration of a backlight drive circuit according to a modification of the first embodiment. FIG. 6 is a block diagram illustrating a detailed configuration of a backlight drive circuit according to Embodiment 2. FIG. It is a circuit diagram which shows an example of a detailed structure of a D / A conversion part. It is a graph which shows the drive current in the lighting period of a backlight with respect to an adjustment value. It is a graph which shows the lighting duty ratio of a backlight with respect to an adjustment value. It is a table | surface which shows the lighting duty ratio, drive current, and light emission luminance of a backlight panel at the time of changing an adjustment value. It is a graph which shows the light emission luminance with respect to the adjustment value shown in FIG. It is a graph which shows the chromaticity of a backlight panel at the time of changing an adjustment value. FIG. 10 is a block diagram showing a detailed configuration of a backlight drive circuit according to a modification of the second embodiment. 6 is a timing chart schematically showing the lighting and extinguishing timings of the backlight panel and the signal voltage writing timing to the liquid crystal panel in the liquid crystal display device according to Comparative Example 1. FIG. 12 is a timing chart schematically showing the lighting and extinguishing timings of the backlight panel and the signal voltage writing timing to the liquid crystal panel in the liquid crystal display device according to Comparative Example 2. 12 is a graph showing a lighting duty ratio with respect to an adjustment value of a liquid crystal display device according to Comparative Example 2. It is a figure for demonstrating animation blur, (a) is a figure which shows the case where a lighting duty ratio is small, (b) is a case where a lighting duty ratio is small.

  First, before describing the embodiment of the present invention, the principle of double-shot and moving image blur that occurs when a moving image is displayed on a display device (for example, a liquid crystal display device) will be described using a comparative example.

(Comparative Example 1)
First, the principle of double image taking place in a liquid crystal display device will be described. FIG. 21 is a timing chart schematically showing the lighting and extinguishing timings of the backlight panel and the writing timing of the signal voltage to the liquid crystal panel in the liquid crystal display device according to the comparative example 1.

  The liquid crystal display device includes a display unit (for example, a liquid crystal panel) including liquid crystal pixel groups arranged in a matrix, and a plurality of light sources (for example, backlights) provided corresponding to a plurality of rows of the liquid crystal pixel group. And a light source driving unit (for example, a backlight driving circuit) for driving a plurality of backlights.

  Writing of the scanning signal to the liquid crystal pixel group is performed by a gate driver that drives the upper part of the liquid crystal panel, a gate driver that drives the central part of the liquid crystal panel, and a gate driver that drives the lower part of the liquid crystal panel. Each gate driver writes a signal voltage corresponding to a scanning signal, which is digital data, to the liquid crystal panel. Here, writing the signal voltage to the liquid crystal panel means applying the signal voltage to a liquid crystal pixel group constituting the liquid crystal panel.

  The plurality of backlights are constituted by, for example, LEDs (Light Emitting Diodes), LEDs provided corresponding to the upper part of the liquid crystal panel (on the LEDs), and LEDs provided corresponding to the central part of the liquid crystal panel (LED center) and LEDs (LED lower) provided corresponding to the lower part of the liquid crystal panel.

  The backlight drive circuit includes a plurality of backlight drivers that drive each backlight, and supplies a drive current for turning on the backlight to the backlight during the lighting period of the backlight. Specifically, during the high period of the scan signal PWM0, a drive current is supplied to the LED provided corresponding to the upper portion of the liquid crystal panel, and the scan signal PWM1 is provided corresponding to the central portion of the liquid crystal panel. A drive current is supplied to the LED, and the drive current is supplied to the LED provided corresponding to the lower portion of the liquid crystal panel during the high period of the scan signal PWM2.

  In Comparative Example 1, the lighting duty ratio is 100%. That is, the scan signals PWM0 to PWM2 are always high, and each backlight is always lit.

  Hereinafter, the operation of the liquid crystal display device according to Comparative Example 1 will be described.

  When the gate driver start signal STV, which is a signal indicating the writing timing of the scanning signal to the first row of the liquid crystal pixel group, rises, the liquid crystal display device sequentially drives each gate driver to write a signal voltage to the liquid crystal panel. .

  The liquid crystal pixel row in which the signal voltage is written transmits light with a transmission amount corresponding to the signal voltage of the next frame, taking time corresponding to the response speed of the liquid crystal pixel. That is, an image corresponding to the scanning signal of the next frame is displayed.

  However, in such a liquid crystal display device, when the signal voltage is rewritten from the previous frame to the next frame, there is a problem that the image is duplicated and blurring occurs due to the response speed of the liquid crystal. is there. Specifically, since the plurality of backlights are always lit when the lighting duty ratio is 100%, the liquid crystal pixels also emit light from the backlight during the response period of the liquid crystal pixels after the signal voltage is rewritten. Transparent. That is, when the signal voltage is rewritten, the image of the frame before rewriting and the image of the frame after rewriting are displayed. In other words, the image appears twice.

(Comparative Example 2)
Therefore, in order to suppress such a double image in the liquid crystal display device, a configuration in which the lighting duty ratio is reduced and the corresponding backlight is turned off when the signal voltage is rewritten can be considered.

  FIG. 22 is a timing chart schematically showing lighting and extinguishing timings of the backlight panel and signal voltage writing timings to the liquid crystal panel in the liquid crystal display device according to the comparative example 2. In this comparative example, the response period of the liquid crystal pixel is assumed to be zero for explanation.

  As shown in FIG. 22, the liquid crystal display device according to the comparative example 2 turns off the corresponding backlight at the next scanning signal writing timing. Specifically, the on-duty of the scan signals PWM0 to PWM2 is set to 2/3 (≈67%), and when the signal voltage of the liquid crystal pixel is rewritten, the scan signals PWM0 to PWM2 are set to low to turn off the corresponding backlight. Let

  As a result, it is possible to suppress double copying when the signal voltage is rewritten. In the above description, the response period of the liquid crystal pixel is set to zero. However, when the response period of the liquid crystal pixel is not zero, the response of the liquid crystal pixel is turned off by turning off the corresponding backlight in the response period of the liquid crystal pixel. It is also possible to suppress moving image blur during the period.

  FIG. 23 is a graph showing the lighting duty ratio with respect to the adjustment value of the liquid crystal display device according to Comparative Example 2. The adjustment value is a value indicating the luminance of the backlight. The higher the adjustment value, the higher the luminance.

  As shown in the figure, the higher the adjustment value, the higher the lighting duty ratio because the backlight needs to emit light with higher luminance. On the other hand, the lower the adjustment value, the lower the brightness of the backlight, and the lower the lighting duty ratio.

  Here, when the backlight of the liquid crystal display device according to Comparative Example 2 has a three-stage configuration and one vertical scanning period is Vs, the response speed of the liquid crystal pixel is, for example, (1/3) Vs.

  In the liquid crystal display device according to the comparative example 2, the lighting duty ratio is set to 1/3 (≈33%), and the backlight is turned off when the signal voltage of the liquid crystal pixel is rewritten and during the response period of the liquid crystal pixel. Therefore, it is possible to suppress the double image. That is, in the case of an adjustment value that can reduce the lighting duty ratio to 33% or less, it is possible to suppress double shots. In other words, in the case of an adjustment value such that the lighting duty ratio exceeds 33%, the effect of suppressing double shots is not sufficiently exhibited.

  However, the adjustment values that can make the lighting duty ratio 33% or less are only 0, 1, and 2. With other adjustment values (adjustment value 3 or more), the lighting duty ratio becomes higher than 33%, so It is difficult to suppress the reflection. That is, it is difficult to suppress double image capturing in a high-luminance region of the backlight that has an adjustment value of 3 or more.

  In addition, since the liquid crystal pixel is hold-driven, there is a problem that moving image blur occurs due to a retina afterimage even if the response speed of the liquid crystal pixel is shortened.

  This moving image blur can also be improved by reducing the lighting duty ratio in the same manner as the above-described method for suppressing double image capturing.

  24A and 24B are diagrams for explaining moving image blur. FIG. 24A shows a case where the lighting duty ratio is large, and FIG. 24B shows a case where the lighting duty ratio is small.

  As is clear when (a) and (b) are compared, the smaller the lighting duty ratio shown in (b), the smaller the motion blur. In other words, the moving image blur can be suppressed as the lighting duty ratio is reduced and the lighting of the backlight is brought closer to the impulse-type lighting.

  Thus, moving image blur can be suppressed by reducing the lighting duty ratio.

  However, as shown in FIG. 23, reducing the lighting duty ratio decreases the luminance of the backlight. That is, the method of reducing the lighting duty ratio in order to suppress moving image blur is difficult to apply when the backlight emits light with high luminance.

  As described above, in the liquid crystal display devices according to Comparative Examples 1 and 2, when the backlight emits light with high luminance, there is a problem that it is difficult to suppress double image capturing and blurring of moving images.

  In order to solve such a problem, the backlight drive circuit according to each embodiment of the present invention supplies the following drive current to each backlight. That is, as each drive current in the lighting period of each backlight, the first current is supplied when the adjustment value is the first adjustment value, and the first current when the adjustment value is the second adjustment value lower than the first adjustment value. A second current having a higher current value is supplied. Further, the lighting duty ratio for obtaining one luminance using the second current is smaller than the lighting duty ratio for obtaining the one luminance using the first current.

