WO2006095743A1

WO2006095743A1 - Display apparatus, liquid crystal monitor, liquid crystal television receiver, and display method

Info

Publication number: WO2006095743A1
Application number: PCT/JP2006/304405
Authority: WO
Inventors: Takeshi Kumakura
Original assignee: Sharp Kabushiki Kaisha
Priority date: 2005-03-11
Filing date: 2006-03-07
Publication date: 2006-09-14
Also published as: JPWO2006095743A1

Abstract

In this display apparatus, a control part (15) divides each frame into former and latter subframes, and causes a black display to be performed in the former subframe for a lower brightness, while causing a white display to be performed in the latter subframe for a higher brightness. This can suppress a white float effect. Moreover, the control part (15) modulates a light source of a display part (14) by use of a PWM light modulation method using a light modulation frequency that is n.5 times the frame frequency and that is equal to or greater than 450 Hz. This can prevent occurrence of horizontal stripes. In addition, since the light modulation frequency is sufficiently raised, the flickers can be made less noticeable.

Description

Specification

Display device, liquid crystal monitor, liquid crystal television receiver and display method

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

Background art

In recent years, CRTs (cathode ray tubes) have been used in liquid crystal display devices, particularly TN (Twisted

Nematic liquid crystal display panels (TN mode liquid crystal panels; TN panels) have become increasingly popular. For example, Patent Document 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.

[0003] By the way, such a TN panel has a slight problem in viewing angle characteristics as compared with a CRT. For this reason, the gradation characteristics change 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, and there is an angle at which the gradation is reversed.

[0004] Therefore, 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.

[0005] In addition, liquid crystal display panels that require a wide viewing angle such as TV (television receiver), such as IPS (In-Plane-Switching) mode and VA (Vertical Alignment) mode, which are not in TN mode. A wide viewing angle is achieved by using liquid crystal. For example, in a VA mode liquid crystal panel (VA panel), the contrast is 10 or more in the range of 170 ° up, down, left, and right, and there is no gradation inversion.

Patent Document 1: Japanese Unexamined Patent Publication No. 2001-296841 (Release Date; October 26, 2001)

Patent Document 2: JP-A-5-68221 (Issue Date; March 19, 1993)

Patent Document 3: Japanese Patent Laid-Open No. 2002-23707 (Publication Date; January 25, 2002) Patent Document 4: Japanese Patent Laid-Open No. 2000-321551 (Publication Date; November 24, 2000) Patent Document 5: Japanese Patent Laid-Open No. 9-127917 (Publication Date; May 16, 1997)

Patent Document 6: Japanese Patent Application Laid-Open No. 2004-4659 (Release Date; January 8, 2004)

Non-Patent Document 1: New edition Color Science Handbook; 2nd edition (University of Tokyo Press; Publication date; June 10, 1998)

Disclosure of the invention

[0006] However, even with a VA panel that is said to have a wide viewing angle, the change in gradation characteristics due to the viewing angle cannot be completely eliminated. For example, if the viewing angle in the horizontal direction increases, Adjustment characteristics deteriorate.

That is, as shown in FIG. 2, when the viewing angle is 60 degrees, the gradation γ characteristic changes and the halftone brightness becomes brighter when the panel is desired from the front (viewing angle 0 degree). White floating phenomenon occurs.

[0008] Also, 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.

[0009] The present invention has been made in view of the above-described conventional problems. And the objective is to provide the display apparatus which can suppress a white floating phenomenon.

[0010] In order to solve the above problems, 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. A display unit that displays an image of luminance based on the voltage of the display signal, and a display signal for the first to m-th subframes so that the total luminance output from the display unit in one frame is not changed by dividing the frame. The first to mth display signals are generated and output to the display unit. This control unit is designed to dimm the light source of the display unit by the PWM dimming method. This is a configuration.

The display device displays an image using a display unit having a display screen made up of a liquid crystal display element. In this display device, the control unit drives the display unit by subframe display. Here, the sub-frame display is a display method in which one frame is divided into a plurality of sub-frames (1st to m-th sub-frames) (m pieces; m is an integer of 2 or more). That is, the control unit outputs a display signal to the display unit m times in one frame period (the first to m-th display signals that are display signals of the first to m-th subframes in order). Output) . As a result, in each subframe period, the control unit turns on all the gate lines on the display screen of the display unit once (m is turned on m times in one frame).

[0013] 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. The normal hold display is a normal display that does not divide the frame into subframes (display that turns on all the gate lines on the display screen only once in one frame period).

[0014] Further, the display unit (display screen) is designed to display an image with a luminance based on the voltage of the display signal (voltage corresponding to the luminance gradation of the display signal) input by the control unit. Talk!

[0015] 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 display of these displays). Set the signal voltage). 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 unit.

[0016] Here, in general, on the display screen of the display unit, when the voltage (liquid crystal voltage) of the display signal is minimum or close to the maximum, the difference between the actual brightness and the expected brightness at a large viewing angle (brightness deviation). ) Can be made sufficiently small.

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

[0018] Further, the planned brightness is the brightness (a 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 causes the voltage of at least one of the first to mth display signals to be minimum or close to the maximum. As a result, the brightness deviation in at least one subframe can be made sufficiently small. As a result, the display device can suppress the lightness deviation compared to when performing normal hold display. It becomes possible to improve the field angle characteristics. For this reason, the white floating phenomenon can be satisfactorily suppressed.

[0020] Further, the display quality of a moving image can be improved by performing the subframe display as described above. In other words, when following the line of sight of the movement of an object displayed in the normal hold display, the color and brightness of the previous frame can be seen at the same time. For this reason, the edge of the object is recognized as blurred.

[0021] 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 is possible to suppress the visual mixing of the image of the currently viewed frame and the image of the immediately preceding frame (color'brightness). Therefore, the edge blur as described above can be avoided and the display quality of the moving image can be improved.

In addition, this 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 required. In addition, at present, a large-sized display element generally uses a fluorescent tube as a light source for efficiency.

[0023] In addition, generally, 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 for controlling the magnitude (brightness) of light emitted from a light source by changing the amplitude of a current (lamp current) applied to the light source. When a fluorescent tube is used as the light source, if the lamp current amplitude is too small, the fluorescent tube will not shine. For this reason, the current dimming method has the disadvantage that the dimming range (brightness range that can be realized) cannot be widened. Therefore, it is preferable to use the PWM dimming method in a device that requires a wide dimming range such as a liquid crystal television.

[0025] Note that, when PWM dimming and subframe display are simply combined, interference phenomena such as flickering force and horizontal stripes may occur. In other words, when PWM dimming is performed in subframe display, the dimming frequency interferes with the subframe frequency, and the frequency of the light waveform that passes through the display (transmission waveform) is higher than the dimming frequency. It may drop greatly. In such a case, the user feels a strong flick force.

[0026] The flitz force is such that the dimming frequency is close to n. 5 times the frame frequency (n is an integer). It becomes violent. In addition, when the dimming frequency is n times the frame frequency, the frequency force S of the transmitted waveform is equal to the S frame frequency, and thus the flicker force can be reduced to an inconspicuous level. However, when the dimming frequency is brought close to n times the frame frequency, horizontal stripes appear on the screen! / ヽぅ Interference phenomenon occurs.

That is, the light source usually irradiates the entire screen with light at the same time. On the other hand, the display

The (liquid crystal display element) is driven by line scanning. Therefore, each line on the display screen is turned ON and OFF at different times depending on the position. For this reason, on the lines at different positions, the ONZOFF timing of the response waveform of the liquid crystal shifts (slides with respect to time).

[0028] Therefore, the ratio of the time for which the transmission waveform is turned on (time for high luminance) varies depending on the line position. For this reason, there is a difference in average brightness between lines, which is recognized as a horizontal stripe phenomenon.

[0029] When the dimming frequency is exactly n times the frame frequency, the horizontal stripes stop on the screen. As the n-power boost is lost, horizontal stripes begin to flow up and down the screen. Furthermore, the horizontal stripes disappear when the dimming frequency deviates significantly from n times and approaches n.

That is, when the dimming frequency is n.times.5 times the frame frequency, the light emission waveform of the light source has an opposite phase between adjacent frames. Therefore, the transmission waveform of each line force 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 compensated for time), so the occurrence of horizontal stripes can be avoided.

[0031] Therefore, in this display device, when PWM dimming and subframe display are combined, the control unit sets the dimming frequency to “a value that is n. 5 times the frame frequency and 450 Hz or higher”. It is preferable to do.

[0032] In this case, since the dimming frequency is n. 5 times the frame frequency, the horizontal stripes as described above do not occur. Regarding the flicker force, although the frequency of the transmission waveform in each line is half the frame frequency, the dimming frequency is sufficiently increased, so that the flicker force can be made inconspicuous.

[0033] That is, the two lines on the display (referred to as line A · Β) have a reversed relationship for each frame (the light intensity of the first frame (second frame) of line 2 the second frame of line B (1 fl The same as the first program). If the lines having such a relationship can be densely arranged on the screen, the flicker force can be spatially compensated by allowing the user to visually recognize the light of these line forces at the same time.

[0034] Here, the two lines having the above relationship are closer to each other on the screen as the dimming frequency is higher. Therefore, by sufficiently increasing the dimming frequency, the flits force can be made inconspicuous even if the value is set to n.5 times the frame frequency.

[0035] It should be noted that, when the luminance is 50% (when the black insertion rate is 50%), the experimental result has been obtained that the flicker force becomes inconspicuous when the dimming frequency is set to 450 Hz or more. In addition, the frits force is most noticeable when the black insertion rate is 50%.

Therefore, in the present display device, by setting the dimming frequency to “a value that is n. 5 times the frame frequency and equal to or greater than 45 OHz”, it is possible to avoid the occurrence of both horizontal stripes and flickering force. It is like this.

[0037] In addition, it is possible to suppress the interference phenomenon without increasing the dimming frequency in this way. For example, “The light emission waveform of the light source is a combination of a main light emission noise 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. This can be achieved.

In this configuration, in the transmission waveform of each line, the transmission amount of the main light emission pulse and the luminance compensation pulse has a reverse ratio for each force frame that increases or decreases for each frame. For example, if the generation ratio of the main light emission pulse (noise) 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.

[0039] Therefore, although the frequency of the transmitted waveform is small, the luminance difference between frames can be reduced by using the luminance compensation pulse. Therefore, it is possible to make the flits force inconspicuous.

