JP6508244B2 - Display device - Google Patents

Description

  The present invention relates to a backlight drive circuit connected to a liquid crystal panel including a liquid crystal pixel group arranged in a matrix and a plurality of backlights 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 increased. However, with the increase in size, there is a problem that blurring of an image when displaying a moving image (hereinafter sometimes referred to as "moving image blur") becomes noticeable.

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

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

  This makes it possible to simultaneously suppress the motion blur and reduce the power consumption.

JP, 2011-232535, A

  In such a backlight scanning method, in order to increase the screen brightness, that is, to increase the backlight brightness, the lighting duty ratio needs to be increased.

  However, in the method disclosed in Patent Document 1, when the movement of the screen is fast, the lighting duty ratio is reduced, and therefore, the luminance of the screen can not be increased. In other words, when the screen brightness is high, there is a problem that moving image blur can not be suppressed.

  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 capable of suppressing motion blur even when the screen brightness is high.

  In order to achieve the above object, a display device according to an aspect of the present invention includes a display unit, a light source which is lit by a drive signal, and a control unit which outputs the drive signal, and the drive signal is predetermined The change rate of the duty ratio of the drive signal to the brightness of the light source less than the brightness is smaller than the change rate of the duty ratio of the drive signal to the brightness of the light source higher than the predetermined brightness. Further, the level of the drive signal at a brightness lower than the predetermined brightness may be larger than the level of the drive signal at a brightness higher than the predetermined brightness.

  That is, a display device according to one aspect of the present invention includes a display unit having 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. And a light source drive unit for supplying a drive signal to the light source, wherein the light source drive unit has a lighting duty ratio which is a ratio of a lighting period in a blinking cycle of each light source as the adjustment value indicating the luminance of the light source is higher. The drive signal is supplied to be large, the liquid crystal pixel group transmits light from a light source corresponding to the liquid crystal pixel with a transmittance according to the signal voltage written to each liquid crystal pixel, and the light source is driven The light source is turned off before the signal voltage is written to the liquid crystal pixel group of the row corresponding to each light source, and the duty ratio characteristic indicating the lighting duty ratio to the brightness, and the driving to the brightness The amplitude characteristic indicating the amplitude of the signal has a first area where the luminance is equal to or lower than a predetermined luminance and a second area where the luminance is higher than the predetermined luminance, and the lighting duty ratio to the luminance in the first area The change rate is smaller than the change rate 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 each in the lighting period in the second region. Higher than the current value of the drive signal.

  As a result, even when the screen brightness is high, it is possible to suppress moving image blur. Moreover, double exposure can also be suppressed by turning off the corresponding light source before writing the signal voltage.

  A display device according to another aspect of the present invention includes a display unit, a light source, and a light source drive unit that outputs a drive signal of the light source according to duty ratio characteristics and amplitude characteristics according to the luminance of the light source. The duty ratio characteristic and the amplitude characteristic may have a first area equal to or less than 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 to the luminance of the light source is smaller than the change rate of the duty ratio of the drive signal 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 than that of the second region.

  For example, the light source drive unit is configured to instruct the light source on / off timing so that the lighting period becomes longer as the luminance is higher, and the first voltage when the luminance is higher than the predetermined luminance. A voltage generator configured to generate a second voltage higher than the first voltage when the luminance is less than the predetermined luminance, and a driver provided corresponding to each light source and supplying the drive signal to the corresponding light source And 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. It may be supplied as the drive signal during a period in which the lighting of the corresponding light source is instructed.

  Thereby, the current can be switched in two stages with a simple configuration.

  Further, the timing instruction unit generates a voltage switching signal indicating whether the luminance is higher than the predetermined luminance, and the voltage generation unit is configured to transmit the voltage switching signal generated by the timing instruction unit to the luminance. May indicate that the luminance is higher than the predetermined luminance, and may generate the first voltage, and may indicate the second voltage if the luminance indicates that the luminance is equal to or less than the predetermined luminance.

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

  Thereby, flicker can be suppressed.

  The voltage generation unit may generate a first voltage if the luminance of the light source is higher than the predetermined luminance, and generate a second voltage higher than the first voltage if the luminance of the light source is less than the predetermined luminance. The control unit may output the drive signal based on the first voltage and the second voltage. The light emitting apparatus further includes a timing instruction unit that instructs lighting and extinguishing timings of the light source 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 the instruction of the timing instructing unit. The drive signal may be output. That is, the light source driving unit is 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 generating unit generates a higher voltage as the luminance is lower. And a driver provided corresponding to each light source and supplying the drive signal to the corresponding light source, the driver converting the voltage generated by the voltage generation unit into a current, and converting the converted current, It may be supplied as the drive signal during a period in which the lighting of the corresponding light source is instructed by the timing instruction unit.

  Thus, 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 DA (digital-analog) converts 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, the smaller the duty of the PWM signal is by inverting the voltage level of the analog voltage generated by the DA converter. , And an inverting circuit that generates a high voltage.

  The D / A converter is an integrator configured by a resistor and a capacitor, and the inverting circuit is applied with an analog voltage generated by the D / A converter at a control terminal, and one of two output terminals is provided. One may have a transistor grounded.

  Further, the brightness may be designated by a user operation. That is, the plurality of luminances may be designated by user operation.

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

FIG. 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. FIG. 5 is a circuit diagram showing an example of a detailed configuration of a voltage switching circuit. FIG. 7 is a timing chart schematically showing an example of the lighting and extinguishing timing of the backlight panel and the writing timing of the signal voltage 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. 7 is a timing chart schematically showing lighting and extinguishing timings of the backlight panel and writing timings of signal voltages to the liquid crystal panel in a comparative example of the first embodiment. 7 is a timing chart schematically showing another example of the lighting and extinguishing timing of the backlight panel and the writing timing of the signal voltage to the liquid crystal panel in the first embodiment. It is a table | surface which shows the lighting duty ratio of a backlight panel, a drive current, and light-emitting luminance at the time of changing 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 back light panel at the time of changing adjustment value. FIG. 7 is a block diagram showing a detailed configuration of a backlight drive circuit according to a modification of the first embodiment. FIG. 7 is a block diagram showing a detailed configuration of a backlight drive circuit according to a second embodiment. FIG. 6 is a circuit diagram showing an example of a detailed configuration of a D / A conversion unit. 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 of a backlight panel, a drive current, and light-emitting luminance at the time of changing adjustment value. It is a graph which shows the light-emitting luminance with respect to the adjustment value shown in FIG. It is a graph which shows the chromaticity of a back light panel at the time of changing adjustment value. FIG. 13 is a block diagram showing a detailed configuration of a backlight drive circuit according to a modification of the second embodiment. FIG. 7 is a timing chart schematically showing lighting and extinguishing timings of the backlight panel and writing timings of signal voltages to the liquid crystal panel in the liquid crystal display device according to Comparative Example 1. FIG. FIG. 18 is a timing chart schematically showing the lighting and extinguishing timing 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 Comparative Example 2. FIG. It is a graph which shows the lighting duty ratio with respect to adjustment value of the liquid crystal display device which concerns on the comparative example 2. FIG. It is a figure for demonstrating moving image blurring, (a) is a figure which shows the case where lighting duty ratio is small, when lighting duty ratio is large.

