JP3618941B2 - Driving method of display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of driving a display device of a type that has a display panel and illumination means that can emit light of different colors, and performs color display by sequentially displaying each single color frame in time series.
[0002]
[Prior art]
Conventionally, a color filterless liquid crystal display panel using liquid crystal as an optical modulation material is driven for each color signal of red (R), green (G), and blue (B) sequentially in a frame, and this liquid crystal display is synchronized with it. A display device that displays a color image by illuminating a panel with each monochromatic light of RGB is widely known (for example, JP-A-62-250425).
[0003]
[Problems to be solved by the invention]
However, in general, the liquid crystal display panel scans sequentially from top to bottom for each horizontal line. Therefore, when each RGB illumination light is simply switched for each frame as in the conventional display device described above, writing of all frames is performed. Each RGB illumination light is lit only during the time between the end of the process and the start of the writing of the next frame, resulting in an effective display time.
[0004]
For this reason, particularly when displaying moving images, for example, when displaying with a general video signal, the effective display time is equivalent to the vertical blanking period of the video signal, so that a color filter is unnecessary. Nevertheless, there is a problem that it is difficult to obtain sufficient brightness of the display.
[0005]
Accordingly, an object of the present invention is to provide a driving method of a display device that performs color display by performing each RGB single color display in a frame sequence in a time series capable of high efficiency and bright display.
[0006]
[Means for Solving the Problems]
The present invention has been made in view of the above circumstances, provided an optical modulation material sandwiched between a pair of substrates and a display panel of the scan-driven with each pixel, on the back side of the display panel, Illuminating means composed of a plurality of planar light sources having a predetermined width extending in the scanning line direction capable of emitting red, green and blue in a single color, and driving the display panel sequentially in accordance with color signals, In a driving method of a display device in which the display panel is illuminated with monochromatic lights of red, green, and blue that are sequentially emitted by the planar light sources , and each red, green, and blue monochromatic display is performed sequentially in frames . the when each horizontal pixel lines of the display panel are scanned selected, the emitting light of colors that the planar light sources corresponding to said selected horizontal pixel lines corresponding to the color signal, before Synchronously with the scanning selection of each horizontal pixel line of the display panel, a black display area having a predetermined width that is scanned with the scanning selection of the frame image is provided between the color frame images of the display panel, and the width of the black display area Larger than the width of the planar light source, and at the time of black display , a voltage having a polarity opposite to that of the applied voltage applied to the optical modulation material in each pixel in the monochrome frame image display before black display is displayed on the black display. the applied predetermined retention time to the optical modulation substance for each pixel to be substantially equal to the absolute value of the product of the applied voltage and the holding time in the previous monochrome frame image being displayed, it is characterized in that.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments according to the present invention will be described below with reference to the drawings.
[0008]
FIG. 1 is a schematic view showing a display device according to an embodiment of the present invention, and FIG. 2 is a sectional view thereof. The display device 1 includes a color filter-less liquid crystal display panel 2 having no color filter, and a plurality of (four in the present embodiment) RGB single-color strip surface light sources (n = 1 to 4) on the back side thereof. And a backlight device 4 composed of 3).
[0009]
The liquid crystal display panel 2 includes a monostable mode ferroelectric liquid crystal 6 sandwiched between a pair of substrates (counter electrode glass substrate) 5a and a substrate (TFT (Thin Film Transistor) glass substrate) 5b. On the substrate 5b, information line electrodes 7a and gate line electrodes 7b are formed in an active matrix structure, and a large number of pixels 9 are formed by TFTs 8 and auxiliary capacitors (not shown) provided at the intersections thereof. (See FIG. 4). The ferroelectric liquid crystal 6 in each pixel is driven in an active matrix by these configurations.
[0010]
As shown in FIG. 3, the backlight device 4 includes four RGB single-color strip surface light sources 3 arranged in parallel so as to extend in the scan line (scan line) direction (the S1 direction in FIGS. 1 and 2). Each RGB single-color strip-shaped surface light source 3 includes RGB single-color fluorescent lamps (cold cathode tubes) 10a, 10b, which emit light in respective single colors of R (red), G (green), and B (blue). 10c. Each RGB single-color strip surface light source 3 is divided into four planar light sources by each concave diffuse reflection plate 11, and a diffusion plate 12 is attached to the light emission side of each RGB single-color strip surface light source 3. ing.