[0040] Further, in this configuration, the dimming frequency can be made lower than 450Hz, so that it is possible to avoid a decrease in the driving efficiency of the light source. Since this configuration uses two pulses, 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 effect of the luminance compensation pulse on the driving efficiency of the light source is sufficiently / J. [0041] 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.

[0042] In this case, although the above horizontal stripes can be avoided, it is preferable to take measures against the flickering force. Therefore, the control unit inserts the above-described luminance compensation pulse having a relatively short pulse width with respect to the light emission waveform of the light source at the same frequency and in the opposite phase as the main light emission noise. Furthermore, the control unit inserts a luminance compensation depletion pulse when there is a luminance compensation added pulse instead of the luminance compensation pulse at the timing when the phase of the main light emitting noise 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 (noise).

That is, in this configuration, when the light amount of the main light emission pulse is too small, the luminance compensation pulse is inserted to increase the light amount. On the other hand, when the light amount of the main light emission pulse is too large, the luminance compensation is reduced. It is designed to reduce the amount of light by inserting a pulse.

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). Accordingly, it is possible to reduce the flick force.

[0046] Further, when subframe display and PWM dimming are combined in the present display device, when the display unit has a plurality of light sources, the control unit sets the emission waveforms of at least two light sources to different phases. It is also preferable to do PWM dimming.

In this configuration, the 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, it is possible to make interference phenomena such as flickering force and horizontal stripes inconspicuous without increasing the frequency of the dimming signal.

[0048] Further, in this case, the control unit divides each light source into p groups (p is a natural number of 2 or more), and controls to shift the phase of the light emission waveform by 360 ° Zp for each group. It is preferable to carry out. This can greatly increase the DC component of the mixed light. [0049] Note that when a plurality of light sources as described above are used, it is possible to use a direct-type backlight, a side-type backlight, a side-type front light, or the like as the light source. When a knock light is used, the display unit is a transmissive or transflective display element. When a front light is used, the display unit is a reflective display element.

[0050] 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 (all gates) having a plurality of gate line forces close to itself. Light is sent to a group that forms part of the line.

[0051] 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 "light emission 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 the “waveform state” is the same for all light sources (all gate line groups).

[0052] In this case, since the dimming frequency is n times the frame frequency, no flickering force is generated. 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 lines, it is possible to avoid the occurrence of horizontal stripes.

[0053] In addition, 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 is overlapped with the constant amplitude. Therefore, the DC component of the emission waveform can be easily increased.

[0055] For this reason, the amount of time variation in the light emission amount of the light source can be reduced. In addition, the difference in the amount of light emitted between lines can be reduced. Therefore, it is possible to make interference phenomena such as flickering force and horizontal stripes inconspicuous without increasing the frequency of the dimming signal.

[0056] When the sub-frame display and PWM dimming are combined, the display unit has a reflection type.

When using a transflective liquid crystal display element, V ヽ should be designed so that the light from the light source is controlled according to the external light. [0057] In this configuration, it is preferable to include a luminance sensor that detects a luminance waveform of the external light applied to the display unit. The control unit preferably performs PWM dimming 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.

Accordingly, in this configuration, it is possible to irradiate the display unit with light having a large DC component mixed with light having the same frequency and opposite phase. Therefore, with this configuration, the amount of time variation in the amount of light emitted from the light source can be reduced. In addition, the difference in light emission between lines can be reduced. Therefore, it is possible to make interference phenomena such as flickering force and horizontal stripes inconspicuous without increasing the frequency of the dimming signal. In addition, a fluorescent tube, LED, EL, FED, or the like can be used as the light source of the display device.

[0059] Further, by combining this display device and an image signal input unit (signal input unit), a liquid crystal monitor used in a personal computer or the like can be configured.

[0060] 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.

[0061] In addition, a liquid crystal television receiver can be configured by combining the present display device and a tuner unit.

Here, the tuner unit is for receiving a television broadcast signal. In this configuration, the control unit power of this display device and the tuner unit power are generated based on the transmitted television broadcast signal and output to the display unit.

[0063] Further, the image display method (the present display method) of the present invention includes:

A display method in which one frame is divided into m (m; an integer greater than or equal to 2) sub-frames for image display, and the sum of the luminances output from the display unit in one frame is divided into frames. In order not to change, an output process of generating 1st to mth display signals, which are display signals of the 1st to mth subframes, and outputting the generated signals to a display unit having a liquid crystal display element power is further included. This is a method including a dimming step of dimming the light source by a PWM dimming method.

[0064] This display method is a method used in the above-described display device. Therefore, in this display method, the brightness deviation can be suppressed to a smaller value than in the case of performing the normal hold display, and the viewing angle characteristics can be improved. For this reason, whitening phenomenon is good Can be suppressed. It is also possible to improve the display quality of moving images.

[0065] Further, by performing dimming by the PWM dimming method, dimming can be performed in a wider range than when the current dimming method is used.

[0066] 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 greater than or equal to 2) sub-frames. The display signal for the first to mth sub-frames so that the sum of the luminances output from the display unit per frame is not changed by dividing the frame. A control unit that generates 1st to mth display signals and outputs them to the display unit. This control unit is designed to dimm the light source of the display unit using the PWM dimming method! It is.

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

[0068] Still other objects, features, and advantages of the present invention will be sufficiently enhanced by the following description. The benefits of the present invention will become apparent from the following description with reference to the accompanying drawings.

Brief Description of Drawings

[0069] FIG. 1 is a block diagram showing a configuration of a display device according to an embodiment of the present invention.

FIG. 2 is a graph showing the display brightness (relationship between planned brightness and actual brightness) output from the liquid crystal panel in the case of normal hold display.

FIG. 3 is a graph showing display luminance (relation between planned luminance and actual luminance) output from the liquid crystal panel when subframe display is performed in the display device shown in FIG.

[FIG. 4] (a) is an explanatory diagram showing an image signal input to the frame memory of the display device shown in FIG. 1, and (b) is a diagram of the frame memory in the case of 3: 1 division. It is explanatory drawing which shows the image signal output to a front | former stage LUT, (c) is explanatory drawing which shows the image signal similarly output to a back | latter stage LUT.

[FIG. 5] In the display device shown in FIG. It is explanatory drawing which shows the ON timing of the gate line regarding a display signal and a back | latter stage display signal.

FIG. 6 is a graph showing the luminance graph shown in FIG. 3 converted to lightness.

FIG. 7 is a graph showing the relationship between planned brightness and actual brightness when the frame is divided into 3: 1 in the display device shown in FIG.

8 is an explanatory diagram showing a display device in which the configuration of the display device shown in FIG. 1 is partially changed. {Circle around (9)} FIG. 9 is an explanatory diagram showing a method of inverting the polarity of the voltage between electrodes at a frame period. {Circle around (9)} FIG. 9B is an explanatory diagram showing a method of inverting the polarity of the interelectrode voltage at the frame period.

FIG. 10 (a) is a diagram for explaining the response speed of the liquid crystal.

FIG. 10 (b) is a diagram for explaining the response speed of the liquid crystal.

FIG. 10 (c) is a diagram for explaining the response speed of the liquid crystal.

FIG. 11 is a graph showing display luminance (relationship between planned luminance and actual luminance) output from a liquid crystal panel when subframe display is performed using liquid crystal with a slow response speed.

FIG. 12 (a) is a graph showing the luminance displayed by the previous subframe and the rear subframe when the display luminance force Lmax is 3Z4 and 1Z4.

[12 (b)] This is a graph showing the transition state of the liquid crystal voltage when the polarity of the voltage (liquid crystal voltage) applied to the liquid crystal is changed in the subframe period.

圆 13 (a)] is an explanatory diagram showing a method of inverting the polarity of the interelectrode voltage at the frame period. 13 (b)] is an explanatory diagram showing a method of inverting the polarity of the voltage between electrodes at a frame period.

FIG. 14 (a) is an explanatory diagram showing four pixels in the liquid crystal panel and the polarity of the liquid crystal voltage of each pixel.

FIG. 14 (b) is an explanatory diagram showing the four pixels in the liquid crystal panel and the polarity of the liquid crystal voltage of each pixel.

FIG. 14 (c) is an explanatory diagram showing the four pixels in the liquid crystal panel and the polarity of the liquid crystal voltage of each pixel.

FIG. 14 (d) is an explanatory diagram showing four pixels in the liquid crystal panel and the polarity of the liquid crystal voltage of each pixel.

[Fig.15] The result of dividing the display into three equal subframes (dashed line and And a solid line) and a result of normal hold display (a chain line and a solid line).

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.

FIG. 17 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 subframe.

圆 18] 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 sub-frame where the luminance is not adjusted ( It is a graph which shows a viewing angle gradation characteristic (actual measurement).

FIG. 19 is an explanatory diagram showing a current dimming method.

FIG. 20 is an explanatory diagram showing a PWM dimming method.

21] A graph showing an example of a waveform of a dimming signal, a lamp current waveform, and a light emission waveform (a waveform of light that also outputs a fluorescent tube force) when a fluorescent tube is used as a light source.

FIG. 22 is a block diagram showing an internal configuration of a display device that performs PWM dimming according to the present invention.

[Figure 23] Relationship between light source emission waveform, liquid crystal electrode voltage waveform (liquid crystal response waveform), and light transmission light waveform (transmission waveform) when PWM dimming is combined with normal hold display It is a graph which shows the example of.

FIG. 24 is a graph showing similar waveforms when PWM dimming is combined with sub-frame display (in the case of low luminance).

FIG. 25 is a graph showing an example of the relationship between the light emission waveform, liquid crystal response waveform, and transmission waveform of a light source when PWM dimming is combined with subframe display.

FIG. 26 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 the dimming frequency is set to “n.5 times the frame frequency and 450 Hz or higher”. It is.

[27] This is a graph showing an example of the relationship between the light emission waveform, the liquid crystal response waveform, and the transmission waveform when the luminance compensation pulse is used.

[FIG. 28] The light emission waveform of the light source when the phase of the light emission waveform of the light source is inverted for each frame. It is a graph which shows the example of the relationship between a liquid crystal response waveform and a transmission waveform.

圆 29] 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 the light emission waveform of the light source is reversed in phase for each frame and a positive compensation pulse and a negative compensation pulse are added. It is.

FIG. 30 is a block diagram showing a configuration of a display device when the light emission waveform of a light source is controlled to include a direct current component (DC component).

[FIG. 31] (a) and (b) show the emission waveform of the first fluorescent tube (first waveform), the emission waveform of the second fluorescent tube (second waveform), and both fluorescent tubes in the configuration shown in FIG. 5 is a graph showing an example of a waveform (mixed waveform) obtained by mixing the light emission waveforms.