  First, before describing the embodiments of the present invention, the principles of double exposure and motion blur that occur 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 exposure occurring in a liquid crystal display device will be described. FIG. 21 is a timing chart schematically showing the on / off timing of the backlight panel and the write timing of the signal voltage to the liquid crystal panel in the liquid crystal display device according to 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 liquid crystal pixel groups. And a light source drive unit (for example, a backlight drive circuit) which drives a plurality of backlights.

  Writing of the scanning signal to the liquid crystal pixel group is performed by a gate driver for driving the upper portion of the liquid crystal panel, a gate driver for driving the central portion of the liquid crystal panel, and a gate driver for driving the lower portion 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 in the liquid crystal panel means applying the signal voltage to the liquid crystal pixel group constituting the liquid crystal panel.

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

  The backlight drive circuit includes a plurality of backlight drivers for driving the respective backlights, and supplies to the backlight a drive current for lighting the backlights in a lighting period of the backlights. Specifically, the drive current is supplied to the LED provided corresponding to the upper part of the liquid crystal panel during the high period of the scan signal PWM0, and provided for the central part of the liquid crystal panel during the high period of the scan signal PWM1. 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 the backlights are always on.

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

  The liquid crystal display device writes the signal voltage to the liquid crystal panel by sequentially driving each gate driver when the gate driver start signal STV, which is a signal indicating the write timing of the scan signal to the first row of the liquid crystal pixel group rises. .

  The liquid crystal pixel row in which the signal voltage is written takes time according to the response speed of the liquid crystal pixel, and transmits light with a transmission amount according to the signal voltage of the next frame. 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, the image is doubled, and the response speed of the liquid crystal causes a problem that blurring occurs. is there. Specifically, since the backlight duty ratio is 100% and the backlights are always lit, the liquid crystal pixel emits light from the backlight even in the response period of the liquid crystal pixel after the signal voltage is rewritten. Through. That is, when the signal voltage is rewritten, the image of the frame before the rewriting and the image of the frame after the rewriting are displayed. In other words, the image appears double.

(Comparative example 2)
Therefore, in order to suppress double reflection in such a liquid crystal display device, it is conceivable to reduce the lighting duty ratio and to turn off the corresponding backlight at the time of rewriting the signal voltage.

  FIG. 22 is a timing chart schematically showing the lighting and extinguishing timing 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 Comparative Example 2. In the present comparative example, the response period of the liquid crystal pixel is described as zero for the sake of explanation.

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

  Thereby, double exposure at the time of signal voltage rewriting can be suppressed. In the above description, although the response period of the liquid crystal pixel is zero, if 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 also in the response period of the liquid crystal pixel. It is also possible to suppress motion blur during a 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. Here, the adjustment value is a value indicating the luminance of the backlight, and the higher the adjustment value, the higher the luminance.

  As shown in the figure, as the adjustment value is higher, the backlight duty ratio needs to be higher because the backlight needs to emit light with higher luminance. On the other hand, as the adjustment value decreases, the backlight may emit light at low luminance, and the lighting duty ratio decreases.

  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 as described above, the lighting duty ratio is set to 1/3 (≒ 33%), and the backlight is turned off during the rewriting of the signal voltage of the liquid crystal pixel and in the response period of the liquid crystal pixel. Therefore, double exposure can be suppressed. That is, in the case of the adjustment value which can make the lighting duty ratio 33% or less, double imaging can be suppressed. In other words, in the case of the adjustment value where the lighting duty ratio exceeds 33%, the effect of suppressing double exposure is not sufficiently exhibited.

  However, the adjustment values that can set the lighting duty ratio to 33% or less are only 0, 1, and 2. With other adjustment values (adjustment value 3 or more), the lighting duty ratio is higher than 33%. It is difficult to suppress the image. That is, it is difficult to suppress double projection in a high brightness area of the backlight which has an adjustment value of 3 or more.

  Further, since the liquid crystal pixel is in the hold drive mode, there is a problem that moving image blur occurs due to a retinal afterimage even if the response speed of the liquid crystal pixel is shortened.

  The motion blur can also be improved by reducing the lighting duty ratio, as in the method for suppressing double exposure described above.

  FIG. 24 is a diagram for explaining moving image blur, in which (a) shows a case where the lighting duty ratio is large and (b) shows a case where the lighting duty ratio is small.

  As is clear from comparison between (a) and (b), the smaller the lighting duty ratio shown in (b) is, the smaller the moving image blur can be. That is, as the lighting duty ratio is reduced and the lighting of the backlight is closer to the lighting of the impulse type, it is possible to suppress the motion blur.

  As described above, the motion blur can be suppressed by reducing the lighting duty ratio.

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

  As described above, in the liquid crystal display devices according to Comparative Examples 1 and 2, there is a problem that it is difficult to suppress double reflection and motion blur when the backlight emits light with high luminance.

  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 with 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.

  As described above, when the adjustment value is the second adjustment value, the backlight drive circuit according to each embodiment of the present invention makes the lighting duty ratio smaller. Therefore, even when the screen brightness is high, it is possible to suppress moving image blur. In addition, double exposure can also be suppressed by turning off the corresponding backlight before writing the signal voltage.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below all show one preferable specific example of the present invention. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components, and the like described 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 components in the following embodiments, components not described in the independent claims are not necessarily required to achieve the object of the present invention, but are described as constituting a more preferable embodiment. Be 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 the first embodiment of the present invention includes a display unit, a light source which is turned on by a drive signal, and a control unit which outputs a drive signal, and the drive signal is a drive for the luminance of the light source less than a predetermined luminance. The rate of change of the duty ratio of the signal is smaller than the rate of change of the duty ratio of the drive signal with respect to the luminance of the light source higher than the predetermined luminance.