  Thus, the backlight drive circuit according to each embodiment of the present invention further reduces the lighting duty ratio when the adjustment value is the second adjustment value. Therefore, even when the screen brightness is high, moving image blur can be suppressed. Further, by turning off the corresponding backlight before the signal voltage is written, the double image can be suppressed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Each of the embodiments described below shows a preferred specific example of the present invention. The numerical values, shapes, materials, constituent elements, arrangement positions and connecting forms of the constituent elements, and the like shown in the following embodiments are merely examples, and are not intended to limit the present invention. The invention is specified by the claims. Therefore, among the constituent elements in the following embodiments, constituent elements that are not described in the independent claims are not necessarily required to achieve the object of the present invention, but are described as constituting more preferable embodiments. Is done.

  The backlight drive circuit according to the embodiment of the present invention drives a plurality of backlights provided corresponding to a plurality of rows of liquid crystal pixel groups arranged in a matrix and is mounted on, for example, a television.

(Embodiment 1)
The display device according to Embodiment 1 of the present invention includes a display unit, a light source that is turned on by a drive signal, and a control unit that outputs a drive signal, and the drive signal is driven with respect to the luminance of the light source having a predetermined luminance or less. The change rate of the duty ratio of the signal is smaller than the change rate of the duty ratio of the drive signal with respect to the luminance of the light source that is higher than the predetermined luminance.

  That is, the backlight drive circuit (corresponding to the control unit) according to Embodiment 1 of the present invention has a drive current (corresponding to the drive signal) to a plurality of backlights (corresponding to the light source). As the adjustment value indicating the luminance of the backlight is higher, the lighting duty ratio, which is the proportion of the lighting period in the flashing cycle of each backlight, is increased, and the signal to the liquid crystal pixel group Turn off the backlight before voltage is written. Here, the backlight driving circuit supplies the first current in the lighting period when the adjustment value exceeds the threshold value, and the current amount larger than the first current in the lighting period when the adjustment value is equal to or less than the threshold value. Supply two currents. Further, the lighting duty ratio for obtaining one luminance using the second current is made smaller than the lighting duty ratio for obtaining the one luminance using the first current.

  As a result, the backlight drive circuit according to Embodiment 1 of the present invention can suppress double image capturing and motion blur even when the backlight emits light with high luminance.

<1-1. Configuration>
Hereinafter, the configuration of the backlight drive circuit according to the first embodiment of the present invention will be described.

[Liquid Crystal Display]
FIG. 1 is a block diagram showing a configuration of a liquid crystal display device 200 on which a backlight drive circuit 100 according to Embodiment 1 of the present invention is mounted.

  A liquid crystal display device 200 shown in the figure is, for example, a liquid crystal television including the backlight drive circuit 100 according to the first embodiment of the present invention, a backlight panel 210, and a liquid crystal panel 220 including a liquid crystal pixel group.

  The backlight driving circuit 100 drives the backlight panel 210 by using an adjustment value indicating the luminance of the backlight panel 210 input from the outside, a signal for instructing the lighting and extinguishing timing of each backlight panel 210, and the like. To do. The detailed configuration of the backlight drive circuit 100 will be described later.

  The backlight panel 210 is disposed immediately below the liquid crystal panel 220 and includes a plurality of backlights 211a to 211c. In the present embodiment, the backlight panel 210 includes three backlights 211a to 211c, but the number of backlights is not limited to this, and may be 10 or 20, for example.

  Each of the backlights 211 a to 211 c is provided corresponding to a plurality of rows of the liquid crystal pixel group constituting the liquid crystal panel 220. Specifically, the backlight 211 a corresponds to the upper part of the liquid crystal panel 220, the backlight 211 b corresponds to the central part of the liquid crystal panel 220, and the backlight 211 c corresponds to the lower part of the liquid crystal panel 220. The backlights 211a to 211c include current-driven light emitting elements such as LEDs. That is, the brightness of the backlights 211a to 211c changes according to the amount of current flowing through the backlights 211a to 211c.

  In addition, in this Embodiment, each backlight 211a-211c is elongate, However, The shape of a backlight is not restricted to this, A substantially square may be sufficient. In the present embodiment, the backlights 211a to 211c are arranged side by side in the row direction, but the arrangement of the backlights is not limited to this, and may be arranged side by side in the column direction. May be arranged. Hereinafter, the backlights 211a to 211c are not particularly distinguished and may be simply referred to as the backlight 211.

  The liquid crystal panel 220 is a display panel having liquid crystal pixel groups arranged in a matrix (eg, 1920 columns, 1080 rows), and displays an image corresponding to a scanning signal input from the outside of the liquid crystal display device 200.

  Each liquid crystal pixel 221 included in the liquid crystal panel 220 applies a signal voltage to a liquid crystal layer, a liquid crystal element having a pixel electrode to which a signal voltage is applied, a counter electrode facing the pixel electrode, and a pixel electrode of the liquid crystal element. TFT (Thin Film Transistor). The liquid crystal element changes the polarization direction of light according to the signal voltage applied to the pixel electrode of the liquid crystal element via the TFT. The TFT is supplied from the source driver (not shown) to each column of the liquid crystal pixel group at a timing corresponding to the high and low levels of the gate pulse output to the gate line provided for each row of the liquid crystal pixel group from the gate driver. The signal voltage output to the source line provided in is applied to the pixel electrode of the liquid crystal pixel 221 in the corresponding column. That is, writing is performed on the liquid crystal pixel 221. As a result, the liquid crystal panel 220 transmits light from the backlight 211 corresponding to the liquid crystal pixel 221 with a transmission amount corresponding to the signal voltage indicating the luminance of the liquid crystal pixel 221 written in each liquid crystal pixel 221.

[Detailed configuration of backlight drive circuit]
Next, a detailed configuration of the backlight drive circuit 100 will be described. FIG. 2 is a block diagram showing a detailed configuration of the backlight drive circuit 100.

  The backlight drive circuit 100 shown in the figure includes a timing instruction unit 110, a voltage switching circuit 120, and backlight drivers 130a to 130c. In the figure, a backlight panel 210 to which a drive current is supplied from the backlight drivers 130a to 130c is also illustrated.

  The timing instructing unit 110 instructs the lighting and extinguishing timing of each backlight 211 so that the lighting period of the backlight 211 becomes longer as the adjustment value is higher. Specifically, the timing instructing unit 110 performs SOC (System-on-a-). Chip) 111 and TCON (Timing Controller) 112, and output pulse signals PWM <b> 0 to PWM <b> 2 indicating the lighting and extinguishing timing of each backlight 211.

  The SOC 111 generates a backlight adjustment pulse having a duty ratio corresponding to an adjustment value indicating the luminance of the backlight panel 210. Specifically, the backlight adjustment pulse having a higher duty ratio is generated as the adjustment value indicating the luminance of the backlight panel 210 is higher. Each backlight 211 of the backlight panel 210 is lit in a period corresponding to the high period of the backlight adjustment pulse. That is, the backlight 211 is lit for a longer period as the duty ratio of the backlight adjustment pulse is higher.

  Here, when the adjustment value indicating the brightness of the backlight panel 210 is higher than a threshold value (for example, 10), the SOC 111 sets the duty ratio of the backlight adjustment pulse as a normal duty ratio. The duty ratio of the write adjustment pulse is made smaller than the normal duty ratio. The normal duty ratio is a duty ratio necessary for obtaining the luminance of the backlight 211 corresponding to the adjustment value by supplying a first current described later to the backlight 211. That is, the lighting duty ratio for obtaining one luminance using the second current is smaller than the lighting duty ratio for obtaining the one luminance using the first current.

  The SOC 111 is high (hereinafter referred to as “H”) when the adjustment value indicating the luminance of the backlight panel 210 is higher than a threshold value (for example, 10), and is low (hereinafter referred to as “L”) when the adjustment value is lower than the threshold value. Such a voltage switching pulse is generated and output to the voltage switching circuit 120. Note that the threshold value of the adjustment value that serves as a reference for the SOC 111 to switch the voltage switching pulse between H and L is not limited to 10, for example, the usage environment and the operating environment of the liquid crystal display device 200 on which the backlight driving circuit 100 is mounted. Depending on the case, it may be appropriately selected.

  The TCON 112 outputs the backlight adjustment pulse input from the SOC 111 in synchronization with the vertical synchronization signal supplied to the liquid crystal panel 220. Specifically, the backlight adjustment pulse is converted so as to be synchronized with the vertical synchronization signal, and the H period and the L period are sequentially delayed, so that the pulse signal PWM0 indicating the lighting and extinguishing timing of each backlight 211 is obtained. ~ PWM2 is generated.