[32] FIG. 32 is a block diagram showing the configuration of the display device when the fluorescent tubes are divided into three types and controlled independently for each type.

FIGS. 33 (a) and 33 (b) are graphs showing examples of fluorescent tubes (first to third waveforms) and mixed waveforms (mixed waveforms) in the configuration shown in FIG.

FIG. 34 is an explanatory diagram showing a configuration of a liquid crystal display element having a direct type backlight.

FIG. 35 is an explanatory diagram showing a configuration of a knock light type liquid crystal display device including two LEDs as light sources on two sides of a light guide plate.

FIG. 36 is an explanatory diagram showing a configuration of a knock light type liquid crystal display device including two LEDs as light sources on one side of a light guide plate.

FIG. 37 is an explanatory diagram showing a configuration of a front-light type liquid crystal display device including two LEDs as light sources on two sides of a light guide plate.

FIG. 38 is an explanatory diagram showing a configuration of a front-light type liquid crystal display device including two LEDs as light sources on one side of a light guide plate.

FIG. 39 is a block diagram showing a configuration of a display device in the case where the light emission timing of the fluorescent tube is synchronized with the ON timing of the gate line of the liquid crystal panel.

40] FIG. 40 is a graph showing an example of the relationship between the light emission waveform of the light source, the liquid crystal response waveform, and the transmission waveform for the display device shown in FIG.

FIG. 41 is a block diagram showing a configuration of a display device that uses both the PWM dimming method and the current dimming method. 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. 41.

FIG. 43 is a diagram showing a configuration of a reflective display device that performs light source control in accordance with external light.

FIG. 44 (a) is a graph showing a luminance waveform of external light incident on the display device shown in FIG.

FIG. 44 (b) is a graph showing the light emission waveform of the light source in the display device shown in FIG.

FIG. 44 (c) is a graph showing a waveform of light incident on the liquid crystal panel of the display device shown in FIG.

FIG. 45 is a diagram showing a configuration of a transflective display device that performs light source control in accordance with external light.

FIG. 46 is an explanatory diagram showing a configuration of a liquid crystal television provided with the display device shown in FIG.

BEST MODE FOR CARRYING OUT THE INVENTION

[0070] One embodiment of the present invention will be described.

The liquid crystal display device (present display device) according to the present embodiment has 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 externally input image signal 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 (F. M.) 11, a front LUT 12, a rear LUT 13, a display unit 14, and a control unit 15.

[0073] The frame memory (image signal input unit) 11 receives an image signal (R

(GB signal) is stored 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.

It should be noted that this display device displays subframes! /. Here, the subframe display is a method of displaying one frame divided into a plurality of subframes.

That is, the present display device performs display using two subframes having the same size (period) at twice the frequency based on the image signal for one frame input in one frame period. Designed. The previous 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 a 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. The control unit 15 also generates a display signal from the image signal power accumulated in the frame memory 11 using the preceding LUT 12 and the latter LUT 13 and outputs the display signal to the display unit 14.

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

Then, the control unit 15 generates a front display signal using the front LUT 12 based on the image signal output for the first time. After that, a rear display signal is generated using the rear LUT 13 based on the image signal output for the second time. These display signals are sequentially output to the display unit 14 with a double clock.

Accordingly, the display unit 14 displays different images once in one frame period based on two display signals that are sequentially input (all gates of the liquid crystal panel 21 in both subframe periods). Turn the line ON once). 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, the general display brightness (the brightness of the image displayed by the panel) related to the liquid crystal panel will be described.

[0083] When displaying normal 8-bit data in one frame without using subframes (In a single frame period, all the gate lines of the liquid crystal panel are turned ON only once, and in normal hold display), the luminance gradation (signal gradation) of the display signal is in the range from 0 to 255.

[0084] Then, the signal gradation and the display luminance in the liquid crystal panel are approximately expressed by the following equation (1).

((T-TO) / (Tmax-TO)) = (L / Lmax) "γ---(1)

Where L is the signal gradation (frame gradation) when displaying an image in one frame (when displaying an image with normal hold display), Lmax is the maximum luminance gradation (255), T is the display luminance, Tmax is the maximum brightness (brightness when L = Lmax = 255; white), TO is the minimum brightness (brightness when L = 0; black), and y is the correction value (usually 2.2). In the actual liquid crystal panel 21, T 0 = 0 is not satisfied. However, in order to simplify the explanation, TO = 0 is assumed below.

[0085] Also, the display brightness Τ output from the liquid crystal panel 21 in this case (in the case of normal hold display) is shown as a graph in FIG. This graph shows “luminance that should be output (scheduled luminance; value according to signal gradation, equivalent to the above display luminance Τ)” on the horizontal axis, and “actually output luminance (actual Brightness) ”.

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 with halftone brightness due to the change in the gradation γ characteristics.

[0087] Next, display luminance in the display device will be described.

In this display device, the control unit 15

(a) “The sum of the luminance (display luminance) of the image displayed by the display unit 14 in each of the previous subframe and the rear subframe (integrated luminance in one frame) Make it equal to the display brightness. ''

(b) “Make one subframe black (minimum brightness) or white (maximum brightness)”

Designed to perform gradation expression to meet the requirements!

[0088] To this end, 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. .

[0089] In other words, luminance up to half of the maximum luminance (threshold luminance; TmaxZ2) 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 adjusts only the display luminance of the subsequent subframe to perform gradation representation (using only the subsequent subframe). Key expression). In this case, the integrated luminance in one frame is “(minimum luminance + luminance of subsequent subframe) Z2”.

[0090] When the luminance higher than the above threshold luminance is output (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 adjust the level. Make a representation.

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

Next, a specific description will be given of the signal gradation setting of display signals (previous display signal and subsequent display signal) for obtaining such display luminance. The signal gradation setting is performed by the control unit 15 shown in FIG. The control unit 15 preliminarily calculates the frame gradation corresponding to the above-described threshold luminance (TmaxZ2) using the above-described equation (1).

[0093] That is, the frame gradation (threshold luminance gradation; Lt) corresponding to such display luminance is obtained from equation (1):

Lt = 0.5 "(ΐ / γ) X Lmax… (2)

However, Lmax = max y (2a

It becomes.

Then, when displaying an image, the control unit 15 obtains a frame gradation L based on the image signal output from the frame memory 11.

[0095] When L is equal to or less than Lt, the control unit 15 sets the luminance gradation (F as the previous stage display signal).

) To the minimum (0) by the front LUT12. On the other hand, the control unit 15 determines the luminance gradation (R) of the subsequent display signal based on the equation (1).

R = 0.5 "(ΐ / γ) X L (3)

Set by using the LUT13 at the latter stage.

[0096] When the frame gradation L is larger than L, 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 determines the luminance gradation F of the previous subframe based on the equation (1). F = (L "y -0. 5 X Lmax" γ) "(1 / γ) (4)

And

Next, the display signal output operation in the present display device will be described in more detail.

In the following, it is assumed that the number of pixels of the liquid crystal panel 21 is a X b. In this case, the control unit 15 accumulates the previous stage display signal of the pixel (a number) of the first gate line with respect to the source driver 23 with a 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 preceding 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 1 frame (1Z2 frame period).

[0099] 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 1Z2 frame period. As a result, the front display signal and the rear display signal are written to each pixel at an equal time (1Z2 frame period).

[0100] 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 and output (the dotted line and the solid line). It is a graph shown together with a chain line and a solid line.

[0101] In this 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. On the other hand, the liquid crystal panel 21 that is the largest in the halftone (near the threshold luminance) is used.

[0102] In this display device, subframe display is performed in which one frame is divided into subframes. Further, 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 the 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 deviation in the previous subframe is minimized, as shown by the broken line in FIG. 3, the total deviation between both subframes can be reduced to about half.

[0103] On the other hand, in the case of high luminance, within the range where the integrated luminance in one frame is not changed, The frame is displayed in white, and only the brightness of the previous subframe is adjusted. For this reason, in this case as well, 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.

[0104] As described above, in this display device, the overall shift can be reduced 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). It is possible. For this reason, it is possible to suppress the phenomenon that a halftone image becomes bright and floats white as shown in FIG.

[0105] 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, the duration of these subframes may be set to different values.

[0106] In other words, the white-floating phenomenon, which is a problem in this display device, has the characteristics shown in Fig. 2 when the viewing angle is large. It is a phenomenon that looks white.

[0107] Note that an image captured by a camera is usually a signal based on luminance. When this image is transmitted in digital format, the image is converted into a display signal using γ shown in equation (1) (that is, the luminance signal is multiplied by (ΐΖ γ) and divided equally. To add gradation). Based on such a display signal, an image displayed by a display device such as a liquid crystal panel has a display luminance represented by equation (1).

[0108] By the way, the human visual sense receives an image not as luminance but as brightness. The lightness (lightness index) Μ is expressed by the following equations (5) and (6) (see Non-Patent Document 1).

[0109] M = 116 XY '(lZ3) — 16, Υ> 0.008856 · · · (5)

Μ = 903. 29 ΧΥ, Υ≤0. 008856 (6)

Here, Υ corresponds to the actual luminance described above, and is an amount Y = (yZyn). Here, y is the y value of tristimulus values in the xyz color system of an arbitrary color, and yn is the y value of standard diffuse reflection surface light, and yn = 100.

[0110] From these equations, humans are sensitive to dark images in terms of brightness and are sensitive to bright images. It tends to become insensitive. And even with regard to whitening, it is considered that human beings receive brightness deviations that are not luminance deviations.

[0111] Here, FIG. 6 is a graph showing the luminance graph shown in FIG. 3 converted to lightness. This graph shows the lightness that should be output on the horizontal axis (scheduled lightness; a value corresponding to the signal tone, equivalent to the lightness M above), and the lightness actually output (actual lightness) on the vertical axis. ing. As shown by the solid line in this graph, the above two brightness values are equal on the front surface of the liquid crystal panel 21 (viewing angle 0 degree).

[0112] 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, the luminance up to half the maximum value is displayed in one subframe) The actual brightness and the scheduled brightness are improved compared to the conventional case of normal hold display. Therefore, it can be seen that the whitening phenomenon can be suppressed to some extent.

[0113] In addition, it can be said that it is more preferable to determine the frame division ratio according to the brightness that is not 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 planned brightness is the largest at the half of the maximum value of the planned brightness, as in the case of luminance.

