(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2002/0044115 A1
`(43) Pub. Date: Apr. 18, 2002
`
`Jinda et al.
`
`US 20020044115A1
`
`(54) LIQUID CRYSTAL DISPLAY DEVICE
`DRIVING METHOD
`
`Publication Classification
`
`(76)
`
`Inventors: Akihito Jinda, Kitakatsuragi-gun (JP);
`Koichi Miyachi, Souraku-gun (JP);
`Hidekazu Miyata, Nagoya-shi (JP)
`
`Correspondence Address:
`Dike, Bronstein, Roberts & Cushman, LLP
`130 Water Street
`
`Boston, MA 02109 (US)
`
`(21) Appl. No.:
`
`09/922,183
`
`(22)
`
`Filed:
`
`Aug. 2, 2001
`
`(30)
`
`Foreign Application Priority Data
`
`Aug. 3, 2000
`Jun. 11, 2001
`
`(JP) ...................................... 2000-235633
`(JP) ...................................... 2001-175453
`
`Int. Cl.7 ....................................................... G09G 3/36
`(51)
`(52) U.S.Cl.
`................................................................ 345/87
`
`(57)
`
`ABSTRACT
`
`While image data is written into either one of first, second,
`third frame memories 1, 2 and 3, image data are repetitively
`read two times from the remaining two memories in one
`vertical synchronization interval and transferred to an arith-
`metic unit 4, and this operation is executed with the frame
`memories changed sequentially. An arithmetic unit 4 refers
`to a look-up table on the basis of two inputted data values
`and, when the data value of the current image signal is
`greater than the data value of the previous image signal, the
`unit 4 transfers image data of a value greater than the data
`value of the current image signal to a liquid crystal display
`device 5. Thus, the step response characteristic is improved
`for the improvement of the dynamic image display quality.
`
`5
`
`1
`
`INPUT
`IMAGE
`
`
`I FIRST FRAME MEMORY a
`
`
` ARITHMETIC
`
`UNIT
`SIGNAL H
`
`
`
`
`SECOND FRAME MEMOR
`
`LIQUID CRYSTAL
`DISPLAY DEVICE
`
`
`
`LGD_000490
`
`LG Display Ex. 1008
`
`LGD_000490
`
`LG Display Ex. 1008
`
`

`

`Patent Application Publication Apr. 18, 2002 Sheet 1 0f 7
`
`US 2002/0044115 A1
`
`Fig.1
`
`1
`
`INPUT
`gI/IéffAEL
`
`
`FIRST FRAME MEMORYH ARITHMETIC
`LIQUID CRYSTAL
`
`
`SECOND FRAME MEMOR
`UNIT
`
`THIRD FRAME MEMORY
`
`D
`
`INTERVAL
`
`VERTICAL
`SYNCHRONIZATION
`
`TIME
`
`FIRST FRAME MEMORYI
`
`SECOND FRAME MEMORY2
`
`THIRD FRAME MEMORY 3
`
`WRITE
`OPERATION
`SIGNAL
`
`LGD_000491
`
`LGD_000491
`
`

`

`Patent Application Publication Apr. 18, 2002 Sheet 2 0f 7
`
`US 2002/0044115 A1
`
`Fig.3
`
`A
`
`A
`
`A
`
`A
`
`FIRST FRAME MEMORY 1
`
`READ
`OPERAHON
`QGNAL
`
`Y
`
`Y
`
`B
`
`B
`
`B
`
`SECOND FRAME MEMORY2
`
`z
`
`z
`
`z
`
`2
`
`C
`
`THIRD FRAME MEMORY3
`
`VERHCAL
`SYNCHRONEAHON
`INTERVAL
`—
`
`'HME
`
`Fig.4
`
`
`
`DATA VALUE OF
`PREVIOUS IMAGE SIGNAL
`
`
`
`
`III-“Elm
`
`
`”In-III
`
`
`
`OF CURRENT
`IMAGE SIGNAL
`
`
`
` DATA VALUE
`
`
`
`
`LGD_000492
`
`LGD_000492
`
`

`

`Patent Application Publication Apr. 18, 2002 Sheet 3 0f 7
`
`US 2002/0044115 A1
`
`Fig.5
`
`(b)
`
`RELATIVE
`INTENSITY
`
`
`
`
`
`ONE VERTICAL
`SYNCHRONIZATION
`<—_——> INTERVAL
`
`TIME
`
`Fig.6
`
`
`
`(C)
`
`RELATIVE
`INTENSITY
`
`ONE VERTICAL
`SYNCHRONIZATION
`
`<———> INTERVAL
`
`TIME
`
`Fig. 7
`
`(b)
`
`
`
`
`ONE VERTICAL
`SYNCHRONIZATION
`<——> INTERVAL
`
`(C)
`
`TIME
`
`RELATIVE
`INTENSITY
`
`LGD_000493
`
`LGD_000493
`
`