  Specifically, the pulse signal PWM0 is a signal that controls the lighting and extinguishing timing of the backlight 211a, the H period of the pulse signal PWM0 corresponds to the lighting period of the backlight 211a, and the L period of the pulse signal PWM0 is the back period. The light 211a corresponds to the extinguishing period. The pulse signal PWM1 is a signal for controlling the lighting and extinguishing timing of the backlight 211b. The H period of the pulse signal PWM1 corresponds to the lighting period of the backlight 211b, and the L period of the pulse signal PWM1 is the extinguishing period of the backlight 211b. Corresponding to The pulse signal PWM1 is a signal for controlling the lighting and extinguishing timing of the backlight 211c. The H period of the pulse signal PWM2 corresponds to the lighting period of the backlight 211c, and the L period of the pulse signal PWM2 is the extinguishing period of the backlight 211c. Corresponding to

  With such pulse signals PWM0 to PWM2, the three backlights 211a to 211c are sequentially turned on and off.

  Here, the TCON 112 switches the pulse signals PWM0 to PWM2 to L before the signal voltage is written to the liquid crystal pixel group in the row corresponding to the backlights 211a to 211c. Specifically, the timing at which the signal voltage is written to the liquid crystal pixel group in the row corresponding to each backlight 211a to 211c is detected using the vertical synchronization signal and the horizontal synchronization signal, and each backlight is detected by the detected timing. The pulse signals PWM0 to PWM2 corresponding to 211a to 211c are switched to L.

  Accordingly, each of the backlights 211a to 211c is turned off before the signal voltage is written to the liquid crystal pixel group in the row corresponding to the backlights 211a to 211c. Therefore, it is possible to suppress the double image due to the backlight 211 being lit when the signal voltage is written.

  The voltage switching circuit 120 is an example of a voltage generation unit in the present invention, and generates a first voltage when the adjustment value is higher than the threshold value, and generates a second voltage higher than the first voltage when the adjustment value is less than or equal to the threshold value. To do. Specifically, when the voltage switching pulse output from the SOC 111 is H, a first voltage (for example, 0.35 [V]) is generated. When the voltage switching pulse is L, a second voltage (for example, higher than the first voltage) (for example, 0.65 [V]). The detailed configuration of the voltage switching circuit 120 will be described later.

  Note that the first voltage and the second voltage are not limited to this. For example, the first voltage may be 0.40 [V], the second voltage may be 0.60 [V], or the first voltage may be 0. .45 [V] and the second voltage may be 0.55 [V], which are appropriately selected according to the usage environment and the operating environment of the liquid crystal display device 200 on which the backlight driving circuit 100 is mounted. May be.

  The backlight drivers 130 a to 130 c supply a driving current for lighting the backlights 211 a to 211 c to the backlight panel 210. Specifically, the backlight driver 130a corresponds to the backlight 211a, the backlight driver 130b corresponds to the backlight 211b, the backlight driver 130c corresponds to the backlight 211c, and the corresponding backlights 211a to 211a. A drive current is supplied to 211c. Hereinafter, the backlight drivers 130a to 130c may be referred to as the backlight driver 130 without being particularly distinguished.

  Each backlight driver 130 converts the first voltage generated by the voltage switching circuit 120 into a first current, converts the second voltage into a second current, and the timing instruction unit 110 indicates the converted current. During the lighting period of the backlight 211, it supplies to each backlight 211 as a drive current.

  Specifically, the backlight driver 130a converts the voltage generated by the voltage switching circuit 120 into a current, and uses the converted current as the drive current of the backlight 211a during the H period of the pulse signal PWM0 input from the TCON 112. The light is supplied to the backlight 211a. On the other hand, during the L period of the pulse signal PWM0, the supply of the drive current to the backlight 211a is stopped. That is, the backlight 211a is turned on during the H period of the pulse signal PWM0, and the backlight 211a is turned off during the L period of the pulse signal PWM0.

  Similarly, the backlight driver 130b converts the voltage generated by the voltage switching circuit 120 into a current, and uses the converted current as the drive current of the backlight 211b during the H period of the pulse signal PWM1 input from the TCON 112. Supply to the light 211b. On the other hand, during the L period of the pulse signal PWM1, the supply of the drive current to the backlight 211b is stopped. That is, the backlight 211b is turned on during the H period of the pulse signal PWM1, and the backlight 211b is turned off during the L period of the pulse signal PWM1.

  Similarly, the backlight driver 130c converts the voltage generated by the voltage switching circuit 120 into a current, and uses the converted current as the drive current of the backlight 211c during the H period of the pulse signal PWM2 input from the TCON 112. Supply to the light 211c. On the other hand, during the L period of the pulse signal PWM2, the supply of the drive current to the backlight 211c is stopped. That is, the backlight 211c is turned on during the H period of the pulse signal PWM2, and the backlight 211c is turned off during the L period of the pulse signal PWM2.

  Here, as described above, the voltage generated by the voltage switching circuit 120 is the first voltage (for example, 0.35 [V]) when the voltage switching pulse is H, and the first voltage when the voltage switching pulse is L. The second voltage is higher (for example, 0.65 [V]). That is, when the adjustment value indicating the luminance of the backlight panel 210 is higher than a threshold value (for example, 10), it is the first voltage (for example, 0.35 [V]). 0.65 [V]).

  Therefore, the currents supplied to the backlights 211a to 211c corresponding to the H periods of the pulse signals PWM0 to PWM2 corresponding to the backlight drivers 130a to 130c are switched according to the adjustment value. Specifically, when the adjustment value is higher than the threshold value, a first current (for example, 350 [mA]) corresponding to the first voltage is supplied, and when the adjustment value is equal to or lower than the threshold value, the second current corresponding to the second voltage is supplied. (For example, 650 [mA]) is supplied.

  As a result, the backlights 211a to 211c emit light by the first current during the high period of the pulse signals PWM0 to PWM2 when the adjustment value is higher than the threshold value, and the pulse signal PWM0 when the adjustment value is equal to or less than the threshold value. During the high period of ~ PWM2, light is emitted by the second current.

  Therefore, in the liquid crystal display device 200 on which the backlight driving circuit 100 according to the present embodiment is mounted, when the adjustment value is equal to or less than the threshold value, the H period of the pulse signals PWM0 to PWM2 is related to Comparative Example 1 and Comparative Example 2. Even if it becomes shorter than the duty ratio of the liquid crystal display device, the luminance of the backlight panel 210 equivalent to that of the liquid crystal display devices according to the comparative example 1 and the comparative example 2 can be realized.

  That is, when the adjustment value is equal to or smaller than the threshold value, lighting of the backlights 211a to 211c can be made closer to impulse-type lighting. Therefore, moving image blur can be improved.

[Detailed configuration of voltage switching circuit]
Next, a detailed configuration of the voltage switching circuit 120 in the present embodiment will be described. FIG. 3 is a circuit diagram illustrating an example of a detailed configuration of the voltage switching circuit 120.

  The voltage switching circuit 120 includes resistors R11 and R12, a capacitor C11, and a transistor Q11.

  The capacitor C11 is a capacitive element for removing noise.

  The transistor Q11 has an emitter grounded, a collector connected to each of the backlight drivers 130a to 130c via the resistor R12, and a voltage switching pulse output from the SOC 111 via the resistor R11 is input to the base. Therefore, when the voltage switching pulse is H, the collector of the transistor Q11 is L voltage (ground potential), and when the voltage switching pulse is L, the collector of the transistor Q11 is H voltage. That is, the transistor Q11 is an inverting circuit that inverts the input voltage switching pulse.

  The resistor R12 is a voltage dividing resistor that is inserted between the collector of the transistor Q11 and the backlight drivers 130a to 130c and determines the H voltage and the L voltage output from the voltage switching circuit 120. That is, the voltage of the terminal of the resistor R12 that is not connected to the collector of the transistor Q11 is the voltage output from the voltage switching circuit 120. Specifically, when the collector of the transistor Q11 is L voltage, the output voltage of the voltage switching circuit 120 is a predetermined voltage determined by a circuit provided between the voltage switching circuit 120 and the backlight drivers 130a to 130c. The voltage is divided by the resistor R12. On the other hand, when the collector of the transistor Q11 is at the H voltage, the output voltage of the voltage switching circuit 120 is a predetermined voltage itself determined by a circuit provided between the voltage switching circuit 120 and the backlight drivers 130a to 130c. Thus, the output voltage of the voltage switching circuit 120 is the first voltage, which is a voltage obtained by dividing the predetermined voltage when the collector of the transistor Q11 is the L voltage, and the predetermined voltage when the collector of the transistor Q11 is the H voltage. Is the second voltage. That is, the second voltage is higher than the first voltage.

  Therefore, the voltage switching circuit 120 generates a first voltage when the voltage switching pulse is H, and generates a second voltage higher than the first voltage when the voltage switching pulse is L. That is, when the adjustment value is higher than the threshold value, the first voltage is generated, and when the adjustment value is lower than the threshold value, the second voltage higher than the first voltage is generated.

  As described above, the backlight driving circuit 100 according to the present embodiment increases the lighting duty ratio of each backlight 211 as the adjustment value indicating the luminance of the backlight increases, and the signal voltage to the liquid crystal pixel group is increased. Each backlight 211 is turned off before writing. Here, the backlight driving circuit 100 supplies the first current in the lighting period of the backlight 211 when the adjustment value exceeds the threshold value, and in the lighting period of the backlight 211 when the adjustment value is equal to or less than the threshold value. A second current having a larger current amount than the first current is supplied. When the adjustment value exceeds the threshold value, the lighting duty ratio of each backlight 211 is set as a normal duty ratio. When the adjustment value is equal to or less than the threshold value, the lighting duty ratio of each backlight 211 is set smaller than the normal duty ratio.

