JPWO2006095743A1 - Display device, liquid crystal monitor, liquid crystal television receiver and display method - Google Patents

Abstract

In this display device, the control unit (15) divides the frame into the period of the subsequent subframe and the previous subframe, and displays the previous subframe in black at low luminance while displaying the subsequent subframe in white at high luminance. To do. Thereby, the white floating phenomenon can be suppressed. Further, the control unit (15) switches the light source of the display unit (14) to n. The light is dimmed by a PWM dimming method at a dimming frequency of 450 Hz or higher. Thereby, generation | occurrence | production of a horizontal stripe can be prevented. Further, since the dimming frequency is sufficiently increased, flicker can be made inconspicuous.

Description

  The present invention relates to a display device that displays an image by dividing one frame into a plurality of subframes.

  In recent years, liquid crystal display devices, particularly color liquid crystal display devices having a TN (twisted nematic) type liquid crystal display panel (TN mode liquid crystal panel; TN panel), are often used in fields where CRTs (cathode ray tubes) have been used. It has become like this. For example, Patent Literature 1 discloses a liquid crystal display device that switches a driving method of a TN panel depending on whether a displayed image is a moving image or a still image.

  By the way, such a TN panel has a slight problem in viewing angle characteristics as compared with a CRT. For this reason, there is an angle at which the gradation characteristics change and the gradation is inverted as the line-of-sight angle (the angle at which the panel is viewed; the angle between the normal direction of the panel and the direction at which the panel is viewed) increases.

  Therefore, conventionally, a technique for improving viewing angle characteristics using an optical film and a description for suppressing gradation inversion by devising a display method have been developed. For example, in Patent Document 2 and Patent Document 3, there is a method in which one frame is divided and signal writing is performed multiple times on one pixel, and the signal writing voltage level is improved in combination.

In addition, in a liquid crystal display panel that requires a wide viewing angle such as a TV (television receiver), a liquid crystal in an IPS (In-Plane-Switching) mode or a VA (Vertical Alignment) mode is used instead of the TN mode. To achieve a wider viewing angle. For example, in a VA mode liquid crystal panel (VA panel), the contrast is 10 or more in the range of 170 ° in the vertical and horizontal directions, and gradation inversion is eliminated.
JP 2001-296841 A (publication date: October 26, 2001) Japanese Patent Laid-Open No. 5-68221 (issue date; March 19, 1993) JP 2002-23707 A (publication date: January 25, 2002) JP 2000-321551 A (publication date; November 24, 2000) Japanese Laid-Open Patent Publication No. 9-127717 (Publication Date: May 16, 1997) JP 2004-4659 (release date; January 8, 2004) New edition Color Science Handbook; Second Edition (University of Tokyo Press; Release date; June 10, 1998)

  However, even with a VA panel, which is said to have a wide viewing angle, the change in gradation characteristics due to the viewing angle cannot be completely eliminated. For example, when the viewing angle in the left-right direction increases, the gradation characteristics deteriorate.

  That is, as shown in FIG. 2, when the viewing angle is 60 degrees, the gray scale γ characteristic changes and the halftone brightness becomes brighter when the panel is desired from the front (viewing angle 0 degree). Will happen.

  In addition, regarding the IPS mode liquid crystal panel, although depending on the design of optical characteristics such as an optical film, the gradation characteristics change depending on the increase in the viewing angle.

  The present invention has been made in view of the conventional problems as described above. And the objective is to provide the display apparatus which can suppress a white floating phenomenon.

  In order to solve the above problems, a display device of the present invention is a display device that displays an image by dividing one frame into m (m; an integer of 2 or more) subframes, A display unit that displays an image having a luminance based on the voltage, and a first display signal that is a display signal of the first to mth subframes so that the sum of the luminances output from the display unit in one frame is not changed by dividing the frame. To a control unit that generates and outputs the m-th display signal to the display unit, and the control unit is configured to dimm the light source of the display unit by a PWM dimming method.

  This display device displays an image using a display unit having a display screen made up of liquid crystal display elements. In this display device, the control unit drives the display unit by sub-frame display. Here, the subframe display is a display method in which one frame is divided into a plurality of (m; m is an integer of 2 or more) subframes (first to mth subframes).

  That is, the control unit outputs the display signal to the display unit m times during one frame period (the first to mth display signals that are the display signals of the first to mth subframes are sequentially output). As a result, the control unit turns on all the gate lines on the display screen of the display unit once each subframe period (m times ON in one frame).

  In addition, the control unit preferably sets the output frequency (clock) of the display signal to m times (m times clock) during normal hold display. Note that the normal hold display is a normal display performed without dividing a frame into subframes (display in which all gate lines on the display screen are turned ON only once in one frame period).

  The display unit (display screen) is designed to display a luminance image based on the voltage of the display signal input from the control unit (voltage corresponding to the luminance gradation of the display signal).

  Then, the control unit generates the first to m-th display signals so as not to change the total luminance (total luminance) output from the screen into one frame by dividing the frame (the voltages of these display signals). Is set). Note that the voltage of the display signal is a voltage (liquid crystal voltage) applied to the liquid crystal of each pixel in the display portion.

  Here, usually, on the display screen of the display unit, when the voltage of the display signal (liquid crystal voltage) is made to be minimum or close to the maximum, the deviation (brightness deviation) between the actual brightness and the planned brightness at a large viewing angle is sufficiently small. it can.

  Here, the brightness is the degree of brightness perceived by humans according to the brightness of the displayed image (see equations (5) and (6) in the embodiments described later). If the sum of luminances output in one frame is unchanged, the sum of brightnesses output in one frame is not changed.

  The planned brightness is the brightness (value corresponding to the liquid crystal voltage) that should be displayed on the display screen. The actual brightness is the brightness actually displayed on the screen and is a value that changes according to the viewing angle. At the front of the screen, the actual brightness and the planned brightness are equal, and there is no brightness deviation. On the other hand, as the viewing angle increases, the brightness shift increases.

  Therefore, in the present display device, when displaying an image, it is preferable that the control unit brings the at least one voltage of the first to m-th display signals to a minimum or a maximum. As a result, the brightness shift in at least one subframe can be sufficiently reduced. As a result, in this display device, the brightness deviation can be suppressed smaller than in the case of performing the normal hold display, so that the viewing angle characteristics can be improved. For this reason, the white floating phenomenon can be satisfactorily suppressed.

  In addition, the display quality of the moving image can be improved by performing the subframe display as described above. That is, when the movement of the object displayed in the normal hold display is followed, the color and brightness of the immediately preceding frame can be seen at the same time. For this reason, the edge of the object is recognized as blurred.

  On the other hand, when a moving image is displayed in subframe display (particularly low luminance), the luminance of any subframe of each frame is low. For this reason, it can suppress that the image of the currently recognized frame and the image (color / brightness) of the immediately preceding frame are visually mixed. Therefore, the edge blur as described above can be avoided and the display quality of the moving image can be improved.

  The display device is designed to perform dimming by the PWM dimming method. The display unit (liquid crystal display element) of this display device expresses gradation by controlling the amount of transmitted light. Therefore, some kind of light source (fluorescent tube, LED, EL, FED, etc.) is necessary. Further, at present, in a large display element, it is common to use a fluorescent tube as a light source for efficiency.

  In general, there are two light source dimming methods: a current dimming method (or voltage dimming method) and a PWM dimming method.

  The current dimming method is a method of controlling the magnitude (brightness) of light emitted from the light source by changing the amplitude of the current (lamp current) applied to the light source. When a fluorescent tube is used as the light source, if the amplitude of the lamp current is too small, the fluorescent tube will not shine. For this reason, the current dimming method has a drawback that the dimming range (brightness range that can be realized) cannot be widened. Therefore, it can be said that it is preferable to adopt the PWM dimming method in an apparatus that requires a wide dimming range such as a liquid crystal television.

  Note that if PWM dimming and subframe display are simply combined, interference phenomena such as flicker and horizontal stripes may occur. That is, in the sub-frame display, when PWM dimming is performed, the dimming frequency and the sub-frame frequency interfere with each other, and the frequency of the light waveform transmitted through the display unit (transmission waveform) is larger than the dimming frequency. It may go down. In such a case, the user feels a strong flicker.

  This flicker has a dimming frequency of n. The closer to 5 times (n is an integer), the more intense it becomes. Further, when the dimming frequency is n times the frame frequency, the frequency of the transmission waveform becomes equal to the frame frequency, so that flicker can be reduced to an inconspicuous level. However, when the dimming frequency is brought close to n times the frame frequency, an interference phenomenon occurs in which horizontal stripes are generated on the screen.

  In other words, the light source usually irradiates the entire screen with light at the same time. On the other hand, the display unit (liquid crystal display element) is driven by line scanning. Therefore, each line on the display screen is turned ON / OFF at different times according to the position. For this reason, on the lines at different positions, the ON / OFF timing of the response waveform of the liquid crystal is shifted (slides with respect to time).

  Therefore, the ratio of the time for which the transmission waveform is turned on (time for high brightness) varies depending on the line position. For this reason, a difference occurs in the average luminance between the lines, and this is recognized as a horizontal stripe phenomenon.

  When the dimming frequency is exactly n times the frame frequency, the horizontal stripes are stopped on the screen. And as it deviates from n times, horizontal stripes begin to flow up and down the screen. Further, the dimming frequency deviates greatly from n times, n. As the frequency approaches five times, the horizontal stripes disappear.

  That is, the dimming frequency is set to n. If it is 5 times, the light emission waveform of the light source has an opposite phase between adjacent frames. Therefore, the transmission waveform from each line also has an opposite phase between adjacent frames. For this reason, the amount of transmitted light in each of the two frames from each line can be made equal (it can be compensated for time), thereby avoiding the occurrence of horizontal stripes.

  Therefore, in this display device, when combining PWM dimming and sub-frame display, the control unit can set the dimming frequency to “a value that is n.5 times the frame frequency and 450 Hz or higher”. preferable.

  In this case, the dimming frequency is set to n. Since it is 5 times, the above horizontal stripes do not occur. As for flicker, although the frequency of the transmission waveform in each line is half the frame frequency, since the dimming frequency is sufficiently increased, the flicker can be made inconspicuous.

  That is, the two lines (referred to as lines A and B) of the display unit have a reversed relationship for each frame (the light amount of the first frame (second frame) of line A is the second frame (1 The same as (frame)). If lines having such a relationship can be densely arranged on the screen, flicker can be spatially compensated by allowing the user to visually recognize the light from these lines simultaneously.

  Here, the distance between the two lines having the relationship as described above becomes closer as the dimming frequency becomes higher. Therefore, by sufficiently increasing the dimming frequency, the value is set to n. Even if it is set to 5 times, flicker can be made inconspicuous.

  In addition, when the luminance is 50% (when the black insertion rate is 50%), an experimental result has been obtained that flicker becomes inconspicuous if the dimming frequency is set to 450 Hz or more. Flicker is most noticeable when the black insertion rate is 50%.

  Therefore, in the present display device, the occurrence of both horizontal stripes and flicker can be avoided by setting the dimming frequency to “a value that is n.5 times the frame frequency and 450 Hz or higher”. .

  In addition, it is possible to suppress the interference phenomenon without increasing the dimming frequency. For example, “the light emission waveform of the light source is a waveform combining a main light emission pulse and a luminance compensation pulse, both having a frequency n.5 times the frequency of the frame, and having opposite pulse phases and different pulse widths.” Can be realized.

  In this configuration, in the transmission waveform of each line, the transmission amount of the main light emission pulse and the luminance compensation pulse increases or decreases for each frame, but the ratio is opposite for each frame. For example, when the generation ratio of the main light emission pulse (high) for one line is 2.5 to 3 in the first frame to the second frame, the luminance compensation pulse is 3 to 2.5 in the opposite direction.

  For this reason, although the frequency of the transmission waveform is small, the luminance difference between frames can be reduced by using the luminance compensation pulse. Accordingly, flicker can be made inconspicuous.

  Further, in this configuration, since the dimming frequency can be made lower than 450 Hz, it is possible to avoid a decrease in driving efficiency of the light source. In this configuration, since two pulses are used, there is a concern that efficiency may deteriorate. However, the pulse width of the luminance compensation pulse is very small compared to the frame period. Therefore, it can be said that the influence of the luminance compensation pulse on the driving efficiency of the light source is sufficiently small.

  Further, it is possible to control the dimming frequency to be n times the frame frequency. For example, the control unit emits a main light emission pulse having a frequency of n times the frame frequency and a relatively long pulse width from the light source. Then, the main light emission pulse is controlled to be phase-inverted every frame.

  In this case, although the above horizontal stripes can be avoided, it is preferable to take measures against flicker. Therefore, the control unit inserts the luminance compensation pulse having a relatively short pulse width into the light emission waveform of the light source at the same frequency as that of the main light emission pulse and in the opposite phase. Further, the control unit inserts a luminance compensation added pulse or a luminance compensation reduced pulse in place of the luminance compensation pulse at the timing when the phase of the main light emission pulse changes.

  Here, the luminance compensation added pulse is a pulse for turning on the light source, which is inserted when the main light emission pulse is continuously turned off (low). On the other hand, the luminance compensation reduced pulse is a pulse for turning off the light source, which is inserted when the main light emission pulse is continuously turned on (high).

  That is, in this configuration, when the light amount of the main light emission pulse is too small, the luminance compensation additional pulse is inserted to increase the light amount, while when the light amount of the main light emission pulse is too large, the luminance compensation reduced pulse is inserted to increase the light amount. Designed to lower.

  Thereby, in this configuration, the difference in luminance between frames in each line can be reduced (the time average luminance of each frame can be made close to constant). Therefore, flicker can be reduced.

  In addition, when combining the sub-frame display and the PWM dimming in the present display device, when the display unit has a plurality of light sources, the control unit makes the emission waveforms of at least two light sources have different phases. It is also preferable to perform PWM dimming.

  In this configuration, the light emission waveform of each light source is shifted, so that the DC component of the mixed light including the light from all the light sources can be increased. Therefore, the amount of time variation in the light emission amount of the light source can be reduced. Further, the difference in light emission amount between the lines can be reduced. Therefore, interference phenomena such as flicker and horizontal stripes can be made inconspicuous without increasing the frequency of the dimming signal.