[0114] Therefore, rather than dividing the frame so that the luminance up to half the maximum value is displayed in one subframe, the frame is divided so that the brightness up to half the maximum value is displayed in one subframe. If you do this, you will be able to improve the gaps that humans feel (ie, whitening).

[0115] Therefore, a preferable value at a frame division point will be described below.

First, in order to perform the calculation easily, the above equation (5) (6) is changed to a form like the following equation (6a) ((1

(Similar to equation)).

Μ = Υ "(1 / α)---(6a)

When converted to this form, α in this equation is about 2.5.

[0116] If the value of a is between 2.2 and 3.0, the relationship between brightness Y and brightness M in equation (6a) is appropriate (corresponding to human visual senses). )It is believed that.

[0117] And in order to display the lightness M that is half the maximum value in one subframe, two The subframe period is preferably about 1: 3 when γ = 2.2 and about 1: 7 when γ = 3.0. 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 when the luminance is high) is set to a short period. Will be.

[0118] 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.

[0119] In this case, when performing low-brightness display in which the maximum luminance of 1 to 4 (threshold luminance; TmaxZ4) is output in one frame, the control unit 15 sets the previous subframe to the minimum luminance (black). ) And gradation expression by adjusting only the display luminance of the subsequent sub-frame (representing gradation using only the subsequent sub-frame). In this case, the integrated luminance in one frame is (minimum luminance + luminance of subsequent subframe) Z4.

[0120] When the luminance higher than the threshold luminance (TmaxZ4) 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 sets the display luminance of the previous subframe. Adjust and perform gradation expression. In this case, the integrated luminance in one frame is (luminance of the previous subframe + maximum luminance) / 4.

[0121] 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 preliminarily calculates the frame gradation corresponding to the above-described threshold luminance (TmaxZ4) using the above-described equation (1).

[0123] That is, the frame gradation (threshold luminance gradation; Lt) corresponding to such display luminance is obtained from equation (1):

Lt = (l / 4) "(l / y) X Lmax (7)

Then, when the image is displayed, the control unit 15 obtains the frame gradation L based on the image signal output from the frame memory 11. When L is equal to or less than Lt, the control unit 15 sets the luminance gradation (F) of the preceding display signal to the minimum (0) using the preceding LUT 12.

On the other hand, the control unit 15 determines the luminance gradation (R) of the rear display signal based on the equation (1).

R = (l / 4) "(l / y) XL (8) Set by using the LUT13 at the latter stage.

[0125] When the frame gradation L is greater than L, 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 determines the luminance gradation F of the previous subframe based on the equation (1).

F = ((L-(1/4) X Lmax "γ)) ΊΐΖ Ύ) (9)

And

[0126] Next, the output operation of the preceding display signal and the succeeding display signal will be described. As described above, in the configuration in which the frame is divided equally, the preceding display signal and the succeeding display signal are respectively included in the pixels. Equal time (1Z2 frame period) is written. 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 write start timing of the subsequent display signal (the gate related to the subsequent display signal)

By changing (ON timing), harm of harm can be changed.

[0128] Fig. 4 (a) is an image signal input to the frame memory 11, (b) is an image signal output from the frame memory 11 to the preceding LUT 12 in the case of 3: 1 division, and ( c)

FIG. 6 is an explanatory view showing an image signal output to the latter LUT 13 in the same manner. FIG. 5 is an explanatory diagram showing the gate line ON timing related to the front display signal and the rear display signal in the same case of 3: 1 division.

As shown in these drawings, in this case, the control unit 15 writes the preceding display signal of the first frame to the pixels of each gate line with a normal clock. Then, after the 3Z4 frame period, writing of the subsequent display signal is started. From this time, the front display signal and the rear display signal are written alternately with a double clock.

[0130] That is, after writing the previous display signal to the pixel of the “3Z4” gate line of all the gate lines, the subsequent display signal related to the first gate line is accumulated in the source driver 23, and this gate line is stored. Turn on. Next, the previous display signal related to “3/4 of all gate lines” + the first gate line is accumulated in the source driver 23, and this gate line is turned ON. [0131] In this way, after the 3Z4 frame period of the first frame, by alternately outputting the front display signal and the rear display signal with the double clock, the ratio of the front subframe and the rear subframe is 3: 1. It becomes possible. The total display luminance (integral sum) in these two sub-frames becomes the integrated luminance in one frame. Note that the data stored in the frame memory 11 is output to the source driver 23 in accordance with the gate timing.

[0132] Fig. 7 is a graph showing the relationship between the planned 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.

That is, in this display device, in the case of low luminance (low brightness) up to “TmaxZ4”, the front subframe is displayed in black and only the rear subframe is used within a range in which the integrated luminance in one frame is not changed. Is displayed. Therefore, the deviation in the previous subframe (the difference between the actual brightness and the planned brightness) is minimized, and the total deviation in both subframes can be reduced to approximately 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, with the subsequent subframe being displayed in white within the range in which the integrated luminance in one frame is not changed. For this reason, in this case as well, 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.

As described above, in the present display device, it is possible to reduce the brightness deviation to about half as a whole 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 the halftone image becomes brighter and whiter as shown in FIG. 2 (whitening phenomenon).

Here, in the above, during the period from the start of display to the 3Z4 frame period, the previous stage display signal of the first frame is written to the pixels of each gate line with a normal clock. This is because the timing for writing the subsequent display signal has not been reached.

[0137] With a force, change to such a measure and start display using a dummy rear display signal The time power may be displayed with a double clock. In other words, during the period from the start of display to the 3Z4 frame period, the former display signal and the latter display signal of signal gradation 0 (dummy latter display signal) may be output alternately.

[0138] Here, a case where the ratio of the front subframe and the rear subframe is generally set to n: 1 will be described below. In this case, the control unit 15 outputs the previous sub-frame with the minimum luminance when outputting the luminance up to lZ (n + 1) (threshold luminance; Tmax / (n + 1)) of the maximum luminance in one frame (when the luminance is low). (Black), and gradation expression is performed by adjusting only the display luminance of the subsequent subframe (tone 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).

[0139] When the luminance higher than the threshold luminance (TmaxZ (n + l)) is output (in the case of high luminance), the control unit 15 sets the rear subframe to the maximum luminance (white) and displays the previous subframe. Adjust the brightness to express the gradation. In this case, the integral luminance in one frame is “(luminance of the previous subframe + maximum luminance) / (n + 1)”.

[0140] Next, a specific description will be given of the signal gradation setting of the display signals (the front display signal and the rear display signal) for obtaining such display luminance. 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 preliminarily calculates the frame gradation corresponding to the above threshold luminance (TmaxZ (n + 1)) using the above-described equation (1).

[0142] That is, the frame gradation (threshold luminance gradation; Lt) according to such display luminance is obtained from the equation (1):

X Lmax (10)

On the other hand, the control unit 15 determines the luminance gradation (R) of the subsequent display signal based on the equation (1).

Set by using the LUT13 at the latter stage. [0144] When the frame gradation L is greater than L, 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 determines the luminance gradation F of the previous subframe based on the equation (1).

F = ((L-(l / (n + l)) XLmax)) "(l / y) --- (12)

And

[0145] In addition, regarding the display signal output operation, in the case where the frame is divided into 3: 1, after the nZ (n + l) frame period of the first frame, the previous display signal is output with a double clock. It is sufficient to design so that and the subsequent display signal are output alternately.

[0146] Further, it can be said that the structure for equally dividing the frame is as follows. That is, one frame is divided into subframe periods of “l + n (= l)”. Then, with a clock that is “l + n (= l)” times the normal clock, the previous stage display signal is output in one subframe period, and the subsequent stage display signal is continued in the subsequent n (= l) subframe periods. To output automatically.

However, in this configuration, when n is 2 or more, the clock needs to be very fast, which increases the device cost. Therefore, 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, by adjusting the output timing of the rear display signal, the ratio of the previous subframe and the rear subframe can be set to n: l. Can be doubled.

[0148] In the present embodiment, the control unit 15 converts the image signal into a display signal using the front LUT 12 and the rear LUT 13. Here, the front LUT12 provided in this display device

The latter LUT 13 may be plural.

[0149] FIG. 8 shows the configuration shown in FIG. 1 by replacing the front LUT 12 with three front LUTs 12a to

12c, the rear stage LUT 13 is replaced with three rear stage LUTs 13a to 13c, and a temperature sensor 16 is further provided.

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

[0151] The first LUTs 12a to 12c are suitable for use in different temperature ranges. The front LUT. The rear LUTs 13a to 13c are also rear LUTs suitable for use in different temperature ranges.

[0152] The temperature sensor 16 measures the ambient temperature in which 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, in 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 a more faithful luminance in the entire assumed temperature range (for example, a range of 0 ° C to 65 ° C).

[0154] The liquid crystal panel 21 is preferably driven by alternating current. This is because by using AC driving, the charge polarity of the pixel (the direction of the voltage between the pixel electrodes (voltage between the electrodes) sandwiching the liquid crystal) can be changed for each frame.

[0155] When direct current drive is used, 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 state in which a potential difference is generated between the electrodes (a so-called seizure state) will occur.

Here, when sub-frame display is performed as in the present display device, the voltage value (absolute value) applied between the pixel electrodes is often different between sub-frames!

Therefore, when the polarity of the interelectrode voltage is inverted at 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 there is a possibility that the above-described seizure will generate a frit force.

[0158] Therefore, in the present display device, it is preferable to reverse the polarity of the voltage between the electrodes at a frame period (period of one frame time width). There are two methods for reversing the polarity of the interelectrode voltage in the frame period. One method is to apply a voltage of the same polarity for one frame. In another method, the voltage between the electrodes 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.

[0159] Figure 9 (a) shows the voltage polarity (polarity of the voltage between electrodes) and the voltage when the former method is used. It shows the relationship with the lemma cycle. Figure 9 (b) shows the relationship between voltage polarity and frame period when the latter method is used. By making the interelectrode voltage alternating in the frame period in this way, even if the interelectrode voltage differs greatly between subframes, it is possible to prevent seizure and flicking force.

[0160] Further, as described above, in the present display device, the liquid crystal panel 21 is driven by sub-frame display, thereby suppressing whitening. However, if the response speed of the liquid crystal (the speed at which the voltage applied to the liquid crystal (interelectrode voltage) becomes equal to the applied voltage) is slow, the effect of such subframe display may be diminished.

[0161] That is, when performing normal hold display, one liquid crystal state corresponds to a certain luminance gradation in the TFT liquid crystal panel. Therefore, the response characteristics of the liquid crystal do not depend on the luminance gradation of the display signal.