  That is, the backlight drive circuit (corresponding to the control unit described above) according to the first embodiment of the present invention is a drive current (corresponding to the drive signal described above) for a plurality of backlights (corresponding to the light source described above). The backlight drive circuit supplies the light to the liquid crystal pixel group by increasing the lighting duty ratio, which is the ratio of the lighting period in the blinking cycle of each backlight, as the adjustment value indicating the brightness of the backlight is higher. Turn off the backlight before writing the voltage. Here, the backlight drive circuit supplies the first current in the lighting period when the adjustment value exceeds the threshold, and the current amount is larger than the first current in the lighting period when the adjustment value is equal to or less than the threshold. 2 Supply current. 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.

  Thereby, the backlight drive circuit according to the first embodiment of the present invention can suppress double imaging and motion blur even when the backlight emits light at high luminance.

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

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

  The liquid crystal display device 200 shown in the figure is, for example, a liquid crystal television including the backlight drive circuit 100 according to Embodiment 1 of the present invention, a backlight panel 210, and a liquid crystal panel 220 composed of a liquid crystal pixel group.

  The backlight drive circuit 100 drives the backlight panel 210 using an adjustment value indicating the luminance of the backlight panel 210, a signal instructing lighting and extinguishing timing of each backlight panel 210, and the like, which are input from the outside. 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 the three backlights 211a to 211c. However, the number of the backlights is not limited to this, and may be ten or twenty, for example.

  The backlights 211 a to 211 c are provided corresponding to a plurality of rows of liquid crystal pixel groups constituting the liquid crystal panel 220. Specifically, the backlight 211 a corresponds to the upper portion of the liquid crystal panel 220, the backlight 211 b corresponds to the central portion of the liquid crystal panel 220, and the backlight 211 c corresponds to the lower portion of the liquid crystal panel 220. The backlights 211a to 211c include, for example, current-driven light emitting elements such as LEDs. That is, the brightness of the backlights 211a to 211c changes in accordance with the amount of current flowing through the backlights 211a to 211c.

  In the present embodiment, the backlights 211a to 211c are elongated, but the shape of the backlights is not limited to this, and may be substantially square. Further, 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. It may be arranged in Hereinafter, the backlights 211 a to 211 c may be simply described as the backlight 211 without particular distinction.

  The liquid crystal panel 220 is a display panel having liquid crystal pixel groups arranged in a matrix (for example, 1920 columns and 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 element having a liquid crystal layer, a pixel electrode to which a signal voltage is applied, and a counter electrode facing the pixel electrode, and a pixel electrode of the liquid crystal element It has a 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 through the TFT. The TFT is driven from the source driver (not shown) to each column of the liquid crystal pixel group at timing according to the high and low of the gate pulse outputted from the gate driver (not shown) to the gate line provided for each row of the liquid crystal pixel group. Are applied to the pixel electrodes of the liquid crystal pixels 221 of the corresponding column. That is, the data is written to the liquid crystal pixel 221. As a result, the liquid crystal panel 220 transmits the light from the backlight 211 corresponding to the liquid crystal pixel 221 by the transmission amount according to the signal voltage indicating the luminance of the liquid crystal pixel 221 written to each liquid crystal pixel 221.

[Detailed Configuration of Backlight Driving Circuit]
Next, the detailed configuration of the backlight drive circuit 100 will be described. FIG. 2 is a block diagram showing the detailed configuration of the backlight drive circuit 100. As shown in FIG.

  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 same drawing, the backlight panel 210 to which the drive current is supplied from the backlight drivers 130a to 130c is also illustrated.

  The timing instructing unit 110 instructs the on / off timing of each backlight 211 so that the on period of the backlight 211 becomes longer as the adjustment value becomes higher, and more specifically, SOC (System-on-a-) Chip (Chip) 111 and TCON (Timing Controller) 112, and outputs pulse signals PWM0 to PWM2 indicating timing of turning on and off each backlight 211.

  The SOC 111 generates a backlight adjustment pulse of a duty ratio corresponding to an adjustment value indicating the brightness of the backlight panel 210. Specifically, as the adjustment value indicating the luminance of the backlight panel 210 is higher, a backlight adjustment pulse having a higher duty ratio is generated. 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 lights up for a longer period as the duty ratio of the backlight adjustment pulse is higher.

  Here, when the adjustment value indicating the luminance of the backlight panel 210 is higher than a threshold (for example, 10), the SOC 111 sets the duty ratio of the backlight adjustment pulse as a normal duty ratio, and when it is below the threshold, back The duty ratio of the light adjustment pulse is made smaller than the normal duty ratio. The normal duty ratio is a duty ratio necessary to obtain the luminance of the backlight 211 corresponding to the adjustment value by supplying a first current to be 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.

  In addition, 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 (for example, 10), and is low (hereinafter referred to as L) when below the threshold. Such a voltage switching pulse is generated and output to the voltage switching circuit 120. The threshold value of the adjustment value used as the reference for switching the H and L of the voltage switching pulse by the SOC 111 is not limited to 10. For example, the operating environment and operating environment of the liquid crystal display device 200 on which the backlight drive circuit 100 is mounted. Depending, you may select suitably.

  The TCON 112 synchronizes the backlight adjustment pulse input from the SOC 111 with the vertical synchronization signal supplied to the liquid crystal panel 220 and outputs it. Specifically, the backlight adjustment pulse is converted 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 on / off timing of each backlight 211. -Generate PWM2.

  Specifically, the pulse signal PWM0 is a signal for controlling the on / off 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 back. The light 211a corresponds to the turn-off 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. Corresponds 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. Corresponds to

  The three backlights 211a to 211c are sequentially turned on and off by such pulse signals PWM0 to PWM2.

  Here, the TCON 112 switches each pulse signal PWM0 to PWM2 to L before the signal voltage to the liquid crystal pixel group in the row corresponding to each backlight 211a to 211c is written. Specifically, the timing at which the signal voltage is written to the liquid crystal pixel group in the row corresponding to each of the backlights 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.