  In this case, the control unit divides each light source into p groups (p is a natural number of 2 or more), and performs control to shift the phase of the light emission waveform of the light source by 360 ° / p for each group. It is preferable. Thereby, the DC component of the mixed light can be greatly increased.

  Note that in the case of using a plurality of light sources as described above, a direct type backlight, a side type backlight, a side type front light, or the like can be used as the light source. Note that when a backlight is used, the display portion is a transmissive or transflective display element. When a front light is used, the display unit is a reflective display element.

  In addition, when the display unit includes a light source group in which a plurality of direct light sources are arranged, each light source has a gate line group including a plurality of gate lines close to itself (a part of all the gate lines). Light will be sent to the group.

  In this case, the control unit sets the frequency of the light emission waveform of the light source to n times the frequency of the frame and “the state of the light emission waveform of the light source when the gate line group assigned to each light source is turned on”. It is preferable to perform PWM dimming so that all light sources (all gate line groups) are the same.

  In this case, flicker does not occur because the dimming frequency is n times the frame frequency. In this configuration, the phase relationship between the light emission waveform of the light source and the response waveform of the liquid crystal is the same in all the gate line groups. Therefore, in this configuration, it is possible to prevent the ratio of the time during which the transmission waveform is turned on (the time during which the luminance is high) from being different depending on the line position. Therefore, since there is no difference in the average luminance between the lines, it is possible to avoid the occurrence of the horizontal stripe phenomenon.

  Further, when sub-frame display and PWM dimming are combined in the present display device, the control unit may be set to perform PWM dimming in a state where constant light emission power is supplied to the light source.

  Thereby, the light emission waveform becomes a waveform in which the amplitude corresponding to the PWM dimming overlaps with a constant amplitude. Therefore, the DC component of the light emission waveform can be easily increased.

  For this reason, the time fluctuation amount in the light emission amount of the light source can be reduced. Further, the difference in light emission amount between the lines can be reduced. Therefore, interference phenomena such as flicker and horizontal stripes can be made inconspicuous without increasing the frequency of the dimming signal.

  When subframe display and PWM dimming are combined, when a reflective or transflective liquid crystal display element is used for the display unit, the light from the light source may be designed to be controlled in accordance with the external light.

  In this configuration, it is preferable to include a luminance sensor that detects a luminance waveform of external light irradiated on the display unit. And it is preferable that a control part performs PWM light control so that the light emission waveform of a light source may be made into the opposite phase with the same frequency as the luminance waveform of external light.

  As a result, in this configuration, it is possible to irradiate the display unit with light having a large DC component, which is a mixture of light having the same frequency and opposite phase. Therefore, with this configuration, the amount of time variation in the light emission amount of the light source can be reduced. Further, the difference in light emission amount between the lines can be reduced. Therefore, interference phenomena such as flicker and horizontal stripes can be made inconspicuous without increasing the frequency of the dimming signal. Further, a fluorescent tube, LED, EL, FED, or the like can be used as a light source of the display device.

  In addition, a liquid crystal monitor used for a personal computer or the like can be configured by combining this display device and an image signal input unit (signal input unit).

  Here, the image signal input unit is for transmitting an image signal input from the outside to the control unit. In this configuration, the control unit of the display device generates a display signal based on the image signal transmitted from the image signal input unit and outputs the display signal to the display unit.

  In addition, a liquid crystal television receiver can be configured by combining the display device and the tuner unit.

  Here, the tuner unit is for receiving a television broadcast signal. In this configuration, the control unit of the display device generates a display signal based on the television broadcast signal transmitted from the tuner unit and outputs the display signal to the display unit.

Further, the image display method of the present invention (the present display method)
A display method for displaying an image by dividing one frame into m (m; an integer greater than or equal to 2) subframes, and the sum of the luminances output from the display unit in one frame is not changed by dividing the frame. As described above, the first to mth display signals, which are display signals of the first to mth subframes, are generated and output to the display unit including the liquid crystal display element, and the light source of the display unit is further PWM-controlled. It is a method including a dimming step of dimming light.

  This display method is a method used in the above-described display device. Therefore, in this display method, the brightness shift can be suppressed smaller than in the case of performing the normal hold display, so that the viewing angle characteristics can be improved. For this reason, the white floating phenomenon can be satisfactorily suppressed. It is also possible to improve the display quality of moving images.

  Further, by performing dimming by the PWM dimming method, it is possible to perform dimming in a wider range than when using the current dimming method.

  As described above, the display device of the present invention is a display device that displays an image by dividing one frame into m (m; an integer of 2 or more) subframes, and is based on the voltage of the display signal. A display unit that displays an image of luminance, and first to mth displays that are display signals of the first to mth subframes so that the sum of the luminances output from the display unit in one frame is not changed by dividing the frame. And a control unit that generates a signal and outputs the signal to the display unit, and the control unit is configured to dimm the light source of the display unit by a PWM dimming method.

  In the present display device, by performing the sub-frame display, it is possible to suppress the brightness deviation as compared with the case of performing the normal hold display. Therefore, since the viewing angle characteristics can be improved, the whitening phenomenon can be satisfactorily suppressed. It is also possible to improve the display quality of moving images. Further, by performing dimming by the PWM dimming method, it is possible to perform dimming in a wider range than when using the current dimming method.

  Other objects, features, and advantages of the present invention will be fully understood from the following description. The benefits of the present invention will become apparent from the following description with reference to the accompanying drawings.

It is a block diagram which shows the structure of the display apparatus concerning one Embodiment of this invention. It is a graph which shows the display luminance (relationship between plan luminance and actual luminance) output from a liquid crystal panel in the case of normal hold display. 3 is a graph showing display luminance (a relationship between planned luminance and actual luminance) output from a liquid crystal panel when subframe display is performed in the display device shown in FIG. 1. (A) is explanatory drawing which shows the image signal input into the frame memory of the display apparatus shown in FIG. 1, (b) is output to the front | former stage LUT from a frame memory in the case of dividing | segmenting into 3: 1. (C) is an explanatory diagram showing the image signal output to the subsequent LUT. FIG. 3 is an explanatory diagram illustrating ON timings of gate lines related to a front display signal and a rear display signal when a frame is divided into 3: 1 in the display device illustrated in FIG. 1. It is a graph which shows what converted the graph of the brightness | luminance shown in FIG. 3 into the brightness. 2 is a graph showing a relationship between planned brightness and actual brightness when a frame is divided into 3: 1 in the display device shown in FIG. 1. It is explanatory drawing which shows the display apparatus which changed the structure of the display apparatus shown in FIG. 1 partially. It is explanatory drawing which shows the method of inverting the polarity of the voltage between electrodes with a frame period. It is explanatory drawing which shows the method of inverting the polarity of the voltage between electrodes with a frame period. It is a figure for demonstrating the response speed of a liquid crystal. It is a figure for demonstrating the response speed of a liquid crystal. It is a figure for demonstrating the response speed of a liquid crystal. It is a graph which shows the display brightness | luminance (relationship between a plan brightness | luminance and actual brightness | luminance) output from a liquid crystal panel when performing a sub-frame display using a liquid crystal with slow response speed. It is a graph which shows the brightness | luminance displayed by a front sub-frame and a back sub-frame when display brightness | luminance is 3/4 and 1/4 of Lmax. It is a graph which shows the transition state of a liquid crystal voltage at the time of changing the polarity of the voltage (liquid crystal voltage) applied to a liquid crystal with a sub-frame period. It is explanatory drawing which shows the method of inverting the polarity of the voltage between electrodes with a frame period. It is explanatory drawing which shows the method of inverting the polarity of the voltage between electrodes with a frame period. It is explanatory drawing which shows the polarity of the four pixels in a liquid crystal panel, and the liquid crystal voltage of each pixel. It is explanatory drawing which shows the polarity of the four pixels in a liquid crystal panel, and the liquid crystal voltage of each pixel. It is explanatory drawing which shows the polarity of the four pixels in a liquid crystal panel, and the liquid crystal voltage of each pixel. It is explanatory drawing which shows the polarity of the four pixels in a liquid crystal panel, and the liquid crystal voltage of each pixel. It is a graph shown together with the result (broken line and solid line) which divided and displayed the frame into three equal subframes, and the result (one-dot chain line and solid line) which performed normal hold display. It is a graph which shows the transition of a liquid-crystal voltage when dividing | segmenting a flame | frame into three and inverting a voltage polarity for every flame | frame. It is a graph which shows the transition of a liquid crystal voltage when dividing | segmenting a flame | frame into 3 and inverting a voltage polarity for every sub-frame. The relationship between the signal gradation (%; luminance gradation of the display signal) output to the display unit and the actual luminance gradation (%) corresponding to each signal gradation in the subframe where the luminance is not adjusted (viewing angle scale) It is a graph which shows a tonal characteristic (measurement). It is explanatory drawing which shows a current light control system. It is explanatory drawing which shows a PWM light control system. It is a graph which shows the example of the waveform of a light control signal, a lamp current waveform, and a light emission waveform (waveform of the light output from a fluorescent tube) at the time of using a fluorescent tube as a light source. It is a block diagram which shows the internal structure of the display apparatus which performs PWM light control regarding this invention. The graph which shows the example of the relationship of the light emission waveform of a light source, the waveform of the voltage between electrodes of a liquid crystal (liquid crystal response waveform), and the waveform of the light which permeate | transmits a liquid crystal (transmission waveform) at the time of combining PWM dimming with a normal hold display. is there. It is a graph which shows the same waveform at the time of combining PWM dimming with sub-frame display (in the case of low brightness). It is a graph which shows the example of the relationship of the light emission waveform of a light source, a liquid crystal response waveform, and a transmission waveform at the time of combining PWM dimming with a sub-frame display. It is a graph which shows the example of the relationship of the light emission waveform of a light source, a liquid crystal response waveform, and a transmission waveform when the light control frequency is set to "a value of n.5 times the frame frequency and 450 Hz or more". It is a graph which shows the example of the relationship of the light emission waveform, liquid crystal response waveform, and transmission waveform of a light source at the time of using a brightness | luminance compensation pulse. It is a graph which shows the example of the relationship of the light emission waveform of a light source, a liquid crystal response waveform, and a transmission waveform in the phase inversion of the light emission waveform of a light source for every flame | frame. It is a graph which shows the example of the relationship of the light emission waveform of a light source, a liquid crystal response waveform, and a transmission waveform when making the light emission waveform of a light source into an antiphase for every flame | frame, and adding a positive compensation pulse and a negative compensation pulse. It is a block diagram which shows the structure of a display apparatus in the case of controlling the light emission waveform of a light source so that a direct current | flow component (DC component) may be included. (A) and (b) show the emission waveform (first waveform) of the first fluorescent tube, the emission waveform (second waveform) of the second fluorescent tube, and the emission waveforms of both fluorescent tubes in the configuration shown in FIG. It is a graph which shows the example of the mixed waveform (mixed waveform). It is a block diagram which shows the structure of a display apparatus in the case where a fluorescent tube is divided into three types and it controls independently for every kind. (A) (b) is a graph which shows the example of the fluorescent tube (1st-3rd waveform) in the structure shown in FIG. 30, and the waveform (mixed waveform) which mixed these. It is explanatory drawing which shows the structure of the liquid crystal display element which has a direct type | mold backlight. It is explanatory drawing which shows the structure of the backlight type liquid crystal display element provided with two LED as a light source in two sides of a light-guide plate. It is explanatory drawing which shows the structure of the backlight type liquid crystal display element provided with two LED as a light source in one side of the light-guide plate. It is explanatory drawing which shows the structure of the liquid crystal display element of a front light type provided with two LED as a light source in two sides of a light-guide plate. It is explanatory drawing which shows the structure of the liquid crystal display element of a front light type provided with two LED as a light source in one side of a light-guide plate. It is a block diagram which shows the structure of a display apparatus in the case of synchronizing the light emission timing of a fluorescent tube, and the ON timing of the gate line of a liquid crystal panel. It is a graph which shows the example of the relationship of the light emission waveform of a light source, a liquid crystal response waveform, and a transmission waveform regarding the display apparatus shown in FIG. It is a block diagram which shows the structure of the display apparatus which uses together a PWM dimming system and a current dimming system. 42 is a graph showing an example of a current dimming control signal, a PWM dimming control signal, a lamp current, and a light emission waveform related to the display device shown in FIG. It is a figure which shows the structure of the reflection type display apparatus which performs light source control according to external light. 44 is a graph showing a luminance waveform of external light incident on the display device shown in FIG. It is a graph which shows the light emission waveform of the light source in the display apparatus shown in FIG. 44 is a graph showing a waveform of light incident on a liquid crystal panel of the display device shown in FIG. It is a figure which shows the structure of the transflective display device which performs light source control according to external light. It is explanatory drawing which shows the structure of the liquid crystal television provided with the display apparatus shown in FIG.

  An embodiment of the present invention will be described.

  The liquid crystal display device (present display device) according to this embodiment includes a vertical alignment (VA) mode liquid crystal panel divided into a plurality of domains. The display device functions as a liquid crystal monitor that displays an image signal input from the outside on a liquid crystal panel.

  FIG. 1 is a block diagram showing an internal configuration of the display device. As shown in this figure, the display device includes a frame memory (FM) 11, a front LUT 12, a rear LUT 13, a display unit 14, and a control unit 15.

  The frame memory (image signal input unit) 11 accumulates image signals (RGB signals) input from an external signal source for one frame. The front-stage LUT (look-up table) 12 and the rear-stage LUT 13 are correspondence tables (conversion tables) between image signals input from the outside and display signals output to the display unit 14.

  Note that this display device performs subframe display. Here, the sub-frame display is a method of performing display by dividing one frame into a plurality of sub-frames.

  In other words, this display device is designed to perform display using two subframes having the same size (period) at twice the frequency based on an image signal for one frame input in one frame period. Yes.

  The front LUT 12 is a correspondence table for display signals (previous display signal; second display signal) output in the previous subframe (previous subframe; second subframe). On the other hand, the rear-stage LUT 13 is a correspondence table for display signals (rear-stage display signals; first display signals) output in the rear-stage subframe (rear subframe; first subframe).

  As shown in FIG. 1, the display unit 14 includes a liquid crystal panel 21, a gate driver 22, and a source driver 23, and performs image display based on an input display signal. Here, the liquid crystal panel 21 is a VA mode active matrix (TFT) liquid crystal panel.