`

`Patent Application Publication Apr. 18, 2002 Sheet 4 0f 7
`
`US 2002/0044115 A1
`
`Fig.8
`1 1
`
`
`FIRST FRAME MEMORY
`
`
`II
`INPUT
`SHIAGAAEAEL
`SECOND FRAME MEMORY
`
`
`
`
`ETI
`ARILHNAIIT C
`
`
`IfillggIPAyCFSET/Iéé
`
`
`
`
`
`RELATIVE
`INTENSITY
`
`
`
`ONE VERTICAL
`SYNCH RONIZATION
`<——-> INTERVAL
`
`TIME
`
`Fig. 10
`
`ARITHMETIC
`UNIT
`
`LIQUID CRYSTAL
`DISPLAY DEVICE
`
`
`
`
`SIGNAL
`
`
`INPUT
`IMAGE
`
`
`
`
`LGD_000494
`
`LGD_000494
`
`

`

`Patent Application Publication Apr. 18, 2002 Sheet 5 0f 7
`
`US 2002/0044115 A1
`
`Fig. 1 1
`
`OPERATION
`SIGNAL
`
` WRITE
`
`VERTICAL
`SYNCHRONIZATION
`INTERVAL
`
`FIRST FIFO MEMORY 21
`
`SECOND FIFO MEMORY 22
`
`TIME
`
`Fig. 12
`
`READ
`OPERATION
`SIGNAL
`
`Z
`
`A
`
`A
`
`B
`
`B
`
`C
`
`C
`
`FIRST FIFO MEMORY21
`
`2
`
`Z
`
`A
`
`A
`
`B
`
`B
`
`C
`
`SECOND FIFO MEMORY22
`
`VERTICAL
`SYNCHRONIZATION
`INTERVAL
`
`TIME
`
`LGD_000495
`
`LGD_000495
`
`

`

`Patent Application Publication Apr. 18, 2002 Sheet 6 0f 7
`
`US 2002/0044115 A1
`
`31
`
`Fig. 13
`
`
`
`
`
`
`
`LIQUID CRYSTAL
` ARITHMETIC
`SIGNAL
`
`UNIT
`DISPLAY DEVICE
`
`
`
`THIRD FRAME MEMORY
`
`INPUT
`IMAGE
`
`FIRST FRAME MEMORY
`
` II
`
`SECOND FRAME MEMORY
`
`Fig. 14
`
`(b3)
`
`RELATIVE
`INTENSITY
`
`
`
`(b4)
`
`
`
`ONE VERTICAL
`SYNCHRONIZATION
`
`6—9 INTERVAL
`
`TIME
`
`41
`
`
`
`Fig. 15
`
`
`
`FIRST FRAME MEMORY
`
`
` II
`SIGNAL
`
`
`SECOND FRAME MEMORY
`
`
`
`ARITHMETIC
`UNIT
`
`THIRD FRAME MEMORY
`
`
`LIQUID CRYSTAL
`DISPLAY DEVICE
`
`
`
`INPUT
`IMAGE
`
`LGD_000496
`
`LGD_000496
`
`

`

`Patent Application Publication Apr. 18, 2002 Sheet 7 0f 7
`
`US 2002/0044115 A1
`
`Fig. 16
`
`RELATIVE
`INTENSITY
`
`
`
`
`
`ONE VERTICAL
`SYNCHRONIZATION
`
`INTERVAL
`
`
`TIME
`
`LGD_000497
`
`LGD_000497
`
`