[0162] On the other hand, when subframe display is performed as in the present display device, when displaying a display signal of intermediate gradation in which the previous subframe has the minimum luminance (white) and the rear subframe has the maximum luminance, 1 The voltage applied to the liquid crystal in the frame varies as shown in Fig. 10 (a). The interelectrode voltage changes as shown by the solid line X in Fig. 10 (b) according to the response speed (response characteristics) of the liquid crystal.

Here, when the response speed of the liquid crystal is slow, when such halftone display is performed, the voltage between electrodes (solid line X) changes as shown in FIG. 10 (c). 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.

[0164] Therefore, the relationship between the planned brightness and the actual brightness is as shown in FIG. In other words, even when subframe display is performed, it is not possible 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.

[0165] Therefore, in order to satisfactorily perform sub-frame display like this display device, the response speed of the liquid crystal in the liquid crystal panel 21 is designed to satisfy the following (c) (d): Is preferred.

[0166] (c) Maximum brightness (white; maximum brightness) on a liquid crystal displaying minimum brightness (black; equivalent to minimum brightness) The voltage of the liquid crystal (the voltage between the electrodes) within the shorter subframe period when a voltage signal (generated by the source driver 23 based on the display signal) is applied. A value of 90% or more in the voltage of the voltage signal is reached (the actual brightness of the front reaches 90% of the maximum brightness)

(d) When the maximum luminance (white) is displayed and a voltage signal is applied to the liquid crystal to achieve the minimum luminance (black), the voltage of the liquid crystal (interelectrode voltage) within the shorter subframe period. However, it reaches a value of 5% or less in the voltage of the voltage signal (the actual brightness of the front reaches 5% of the minimum brightness).

[0167] Further, the control unit 15 is preferably designed so that the response speed of the liquid crystal can be monitored. If 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) are not satisfied, the control unit 15 interrupts the sub-frame display, and the liquid crystal panel 21 May be set to be driven by normal hold display.

[0168] This makes it possible to switch the display method of the liquid crystal panel 21 to the normal hold display when the white floating phenomenon becomes noticeable due to the subframe display.

[0169] In this 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 including a 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.

[0170] With 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.

[0171] 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, even if the subframe contexts are exchanged (if the luminance is low, the subsequent subframe is black and the gradation is expressed using only the previous subframe), the same display is obtained. can get. In this embodiment, the luminance gradation (signal gradation) of the display signal (the preceding display signal and the succeeding display signal) is set using 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 must be taken into account when setting the signal gradation. Is preferred. In other words, an actual image is displayed on the liquid crystal panel 21, the relationship between the signal gradation and the display luminance is measured, and the LUT (output table) is determined so as to meet the equation (1) based on the actual measurement result. Is preferred.

[0173] Further, in the present embodiment, a shown in Formula (6a) is assumed to be in the range of 2.2 to 3.

This range is not strictly derived, but is a range that is considered to be almost appropriate for human visual sense.

[0174] In addition, when one source driver for normal hold display is used as the source driver 23 of this display device, y = 2.2 is set according to the input signal gradation (display signal luminance gradation). A voltage signal is output to each pixel (liquid crystal) so that the display brightness obtained using equation (1) can be obtained.

[0175] Such a source driver 23 outputs the voltage signal used in the normal hold display as it is in each subframe according to the input signal gradation even when performing the subframe display. It becomes.

[0176] However, with such a voltage signal output method, the sum of the luminance within one frame in the subframe display cannot be made the same as the value in the normal hold display (the signal gradation cannot be fully expressed). )Sometimes.

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 described above can be performed.

[0178] In the present embodiment, it is assumed that 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 this display device. [0179] In other words, the sub-frame display of this display device is a liquid crystal panel in which the planned brightness (scheduled brightness) and actual brightness (actual brightness) deviate when the viewing angle is increased. It is possible to suppress the white floating phenomenon for liquid crystal panels in changing modes.

[0180] 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). Further, in this display device, another display panel (for example, an organic EL panel or a plasma display panel) may be used instead of the liquid crystal panel 21.

[0181] 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 within the range of l: n or n: l (n is a natural number of 1 or more)!

[0182] 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 Oms and TO (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 subframe (sub-subframe) is TmaxZ (n + l) when the liquid crystal response is Oms and T0 = 0. The threshold luminance gradation Lt is a frame gradation of this luminance.

Lt = ((Tmax / (n + 1) — TO) Z (Tmax -ΤΟ)) "(ΐ / γ)

(γ = 2.2, Τ0 = 0)

If the response speed of the liquid crystal is not 0, for example, black → white is Υ% response in the subframe, white → black is Ζ% response in the subframe, and ΤΟ = ΤΟ, the threshold brightness (Lt brightness) Tt is Tt = ((Tmax-TO) XY / 100 + (Tmax -TO) XZ / 100) / 2

It becomes. Therefore,

Lt = ((Tt TO) / (Tmax -TO)) "(ΐ / γ)

(y = 2.2) It becomes.

[0184] 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 with Lmax. In such a case, to obtain Lt, it is preferable to use the result of measuring the luminance of the liquid crystal panel. In other words, when the sub-frame on one side has the maximum luminance and the luminance of the other sub-frame has the minimum luminance, the luminance emitted from the liquid crystal panel is measured and the luminance is defined as Tt. Then, the gradation Lt of spillage is determined by the following formula.

Lt = ((Tt TO) / (Tmax-TO)) "(ΐ / γ)

(y = 2.2)

Thus, Lt obtained using Equation (10) is an ideal value, and is preferably used as a guideline.

Here, in the present display device, the point that it is preferable to invert the polarity of the interelectrode voltage at the frame period will be described in more detail. FIG. 12 (a) is a graph showing the luminance displayed by the previous subframe and the rear subframe when the display luminance power Lmax is 3Z4 and 1Z4. As shown in this figure, when sub-frame display is performed as in the present display device, the voltage value applied to the liquid crystal (voltage value applied between pixel electrodes; absolute value) differs between sub-frames.

Therefore, when the polarity of the voltage applied to the liquid crystal (liquid crystal voltage) is reversed at the subframe period, the difference in voltage value between the previous subframe and the subsequent subframe as shown in FIG. 12 (b). As a result, the applied liquid crystal voltage is biased (the total applied voltage is (never)). For this reason, the DC component of the liquid crystal voltage cannot be canceled and the liquid crystal panel 21 is driven for a long time. There is a possibility that flickering force may occur if the image is accumulated.

[0187] Therefore, in this display device, it is preferable to invert the polarity of the liquid crystal voltage at the frame period. There are two ways to invert the polarity of the liquid crystal voltage with the frame period. One method is to apply a voltage of 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. is there.

[0188] Figure 13 (a) shows the voltage polarity (the polarity of the liquid crystal voltage) and the voltage when the former method is used. It is a graph which shows the relationship between a frame period and a liquid crystal voltage. On the other hand, Fig. 13 (b) is a similar graph when the latter method is used.

[0189] As shown in these graphs, when the liquid crystal voltage is inverted in one frame period, the total voltage of the previous subframe and the total voltage of the subsequent subframe are set to 0 V between two adjacent frames. And can. Therefore, the total voltage in two frames can be set to 0V, so that the DC component of the applied voltage can be canceled.

By making the liquid crystal voltage alternating in the frame period in this way, even if the liquid crystal voltage is greatly different between subframes, it is possible to prevent the flicking force if it is burned.

[0190] FIGS. 14A to 14D are explanatory diagrams showing the four pixels in the liquid crystal panel 21 and the polarities of the liquid crystal voltages of the respective pixels. 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. 14 (a) to (d) 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 set to OV. Such control can be realized, for example, by changing the voltage polarity between adjacent pixels as shown in FIGS. 14 (a) to (d).

[0192] Also, in this 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.

[0193] 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 to the normal hold display. In addition, as shown in Fig. 6, regarding the brightness, the actual brightness can be made closer to the planned brightness compared to the normal hold display. Accordingly, even in this case, it is clear that the viewing angle characteristics can be improved as compared with the normal hold display.

[0194] In addition, 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. [0195] Therefore, by setting the ratio of the previous subframe period to the subsequent subframe period to 1: 1 or 2: 1, it is possible to prevent one of the subframe periods from becoming too short. Therefore, an appropriate display can be performed even with a liquid crystal having a slow response speed.

[0196] For the frame division ratio (ratio between the previous subframe and the subsequent subframe), n: 1

(n is a natural value of 7 or more). The division ratio may be n: l (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, viewing angle characteristics can be improved as compared to 1: 1. In addition, it becomes easier to use a liquid crystal material with a slow response speed as compared with the case of 2: 1.

[0197] Even when the frame division ratio is n: 1 (n is a real number greater than or equal to 1), the maximum luminance (n

+1) When displaying low-brightness (low brightness) images up to 1 / (TmaxZ (n + l)) j, the front subframe should be displayed in black and only the back subframe should be used for display. Is preferred. Further, when displaying an image with a high luminance (high brightness) equal to or higher than “TmaxZ (n + 1)”, it is preferable to display the rear subframe with white and adjust only the luminance of the previous subframe. This ensures that one subframe is always 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.

[0198] Here, when the frame division ratio is n: 1, the same effect can be aimed at whether the previous frame is n or the subsequent frame n. That is, n: l and l: n are the same in terms of viewing angle improvement effect. In addition, even when n is a real number of 1 or more, it is effective for controlling the luminance gradation using the above equations (10) to (12).

[0199] 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 display device may be designed to perform subframe display in which a frame is divided into three or more subframes.

[0200] In the subframe display when the frame is divided into m, if the luminance is very low, m—one subframe is displayed in black, while the luminance of one subframe (luminance gradation) ) Only to display. Then, when the luminance becomes so high that it cannot be expressed only by this subframe, this subframe is displayed in white. M—Two subframes are displayed in black, while the luminance of the remaining one subframe is adjusted for display. I do.

[0201] That is, even when a frame is divided into m pieces, as in the case of dividing into two pieces, one subframe for adjusting (changing) the luminance is always set to one, and the other subframes are displayed in white. Is preferably displayed in black. As a result, m−l subframes can be in a state where there is no deviation between the actual luminance and the planned luminance. Therefore, the viewing angle characteristics of the display device can be improved.

[0202] Fig. 15 shows the result of dividing the frame 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). The same as in FIG. 2). As shown in this graph, when the number of subframes is increased to 3, the actual brightness can be made very close to the planned brightness. Therefore, it can be seen that the viewing angle characteristics of the present display device can be improved.

