JP4335904B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a field sequential color liquid crystal display device using a ferroelectric liquid crystal (FLC) that realizes high-speed response, and in particular, among the ferroelectric liquid crystals, isotropic phase, Utilization of light using a ferroelectric liquid crystal having a phase sequence of a chiral nematic phase (cholesteric phase) and a smectic C phase (in the following explanation, such a liquid crystal is referred to as a half-V shape ferroelectric liquid crystal). The present invention relates to a liquid crystal display device that realizes improvement in efficiency and moving image response.

  In addition to attractive features such as low power consumption and thinness, liquid crystal display devices are widely used in flat TVs, portable computers, monitors, and the like due to rapid improvement in display performance itself. Among such liquid crystal display devices, it is known that a ferroelectric liquid crystal using a smectic C phase can obtain a high-speed response with a time constant of 10 μs to several 100 μs.

  More specifically, when a liquid crystal panel filled with a ferroelectric liquid crystal of Half-V Shape is cooled from a high temperature, the projection component of the liquid crystal molecule itself at the phase transition temperature from the chiral nematic phase (cholesteric phase) to the smectic C phase. Are substantially the same in the direction of alignment treatment. However, two domains may occur at that time. Therefore, in order to obtain a single domain, a method of applying DC near the phase transition temperature has been proposed. The liquid crystal panel thus obtained has a feature of responding at high speed while maintaining good image quality.

  Such a Half-V Shape ferroelectric liquid crystal can be easily applied to a field sequential color system. Here, the field sequential color system is a method in which red (R), green (G), and blue (B) images are sequentially displayed in time, and these images are mixed in time to obtain a full color display. It is.

  In order to apply this field sequential color system to a liquid crystal display device, the display of the backlight is switched by temporally switching between red, green and blue, and the image corresponding to the color lit by the backlight is displayed on the liquid crystal panel. Can be realized in synchronization with the switching of the backlight.

  Assuming that the frame period for displaying an image is a normal 60 Hz, the color switching frequency by the field sequential color system is required to be 180 Hz, which is three times that. Therefore, the above-described Half-V Shape ferroelectric liquid crystal having excellent responsiveness is suitable for realizing such a field sequential color system that requires high-speed responsiveness.

  FIG. 7 is a general plan view of a liquid crystal display device using a general ferroelectric liquid crystal. Employing the field sequential color method has the advantage that the display pixel does not need to be divided into three parts of red, green, and blue, and that the same technology can be used to achieve a three times higher definition.

  However, in the ferroelectric liquid crystal, due to the characteristics of the liquid crystal aligned as described above, data can be displayed only when the polarity voltage is on one side, and cannot be displayed when the polarity is reversed. Therefore, in order to avoid problems such as burn-in due to DC application, it is necessary to perform AC driving as driving, and in the case of AC driving, the light utilization efficiency becomes less than 50%. End up.

  FIG. 8 is a diagram showing a driving sequence when a field sequential color system is implemented in a liquid crystal display device using a general ferroelectric liquid crystal. As shown in FIG. 8, as a result of AC driving, red, green and blue lights on the backlight side only contribute to the display, respectively, “A part” “B part” “C part”. It will be about 50%.

  On the other hand, a driving method for improving the light utilization efficiency has been proposed (see, for example, Patent Document 1). FIG. 9 is a diagram showing a driving sequence in a driving method of a conventional liquid crystal display device for improving the light utilization efficiency.

  In this conventional driving method, a data erasing period (corresponding to T2 in FIG. 9) is provided after a data holding period (corresponding to T1 in FIG. 9), and a voltage having a polarity opposite to that of the previous data is applied. Further, after that, the voltage difference between the pixel electrode and the common electrode is set to 0 V as a reset period (corresponding to T3 in FIG. 9).

  As described above, by providing the data erasing period (T2) and the reset period (T3), it is possible to eliminate the bias of charge with respect to the liquid crystal while improving the light use efficiency, and to prevent deterioration of the liquid crystal substance. It can prevent burn-in of the liquid crystal panel.

  Furthermore, impulse driving in which a partial period of one frame contributes to display can be performed, and moving image characteristics can be improved as compared with the conventional hold-type driving in which the entire period in one frame contributes to display.

JP 2004-219938 A

  However, the prior art has the following problems. By adopting the conventional driving method, it is possible to improve the light use efficiency and the moving image characteristics of R, G, and B images. However, the display image itself is composed of R, G, and B, and there is a problem that the moving image response of such a combined display image cannot be sufficiently improved.

  The present invention has been made to solve the above-described problems. In a liquid crystal display device using a field-sequential color system using a half-V shape ferroelectric liquid crystal that realizes high-speed response, the light use efficiency is improved. It is an object of the present invention to obtain a liquid crystal display device that can improve the moving image responsiveness of a display image formed by combining R, G, and B.

