JPS6385524A - Color electrooptic device by ferroelectric liquid crystal - Google Patents

Abstract

PURPOSE:To make color display of distinct hues by setting the emission time of respective colors of a plane light emitting element to start light emission from the 2nd frame of two frames and before the end of the 1st frame of the ensuing two frames. CONSTITUTION:A picture element desired to emit red light is written white in the 2nd frame of the two frames of the time A. On the other hand, the red light source of the plane light emitting element starts the light emission from the 2nd frame of the time A. The picture element desired to emit blue light is then written white in the 2nd frame of the time 8. However, the light emission of the red light source is continued up to the 1st frame of the time B. The light emission of the blue light source is thereafter started from the 2nd frame and the emission of the blue light source is continued up to the 1st frame of the time C where the white is written to the picture element desired to emit green light. The light emission of the green light source is continued from the 2nd frame of the time C. The light emission of the green light source is started from the 2nd frame of the time C and the light emission of the green light source is continued up to the 1st frame of the time A where the white is written to the picture element desired to emit red light and from this time on, the initial procedures are repeated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferroelectric liquid crystal color electro-optical device. In particular, the present invention relates to a method of driving a ferroelectric liquid crystal color electro-optical uM that uses ferroelectric liquid crystals to provide a color display through time-based additive color mixing.

[Summary of the invention]

The present invention produces additive color mixture by sequentially irradiating the ferroelectric liquid crystal element with light of different colors from a light source that emits light of different colors and installed on the back side of the ferroelectric liquid crystal element. In the ferroelectric liquid crystal color electro-optical device, the hue can be changed by shifting the light emitting period of each color of the light source that sequentially emits light of the color of the stomach and the driving period of the ferroelectric liquid crystal element. It is possible to obtain a clear color display.

[Conventional technology]

Conventionally, it has been announced that a liquid crystal cell is used as a shutter and a light emitting element (for example, an LED, CR"l", etc.) is installed behind it to realize a color display by the phenomenon of sequential additive mixing. For example, Ph1lip 8os announced at Eurodisplay '84, Thomas
7-9 of BLIzak, Rolf Vatne et al.
4 AFull-Color Field-5eque
ntial Co1or DisplayJ (198
4/9/1B-20) and H announced at SID'85
Asebe, Kobayashi et al.'s ``'' is cited as a prior literature.

However, no invention has been disclosed regarding a specific driving method when this method is applied to a ferroelectric liquid crystal display element. First, a conventional method for driving a ferroelectric liquid crystal will be explained. A ferroelectric liquid crystal cell (hereinafter simply referred to as a liquid crystal cell) that drives the bistable states of ferroelectric liquid crystal molecules, such as chiral smectic liquid crystal (hereinafter referred to as "SmC"), by electrically switching between them (hereinafter referred to as switching), and its driving circuit. is disclosed in Japanese Unexamined Patent Publication No. 61-94026. Fig. 2 shows a perspective view of a conventional liquid crystal cell. Reference numeral 1-1 indicates a pair of substrates facing each other. Reference numeral 2-2 indicates a pair of substrates arranged on the inner plane of the substrates. A uniaxial or random horizontal alignment film provided. 3 is an alignment film 2
It is a thin film of SmC narrowed by −2.3mC”
Originally exists in a spiral structure, but when it is made into a thin film sandwiched between alignment films, the liquid crystal molecules form layers and are horizontally aligned as shown in the figure.

However, when looking at the SmC"i film 3 from above, the molecular axis is 0 degrees relative to the layer normal 4. There are two positions for this, a first stable state 5 and a second stable state 6. The SmC'' molecule has spontaneous polarization 7 in the direction perpendicular to the molecular axis. The direction of the spontaneous polarization 7 is perpendicular to the substrate 1, and
The polarity is reversed between the bistable states. It is therefore possible to switch between stable states by applying pulses of a predetermined polarity. 8-8 is a pair of polarizing plates having polarization axes orthogonal to each other, and is an optical conversion member that identifies the first stable state and the second stable state of liquid crystal molecules as light passing and light blocking by birefringence. . Electrodes 9 and 10 are arranged opposite to each other and apply a pulse to SmC''.

Figure 3 shows the electrode configuration. 9 is a scanning electrode, and 10 is a signal electrode. A well-known time-division drive is performed by forming a matrix with both electrodes.

FIG. 4 is an example of a driving waveform applied to one of the matrix pixels shown in FIG. 3. First, during the first selection period, an AC pulse having a peak value Vop and a pulse width T greater than or equal to the threshold value is selected.
Add cycle. Assuming that the polarity of all first half pulses P1 is in the direction of switching the liquid crystal molecules from the first stable state to the second stable state, the polarity of the second half pulse P2 is in the opposite direction switching (from the second stable state to the first stable state). to a stable state). As a result, the switching of the P pulse is not maintained and the switching of the P2 pulse is always effective. Next, during the non-selection period, an AC pulse having a peak value below the dark value is applied, and the previously obtained first stable state is preserved. Hereinafter, the spacing up to this point will be referred to as the first frame.