  The control unit 15 is a central part of the display device that controls all operations in the display device. Then, the control unit 15 generates a display signal from the image signal stored in the frame memory 11 using the preceding LUT 12 and the subsequent LUT 13 and outputs the display signal to the display unit 14.

  That is, the control unit 15 stores an image signal transmitted at a normal output frequency (normal clock; for example, 25 MHz) in the frame memory 11. Then, the control unit 15 outputs the image signal from the frame memory 11 twice by a clock having a frequency twice that of the normal clock (double clock; 50 MHz).

  And the control part 15 produces | generates a front | former stage display signal using the front | former stage LUT12 based on the image signal output for the first time. After that, based on the image signal output for the second time, a rear stage display signal is generated using the rear stage LUT 13. Then, these display signals are sequentially output to the display unit 14 with a double clock.

  Accordingly, the display unit 14 displays different images once each in one frame period based on two display signals that are sequentially input (all gate lines of the liquid crystal panel 21 are displayed as one in both subframe periods). Turn on once at a time). The display signal output operation will be described in detail later.

  Here, generation of the front display signal and the rear display signal by the control unit 15 will be described. First, general display brightness (the brightness of an image displayed on the panel) related to the liquid crystal panel will be described.

  Display signal when normal 8-bit data is displayed in one frame without using subframes (in case of normal hold display in which all the gate lines of the liquid crystal panel are turned ON only once in one frame period) The luminance gradation (signal gradation) is in a range from 0 to 255.

The signal gradation and display luminance in the liquid crystal panel are approximately expressed by the following equation (1).
((T−T0) / (Tmax−T0)) = (L / Lmax) ^ γ (1)
Here, L is a signal gradation (frame gradation) when an image is displayed in one frame (when an image is displayed in normal hold display), Lmax is a maximum luminance gradation (255), T is a display luminance, Tmax is the maximum luminance (luminance when L = Lmax = 255; white), T0 is the minimum luminance (luminance when L = 0; black), and γ is a correction value (normally 2.2). In the actual liquid crystal panel 21, T0 is not 0. However, in order to simplify the description, T0 = 0 is assumed below.

  In this case (in the case of normal hold display), the display luminance T output from the liquid crystal panel 21 is shown as a graph in FIG. In this graph, “brightness to be output (scheduled luminance; value corresponding to signal gradation, equivalent to the above display luminance T)” is plotted on the horizontal axis, and “brightness actually output (actual luminance is plotted on the vertical axis). ) ”.

  As shown in this graph, in this case, the above two luminances are equal on the front surface (viewing angle 0 degree) of the liquid crystal panel 21. On the other hand, when the viewing angle is set to 60 degrees, the actual brightness becomes brighter at a halftone brightness due to a change in the gradation γ characteristic.

Next, display luminance in the present display device will be described.
In the present display device, the control unit 15
(A) “Display of one frame when normal hold display is performed on the sum of the luminance (display luminance) of the images displayed by the display unit 14 in each of the previous subframe and the subsequent subframe (integrated luminance in one frame) Equal to brightness. ''
(B) “Make one subframe black (minimum luminance) or white (maximum luminance)”
It is designed to perform gradation expression so as to satisfy.

  For this reason, in the present display device, the control unit 15 is designed to divide the frame equally into two subframes and display the luminance up to half of the maximum luminance by one subframe.

  That is, when the luminance up to half of the maximum luminance (threshold luminance; Tmax / 2) is output in one frame (in the case of low luminance), the control unit 15 sets the previous subframe to the minimum luminance (black) and sets the subsequent subframe. The gradation expression is performed by adjusting only the display luminance of (the gradation expression is performed using only the subsequent subframe). In this case, the integrated luminance in one frame is “(minimum luminance + brightness of subsequent subframe) / 2”.

  Further, when outputting a luminance higher than the above threshold luminance (in the case of high luminance), the control unit 15 sets the rear subframe to the maximum luminance (white), and adjusts the display luminance of the previous subframe to express the gradation expression. Do.

  In this case, the integrated luminance in one frame is “(luminance of the previous subframe + maximum luminance) / 2”.

  Next, the signal gradation setting of display signals (previous display signal and subsequent display signal) for obtaining such display luminance will be specifically described. The signal gradation setting is performed by the control unit 15 shown in FIG. The control unit 15 calculates in advance the frame gradation corresponding to the above-described threshold luminance (Tmax / 2) using the above-described equation (1).

That is, the frame gradation (threshold luminance gradation; Lt) corresponding to such display luminance is expressed by the following equation (1):
Lt = 0.5 ^ (1 / γ) × Lmax (2)
However, Lmax = Tmax ^ γ (2a)
It becomes.

  The control unit 15 obtains the frame gradation L based on the image signal output from the frame memory 11 when displaying the image.

When L is equal to or less than Lt, the control unit 15 sets the luminance gradation (F) of the previous display signal to the minimum (0) by the previous LUT 12. On the other hand, the control unit 15 sets the luminance gradation (R) of the subsequent display signal based on the equation (1).
R = 0.5 ^ (1 / γ) × L (3)
Is set using the latter-stage LUT 13.

When the frame gradation L is greater than Lt, the control unit 15 sets the luminance gradation R of the subsequent display signal to the maximum (255). On the other hand, the control unit 15 sets the luminance gradation F of the previous subframe based on the expression (1).
F = (L ^ γ−0.5 × Lmax ^ γ) ^ (1 / γ) (4)
And

  Next, the display signal output operation in the present display device will be described in more detail. Hereinafter, the number of pixels of the liquid crystal panel 21 is a × b. In this case, the control unit 15 accumulates the previous stage display signal of the pixel (a number) of the first gate line in the source driver 23 with the double clock.

  Then, the control unit 15 turns on the first gate line by the gate driver 22 and writes the previous stage display signal to the pixels of this gate line. Thereafter, the control unit 15 similarly turns on the second to b-th gate lines with a double clock while changing the previous display signal accumulated in the source driver 23. As a result, the previous stage display signal can be written to all the pixels in a half period of one frame (1/2 frame period).

  Further, the control unit 15 performs the same operation, and writes the post-stage display signal to the pixels of all the gate lines in the remaining ½ frame period. As a result, the front display signal and the rear display signal are written to each pixel at an equal time (1/2 frame period).

  FIG. 3 shows the result (broken line and solid line) of the subframe display in which the preceding display signal and the subsequent display signal are divided into the front and rear subframes for output (broken line and solid line). ).

  In the present display device, as shown in FIG. 2, the deviation between the actual luminance at a large viewing angle and the planned luminance (equivalent to the solid line) is minimum (0) when the display luminance is minimum or maximum, The liquid crystal panel 21 that is the largest in the halftone (near the threshold luminance) is used.

  And in this display apparatus, the sub-frame display which divides | segments one frame into a sub-frame is performed. Furthermore, the period of the two subframes is set to be equal, and in the case of low luminance, the previous subframe is displayed in black and display is performed using only the rear subframe within a range in which the integrated luminance in one frame is not changed. Therefore, since the shift in the previous subframe is minimized, the total shift in both subframes can be reduced to about half as shown by the broken line in FIG.

  On the other hand, in the case of high luminance, the display is performed by adjusting the luminance of only the previous subframe while the subsequent subframe is displayed in white within a range in which the integrated luminance in one frame is not changed. For this reason, also in this case, the shift of the subsequent subframe is minimized, so that the total shift of both subframes can be reduced to about half as shown by the broken line in FIG.

  Thus, in this display device, it is possible to reduce the overall displacement by about half compared to a configuration in which normal hold display is performed (a configuration in which an image is displayed in one frame without using a subframe). ing. For this reason, it is possible to suppress a phenomenon (white floating phenomenon) in which a halftone image becomes bright and floats white as shown in FIG.

  In the present embodiment, it is assumed that the periods of the previous subframe and the subsequent subframe are equal. This is because the luminance up to half of the maximum value is displayed in one subframe. However, these subframe periods may be set to different values.

  In other words, the whitening phenomenon, which is a problem in this display device, is that when the viewing angle is large, the actual luminance has the characteristics as shown in FIG. It is a phenomenon.

  Normally, an image captured by the camera is a signal based on luminance. When this image is transmitted in a digital format, the image is converted into a display signal using γ shown in equation (1) (that is, the luminance signal is raised to (1 / γ) and divided equally. To add gradation). And based on such a display signal, the image displayed by display devices, such as a liquid crystal panel, will have the display brightness shown by (1) Formula.

  By the way, the human visual sense receives an image not as luminance but as brightness. The lightness (lightness index) M is expressed by the following equations (5) and (6) (see Non-Patent Document 1).

M = 116 × Y ^ (1/3) -16, Y> 0.008856 (5)
M = 903.29 × Y, Y ≦ 0.008856 (6)
Here, Y corresponds to the actual luminance described above, and is an amount Y = (y / yn). Here, y is the y value of the tristimulus value in the xyz color system of any color, and yn is the y value of the standard diffuse reflection surface with yn = 100.

  From these equations, humans tend to be sensitive to dark images and become insensitive to bright images. And it is considered that human beings receive whiteness as brightness deviation, not brightness deviation.

  Here, FIG. 6 is a graph showing the luminance graph shown in FIG. 3 converted to lightness. This graph shows the lightness to be output on the horizontal axis (scheduled lightness; a value corresponding to the signal gradation, corresponding to the above lightness M), and the lightness actually output (actual lightness) on the vertical axis. Yes. As indicated by the solid line in this graph, the two brightness values described above are equal on the front surface of the liquid crystal panel 21 (viewing angle 0 degree).

  On the other hand, as shown by the broken line in this graph, when the viewing angle is 60 degrees and the period of each subframe is equal (that is, when the luminance up to half of the maximum value is displayed in one subframe) On the other hand, the deviation between the actual brightness and the scheduled brightness is improved as compared with the conventional case in which the normal hold display is performed. Therefore, it can be seen that the whitening phenomenon can be suppressed to some extent.

  In addition, it can be said that it is more preferable to determine the frame division ratio according to the brightness rather than the luminance in order to suppress the white floating phenomenon more greatly in accordance with the human visual sense. The deviation between the actual brightness and the scheduled brightness is the largest at the half of the maximum value of the scheduled brightness, as in the case of the luminance.

  Therefore, rather than dividing the frame so that the luminance up to half the maximum value is displayed in one subframe, it is better to divide the frame so that the brightness up to half the maximum value is displayed in one subframe. It will be possible to improve the deviation (ie, whitening) felt by humans.

Therefore, a preferable value at a frame division point will be described below.
First, in order to perform the calculation easily, the above-described equations (5) and (6) are collectively approximated into a form like the following equation (6a) (a form similar to equation (1)).
M = Y ^ (1 / α) (6a)
When converted into such a form, α in this equation is about 2.5.

  If the value of α is between 2.2 and 3.0, the relationship between the luminance Y and the lightness M in equation (6a) is considered appropriate (corresponds to human visual sense). It has been.

  In order to display the lightness M that is half of the maximum value in one subframe, the period of two subframes is approximately 1: 3 when γ = 2.2 and γ = 3.0. Has been found to be preferably about 1: 7. When dividing a frame in this way, the subframe used for display when the luminance is low (the subframe that is maintained at the maximum luminance in the case of high luminance) is set to a short period. It becomes.

  The case where the period between the previous subframe and the subsequent subframe is 3: 1 will be described below. First, display luminance in this case will be described.

  In this case, when performing low-brightness display in which the luminance up to 1/4 of the maximum luminance (threshold luminance; Tmax / 4) is output in one frame, the control unit 15 sets the previous subframe to the minimum luminance (black). ), And gradation expression is performed by adjusting only the display luminance of the subsequent subframe (the gradation expression is performed using only the subsequent subframe). At this time, the integrated luminance in one frame is (minimum luminance + luminance of subsequent subframe) / 4.

  In addition, when the luminance higher than the threshold luminance (Tmax / 4) is output in one frame (in the case of high luminance), the control unit 15 sets the rear subframe to the maximum luminance (white) and adjusts the display luminance of the previous subframe. Then, gradation expression is performed. In this case, the integral luminance in one frame is (luminance of the previous subframe + maximum luminance) / 4.

  Next, the signal gradation setting of display signals (previous display signal and subsequent display signal) for obtaining such display luminance will be specifically described. Also in this case, the signal gradation (and output operation described later) is set so as to satisfy the conditions (a) and (b) described above.

  First, the control unit 15 calculates a frame gradation corresponding to the above-described threshold luminance (Tmax / 4) in advance using the above-described equation (1).

That is, the frame gradation (threshold luminance gradation; Lt) corresponding to such display luminance is expressed by the following equation (1):
Lt = (1/4) ^ (1 / γ) × Lmax (7)
The control unit 15 obtains the frame gradation L based on the image signal output from the frame memory 11 when displaying the image. When L is equal to or less than Lt, the control unit 15 sets the luminance gradation (F) of the previous display signal to the minimum (0) using the previous LUT 12.

On the other hand, the control unit 15 determines the luminance gradation (R) of the subsequent display signal based on the expression (1).
R = (1/4) ^ (1 / γ) × L (8)
Is set using the latter-stage LUT 13.

When the frame gradation L is greater than Lt, the control unit 15 sets the luminance gradation R of the subsequent display signal to the maximum (255). On the other hand, the control unit 15 sets the luminance gradation F of the previous subframe based on the expression (1).
F = ((L ^ γ− (1/4) × Lmax ^ γ)) ^ (1 / γ) (9)
And

Next, the output operation of such a front display signal and a rear display signal will be described.
As described above, in the configuration in which the frame is divided equally, the front display signal and the rear display signal are written to the pixels for an equal time period (1/2 frame period). This is because the ON-period of the gate line for each display signal is equalized because the subsequent display signal is written after all the previous display signals are written with the double clock.

  Therefore, the division ratio can be changed by changing the write start timing of the subsequent display signal (gate ON timing related to the subsequent display signal).

  4A shows an image signal input to the frame memory 11, FIG. 4B shows an image signal output from the frame memory 11 to the preceding LUT 12 in the case of 3: 1 division, and FIG. FIG. 6 is an explanatory diagram showing image signals output to the subsequent LUT 13 in the same manner. FIG. 5 is an explanatory diagram showing the ON timing of the gate line related to the front display signal and the rear display signal in the case of the same 3: 1 division.