  Here, the normal duty ratio is a duty ratio necessary for obtaining the luminance of the backlight 211 corresponding to the adjustment value by supplying the first current to the backlight 211 as described above.

<1-2. Operation>
Next, the operation of the liquid crystal display device 200 in the present embodiment will be described with reference to the drawings.

  FIG. 4 is a timing chart schematically showing the lighting and extinguishing timings of the backlight panel 210 and the signal voltage writing timing to the liquid crystal panel 220.

  In FIG. 4, in order from the top, the backlight adjustment pulse, the vertical synchronization signal STV, the pulse signal PWM0 corresponding to the backlight 211a, and the signal voltage to the liquid crystal pixels 221 in the pixel row corresponding to the backlight 211a. Rewrite timing, pulse signal PWM1 corresponding to the backlight 211b, signal voltage rewrite timing to the liquid crystal pixels 221 in the pixel row corresponding to the backlight 211b, pulse signal PWM2 corresponding to the backlight 211c, and The rewrite timing of the signal voltage to the liquid crystal pixel 221 in the pixel row corresponding to the backlight 211c is schematically shown.

  As shown in the figure, the backlight adjustment pulse generated by the SOC 111 and the pulse signals PWM0 to PWM2 have the same duty ratio. Specifically, the pulse signals PWM <b> 0 to PWM <b> 2 are signals obtained by delaying a pulse signal having the same duty ratio as the backlight adjustment pulse by shifting by a predetermined time within one display period.

  First, when the vertical synchronization signal STV rises at time t0, signal voltage writing is started in a row sequential manner for each liquid crystal pixel 221 on the liquid crystal panel 220 corresponding to the backlight 211a. At this time, the pulse signal PWM0 is L until time t0. In other words, the backlight driving circuit 100 turns off the backlight 211 a corresponding to the upper part of the liquid crystal panel 220 until writing is started for each liquid crystal pixel 221 on the upper part of the liquid crystal panel 220.

  Thereafter, the signal voltage is written to each liquid crystal pixel 221 above the liquid crystal panel 220 until time t1. Here, the time required from the writing of the signal voltage to the liquid crystal pixel 221 to the transmission of the amount of light corresponding to the written signal voltage of the liquid crystal pixel is defined as a response speed Trs. This response speed is determined by the configuration and material of each liquid crystal pixel 221. Therefore, each liquid crystal pixel 221 transmits a light amount corresponding to the written signal voltage after Trs has elapsed since the signal voltage was written.

  At time t0, the pulse signal PWM1 rises to H. That is, the backlight drive circuit 100 switches the backlight 211b corresponding to the central part of the liquid crystal panel 220 from turning off to turning on. Therefore, an image corresponding to the signal voltage written in the previous frame is displayed at the center of the liquid crystal panel 220.

  Thereafter, until just before time t1, the backlight driving circuit 100 lights the backlight 211b. Therefore, an image corresponding to the signal voltage written in the previous frame is displayed at the center of the liquid crystal panel 220 until just before time t0 to t1.

  Next, at time t1, signal voltage writing is started in a row sequential manner for each liquid crystal pixel 221 in the central portion of the liquid crystal panel 220 corresponding to the backlight 211b. At this time, the pulse signal PWM1 is L just before time t1. In other words, the backlight driving circuit 100 turns off the backlight 211b corresponding to the central portion of the liquid crystal panel 220 until writing is started for each liquid crystal pixel 221 in the central portion of the liquid crystal panel 220. Thereafter, the signal voltage is written to each liquid crystal pixel 221 in the central portion of the liquid crystal panel 220 until time t2.

  At time t1, the pulse signal PWM2 rises to H. That is, the backlight drive circuit 100 switches the backlight 211c corresponding to the lower part of the liquid crystal panel 220 from turning off to turning on. Therefore, an image corresponding to the signal voltage written in the previous frame is displayed below the liquid crystal panel 220.

  Thereafter, until just before time t2, the backlight drive circuit 100 lights the backlight 211c. Therefore, an image corresponding to the signal voltage written in the previous frame is displayed at the lower part of the liquid crystal panel 220 until just before time t0 to t1.

  Next, at time t2, signal voltage writing is started in a row sequential manner for each liquid crystal pixel 221 below the liquid crystal panel 220 corresponding to the backlight 211c. At this time, the pulse signal PWM2 is L immediately before time t2. That is, the backlight driving circuit 100 turns off the backlight 211c corresponding to the lower part of the liquid crystal panel 220 until writing is started for each liquid crystal pixel 221 below the liquid crystal panel 220. Thereafter, the signal voltage is written to each liquid crystal pixel 221 below the liquid crystal panel 220 until time t4.

  Next, at time t3, the pulse signal PWM0 rises to H. That is, the backlight drive circuit 100 switches the backlight 211a corresponding to the upper part of the liquid crystal panel 220 from turning off to turning on. Therefore, an image corresponding to the signal voltage written immediately before (time t0 to t1) is displayed on the upper part of the liquid crystal panel 220.

  Thereafter, until just before time t5, the backlight drive circuit 100 lights the backlight 211a. Therefore, an image corresponding to the signal voltage written in the previous frame is displayed at the lower part of the liquid crystal panel 220 until just before time t3 to t5.

  Thereafter, at time t5, the vertical synchronization signal STV rises in the same manner as at time t0, and thereafter, the above operation is repeated. That is, the times t0 to t5 are one frame period (1 frame) of the liquid crystal panel 220.

  Here, time t4 to t5 is a vertical blanking period (Blank period), and time t3 is a time after the vertical blanking period has elapsed from time t2. Therefore, the lighting period of the backlight 211a (time t3 to t5), the lighting period of the backlight 211b (time t0 to t1), and the lighting period of the backlight 211c (time t1 to t2) are Are the same.

  As described above, the liquid crystal display device 200 on which the backlight driving circuit 100 according to the present embodiment is mounted has a signal voltage to the liquid crystal pixel group on the liquid crystal panel 220 corresponding to the backlight 211a at time t0 (= t5). Is written before the backlight 211a is turned off. Further, the backlight 211b is turned off before the signal voltage is written to the liquid crystal pixel group in the central portion of the liquid crystal panel 220 corresponding to the backlight 211b at time t1. Furthermore, the backlight 211c is turned off before the signal voltage is written to the liquid crystal pixel group below the liquid crystal panel 220 corresponding to the backlight 211c at time t3.

  As a result, it is possible to suppress double copying when the signal voltage is rewritten. Further, by turning off the corresponding backlights 211a to 211c during the response period of the liquid crystal pixel 221, the moving image blur during the response period of the liquid crystal pixel 221 can also be suppressed.

  In the above description, the lighting periods of the backlights 211a to 211c do not overlap, but the lighting periods of the backlights 211a to 211c are not limited to this. For example, the lighting start times of the backlights 211a to 211c may be advanced by advancing the rising edges of the pulse signals PWM0 to PWM2 as indicated by the dotted lines in FIG. Accordingly, a long lighting period can be secured for each of the backlights 211a to 211c in one frame period, and the same luminance can be secured even if the current per unit time supplied to each of the 211a to 211c is reduced. it can. Here, when the rise of each of the pulse signals PWM0 to PWM2 is advanced, the rise of the pulse signals PWM0 to PWM2 is prevented from overlapping with the writing period and the response period of the liquid crystal pixel group corresponding to the pulse signals PWM0 to PWM2. As a result, the above-described effects can be obtained. That is, it is possible to suppress double image capturing at the time of rewriting the signal voltage and during the response period of the liquid crystal pixel 221.

<1-3. Effect>
As described above, in the backlight drive circuit 100 according to the present embodiment, the drive current supplied during the period in which each backlight 211 is lit is the first current when the adjustment value is higher than the threshold value. The second current is higher than the first current when it is equal to or less than the threshold value. The lighting duty ratio is a normal duty ratio when the adjustment value is higher than the threshold value, and is smaller than the normal duty ratio when the adjustment value is lower than the threshold value. Hereinafter, the drive current during the lighting period of the backlight 211 and the lighting duty ratio of the backlight 211 will be described with reference to FIGS. 5 and 6.

  FIG. 5 is a graph showing the drive current during the lighting period of the backlight 211 with respect to the adjustment value. In the drawing, the driving current supplied to the backlight 211 in the first embodiment and the driving current supplied to the backlight in the above-described comparative example 2 are shown.

  As shown in the figure, in Comparative Example 2, the drive current supplied to the backlight is always a constant current of 350 [mA] (first current) regardless of the adjustment value. On the other hand, the backlight drive circuit 100 according to the present embodiment applies 350 [mA] as the first current to the backlight 211 when the adjustment value is higher than the threshold value of 10, as in Comparative Example 2. When the adjustment value is equal to or less than the threshold value, 650 [mA], which is a second current having a current value higher than the first current, is supplied to the backlight 211.

  The first current and the second current may be determined as follows. That is, when the backlight 211 is configured by an LED, the rated current that can flow through the backlight 211 varies depending on the lighting duty ratio, and the rated current increases as the lighting duty ratio decreases. Therefore, the rated current of the LED when the lighting duty ratio is 100% may be the first current, and the rated current of the LED when the lighting duty ratio is 33% may be the second current.

