JPS6385523A - Color electrooptic device by ferroelectric liquid crystal - Google Patents

Abstract

PURPOSE:To permit desired color display by providing a period for holding image plane information after writing of said information to a ferroelectric liquid crystal and continuing the light emission of a plane light emitting element during said holding period. CONSTITUTION:An OPEN signal controls the transfer from a writing action to memory action to a driving circuit when the OPEN signal changes from L to H. The signal DATA to be inputted to a segment driving circuit 11 via an OR gate 14 is forcibly brought to the H when the signal OPEN goes to the H. A signal DF is forcibly brought to the L via an inverter 15 and an AND circuit 16. All the segments of an LC panel 12 attain a VDD level as is evident from the segment output truth table. An FLM inputted to a common driver 13 via an OR gate 17 is forcibly brought to the H when the signal OPEN goes to the H. The signal DF is forcibly brought to the H via an OR gate 18. All the common values of the LC panel attain the VDD level at this time. The segments and common values maintain the memory state.

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 for driving a ferroelectric liquid crystal color electro-optical device that uses ferroelectric liquid crystal to provide a color display by time-based additive color mixing.

[Summary of the invention]

The present invention produces Calo method 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 installed on the back side of the ferroelectric liquid crystal element. In the ferroelectric liquid crystal color electro-optical device, after the screen of the ferroelectric liquid crystal element is rewritten, a screen retention period is provided by utilizing the memory property of the ferroelectric liquid crystal element, and light is irradiated from the light source during the screen retention period. This makes it possible to obtain a color display with high brightness.

[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, a CRT, etc.) is provided behind it to realize a color display by the phenomenon of sequential additive mixing. For example, Ph1fip Ros, Thom, 1s announced at Eurodisplay '84.
Buzak, Rolf Vatne et al. 7 9 “-
1AFull-Color Field-3equen
tial Co1or Display (1984/
It was announced at 9/18-20) and SID'85. 1 la
Sebe, Kobayashi et al.'s ``is cited as a prior document.

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 is driven by electrically switching (hereinafter referred to as switching) the bistable states of ferroelectric liquid crystal molecules, such as chiral smectic liquid crystal (hereinafter referred to as SmC"+!); and Its driving circuit is disclosed in Japanese Patent Laid-Open 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 substrate. It is a uniaxial or random horizontal alignment film provided on the inner plane. 3 is a SmC" thin film narrowed by the alignment film 2-2.
C'' originally has a helical layer 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"l film 3 from above, the molecular axis is tilted at 0 with respect 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 a 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 fat is an example of a driving waveform applied to one of the matrix pixels shown in FIG. First, during the first selection period, an alternating current pulse having a peak value Vop and a pulse width T that is equal to or greater than the threshold value is applied for -cycles. Assuming that the polarity of all the first half pulses P, 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 direction of switching the liquid crystal molecules from the first stable state to the second stable state. 1) to the 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 period up to this point will be referred to as the first frame.

Next P3. In the second frame containing the P a pulse,
P3. 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
The first stable state written by the P2 pulse in the 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, P2 pulse below the dark value.
On the other hand, P'3. The peak value of the P4 pulse should be greater than the dark value. In other words, since the driving method writes pixels that should be in the first stable state in the first frame, and pixels that should be in the second stable state in the second frame, one screen is formed by scanning two frames. be done. 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. By the way, FIG. 4('b) shows the transmitted light characteristics when the waveform of FIG. , which causes a decrease in contrast.

[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 light is emitted only during the two frames, and the first stable state is the light blocking state (hereinafter referred to as the tool) and the second stable state is the light transmitting state (hereinafter referred to as the mortar). ). 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 for the top pixel to become white until the end of two frames is (2m-1)T, and on the other hand,
The bottom pixel is T. By the way, the T of “SmC” is 20.
0 to 300 p see, and within this amount of time, the transmitted emitted light color cannot be recognized, 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 after writing screen information to a ferroelectric liquid crystal element, it provides a period for retaining the written screen by utilizing its memory property. The planar light emitting element continues to emit light during the period when the screen is held.

〔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 in time. - In all cases, the red light source of the surface emitting device continues to emit light for some time.

After that, the screen holding signal (
This is hereinafter referred to as the 0PEN signal) and the screen is held for a desired time. Red light emission is continued during the holding period A'. Similarly, change the pixel you want to emit blue to time B.
Write in white in the second frame of 2 frames, while
The blue light emission is continued, and the 0PEN signal is sent, and the B'C blue light emission is continued during the period when the blue display board surface is maintained.

The same procedure is followed for green emission, A, A', B, B', c
, c' is repeated to perform additive color mixing over time. As pointed out above, the problem of the conventional example is that the bottom pixel only transmits light for T time, but in the present invention,
By providing retention periods A', B', and C', the transmission time can be lengthened. These retention periods A', B',
The time C' can be arbitrarily set depending on the pulse width of the 0PEN signal. Therefore, if you lengthen the time for A'=B'=C', the amount of i3 excess light will increase, so you can get a color display with high brightness, and if you choose the relationship A'≠B゛≠C', you can change the hue. can be done.