Next, P3. In the second frame containing P, pulses, P, ,
The peak value of the P4 pulse is less than the dark value, and the phase is reversed compared to the first frame. Therefore, the first stable state written by the P2 pulse in the first frame is maintained.

The above is the waveform that should be applied to the pixel that you want to write into the first stable state, but for the pixel you want to write into the second stable state, set the peak value of the P l + P 2 pulse below the dark value, and ,, The peak value of the P4 pulse should be made equal to or higher than the dark value. In other words, the pixel that should be in the first stable state is
Since the driving method is such that pixels to be in the second stable state are written in the second frame, one screen is formed by scanning two frames. Therefore, a time lag occurs between the two, and after two frames have been scanned, the first stable state is displayed longer than the second stable state by one frame.

[Problem that the invention seeks to solve]

Now, one of the different colors of the flat light emitting elements placed on the back side.
As shown in FIG. 5, the first stable state is a light blocking state (hereinafter referred to as black), and the second stable state is a light transmitting state (hereinafter referred to as white). ). Here, let us consider the topmost pixel, that is, the first row, and the bottommost pixel, that is, the mth row, of the cells arranged in a matrix of m rows and n columns in FIG. If the previous state of each pixel is black and should be inverted to white between these two frames, then black will be maintained in the first frame and inverted to white in the second frame, but the pixel will be inverted to white in the second frame. The time it takes for the top pixel to become white until the end of 2 frames is 2m-1)T, and on the other hand,
The bottom pixel is T. By the way, 'r' of "SmC" is 2
00 to 300 μsee, and within this time period, it is impossible to recognize the transmitted emitted light color, and there is a problem that the desired color display cannot be obtained in the bottom pixel.

[Means for solving problems]

The present invention aims to solve the problems of the conventional technology, and the light emitting time of each color of the planar light emitting element is such that the light emitting time of each color of the planar light emitting element starts from the second frame of two frames and starts from the first frame of the next two frames. This is to be set by the end of the process.

〔Example〕

FIG. 1 shows the driving timing of the ferroelectric liquid crystal element and the light emission timing of the planar light emitting element. In FIG. 1, a pixel that is desired to emit red light is written white in the second frame of two frames at time A. -The red light source of the surface emitting device is time A
Light emission starts from the second frame. Next, the pixel that is desired to emit blue light is written in white in the second frame of the two frames at time B. However, until the first frame of time B, the red light source continues to emit light. Thereafter, the blue light source starts emitting light from the second frame 1, and continues to emit light by '+1' until the first frame at time C, when white is injected into the pixels that are desired to emit green light. Further, the green light source starts emitting light from the second frame at time C, and continues to emit light from the green light source until the first frame at time A, when white is written into the pixel to be emitted red.

From now on, return to the first step above and repeat this.

According to this method, the lowest pixel in the matrix cell of FIG.
Since the time of mT is maintained as white, sufficient brightness can be obtained by transmitting the red light source. However, in this case, adjust the phase of the %f<dynamic source shape in Figure 4 so that the village is written in the first frame and the white in the second frame, or the polarizing plate 8
Adjust the angles of the polarization axes of -8 to make them parallel. In this way, all pixels on the matrix cell screen can transmit each luminescent color for at least 2 mT time.

[Effects of the Invention] As described above, according to the present invention, the time for the light emitting light source of each color to pass through the ferroelectric liquid crystal element over time can be secured by at least 2nT, so that the hue can be clearly defined. This has the advantage that a bright color display can be obtained.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a diagram chronologically showing the drive timing of the SmC" of the present invention and the light emission timing of the flat light emitting element, FIG. 2 is a perspective view of a conventional liquid crystal cell, and FIG. Figure 4 is a diagram of the electrode arrangement of a conventional liquid crystal cell, Figure 4 is a drive waveform diagram of a conventional liquid crystal cell, and Figure 5 is a diagram chronologically showing the drive timing of a conventional SmC'' and the light emission timing of a planar light emitting element. It is. 1-1... 2゜((Anti-2-2... Alignment film 3... Chiral smectic liquid crystal Fit[128
-8... Polarizing plate 9, lO... Electric melon. Applicant: Seiko Electronics Co., Ltd. Akira Ruhe f weight waveform Figure 4

Claims (1)

[Claims] It consists of a ferroelectric liquid crystal element consisting of a ferroelectric liquid crystal thin film sandwiched between two transparent members, and a plurality or single light source that can sequentially irradiate the display surface with light of different colors. In a ferroelectric liquid crystal color electro-optical device comprising a flat light source, light emission of at least one color in the flat light source starts from a second frame in which a light transmission state is written in the ferroelectric liquid crystal element, and continues. A ferroelectric liquid crystal color electro-optical device characterized by continuing light emission until the end of the next frame.