  As shown in these drawings, in this case, the control unit 15 writes the first stage display signal of the first frame to the pixels of each gate line with a normal clock. Then, after the 3/4 frame period, writing of the subsequent display signal is started. From this time, the front display signal and the rear display signal are alternately written with a double clock.

  That is, after writing the previous display signal to the pixels of the “3 / 4th of all gate lines” gate line, the subsequent display signal related to the first gate line is accumulated in the source driver 23, and this gate line is turned ON. Next, the previous stage display signal relating to “3/4 of all gate lines” + 1st gate line is accumulated in the source driver 23, and this gate line is turned ON.

  In this manner, after the 3/4 frame period of the first frame, the front display signal and the rear display signal are alternately output with the double clock, so that the ratio of the front subframe and the rear subframe is 3: 1. It becomes possible to do. The total display luminance (integral sum) in these two sub-frames becomes the integrated luminance in one frame. The data stored in the frame memory 11 is output to the source driver 23 in accordance with the gate timing.

  FIG. 7 is a graph showing the relationship between the scheduled brightness and the actual brightness when the frame is divided into 3: 1. As shown in this figure, in this configuration, the frame can be divided at the point where the difference between the planned brightness and the actual brightness is the largest. Therefore, compared with the result shown in FIG. 6, the difference between the planned brightness and the actual brightness when the viewing angle is 60 degrees is very small.

  In other words, in the present display device, in the case of low luminance (low brightness) up to “Tmax / 4”, the previous subframe is displayed in black and only the rear subframe is displayed within a range in which the integrated luminance in one frame is not changed. It is carried out. Accordingly, the deviation (the difference between the actual brightness and the scheduled brightness) in the previous subframe is minimized, so that the total deviation between both subframes can be reduced to about half as shown by the broken line in FIG.

  On the other hand, in the case of high luminance (high lightness), the display is performed by adjusting the luminance of only the previous subframe while the subsequent subframe is displayed in white within a range in which the integrated luminance in one frame is not changed. For this reason, also in this case, since the shift of the subsequent subframe is minimized, the total shift of both subframes can be reduced to about half as shown by the broken line in FIG.

  As described above, in this display device, it is possible to reduce the brightness deviation to about a half as compared with the configuration in which the normal hold display is performed. For this reason, it is possible to more effectively suppress the phenomenon in which a halftone image becomes bright and floats white as shown in FIG. 2 (white float phenomenon).

  Here, in the above description, it is assumed that the previous stage display signal of the first frame is written to the pixels of each gate line with a normal clock during the period of 3/4 frame from the start of display. This is because the timing for writing the subsequent display signal has not been reached.

  However, instead of such a measure, display with a double clock may be performed from the start of display using a dummy subsequent display signal. That is, during the period from the start of display to the 3/4 frame period, the preceding display signal and the succeeding display signal (dummy succeeding display signal) with the signal gradation 0 may be alternately output.

Here, the case where the ratio of the front subframe and the rear subframe is n: 1 will be described below in general. In this case, when the luminance up to 1 / (n + 1) (threshold luminance; Tmax / (n + 1)) of the maximum luminance is output in one frame (in the case of low luminance), the control unit 15 sets the previous subframe to the minimum luminance ( Black), and gradation expression is performed by adjusting only the display luminance of the subsequent subframe (the gradation expression is performed using only the subsequent subframe).
In this case, the integrated luminance in one frame is (minimum luminance + luminance of subsequent subframe) / (n + 1).

  Further, when outputting a luminance higher than the threshold luminance (Tmax / (n + 1)) (in the case of high luminance), the control unit 15 sets the rear subframe to the maximum luminance (white) and adjusts the display luminance of the previous subframe. To express gradation. In this case, the integrated luminance in one frame is “(luminance of the previous subframe + maximum luminance) / (n + 1)”.

  Next, the signal gradation setting of display signals (previous display signal and subsequent display signal) for obtaining such display luminance will be specifically described. Also in this case, the signal gradation (and output operation described later) is set so as to satisfy the conditions (a) and (b) described above.

  First, the control unit 15 calculates a frame gradation corresponding to the above threshold luminance (Tmax / (n + 1)) in advance using the above-described equation (1).

That is, the frame gradation (threshold luminance gradation; Lt) corresponding to such display luminance is expressed by the following equation (1):
Lt = (1 / (n + 1)) ^ (1 / γ) × Lmax (10)
The control unit 15 obtains the frame gradation L based on the image signal output from the frame memory 11 when displaying the image. When L is equal to or less than Lt, the control unit 15 sets the luminance gradation (F) of the previous display signal to the minimum (0) using the previous LUT 12.

On the other hand, the control unit 15 determines the luminance gradation (R) of the subsequent display signal based on the expression (1).
R = (1 / (n + 1)) ^ (1 / γ) × L (11)
Is set using the latter-stage LUT 13.

When the frame gradation L is greater than Lt, the control unit 15 sets the luminance gradation R of the subsequent display signal to the maximum (255). On the other hand, the control unit 15 sets the luminance gradation F of the previous subframe based on the expression (1).
F = ((L ^ γ− (1 / (n + 1)) × Lmax ^ γ)) ^ (1 / γ) (12)
And

  As for the output operation of the display signal, in the operation when the frame is divided into 3: 1, after the n / (n + 1) frame period of the first frame, the front display signal and the rear display signal are generated with a double clock. What is necessary is just to design so that it may output alternately.

  Further, it can be said that the structure for equally dividing the frame is as follows. That is, one frame is divided into “1 + n (= 1)” subframe periods. Then, a preceding display signal is output in one subframe period with a clock that is “1 + n (= 1)” times the normal clock, and the succeeding display signal is continuously output in the subsequent n (= 1) subframe periods. Output.

  However, in this configuration, when n is 2 or more, it is necessary to speed up the clock very much, which increases the device cost. Accordingly, when n is 2 or more, it is preferable to alternately output the preceding display signal and the succeeding display signal as described above. In this case, the ratio of the preceding subframe and the succeeding subframe can be set to n: 1 by adjusting the output timing of the subsequent stage display signal. Can be doubled.

  In the present embodiment, the control unit 15 converts the image signal into a display signal using the front-stage LUT 12 and the rear-stage LUT 13. Here, a plurality of front-stage LUTs 12 and rear-stage LUTs 13 included in the display device may be provided.

  FIG. 8 is a configuration in which, in the configuration shown in FIG.

  That is, the response characteristics and gradation luminance characteristics of the liquid crystal panel 21 change depending on the environmental temperature (the temperature (air temperature) of the environment where the display unit 14 is placed). For this reason, the optimal display signal corresponding to the image signal also changes according to the environmental temperature.

  The preceding LUTs 12a to 12c are the preceding LUTs suitable for use in different temperature ranges. The rear-stage LUTs 13a to 13c are also rear-stage LUTs suitable for use in different temperature ranges.

  The temperature sensor 16 measures the environmental temperature where the display device is placed, and transmits the measurement result to the control unit 15.

  In this configuration, the control unit 15 is designed to switch the LUT to be used based on the environmental temperature information transmitted from the temperature sensor 16. Therefore, with this configuration, a more appropriate display signal can be transmitted to the liquid crystal panel 21 with respect to the image signal. Therefore, it is possible to display an image with more faithful luminance in all assumed temperature ranges (for example, a range of 0 ° C. to 65 ° C.).

  The liquid crystal panel 21 is preferably driven by alternating current. This is because the alternating current drive can change the charge polarity of the pixel (the direction of the voltage between the pixel electrodes (interelectrode voltage) sandwiching the liquid crystal) for each frame.

  In the case of direct current drive, a biased voltage is applied between the electrodes, so that charges accumulate on the electrodes. If this state continues, even when no voltage is applied, a potential difference occurs between the electrodes (so-called burn-in state).

  Here, when performing subframe display as in the present display device, the voltage value (absolute value) applied between the pixel electrodes is often different between subframes.

  Therefore, when the polarity of the interelectrode voltage is inverted in the subframe period, the applied interelectrode voltage is biased due to the difference in voltage value between the previous subframe and the subsequent subframe. For this reason, when the liquid crystal panel 21 is driven for a long time, electric charges are accumulated on the electrodes, and the above-described image sticking or flicker may occur.

  Therefore, in this display device, it is preferable to invert the polarity of the voltage between the electrodes at a frame period (period of one frame time width). There are two methods for inverting the polarity of the voltage between the electrodes at the frame period. One method is a method of applying a voltage having the same polarity for one frame. In another method, the interelectrode voltage is reversed between two subframes in one frame, and the subsequent subframe and the previous subframe of the next frame are driven with the same polarity. It is.

  FIG. 9A shows the relationship between the voltage polarity (polarity of the voltage between electrodes) and the frame period when the former method is adopted. FIG. 9B shows the relationship between the voltage polarity and the frame period when the latter method is used. By making the interelectrode voltage alternating in the frame period in this manner, even if the interelectrode voltage differs greatly between subframes, burn-in and flicker can be prevented.

  In addition, as described above, in the present display device, the liquid crystal panel 21 is driven by sub-frame display, thereby suppressing whitening. However, when the response speed of the liquid crystal (the speed until the voltage applied to the liquid crystal (voltage between electrodes) becomes equal to the applied voltage) is slow, the effect of such subframe display may be diminished.

  That is, when performing normal hold display, in the TFT liquid crystal panel, one liquid crystal state corresponds to a certain luminance gradation. Therefore, the response characteristics of the liquid crystal do not depend on the luminance gradation of the display signal.

  On the other hand, when sub-frame display is performed as in the present display device, when displaying a halftone display signal in which the previous sub-frame has the minimum luminance (white) and the subsequent sub-frame has the maximum luminance, the liquid crystal is displayed in one frame. The applied voltage varies as shown in FIG. Further, the voltage between the electrodes changes according to the response speed (response characteristics) of the liquid crystal as shown by the solid line X in FIG.

  Here, when the response speed of the liquid crystal is slow, when such halftone display is performed, the voltage between the electrodes (solid line X) changes as shown in FIG. Therefore, in this case, the display brightness of the previous subframe is not minimized, and the display brightness of the subsequent subframe is not maximized.

Therefore, the relationship between the planned brightness and the actual brightness is as shown in FIG. That is, even when subframe display is performed, it is impossible to perform display with luminance (minimum luminance / maximum luminance) in which the difference (shift) between the planned luminance and the actual luminance when the viewing angle is large is small.
For this reason, the effect of suppressing the whitening phenomenon is reduced.

  Therefore, in order to satisfactorily perform sub-frame display as in the present display device, it is preferable that the response speed of the liquid crystal in the liquid crystal panel 21 is designed to satisfy the following (c) and (d).

(C) A voltage signal (generated by the source driver 23 based on the display signal) for achieving the maximum luminance (white; equivalent to the maximum brightness) on the liquid crystal displaying the minimum luminance (black; equivalent to the minimum brightness). ), The voltage of the liquid crystal (interelectrode voltage) reaches a value of 90% or more in the voltage signal voltage within the shorter subframe period (the actual brightness of the front is 90% of the maximum brightness). To reach.)
(D) When a voltage signal for achieving the minimum luminance (black) is given to the liquid crystal displaying the maximum luminance (white), the voltage of the liquid crystal (interelectrode voltage) is reduced within the shorter subframe period. A value of 5% or less in the voltage of the voltage signal is reached (the actual brightness of the front reaches 5% of the minimum brightness).

  Moreover, it is preferable that the control part 15 is designed so that the response speed of a liquid crystal can be monitored. When it is determined that the response speed of the liquid crystal becomes slow due to a change in the environmental temperature or the like and the above (c) and (d) cannot be satisfied, the control unit 15 interrupts the sub-frame display and causes the liquid crystal panel 21 to be stopped. Alternatively, it may be set to be driven by normal hold display.

  As a result, when the white floating phenomenon becomes noticeable due to the subframe display, the display method of the liquid crystal panel 21 can be switched to the normal hold display.

  In the present embodiment, the display device functions as a liquid crystal monitor. However, this display device can also function as a liquid crystal television receiver (liquid crystal television). As shown in FIG. 46, such a liquid crystal television can be realized by providing the tuner unit 17 in the display device shown in FIG. The tuner unit 17 receives a television broadcast signal and transmits the television broadcast signal to the control unit 15 via the frame memory 11.

  In this configuration, the control unit 15 generates a display signal based on the television broadcast signal. Note that a liquid crystal television can also be realized by including the tuner unit 17 in the display device shown in FIG.

  Note that in this embodiment, in the case of low luminance, the previous subframe is black, and gradation expression is performed using only the rear subframe. However, the same display can be obtained even if the context of the subframes is exchanged (even if the subsequent subframe is black in the case of low luminance and the gradation representation is performed using only the previous subframe).

  In the present embodiment, the luminance gradation (signal gradation) of the display signal (the front display signal and the rear display signal) is set using the equation (1). However, the actual panel has brightness even in the case of black display (gradation 0), and the response speed of the liquid crystal is finite. Therefore, these factors should be taken into account when setting the signal gradation. Is preferred. In other words, it is preferable to display an actual image on the liquid crystal panel 21, measure the relationship between the signal gradation and the display luminance, and determine the LUT (output table) so as to meet the equation (1) based on the measurement result. .

  Moreover, in this Embodiment, (alpha) shown to Formula (6a) shall be the range of 2.2-3. This range is not strictly derived, but is a range that is considered to be almost appropriate for human visual sense.

  Further, when a source driver for normal hold display is used as the source driver 23 of the present display device, γ = 2.2 is set according to the input signal gradation (luminance gradation of the display signal) (1) A voltage signal is output to each pixel (liquid crystal) so that the display luminance obtained using can be obtained.

  Such a source driver 23 outputs the voltage signal used in the normal hold display as it is in each subframe in accordance with the input signal gradation even when performing the subframe display.

  However, in such a voltage signal output method, the sum of luminance in one frame in sub-frame display may not be the same as the value in normal hold display (signal gradation cannot be expressed).

  Therefore, in the sub-frame display, it is preferable that the source driver 23 is designed to output a voltage signal converted into divided luminance. That is, it is preferable that the source driver 23 is set so as to finely adjust the voltage (interelectrode voltage) applied to the liquid crystal according to the signal gradation. For this reason, it is preferable to design the source driver 23 for sub-frame display so that the fine adjustment as described above can be performed.