`

`US 2002/0044115 A1
`
`Apr. 18, 2002
`
`LIQUID CRYSTAL DISPLAY DEVICE DRIVING
`METHOD
`
`BACKGROUND OF THE INVENTION
`
`[0001] The present invention relates to a liquid crystal
`display device driving method for improving the display
`quality of dynamic images (moving images).
`
`the liquid crystal display that
`In recent years,
`[0002]
`employs a matrix type liquid crystal display device has a
`spreading market in a variety of commercial fields as a
`display device for a television set inclusive of OA (Office
`Automation) equipment taking advantage of its features of a
`thin configuration, light weight and low consumption of
`power. According to this trend, the liquid crystal display is
`used for displaying not only characters and pictures but also
`dynamic images such as images based on a television signal
`and a video signal. However, in the present circumstances,
`the liquid crystal display cannot obtain vivid images in
`displaying dynamic images in comparison with the CRT
`(Cathode Ray Tube)
`type display. The liquid crystals
`employed in the liquid crystal display have a slower
`response speed with regard to its transmittance to the applied
`voltage and a poor charge characteristic in compliance with
`the change in permittivity of the liquid crystals and are
`accordingly unable to sufficiently respond to rapid changes
`in the image signal.
`
`In order to improve the aforementioned drawbacks
`[0003]
`with regard to the dynamic image display, National Publi-
`cation of the Translation No. No. HEI 8-500915 turns on the
`
`backlight illumination for displaying the image written in
`the liquid crystal display device only in a part of time for
`display and is provided with a dark period with the backlight
`illumination turned off in the remaining part of time. By so
`doing,
`the image is visually perceived as if it moved
`smoothly, improving the dynamic image display.
`
`[0004] The transmittance of liquid crystals changes as a
`consequence of the change in the orientation of liquid crystal
`molecules due to the written (applied) voltage. However, the
`permittivity also changes when the orientation of the liquid
`crystal molecules change, and the value of the applied
`voltage accordingly changes due to the change in the per-
`mittivity. Therefore, in order to obtain a specified transmit-
`tance, it is required to repetitively supply the voltage during
`several vertical synchronization intervals, and the liquid
`crystals are to have a step response characteristic. As a
`method for improving the reduction in the response speed of
`liquid crystals due to this step response characteristic, Japa-
`nese Patent Laid-Open Publication No. HEI 6-62355 dis-
`closes the improvement in the step response characteristic of
`liquid crystals by superimposing a difference component by
`comparison with the previous image signal.
`
`[0005] However, the aforementioned conventional method
`for improving the drawback of dynamic image display has
`the problems as follows. That is, in the case of National
`Publication of the Translation No. HEI 8-500915 in which
`
`is visually superimposed since the response speed of the
`liquid crystals is not improved, resulting in a double or triple
`vision.
`
`In the case of Japanese Patent Laid-Open Publica-
`[0006]
`tion No. HEI 6-62355 in which the component of difference
`with respect to the previous image signal is superimposed in
`repetitively supplying the voltage during several vertical
`synchronization intervals, the response characteristic of the
`liquid crystals is utterly insufficient for display within one
`vertical synchronization interval. Even if the illumination is
`darkened during a part of the period as in the case of, for
`example, Japanese Patent Publication No. HEI 8-500915,
`there is a problem that the period during which the change
`in the liquid crystals is insufficient is disadvantageously
`displayed. Moreover, it is required to increase the value of
`the voltage to be superimposed in order to make the liquid
`crystals have a rapid response, in this case the transmittance
`becomes larger than the intended transmittance. Accord-
`ingly, there arises the need for restoring the transmittance in
`the next one vertical synchronization interval, and this
`consequently leads to a reverse step response, causing a
`problem that the response characteristic is not improved.
`
`SUMMARY OF THE INVENTION
`
`[0007] Accordingly, the object of the present invention is
`to provide a liquid crystal display device driving method
`capable of improving the response characteristic of liquid
`crystals and further
`improving the display quality of
`dynamic images.
`
`there is
`In order to achieve the above object,
`[0008]
`provided a liquid crystal display device driving method for
`driving a liquid crystal display device by supplying image
`data to be written into each pixel of the liquid crystal display
`device to the liquid crystal display device a plurality of times
`in one vertical synchronization interval, comprising the step
`of:
`
`obtaining the whole image data supplied the
`[0009]
`plurality of times in one vertical synchronization
`interval on the basis of a data value of an image
`signal in a previous vertical synchronization interval
`and a data value of an image signal in a current
`vertical synchronization interval.
`
`[0010] According to the above-mentioned construction,
`the image data obtained on the basis of the data value of the
`image signal in the previous vertical synchronization inter-
`val and the data value of the image signal in the current
`vertical synchronization interval is supplied the plurality of
`times within one vertical synchronization interval and writ-
`ten into each pixel. Therefore, for example, when the data
`value of the current image signal is greater than the data
`value of the previous image signal, by supplying image data
`of a value greater than the data value of the current image
`signal
`to the liquid crystal display device,
`the response
`characteristic of the light transmittance of the liquid crystals
`is improved in comparison with the case where the image
`data of the value identical to the data value of the current
`
`the backlight illumination is turned on only in a part of time,
`there is a problem that
`the image becomes dark as a
`consequence of the reduction in illuminance of the liquid
`crystal display device due to the occurrence of a period
`during which the backlight is turned off. Moreover, there is
`another problem that the image signal of the previous frame
`
`image signal is supplied repetitively a plurality of times once
`per vertical synchronization interval. Moreover, the rise of
`the light transmittance of the liquid crystals is improved in
`comparison with the case where the image data of the value
`greater than the data value of the current image signal is
`supplied only once per vertical synchronization interval.
`
`LGD_000498
`
`LGD_000498
`
`

