JPH10254390A - Liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal device capable of executing a uniform full color display without causing any vertical luminance sag. SOLUTION: A black display frame period performing a whole black display is provided between a frame period displaying a prescribed primary color among red, green, blue and the frame period displaying another primary color among next red, green, blue by a timing controller 14, and a backlight 4 is lighting color switch lighted making the period of two frames much of the black display frame and the primary color display frame one cycle. Thus, a primary color image display and a black display are displayed by vertical scan write-in also, and all display times of even respective pixel lines on any positions are equalized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device,
In particular, a liquid crystal panel and a backlight disposed behind the liquid crystal panel and capable of emitting red, green, and blue primary colors are provided, and color display is performed by sequentially displaying RGB primary color images in a time-series manner for each frame. About what to do.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal panel sandwiching liquid crystal between a pair of substrates facing each other and having information electrodes and scanning electrodes arranged in a matrix on one of the pair of substrates, and a red panel disposed behind the liquid crystal panel. There is a liquid crystal device including a backlight capable of emitting green, blue and primary colors.

In such a liquid crystal device,
For example, as disclosed in JP-B-63-41078, a so-called color filterless liquid crystal panel is driven for each frame, and sequentially for each of R (RED), G (GREEN), and B (BLUE) primary color image signals. Then, in synchronization with this, the liquid crystal panel is illuminated with each color light of RGB from the backlight to display a color image. In a recent example, a similar system is applied to a ferroelectric liquid crystal display panel, as disclosed in Japanese Patent Application Laid-Open No. Hei 6-222360,
-27453.

[0004]

However, in a conventional liquid crystal device having such a configuration, the liquid crystal panel is generally scanned and driven from top to bottom for each horizontal line. In the case of switching between the RGB illumination lights, there is a problem that uneven brightness (upper / lower luminance sag) occurs due to a difference in display time for each pixel line in accordance with the vertical scanning.

In order to completely eliminate the upper and lower luminance sag, the time between the end of writing of all frames and the start of writing of the next frame may be set as the effective display time. The effective display time is equivalent to the vertical blanking period, and there is a limit to setting this to be long, and it is difficult to obtain sufficient brightness of the display even though the color filter is unnecessary. There is a problem.

Accordingly, the present invention has been made to solve such a conventional problem, and has as its object to provide a liquid crystal device capable of uniform full-color display without vertical sag. It is.

[0007]

SUMMARY OF THE INVENTION The present invention provides a liquid crystal panel in which liquid crystal is sandwiched between a pair of opposing substrates, and information electrodes and scanning electrodes are arranged in a matrix on the pair of substrates. And a backlight capable of emitting each of the primary colors of red, green, and blue.The liquid crystal panel is sequentially driven by the red, green, and blue primary color image signals for each frame, and is synchronized with the primary color image signals. A liquid crystal device for switching the backlight to a lighting color, and
A black display frame that performs full black display between a frame period for displaying a predetermined primary color of the red, green, and blue and a frame period for displaying another primary color of the next red, green, and blue. A period is provided, and a color display control means is provided for switching and lighting the backlight with a period of two frames of the black display frame period and the primary color display frame period as one cycle. .

In the present invention, the color display control means may form the primary color display frame and the black display frame by sequentially writing the primary color image signal and the black display signal along the scanning electrodes. It is assumed that.

Further, the present invention is characterized in that the color display control means makes the black display frame period and the primary color display frame period equal.

Further, in the invention, it is preferable that the color display control means includes: a black display signal voltage applied to the liquid crystal during the black display frame period; and a primary color display frame period before or after the black display frame period. And the primary color image signal voltage applied to the liquid crystal is set to have the same absolute value and opposite polarity in all pixels.

Further, the present invention is characterized in that the liquid crystal is a monostable mode ferroelectric liquid crystal.

Also, as in the present invention, the color display control means displays a frame period in which a predetermined primary color of red, green, and blue is displayed, and another primary color in the next red, green, and blue. A black display frame period for performing full black display is provided between the two frame periods, and a backlight is switched and illuminated by turning on a backlight with a period corresponding to two frames of the black display frame period and the primary color display frame period as one cycle. In addition, both the primary color image display and the black display can be displayed by vertical scan writing, and the display time can be made equal for any pixel line at any position.