  In the present embodiment, the liquid crystal panel 21 is a VA panel. However, the present invention is not limited to this, and even when a liquid crystal panel of a mode other than the VA mode is used, the white-out phenomenon can be suppressed by the sub-frame display of the display device.

  In other words, the sub-frame display of this display device is a liquid crystal panel in which the planned brightness (scheduled brightness) and the actual brightness (actual brightness) deviate when the viewing angle is increased (in a mode in which the viewing angle characteristics of the gradation gamma change) For a liquid crystal panel), it is possible to suppress the white floating phenomenon.

  In particular, the sub-frame display of the present display device is effective for a liquid crystal panel having a characteristic that the display luminance increases as the viewing angle is increased. Further, the liquid crystal panel 21 in the present display device may be NB (Normally Black) or NW (Normally White). Furthermore, in this display device, instead of the liquid crystal panel 21, another display panel (for example, an organic EL panel or a plasma display panel) may be used.

  In the present embodiment, it is preferable to divide the frame into 1: 3 to 1: 7. However, the present invention is not limited to this, and the display device may be designed to divide the frame in a range of 1: n or n: 1 (n is a natural number of 1 or more).

  In the present embodiment, the signal gradation of the display signal (the front display signal and the rear display signal) is set using the above-described equation (10). However, this setting is a setting method in which the response speed of the liquid crystal is set to 0 ms and T0 (minimum luminance) = 0. For this reason, it is preferable to further devise in actual use.

That is, the maximum luminance (threshold luminance) that can be output in one side subframe (subsequent subframe) is Tmax / (n + 1) when the liquid crystal response is 0 ms and T0 = 0. The threshold luminance gradation Lt is a frame gradation of this luminance.
Lt = ((Tmax / (n + 1) −T0) / (Tmax−T0)) ^ (1 / γ)
(Γ = 2.2, T0 = 0)
When the response speed of the liquid crystal is not 0, for example, black → white is Y% response in the subframe, white → black is Z% response in the subframe, and T0 = T0, the threshold luminance (Lt luminance) Tt is
Tt = ((Tmax−T0) × Y / 100 + (Tmax−T0) × Z / 100) / 2
It becomes. Therefore,
Lt = ((Tt−T0) / (Tmax−T0)) ^ (1 / γ)
(Γ = 2.2)
It becomes.

In practice, Lt may be a little more complicated, and the threshold luminance Tt may not be expressed by a simple formula. Therefore, it may be difficult to express Lt by Lmax. In order to obtain Lt in such a case, it is preferable to use the result of measuring the luminance of the liquid crystal panel. That is, when the luminance of the sub-frame on one side is the maximum luminance and the luminance of the other sub-frame is the minimum luminance, the luminance irradiated from the liquid crystal panel is measured, and the luminance is defined as Tt. The spillage gradation Lt is determined by the following equation.
Lt = ((Tt−T0) / (Tmax−T0)) ^ (1 / γ)
(Γ = 2.2)
Thus, it can be said that Lt obtained using equation (10) is an ideal value and may be preferably used as a guide.

  Here, in the present display device, the point that it is preferable to reverse the polarity of the voltage between the electrodes at the frame period will be described in more detail. FIG. 12A is a graph showing the luminance displayed by the previous subframe and the subsequent subframe when the display luminance is 3/4 and 1/4 of Lmax. As shown in this figure, when the sub-frame display is performed as in the present display device, the voltage value applied to the liquid crystal (voltage value applied between the pixel electrodes; absolute value) differs between the sub-frames.

  Therefore, when the polarity of the voltage applied to the liquid crystal (liquid crystal voltage) is reversed at the subframe period, the voltage is applied due to the difference in voltage value between the previous subframe and the subsequent subframe as shown in FIG. The liquid crystal voltage is biased (the total applied voltage is not 0V). For this reason, it becomes impossible to cancel the direct current component of the liquid crystal voltage, and if the liquid crystal panel 21 is driven for a long time, electric charges accumulate on the electrodes, which may cause image sticking or flicker.

  Therefore, in the present display device, it is preferable to reverse the polarity of the liquid crystal voltage at the frame period. There are two methods for inverting the polarity of the liquid crystal voltage with the frame period. One method is a method of applying a voltage having the same polarity for one frame. The other method is a method in which the liquid crystal voltage is reversed in polarity between two subframes in one frame, and the subsequent subframe and the previous subframe of the next frame are in the same polarity. .

  FIG. 13A is a graph showing the relationship between the voltage polarity (liquid crystal voltage polarity), the frame period, and the liquid crystal voltage when the former method is adopted. On the other hand, FIG. 13B is a similar graph when the latter method is adopted.

As shown in these graphs, when the liquid crystal voltage is inverted at a cycle of one frame, the total voltage of the previous subframe and the total voltage of the subsequent subframe can be set to 0 V between two adjacent frames. Accordingly, since the total voltage in two frames can be set to 0 V, the DC component of the applied voltage can be canceled.
By alternating the liquid crystal voltage at the frame period in this manner, image sticking and flicker can be prevented even if the liquid crystal voltage varies greatly between subframes.

  14A to 14D are explanatory diagrams showing the four pixels in the liquid crystal panel 21 and the polarity of the liquid crystal voltage of each pixel. As described above, it is preferable to reverse the polarity of the voltage applied to one pixel in the frame period. In this case, the polarity of the liquid crystal voltage of each pixel changes as shown in the order of FIGS. 14A to 14D for each frame period.

  Here, the sum of the liquid crystal voltages applied to all the pixels of the liquid crystal panel 21 is preferably 0V. Such control can be realized, for example, by changing the voltage polarity between adjacent pixels as shown in FIGS.

  Further, in the present embodiment, it is preferable to set the ratio (frame division ratio) between the previous subframe period and the subsequent subframe period to 3: 1 to 7: 1. However, the present invention is not limited to this, and the frame division ratio may be set to 1: 1 or 2: 1.

  For example, when the frame division ratio is 1: 1, as shown in FIG. 3, it is possible to bring the actual luminance closer to the planned luminance as compared with the normal hold display. Further, as shown in FIG. 6, regarding the lightness, the actual lightness can be close to the planned lightness as compared with the normal hold display. Therefore, even in this case, it is clear that the viewing angle characteristics can be improved as compared with the normal hold display.

  In the liquid crystal panel 21, it takes time according to the response speed of the liquid crystal before the liquid crystal voltage (voltage applied to the liquid crystal; voltage between electrodes) is set to a value corresponding to the display signal. Therefore, if any of the subframe periods is too short, there is a possibility that the voltage of the liquid crystal cannot be increased to a value corresponding to the display signal within this period.

  Therefore, by setting the ratio of the previous subframe and the subsequent subframe period to 1: 1 or 2: 1, it is possible to prevent one of the subframe periods from being shortened too much. Therefore, even if a liquid crystal having a slow response speed is used, an appropriate display can be performed.

  Further, the frame division ratio (ratio between the previous subframe and the subsequent subframe) may be set to n: 1 (n is a natural value of 7 or more). The division ratio may be n: 1 (n is a real number of 1 or more (more preferably, a real number greater than 1)). For example, by setting this division ratio to 1.5: 1, the viewing angle characteristics can be improved as compared with the case of 1: 1. In addition, it becomes easier to use a liquid crystal material having a slow response speed as compared with the case of 2: 1.

  Even when the frame division ratio is n: 1 (n is a real number equal to or greater than 1), the luminance is low (low brightness) up to (1 / n + 1) of the maximum luminance (Tmax / (n + 1)). When displaying an image, it is preferable to display the front subframe in black and use only the rear subframe. Further, when displaying an image with a high luminance (high brightness) of “Tmax / (n + 1)” or more, it is preferable to display the rear subframe with white and adjust only the luminance of the previous subframe. As a result, one subframe can always be kept in a state where there is no difference between the actual luminance and the planned luminance. Therefore, the viewing angle characteristics of the display device can be improved.

  Here, when the frame division ratio is n: 1, substantially the same effect can be aimed at whether the previous frame is n or the subsequent frame n. That is, n: 1 and 1: n are the same regarding the viewing angle improvement effect. Even when n is a real number of 1 or more, it is effective for the control of the luminance gradation using the above equations (10) to (12).

  In the present embodiment, the sub-frame display of the display device is a display performed by dividing the frame into two sub-frames. However, the present invention is not limited to this, and the present display device may be designed to perform subframe display in which a frame is divided into three or more subframes.

  In the sub-frame display when the frame is divided into m, if the luminance is very low, m−1 sub-frames are displayed in black, while only the luminance (luminance gradation) of one sub-frame is displayed. Adjust and display. When the luminance is so high that it cannot be expressed only by this subframe, this subframe is displayed in white. Then, while displaying m−2 subframes in black, display is performed by adjusting the luminance of the remaining one subframe.

  That is, even when the frame is divided into m pieces, as in the case of dividing the frame into two pieces, one subframe for adjusting (changing) the luminance is always set to one, and the other subframes are set to white display or black display. It is preferable. Thereby, m−1 subframes can be in a state in which there is no deviation between the actual luminance and the planned luminance. Therefore, the viewing angle characteristics of the display device can be improved.

  FIG. 15 shows the result of dividing the display into three equal sub-frames by this display device (dashed line and solid line) and the result of normal hold display (dashed line and solid line; shown in FIG. 2). It is a graph shown together with the same. As shown in this graph, when the number of subframes is increased to three, the actual luminance can be made very close to the planned luminance. Therefore, it can be seen that the viewing angle characteristics of the present display device can be made better.

  Even when the frame is divided into m, it is preferable to perform the polarity inversion driving described above. FIG. 16 is a graph showing the transition of the liquid crystal voltage when the frame is divided into three and the voltage polarity is inverted for each frame. As shown in this figure, even in this case, the total liquid crystal voltage in two frames can be set to 0V.

  FIG. 17 is a graph showing the transition of the liquid crystal voltage when the frame is similarly divided into three and the voltage polarity is inverted for each subframe. As described above, when the frame is divided into an odd number, even if the voltage polarity is inverted for each subframe, the total liquid crystal voltage in two frames can be set to 0V. Therefore, when the frame is divided into m (m; an integer greater than or equal to 2), the control unit 15 causes the Mth (M; 1 to m) subframes between adjacent frames to have different polarities. It can be said that it is preferable to apply a voltage. Thereby, the total liquid crystal voltage in two frames can be set to 0V.

  Further, when the frame is divided into m (m; an integer of 2 or more), the polarity of the liquid crystal voltage is inverted so that the total liquid crystal voltage in 2 frames (or more frames) is 0V. It can be said that it is preferable.

  Also, in the above, when dividing a frame into m, it is preferable that there is always one subframe for adjusting the luminance, and other subframes are displayed in white (maximum luminance) or black (minimum luminance). Yes.

  However, the present invention is not limited to this, and two or more subframes for adjusting the luminance may be used. Even in this case, the viewing angle characteristics can be improved by displaying at least one subframe in white display (maximum luminance) or black display (minimum luminance).

  Further, the luminance of the sub-frame whose luminance is not adjusted may be “maximum or a value larger than the second predetermined value” instead of the maximum luminance. Further, instead of the minimum luminance, a “minimum value or a value smaller than the first predetermined value” may be used. Even in this case, the deviation (brightness deviation) between the actual brightness and the scheduled brightness in the subframe in which the luminance is not adjusted can be sufficiently reduced. Therefore, the viewing angle characteristics of the present display device can be improved.

  Here, FIG. 18 shows the signal gradation (%; luminance gradation of the display signal) output to the display unit 14 and the actual luminance gradation (%) corresponding to each signal gradation in the subframe where the luminance is not adjusted. ) (Viewing angle gradation characteristics (actual measurement)).

  The actual luminance gradation means “the luminance (actual luminance) output from the liquid crystal panel 21 of the display unit 14 in accordance with each signal gradation is converted into the luminance gradation using the above-described equation (1). Things ".

  As shown in this graph, the above-described two gradations are equal on the front surface of the liquid crystal panel 21 (viewing angle 0 degree). On the other hand, when the viewing angle is 60 degrees, the actual luminance gradation is halftone and brighter than the signal gradation due to whitening. Further, the whitening takes a maximum value when the luminance gradation is between 20% and 30% regardless of the viewing angle.

  Here, with respect to such white floating, when the “10% of the maximum value” indicated by the broken line in the above graph is not exceeded, the display quality of the present display device can be sufficiently maintained (the above-described brightness deviation is reduced). I know it can be small enough). Further, the range of the signal gradation in which the whitening does not exceed “10% of the maximum value” is 80 to 100% of the maximum value of the signal gradation and 0 to 0.02%. This range does not change even if the viewing angle changes.

  Accordingly, it can be said that the above-mentioned second predetermined value is preferably set to 80% of the maximum luminance, and the first predetermined value is preferably set to 0.02% of the maximum luminance.

  In addition, it is not necessary to provide a subframe that does not adjust the luminance. That is, when displaying with m subframes, it is not necessary to make a difference in the display state of each subframe. Even with such a configuration, it is preferable to perform polarity inversion driving that inverts the polarity of the liquid crystal voltage at the frame period as described above. Note that, when displaying in m subframes, the viewing angle characteristics of the liquid crystal panel 21 can be improved by making a slight difference in the display state of each subframe.

  In the present embodiment, the viewing angle characteristics of the liquid crystal can be improved (whitening can be improved) by the sub-frame display. However, the present invention is not limited to this, and the display quality of moving images can be improved by performing the subframe display as described above.

  That is, when the movement of the object displayed in the normal hold display is followed, the color and brightness of the immediately preceding frame can be seen at the same time. For this reason, the edge of the object is recognized as blurred. On the other hand, when a moving image is displayed in subframe display (particularly low luminance), the luminance of any subframe of each frame is low. For this reason, it can suppress that the image of the currently recognized frame and the image (color / brightness) of the immediately preceding frame are visually mixed. Therefore, the edge blur as described above can be avoided and the display quality of the moving image can be improved.

Moreover, you may design this display apparatus so that it may dimming by a PWM dimming system.
A liquid crystal display element such as the liquid crystal panel 21 expresses gradation by controlling the amount of light transmission. Therefore, some kind of light source (fluorescent tube, LED, etc.) is necessary. In addition, at present, a large-sized liquid crystal display element generally uses a fluorescent tube as a light source for efficiency.

  In general, there are two light source dimming methods: a current dimming method (or voltage dimming method) and a PWM dimming method.