[0011]
Each RGB single color fluorescent lamp 10a, 10b, 10c of each RGB single color strip surface light source 3 is connected to a scan lighting circuit 15 comprising an inverter 13 and a high voltage switch 14, respectively, and a timing control signal T ₁ inputted thereto. , T ₂ , T ₃ , and T ₄ , each RGB single color fluorescent lamp 10 a, 10 b, 10 c of each RGB single color strip surface light source 3 is arbitrarily controlled to be turned on, off, and scanned.
[0012]
As shown in FIG. 4, the drive system of the liquid crystal display panel 2 and the backlight device 4 includes an information line driver 16, a gate line driver 17, a liquid crystal drive signal generation circuit 18, and a scan lighting of the backlight device 4. The circuit 15 and a timing controller (ASIC) 19 are configured. In response to a control signal from the timing controller 19, each horizontal line pixel of the liquid crystal display panel 2 is sequentially passed through a gate line electrode 7b and each TET 8 by a gate line driver 17. Scanning is performed (in this case, each image signal is simultaneously supplied from the information line driver 16 to each information line electrode 7a so that an image signal is appropriately supplied to each horizontal line pixel), and the backlight is synchronized with this. Each RGB single-color strip surface light source 3 of the device 4 is scanned and turned on. 15 by scanning light up (details will be described later).
[0013]
In addition, a digital RGB image signal (RGB serial), a temperature control signal, and the like are input to a liquid crystal drive signal generation circuit 18 from a general control circuit centering on an MCU (control microcomputer) (not shown), and a clock, A control signal or the like is input. This digital RGB image signal is from an interface circuit (not shown) such as a personal computer and a video device, and is an image signal after serial conversion in which reading from the image frame memory is performed in RGB serial for each frame. .
[0014]
Next, a method for driving the display device 1 will be described.
[0015]
The liquid crystal display panel 2 and the backlight device 4 are controlled by an information line driver 16, a gate line driver 17, a liquid crystal drive signal generation circuit 18, each TFT 8, a scan lighting circuit 15 of the backlight device 4, and a timing controller 19. By the signal, each pixel 9 is sequentially double-scan driven from the top to the bottom (arrow S1 direction) in FIG. 1 and from the left to the right (arrow S1 direction) in FIG.
[0016]
That is, first, a black reset scan (which is black writing unique to the ferroelectric liquid crystal 6 and will be described in detail later) is sequentially performed for each horizontal pixel line (one pixel line arranged in the horizontal direction), and then sequentially. Scan image signal writing. At the time of this writing scan, the color image signal is written for each primary color image signal of RGB in a frame sequence in time series.
[0017]
In synchronism with this scan drive, the RGB single-color fluorescent lamps 10a, 10b, 10c of the RGB single-color strip surface light sources 3 are sequentially turned in the direction of arrow S2 (the same direction as the direction of arrow S1), and the monochromatic light corresponding to the primary color signal. Lights on. FIG. 2 shows that the R image of the previous frame is rewritten to the G image, and the lighting of the backlight device 4 is also switched from the R light to the G light.
[0018]
FIG. 5 shows the driving signals of the liquid crystal display panel 2 at this time and the lighting of the RGB single-color fluorescent lamps 10a, 10b, 10c of the RGB single-color strip surface light sources (BL) 3 constituting the backlight device 4 (on). / Off timing chart, n = 1 to 4 RGB single color strip surface light sources (n = 1 corresponds to the first scan position, n = 4 corresponds to the last scan position) ) 3 indicates that the lighting color is switched in the order of the RGB frames when the scanning is sequentially performed. In this embodiment, the frame period is set to 180 Hz (ie 1/180 sec).
[0019]
In the present embodiment, since the ferroelectric liquid crystal 6 is used as the liquid crystal, as described above, the ferroelectric liquid crystal 6 is reset by the black reset signal before applying the write signal (ferroelectric liquid crystal). It is necessary to return to the home position of the molecule and become black).