  Therefore, each of the backlights 211a to 211c is extinguished before the signal voltage to the liquid crystal pixel group in the row corresponding to the backlights 211a to 211c is written. Therefore, double exposure due to the backlight 211 being lit at the time of writing the signal voltage can be suppressed.

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

  The first voltage and the second voltage are not limited to this, and for example, the first voltage may be 0.40 [V] and the second voltage may be 0.60 [V], and the first voltage may be zero. The second voltage may be 0.55 V, and is appropriately selected according to the use environment and the operating environment of the liquid crystal display device 200 on which the backlight drive circuit 100 is mounted. May be

  The backlight drivers 130 a to 130 c supply the backlight panel 210 with a driving current for lighting the backlights 211 a to 211 c. Specifically, the backlight driver 130a corresponds to the backlight 211a, the backlight driver 130b corresponds to the backlight 211b, and the backlight driver 130c corresponds to the backlight 211c, and the corresponding backlights 211a to The drive current is supplied to 211c. Hereinafter, the backlight drivers 130 a to 130 c may be described as the backlight driver 130 without particular distinction.

  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 converted current is indicated by the timing instruction unit 110. During the lighting period of the backlight 211, it is supplied 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 converts the converted current into a driving current of the backlight 211a during the H period of the pulse signal PWM0 input from the TCON 112. It supplies to the said 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 in the H period of the pulse signal PWM0, and the backlight 211a is turned off in 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 converts the converted current into a driving 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 in the H period of the pulse signal PWM1, and the backlight 211b is turned off in 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 converts the converted current into a driving 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 in the H period of the pulse signal PWM2, and the backlight 211c is turned off in 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 is L). A higher second voltage (e.g., 0.65 [V]). That is, the first voltage (e.g., 0.35 [V]) is the first voltage (e.g., 0.35 [V]) when the adjustment value indicating the brightness of the backlight panel 210 is higher than the threshold (e.g., 10), and the second voltage (e.g., the threshold) 0.65 [V]).

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

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

  Therefore, in the liquid crystal display device 200 equipped with the backlight drive circuit 100 according to the present embodiment, when the adjustment value is equal to or less than the threshold value, the H period of the pulse signals PWM0 to PWM2 relates to Comparative Example 1 and Comparative Example 2. Even when the duty ratio of the liquid crystal display device is shorter than that of the liquid crystal display device, the brightness of the backlight panel 210 equivalent to that of the liquid crystal display device according to Comparative Example 1 and Comparative Example 2 can be realized.

  That is, when the adjustment value is equal to or less than the threshold value, lighting of the backlights 211a to 211c can be made closer to lighting of the impulse type. Thus, the motion blur can be improved.

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

  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 emitter of the transistor Q11 is grounded, the collector is connected to each of the backlight drivers 130a to 130c via the resistor R12, and the voltage switching pulse output from the SOC 111 is input to the base via the resistor R11. 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 which 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, among the terminals of the resistor R12, the voltage of a terminal not connected to the collector of the transistor Q11 is a voltage output from the voltage switching circuit 120. Specifically, when the collector of transistor Q11 is at L voltage, the output voltage of voltage switching circuit 120 is a predetermined voltage determined by a circuit provided between voltage switching circuit 120 and 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 H voltage, the output voltage of the voltage switching circuit 120 is the predetermined voltage itself determined by the circuit provided between the voltage switching circuit 120 and the backlight drivers 130a to 130c. As described above, the output voltage of the voltage switching circuit 120 is the first voltage obtained by dividing the predetermined voltage by resistance when the collector of the transistor Q11 is L voltage, and the predetermined voltage when the collector of the transistor Q11 is H voltage. And 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, the first voltage is generated when the adjustment value is higher than the threshold value, and the second voltage higher than the first voltage is generated when the adjustment value is lower than the threshold value.

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

  FIG. 4 is a timing chart schematically showing the on / off timing of the backlight panel 210 and the write timing of the signal voltage to the liquid crystal panel 220. As shown in FIG.

  In FIG. 4, 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 pixel 221 of the pixel row corresponding to the backlight 211a in order from the top , The pulse signal PWM1 corresponding to the backlight 211b, the timing of rewriting the signal voltage to the liquid crystal pixel 221 of the pixel row corresponding to the backlight 211b, the pulse signal PWM2 corresponding to the backlight 211c, and The timing for rewriting the signal voltage to the liquid crystal pixels 221 in the pixel row corresponding to the backlight 211 c 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 PWM0 to PWM2 are signals in which pulse signals having the same duty ratio as the backlight adjustment pulse are delayed by being shifted by a predetermined time within one display period (one display period).

  First, at time t0, when the vertical synchronization signal STV rises, writing of signal voltages is started row by row in each liquid crystal pixel 221 in the upper part of the liquid crystal panel 220 corresponding to the backlight 211a. At this time, the pulse signal PWM0 has become L by time t0. That is, the backlight drive circuit 100 turns off the backlight 211 a corresponding to the upper portion of the liquid crystal panel 220 until the writing on each liquid crystal pixel 221 in the upper portion of the liquid crystal panel 220 is started.

  Thereafter, writing of a signal voltage is performed on each liquid crystal pixel 221 in the upper part of the liquid crystal panel 220 until time t1. Here, the time required for writing the signal voltage to the liquid crystal pixel 221 and transmitting the light quantity corresponding to the signal voltage to which the liquid crystal pixel has been written is the response speed Trs. The response speed is determined by the configuration, material, and the like of each liquid crystal pixel 221. Therefore, each liquid crystal pixel 221 transmits the light amount corresponding to the written signal voltage after the signal voltage is written and Trs has elapsed.

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

  Thereafter, the backlight drive circuit 100 turns on the backlight 211 b until immediately before time t1. Therefore, an image corresponding to the signal voltage written in the previous frame is displayed in the central portion of the liquid crystal panel 220 until time t0 to just before time t1.

  Next, at time t1, writing of the signal voltage is started row by row in 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 immediately before time t1. That is, the backlight drive circuit 100 turns off the backlight 211 b corresponding to the central portion of the liquid crystal panel 220 before writing is started to each liquid crystal pixel 221 in the central portion of the liquid crystal panel 220. Thereafter, writing of the signal voltage is performed on 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 211 c corresponding to the lower portion of the liquid crystal panel 220 from off to on. Therefore, an image corresponding to the signal voltage written in the previous frame is displayed in the lower part of the liquid crystal panel 220.