  As shown in FIG. 19, the current dimming method is a method of controlling the magnitude (brightness) of light emitted from the light source by changing the amplitude of the current (lamp current) applied to the light source. When a fluorescent tube is used as the light source, if the amplitude of the lamp current is too small, the fluorescent tube will not shine. For this reason, the current dimming method has a drawback that the dimming range (brightness range that can be realized) cannot be widened. Therefore, it can be said that it is preferable to adopt the PWM dimming method in an apparatus that requires a wide dimming range such as a liquid crystal TV.

  In the PWM dimming method, as shown in FIG. 20, the light source (fluorescent tube) is turned on (ON) / off (OFF) at a frequency of 90 Hz or higher so that humans do not feel flicker, and the time average output light quantity is set as brightness. This is a method that lets the user perceive. Note that lighting / extinguishing control is generally performed by a dimming signal (PWM dimming control signal) input from the outside.

  FIG. 21 is a graph showing an example of a dimming signal waveform, a lamp current waveform, and a light emission waveform (waveform of light output from the fluorescent tube) when a fluorescent tube is used as the light source. As shown in this figure, in this case, the lamp current waveform has a constant amplitude and is OFF at a predetermined cycle. In practice, the frequency of the lamp current waveform is tens of thousands of Hz, while that of the dimming signal is several hundreds of Hz. Therefore, the lamp current waveform is finer than that shown in the figure.

  FIG. 22 is a block diagram illustrating an internal configuration of the display device when such PWM dimming is performed in the display device. This configuration includes the PWM dimming control circuit 31 and the light source drive circuit 32 in the configuration shown in FIG. In the example shown in this figure, the light source of the liquid crystal panel 21 is a plurality of fluorescent tubes 33 which are direct type backlights (backlights on the back surface of the liquid crystal panel 21).

  In this configuration, the control unit 15 generates a dimming rate signal indicating the amount of light to be output from the fluorescent tube 33 and outputs it to the PWM dimming control circuit 31. Further, the PWM dimming control circuit 31 generates a signal indicating a cycle related to ON / OFF of the lamp current according to the dimming rate signal, and transmits the signal to the light source driving circuit 32. The light source driving circuit 32 is designed to generate a lamp current (pulse current) according to the transmitted signal and output it to all the fluorescent tubes 33.

  Such PWM dimming can be combined with the above-described subframe display. However, if PWM dimming and subframe display are simply combined, interference phenomena such as flicker and horizontal stripes may occur.

  FIG. 23 shows an example of the relationship between the light emission waveform of the light source, the waveform of the liquid crystal electrode voltage (liquid crystal response waveform), and the waveform of light transmitted through the liquid crystal (transmission waveform) when PWM dimming is combined with the normal hold display. It is a graph which shows.

  FIG. 24 is a graph showing similar waveforms when PWM dimming is combined with sub-frame display (in the case of low luminance). In the examples shown in these drawings, the frame frequency is 60 Hz, the dimming frequency (ON / OFF frequency of the light source) is 150 Hz, and the dimming ratio (ON / OFF period ratio of the light source) is 50%. For simplicity, all waveforms are shown as rectangular waves.

  As shown in FIG. 23, in the normal hold display, even when PWM dimming is performed, the frequency of the transmission waveform is the same as the dimming frequency (150 Hz). Here, flicker starts to be perceived when the frequency of the transmission waveform is equal to or lower than the flicker threshold (90 Hz), and is clearly visible when the frequency falls below 60 Hz. Therefore, in the normal hold display, the user does not feel flicker.

  On the other hand, as shown in FIG. 24, in the sub-frame display, when PWM dimming is performed, the dimming frequency and the sub-frame frequency interfere with each other, and the frequency of the transmission waveform is greatly reduced from the dimming frequency. (In FIG. 24, it is 30 Hz). For this reason, the user feels flicker strongly.

  Note that such flicker has a dimming frequency of n. The closer to 5 times (n is an integer), the more intense it becomes. When the dimming frequency is n times the frame frequency, the frequency of the transmission waveform is equal to the frame frequency. Therefore, it is possible to reduce the flicker to an inconspicuous level. However, when the dimming frequency is brought close to n times the frame frequency, an interference phenomenon occurs in which horizontal stripes are generated on the screen.

  FIG. 25 is a graph showing an example of the relationship between the light emission waveform, liquid crystal response waveform, and transmission waveform of the light source when PWM dimming is combined with subframe display. In the example shown in this graph, the dimming frequency (180 Hz) is three times the frame frequency (60 Hz). Also, in this figure, unlike FIG. 24, liquid crystal response waveforms and transmission waveforms are shown for two lines A and B at different positions. As shown in this figure, in both lines A and B, the frequency of the transmission waveform is 60 Hz, which is the same as the frame frequency.

  Here, the light source usually irradiates the entire screen with light at the same time. On the other hand, the liquid crystal panel is line scan driven. Therefore, each line on the screen is turned ON / OFF at different times according to the position. Therefore, as shown in FIG. 25, the ON / OFF timing of the response waveform of the liquid crystal is shifted (sliding with respect to time) in the lines A and B at different positions.

  For this reason, the ratio of the time when the transmission waveform is turned on (the time when the luminance is high) differs depending on the line position. Therefore, a difference occurs in the average luminance between the lines, and this is recognized as a horizontal stripe phenomenon.

  When the dimming frequency is exactly n times the frame frequency, the horizontal stripes are stopped on the screen. And as it deviates from n times, horizontal stripes begin to flow up and down the screen. Further, the dimming frequency deviates greatly from n times, n. As the frequency approaches five times, the horizontal stripes disappear.

  That is, the dimming frequency is set to n. If it is 5 times, as shown in FIG. 24, the light emission waveform of the light source has an opposite phase between adjacent frames. Therefore, the transmission waveform from each line also has an opposite phase between adjacent frames. For this reason, the amount of transmitted light in two frames from each line can be made equal (it can be time-compensated), so that no horizontal stripes are generated.

  Therefore, in the present display device, when PWM dimming and subframe display are combined, the following control is performed. That is, the control unit 15 controls the circuits 31 and 32 to set the dimming frequency to “a value that is n.5 times the frame frequency and 450 Hz or more”.

  FIG. 26 is a graph showing an example of the relationship between the light emission waveform, the liquid crystal response waveform, and the transmission waveform of the light source (fluorescent tube 33) in this case. In the example shown in this graph, the dimming frequency (450 Hz) is 7.5 times the frame frequency (60 Hz). Also in this figure, similarly to FIG. 25, liquid crystal response waveforms and transmission waveforms are shown for two lines A and B at different positions.

  In this case, the dimming frequency is set to n. Since it is 5 times, the above horizontal stripes are not generated. As for flicker, although the frequency of the transmission waveform is 30 Hz, which is half the frame frequency, in both lines A and B, since the dimming frequency is sufficiently increased, flicker can be made inconspicuous. It has become.

  That is, the transmitted light amounts of lines A and B shown in FIG. 26 are reversed for each frame (the light amount of the first frame (second frame) of line A is the same as the second frame (first frame) of line B. The same). If lines having such a relationship can be densely arranged on the screen, flicker can be spatially compensated by allowing the user to visually recognize the light from these lines simultaneously.

  Here, the distance between the two lines having the relationship as described above becomes closer as the dimming frequency becomes higher. Therefore, by sufficiently increasing the dimming frequency, the value is set to n. Even if it is set to 5 times, flicker can be made inconspicuous. In the case where the previous subframe has a luminance of 50% at which black display is almost possible (when the black insertion rate is 50%), an experimental result has been obtained that flicker becomes inconspicuous if the dimming frequency is set to 450 Hz or more. Flicker is most noticeable when the black insertion rate is 50%.

  Therefore, in the present display device, the occurrence of both horizontal stripes and flicker can be avoided by setting the dimming frequency to “a value that is n.5 times the frame frequency and 450 Hz or higher”. .

  In addition, it is possible to suppress the interference phenomenon without increasing the dimming frequency. For example, the dimming frequency is set to the frame frequency n. This can be realized by setting it to 5 times and inserting a luminance compensation pulse into the light emission waveform.

  FIG. 27 is a graph showing an example of the relationship between the light emission waveform, the liquid crystal response waveform, and the transmission waveform of the light source (fluorescent tube 33) in this case. This figure also shows the liquid crystal response waveform and transmission waveform for two lines A and B at different positions, as in FIG. In the example shown in this graph, the control unit 15 emits a main light emission pulse having a relatively long pulse width from the fluorescent tube 33 at a dimming frequency (330 Hz; 5.5 times the frame frequency (60 Hz)). In this case, the dimming frequency is set to n. Since it is 5 times, the above horizontal stripes do not occur.

  As for flicker, in both lines A and B, the frequency of the transmission waveform by the main light emission pulse is 30 Hz, which is half the frame frequency. However, in this configuration, a luminance compensation pulse having a relatively short pulse width is inserted at the same frequency (330 Hz) as that of the main light emission pulse and in an opposite phase.

  In the transmission waveforms of the lines A and B, the transmission amounts of the main light emission pulse and the luminance compensation pulse increase or decrease for each frame, but have a reverse ratio for each frame. For example, the generation ratio of the main light emission pulse (high) is 2.5 to 3 in the first frame to the second frame (pulses 3 to 5 and pulses 8 to 10). On the other hand, in the luminance compensation pulse, the reverse is 3 to 2.5.

  For this reason, although the frequency (30 Hz) of the transmission waveform is small, the luminance difference within one cycle (within two frames) can be reduced by using the luminance compensation pulse (the luminance difference between frames can be reduced). . Accordingly, flicker can be made inconspicuous.

  Also, with this configuration, the PWM dimming frequency can be made lower than 450 Hz, so that it is possible to avoid a reduction in the driving efficiency of the light source. In this configuration, since a luminance compensation pulse of 330 Hz is inserted, there is a concern that efficiency may deteriorate. However, the pulse width of the luminance compensation pulse is very small compared to the frame period. Therefore, the influence of the luminance compensation pulse insertion on the driving efficiency of the light source is sufficiently small.

  In the above description, the dimming frequency is set to the frame frequency n. It is supposed to be 5 times. However, the present invention is not limited to this, and the dimming frequency may be n times the frame frequency. In this case, in order to prevent the occurrence of the above-mentioned horizontal stripes, as shown in FIG. 28, the emission waveform of the light source may be controlled so as to invert the phase for each frame. As a result, the transmission waveform from each line can be reversed in phase for each frame. Accordingly, the amount of transmitted light in two frames in each line can be made equal (it can be compensated for time), so that no horizontal stripes are generated.

  However, if the emission waveform of the light source is simply reversed in phase for each frame, as shown in FIG. 28, the cycle of the transmission waveform of each line A and B is 30 Hz, and flicker is generated.

  Therefore, when the light emission waveform of the light source has an opposite phase for each frame as described above, as shown in FIG. 29, the control unit 15 first has a dimming frequency (300 Hz; five times the frame frequency (60 Hz)). The main light emission pulse having a relatively long pulse width is emitted from the fluorescent tube 33. Then, the main light emission pulse is controlled to be phase-inverted every frame.

Further, the control unit 15 inserts a luminance compensation pulse having a relatively short pulse width into the light emission waveform of the light source at the same frequency (330 Hz) as that of the main light emission pulse and in an opposite phase.
Further, the control unit 15 inserts a luminance compensation added pulse or a luminance compensation reduced pulse in place of the luminance compensation pulse at the timing when the phase of the main light emission pulse changes (frame boundary point in FIG. 29).

  Here, the luminance compensation added pulse is a pulse for turning on the light source, which is inserted when the main light emission pulse is continuously turned off (low). On the other hand, the luminance compensation reduced pulse is a pulse for turning off the light source, which is inserted when the main light emission pulse is continuously turned on (high).

  That is, in this configuration, when the light amount of the main light emission pulse is too small, the luminance compensation additional pulse is inserted to increase the light amount, while when the light amount of the main light emission pulse is too large, the luminance compensation reduced pulse is inserted to increase the light amount. Designed to lower.

  Thereby, in this configuration, the difference in luminance between frames in each line can be reduced (the time average luminance of each frame can be made close to constant). Therefore, flicker can be reduced.

  When PWM dimming and sub-frame display are combined, it is also possible to suppress interference phenomena such as flicker and horizontal stripes by controlling the light emission waveform of the light source so as to include a direct current component (DC component). .

  FIG. 30 is a block diagram illustrating a configuration of the present display device when such control is performed. This configuration includes a first light source drive circuit 34 and a second light source drive circuit 35 in place of the light source drive circuit 32 in the configuration shown in FIG. 22, and further includes these circuits 34 and 35 and a PWM dimming control circuit 31. The phase control circuit 36 is provided between the two.

  In this configuration, every other fluorescent tube 33 is divided into a first fluorescent tube 33a and a second fluorescent tube 33b (the fluorescent tubes 33a and 33b are alternately arranged). Here, the first fluorescent tube 33 a is a fluorescent tube 33 connected to the first light source drive circuit 34. The second fluorescent tube 33 b is a light source connected to the second light source driving circuit 35.

  In this configuration, the control unit 15 generates a dimming rate signal indicating the amount of light to be output from the fluorescent tubes 33 a and 33 b and outputs the dimming rate signal to the PWM dimming control circuit 31. Then, in response to the dimming rate signal, the PWM dimming control circuit 31 and the phase control circuit 36 generate a signal indicating a cycle related to ON / OFF of the lamp current for the first fluorescent tube 33a, and the first light source driving circuit 34, a signal indicating a cycle related to ON / OFF of the lamp current with respect to the second fluorescent tube 33 b is generated and transmitted to the second light source driving circuit 35. Further, the light source drive circuits 34 and 35 are designed to generate a lamp current (pulse current) according to the transmitted signal and output it to the fluorescent tubes 33a and 33b.

  As described above, in the configuration of FIG. 30, the two sets of fluorescent tubes 33a and 33b can emit light independently of each other. 31 (a) and 31 (b) show the emission waveform (first waveform) of the first fluorescent tube 33a, the emission waveform (second waveform) of the second fluorescent tube 33b, and both fluorescent lights in the configuration shown in FIG. It is a graph which shows the example of the waveform (mixed waveform) which mixed the light emission waveform of the pipe | tube 33a * 33b. FIG. 31A shows the case where the dimming rate (ratio of the light emission amount with respect to the maximum light emission amount in each fluorescent tube) is 75%, and FIG. 31B shows the case where the dimming rate is 50%. .