Further, as in the present invention, at the time of writing driving of each image signal by the color display control means, the black display signal voltage applied to the liquid crystal during the black display frame period and the black display signal voltage are applied to all the pixels. During the primary color display frame period before or after the frame period, the residual DC voltage component is applied to the liquid crystal by making the primary color image signal voltage applied to the liquid crystal have the same absolute value and opposite polarity. It can be prevented from remaining.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a liquid crystal device according to an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a liquid crystal device. The liquid crystal device 1 includes a liquid crystal display panel 2 having no color filter and an R (RED) G
(GREEN) B (BLACK) A backlight 4 having a planar light emitting surface 3 that emits light in each primary color.

Here, the liquid crystal display panel 2 has an active matrix configuration, and uses a monostable mode ferroelectric liquid crystal which is a high-speed response liquid crystal (hereinafter referred to as FLC). The FLC has a high response speed (several hundreds μs to several ms) and usually has a response speed close to the horizontal scan cycle (depending on the number of pixels constituting the panel and the driving voltage). .

FIG. 2 is a cross-sectional view of the liquid crystal device 1. In FIG. 2, reference numeral 5a denotes a counter electrode glass substrate of the liquid crystal display panel 2, 5b denotes a TFT glass substrate, and 6 denotes a pair of opposing substrates 5a and 5a. FLC sandwiched between 5b. Here, a scanning line electrode and an information line electrode are formed on the TFT glass substrate 5b, and a pixel 7 composed of a TFT, a pixel electrode, and an auxiliary capacitor is formed at the intersection thereof.

The FLC 6 of each pixel 7 has the TF
The so-called active matrix drive is performed by the T, the pixel electrode, and the auxiliary capacitance. In FIG. 2, the liquid crystal display panel 2 is sequentially driven to scan from left to right (in the direction of arrow S1; corresponding to the direction from top to bottom in FIG. 1).

FIG. 3 is a cross-sectional view showing the structure of the backlight 4 of the liquid crystal device 1 (cut in the vertical direction of the liquid crystal screen). This backlight 4 has four RGB and four primary color fluorescent lamps (cold cathodes). Tubes) 31R, 31G, and 31B, a U-groove diffuse reflection plate 32, and a diffusion plate 33 are basic elements.

Here, the RGB primary color fluorescent lamps 31R, 31R
G and 31B are arranged four by four for each primary color, so that these are grouped in groups of four and sequentially lit for each color, so that the light is reflected and diffused by the diffuse reflection plate 32 and the diffusion plate 33 so that the color is dispersed. Switching type RGB primary color planar light emission becomes possible.

By the way, each of the RGB primary color fluorescent lamps 31
Each of R, 31G, and 31B includes a color switching lighting circuit 40 including an inverter 42 and a high-voltage switch 41, as shown in the figure. The color of the backlight light is arbitrarily determined by a timing control signal from a timing controller described later. A switching operation can be performed. In addition,
In such a configuration, since it is only necessary to switch the high-voltage switch 41 while the inverter 42 is operating, a change in the load of the inverter is small and the lighting color can be switched at high speed.

FIG. 4 is a diagram showing the configuration of a drive system for driving the liquid crystal display panel 2 and the backlight 4. In FIG. 4, reference numeral 11 denotes an information line driver, which displays an image through an information line electrode 22. The signal is transmitted to each pixel 7. Reference numeral 12 denotes a scanning line driver, and each T on the scanning line passes through a scanning line electrode 21.
This is for driving the FT23.

Further, reference numeral 13 denotes a liquid crystal drive signal generation circuit for generating a liquid crystal drive signal to be described later, and reference numeral 14 denotes a timing controller serving as color display control means. Each horizontal line pixel (one pixel row arranged in the horizontal direction) is sequentially scanned and driven by the scanning line driver 12 through the scanning line electrode 22 and each TFT 23, and each information line electrode 22 of each horizontal line pixel is scanned.
Are supplied with respective image display signals via the information line driver 11.

In synchronization with such an image display signal writing operation, the backlight 4 is also switched by the color switching lighting circuit 40 to a light emission color corresponding to the written image display signal (primary color), as described later. Has become.

The externally applied clock, control signal and temperature control signal shown in the figure are from a general control circuit centered on an MCU (control microcomputer) not shown. The digital RGB image signal is also supplied from an interface circuit (not shown) with a personal computer and a video device, and is a primary color image signal after serial conversion in which reading from an image frame memory is performed for each frame in RGB order.

In the driving system having such a configuration, first, the scanning line driver 12 scans each horizontal line pixel of the liquid crystal display panel 2 with the scanning line electrode 22 and each TF according to a control signal from the timing controller 14.
Scan drive is sequentially performed through T23. At this time, at the same time, the information line driver 11 appropriately supplies each image display signal to each information line electrode 22 of each horizontal line pixel. As a result, an image display signal voltage is supplied to each pixel electrode, and a corresponding liquid crystal response and display operation occur.