By the way, next, a method of holding the screen using the 0PEN signal will be explained.

FIG. 6 shows an example of a waveform applied to the matrix electrode when writing white by line sequential driving using the 1/5 bias averaging method. φ is the selection signal electrode waveform, the first half ■8,
The second half VDD is applied. φ8 is a non-selected No. 13 electrode waveform, and the first half ■2 and the second half V are applied. φ is the waveform applied to the selected scanning electrode, and the first half ■. , the second half VS is applied. φ7 is the waveform applied to the non-selected scanning electrode, and the first half V4
However, the second half v1 is applied. This is expressed in the output truth table of the signal electrodes (hereinafter referred to as segments) and the output truth table of the scanning electrodes (hereinafter referred to as common) as follows.

Segment output truth table Common output truth table Here, DATA is the video signal input to the drive circuit and is H.
indicates segment selection, and L indicates segment non-selection. F
LM is the scanning number 53 input to the drive circuit, H indicates common selection, and L indicates common non-selection. DF is an alternating current signal input to the drive circuit, H indicates the first half of the fundamental level of the applied voltage waveform, and H indicates the second half. For example, segment output true Fl! In the value table, when DATA is H, the first half of the selected segment is V, and the second half is ■. . applied. This is φ8 in FIG.

Now, if we look at both truth tables, ■. 0 potential is commonly used for segments and common. Therefore, the DATA signal input to the segment driver is forcibly set to H by logic control, and the DF multiplied signal is set to L. Then ■ is applied to all segments.

At the same time, the FLM (No. 8) input to the common driver is forcibly set to H by logic control, and the DF multiplied signal is set to H. Then, vllllll is applied to all segments.

This forces both electrodes to connect to the VII++ potential.

FIG. 7 shows a drive circuit for forcibly connecting the above-mentioned matrix electric bridge to VO, and will be explained in conjunction with the time chart of FIG. 8. A segment driver 11 drives the segments of the LC panel 12. Necessary potential level■
. D%V is input, and φ and φO are synthesized and output based on the DATA and DF multiplied signals. CL2 is a high-speed clock for converting serial or ATA to parallel DATA, and CL1 is a clock for controlling line sequential timing. CL + is synchronous and parallel DATA
Output lunch. A common driver 13 drives the common of the LC panel 12. Necessary potential level VDD
~■, are input, and φV and φ are synthesized and output based on the FLM and DF multiplied signals. CL + is a clock that controls line sequential timing. Now, suppose that the 0PEN signal changes from L to H. The 0PEN signal is a signal that controls the drive circuit to transition from write operation to memory operation. When the signal 0PEN becomes H, the DATA input to the segment driver 11 via the OR gate 14 is forced to become H. Also inverter 1
5 and the AND gate 16, DF is forced to become L. Therefore, as is clear from the segment output truth table, all segments of the LC panel 12 are at the ■no level. Furthermore, when the 0PEN signal becomes H, the FLM input to the common driver 13 via the OR gate 17 is forced to become H. Also, DF is forced to become H through one day of ORGATE. Therefore, as is clear from the common output truth table, all the commons of the MILC panel 12 are at the VOO level. As a result of the above, the segment and common are held at the same potential as VDD, and the memory state is maintained.

This memory state is different from the state shown in FIG.
Since no fluctuation occurs in the transmitted light of I, the amount of irradiated light can be transmitted without deterioration of contrast.

〔Effect of the invention〕

As described above, according to the present invention, the time during which the light emitting light source of each color passes through the ferroelectric liquid crystal element over time can be arbitrarily adjusted by setting the screen retention period. This has the advantage that it is possible to obtain a color display whose color and hue can be adjusted.

[Brief explanation of the drawing]

FIG. 1 is a diagram chronologically showing the drive timing of 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. 3 is a diagram of a conventional liquid crystal cell. Figure 4 is a diagram showing the drive waveform of a conventional liquid crystal cell and its transmitted light characteristics; Figure 5 is a diagram showing the drive timing of a conventional SmC' and the light emission timing of a planar light emitting element over time. , FIG. 6 is a waveform diagram applied to the segment and common, FIG. 7 is an LC panel drive circuit diagram, and FIG. 8 is a time chart of the drive circuit shown in FIG. 7. 11...Segment driver 12...LC panel 13...Common driver! 4.15.16, 17.18...Logic circuits and above Applicant: Seiko Electronics Co., Ltd. Figure 3 Figure 9 Kyoto product cell in Shiba pot (dynamic waveform and graph showing 5-nine mark Takao) (7 Figure 4 ψX φX cPY φy Hi-i g chant t?mi E1: Egg power p-sho "35 skin-shaped prisoner figure 6 Bahanru pottery" RU box I each figure figure 7 Time Namat figure figure 8

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 equipped with a flat light source, after writing screen information to the ferroelectric liquid crystal to be transmitted corresponding to each color light source, the written screen is held for an arbitrary period of time. A ferroelectric liquid crystal color electro-optical device characterized by: