JP4843295B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device used for a liquid crystal television, a liquid crystal monitor, a car navigation system, and the like.

  Conventionally, a TN liquid crystal display element has been generally used as the liquid crystal display element.

  An OCB type liquid crystal display element has been studied as a liquid crystal display element characterized by high-speed response (for example, Non-Patent Document 1).

  In this OCB type liquid crystal display element, a liquid crystal is sandwiched between substrates, and a transparent electrode is formed on the substrate as a voltage applying means. In the state before the power is turned on, the alignment state of the liquid crystal is a state called splay alignment. When the device is turned on, a relatively large voltage is applied to the voltage applying means in a short time to shift the liquid crystal alignment to the bend alignment state. It is a feature of the OCB type liquid crystal display mode that display is performed using this bend alignment state.

  Further, this OCB type liquid crystal display element is often used in combination with an active matrix substrate having a TFT transistor or the like.

  This OCB liquid crystal can respond at high speed, and can be written twice in one frame period. A technique for making use of this characteristic and writing a black display period separately from a display signal in one frame is disclosed (for example, Patent Document 1 and Patent Document 2). This is called black insertion driving. The purpose of this black insertion is to prevent “reverse transition” to return to the splay orientation and to improve the visibility of moving images.

In general, a liquid crystal display device has a function of adjusting brightness, which is performed by changing the driving frequency of the backlight.
The Institute of Electrical Communication IEICE Technical Report EDI 98-144, page 199 Japanese Patent Application No. 2000-214827 Japanese Patent Application No. 2002-107695

  However, in the liquid crystal display device using the black insertion drive, there is a problem that flickering of the screen occurs when the light is adjusted by changing the drive frequency of the backlight.

  An object of the present invention is to provide a liquid crystal display device that can prevent flickering of a screen when dimming by changing a drive frequency of a backlight in a liquid crystal display device using black insertion driving.

According to the present invention, there is provided a liquid crystal display device for displaying on a liquid crystal display panel according to an input signal, the control means for driving and controlling the liquid crystal display panel, and the backlight for illuminating the liquid crystal display panel from the display back side. A backlight control means for controlling lighting of the backlight, and a black writing period and a signal writing period for the liquid crystal display panel by the control means are paired in each horizontal scanning period, and in a continuous horizontal scanning period. And the control means controls the liquid crystal display panel via a gate driver circuit and a source driver circuit, and inserts black by shifting a predetermined period from the scanning gate start pulse of the input signal. A gate start pulse for scanning is applied to the gate driver circuit, and the black display time ratio of the liquid crystal display panel is black. The liquid crystal display device is provided, wherein a varied markups to adjust the brightness of light emitted from the liquid crystal display panel.

  In the liquid crystal display device of the present invention, since the backlight frequency can be constant, continuous light control without flickering is possible.

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

  FIG. 1 shows a configuration of a liquid crystal display device of the present invention. The liquid crystal display device 1 includes a backlight unit 2 on the back surface and a transmissive liquid crystal display panel 3. The liquid crystal display panel 3 has a plurality of gate lines 4 and a plurality of source lines 5, and is connected to a gate driver circuit 6 and a source driver circuit 7, respectively. The controller 10 controls the liquid crystal display panel 3 via the gate driver circuit 6 and the source driver circuit 7, and controls the backlight unit 2 via the backlight control circuit 11. The gate driver circuit 6 includes a shift register circuit 61 and a buffer circuit 62, which will be described in detail later.

  The liquid crystal display panel 3 uses an OCB type liquid crystal display element.

  The OCB type liquid crystal display element has a basic configuration in which rubbing treatment is performed on upper and lower substrates so that these directions are parallel to each other. This OCB type liquid crystal display element is in a splay alignment state in which liquid crystal molecules are arranged substantially in parallel when an initial voltage is not applied.

  2A and 2B show the configuration of the liquid crystal display element in the liquid crystal display panel 3. FIG. A liquid crystal layer 31 is sandwiched between substrates 32 and 33, and phase difference plates 34 and 35 and polarizing plates 36 and 37 are provided outside the substrate.

  As shown in FIG. 2A, the liquid crystal layer 31 is splayed when no voltage is applied. Here, the substrate 32 is subjected to an alignment process, which is a parallel alignment process so that the liquid crystal molecules are aligned as shown in FIG.

  As shown in FIG. 2B, the alignment of the liquid crystal layer 31 is changed to a bend alignment state used for display. In order to perform this transition, a relatively large transition voltage, for example, about 25 V is applied to the liquid crystal layer 31. This transition voltage and application time are specific to the device and are not adjusted.

  FIG. 3 shows an equivalent circuit showing a pixel structure on the substrate 33 of the liquid crystal display panel 3. The substrate 33 includes a plurality of pixel electrodes PE arranged in a substantially matrix shape, a plurality of gate wirings 4 arranged along a row of the plurality of pixel electrodes PE, and a plurality arranged along a column of the plurality of pixel electrodes PE. Source wiring 5, and the gate TFT 4 and the pixel TFT disposed near the intersection of the source wiring 5. The substrate 32 facing the substrate 33 has a counter electrode CE arranged facing the plurality of pixel electrodes PE.

  A signal corresponding to display data is applied to the source line 5, and a gate signal for operating the pixel TFT at a specific timing to electrically connect the pixel electrode PE and the source line 5 is applied to the gate line 4.

  FIG. 4 shows a concept of a waveform for driving the liquid crystal display panel 3.

From the gate driver circuit 6, a gate pulse is input to the gate wiring 4, which is sequentially scanned and makes a round in one field period. At this time, there are a gate pulse group for black writing and a gate pulse group for signal writing, and two gate pulses for black writing and signal writing are input to one gate wiring 4.

The gate pulse for black writing and the gate pulse for signal are not opened at the same time, and are shifted by one pulse. That is, the black insertion period and the signal writing period are alternately arranged. A black signal is applied to the source line 5 during the black insertion period, and a predetermined signal voltage is applied to the source line 5 during the signal writing period. Here, the source signal and the black signal are shown with the same polarity, and the signal becomes larger as it moves up and down in the figure. However, since dot inversion driving is actually used, display is performed while switching the polarity, which is somewhat complicated. FIG. 4 is conceptually simplified.

In this way, the black writing gate pulse and the signal gate pulse are shifted from each other for a certain period. At this time, if the black insertion period is defined as the time during which a black signal is input for a frame, it can be defined as the timing from when the black signal is written until the next signal is written.

  FIG. 5 shows how black areas are sequentially scanned. That is, as shown in FIG. 5, a phenomenon occurs in which black areas are sequentially scanned.

The gate driver circuit 6 includes a shift register circuit 61 that sequentially forwards a gate scanning signal and a buffer circuit 62 that amplifies the signal of the shift register circuit 61 . The shift register circuit 61 can be operated by inputting a clock signal for controlling timing and a start pulse for inputting a start signal to the first line.

  Here, in order to perform dimming of the backlight unit 2, when the blinking cycle of the backlight is adjusted, there is a problem that a band-like unevenness is seen or blinks slowly by synchronizing with the scanning of black insertion. In order to avoid this, the backlight had to blink at a timing synchronized with the scanning timing for black insertion, and the options for the backlight dimming frequency were reduced, and dimming was possible only with a jump value.

  In practice, continuous dimming is desirable.

  Next, a first embodiment of the present invention will be described.

In this embodiment, the width of the black insertion period is adjusted by changing the time width between the black insertion start pulse corresponding to the black writing gate pulse and the signal start pulse corresponding to the signal gate pulse. Here, the ratio of the black insertion period to the frame is defined as the black insertion rate.

  Since the clock is the same, the frame period and the scanning speed are constant. Therefore, in order to lengthen the black insertion period, the time from when the black insertion start pulse is input until when the signal start pulse is input is increased. Conversely, in order to shorten the black insertion period, the time from when the black insertion start pulse is input to when the signal start pulse is input is shortened.

  When the black insertion rate is changed, the period during which black is displayed in one screen is changed, so that the overall brightness is changed and light control can be realized.

  In the present invention, the black insertion rate can be changed from 16% to 99%, and the brightness can be adjusted by almost 1%. If it is 16% or less, there is a concern of returning to the splay orientation.

  Specifically, in the configuration shown in FIG. 1, the controller 10 performs dimming by changing and controlling the black insertion period of the liquid crystal display panel 3 via the gate driver circuit 6.

  FIG. 5 shows a comparatively bright case, and the black insertion period is controlled to be relatively short. That is, the controller 10 starts black writing by inputting a black insertion start pulse to the gate driver circuit 6, and after a predetermined black insertion period ends, inputs a signal start pulse to the gate driver circuit 6 and starts signal writing.

  The positions of black writing and signal writing shown in (a) of FIG. 5 are sequentially controlled as shown in (b), (c), and (d) (scanning in the arrow direction).

  FIG. 6 shows a comparatively dark case, and the black insertion period is controlled to be relatively long. The positions of black writing and signal writing shown in (a) of FIG. 6 are sequentially controlled as shown in (b), (c), and (d) (scanning in the arrow direction).

  As described above, according to the first embodiment, since it actually depends on the number of lines, it is strictly a jump value, but in practice it can be changed continuously. As a result, since the backlight frequency can be made constant, practically continuous light control without flickering is possible.

  The first embodiment is not limited to this driving method, and the black insertion pulse may be applied a plurality of times in order to increase the charging capability, or the black insertion pulse may be applied simultaneously on a plurality of lines.

  Next, a second embodiment will be described.

  In this embodiment, the scanning backlight unit 2 is used.

  FIG. 7 shows the scanning backlight unit 2. This scanning backlight unit 2 has a direct tube type fluorescent tube 21, 22, 23, 24, 25, 26 in a direct type configuration.

  The scanning backlight unit 2 according to the present embodiment sequentially scans the non-lighting periods of the fluorescent tubes 21 to 26.

  A liquid crystal display panel 3 for scanning black insertion is disposed on the scanning backlight unit 2, and the black insertion of the scanning backlight unit 2 and the black insertion of the liquid crystal display panel 3 are driven in synchronization. At this time, if the lighting frequency of the fluorescent tubes 21 to 26 of the scanning backlight unit 2, the scanning timing of the fluorescent tubes 21 to 26, and the black insertion timing of the liquid crystal display panel 3 are not matched, the flickering is caused. Unevenness or coloring occurs.

  Therefore, the controller 10 of the present embodiment is connected to the lighting frequency of the fluorescent tubes 21 to 26 of the scanning backlight unit 2 through the backlight control circuit 11, the scanning timing of the fluorescent tubes 21 to 26, and the gate driver circuit 6. Thus, matching control with the black insertion timing of the liquid crystal display panel 3 is performed.

  That is, in the scanning backlight unit 2, the fluorescent tubes 21 and 22 are turned off in FIG. 7A, the fluorescent tubes 23 and 24 are turned off in FIG. In c), the fluorescent tubes 24 and 25 are scanned in the direction of the arrow so that they are not lit.

  In addition, in the conventional dimming with the lighting frequency of the fluorescent tube, a more difficult adjustment is required.

  As described above, according to the second embodiment, the black insertion period of the liquid crystal display panel can be changed in small increments according to the number of gate lines, so that it can be adjusted pseudo-continuously.

  It is also effective to vary the black insertion period of the liquid crystal display panel when dimming with the above-described scanning backlight.

  Also, the brightness adjustment by the black insertion rate is effective even in the scanning backlight.

  Next, a third embodiment will be described.

  In this embodiment, the scanning backlight unit 2 of the second embodiment described above is an LED backlight. That is, in this embodiment, a plurality of light emitting diodes (LEDs) are used instead of a plurality of fluorescent tubes (not shown).

  The light emitting diode has a merit that the brightness can be adjusted by using a current amount by continuously lighting. Therefore, dimming with black insertion driving is possible. However, since the variation among the elements of the LED cannot be controlled uniformly, non-uniformity may occur in the surface of the liquid crystal display panel 3 when current dimming is performed.

  Also in this method, the light control by the black insertion drive is effective.

  Moreover, there is also an advantage that moving image visibility can be improved by taking as much black insertion rate as possible.

  Next, a fourth embodiment will be described.

  FIG. 8 shows a configuration of a liquid crystal display device 51 according to the fourth embodiment. The same parts as those of the liquid crystal display device 1 shown in FIG. The present liquid crystal display device 51 is a liquid crystal display device 1 provided with a light control circuit 12.

  In other words, the liquid crystal display device 51 includes a light control circuit 12 that sends a digital signal (light control signal) to the controller 10 that determines the timing of liquid crystal driving in accordance with the light control signal.

In the liquid crystal display device 51, the gate driver circuit 6 generates a gate pulse for signal and a gate pulse for black writing by the controller 10 that is controlled according to the dimming signal from the dimming circuit 12. The source driver circuit 7 drives the liquid crystal display panel 3 while switching the timing for writing signals and black .

  The dimming method of the fourth embodiment is not limited to the adjustment of the black insertion period.

  Also, the blinking period of the backlight may be adjusted and changed within a range where there is no problem in image quality.

  In addition, the backlight may be dimmed while changing the backlight extinction period in the scanning backlight. If the black insertion rate is increased, the contrast may be lowered. In this case, the backlight may be adjusted as needed.

  Furthermore, since black insertion can be performed continuously, it is realistic to adjust the backlight in large steps.

  As described above, according to the embodiment of the present invention, it is possible to provide a liquid crystal display device capable of continuously adjusting the luminance while adopting the black insertion driving method.

  Note that the present invention is a liquid crystal display device that adjusts the brightness by changing the black insertion rate, whether it is a single system or a composite system.

1 is a block diagram schematically showing a circuit configuration of a liquid crystal display device. The figure which shows the structure of the liquid crystal display element in a liquid crystal display panel. FIG. 6 is a diagram showing an equivalent circuit showing a pixel structure in a substrate of a liquid crystal display panel. The figure which shows the concept of the waveform which drives a liquid crystal display panel. The figure which shows a black area being scanned sequentially. The figure which shows how black insertion period is controlled comparatively long. The figure which shows a scanning type backlight unit. The figure which shows the structure of the liquid crystal display device which concerns on 4th Example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1,51 ... Liquid crystal display device, 2 ... Backlight unit, 3 ... Liquid crystal display panel, 4 ... Gate line, 5 ... Source line, 6 ... Gate driver circuit, 7 ... Source driver circuit, 10 ... Controller, 11 ... Backlight Control circuit, 12 ... light control circuit, 21-26 ... fluorescent tube, 31 ... liquid crystal layer, 32, 33 ... substrate, 34, 35 ... phase difference plate, 36, 37 ... polarizing plate, 61 ... shift register circuit, 62 ... Buffer circuit.

Claims (6)

A liquid crystal display device that displays on a liquid crystal display panel according to an input signal,
Control means for driving and controlling the liquid crystal display panel;
A backlight for illuminating the liquid crystal display panel from the display back side;
A backlight control means for controlling lighting of the backlight,
The black writing period and the signal writing period for the liquid crystal display panel by the control means are combined in each horizontal scanning period, and are alternately arranged over successive horizontal scanning periods , and the control means includes the liquid crystal display panel. The display panel is controlled through a gate driver circuit and a source driver circuit, and a black insertion scanning gate start pulse is input to the gate driver circuit while being shifted from the scanning gate start pulse of the input signal by a predetermined period. A liquid crystal display device, wherein the brightness of light emitted from the liquid crystal display panel is adjusted by changing a black insertion rate which is a ratio of a black display time of the panel.   The liquid crystal display device according to claim 1, wherein the backlight is a scanning backlight.   3. The backlight is composed of a plurality of fluorescent tubes, and the control means performs control to sequentially scan individual non-lighting periods in the plurality of fluorescent tubes via the backlight control means. The liquid crystal display device described.   3. The backlight is composed of a plurality of light emitting diodes, and the control means performs control to sequentially scan individual non-lighting periods in the plurality of light emitting diodes through the backlight control means. The liquid crystal display device described.   5. The liquid crystal display device according to claim 1, wherein the control means continuously changes a black insertion rate of the liquid crystal display panel.   The liquid crystal display device according to claim 1, wherein the liquid crystal display panel is composed of OCB liquid crystal.

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