Further, in synchronization with such an image display signal writing operation, the backlight 4 is also switched by the color switching lighting circuit 40 to a light emission color corresponding to the written image display signal (primary color).

Next, the driving method of the liquid crystal device 1 will be described in more detail.

As shown in FIG. 2, the driving system of the liquid crystal display panel 2 is controlled by the information line driver 11, the scanning line driver 12, the liquid crystal driving signal generating circuit 13, the TFT 23 and the control signal input from the timing controller 14 from the left side. Each pixel 7 is sequentially scanned and driven toward the right side. First, a black display signal (a black display signal utilizing the characteristics of the FLC mode used in this embodiment) is sequentially provided for each horizontal pixel line. , The details of which will be described later) for one frame. Next, the writing scan of the R primary color image signal is performed for one frame.

Next is black, next is G primary color, next is black, next is B
The primary colors are repeated in black and the primary color image for each frame, and the RGBRG is sequentially and chronologically separated for each frame.
Each primary color image signal is written in the order of B ... in color.

Then, in synchronization with such frame sequential driving, the backlight 4 is also driven by each RG during driving of the liquid crystal display panel.
Lights are sequentially turned on with primary color light corresponding to the B primary color image signal. For example, FIG. 2 shows a state in which the black display image of the previous frame is being rewritten to the G primary color image, and the backlight 4 is also illuminated with G light.

FIG. 5 is a timing chart of the image display by writing each of the primary color image signals and the black display signal of the liquid crystal display panel 2 and the switching of the lighting color of the backlight 4. As shown in this figure, the backlight 4 has a period of two frames of black display by writing a black display signal to the liquid crystal display panel 2 and the next primary color image display as one cycle, and in synchronization with this, the primary color image is displayed. The lighting color is sequentially switched so as to emit the same color as the primary color of the display. In this example, the frame period is set to 360 Hz, which is six times the normal 60 Hz.
It is set to be equivalent (that is, 1/360 sec).

In this embodiment, as described above, the black display signal is applied before the application of the primary color image signal, but this signal resets the FLC (by returning the liquid crystal molecules to the home position). And black display).

By the way, in this embodiment, the monostable mode is adopted as described above, and FIG. 6 shows a conceptual diagram of this mode. Here, in the same figure, P and A represent the polarization directions of the cross Nicol polarizer and the analyzer. Further, 8 schematically represents an FLC molecule,
The direction of the molecule along P is the direction of the monostable state (home position), and the state is a black display state.

When a write voltage Vw is applied to the FLC, the FLC molecules tilt by an angle θa. Here, since the tilt angle θa is determined by the balance between the spray elasticity of the FLC molecules and the driving force by Vw, the tilt angle θa is proportional to Vw up to the saturation value. Therefore, the transmitted light intensity also has a substantially proportional relationship with Vw, and it is possible to display a halftone of light and shade by the value of Vw.

On the other hand, it is preferable to return the FLC molecules to the home position after the writing in order to eliminate the influence on the next writing. For this reason, the predetermined black display voltage Vr (Vw
With the opposite polarity and the same absolute value). It should be noted that although it returns only by turning off Vw for monostable, it is preferable to apply a reverse voltage in order to return earlier.

FIG. 7 shows the relationship between the liquid crystal voltage waveform in the active drive pixel in such a monostable mode and the optical response (transmitted light intensity) to the waveform. In the figure, Vw is the primary color image display application voltage, Vr
Indicates the black display application voltage, and the time axis position indicated by t indicates the voltage of the counter electrode (the solid electrode on the counter glass substrate 5a) in terms of voltage, which corresponds to zero liquid crystal application voltage.

TG represents a scanning line selection period, that is, an ON period of each TFT.
Each signal voltage of w and Vr is applied to the liquid crystal of each pixel. After these signals are applied, the TFT is in an open state, and its voltage is almost maintained until the next Vw or Vr is applied (strictly speaking, the oscillation due to the proximity signal line or the spontaneous polarization of FLC). Although there is an effect, it can be reduced by designing the so-called auxiliary capacitance and the drivability of the TFT to be large.)

Further, 1F represents a frame period,
In the present embodiment, the first 1F period is the black display period,
The period F is a primary color image display period. Then, as described above, the pair of black display and primary color image display is repeated in RGB order. Here, the value of Vr is Vw of the next frame.
And the absolute value are equal, and are set to have the opposite polarity voltages. That is, after writing the polarity inversion signal of the primary color image signal for one frame as a black display signal, the original primary color image information is written and displayed.