[0020]
In the present embodiment, the monostable mode ferroelectric liquid crystal 6 is used, and FIG. 6 is a conceptual diagram of the monostable mode of the ferroelectric liquid crystal 6. In this figure, the vertical axis P represents a crossed Nicol polarizer, the horizontal axis A represents the polarization direction of the analyzer, and 20 in the figure schematically represents ferroelectric liquid crystal molecules, and P (crossed Nicol). The direction of the molecules along the polarizer) is the direction of the monostable state (home position), resulting in a black display state. When a write voltage Vw is applied to the ferroelectric liquid crystal 6, the ferroelectric liquid crystal molecules are inclined by the angle θa. Since the inclination angle θa is determined by the balance between the spray elasticity of the ferroelectric liquid crystal molecules and the driving force by the writing voltage Vw, the inclination angle θa is substantially proportional to the writing voltage Vw until the saturation value (θa ≦ 45 °). Accordingly, the transmitted light intensity has a substantially proportional relationship with the writing voltage Vw, and it is possible to display a light gray scale according to the value of the writing voltage Vw.
[0021]
On the other hand, it is preferable to return to the home position after writing in order to eliminate the influence on the next writing. For this purpose, it is preferable to apply a predetermined black reset voltage Vr (polarity opposite to the writing voltage Vw) (monostable). Therefore, it can be restored only by turning off the write voltage Vw, but to reverse it, it is necessary to apply some reverse voltage).
[0022]
Then, the relationship between the liquid crystal voltage waveform in the active drive pixel in such a monostable mode and the optical response thereto is as shown in FIG. In this figure, Vr is a black reset voltage, Vw is a writing voltage, and time axis t is a counter electrode (solid electrode on the counter electrode glass substrate 5a) voltage in terms of voltage, and the liquid crystal applied voltage is zero (0). It corresponds to.
[0023]
Note that Tg represents a gate line selection period. During this Tg period, the signal voltages of the black reset voltage Vr and the write voltage Vw are applied to the ferroelectric liquid crystal 6 of each pixel 9. After these signals are applied, the TFT 8 is in an open state, so that the voltage is substantially maintained until the next black reset voltage Vr or the write voltage Vw is applied (strictly speaking, the fluctuations caused by the proximity signal line and Although there is some influence of the spontaneous polarization of the ferroelectric liquid crystal 6, it can be reduced by designing the auxiliary capacitance (not shown) and the drivability of the TFT 8 to be large).
[0024]
Further, in this monostable mode, the optical response level (corresponding to the transmittance) changes according to the magnitude of the write voltage Vw and gradation display is possible. However, for black reset, the value of the black reset voltage Vr (negative electrode) If the property is equal to or higher than the threshold voltage (usually about 1 V; absolute value), all black display is obtained.
[0025]
Further, 1F in the figure represents a frame period. In this embodiment, a 2 / 3F period is a display period of a write image signal (write display period) , and the remaining 1 / 3F period is a black display period by black reset ( Black reset period) . Further, the value of the black reset voltage Vr is set so as to be a reverse polarity voltage twice as large as the write voltage Vw. As a result, the effective V · t product (effective applied voltage × holding time) applied to the ferroelectric liquid crystal 6 of each pixel 9 is canceled during the writing display period and the black reset period, and the ferroelectric liquid crystal 6 is adversely affected (burn-in). Etc.) is eliminated.
[0026]
As described above, in this embodiment, since the method of sequentially scanning the writing and the black reset is employed, the writing display period as the effective display period is 2/3 of the frame period, and the remaining 1/3 frame period. Is the black display period. Therefore, as an instantaneous image display, for example, there is a black display region 30 (horizontal band shape) having a width corresponding to 1/3 of the screen vertical width as shown in FIG. Actually, the black display area 30 moves from the top to the bottom of the screen together with the scan drive from the top to the bottom (arrow S1 direction) of the write voltage Vw and the black reset voltage Vr. A pixel line one level above the upper end of the black display region 30 (corresponding to the black reset pixel line 22 in FIG. 2) is a position where the write voltage Vw is applied (image signal writing), and the lower end pixel line of the black display region 30 ( In FIG. 2, the writing pixel line 21) corresponds to the black reset voltage Vr application (black reset) position.