  FIG. 6 is a graph showing the lighting duty ratio of the backlight 211 with respect to the adjustment value.

  As shown in the figure, in Comparative Example 2, the lighting duty ratio of the backlight 211 corresponds linearly to the adjustment value. On the other hand, the lighting duty ratio of the backlight 211 by the backlight driving circuit 100 according to the present embodiment is the same duty ratio as in the comparative example 2 when the adjustment value is higher than the threshold value of 10. On the other hand, when the adjustment value is less than or equal to the threshold value, the duty ratio is about half of the duty ratio of Comparative Example 2.

  Thereby, in the liquid crystal display device 200 according to the present embodiment, when the adjustment value is 10 or less, it is possible to suppress the moving image blur and the double shot more than the liquid crystal display device according to the comparative example 2. For this reason, the liquid crystal according to Comparative Example 2 in the case where the backlight 211 has a three-stage configuration and the response speed of the liquid crystal pixel 221 is (1/3) Vs which is 1/3 of Vs in one vertical scanning period. The adjustment value region in which the scan effect of the display device appears and the adjustment value region in which the scan effect of the liquid crystal display device 200 in this embodiment appears will be described with reference to FIG. Note that the scan effect refers to suppressing double image capturing by sequentially turning on and off the plurality of backlights 211.

  In both the liquid crystal display device according to the comparative example 2 and the liquid crystal display device 200 in the present embodiment, in order to obtain a scanning effect, it is necessary to write a signal voltage to the liquid crystal pixel group corresponding to each backlight. It is necessary not to turn on the backlight between the time and the response period of the liquid crystal pixel 221 in which the signal voltage is written. Here, the time required to write the signal voltage to the liquid crystal pixel 221 in the row corresponding to one backlight 211 is about (1/3) Vs as described above, and the response speed of the liquid crystal pixel 221 is also (1 / 3) Vs. Therefore, in both the liquid crystal display device according to the comparative example 2 and the liquid crystal display device 200 in the present embodiment, in order to obtain a scanning effect, the time required for writing the signal voltage from one vertical scanning period and the liquid crystal It is necessary to turn on the backlight during a period excluding the response speed of the pixel 221. That is, the scanning effect can be obtained when the backlight lighting period is (1/3) Vs, that is, when the adjustment value is such that the backlight lighting duty ratio is 33% or less.

  Here, an adjustment value that can reduce the lighting duty ratio of the backlight to 33% or less is confirmed with reference to FIG.

  As shown in FIG. 6, in the liquid crystal display device according to Comparative Example 2, only 0, 1, and 2 are adjustment values that can make the backlight lighting duty ratio 33% or less, and other adjustment values (adjustment values). 3 or more), the lighting duty ratio of the backlight is higher than 33%, so that it is difficult to obtain a scanning effect. That is, in the liquid crystal display device according to Comparative Example 2, it is possible to obtain a scanning effect only in the regions where the adjustment values are 0, 1, and 2.

  On the other hand, in the liquid crystal display device 200 according to the present embodiment, the adjustment value that can reduce the lighting duty ratio of the backlight to 33% or less is 0 to 10. That is, in the liquid crystal display device 200 according to the present embodiment, a scanning effect can be obtained in a region where the adjustment value is 10 or less. Therefore, compared with the liquid crystal display device according to Comparative Example 2, it is possible to obtain a scanning effect even in a region where the adjustment value is large. That is, even when the backlight 211 emits light with high luminance from the liquid crystal display device according to the comparative example 2, it is possible to obtain a scanning effect.

  Thus, the backlight drive circuit 100 according to Embodiment 1 of the present invention uses the drive current supplied to the backlight 211 as the first current when the adjustment value is equal to or greater than the threshold value, and the first current when the adjustment value is equal to or less than the threshold value. A higher second current is assumed. Further, the lighting duty ratio of the backlight 211 is set to a normal duty ratio when the adjustment value is higher than the threshold value, and is set to be smaller than the normal duty ratio when the adjustment value is lower than the threshold value. Therefore, even when the brightness of the backlight panel 210 is high, moving image blur can be suppressed.

  Further, the backlight drive circuit 100 according to Embodiment 1 of the present invention turns off the backlight 211 before the signal voltage is written to the liquid crystal pixel group in the row corresponding to each backlight 211. Therefore, when the signal voltage is written to the liquid crystal pixel 221, it is possible to suppress the double image due to the backlight 211 corresponding to the liquid crystal pixel 221 being lit.

  FIG. 7 shows, as a comparative example of the first embodiment, the lighting and extinguishing timing of the backlight panel when the backlight corresponding to the liquid crystal pixel is turned on when the signal voltage is written to the liquid crystal pixel, 4 is a timing chart schematically showing signal voltage write timing.

  As shown in the figure, when the scanning order of turning on and off the backlight panel is different from the scanning order of writing the signal voltage to the liquid crystal panel, the liquid crystal pixel is applied when the signal voltage is written to the liquid crystal pixel. The corresponding backlight may turn on.

  Therefore, like the backlight drive circuit 100 according to Embodiment 1 of the present invention, the scanning order of turning on and off the backlight panel 210 and the scanning order of writing the signal voltage to the liquid crystal panel 220 are made to coincide. It is important to turn off the backlight 211 before the signal voltage is written to the liquid crystal pixel group in the row corresponding to each backlight 211, in order to suppress double image capturing.

  In FIG. 4, scanning for turning on and off the backlight panel 210 and scanning for writing a signal voltage to the liquid crystal panel 220 are performed from the upper side to the lower side of the backlight panel 210 and the liquid crystal panel 220. Although scanning (normal scanning) is used, reverse scanning (reverse scanning) performed from the bottom to the top as shown in FIG. 8 may be used.

  Further, the backlight drive circuit 100 according to Embodiment 1 of the present invention further supplies a drive current to the backlight 211 corresponding to the liquid crystal pixel 221 in the response period of the liquid crystal pixel 221 in which the signal voltage is rewritten. Has stopped. That is, the backlight 211 is turned off. Therefore, it is possible to suppress double image capturing due to the backlight 211 corresponding to the liquid crystal pixel 221 being lit during the response period of the liquid crystal pixel 221.

  In the above description, the backlight driving circuit 100 stops supplying the driving current to the backlight 211 corresponding to the liquid crystal pixel 221 during the response period of the liquid crystal pixel 221 in which the signal voltage is rewritten. The drive circuit 100 may supply a drive current to the backlight 211 corresponding to the liquid crystal pixel 221 during the response period of the liquid crystal pixel 221 in which the signal voltage is rewritten. The reason is described below.

  The liquid crystal pixel 221 whose signal voltage has been rewritten changes its transmission amount rapidly immediately after the rewriting, but the subsequent change in transmission amount is gradual. Therefore, in the response period of the liquid crystal pixel 221 in which the signal voltage is rewritten, even when the backlight 211 is turned on by supplying a drive current to the backlight 211 in a period after the change in the transmission amount becomes moderate. , Video blur is not noticeable. Therefore, the backlight drive circuit 100 may supply a drive current to the backlight 211 corresponding to the liquid crystal pixel 221 during the response period of the liquid crystal pixel 221 in which the signal voltage is rewritten.

  Next, the light emission characteristics of the backlight panel 210 to which the backlight drive circuit 100 according to Embodiment 1 of the present invention is connected will be described with reference to FIGS.

  FIG. 9 is a table showing the lighting duty ratio, the drive current, and the light emission luminance of the backlight panel 210 when the adjustment value is changed. This table also shows the lighting duty ratio, drive current, and light emission luminance of the backlight panel in the liquid crystal display device according to Comparative Example 2.

  As shown in the table of the figure, the backlight panel 210 to which the backlight driving circuit 100 according to the present embodiment is connected has an adjustment value compared to the backlight panel in the liquid crystal display device according to the comparative example 2. In the case of 10 or less, the lighting duty ratio is about ½ times and the drive current is about twice. As a result, the luminance of the backlight panel 210 is equal to the luminance of the backlight panel in the liquid crystal display device according to Comparative Example 2. FIG. 10 is a graph showing the light emission luminance with respect to the adjustment value shown in FIG.

  That is, the backlight panel 210 to which the backlight driving circuit 100 according to the present embodiment is connected has a lighting duty ratio smaller than that of the backlight panel in the liquid crystal display device according to the comparative example 2 when the adjustment value is 10 or less. Thus, the liquid crystal display device according to Comparative Example 2 can be lit with the same brightness as the backlight panel. In other words, when the adjustment value is 10 or less, the backlight panel 210 can be lit at a lighting duty ratio closer to the impulse response than the backlight panel in the liquid crystal display device according to the comparative example 2.

  As described above, the backlight panel 210 has a lighting duty ratio of approximately ½ times and the backlight driving when the adjustment value is 10 or less, as compared with the backlight panel in the liquid crystal display device according to the comparative example 2. By doubling the current, a luminance equivalent to that of the backlight panel in the liquid crystal display device according to Comparative Example 2 can be realized.

  FIG. 11 is a graph showing the chromaticity of the backlight panel 210 when the adjustment value is changed in this embodiment, and (a) shows the chromaticity of the backlight panel 210 in the xy chromaticity diagram. (B) is a partially enlarged view of (a).