As a result, the effective VT product (effective voltage × time) applied to the liquid crystal layer of each pixel is completely canceled between the black display period and the primary color image display period, and the residual DC voltage that adversely affects the liquid crystal (burn-in, etc.) Since there is no component, the reliability of display quality is significantly improved.

By adopting the method of sequentially scanning and driving the black display and the primary color image display as described above, the effective display period becomes just 50% (half) as compared with a normal liquid crystal panel. Therefore, as shown schematically in FIG. 8 for instantaneous image display, in the case of a primary color image display frame, a black display area exists below the Vw-applied pixel line, and
The display is switched to the primary color image display as the w printable line goes down, and in the case of a black display frame, Vr
The primary color image display area of the previous frame exists below the applied pixel line, and the display is switched to black as the Vr applied line goes down. In this way, the boundary between the black display area and the primary color display flows from the top to the bottom of the screen together with the vertical scanning drive of Vw and Vr.

Here, the pixel line immediately above the upper end of the black display area is at the Vw application (primary color image signal writing) position,
Similarly, the lower pixel line of the black display area corresponds to the Vr application (black display signal writing) position. As described above, the primary color image display is performed for each of the RGB primary colors in the order of the separated frames with the black display frame interposed therebetween. Also switches sequentially in RGB while scanning up and down.

FIG. 8 shows the moment when the black display is rewritten to the R image and the moment when the G image is rewritten to the black display. Although FIG. 2 is a cross-sectional view, it shows the moment when black display is rewritten into a G image. Also, as described above, since the frame period is set to be equivalent to 360 Hz, even if such black display and primary color image display occur alternately, it exceeds the flicker limit, and there is no problem such as flickering. Does not occur.

As described above, in the present embodiment, there is a black display area for exactly one screen (one frame). And
As shown in the timing chart of FIG. 5, when the color light of the backlight 4 is switched from the black display frame to the primary color image display frame, the backlight 4 is switched to the same lighting color as the display image primary color.

Accordingly, the display state of each scanning pixel line is represented by a timing chart as shown in FIG. In other words, the display time of each primary color image is equivalent to one frame at any pixel line position on the screen, and there is no crosstalk between the primary color frame images due to the presence of one frame of black display.

By displaying both the primary color image display and the black display by vertical scan writing in this manner, the display time of each pixel line at any position becomes equal, and the brightness as described above is obtained. Very good full-color display without unevenness (upper and lower luminance sags) is formed.

FIG. 10 shows the FL of the liquid crystal display panel 2.
It is a timing chart of driving and response operation of C6, and corresponding lighting color switching of the backlight 4. Although this is a timing chart focusing on one horizontal pixel line, it illustrates various operations of the liquid crystal display panel and the backlight described above.

Here, it should be noted that as described above, Vr of the black display signal and Vw of the next primary color image signal form a pair because they are polarity inversion signals of the same primary color image signal. However, the backlight lighting period of a certain primary color extends over the image display frame period of the primary color and the next black display frame period. Here, the fact that the lighting period of the backlight extends to the next black display frame in this manner is to maintain the display period of the horizontal pixel line at the lower end particularly, as apparent from the chart of FIG. Required for

On the other hand, the application of Vr having the purpose of canceling the next Vw in a DC manner together with black display before the Vw is generated by the primary color image signal applied one frame before this Vr application. Possible residual phenomena (electrochemical phenomena, etc.) are applied to the polarity-reversed Vr generated from the next primary color image signal (Vw) (including resetting of liquid crystal molecules).
Is performed, there is an advantage that almost no influence can be given to the next Vw write.

However, this effect is minute, and in this embodiment, the order of Vr and Vw forming a pair is reversed, and after Vw, DC-like cancellation of Vw and Vr of black display are applied. There is no significant problem even if the frame driving is performed in the opposite relationship (Vw and Vr) to the embodiment.

The liquid crystal drive signals Vw and Vr are generated by the liquid crystal drive signal generation circuit 13 and are based on digital RGB primary color image signals input from the outside. (See FIG. 3). Both Vw and Vr are supplied to each pixel through the same information line electrode 22.

By the way, as described above, the black display and the RGB primary color image display are performed alternately and frame-sequentially to display a full-color image, so that the effective display period is one frame per two frame periods. Although the cycle becomes (efficiency 50%), since there is no transmission loss due to the color filter, overall brightness (light use efficiency) equivalent to that of the conventional liquid crystal panel can be obtained, and uniform brightness without any vertical luminance sag. A full-color display image can be displayed.