[0027]
As described above, since writing is performed for each RGB primary color image signal in frame order, each single-color frame image is sequentially switched above and below the black display area 30 that moves up and down, and in FIG. This represents the moment when the R image is rewritten to the G image. Further, as described above, since this frame period is set to 180 Hz, even if such a black display area 30 scans and moves within the screen, it exceeds the flicker limit, and there is no problem such as flickering. It does not occur at all.
[0028]
Thus, in the present embodiment, there are black display areas 30 that are 1/3 vertical and horizontal of the screen of the liquid crystal display panel 2, and the width is the width of each RGB single-color strip surface light source 3 of the backlight device 4. In the embodiment, since n = 4 is used for the entire screen, it is wider than approximately 1/4 of the horizontal and vertical directions). Therefore, in the present embodiment, switching of the color light of each RGB single-color strip surface light source 3 is performed by covering the RGB single-color strip surface light source 3 located below the black display region 30 in FIG. At this time, the lighting color of the RGB single-color strip surface light source 3 is switched (in this case, the R light is turned off and the G light is turned on simultaneously).
[0029]
Therefore, since the lighting color of the backlight device 4 is switched between the RGB single-color frame images, a good color image without color mixture between the single-color frame images is obtained, and each of the RGB single-color strip surface light sources 3 is obtained. As a driving method of the RGB single-color fluorescent lamps 10a, 10b, and 10c, it is only necessary to switch each high-voltage switch 14 while each inverter 13 is operating. Therefore, the lighting color is switched at high speed with little load fluctuation of the inverter 13. It becomes possible.
[0030]
FIG. 9 is a timing chart for driving and responding to the ferroelectric liquid crystal 6 of the liquid crystal display panel 2 in the present embodiment, and for turning on / off the backlight device 4 corresponding thereto.
[0031]
In this figure, it is a timing chart paying attention to one horizontal pixel line, and it is set so that the timings of the write voltage Vw and the black reset voltage Vr never overlap even between different horizontal pixel lines. In addition, since both the write voltage Vw and the black reset voltage Vr are supplied to each pixel 9 through the same information line electrode 7a, it is essential to send these signals at different gate line selection timings. For this, in the gate line driver 17, the duty ratio with respect to the transfer clock cycle of the gate line selection scan pulse is set to 50% or less, the gate line selection scan pulse transfer for the write voltage Vw and the gate line selection scan pulse transfer for the black reset voltage Vr. This can be done easily by shifting the phase by 180 °.
[0032]
Each liquid crystal drive signal of the write voltage Vw and the black reset voltage Vr is generated by the liquid crystal drive signal generation circuit 18, and based on the digital RGB image signal, temperature compensation by the temperature control signal from the MCU (not shown) or liquid crystal The signal (voltage) incorporates correction of specific gradation characteristics.
[0033]
As described above, according to the present embodiment, the display device 1 of a type that performs color display by sequentially displaying each RGB single color display in a time-series manner, at least 2/3 periods per frame period than the conventional one. A long effective display period is obtained, and brighter display is possible.
[0034]
Further, in the present embodiment, the writing state (Vw voltage) in the previous frame is the following by a driving method that performs black reset that cancels the DC voltage component applied to the ferroelectric liquid crystal 6 after writing. It is possible to obtain a very good image (especially a moving image) having no influence on writing in a frame and having no afterimage or tailing.
[0035]
In this embodiment, an active matrix structure using TFTs and an active drive type TFT are used as the liquid crystal display panel. However, for example, a liquid crystal display panel with a simple matrix structure and passive drive also has a frame period of at least 100 to 200 Hz. Can be driven (actual liquid crystal drive speed is required to be several times the scanning frequency of this frame frequency), especially by using high-speed type or high-speed mode ferroelectric liquid crystal, etc. Can do.