[0203] Also, 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 OV.

[0204] 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. Thus, when the frame is divided into an odd number, the total liquid crystal voltage in two frames can be set to OV even if the voltage polarity is inverted for each subframe. 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; l to! N) subframes between adjacent frames to have different polarities. It can be said that it is preferable to apply a voltage. As a result, the total liquid crystal voltage in two frames can be set to OV.

[0205] When the frame is divided into m (m; an integer greater than or equal to 2), the liquid crystal voltage is set so that the total liquid crystal voltage in 2 frames (or more frames) is OV. It is preferable to reverse the polarity.

[0206] Also, in the above, when dividing a frame into m frames, there is always one subframe for adjusting the luminance, and the other subframes are displayed as white (maximum luminance) or black (minimum luminance). U prefer to do as

[0207] Although not limited to this, it is possible to have two or more subframes for adjusting the brightness.

Even in this case, viewing angle characteristics can be improved by displaying at least one subframe in white (maximum luminance) or black (minimum luminance).

[0208] Also, the luminance is not adjusted! The luminance of the sub-frame may be set to "a value greater than the maximum or second predetermined value" instead of the maximum luminance. Further, instead of setting the minimum luminance, “a minimum 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 sub-frame where the brightness 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 scale corresponding to each signal gradation in the sub-frame where the luminance is not adjusted. It is a graph showing the relationship (viewing angle gradation characteristics (actual measurement)) with tone (%).

[0210] The actual luminance gradation is defined as “the luminance (actual luminance) output from the liquid crystal panel 21 of the display unit 14 in accordance with each signal gradation, using the above equation (1). Converted into a key. ”

[0211] As shown in this graph, the above two gradations are equal on the front surface of the liquid crystal panel 21 (viewing angle 0 °). On the other hand, when the viewing angle is set to 60 degrees, the brightness gradation is actually halftone and brighter than the signal gradation due to whitening. In addition, this whitening takes the maximum value when the luminance gradation is between 20% and 30% regardless of the viewing angle.

[0212] Here, with regard to such whitening, it exceeds "10% of the maximum value" indicated by the broken line in the above graph. In this case, the display quality of the display device can be sufficiently maintained ( The brightness deviation mentioned above can be made sufficiently small. In addition, the range of signal gradation that does not exceed 10% of the maximum value is 80 to 100% and 0 to 0.02% of the maximum value of the signal gradation. This range does not change even if the viewing angle changes.

[0213] Therefore, it is preferable to set 80% of the maximum luminance as the second predetermined value. Also, it is preferable to set the first predetermined value to 0.02% of the maximum luminance. I can say that.

[0214] Further, it is not necessary to provide a subframe in which the luminance is not adjusted. That is, when displaying with m subframes, there is no need to make a difference in the display state of each subframe. this Even with such a configuration, it is preferable to perform the polarity inversion driving that inverts the polarity of the liquid crystal voltage in 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.

[0215] In this 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.

[0216] That is, when the movement of an object displayed in the normal hold display is followed by the line of sight, 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 is possible to suppress the visual mixing of the image of the currently viewed frame and the image of the previous frame (color 'brightness). Therefore, the edge blur as described above can be avoided and the display quality of the moving image can be improved.

[0217] In addition, the present display device may be designed to perform dimming by a PWM dimming method.

A liquid crystal display element such as the liquid crystal panel 21 expresses gradation by controlling the amount of transmitted light. Therefore, some kind of light source (such as a fluorescent tube or LED) is required. In addition, at present, a large-sized liquid crystal display element generally uses a fluorescent tube as a light source for efficiency.

[0218] Also, as the light source dimming method, there are generally used two methods: a current dimming method (or voltage dimming method) and a PWM dimming method.

[0219] As shown in Fig. 19, the current dimming method is a method that controls the light intensity (brightness) by changing the amplitude of the current (lamp current) applied to the light source. is there. When using a fluorescent tube 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, for devices that require a wide dimming range, such as LCD TVs, it is preferable to use the PWM dimming method.

[0220] As shown in Fig. 20, the PWM dimming method turns on the light source (fluorescent tube) at a frequency of 90 Hz or higher where humans do not feel flickering force (ON) Z turns off (OFF), and outputs time average Light intensity It is a method to let the user perceive as. In general, lighting Z extinction is controlled 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 force) 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 turned 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 hundred Hz. Therefore, the lamp current waveform is more powerful than shown in the figure.

FIG. 22 is a block diagram showing the 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. In addition, the PWM dimming control circuit 31 generates a signal indicating a cycle related to the ONZOFF of the lamp current in accordance with 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.

[0224] 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 flickering force and horizontal stripes may occur.

[0225] Figure 23 shows the light source emission waveform, liquid crystal electrode voltage waveform (liquid crystal response waveform), and light transmission light waveform (transmission waveform) when PWM dimming is combined with normal hold display. ) Is a graph showing an example of the relationship.

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 figures, the frame frequency is 60 Hz, the dimming frequency (ONZOFF frequency of the light source) is 150 Hz, and the dimming ratio (ONZOFF period ratio of the light source) is 50%. Also, for simplicity, all waveforms Is shown by a rectangular wave.

As shown in FIG. 23, in the normal hold display, the frequency of the transmitted waveform is the same as the dimming frequency (150 Hz) even when PWM dimming is performed. Here, the flicker force starts to be perceived when the frequency of the transmitted waveform falls below the fleat force threshold (90 Hz), and is clearly recognized when it falls below 60 Hz. Therefore, in the normal hold display, the user does not feel flickering force.

On the other hand, as shown in FIG. 24, when PWM dimming is performed in the subframe display, the dimming frequency interferes with the subframe frequency, and the frequency of the transmitted waveform is greater than the dimming frequency. (The frequency is 30Hz in Fig. 24). For this reason, the user feels a strong flick force.

[0229] Note that such flickering force increases as the dimming frequency approaches n.5 times the frame frequency (n is an integer). When the dimming frequency is n times the frame frequency, the frequency of the transmitted waveform is equal to the frame frequency. Therefore, it is possible to reduce the flickering force to an inconspicuous level. However, when the dimming frequency is made close to n times the frame frequency, horizontal stripes appear on the screen! / ヽぅ Interference phenomenon occurs.

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

Here, the light source normally 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 and OFF at different times depending on 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 Α · Β at different positions.

[0232] For this reason, the ratio of the time when the transmission waveform is turned on (time when the luminance is high) differs depending on the line position. Therefore, there is a difference in average brightness between lines, which is recognized as a horizontal stripe phenomenon. [0233] When the dimming frequency is exactly n times the frame frequency, the horizontal stripes stop on the screen. As the n-power boost is lost, horizontal stripes begin to flow up and down the screen. Furthermore, the horizontal stripes disappear when the dimming frequency deviates significantly from n times and approaches n.

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

[0235] 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 (450Hz) is 7.5 times the frame frequency (60Hz). Also in this figure, as in Figure 25, show the liquid crystal response waveform and transmission waveform for two lines A and B at different positions! /

[0237] In this case, since the dimming frequency is n. 5 times the frame frequency, the above horizontal stripes are not generated. Regarding the flicker force, the frequency of the transmitted waveform is 30 Hz, which is half the frame frequency, in both lines A and Β, but the dimming frequency is sufficiently raised, so the flicker force is not noticeable. It is possible to do.

That is, the transmitted light quantity of lines Β and 示し shown in FIG. 26 is reversed for each frame (the light quantity of the first frame (second frame) of line Α is the second frame of line B (one frame). Same as eye)). If the lines having such a relationship can be densely arranged on the screen, the flicker force can be spatially compensated by allowing the user to visually recognize the light of these line forces at the same time.

[0239] Here, the two lines having the above relationship become closer to each other on the screen as the dimming frequency becomes higher. Therefore, by sufficiently increasing the dimming frequency, the flits force can be made inconspicuous even if the value is set to n.5 times the frame frequency. If the brightness of the previous sub-frame is barely black, and the brightness is 50% (when the black insertion rate is 50%), dimming Experimental results have shown that if the frequency is set to 450 Hz or higher, the flicker force will not be noticeable. In addition, the frits force is most noticeable when the black insertion rate is 50%.

[0241] In addition, it is possible to suppress the interference phenomenon without increasing the dimming frequency in this way. This can be achieved, for example, by setting the dimming frequency to n.5 times the frame frequency 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, liquid crystal response waveform, and transmission waveform of the light source (fluorescent tube 33) in this case. This figure also shows the liquid crystal response waveforms and transmission waveforms 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, since the dimming frequency is n.5 times the frame frequency, the horizontal stripes as described above do not occur.

[0243] Regarding the flits force, the frequency of the transmission waveform by the main light emission pulse is 30 Hz, which is half the frame frequency, in both lines Α and Β. However, in this configuration, a luminance compensation pulse with a relatively short pulse width is inserted at the same frequency (330 Hz) as the main light emission pulse with strong anti-phase!

[0244] In the transmission waveform of line A · 量, the transmission amount of the main light emission pulse and the luminance compensation pulse has a reverse ratio for each force frame that increases or decreases 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, pulses 8 to 10). On the other hand, for luminance compensation pulses, the reverse is 3 to 2.5.

[0245] Therefore, although the frequency (30Hz) of the transmitted 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). Therefore, it is possible to make the flits force inconspicuous.

[0246] Also, with this configuration, the PWM dimming frequency can be made lower than 450Hz, so a reduction in the driving efficiency of the light source can be avoided. In this configuration, 330Hz luminance compensation pulse is inserted. Therefore, there is a concern about inefficiency. 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.

[0247] In the above description, the dimming frequency is assumed to be n. 5 times the frame frequency. 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 horizontal stripes described above, 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 (time compensation can be performed), so that no horizontal stripes are generated.

However, if the light emission waveform of the light source is simply reversed in phase for each frame, the cycle of the transmission waveform of each line Α · Β becomes 30 Hz as shown in FIG.

[0249] 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 sets the dimming frequency (300 Hz; frame frequency (60 Hz) 5 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.

[0250] In addition, 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.

Furthermore, 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 (the boundary point of the frame in FIG. 29).

Here, the luminance compensation added pulse is a pulse that turns on the light source and 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 (noise).

[0253] Thus, with 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, reducing the flickering force It becomes possible.

[0254] Also, when combining PWM dimming and subframe display, the light emission waveform is controlled to include a direct current component (DC component), thereby suppressing interference phenomena such as flaw force and horizontal stripes. Is also possible.