In addition, since the driving method for canceling the DC voltage applied to the liquid crystal layer between the black display and each of the RGB primary color image displays is employed, the write state (V
w voltage) does not affect the writing in the next frame, and a very good image (especially a moving image) without so-called afterimages and image sticking can be obtained in a stable state even during long-time operation.

In this embodiment, a liquid crystal display panel having an active matrix structure using TFTs and an active drive is used. However, for example, a liquid crystal display panel having a simple matrix structure and passive drive is at least 180 to 360 Hz. By using a particularly high-speed type or mode FLC or the like, it is possible to handle the liquid crystal in a very similar manner.

The backlight is basically RG.
A large number of B primary color fluorescent lamps are arranged side by side, but as the fluorescent material of each fluorescent lamp, use a type with less afterglow of 1 ms or less as a fall-off characteristic in order to prevent crosstalk between image frames of each primary color. Is preferred. In configuring the backlight, an LED capable of emitting RGB primary colors may be used as a light source instead of the primary color fluorescent lamp, and a similar color switching lighting circuit may be used.

[0056]

As described above, according to the present invention, a black display frame period for performing full-screen black display is provided between primary color display frame periods, and two frames of the black display frame period and the primary color display frame period are provided. By turning on and off the backlight with the lighting color being switched for one period, both the primary color image display and the black display can be displayed by vertical scan writing. As a result, the display time of each pixel line at any position can be made equal, and uniform full-color display without vertical luminance sag can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a liquid crystal device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of the liquid crystal device.

FIG. 3 is a diagram showing a structure of a backlight of the liquid crystal device.

FIG. 4 is a block diagram showing a configuration of a driving system for driving a liquid crystal display panel and a backlight of the liquid crystal device.

FIG. 5 is a timing chart of image display of the liquid crystal display panel and switching of a backlight lighting color.

FIG. 6 is a conceptual diagram of a monostable mode FLC used for the liquid crystal display panel.

FIG. 7 is a diagram showing a liquid crystal voltage waveform applied to the FLC and an optical response waveform thereof.

FIG. 8 is a schematic diagram showing a display state of the liquid crystal display panel at a certain moment.

FIG. 9 is a timing chart of a display state in each horizontal pixel line of the liquid crystal display panel.

FIG. 10 shows image signal writing of the liquid crystal display panel,
4 is a timing chart of liquid crystal response and switching of a backlight lighting color.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 liquid crystal device 2 liquid crystal display panel 3 planar light emitting surface 4 backlight 5 a counter electrode glass substrate 5 b TFT glass substrate 6 ferroelectric liquid crystal (FLC) 7 pixel 8 ferroelectric liquid crystal (FLC) molecule 14 timing controller 21 scanning line electrode 22 Information line electrode 23 TFT 31 RGB primary color fluorescent lamp 40 Backlight color switching lighting circuit

Claims (5)

[Claims] 1. A liquid crystal panel in which liquid crystal is sandwiched between a pair of substrates facing each other, and information electrodes and scanning electrodes are arranged in a matrix on the pair of substrates, and red, green, and A backlight capable of emitting blue primary colors, the liquid crystal panel is sequentially driven by the red, green, and blue primary color image signals for each frame, and the backlight is turned on and off in synchronization with the primary color image signals. A liquid crystal device to be turned on, wherein the red, green, and blue between a frame period for displaying a predetermined primary color, and the next red, green, between the frame period for displaying another primary color of blue A black display frame period for performing full black display is provided, and the backlight is switched and illuminated by setting a period of two frames of the black display frame period and the primary color display frame period as one cycle. A liquid crystal device characterized by including a color display control unit. 2. The color display control unit according to claim 1, wherein the primary color display frame and the black display frame are formed by sequentially writing the primary color image signal and the black display signal along the scanning electrodes. Item 2. The liquid crystal device according to item 1. 3. The liquid crystal device according to claim 1, wherein the color display control means makes the black display frame period and the primary color display frame period equal. 4. The color display control means includes: a black display signal voltage applied to the liquid crystal during the black display frame period; and the primary color display frame period before or after the black display frame period. 2. The liquid crystal device according to claim 1, wherein the absolute value of the primary color image signal voltage applied to the pixel and the absolute value of the pixel voltage applied to all the pixels are opposite. 5. The liquid crystal device according to claim 1, wherein the liquid crystal is a monostable mode ferroelectric liquid crystal.