[0036]
In addition, as the backlight device of the present embodiment, basically a large number of RGB single-color fluorescent lamps are arranged side by side. It is preferable to use a type with less afterglow of ˜1 ms.
[0037]
Further, in the present embodiment, the number of planar light sources (RGB single-color strip surface light sources) constituting the backlight device is set to four, but the present invention is not limited to this. Any number can be set, and the width of the black display area can be varied accordingly. Therefore, by increasing the number of surface light sources (RGB single-color strip surface light sources) (the number of scan lighting divisions), the width of the surface light source becomes narrower, and the width of the black display area can be set narrower accordingly. Therefore, the effective display period is increased and a brighter display screen can be obtained.
[0038]
【The invention's effect】
As described above, according to the driving method of the display device according to the present invention, a sufficiently long display period excluding the black display region is possible, and a bright display with high efficiency can be performed.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a display device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a display device according to an embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view showing a backlight device of a display device according to an embodiment of the present invention.
FIG. 4 is a block diagram showing a drive system of the display device according to the embodiment of the present invention.
FIG. 5 is a timing chart of a driving signal of the liquid crystal display panel and lighting (on) / lighting (off) of the backlight device.
FIG. 6 is a conceptual diagram of a monostable mode of a ferroelectric liquid crystal.
FIG. 7 is a diagram showing a liquid crystal response and its optical response waveform.
FIG. 8 is a diagram showing a display state at a certain moment on the display screen.
FIG. 9 is a timing chart of liquid crystal response and turning on / off of the backlight device.
[Explanation of symbols]
1 Display device 2 Liquid crystal display panel (display panel)
3 RGB single color strip surface light source (surface light source)
4 Backlight device (lighting means)
5a Counter electrode glass substrate (substrate)
5b TFT glass substrate (substrate)
6 Ferroelectric liquid crystal (liquid crystal)
9 pixels 10a, 10b, 10c RGB single color fluorescent lamp (linear light source)
11 Diffuse reflector (reflector)
12 Diffuser 15 Scan lighting circuit 17 Gate line driver 18 Liquid crystal drive signal generation circuit 19 Timing controller 30 Black display area

Claims (6)

An optical modulation material sandwiched between a pair of substrates and a display panel of the scan-driven with each pixel provided on the back side of the display panel, red, green and blue extending monochromatic emission possible scanning direction Lighting means comprising a plurality of planar light sources having a predetermined width, and the display panel is driven in a frame sequence according to a color signal, and red, green and blue light emitted sequentially by the respective planar light sources. In a driving method of a display device that illuminates the display panel with each monochromatic light and displays each color image by sequentially performing red, green, and blue monochromatic display in a frame ,
When each horizontal pixel line of the display panel is selected for scanning, the planar light source corresponding to the selected horizontal pixel line emits light of a color corresponding to the color signal, and each horizontal pixel line of the display panel Synchronously with the scanning selection of the pixel line, a black display region having a predetermined width that is scanned together with the scanning selection of the frame image is provided between the color frame images of the display panel,
The width of the black display area is made larger than the width of the planar light source, and at the time of black display, the polarity is opposite to the applied voltage applied to the optical modulation material in each pixel during monochrome image display before black display. voltage, the applied predetermined retention time to the optical modulation substance for each pixel to be substantially equal to the absolute value of the product of the applied voltage and the holding time in the black display previous monochrome frame image being displayed,
A driving method of a display device. The planar light source includes a plurality of linear light sources arranged in the scanning line direction, a concave reflector disposed on the back side of the linear light source, and a diffuser disposed in front of the linear light source. Become,
The display device driving method according to claim 1. The linear light source has at least three fluorescent lamps that emit red, green, and blue, respectively.
The method for driving a display device according to claim 2. The optical modulation material is a ferroelectric liquid crystal having a monostable mode,
The display device driving method according to claim 1. The applied voltage is a writing voltage, a voltage having a polarity opposite to the applied voltage is a black reset voltage, and the applied voltage is an effective voltage.
  The display device driving method according to claim 1. The holding time before black display is a writing display period, and the predetermined holding time during black display is a black reset period.
  The display device driving method according to claim 1.

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