  As shown in the figure, the backlight panel 210 has substantially the same chromaticity even when the adjustment value is changed. That is, there is almost no chromaticity difference.

  Thus, the light emission characteristics of the backlight panel 210 to which the backlight drive circuit 100 according to Embodiment 1 of the present invention is connected are equivalent to the light emission characteristics of the backlight panel in the liquid crystal display device according to Comparative Example 2. it can. That is, the backlight panel 210 to which the backlight driving circuit 100 according to the present embodiment is connected has a lighting duty ratio smaller than that of the backlight panel in the liquid crystal display device according to the comparative example 2 when the adjustment value is 10 or less. Thus, light emission characteristics equivalent to those of the backlight panel in the liquid crystal display device according to Comparative Example 2 can be realized. In other words, it is possible to illuminate with a lighting duty ratio closer to the impulse response than the backlight panel in the liquid crystal display device according to Comparative Example 2. Thereby, moving image blur can be suppressed.

  In addition, the backlight drive circuit 100 according to Embodiment 1 of the present invention generates a first voltage when the adjustment value is higher than the threshold value, and generates a second voltage higher than the first voltage when the adjustment value is less than or equal to the threshold value. A voltage switching circuit 120 (voltage generation unit) to be generated, and a backlight that converts the first voltage generated by the voltage switching circuit 120 into a first current, converts the second voltage into a second current, and supplies the second current as a drive current And a driver 130. As a result, the current can be switched between two stages with a simple configuration.

(Modification of Embodiment 1)
Next, a backlight drive circuit according to a modification of the first embodiment of the present invention will be described.

  In the backlight drive circuit 100 according to the first embodiment, the SOC 111 and the TCON 112 are used to generate the pulse signals PWM0 to PWM2 corresponding to the backlight drivers 130a to 130c. However, the SOC is a pulse signal without using the TCON112. PWM0 to PWM2 may be configured.

  FIG. 12 is a block diagram showing a detailed configuration of a backlight drive circuit 300 according to a modification of the first embodiment.

  The backlight drive circuit 300 shown in the figure is substantially the same as the backlight drive circuit 100 according to the first embodiment, except that it includes a timing instruction unit 310 composed of an SOC 311 instead of the timing instruction unit 110.

  The SOC 311 has functions of the SOC 111 and the TCON 112. That is, based on the signal indicating the input adjustment value, three pulse signals PWM0 to PWM2 that are synchronized with the vertical synchronization signal are generated. Further, a voltage switching pulse that is H when the adjustment value indicating the luminance of the backlight panel 210 is higher than a threshold value (for example, 10) and becomes L when the adjustment value is lower than the threshold value is generated and output to the voltage switching circuit 120.

  The backlight drive circuit 300 according to the modification of the first embodiment also has the same effect as that of the first embodiment. That is, even when the adjustment value is high, it is possible to suppress the moving image blur and the double image more than the liquid crystal display device according to the comparative example 2.

(Embodiment 2)
Next, a second embodiment of the present invention will be described. The backlight drive circuit according to the present embodiment is substantially the same as the backlight drive circuit 100 according to the first embodiment, but the drive current is increased steplessly as the adjustment value decreases. Different. Thereby, the backlight drive circuit according to the present embodiment can achieve the same effects as the backlight drive circuit 100 according to the first embodiment and can suppress flicker.

  Hereinafter, the backlight driving circuit according to the second embodiment of the present invention will be described focusing on differences from the backlight driving circuit 100 according to the first embodiment.

<2-1. Configuration>
[Detailed configuration of backlight drive circuit]
FIG. 13 is a block diagram showing a detailed configuration of the backlight drive circuit 400 according to Embodiment 2 of the present invention.

  In the figure, the backlight drive circuit 400 includes a timing instruction unit 410 instead of the timing instruction unit 110 and a D / A conversion unit 420 instead of the voltage switching circuit 120, as compared with the backlight drive circuit 100 shown in FIG. The point to prepare is different. In the figure, a backlight panel 210 to which a drive current is supplied from the backlight drivers 130a to 130c is also illustrated.

  Compared to the timing instruction unit 110 in the first embodiment, the timing instruction unit 410 includes an SOC 411 instead of the SOC 111, and the timing of turning on and off each backlight 211 is set so that the lighting period becomes longer as the adjustment value is higher. Instruct.

  The SOC 411 generates a backlight adjustment pulse having a duty ratio corresponding to an adjustment value indicating the luminance of the backlight panel 210, similar to the SOC 111. In addition, the SOC 411 outputs this backlight adjustment pulse to the D / A conversion unit 420.

  Here, when the adjustment value indicating the brightness of the backlight panel 210 is a maximum value (for example, 20), the SOC 411 uses the normal duty ratio as the duty ratio of the backlight adjustment pulse. The duty ratio of the backlight adjustment pulse is made smaller than the normal duty ratio. Note that the normal duty ratio is a duty ratio necessary for obtaining the luminance of the backlight 211 corresponding to the adjustment value by supplying a minimum current described later to the backlight 211.

  The D / A converter 420 is an example of a voltage generator in the present invention, and generates a higher voltage as the adjustment value is lower. Specifically, a lower voltage is generated as the duty ratio of the backlight adjustment pulse output from the SOC 411 is larger, and a higher voltage is generated as the duty ratio of the backlight adjustment pulse is smaller. The maximum voltage generated by the D / A converter is, for example, 0.95 [V], and the minimum voltage is, for example, 0.35 [V].

  Specifically, the D / A converter 420 performs DA (digital-analog) conversion on the duty ratio of the backlight adjustment pulse input from the SOC 411, so that the smaller the duty ratio of the backlight adjustment pulse, the lower the analog voltage. And an inversion circuit for generating a higher voltage as the duty ratio of the backlight adjustment pulse is smaller by inverting the voltage level of the analog voltage generated by the DA converter.

  Therefore, the drive current supplied from the backlight drivers 130a to 130c to the backlights 211a to 211c corresponding to the H periods of the corresponding pulse signals PWM0 to PWM2 switches steplessly according to the adjustment value. Specifically, a larger current is supplied as the adjustment value is higher, and a smaller current is supplied as the adjustment value is lower. For example, when the adjustment value changes by 1 from 0 to 20, a minimum current (350 [mA]) is supplied when the adjustment value is the maximum value 20, and a maximum current (930 [mA] when the adjustment value is the minimum value 0. ]).

  As a result, the backlights 211a to 211c emit light with a low current in the high period of the pulse signals PWM0 to PWM2 as the adjustment value is high, and emit light with a large current in the high period of the pulse signals PWM0 to PWM2 as the adjustment value is low. To do.

  Therefore, in the liquid crystal display device on which the backlight drive circuit 400 according to the present embodiment is mounted, when the adjustment value is other than the maximum value, the H period of the pulse signals PWM0 to PWM2 is related to Comparative Example 1 and Comparative Example 2. Even if it becomes shorter than the duty ratio of the liquid crystal display device, the luminance of the backlight panel 210 equivalent to that of the liquid crystal display devices according to the comparative example 1 and the comparative example 2 can be realized. That is, when the adjustment value is other than the maximum value, the lighting of the backlights 211a to 211c can be brought close to the impulse response. Therefore, moving image blur can be improved.

  Moreover, in the backlight drive circuit 100 according to Embodiment 1, the first current is supplied when the adjustment value is higher than the threshold value, and the second current is supplied when the adjustment value is lower than the threshold value. When the value is changed, the current supplied to the backlight 211 is largely switched, and flicker may occur.

  On the other hand, in the backlight drive circuit 400 according to the present embodiment, the higher the adjustment value, the larger current is supplied, and the lower the adjustment value, the smaller current is supplied to the backlights 211a to 211c. The current to be switched is steplessly changed according to the adjustment value. As a result, even if the adjustment value is changed, the current supplied to the backlight 211 is rarely switched.

  Therefore, the backlight drive circuit 400 according to the present embodiment can suppress flicker compared to the backlight drive circuit 100 according to the first embodiment.

[Detailed Configuration of D / A Converter]
Next, a detailed configuration of D / A conversion section 420 in the present embodiment will be described. FIG. 14 is a circuit diagram illustrating an example of a detailed configuration of the D / A conversion unit 420.

  The D / A conversion unit 420 includes resistors R21 to R25, capacitors C21 to C23, and a transistor Q21.

  The capacitor C21 is a capacitive element for removing noise.

  The transistor Q21 has an emitter grounded, a collector connected to each of the backlight drivers 130a to 130c via resistors R22 and R24, and a duty ratio of a backlight adjustment pulse output from the SOC 411 via the resistor R21 to the base. A voltage corresponding to is input. Therefore, as the voltage input to the base is higher, the current flowing between the collector and emitter of the transistor Q21 increases, and the voltage at the connection point of the resistors R22, R23, and R24 decreases. Therefore, the voltage supplied to the backlight drivers 130a to 130c decreases. On the other hand, as the voltage input to the base is lower, the current flowing between the collector and the emitter of the transistor Q21 decreases, and the voltage at the connection point of the resistors R22, R23, R24 increases. Therefore, the voltage supplied to the backlight drivers 130a to 130c increases. That is, the transistor Q21 is an inverting circuit that inverts the voltage.