FIG. 30 is a block diagram showing 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.

[0256] In this configuration, every other fluorescent tube 33 is divided into a first fluorescent tube 33a and a second fluorescent tube 33b (fluorescent tubes 33a '33b are alternately arranged). Here, the first fluorescent tube 33a is a fluorescent tube 33 connected to the first light source drive circuit. The second fluorescent tube 33b 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 ′ 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 period related to ONZOFF of the lamp current for the first fluorescent tube 33a, and the first light source driving circuit 34 And a signal indicating a period related to ONZOFF of the lamp current for the second fluorescent tube 33b 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) in accordance with the transmitted signal and output it to the fluorescent tubes 33a'33b.

As described above, in the configuration of FIG. 30, the two sets of fluorescent tubes 33a ′ 33b can emit light independently of each other. 31 (a) and 31 (b) show the emission waveform of the first fluorescent tube 33a (first waveform), the emission waveform of the second fluorescent tube 33b (second waveform), and the two fluorescent tubes 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 light tube 33a'33b. Fig. 31 (a) is for the case where the dimming rate (the ratio of the light emission amount to the maximum light emission amount in each fluorescent tube) is 75%, and Fig. 31 (b) is for the case where the dimming rate is 50%. is there.

[0259] In the examples shown in these figures, the control unit 15 controls the phases of the first waveform and the second waveform to change 180 ° from each other. Therefore, as shown in Fig. 31 (a), when the dimming rate is 75%, 75% of the emitted light is DC component. In addition, as shown in Fig. 31 (b), when the dimming rate is 50%, all of the light emission amount (100%) becomes the DC component (DC drive can be performed).

By performing such control, it is possible to reduce the amount of time fluctuation 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, it is possible to make the interference phenomenon such as flickering force and horizontal stripes inconspicuous without increasing the frequency of the dimming signal.

[0261] Here, as described above, the control for including the DC component in the light emission waveform of the light source is performed as described above. "Set the dimming frequency to n. 5 times the frame frequency and to a value of 450 Hz or more." Such control may be combined with control using a luminance compensation pulse.

[0262] In the control that includes the DC component in the light emission waveform of the light source, even if the dimming frequency is set to a value that is n. Experiments have confirmed that the interference phenomenon can be made sufficiently inconspicuous.

[0263] In the configuration shown in Fig. 30, the fluorescent tube 33 is divided into two types in order to create 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 showing a configuration of the present display device when such control is performed.

[0264] In this configuration, the fluorescent tube 33 is divided into three types (first fluorescent tube 33a, second fluorescent tube 33b, and third fluorescent tube 33c). The fluorescent tubes 33a, 33b, and 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 driving circuit 37 drives the third fluorescent tube 33c (lamp current is applied!).

[0265] In this configuration, the three sets of fluorescent tubes 33a to 33c can emit light independently of each other. FIGS. 33 (a) and (b) are graphs showing examples of fluorescent tubes 33a to 33c (first to third waveforms) and their mixed waveforms (mixed waveforms) in the configuration shown in FIG. is there.

Note that FIG. 33 (a) relates to the case where the dimming rate is 50%, and FIG. 31 (b) relates to the case where the dimming rate is 25%. In the examples shown in these figures, the phases of the first to third waveforms are controlled to be shifted from each other by 120 °. Therefore, as shown in Fig. 33 (a) and (b), the dimming rate Even when 50% is the same, the DC component can be increased as compared with the case where the fluorescent tubes 33 are not blinked at the same time.

By performing such control, the amount of time variation 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, it is possible to make the interference phenomenon such as flickering force and horizontal stripes inconspicuous without increasing the frequency of the dimming signal.

[0268] 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 as many light source driving circuits as the number of groups. As shown in Fig. 34, when the number of fluorescent tubes 33 is p (p is a natural number of 2 or more), the phases of the 1st to p-th waveforms are controlled to be shifted by 360 ° Zp from each other. 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, 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.

[0269] 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) that serves as a side-type knock light (a backlight at the side edge 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 a 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 the light emitted from the LED 42'43 is expanded by the light guide plate 41 and 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 causes 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 to mutually differ. Control to change 180 degrees. Thereby, in the light guide plate 41, the light emission waveforms having the opposite phases can be mixed to create a DC component. Therefore, even in this configuration, the DC component of the light irradiated on the liquid crystal panel 21 is reduced.

[0271] When two LEDs 42.43 are used as described above, two LEDs 42.43 may be disposed along the same side of the light guide plate 41 as shown in FIG. . In this configuration, similarly to the configuration in FIG. 35, the liquid crystal panel 21 can be irradiated with light containing a large amount of DC components. [0272] The two LEDs 42.43 can also be used as a side-type front light (a front light disposed on the side end 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.

[0273] 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 the 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 the internal reflector.

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 ° Zp. . 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, it is preferable to shift the phase of the emission waveform from each fluorescent tube 33 by 360 ° / τ.

[0275] 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.

[0276] Fig. 39 is a block diagram showing 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 drive circuits 32a to 32r!

[0277] Further, in the above configuration, each fluorescent tube 33 irradiates 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.

[0278] 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 (the scanning of this gate line group is started). ) To start driving the fluorescent tube 33 (more specifically, since the gate line groups are not all turned on at the same time, the drive start timing of the fluorescent tube 33 is Set to the average ON timing of the line group).

FIG. 40 is a graph showing an example of the relationship between the light emission waveform of the light source, the liquid crystal response waveform, and the transmission waveform 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). This figure also shows the light source emission waveform, liquid crystal response waveform, and transmission waveform for two different gate line groups Α · Β. 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.

[0280] 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. Therefore, in both the line groups となり and Β, the frequency of the transmission waveform is 60 Hz, which is the same as the frame frequency, and the generation of flickering force can be avoided.

[0281] 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 Α and ((the light source emission waveform for the line group Α and the line The time lag from the light source emission waveform for Β coincides with the lag in the liquid crystal response waveform between the line groups Α and Β).

[0282] Therefore, with 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, there is no difference in average brightness between lines.

V, so 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 this gate line group is started), the driving of the fluorescent tube 33 is started. To control.

[0284] However, “The state of the waveform of the fluorescent tube 33 when the gate line group corresponding to each fluorescent tube 33 is turned ON” is expressed by the total fluorescent tube 33 (all gate line group). By controlling so that they are the same ”, 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 the horizontal stripes by synchronizing the light emission of the fluorescent tube 33 and the ON timing of the gate line group.

[0285] In the present 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.

[0286] In the above configuration, the dimming rate signal indicating the amount of light that should be output from the fluorescent tube 33 by the control unit 15 Is output to the PWM dimming control circuit 31 and the current dimming control circuit 51. Also, the dimming control circuits 31 and 51 generate signals (current dimming control signal, PWM dimming control signal) indicating the period related to ONZOFF of the lamp current according to the dimming rate signal, and drive the light source Communicate to circuit 32. The light source drive 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 examples of the current dimming control signal, the PWM dimming control signal, the lamp current, and the 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 that gives constant light emission power) and PWM dimming control. The signal is output together with the signal.

As a result, the lamp current waveform of the fluorescent tube 33 becomes 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 light 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.

[0289] 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. This makes it possible to reduce the amount of time fluctuation in the light emission amount of the light source within one cycle (within 2 frames). Further, the difference in light emission amount between the lines can be reduced. Therefore, it is possible to make the interference phenomenon such as flickering force and horizontal stripes inconspicuous without increasing the frequency of the dimming signal.

[0290] Further, when a reflective liquid crystal display element is used as the liquid crystal panel 21 and the display device is configured as a front light type reflective liquid crystal display device, the light from the light source can be controlled in accordance with the external light. preferable.

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 the light source into a planar light, and receives this from the front surface (user side surface). Then, the planar light is reflected by an internal reflecting plate to display an image to the user.

[0292] Also, this configuration includes a light source dimming control circuit 62 for controlling the luminance of the LED 63. This 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 irradiated on 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 performs the luminance waveform (light emission waveform) of the LED 63 as shown in FIG. 44 (b). ) Is controlled to have the same frequency as the external light luminance waveform and in the opposite phase. Therefore, the liquid crystal panel 21 can be irradiated with light having a large DC component as shown in FIG. 44 (c).

[0294] Thus, in this configuration, the amount of time variation 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, it is possible to make interference phenomena such as flickering force and horizontal stripes inconspicuous without increasing the frequency of the dimming signal.

[0295] 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 is possible. The The transflective display device performs transmissive display using knocklight light under a relatively dark illumination such as indoors (transmission mode), whereas it emits the illumination light under a relatively bright illumination such as outdoors. It is used to perform reflection display (reflection mode). Thereby, a display with a high contrast ratio can be realized regardless of the brightness of the surroundings.

[0296] 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, as shown in FIG. 44 (c), in which light of the same frequency and opposite phase is mixed.

[0297] In the present embodiment, it is assumed that a fluorescent tube or an 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 with either EL (Electro luminescence) or FED (Field Emission Display). The light source may also be configured with a combination of fluorescent tubes, LEDs, EL and FED. Further, in FIGS. 34 to 38, etc., 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.

[0298] When subframe display and PWM dimming are combined, the display unit 14 of the present display device is not limited to a liquid crystal display element, but is a non-self-luminous display element (an element that requires a light source). Any display element can be used. [0299] Also, in the present embodiment, the control unit 15 sends 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. A display unit with a display screen that displays the power of the device and a display signal for the 1st to mth sub-frames so that the total luminance output from the display unit per frame is not changed by dividing the frame. And a PWM dimming control unit that dimmes the light source of the display unit using the PWM dimming method. It can be expressed as a structure that speaks.

[0300] When the display device is a liquid crystal television, the tuner unit 17 selects a channel of a television broadcast signal and transmits the television image signal of the selected channel to the control unit 15 via the frame memory 11. You may use what you do. 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. It's okay.

[0301] In addition, in the display device that displays an image by dividing one frame into two subframes having the first and second subframe forces, the display device of the present invention has a luminance scale of an input display signal. A display unit that displays an image with luminance based on the key, and a display signal that is a display signal 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. And a control unit that generates and outputs the first and second display signals to the display unit. When the control unit displays a low brightness image, the control unit adjusts the luminance gradation of the first display signal. When the brightness gradation of the second display signal is set to a minimum or smaller value than the first predetermined value (e.g., 0.02% of the maximum gradation) and a high brightness image is displayed, the brightness of the first display signal is The gradation is greater than the maximum or second predetermined value (for example, 80% of the maximum gradation) On the other hand, the luminance gradation of the second display signal is adjusted, and the ratio between the period of the first subframe and the period of the second subframe is 1 _{: n} or _n: 1 (n is a real number greater than 1) And set to It can also be expressed that the light source of the display unit is dimmed by the PWM dimming method.