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

  Next, at time t2, writing of the signal voltage is started row by row in each liquid crystal pixel 221 in the lower part of 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 drive circuit 100 extinguishes the backlight 211 c corresponding to the lower portion of the liquid crystal panel 220 until the writing to each liquid crystal pixel 221 in the lower portion of the liquid crystal panel 220 is started. Thereafter, writing of the signal voltage is performed on each liquid crystal pixel 221 in the lower part of 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 211 a corresponding to the top of the liquid crystal panel 220 from off to on. Therefore, an image according to the signal voltage written immediately before (time t0 to t1) is displayed on the liquid crystal panel 220 upper part.

  After that, the backlight drive circuit 100 turns on the backlight 211a until just before time t5. Therefore, an image according to the signal voltage written in the previous frame is displayed in the lower part of the liquid crystal panel 220 until immediately before time t3 to t5.

  Thereafter, at time t5, the vertical synchronization signal STV rises, as in the time t0, and the above operation is repeated thereafter. That is, time t0 to t5 is one frame period (one 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 time of the lighting period (time t3 to t5) of the backlight 211a, the time of the lighting period (time t0 to t1) of the backlight 211b, and the time of the lighting period (time t1 to t2) of the backlight 211c , Is the same.

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

  Thereby, double exposure at the time of signal voltage rewriting can be suppressed. Further, by turning off the corresponding backlights 211 a to 211 c also in the response period of the liquid crystal pixel 221, it is possible to suppress moving image blur in the response period of the liquid crystal pixel 221.

  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 211 are not limited to this. For example, the lighting start time of each of the backlights 211a to 211c may be advanced by advancing the rising of each of the pulse signals PWM0 to PWM2 as indicated by a dotted line in FIG. Thus, 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 backlights 211a to 211c is reduced. it can. Here, in the case where the rising of each of the pulse signals PWM0 to PWM2 is advanced, the risings of the pulse signals PWM0 to PWM2 do not overlap with the writing period and the response period of the liquid crystal pixel group corresponding to the pulse signals PWM0 to PWM2. The above effects are achieved. That is, it is possible to suppress double imaging in the time of signal voltage rewriting and in the response period of the liquid crystal pixel 221.

<1-3. Effect etc>
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, The second current is higher than the first current when it is below the threshold. The lighting duty ratio is a normal duty ratio when the adjustment value is higher than the threshold, and is smaller than the normal duty ratio when the adjustment value is equal to or less than the threshold. Hereinafter, the drive current in the lighting period of the backlight 211 and the lighting duty ratio of the backlight 211 will be described using FIGS. 5 and 6.

  FIG. 5 is a graph showing the drive current in the lighting period of the backlight 211 with respect to the adjustment value. The figure shows the drive current supplied to the backlight 211 in Embodiment 1 and the drive current supplied to the backlight in Comparative Example 2 described above.

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

  The first current and the second current may be determined as follows. That is, when the backlight 211 is formed of an LED, the rated current that can be supplied to the backlight 211 differs depending on the lighting duty ratio, and the lower the lighting duty ratio, the higher the rated current. Therefore, the rated current of the LED when the lighting duty ratio is 100% may be set as the first current, and the rated current of the LED when the lighting duty ratio is 33% may be set as 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 the 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 the comparative example 2 when the adjustment value is higher than 10 which is the threshold value. On the other hand, when the adjustment value is equal to or less than the threshold value, the duty ratio is about half 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 moving image blur and double reflection more than the liquid crystal display device according to the second comparative example. 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 as one vertical scanning period. The area of the adjustment value in which the scan effect of the display device appears and the area of the adjustment value in which the scan effect of the liquid crystal display device 200 in this embodiment appears will be described. Note that the scan effect refers to suppressing double shot by sequentially turning on and off the plurality of backlights 211.

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

  Here, an adjustment value that can make the lighting duty ratio of the backlight 33% or less will be confirmed using FIG.

  As shown in FIG. 6, in the liquid crystal display device according to Comparative Example 2, the adjustment values that can make the lighting duty ratio of the backlight 33% or less are only 0, 1 and 2, and other adjustment values (adjustment values In 3 or more, since the lighting duty ratio of a backlight becomes higher than 33%, it is difficult to acquire a scanning effect. That is, in the liquid crystal display device according to Comparative Example 2, the scan effect can be obtained only in the region 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, an adjustment value that allows the lighting duty ratio of the backlight to be 33% or less is 0 to 10. That is, in the liquid crystal display device 200 according to the present embodiment, the scan effect can be obtained in the region where the adjustment value is 10 or less. Therefore, as compared with the liquid crystal display device according to Comparative Example 2, the scan effect can be obtained even in the region where the adjustment value is large. That is, even when the backlight 211 emits light with high luminance as compared with the liquid crystal display device according to Comparative Example 2, the scan effect can be obtained.

  Thus, the backlight drive circuit 100 according to the first embodiment of the present invention sets the drive current supplied to the backlight 211 as the first current when the adjustment value is the threshold or more and the first current when the adjustment value is the threshold or less. A higher second current is used. In addition, the lighting duty ratio of the backlight 211 is set to a normal duty ratio when the adjustment value is higher than the threshold, and smaller than the normal duty ratio when the adjustment value is equal to or less than the threshold. Therefore, even when the luminance of the backlight panel 210 is high, it is possible to suppress moving image blur.

  In addition, the backlight drive circuit 100 according to the first embodiment 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, it is possible to suppress double projection due to the backlight 211 corresponding to the liquid crystal pixel 221 being lit when the signal voltage is written to the liquid crystal pixel 221.

  FIG. 7 shows, as a comparative example of the first embodiment, the timing of turning on and off the backlight panel and the timing of turning on the liquid crystal panel when the backlight corresponding to the liquid crystal pixel is turned on at the time of writing the signal voltage to the liquid crystal pixel. 5 is a timing chart schematically showing a write timing of a signal voltage.

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

  Therefore, as in the backlight drive circuit 100 according to the first embodiment of the present invention, the scanning order of lighting and extinguishing of the backlight panel 210 and the scanning order of writing of the signal voltage to the liquid crystal panel 220 coincide with each other. Before the signal voltage is written to the liquid crystal pixel group of the row corresponding to each backlight 211, it is important to turn off the backlight 211 in order to suppress double reflection.