  Further, the transistor Q21, the resistors R22 to R25, and the capacitors C22 and C23 constitute an RC integrating circuit. This RC integration circuit passes a frequency component equal to or lower than a frequency corresponding to a time constant determined by the transistor Q21, resistors R22 to R25, and capacitors C22 and C23. That is, the RC integration circuit is a low-pass filter.

  Here, since the backlight adjustment pulse output from the SOC 411 is a pulse whose duty ratio is higher as the adjustment value of the backlight panel is higher, the pulse output from the inverting circuit is the adjustment value of the backlight panel. The higher the value, the lower the duty ratio. For this reason, the voltage of the signal that has passed through the RC integration circuit decreases as the duty ratio increases. That is, the higher the backlight panel adjustment value, the lower the value.

  More specifically, the higher the adjustment value of the backlight panel and the higher the duty ratio of the voltage input to the base of the transistor Q21, the higher the duty ratio of the current flowing between the collector and emitter of the transistor Q21, and the resistors R22 to R24. The duty ratio of the voltage at the connection point becomes low. Therefore, the higher the duty ratio of the voltage input to the base of the transistor Q21 (the higher the adjustment value of the backlight panel), the lower the duty ratio of the voltage supplied from the backlight drivers 130a to 130c.

  On the other hand, the pulse output from the inverting circuit becomes a pulse with a higher duty ratio as the adjustment value of the backlight panel is lower. For this reason, the voltage of the signal that has passed through the RC integration circuit increases as the duty ratio decreases. That is, the lower the adjustment value of the backlight panel, the higher the value.

  More specifically, the lower the adjustment value of the backlight panel and the lower the duty ratio of the voltage input to the base of the transistor Q21, the lower the duty ratio of the current flowing between the collector and emitter of the transistor Q21, and the resistors R22 to R24. The duty ratio of the voltage at the connection point becomes higher. Therefore, the lower the duty ratio of the voltage input to the base of the transistor Q21 (the lower the adjustment value of the backlight panel), the higher the duty ratio of the voltage supplied from the backlight drivers 130a to 130c.

  Accordingly, the D / A conversion unit 420 outputs a lower voltage as the duty ratio of the backlight adjustment pulse is higher, and outputs a higher voltage as the duty ratio of the backlight adjustment pulse is lower. That is, the higher the adjustment value, the lower the voltage is generated, and the lower the adjustment value, the higher the voltage.

<2-2. Effect>
As described above, in the backlight drive circuit 400 according to this embodiment, the drive current during the period in which each backlight 211 is lit is smaller as the adjustment value is higher, and the current is lower as the adjustment value is lower. It is. The lighting duty ratio is a normal duty ratio when the adjustment value is the maximum value, and is smaller than the normal duty ratio when the adjustment value is other than the maximum value. Hereinafter, the drive current during the lighting period of the backlight 211 and the lighting duty ratio of the backlight 211 will be described with reference to FIGS. 15 and 16.

  FIG. 15 is a graph showing the drive current during the lighting period of the backlight 211 with respect to the adjustment value. In the drawing, the driving current supplied to the backlight 211 in the second embodiment and the driving current supplied to the backlight in the above-described comparative example 2 are shown.

  As shown in the figure, in Comparative Example 2, the drive current supplied to the backlight is always a constant current of 350 [mA] regardless of the adjustment value. On the other hand, when the adjustment value is the maximum value 20, the backlight drive circuit 400 according to the present embodiment supplies 350 [mA] to the backlight 211 as in the comparative example 2, and the adjustment value is low. Indeed, a large current is supplied. Specifically, the minimum current (350 [mA]) is supplied when the adjustment value is the maximum value 20, and the maximum current (930 [mA]) is supplied when the adjustment value is the minimum value 0.

  The current value of the drive current may be determined as follows. That is, when the backlight 211 is configured by an LED, the rated current that can flow through the backlight 211 varies depending on the lighting duty ratio, and the rated current increases as the lighting duty ratio decreases. Therefore, the rated current corresponding to the minimum lighting duty ratio among the combinations of the lighting duty ratio and the rated current capable of realizing the luminance corresponding to the adjustment value may be set as the current value of the drive current.

  Thus, in the backlight drive circuit 400 according to the second embodiment, the drive current supplied to the backlight 211 switches steplessly according to the adjustment value. Thereby, the backlight drive circuit 400 according to the present embodiment can suppress flicker.

  Specifically, in the backlight drive circuit 100 according to the first embodiment, as illustrated in FIG. 5, when the adjustment value is switched from 10 to 11, the drive current supplied to the backlight 211 is 650. It changes from [mA] to 350 [mA]. The amount of change in current is as large as 300 [mA], and flicker may occur when the adjustment value is switched.

  On the other hand, in the backlight drive circuit 400 according to the second embodiment, when the adjustment value is switched from 10 to 11, the drive current supplied to the backlight 211 is about 640 [mA] to about 610. Change to [mA]. The amount of change in current is 30 [mA], which is sufficiently smaller than the amount of change in current in the backlight drive circuit 100 according to Embodiment 1. Therefore, the backlight drive circuit 400 according to the second embodiment can suppress flicker that occurs when the adjustment value is switched.

  FIG. 16 is a graph showing the lighting duty ratio of the backlight 211 with respect to the adjustment value.

  As shown in the figure, in Comparative Example 2, the lighting duty ratio of the backlight 211 corresponds linearly to the adjustment value. On the other hand, the lighting duty ratio of the backlight 211 by the backlight driving circuit 100 according to the present embodiment is the same as that of the comparative example 2 when the adjustment value is the maximum value 20. On the other hand, when the adjustment value is other than the maximum value, the duty ratio is smaller than that of Comparative Example 2.

  Thereby, the liquid crystal display device in which the backlight drive circuit 400 according to the present embodiment is mounted has the same effect as the liquid crystal display device in which the backlight drive circuit 100 according to the first embodiment is mounted. That is, when the adjustment value is 10 or less, it is possible to suppress the moving image blur and the double image more than the liquid crystal display device according to the comparative example 2.

  That is, also in the liquid crystal display device on which the backlight drive circuit 400 according to the present embodiment is mounted, the backlight lighting period can be (1/3) Vs, that is, the backlight lighting duty ratio can be 33% or less. In the case of such adjustment values, a scanning effect can be obtained.

  Here, an adjustment value that can reduce the lighting duty ratio of the backlight to 33% or less is confirmed with reference to FIG.

  As shown in FIG. 16, in the liquid crystal display device according to the comparative example 2, only 0, 1, and 2 are adjustment values that can reduce the lighting duty ratio of the backlight to 33% or less, and other adjustment values (adjustment values) 3 or more), the lighting duty ratio of the backlight is higher than 33%, so that it is difficult to obtain a scanning effect. That is, in the liquid crystal display device according to Comparative Example 2, it is possible to obtain a scanning effect only in the regions where the adjustment values are 0, 1, and 2.

  On the other hand, in the liquid crystal display device on which the backlight drive circuit 400 according to the present embodiment is mounted, the adjustment value that can reduce the lighting duty ratio of the backlight to 33% or less is 0 to 10. That is, similarly to the liquid crystal display device 200 in the first embodiment, a scan effect can be obtained in a region where the adjustment value is 10 or less. Therefore, compared with the liquid crystal display device according to Comparative Example 2, it is possible to obtain a scanning effect even in a region where the adjustment value is large. That is, the scanning effect can be obtained even when the backlight 211 emits light with high luminance from the liquid crystal display device according to the comparative example 2.

  As described above, in the backlight drive circuit 400 according to Embodiment 2 of the present invention, when the adjustment value is the maximum value, the drive current supplied to the backlight 211 is the normal current, and the backlight decreases as the adjustment value decreases. The drive current supplied to 211 is reduced. Further, the lighting duty ratio of the backlight 211 is set to a normal duty ratio when the adjustment value is the maximum value, and is smaller than the normal duty ratio when the adjustment value is other than the maximum value.

  Further, in the backlight drive circuit 400 according to the second embodiment, the drive current supplied to the backlight 211 switches steplessly according to the adjustment value. Thereby, the backlight drive circuit 400 according to the present embodiment can suppress flicker.

  Next, the light emission characteristics of the backlight panel 210 to which the backlight drive circuit 400 according to Embodiment 2 of the present invention is connected will be described with reference to FIGS.

  FIG. 17 is a table showing the lighting duty ratio, the drive current, and the light emission luminance of the backlight panel 210 when the adjustment value is changed. This table also shows the lighting duty ratio, drive current, and light emission luminance of the backlight panel in the liquid crystal display device according to Comparative Example 2.

  As shown in the table of the figure, the backlight panel 210 to which the backlight driving circuit 400 according to the present embodiment is connected has an adjustment value compared to the backlight panel in the liquid crystal display device according to the comparative example 2. In the case of the maximum value, the lighting duty ratio is the same and the drive current is almost the same. On the other hand, when the adjustment value is other than the maximum value, the lighting duty ratio is small, and the drive current is higher as the adjustment value is lower. As a result, the luminance of the backlight panel 210 is equal to the luminance of the backlight panel in the liquid crystal display device according to Comparative Example 2. FIG. 18 is a graph showing the light emission luminance with respect to the adjustment value shown in FIG.