  In the examples shown in these drawings, the control unit 15 controls the phase of the first waveform and the second waveform to change by 180 °. Therefore, as shown in FIG. 31A, when the dimming rate is 75%, 75% of the light emission amount is the DC component. Further, as shown in FIG. 31 (b), when the light control rate is 50%, all of the light emission amount (100%) becomes a DC component (DC-like driving can be performed).

  By performing such control, it is possible to reduce the amount of time variation in the light emission amount of the light source within one cycle (within two frames). Further, the difference in light emission amount between the lines can be reduced. Therefore, interference phenomena such as flicker and horizontal stripes can be made inconspicuous without increasing the frequency of the dimming signal.

  Here, as described above, the control for including the DC component in the light emission waveform of the light source is the control as described above “the dimming frequency is set to a value of n.5 times the frame frequency and 450 Hz or more”. Alternatively, it may be combined with control using a luminance compensation pulse.

  In the control for including the DC component in the light emission waveform of the light source, the dimming frequency is set to n. It has been confirmed by experiments that interference phenomena such as flicker and horizontal stripes can be made sufficiently inconspicuous even when the value is set to 5 times and 270 Hz or more.

  In the configuration shown in FIG. 30, the fluorescent tube 33 is divided into two types in order to generate a DC component in the light emission waveform of the light source. However, the present invention is not limited to this, and the fluorescent tube 33 may be divided into three types and controlled independently for each type. FIG. 32 is a block diagram illustrating a configuration of the present display device when such control is performed.

  In this configuration, the fluorescent tube 33 is divided into three types (a first fluorescent tube 33a, a second fluorescent tube 33b, and a third fluorescent tube 33c). The fluorescent tubes 33a, 33b, 33c are arranged in this order and periodically (every two fluorescent tubes of the same type are arranged). In this configuration, a third light source driving circuit 37 is added between the phase control circuit 36 and the fluorescent tube 33. The third light source drive circuit 37 drives the third fluorescent tube 33c (applies a lamp current).

  In this configuration, the three sets of fluorescent tubes 33a to 33c can emit light independently. FIGS. 33A and 33B are graphs showing examples of the fluorescent tubes 33a to 33c (first to third waveforms) and a waveform obtained by mixing them (mixed waveform) in the configuration shown in FIG. .

  Note that FIG. 33A relates to a case where the dimming rate is 50%, and FIG. 31B relates to a case where the dimming rate is 25%. In the examples shown in these drawings, the phases of the first to third waveforms are controlled to be shifted from each other by 120 °. Therefore, as shown in FIGS. 33A and 33B, even when the dimming rate is 50%, the DC component is larger than when the fluorescent tubes 33 are simultaneously blinked without being classified into groups. it can.

  By performing such control, it is possible to reduce the amount of time variation in the light emission amount of the light source within one cycle (within two frames). Further, the difference in light emission amount between the lines can be reduced. Therefore, interference phenomena such as flicker and horizontal stripes can be made inconspicuous without increasing the frequency of the dimming signal.

  Note that the number of fluorescent tubes 33 (the number of groups of fluorescent tubes that are driven separately) can be set to an arbitrary number by providing light source driving circuits for the number of groups. As shown in FIG. 34, when the classification number of the fluorescent tubes 33 is p (p is a natural number of 2 or more), the phases of the first to p-th waveforms are controlled to be shifted from each other by 360 ° / p. It is preferable to do. However, PWM dimming may be performed so that the emission waveforms of at least two fluorescent tubes 33 have different phases. Even in this configuration, since the light emission waveform of each light source is shifted, it is possible to increase the DC component of the mixed light including the light from all the light sources.

  In the above description, the light source of the liquid crystal panel 21 is a plurality of fluorescent tubes 33 which are direct type backlights. However, the present invention is not limited to this, and an LED (light emitting diode) serving as a side-type backlight (a backlight at the side end of the liquid crystal panel 21) may be used as the light source. The display element shown in FIG. 35 has a configuration in which the light guide plate 41 is disposed on the back surface of the liquid crystal panel 21 and the first LED 42 and the second LED 43 are arranged on two opposite sides of the light guide plate 41. This configuration is designed so that light emitted from the LEDs 42 and 43 is spread by the light guide plate 41 and is output to the liquid crystal panel 21 as planar light.

  In this configuration, similarly to the configuration shown in FIG. 30, the control unit 15 changes the phase of the light emission waveform (first waveform) of the first LED 42 and the light emission waveform (second waveform) of the second LED 43 by 180 degrees. To control. Thereby, in the light-guide plate 41, the light emission waveform of an antiphase can be mixed and a DC component can be produced. Therefore, even with this configuration, the DC component of the light irradiated to the liquid crystal panel 21 can be increased.

  In addition, when using two LED42 * 43 as mentioned above, as shown in FIG. 36, you may arrange | position two LED42 * 43 along the same edge | side of the light-guide plate 41. As shown in FIG. Even in this configuration, the liquid crystal panel 21 can be irradiated with light containing a large amount of DC components, as in the configuration of FIG.

  In addition, the two LEDs 42 and 43 can be used as side-type front lights (front lights arranged on the side end portions of the liquid crystal panel 21). In this case, as shown in FIGS. 37 and 38, the liquid crystal panel 21 is configured as a front light type.

  In the above configuration, the liquid crystal panel 21 is a reflective liquid crystal display element. That is, in this configuration, the liquid crystal panel 21 receives planar light from the light guide plate 41 from the front surface (user side surface). And it is designed to display an image to the user by reflecting this planar light by an internal reflection plate.

  In the configuration shown in FIG. 34, a large number of fluorescent tubes 33 are classified into p groups, and the phases of the first to p-th waveforms are controlled to be shifted from each other by 360 ° / p. However, the present invention is not limited to this, and each fluorescent tube 33 may be driven individually. In this case, if r fluorescent tubes 33 are used, the phase of the emission waveform from each fluorescent tube 33 is preferably shifted by 360 ° / r.

  Further, in such a configuration in which a large number of fluorescent tubes 33 are individually driven, it is preferable to synchronize the light emission timing of the fluorescent tubes 33 and the ON timing of the gate lines of the liquid crystal panel 21.

  FIG. 39 is a block diagram illustrating a configuration of the present display device in the case of performing the synchronization as described above. In this configuration, the r fluorescent tubes 33 immediately below the liquid crystal panel 21 are designed to be driven by the first to r-th light source driving circuits 32a to 32r.

  Further, in the above configuration, each fluorescent tube 33 emits light to a plurality of gate lines close to itself. The number of gate lines corresponding to each fluorescent tube 33 is, for example, 42 to 43 when 18 fluorescent tubes 33 and 768 gate lines are provided.

  Then, the control unit 15 sends a synchronization signal to the phase control circuit 36 to turn on the gate line group corresponding to each fluorescent tube 33 (when scanning of this gate line group is started). Control is performed so as to start driving the fluorescent tube 33 (more specifically, since not all the gate line groups are turned on simultaneously, the driving start timing of the fluorescent tube 33 is the average of the gate line group. Set to ON timing).

  FIG. 40 is a graph showing an example of the relationship between the light emission waveform, liquid crystal response waveform, and transmission waveform of the light source when such control is performed. In the example shown in this graph, the dimming frequency (180 Hz) is three times the frame frequency (60 Hz). In this figure, the light emission waveform, the liquid crystal response waveform, and the transmission waveform of the light source regarding two different gate line groups A and B are shown. The liquid crystal response waveform represents the voltage that is written to the pixel of the liquid crystal panel 21 at the ON timing of the gate line and is held until the next ON timing.

  As shown in this figure, in this configuration, the frequency of the light emission waveform of the light source is three times the frequency of the frame. Accordingly, in both the line groups A and B, the frequency of the transmission waveform is 60 Hz, which is the same as the frame frequency, and flicker can be avoided.

  Further, in this configuration, the phase relationship between the emission waveform of the fluorescent tube 33 and the response waveform of the liquid crystal is the same in both the line groups A and B (the light source emission waveform for the line group A and the line B emission line). The temporal deviation from the light source emission waveform coincides with the deviation in the liquid crystal response waveform between the line groups A and B).

  Therefore, in this configuration, it is possible to prevent the ratio of the time during which the transmission waveform is turned on (the time during which the luminance is high) from being different depending on the line position. Therefore, since there is no difference in the average luminance between the lines, it is possible to avoid the occurrence of the horizontal stripe phenomenon.

  In the above description, when the gate line group corresponding to each fluorescent tube 33 is turned on (when scanning of the gate line group is started), the fluorescent tube 33 is controlled to start driving. It is said.

  However, “the waveform state of the fluorescent tube 33 when the gate line group corresponding to each fluorescent tube 33 is turned ON” is controlled so as to be the same in all the fluorescent tubes 33 (all gate line groups). By doing so, the phase relationship between the light emission waveform of the fluorescent tube 33 and the response waveform of the liquid crystal can be matched in all the gate line groups. Therefore, even by such control, it is possible to prevent horizontal stripes by synchronizing the light emission of the fluorescent tube 33 and the ON timing of the gate line group.

  In this embodiment, the PWM dimming method is used as the dimming method of the light source. However, the present invention is not limited to this, and the PWM dimming method and the current dimming method may be used in combination. FIG. 41 is a block diagram showing a configuration of the display device in this case. In this configuration, a current dimming control circuit 51 is newly provided in the configuration shown in FIG.

  In the above configuration, the control unit 15 generates a dimming rate signal indicating the amount of light to be output from the fluorescent tube 33 and outputs the dimming rate signal to the PWM dimming control circuit 31 and the current dimming control circuit 51. Further, the dimming control circuits 31 and 51 generate signals (current dimming control signal, PWM dimming control signal) indicating a cycle related to ON / OFF of the lamp current in accordance with the dimming rate signal, and drive the light source. To the circuit 32. The light source driving circuit 32 is designed to generate a lamp current (pulse current) according to the transmitted signal and output it to all the fluorescent tubes 33.

  FIG. 42 is a graph showing an example of a current dimming control signal, a PWM dimming control signal, a lamp current, and a light emission waveform in this configuration. As shown in this figure, in this configuration, the control unit 15 controls the dimming control circuits 31 and 51 to generate a constant current dimming control signal (a signal for giving a constant light emission power) by PWM dimming control. The signal is output together with the signal.

  Thereby, the lamp current waveform of the fluorescent tube 33 is a waveform in which the amplitude according to the PWM dimming control signal overlaps with the constant amplitude according to the current dimming control signal. Therefore, the emission waveform of the fluorescent tube 33 is a waveform having a DC component corresponding to a constant current dimming control signal, as shown in FIG.

  Thus, the DC component of the light emission waveform can be easily increased by using the PWM dimming method and the current dimming method together. Thereby, the amount of time fluctuation in the light emission amount of the light source within one cycle (within two frames) can be reduced. Further, the difference in light emission amount between the lines can be reduced. Therefore, interference phenomena such as flicker and horizontal stripes can be made inconspicuous without increasing the frequency of the dimming signal.

  Further, when a reflective liquid crystal display element is used as the liquid crystal panel 21 and this display device is configured as a front light type reflective liquid crystal display device, it is preferable to control the light of the light source in accordance with the external light.

  FIG. 43 is a diagram showing a configuration of the present display device that performs such control. As shown in this figure, in this configuration, the liquid crystal panel 21 uses the light guide plate 41 to convert the light of the LED 63 serving as a light source into planar light and receives it from the front surface (user-side surface). Then, the planar light is reflected by the internal reflection plate to display an image to the user.

  In addition, this configuration includes a light source dimming control circuit 62 for controlling the luminance of the LED 63. The light source dimming control circuit 62 detects the luminance waveform of the external light and adjusts the luminance of the LED 63 so as to increase the DC component of the light applied to the liquid crystal panel 21.

  That is, when there is external light having a luminance waveform as shown in FIG. 44 (a), the light source dimming control circuit 62 converts the luminance waveform (light emission waveform) of the LED 63 into an external waveform as shown in FIG. 44 (b). It controls so that it may become an antiphase with the same frequency as a light-luminance waveform. For this reason, the liquid crystal panel 21 can be irradiated with light having a large DC component as shown in FIG.

  Thereby, in this structure, the amount of time fluctuations in the light emission amount of the light source within one cycle (within two frames) can be reduced. Further, the difference in light emission amount between the lines can be reduced. Therefore, interference phenomena such as flicker and horizontal stripes can be made inconspicuous without increasing the frequency of the dimming signal.

  Even when a backlight-type transflective liquid crystal display element as shown in FIG. 45 is used as the liquid crystal panel 21, control using the light source dimming control circuit 62 can be performed. A transflective display device uses a backlight to perform transmissive display under relatively dark illumination such as indoors (transmission mode), while it emits illumination light under relatively bright illumination such as outdoors. This is used for reflection display (reflection mode). Thereby, a display with a high contrast ratio can be realized regardless of the surrounding brightness.

  Even in the above configuration, the light source dimming control circuit 62 controls the luminance waveform of the LED 63 so that the phase of the LED 63 differs from that of the external light luminance waveform by 180 °. As a result, it is possible to irradiate the liquid crystal panel 21 with light having a large DC component mixed with light having the same frequency and opposite phase as shown in FIG.

  In the present embodiment, a fluorescent tube or LED is used as the light source of the display device. However, the present invention is not limited to this, and the light source of the present display device may be configured by either EL (Electro Luminescence) or FED (Field Emission Display). Moreover, you may comprise a light source from what combined the fluorescent tube, LED, EL, and FED. Further, in FIGS. 34 to 38 and the like, the light source is expressed in a bar shape. However, the shape of the light source may be round or U-shaped. That is, in the present invention, the shape of the light source is not particularly limited.

  Further, when combining sub-frame display and PWM dimming, the display unit 14 of the present display device is not limited to a liquid crystal display element, but may be a non-self-luminous display element (an element that requires a light source). Any display element may be used.

  In the present embodiment, the control unit 15 transmits a display signal to the liquid crystal panel 21 and also controls PWM dimming. However, the present invention is not limited to this, and a member for controlling PWM dimming (PWM dimming control unit) may be provided separately from the control unit 15. Therefore, this display device is a display device that displays an image by dividing one frame into m (m; an integer greater than or equal to 2) sub-frames, and displays an image with luminance based on the voltage of the display signal. And a display unit having a display screen composed of a liquid crystal display element and display signals for the first to mth sub-frames so that the sum of luminances output from the display unit in one frame is not changed by dividing the frame. And a control unit that generates the first to m-th display signals and outputs them to the display unit, and further includes a PWM dimming control unit that dimmes the light source of the display unit by a PWM dimming method. It can also be expressed as being.

  When the display device is a liquid crystal television, the tuner unit 17 selects a channel of a television broadcast signal and transmits a television image signal of the selected channel to the control unit 15 via the frame memory 11. It may be used. In this configuration, the control unit 15 generates a display signal based on the television image signal. Further, the tuner unit 17 is used to select a channel of a television broadcast signal and transmit a television image signal of the selected channel to the control unit 15 via a circuit (not shown) that performs various video processing. Also good.

  The display device of the present invention is a display device that displays an image by dividing one frame into two sub-frames composed of the first and second sub-frames, and is based on the luminance gradation of the input display signal. A display unit that displays an image of luminance, and first and second displays that are display signals of the first and second subframes so that the total luminance output from the display unit in one frame is not changed by dividing the frame. A control unit that generates a signal and outputs the signal to the display unit. When the control unit displays a low-lightness image, the control unit adjusts the luminance gradation of the first display signal, while the second display signal. The luminance gradation of the first display signal is set to the maximum or the second when the luminance gradation of the first display signal is set to a minimum value or smaller than a first predetermined value (for example, 0.02% of the maximum gradation) and a high brightness image is displayed. A predetermined value (for example, 80 of the maximum gradation) ), While adjusting the luminance gradation of the second display signal, the ratio between the period of the first subframe and the period of the second subframe is 1: n or n: 1 (where n is 1). It is possible to express that the light source of the display unit is dimmed by the PWM dimming method.

  The display device shown in FIG. 39 is a display device that displays an image by dividing one frame into m (m; an integer of 2 or more) subframes, and the luminance based on the voltage of the display signal. Of the first to mth sub-frames so that the sum of luminances output from the display unit per frame is not changed by dividing the frame. A control unit that generates the first to m-th display signals that are display signals and outputs them to the display unit, and the control unit dims the light source of the display unit by a PWM dimming method. The display unit has a light source group in which a plurality of direct light sources are arranged, and each light source is designed to irradiate a gate line group including a plurality of gate lines close to itself. The above control unit is the light emission waveform of the light source. The frequency is set to n times the frequency of the frame, and "the state of the light emission waveform of the light source when the response waveform of the liquid crystal corresponding to the gate line group assigned to each light source is ON" It can also be expressed as a configuration that performs PWM dimming so as to be the same.

  In the above description, all processes in the display device are performed under the control of the control unit 15. However, the present invention is not limited to this, and an information processing apparatus capable of recording a program for performing these processes on a recording medium and reading the program may be used instead of the control unit 15.

  In this configuration, the arithmetic unit (CPU or MPU) of the information processing apparatus reads the program recorded on the recording medium and executes the process. Therefore, it can be said that this program itself realizes the processing.

  Here, as the information processing apparatus, in addition to a general computer (workstation or personal computer), a function expansion board or a function expansion unit mounted on the computer can be used.

  The above program is a program code (execution format program, intermediate code program, source program, etc.) of software for realizing processing. This program may be used alone or in combination with other programs (such as OS). The program may be read from a recording medium, temporarily stored in a memory (RAM or the like) in the apparatus, and then read and executed again.

  The recording medium for recording the program may be easily separable from the information processing apparatus, or may be fixed (attached) to the apparatus. Furthermore, it may be connected to the apparatus as an external storage device.

  Such recording media include magnetic tapes such as video tapes and cassette tapes, magnetic disks such as floppy (registered trademark) disks and hard disks, optical disks (magneto-optical disks) such as CD, MO, MD, and DVD, IC cards, A memory card such as an optical card, a semiconductor memory such as a mask ROM, EPROM, EEPROM, or flash ROM can be applied.

  Also, a recording medium connected to the information processing apparatus via a network (intranet / Internet) may be used. In this case, the information processing apparatus acquires the program by downloading via the network. That is, the above program may be acquired via a transmission medium (a medium that dynamically holds the program) such as a network (connected to a wired line or a wireless line). The program for downloading is preferably stored in advance in the apparatus (or in the transmission side apparatus / reception side apparatus).

  The liquid crystal response waveform is output at the ON timing of the gate line. It can be said that the voltage is written to the liquid crystal pixel and the voltage of the liquid crystal pixel is held and formed until the next ON timing. Also, Patent Document 6 describes a method for improving interference fringes that occurs when a black driving method that realizes a pseudo impulse mode by inserting black in one frame in a liquid crystal display device and a PWM dimming method of a light source. It has been. In the technique of this document, one frame period is divided into a black display period and an image display period, and a method of driving the liquid crystal under a certain ratio condition with respect to one black display period or a certain PWM dimming frequency condition Improvement is made by a method of driving the backlight in the above or a method of shifting the phase of the PWM dimming signals of the plurality of backlights.

  On the other hand, as a technique for realizing the pseudo impulse mode by the liquid crystal driving method, as in Patent Document 3, one frame is divided into a plurality of subframe periods, which have high and low luminance subframes. There is a method (time division gradation driving method) that expresses gradation by time integration. This method has the advantage that it can improve the video performance such as edge blurring while suppressing the decrease in the display brightness of the screen compared with the method of always inserting black. When combined with a PWM dimming light source, an interference phenomenon occurs.

  Furthermore, in the pseudo impulse mode using the black drive method, the light source is completely shut off, so changing the black insertion time does not change the gradation even if the overall absolute brightness changes, but the time-division gradation In the case of the driving method, there is a restriction that the luminance and the gradation change when the time of each subframe is changed. In addition, the light of the light source is modulated with the response waveform of the liquid crystal and transmitted even in the low-luminance subframe period, and the control timing such as synchronizing the light-off period of the light source during the insertion period is improved by adjusting the control timing. Neither method can be adopted.

  In view of the above, an object of the present invention is to divide one frame period into two or more subframe periods, and to provide a time-division floor having a display mechanism for expressing gradation by time integration of each subframe. It can be said that the interference phenomenon such as flicker caused by combining the pseudo impulse driving method by the tone and the light source of the PWM dimming method is improved without impairing the gradation expression and the screen display.

  Further, the present invention can also be expressed as the following first to twenty-third display devices. That is, the first display device divides one frame period into two or more subframe periods, and includes a drive method including a display mechanism that expresses gradation by time integration of each subframe, and a PWM dimming method. In this configuration, the PWM dimming signal is controlled so as to improve the interference phenomenon that occurs when the light source is combined.

  Further, the second display device is configured to control the PWM dimming signal so that the light emission waveform of the light source is compensated temporally and spatially in the first display device in order to improve the interference phenomenon.

  In addition, the third display device is configured to control the PWM dimming signal in the first display device so as to include as much DC component as possible in the light emission waveform of the light source in order to improve the interference phenomenon.

  The fourth display device controls the PWM dimming signal so that the light emission waveform of the light source is temporally and spatially compensated in the first display device in order to improve the interference phenomenon. In order to improve, the PWM dimming signal is controlled so as to include as much DC component as possible in the light emission waveform of the light source.

  Further, in the second display device, the fifth display device transmits the PWM dimming control signal to the frame frequency n. It is the structure which drives by 5 times.

  The sixth display device is configured to be driven at a PWM dimming frequency of 450 Hz or more in the fifth display device at a black insertion rate of 50%.

  Further, the seventh display device is configured to include control means for generating a compensated dimming pulse so that the luminance is constant in the fifth display device.

  Further, the eighth display device is configured to drive the PWM dimming control signal at n times the frame frequency and invert the phase for each frame in the second display device.

  Further, the ninth display device is configured to include control means for generating a dimming pulse for compensating for the luminance to be constant in the eighth display device.

  Further, the tenth display device includes the first light source and the second light source in the third display device, and includes means for controlling the respective PWM dimming phases to be 180 ° different from each other.

  The eleventh display device includes a first light source, a second light source, and a third light source in the third display device, and includes means for controlling the PWM dimming phases to be 120 ° different from each other. It is.

  The twelfth display device includes the first to nth light sources in the third display device, and includes means for controlling each of the PWM dimming phases to be different (360 ° / n).

  The thirteenth display device has a configuration in which the light source is a direct-type backlight and is spatially arranged alternately in the tenth to twelfth display devices.

  Further, the fourteenth display device in the tenth to twelfth display devices has a configuration in which the light source is a side-type backlight, and light sources having opposite phases are arranged at both ends.

  The fifteenth display device has a configuration in which the light source is a side-type backlight in the tenth to twelfth display devices, and a light source having an opposite phase is arranged at one end.

  In addition, the sixteenth display device has a configuration in which, in the tenth to twelfth display devices, the light source is a front light, and light sources having opposite phases are arranged at both ends.

  The seventeenth display device has a configuration in which, in the tenth to twelfth display devices, the light source is a front light, and the light source having the opposite phase is arranged at one end together.

  Further, the eighteenth display device is configured by combining any one of the fifth to eighth display devices and any one of the thirteenth to sixteenth display devices.

  In addition, the nineteenth display device is configured to scan-control a plurality of light sources arranged in parallel in synchronization with the line scan drive of the liquid crystal panel in order to improve the interference phenomenon.

  The twentieth display device has a PWM dimming method and a current dimming method, and is configured to suppress the interference phenomenon by increasing the DC component of the light emission waveform of the light source in advance by the current dimming method.

  The twenty-first display device is configured to control the PWM dimming of the light source in the second display device so that the sensor unit for detecting external light and the detected luminance component have an opposite phase.

  The twenty-second display device is configured to control the PWM dimming of the front light source in the twenty-first display device so that the reflective liquid crystal has an opposite phase to the external light. Further, in the twenty-first display device, the PWM light control of the backlight source is controlled so that the transflective liquid crystal has an opposite phase to the external light.

  The twenty-third display device has a configuration in any one of the first to twenty-second display devices, in which the light source is any one of fluorescent lamps, LEDs, ELs, FEDs, or a combination thereof.

  INDUSTRIAL APPLICABILITY The present invention can be suitably used for an apparatus having a display screen in which whitening occurs.

Claims (17)

A display device that displays an image by dividing one frame into m (m; an integer of 2 or more) subframes,
A display unit having a display screen composed of a liquid crystal display element for displaying an image having a luminance based on a voltage of a display signal;
First to m-th display signals, which are display signals of the first to m-th sub-frames, are generated and output to the display unit so that the total luminance output from the display unit in one frame is not changed by dividing the frame. And a control unit,
A display device in which the control unit dimmes the light source of the display unit by a PWM dimming method.   The above control unit sets the frequency of the light emission waveform of the light source to n. 2. The display device according to claim 1, wherein PWM dimming is performed so as to be 5 times (n is an integer) and to be a value of 450 Hz or more.   The above-mentioned control unit determines the light emission waveform of the light source together with the frame frequency n. 2. The display according to claim 1, wherein PWM dimming is performed so as to obtain a waveform having a combination of a main light emission pulse and a luminance compensation pulse having a frequency five times and having opposite pulse phases and different pulse widths. apparatus. The above control unit
The light emission waveform of the light source has a frequency which is n times the frame frequency, and a main light emission pulse whose phase is inverted every frame, and a luminance compensation pulse having the same frequency as that of the main light emission pulse and a luminance compensation pulse having an opposite phase. As a waveform,
For the emission waveform of the light source,
When the main light emission pulse is continuously OFF, instead of the luminance compensation pulse, a luminance compensation additional pulse for turning on the light source is inserted,
2. The PWM dimming is performed so that a luminance compensation reduced pulse for turning off the light source is inserted instead of the luminance compensation pulse when the main light emission pulse is continuously turned on. Display device. The display unit has a plurality of light sources,
The display device according to claim 1, wherein the control unit performs PWM dimming so that light emission waveforms of at least two light sources have different phases.   The above control unit is designed so that each light source is divided into p groups (p is a natural number of 2 or more), and the phase of the light emission waveform of the light source is shifted by 360 ° / p for each group. The display device according to claim 5, wherein   The display device according to claim 5, wherein the light source is a direct backlight.   The display device according to claim 5, wherein the light source is a side-type backlight.   The display device according to claim 5, wherein the light source is a side-type front light. The display section has a light source group in which a plurality of direct light sources are arranged, and each light source is designed to irradiate light to a gate line group composed of a plurality of gate lines close to itself. ,
The above control unit
The frequency of the light emission waveform of the light source is set to n times the frequency of the frame,
The PWM dimming is performed so that the state of the light emission waveform of each light source when the gate line group assigned to each light source is turned on is the same for all light sources. Display device. The control unit
The display device according to claim 1, wherein PWM dimming is performed in a state where constant light emission power is supplied to the light source. The display unit is a reflective display element having a front light type light source,
Provided with a brightness sensor that detects the brightness waveform of the external light irradiated on the display unit,
The control unit
2. The display device according to claim 1, wherein PWM dimming is performed so that the light emission waveform of the light source has the same frequency as that of the luminance waveform of the external light and has an opposite phase. The display unit is a transflective display element,
Provided with a brightness sensor that detects the brightness waveform of the external light irradiated on the display unit,
The control unit
2. The display device according to claim 1, wherein PWM dimming is performed so that the light emission waveform of the light source has the same frequency as that of the luminance waveform of the external light and has an opposite phase.   The display device according to claim 1, wherein the light source includes any one of a fluorescent tube, an LED, an EL, and an FED. A display device according to claim 1;
A signal input unit for transmitting an image signal input from the outside to the control unit,
A liquid crystal monitor, wherein the control unit of the display device is designed to generate a display signal based on the image signal. A display device according to claim 1;
A tuner unit for receiving TV broadcast signals,
A liquid crystal television receiver, wherein the control unit of the display device is designed to generate a display signal based on the television broadcast signal. A display method for displaying an image by dividing one frame into m (m; an integer of 2 or more) subframes,
The first to m-th display signals, which are display signals of the first to m-th sub-frames, are generated to make up the liquid crystal display element so that the total luminance output from the display unit in one frame is not changed by dividing the frame. Including an output process for outputting to the display unit;
The display method further includes a dimming step of dimming the light source of the display unit by a PWM dimming method.

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