  Note that in FIG. 4, the scanning for turning on and off the backlight panel 210 and the scanning for writing the 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 the scan (normal scan) is used, a reverse scan (reverse scan) may be performed from the lower side to the upper side as shown in FIG.

  Further, the backlight drive circuit 100 according to the first embodiment of the present invention further supplies the 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. Have stopped. That is, the backlight 211 is turned off. Therefore, it is possible to suppress double projection due to the backlight 211 corresponding to the liquid crystal pixel 221 being lit in the response period of the liquid crystal pixel 221.

  In the above description, the backlight drive circuit 100 stops the supply of the 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. The drive circuit 100 may supply 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. The reason is described below.

  Although the transmission amount of the liquid crystal pixel 221 whose signal voltage has been rewritten changes rapidly immediately after the rewriting, the change of the transmission amount thereafter is gradual. Therefore, in the response period of the liquid crystal pixel 221 in which the signal voltage has been rewritten, even if the backlight 211 is lit by supplying the drive current to the backlight 211 in a period after the change in transmission amount becomes gentle. , The motion 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 in 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 the first embodiment of the present invention is connected will be described using FIGS. 9 to 11.

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

  As shown in the table in the figure, in the backlight panel 210 to which the backlight drive circuit 100 according to the present embodiment is connected, the adjustment value is smaller than that of the backlight panel in the liquid crystal display device according to Comparative Example 2. In the case of 10 or less, the lighting duty ratio is about 1/2 and the drive current is about 2 times. 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 drive 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 Comparative Example 2 when the adjustment value is 10 or less. Thus, the liquid crystal display device according to Comparative Example 2 can be lighted at the same level of 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 Comparative Example 2.

  As described above, when the adjustment value is 10 or less, the backlight panel 210 has a lighting duty ratio of about 1⁄2 times and driving of the backlight as compared with the backlight panel in the liquid crystal display device according to Comparative Example 2. By doubling the current, 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 the present 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 almost the same chromaticity even when the adjustment value is changed. That is, there is almost no difference in chromaticity.

  As described above, the light emission characteristic of the backlight panel 210 to which the backlight drive circuit 100 according to the first embodiment of the present invention is connected realizes the light emission characteristic equivalent to 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 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 Comparative Example 2 when the adjustment value is 10 or less. Thus, light emission characteristics equivalent to the backlight panel in the liquid crystal display device according to Comparative Example 2 can be realized. In other words, it 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 Comparative Example 2. This can suppress motion blur.

  Further, the backlight drive circuit 100 according to the first embodiment of the present invention generates the first voltage when the adjustment value is higher than the threshold, and generates the second voltage higher than the first voltage when the adjustment value is equal to or less than the threshold. A backlight that converts a first voltage generated by the voltage switching circuit 120 (voltage generation unit) to be generated and the voltage switching circuit 120 into a first current, converts a second voltage into a second current, and supplies it as a driving current And a driver 130. Thereby, the current can be switched in 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 pulse signals PWM0 to PWM2 corresponding to the backlight drivers 130a to 130c are generated using the SOC 111 and the TCON 112, but the SOC is a pulse signal without using the TCON 112. 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, but differs in that a timing instruction unit 310 made of an SOC 311 is provided instead of the timing instruction unit 110.

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

  Also in the backlight drive circuit 300 according to the modification of the first embodiment, the same effects as those of the first embodiment can be obtained. That is, even when the adjustment value is high, it is possible to suppress moving image blur and double reflection as compared with the liquid crystal display device according to Comparative Example 2.

Second Embodiment
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 as the adjustment value decreases, the drive current increases steplessly. It is different. Thus, the backlight drive circuit according to the present embodiment can suppress flicker while achieving the same effects as the backlight drive circuit 100 according to the first embodiment.

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

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

  In the same figure, the backlight drive circuit 400 includes a timing instruction unit 410 instead of the timing instruction unit 110 as compared with the backlight drive circuit 100 shown in FIG. 2 and a D / A conversion unit 420 instead of the voltage switching circuit 120. The point to prepare is different. In the same drawing, the backlight panel 210 to which the drive current is supplied from the backlight drivers 130a to 130c is also illustrated.

  The timing instruction unit 410 includes the SOC 411 instead of the SOC 111 as compared with the timing instruction unit 110 in the first embodiment, and the lighting and extinguishing timing of each backlight 211 is longer so that the lighting period becomes longer as the adjustment value is higher. To direct.

  Similar to the SOC 111, the SOC 411 generates a backlight adjustment pulse of a duty ratio corresponding to an adjustment value indicating the luminance of the backlight panel 210. Also, the SOC 411 outputs this backlight adjustment pulse to the D / A converter 420.

  Here, when the adjustment value indicating the luminance of the backlight panel 210 is high (for example, 20), the SOC 411 sets the duty ratio of the backlight adjustment pulse as the normal duty ratio, and in cases other than the maximum value. , The duty ratio of the backlight adjustment pulse is made smaller than the normal duty ratio. The normal duty ratio is a duty ratio necessary to obtain 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 conversion unit 420 is an example of a voltage generation unit 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 this D / A conversion unit is, for example, 0.95 [V], and the minimum voltage is, for example, 0.35 [V].

  Specifically, the D / A conversion unit 420 performs a DA (digital-analog) conversion of 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 inverting circuit that generates 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 to the backlights 211a to 211c corresponding to the H period of the corresponding pulse signals PWM0 to PWM2 switches steplessly according to the adjustment value. Specifically, the higher the adjustment value is, the larger current is supplied, and the lower the adjustment value is, the smaller current is supplied. For example, when the adjustment value changes by 1 from 0 to 20, the minimum current (350 mA) is supplied when the adjustment value is the maximum value 20, and the maximum current (930 mA when the adjustment value is the minimum value 0). ]) Supply.

  As a result, the backlights 211a to 211c emit light by the low current in the high period of the pulse signals PWM0 to PWM2 as the adjustment value is high, and emit light by the large current in the high period of the pulse signals PWM0 to PWM2 as the adjustment value is low. 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 relates to Comparative Example 1 and Comparative Example 2. Even when the duty ratio of the liquid crystal display device is shorter than that of the liquid crystal display device, the brightness of the backlight panel 210 equivalent to that of the liquid crystal display device according to Comparative Example 1 and Comparative Example 2 can be realized. That is, when the adjustment value is other than the maximum value, lighting of the backlights 211a to 211c can be made closer to the impulse response. Thus, the motion blur can be improved.