  That is, the backlight panel 210 to which the backlight drive circuit 400 according to the present embodiment is connected has a lighting duty smaller than that of the backlight panel in the liquid crystal display device according to the comparative example 2 when the adjustment value is other than the maximum value. Thus, the liquid crystal display device according to the comparative example 2 can be lit with the same luminance as the backlight panel in the liquid crystal display device. In other words, when the adjustment value is other than the maximum value, the backlight panel 210 can be lit with a lighting duty ratio closer to the impulse response than the backlight panel in the liquid crystal display device according to Comparative Example 2.

  As described above, when the backlight panel 210 to which the backlight driving circuit 400 according to the present embodiment is connected is compared with the backlight panel in the liquid crystal display device according to the comparative example 2, the adjustment value is other than the maximum value. In addition, by reducing the lighting duty ratio and increasing the backlight driving current, it is possible to achieve the same luminance as the backlight panel in the liquid crystal display device according to Comparative Example 2.

  FIG. 19 is a graph showing the chromaticity of the backlight panel 210 when the adjustment value is changed in this embodiment, and (a) shows the chromaticity of the backlight panel 210 in the xy chromaticity diagram. (B) is a partially enlarged view of (a).

  As shown in the figure, the backlight panel 210 has substantially the same chromaticity even when the adjustment value is changed. That is, there is almost no chromaticity difference.

  As described above, the light emission characteristics of the backlight panel 210 to which the backlight drive circuit 400 according to the second embodiment of the present invention is connected are equivalent to the light emission characteristics of the backlight panel in the liquid crystal display device according to the comparative example 2. it can. That is, the backlight panel 210 to which the backlight drive circuit 400 according to the present embodiment is connected has a lighting duty smaller than that of the backlight panel in the liquid crystal display device according to the comparative example 2 when the adjustment value is other than the maximum value. Thus, the light emission characteristics equivalent to those of the backlight panel in the liquid crystal display device according to Comparative Example 2 can be realized. In other words, it is possible to illuminate with a lighting duty ratio closer to the impulse response than the backlight panel in the liquid crystal display device according to Comparative Example 2. Thereby, the backlight drive circuit 400 according to the present embodiment can suppress the blurring of the moving image similarly to the backlight drive circuit 100 according to the first embodiment.

  Further, in the backlight drive circuit 400 according to the second embodiment, the drive current supplied to the backlight 211 switches steplessly according to the adjustment value. Thereby, the backlight drive circuit 400 according to the present embodiment can further suppress flicker compared to the backlight drive circuit 100 according to the first embodiment.

  Further, the backlight drive circuit 400 according to Embodiment 2 of the present invention is generated by the D / A converter 420 (voltage generator) that generates a higher voltage as the adjustment value is lower, and the D / A converter 420. A backlight driver 130 that converts the obtained voltage into a current and supplies it as a drive current. As a result, the current can be adjusted steplessly with a simple configuration.

(Modification of Embodiment 2)
Next, a backlight drive circuit according to a modification of the second embodiment of the present invention will be described.

  In the backlight driving circuit 400 according to the second embodiment, the SOC 411 and the TCON 112 are used to generate the pulse signals PWM0 to PWM2 corresponding to the backlight drivers 130a to 130c. PWM0 to PWM2 may be configured.

  FIG. 20 is a block diagram showing a detailed configuration of a backlight drive circuit 500 according to a modification of the second embodiment.

  The backlight drive circuit 500 shown in the figure is substantially the same as the backlight drive circuit 400 according to the second embodiment, except that a timing instruction unit 510 composed of an SOC 511 is provided instead of the timing instruction unit 410.

  The SOC 511 has functions of the SOC 411 and the TCON 112. That is, based on the signal indicating the input adjustment value, three pulse signals PWM0 to PWM2 that are synchronized with the vertical synchronization signal are generated. Further, a backlight adjustment pulse having a duty ratio corresponding to the adjustment value indicating the luminance of the backlight panel 210 is generated and output to the D / A conversion unit 420.

  The backlight drive circuit 500 according to the modification of the second embodiment has the same effect as that of the second embodiment. That is, it is possible to suppress flickering and suppress moving image blur and double image even when the adjustment value is high.

  The backlight drive circuit according to the embodiment of the present invention has been described above, but the present invention is not limited to this embodiment.

  For example, the adjustment value may be specified by a user operation, or may be specified by an illuminance sensor attached to the liquid crystal display device. Further, it may be designated according to the scanning signal (that is, dynamic backlight). Further, the adjustment values of the backlights 211a to 211c may be specified independently, for example, may be specified independently according to the scanning signal.

  Moreover, in the said Embodiment 1 and its modification, the voltage switching circuit 120 switched the voltage to generate | occur | produce using the voltage switching pulse output from SOC, However, It is not restricted to this structure. For example, the voltage switching circuit 120 may include an integration circuit and a comparator, and may be configured such that a backlight adjustment pulse is input from the SOC 111.

  In the above embodiment, the transistors Q11 and Q21 have been described as bipolar transistors, but may be metal-oxide-semiconductor (MOS) transistors. In the above embodiment, the transistors Q11 and Q21 have been described as n-type transistors. However, p-type transistors may be used. In this case, the equivalent functions can be obtained by changing the connection of peripheral circuit elements and power supplies. It may be realized.

  In the above embodiment, the backlight panel 210 is described as a three-stage configuration of the backlight 211. However, the backlight may be n stages (n ≧ 2), and in this case, the response speed of the liquid crystal pixel 221 is set. Assuming that Trs is used, a scanning effect can be obtained when the adjustment value is such that the lighting duty ratio can be ((n−1) / n) −Trs or less. Also, in the same display period (Display period), the timing of turning off the backlight 211 that is turned on m-th (1 ≦ m ≦ n) is T (d), from the start of the display period ((m− The light may be turned off before 1) / n) × Td time.

  Further, some or all of the constituent elements constituting the backlight driving circuit may be configured by one system LSI (Large Scale Integration). The system LSI is an ultra-multifunctional LSI manufactured by integrating a plurality of components on a single chip, and specifically, a computer system including a microprocessor, ROM, RAM, and the like. . A computer program is stored in the RAM. The system LSI achieves its functions by the microprocessor operating according to the computer program.

  The circuit configuration shown in the circuit diagram is an example, and the present invention is not limited to the circuit configuration. That is, like the above circuit configuration, a circuit that can realize a characteristic function of the present invention is also included in the present invention. For example, the present invention includes a device in which an element such as a transistor, a resistor, or a capacitor is connected in series or in parallel to a certain element within a range in which a function similar to the above circuit configuration can be realized. In other words, the term “connected” in the above embodiment is not limited to the case where two terminals (nodes) are directly connected, and the two terminals ( Node) is connected through an element.

  Furthermore, the above embodiment and the above modification examples may be combined.

  The present invention can be applied to a display device such as a television that displays video, a smartphone, or a tablet terminal.

100, 300, 400, 500 Backlight drive circuit 110, 310, 410, 510 Timing indicator 111, 311, 411, 511 SOC
112 TCON
120 Voltage switching circuit 130, 130a, 130b, 130c Backlight driver 200 Liquid crystal display device 210 Backlight panel 211, 211a, 211b, 211c Backlight 220 Liquid crystal panel 221 Liquid crystal pixel 420 D / A converter C11, C21, C22, C23 Capacitor Q11, Q21 Transistors R11, R12, R21-R25 Resistance

Claims (8)

A display unit;
A light source lit by a drive signal;
A control unit for outputting the drive signal,
The drive signal has a change rate of the duty ratio of the drive signal with respect to the brightness of the light source equal to or lower than a predetermined brightness smaller than a change rate of the duty ratio of the drive signal with respect to the brightness of the light source higher than the predetermined brightness.
Display device. A level of the drive signal at a luminance equal to or lower than the predetermined luminance is greater than a level of the drive signal at a luminance higher than the predetermined luminance;
The display device according to claim 1. 3. The display according to claim 1, wherein a level of the driving signal at a first luminance equal to or lower than the predetermined luminance is substantially equal to a level of the driving signal at a second luminance different from the first luminance equal to or lower than the predetermined luminance. apparatus. The level of the drive signal at a third brightness higher than the predetermined brightness is substantially equal to the level of the drive signal at a fourth brightness different from the third brightness higher than the predetermined brightness. The display device according to claim 1. The display device according to claim 1, wherein the driving signal during the lighting period of the light source has a higher level as the luminance of the light source is lower. A voltage generator configured to generate a first voltage when the luminance of the light source is higher than the predetermined luminance, and to generate a second voltage higher than the first voltage when the luminance of the light source is equal to or lower than the predetermined luminance;
The display device according to claim 1, wherein the control unit outputs the drive signal based on the first voltage and the second voltage. A timing instruction unit for instructing the lighting and extinguishing timing of the light source so that the lighting period of the light source becomes longer as the luminance of the light source is higher;
The display device according to claim 1, wherein the control unit outputs the drive signal based on an instruction from the timing instruction unit. The display device according to claim 1, wherein the luminance is designated by a user operation.

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