The liquid crystal display device according to the present invention is a field sequential color liquid crystal display device using ferroelectric liquid crystal, and is divided into a data writing period and an AC driving period after the data writing period within one frame period. In the data writing period, in synchronization with the lighting period of the red, green, and blue backlights, voltages of the same polarity are sequentially applied to generate red, green, and blue display images. A reverse polarity voltage is applied to the generation of the display image, and the reverse polarity voltage application period in the AC drive period is provided in a lump for each of the red, green, and blue display images. A voltage that is the same as the integrated value of the applied voltage of the green and blue display images and has the opposite sign is applied .

  According to the present invention, one frame period is divided into a data writing period and an AC driving period after the data writing period, and in the data writing period, voltages of the same polarity are sequentially applied to display red, green, and blue. After the image is generated, a half-V shape ferroelectric liquid crystal that realizes high-speed response by a field sequential method by applying a voltage having a polarity opposite to that of the display image during the AC drive period is used. In the liquid crystal display device, it is possible to obtain a liquid crystal display device that can improve the use efficiency of light and improve the moving image responsiveness of the display image formed by combining R, G, and B.

Hereinafter, preferred embodiments of a liquid crystal display device of the present invention will be described with reference to the drawings.
The liquid crystal display device of the present invention can display data only with a voltage of one polarity using a half-V shape ferroelectric liquid crystal excellent in high-speed response, and is almost black at a reverse polarity voltage. By performing a driving method that takes advantage of the characteristics of the ferroelectric liquid crystal of Half-V Shape, it is possible to improve the moving image response without increasing the liquid crystal driving frequency.

Embodiment 1 FIG.
First, a method for improving the moving image response of the liquid crystal display device will be described.
FIG. 1 is an explanatory diagram schematically showing the moving image response. Specifically, the vertical axis represents time and the horizontal axis represents the location, indicating that the gray screen is moving from the left of the black screen.

  In a liquid crystal display device, each pixel performs a hold type display that continuously emits transmitted light during the frame period, so when viewed by an observer, a black screen is displayed as shown in the bottom bar. It appears as if the brightness is gradually changing over the gray screen.

  In order to improve this, a high-speed driving method or a black insertion method has been proposed. FIG. 2 is an explanatory diagram schematically showing the improvement of moving image response by the high-speed driving method. Similar to FIG. 1, the vertical axis represents time, the horizontal axis represents location, and the gray screen is moving from the left of the black screen.

  In the high-speed driving method shown in FIG. 2, the driving frequency is doubled as compared with the driving method shown in FIG. 1, so that the period in which the luminance changes gradually is shortened to improve the moving image response.

  FIG. 3 is an explanatory diagram schematically showing the improvement of the moving image response by the black insertion method. Similar to FIGS. 1 and 2, the vertical axis represents time and the horizontal axis represents location, indicating that the gray screen is moving from the left of the black screen. The black insertion method shown in FIG. 3 uses the same drive frequency as that of the drive method of FIG. 1, but by inserting a large number of black display periods with respect to the video display period, pseudo impulse display is performed and an equivalent frequency is obtained. The video response has been improved by obtaining the same effect as when raising.

  Here, as described above, the half-V shape ferroelectric liquid crystal has a characteristic that data can be displayed only with a voltage of one polarity, and a black state is obtained with a voltage of opposite polarity. Therefore, by making use of this characteristic, the driving of the black insertion method shown in FIG. 3 can be easily realized, and the moving image response can be improved without increasing the liquid crystal driving frequency.

  Furthermore, the liquid crystal display device of the present invention first generates a display image composed of R, G, and B within one frame period, and then applies a voltage having a polarity opposite to that of the generation of the display image. It is characterized by realizing the drive and the drive by the black insertion method at the same time. Hereinafter, the drive system of the present invention will be specifically described with reference to the drawings.

  FIG. 4 is a diagram showing a driving sequence when the first driving method with improved moving image response in the first embodiment of the present invention is implemented. As shown in FIG. 4, one frame period is divided into a data writing period and an AC driving period. In the first driving method, first, R, G, and B are continuously displayed with the same polarity voltage in the data writing period. Thereafter, in the AC drive period, a voltage having the same polarity and the opposite polarity to the voltage applied in the previous data write period is applied corresponding to each of R, G, and B.

  As described above, first, after a display image is generated by R, G, and B signals in the data writing period, the display is generated by applying the reverse polarity to AC in the AC driving period. In addition, it is possible to eliminate problems such as image sticking due to DC application.

  In FIG. 4, for convenience, R, G, and B data written to the pixels are shown as different values. When such driving is performed, not only AC driving but also the same effect as the black data insertion as shown in FIG. 3 can be obtained, and as a result, the moving image response can be improved. . That is, during the AC driving period, the AC driving is performed, and at the same time, the role of black insertion is played.