[0302] The display device shown in FIG. 39 is a display device that displays an image by dividing one frame into m (m; an integer greater than or equal to 2) subframes. A display unit with a display screen that has the power of a liquid crystal display element that displays images based on the brightness of the display, and the first to the second so that the total luminance 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 of the m-th subframe and outputs them to the display unit. This control unit dims the light source of the display unit by the PWM dimming method. The above display unit has a light source group in which a plurality of direct light sources are arranged, and each light source irradiates light to a gate line group having a plurality of gate line forces close to itself. The above control unit is designed so that the frequency of the light emission waveform of the light source And the state of the emission waveform of the light source when the response waveform force SON of the liquid crystal corresponding to the gate line group assigned to each light source is SON. It can also be expressed as a configuration that performs PWM dimming so that the light source is the same.

[0303] In the above description, all the processes in the display device are performed under the control of the control unit 15. However, the present invention is not limited thereto, and a program for performing these processes may be recorded on a recording medium, and an information processing apparatus that can read the program may be used instead of the control unit 15. .

[0304] 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 processing.

[0305] Here, as the above information processing apparatus, a function expansion board or a function expansion boot mounted on a computer can be used in addition to a general computer (workstation or personal computer).

[0306] Also, the above-mentioned program is a program code (execution format program, intermediate code program, source program, etc.) of software that realizes processing. This program may be used alone or in combination with other programs (such as OS). Also, this program is stored in memory (RAM etc.) in the device after it has been read, and then read and executed again. But you can.

[0307] Further, the recording medium on which the program is recorded may be one that can be easily separated from the information processing apparatus, or one that is fixed (attached) to the apparatus. It can also be connected to the device as an external storage device.

[0308] 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 such as CD, MO, MD, and DV D (magneto-optical disks). ), Memory cards such as IC cards and optical cards, semiconductor memories such as mask ROM, EPROM, EEPROM, and flash ROM.

[0309] Further, a recording medium connected to the information processing apparatus via a network (intranet 'Internet or the like) may be used. In this case, the information processing apparatus acquires the program by downloading via the network. That is, the above program

You may make it acquire via transmission media (medium which holds a program fluidly), such as (a thing connected to a wired line or a wireless line). It is preferable that the program for downloading is stored in advance in the device (or in the transmitting device 'receiving device)! /.

[0310] The liquid crystal response waveform is output at the ON timing of the gate line. It can be said that the voltage written in 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 drive 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 is stated in. In the technique of this document, one frame period is divided into a black display period and an image display period, and the method of driving the liquid crystal under a certain ratio condition with respect to one black display period or a certain PWM dimming frequency. Improvements can be made by driving the knocklight under certain conditions, or by shifting the phase of the PWM dimming signal of multiple knocklights.

[0311] On the other hand, as a technique for realizing the pseudo impulse mode by the liquid crystal drive method, as shown in Patent Document 3, one frame is divided into a plurality of subframe periods, and each has high and low luminance subframes. There is a method (time-division gradation drive method) that expresses gradation by time integration of subframes. In this method, compared to the method of always inserting black, the screen Although it has the advantage of improving video performance such as edge blurring while suppressing the drop in display brightness, it causes interference when combined with a PWM dimming light source in the same way as black insertion. To do.

[0312] 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. In the case of the time-division gradation driving method, there is a restriction that the luminance and gradation change when the time of each subframe is changed. In addition, the light source light is modulated with the response waveform of the liquid crystal and transmitted even in the low-luminance subframe period, and the control timing is improved by synchronizing the light-off period of the light source during the insertion period. This method cannot be used.

[0313] For these reasons, the object of the present invention is to provide a display mechanism that mainly divides one frame period into two or more subframe periods and expresses gradation by time integration of each subframe. It is also possible to improve the interference phenomenon such as flick force that occurs when combining the pseudo impulse drive method with time division gradation and the light source of PWM dimming method without impairing gradation expression and screen display. .

[0314] 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 a driving method including a display mechanism that expresses gradation by time integration of each subframe, and PWM dimming This configuration includes means for controlling the PWM dimming signal so as to improve the interference phenomenon that occurs when combined with a light source of the type.

[0315] In addition, the second display device is configured to control the PWM dimming signal so that the light emission waveform of the light source is temporally and spatially compensated in order to improve the interference phenomenon in the first display device. It is.

[0316] In addition, the third display device is configured to control the PWM dimming signal so as to include as much DC components as possible in the light emission waveform of the light source in order to improve the interference phenomenon in the first display device. is there.

[0317] Also, 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. Furthermore, in order to improve the interference phenomenon, the PWM dimming signal is controlled so that as much DC component as possible is included in the light emission waveform of the light source.

[0318] The fifth display device is configured to drive the PWM dimming control signal at n. 5 times the frame frequency in the second display device.

[0319] 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%.

[0320] 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.

[0321] 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.

[0322] 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.

[0323] 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 each of the PWM dimming phases to be 180 ° different from each other. The

[0324] Also, the eleventh display device includes the first light source, the second light source, and the third light source in the third display device, and controls each of the PWM dimming phases to be different by 120 °. It is the composition which is equipped with.

[0325] The twelfth display device includes the first to nth light sources in the third display device.

This is a configuration comprising means for controlling the WM dimming phase to be different by (360 ° Zn).

[0326] Further, the thirteenth display device has a configuration in which the light source is a direct type knock light in the tenth to twelfth display devices and is spatially arranged alternately.

[0327] Further, the fourteenth display device in the tenth to twelfth display devices has a configuration in which the light source is a side-type knock light, and light sources having opposite phases are arranged at both ends, respectively.

[0328] Further, the fifteenth display device is a configuration in which in the tenth to twelfth display devices, the light source is a side-type knock light, and a light source having an opposite phase is arranged at one end.

[0329] In addition, the sixteenth display device in the tenth to twelfth display devices has a configuration in which the light source is a front light and light sources having opposite phases are arranged at both ends. [0330] In addition, the seventeenth display device is a configuration in which the light source is a front light, and a light source having an opposite phase is arranged at one end along the other end in the tenth to twelfth display devices.

[0331] Further, the eighteenth display device is configured by combining any one of the fifth to eighth display devices with! Or the deviation 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.

[0333] Further, 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. .

[0334] In addition, the 21st 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.

[0335] The twenty-second display device is configured to control 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. In the twenty-first display device, the PWM light control of the backlight light source is controlled so that the transflective liquid crystal has an opposite phase to the external light.

[0336] Further, 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 or a combination of a fluorescent lamp, LED, EL, and FED.

Industrial applicability

[0337] The present invention can be suitably used for an apparatus having a display screen in which whitening occurs.

Claims

The scope of the claims

[1] A display device that displays an image by dividing one frame into m (m; an integer of 2 or more) subframes,

Based on the voltage of the display signal! A display unit having a display screen made up of a liquid crystal display element for displaying an image with high brightness; and

Generates 1st to mth display signals, which are display signals of the 1st to mth sub-frames, and outputs them to the display unit so that the total luminance output from the display unit in 1 frame is not changed by dividing the frame. And a control unit to

A display device in which the control unit dimmes the light source of the display unit by a PWM dimming method.

[2] The above control unit performs PWM dimming so that the frequency of the light emission waveform of the light source is n.5 times the frequency of the frame (n is an integer) and is a value of 450 Hz or more. The display device according to claim 1, wherein the display device is characterized.

[3] The above control unit combines the light emission waveform of the light source with the main light emission pulse and the luminance compensation pulse, both of which have a frequency n. 5 times the frequency of the frame and have opposite pulse phases and different pulse widths. 2. The display device according to claim 1, wherein PWM dimming is performed so as to obtain a waveform.

[4] The above control unit

The light emission waveform of the light source has a frequency that is n times the frame frequency, and a main light emission pulse that inverts the phase for each frame, and a luminance compensation pulse that has the same frequency as that of the main light emission pulse and an inverted phase luminance compensation pulse. As a combined waveform,

For the emission waveform of the light source,

When the main light emission noise is continuously turned OFF, instead of the luminance compensation pulse, a luminance compensation additional pulse for turning on the light source is inserted,

The PWM dimming is performed in such a manner that when the main light emission noise is continuously turned on, a luminance compensation reduced pulse for turning off the light source is inserted instead of the luminance compensation pulse. The display device described.

[5] The display unit has a plurality of light sources, 5. The display device according to claim 1, wherein PWM dimming is performed so that the light emission waveforms of at least two light sources have different phases from each other.

[6] The above control unit is designed to divide each light source into p groups (p is a natural number of 2 or more) and to shift the phase of the light emission waveform by 360 ° Zp for each group. The display device according to claim 5, wherein:

7. The display device according to claim 5, wherein the light source is a direct type backlight.

[8] The display device according to [5], wherein the light source is a side-type backlight.

[9] The display device according to [5], wherein the light source is a side-type front light.

[10] The display unit described above has a light source group in which a plurality of direct light sources are arranged, and is designed to irradiate light to a gate line group having a plurality of gate line forces close to each light source force itself. And

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 such that when the gate line group assigned to each light source is turned ON, the state of the light emission waveform of the light source is the same for all the light sources. The display device described.

[11] The control unit

2. 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.

[12] The display unit is a reflective display element having a front light type light source,

A luminance sensor for detecting a luminance waveform of external light irradiated on the display 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 external light and has an opposite phase.

[13] The display unit is a transflective display element, A luminance sensor for detecting a luminance waveform of external light irradiated on the display unit;

[14] The display device according to any one of claims 1 to 13, wherein the light source includes any one of a fluorescent tube, LED, EL, and FED.

[15] The display device according to claim 1,

A signal input unit for transmitting an image signal input from an external cover to the control unit, and the control unit of the display device is designed to generate a display signal based on the image signal. LCD monitor characterized by that.

[16] The display device according to claim 1,

A tuner unit for receiving TV broadcast signals,

A liquid crystal television receiver, wherein a control unit of a display device is designed to generate a display signal based on the television broadcast signal.

[17] A display method for displaying an image by dividing one frame into m (m; an integer of 2 or more) subframes,

The 1st to mth display signals, which are the display signals of the 1st to mth sub-frames, are generated 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.