  In the backlight drive circuit 100 according to the first embodiment, the first current is supplied when the adjustment value is higher than the threshold, and the second current is supplied when the adjustment value is lower than the threshold. When the value is changed, the current supplied to the backlight 211 is largely switched, which may cause flicker.

  On the other hand, in backlight drive circuit 400 according to the present embodiment, the larger the adjustment value is, the larger current is supplied, and the smaller the adjustment value is, the smaller current is supplied to backlights 211a to 211c. The switching current changes steplessly according to the adjustment value. As a result, even if the adjustment value is changed, the current supplied to the backlight 211 is not largely 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, the detailed configuration of the D / A converter 420 in the present embodiment will be described. FIG. 14 is a circuit diagram showing an example of a detailed configuration of D / A converter 420. Referring to FIG.

  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.

  In the transistor Q21, the emitter is grounded, the collector is connected to each of the backlight drivers 130a to 130c through the resistors R22 and R24, and the duty ratio of the backlight adjustment pulse output from the SOC 411 to the base through the resistor R21. The voltage according to is input. Therefore, as the voltage input to the base increases, the current flowing between the collector and the 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 is reduced. 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 and R24 rises. Thus, the voltages supplied to the backlight drivers 130a to 130c are increased. That is, the transistor Q21 is an inverting circuit that inverts the voltage.

  Furthermore, the transistor Q21, the resistors R22 to R25, and the capacitors C22 and C23 constitute an RC integration circuit. This RC integration circuit passes frequency components lower than the frequency according to the time constant determined by the transistor Q21, the resistors R22 to R25, and the 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, the lower the duty ratio of the pulse. Therefore, the voltage of the signal that has passed through the RC integration circuit decreases as the duty ratio increases. That is, the higher the adjustment value of the backlight panel, the lower it becomes.

  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 the emitter of the transistor Q21. The duty ratio of the voltage at the connection point of Therefore, as the duty ratio of the voltage input to the base of the transistor Q21 is higher (the adjustment value of the backlight panel is higher), the duty ratio of the voltage supplied from the backlight drivers 130a to 130c is lower.

  On the other hand, the pulse output from the inverting circuit is a pulse with a higher duty ratio as the adjustment value of the backlight panel is lower. Therefore, 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.

  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 the emitter of the transistor Q21. The duty ratio of the voltage at the connection point of is increased. Thus, 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.

  Therefore, the D / A converter 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, and the lower the adjustment value, the higher the voltage.

2-2. Effect etc>
As described above, in the backlight drive circuit 400 according to the present embodiment, the drive current during the period in which each backlight 211 is lit is a smaller current as the adjustment value is higher, and a larger current 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 in 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 in the lighting period of the backlight 211 with respect to the adjustment value. The same drawing shows the drive current supplied to the backlight 211 in Embodiment 2 and the drive current supplied to the backlight in Comparative Example 2 described above.

  As shown in the figure, in Comparative Example 2, the drive current supplied to the backlight is always 350 [mA], which is a constant current, 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 Comparative Example 2, and the adjustment value is low. The larger the current, the larger the current. 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 formed of an LED, the rated current that can be supplied to the backlight 211 differs depending on the lighting duty ratio, and the lower the lighting duty ratio, the higher the rated current. Therefore, the rated current corresponding to the minimum lighting duty ratio of the combination of the lighting duty ratio capable of realizing the luminance corresponding to the adjustment value and the rated current may be used as the current value of the driving current.

  As described above, in the backlight drive circuit 400 according to the second embodiment, the drive current supplied to the backlight 211 is switched steplessly according to the adjustment value. Thus, 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 shown 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 of this current is as large as 300 [mA], and flicker may occur when switching the adjustment value.

  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 of this current is 30 [mA], which is sufficiently smaller than the amount of change of the current in the backlight drive circuit 100 according to the first embodiment. Therefore, the backlight drive circuit 400 according to the second embodiment can suppress flicker that occurs at the time of switching the adjustment value.

  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 the 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 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 the duty ratio of Comparative Example 2.

  Thus, the liquid crystal display device on which the backlight drive circuit 400 according to the present embodiment is mounted achieves the same effect as the liquid crystal display device on which the backlight drive circuit 100 according to the first embodiment is mounted. That is, when the adjustment value is 10 or less, the motion blur and double reflection can be suppressed more than in the liquid crystal display device according to Comparative Example 2.

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

  Here, an adjustment value that can make the lighting duty ratio of the backlight 33% or less will be confirmed using FIG.

  As shown in FIG. 16, in the liquid crystal display device according to Comparative Example 2, the adjustment values that can make the lighting duty ratio of the backlight 33% or less are only 0, 1 and 2, and other adjustment values (adjustment values In 3 or more, since the lighting duty ratio of a backlight becomes higher than 33%, it is difficult to acquire a scanning effect. That is, in the liquid crystal display device according to Comparative Example 2, the scan effect can be obtained only in the region 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 enables the lighting duty ratio of the backlight to be 33% or less is 0 to 10. That is, as in the liquid crystal display device 200 according to the first embodiment, the scan effect can be obtained in the region where the adjustment value is 10 or less. Therefore, as compared with the liquid crystal display device according to Comparative Example 2, the scan effect can be obtained even in the region where the adjustment value is large. That is, according to the liquid crystal display device according to the comparative example 2, even when the backlight 211 emits light with high luminance, a scan effect can be obtained.

  Thus, in the backlight drive circuit 400 according to the second embodiment 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 lower the adjustment value, the backlight The drive current supplied to 211 is reduced. Further, the lighting duty ratio of the backlight 211 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.

  Further, in the backlight drive circuit 400 according to the second embodiment, the drive current supplied to the backlight 211 is switched steplessly according to the adjustment value. Thus, 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 using FIGS. 17 to 19.

  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. The table also shows the lighting duty ratio, the driving current, and the 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, in the backlight panel 210 to which the backlight drive circuit 400 according to the present embodiment is connected, the adjustment value is smaller in comparison with 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 driving 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 smaller lighting duty than the backlight panel in the liquid crystal display device according to Comparative Example 2 when the adjustment value is other than the maximum value. It is possible to turn on with the same level of brightness as the backlight panel in the liquid crystal display device according to Comparative Example 2 in terms of ratio. In other words, when the adjustment value is other than the maximum value, 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 Comparative Example 2.