  FIG. 5 is a diagram showing a driving sequence when the second driving method with improved moving image response in the first embodiment of the present invention is implemented. In the second driving method, as compared with the first driving method shown in FIG. 4, the reset period (T3R, T3G, T3B in FIG. Is equivalent).

  A reset period for resetting data is inserted in synchronism with the turn-off timing of each backlight contributing to the display performance. In this way, each R, G, B data write operation is a write operation from a constant voltage after data reset, eliminating the influence of hysteresis associated with the previous data write voltage and enabling stable color display. Become.

  FIG. 6 is a diagram showing a driving sequence when the third driving method with improved moving image response in the first embodiment of the present invention is implemented. In the third driving method, as in the first driving method shown in FIG. 4, R, G, and B are displayed first, and then a data erasing period is provided in a lump. ing.

  As an example, it is conceivable to apply the integrated value of the applied voltage of R, G, B and the integrated value of the applied voltage in the data erasing period so as to have the same magnitude but opposite signs. By providing a collective data erasing period, AC driving can be achieved, a data writing period with respect to the AC driving period can be made longer, backlight use efficiency can be improved, and luminance can be improved.

  Further, even when a collective data erasing period as shown in FIG. 6 is provided, a reset period (corresponding to T3R, T3G, and T3B in FIG. 5) as shown in FIG. 5 can be inserted. The effect of hysteresis associated with the previous data write voltage is eliminated, and stable color display can be realized.

  As described above, according to the first embodiment, in the half-V shape ferroelectric liquid crystal, one frame period is divided into the data writing period and the subsequent AC driving period, and R, G in the data writing period. , B preferentially generates a display image and then realizes both AC drive and black insertion drive during the AC drive period, improving light utilization efficiency and combining R, G, and B Thus, it is possible to obtain a liquid crystal display device that can improve the moving image response of the display image.

  Furthermore, the application period of the reverse polarity voltage during the AC drive period can be provided not only for each of the red, green and blue display images, but also collectively, and the use of light. Efficiency can be further improved.

  Further, by providing a reset period in the data write period, each data write of R, G, and B can be a write operation from a constant voltage after the data reset, and hysteresis associated with the write voltage of the previous data It is possible to eliminate the influence of the above and to achieve stable color display.

  It should be noted that the present invention effectively utilizes the feature that data can be displayed only with a polar voltage on one side in the case of a ferroelectric liquid crystal having an isotropic phase, a chiral nematic phase (cholesteric phase), and a smectic C phase sequence. is doing. As a result, black display can be inserted without increasing the drive frequency, and moving image response can be improved.

  Actually, the present invention can be applied to a field sequential display using nematic liquid crystal capable of displaying data equally with bipolar voltages. However, in this case, black display is performed by voltage, and as a result, the driving frequency of the liquid crystal increases, and the response of the liquid crystal may not follow.

It is explanatory drawing which expressed animation responsiveness typically. It is explanatory drawing which expressed typically the improvement of the moving image responsiveness by a high-speed drive system. It is explanatory drawing which expressed the improvement of the moving image responsiveness by a black insertion system typically. It is the figure which showed the drive sequence at the time of implementing the 1st drive system which improved the moving image response in Embodiment 1 of this invention. It is the figure which showed the drive sequence at the time of implementing the 2nd drive system which improved the moving image response in Embodiment 1 of this invention. It is the figure which showed the drive sequence at the time of implementing the 3rd drive system which improved the moving image response in Embodiment 1 of this invention. 1 is a general plan view of a liquid crystal display device using ferroelectric liquid crystal. It is the figure which showed the drive sequence at the time of implementing a field sequential color system in the liquid crystal display device using a general ferroelectric liquid crystal. It is the figure which showed the drive sequence in the drive system of the conventional liquid crystal display device for improving the utilization efficiency of light.

Claims (2)

It is a liquid crystal display device by a field sequential color method using a ferroelectric liquid crystal,
One frame period is divided into a data writing period and an AC driving period after the data writing period. In the data writing period, voltages having the same polarity are synchronized with the lighting period of the red, green, and blue backlights. Are sequentially applied to generate red, green, and blue display images, and in the AC drive period, a voltage having a polarity opposite to that of the display image generation is applied ,
The application period of the reverse polarity voltage in the AC drive period is provided in a lump for each of the red, green, and blue display images, and the application voltage of the red, green, and blue display images in the application period. A liquid crystal display device characterized in that a voltage having the same integral value and a reverse sign is applied . The liquid crystal display device according to claim 1 .
The liquid crystal display device according to claim 1, wherein the data writing period further includes a reset period in which a predetermined reset voltage is applied while voltages corresponding to red, green, and blue are sequentially applied.

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