  As described above, the backlight panel 210 to which the backlight drive circuit 400 according to the present embodiment is connected has a case where the adjustment value is other than the maximum value as compared with the backlight panel in the liquid crystal display device according to Comparative Example 2. In addition, by setting the lighting duty ratio small and increasing the driving current of the backlight, it is possible to realize the same brightness as that of 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 the present 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 almost the same chromaticity even when the adjustment value is changed. That is, there is almost no difference in chromaticity.

  Thus, 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 realize the light emission characteristics equivalent to 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 smaller lighting duty than the backlight panel in the liquid crystal display device according to Comparative Example 2 when the adjustment value is other than the maximum value. By the ratio, it is possible to realize the light emission characteristics equivalent to the backlight panel in the liquid crystal display device according to Comparative Example 2. In other words, it 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 Comparative Example 2. Thus, the backlight drive circuit 400 according to the present embodiment can suppress motion blur as in 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 is switched steplessly according to the adjustment value. Thereby, the backlight drive circuit 400 according to the present embodiment can further suppress flicker as compared to the backlight drive circuit 100 according to the first embodiment.

  Further, the backlight drive circuit 400 according to the second embodiment of the present invention is generated by the D / A conversion unit 420 (voltage generation unit) that generates a higher voltage as the adjustment value is lower, and the D / A conversion unit 420. And a backlight driver 130 which converts the voltage into a current and supplies the current as a drive current. Thus, 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 drive circuit 400 according to the second embodiment, the pulse signals PWM0 to PWM2 corresponding to the backlight drivers 130a to 130c are generated using the SOC 411 and the TCON 112, but the SOC is a pulse signal without using the TCON 112. 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, but differs in that a timing instruction unit 510 made 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. In other words, three pulse signals PWM0 to PWM2 synchronized with the vertical synchronization signal are generated based on the signal indicating the input adjustment value. Further, it generates a backlight adjustment pulse of a duty ratio corresponding to the adjustment value indicating the luminance of the backlight panel 210, and outputs it to the D / A converter 420.

  In the backlight drive circuit 500 according to the modification of the second embodiment, the same effect as that of the second embodiment can be obtained. That is, it is possible to suppress the flicker and to suppress the motion blur and double reflection 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 designated by a user operation or may be designated by an illumination sensor attached to the liquid crystal display device. Also, it may be specified according to the scanning signal (ie, dynamic backlight). Further, the adjustment values of the backlights 211a to 211c may be independently designated, or may be independently designated according to, for example, a scanning signal.

  In the first embodiment and its modification, the voltage switching circuit 120 switches the voltage to be generated using the voltage switching pulse output from the SOC. However, the present invention is not limited to this configuration. For example, the voltage switching circuit 120 may have an integration circuit and a comparator, and may be configured to receive a backlight adjustment pulse from the SOC 111.

  Further, although the transistors Q11 and Q21 have been described as bipolar transistors in the above embodiment, they may be MOS (metal-oxide-semiconductor) transistors. Further, in the above embodiment, the transistors Q11 and Q21 have been described as n-type transistors, but p-type transistors may be used. In this case, the same function 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). In this case, the response speed of the liquid crystal pixel 221 is If Trs is used, a scan effect can be obtained in the case of an adjustment value that allows the lighting duty ratio to be ((n-1) / n) -Trs or less. In addition, in the same display period (Display period), the timing of turning off the mth (1 ≦ m ≦ n) backlight 211 is from the start of the display period, assuming that one display period is Td. 1) / n) × Td may be turned off after time.

  In addition, part or all of the components constituting the above-described backlight drive circuit may be configured from one system LSI (Large Scale Integration: large scale integrated circuit). The system LSI is a super-multifunctional LSI manufactured by integrating a plurality of components on one chip, and more specifically, a computer system including a microprocessor, a ROM, a 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.

  Further, the circuit configuration shown in the above circuit diagram is an example, and the present invention is not limited to the above circuit configuration. That is, like the above circuit configuration, a circuit capable of realizing the characteristic function of the present invention is also included in the present invention. For example, 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 is included in the present invention as long as the same function as the above circuit configuration can be realized. In other words, “connected” in the above embodiment is not limited to the case where two terminals (nodes) are directly connected, but the two terminals (in the range where similar functions can be realized). Also includes the case where nodes are connected via elements.

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

  The present invention can be applied to a display device such as a television for displaying an image, a smartphone or a tablet terminal.

100, 300, 400, 500 backlight drive circuit 110, 310, 410, 510 timing instruction unit 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 Transistor R11, R12, R21-R25 Resistance

Claims (6)

A display unit,
A light source that lights up by a drive signal,
A control unit that outputs the drive signal;
The drive signal has a change ratio of a duty ratio of the drive signal to a change of the adjustment value indicating the brightness of the light source in a brightness range lower than a predetermined brightness, a change of the adjustment value in a brightness range higher than the predetermined brightness. Less than the rate of change of the duty ratio of the drive signal with respect to
When the adjustment value is higher than the threshold value which is the predetermined brightness and when the adjustment value is the threshold value or less, the drive signal at the brightness less than the predetermined brightness under the condition that the level of the drive signal is constant . level is greater than the level of the drive signal in the brightness higher than the previous SL predetermined luminance,
Display device. 2. The display device according to claim 1, wherein the level of the drive signal at the first brightness equal to or less than the predetermined brightness is substantially equal to the level of the drive signal at the second brightness different from the first brightness equal to or less than the predetermined brightness. 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. Display device. A voltage generation unit that generates a first voltage when the luminance of the light source is higher than the predetermined luminance, and generates a second voltage higher than the first voltage when the luminance of the light source is less than the predetermined luminance,
The display device according to any one of claims 1 to 3, wherein the control unit outputs the drive signal based on the first voltage and the second voltage. The light emitting apparatus further includes a timing instruction unit that instructs lighting and extinguishing timings 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 any one of claims 1 to 4 , wherein the control unit outputs the drive signal based on an instruction of the timing instruction unit. The display device according to any one of claims 1 to 5 , wherein the luminance is designated by a user operation.

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