`

`US 2002/0044115 A1
`
`Apr. 18, 2002
`
`there is provided a liquid crystal display
`[0011] Also,
`device driving method for driving a liquid crystal display
`device by supplying image data to be written into each pixel
`of the liquid crystal display device to the liquid crystal
`display device a plurality of times in one vertical synchro-
`nization interval, comprising the step of:
`
`obtaining image data supplied at least at a first
`[0012]
`time out of the image data supplied the plurality of
`times in one vertical synchronization interval on the
`basis of a data value of an image signal in a previous
`vertical synchronization interval and a data value of
`an image signal in a current vertical synchronization
`interval.
`
`[0013] According to the above-mentioned construction,
`the image data supplied at least at a first time out of the
`image data supplied the plurality of times in one vertical
`synchronization interval to the liquid crystal display device
`is obtained on the basis of the data value of the image signal
`in the previous vertical synchronization interval and the data
`value of the image signal in the current vertical synchroni-
`zation interval. Therefore, for example, when the data value
`of the current image signal is greater than the data value of
`the previous image signal, by supplying image data of a
`value greater than the data value of the current image signal
`at a first
`time,
`the response characteristic of the light
`transmittance of the liquid crystals is improved in compari-
`son with the case where the image data of the value identical
`to the data value of the current image signal is supplied
`repetitively a plurality of times in one vertical synchroniza-
`tion interval or in the case where the image data of the value
`greater than the data value of the current image signal is
`supplied only once per vertical synchronization interval.
`
`In one embodiment of the present invention, the
`[0014]
`image data supplied at second and subsequent times out of
`the image data supplied the plurality of times in one vertical
`synchronization interval is provided by image data that has
`a value identical to the data value of the image signal in the
`vertical synchronization interval.
`
`the image data
`[0015] According to the embodiment,
`supplied at second and subsequent times out of the image
`data supplied the plurality of times in one vertical synchro-
`nization interval is provided by image data that has a value
`identical to the data value of the image signal in the vertical
`synchronization interval. Therefore, by appropriately setting
`the image data supplied at a first time,
`the time for the
`attainment of the target light transmittance of the liquid
`crystals is shortened. Therefore, the dynamic image display
`quality is further improved.
`
`In one embodiment of the present invention, at
`[0016]
`least one piece of image data out of the image data supplied
`at second and subsequent
`times out of the image data
`supplied the plurality of times in one vertical synchroniza-
`tion interval is provided by image data that has a specified
`value intermediate between the data value of the image
`signal in the previous vertical synchronization interval and
`the data value of the image signal in the current vertical
`synchronization interval.
`
`by image data that has a specified value intermediate
`between the data value of the image signal in the previous
`vertical synchronization interval and the data value of the
`image signal in the current vertical synchronization interval.
`Therefore, by appropriately setting the image data supplied
`at a first time and the image data supplied at second and
`subsequent times, the rise of the light transmittance of the
`liquid crystals is improved, and the target light transmittance
`is attained within one vertical synchronization interval.
`Furthermore,
`the quantity of light integrated timewise is
`perceived equal to the quantity of light with the target light
`transmittance in one vertical synchronization interval, and
`therefore, the light transmittance is improved.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`invention will become more fully
`[0018] The present
`understood from the detailed description given hereinbelow
`and the accompanying drawings which are given by way of
`illustration only, and thus are not limitative of the present
`invention, and wherein:
`
`[0019] FIG. 1 is a block diagram of a drive circuit for
`materializing the liquid crystal display device driving
`method of the present invention;
`
`[0020] FIG. 2 is a graph showing the write operation
`signals of the frame memories of FIG. 1;
`
`[0021] FIG. 3 is a graph showing the read operation
`signals of the frame memories of FIG. 1;
`
`[0022] FIG. 4 is a diagram showing a look-up table of one
`example;
`
`[0023] FIG. 5 is a graph showing the data value of an
`image signal inputted to the liquid crystal display device of
`FIG. 1 and the change of light transmittance dependent on
`time;
`
`[0024] FIG. 6 is a graph showing the data value and the
`change of light transmittance dependent on time when an
`identical data value is repetitively inputted three times once
`per vertical synchronization interval;
`
`[0025] FIG. 7 is a graph showing the data value and the
`change of light transmittance dependent on time when a data
`value is inputted once per vertical synchronization interval;
`
`[0026] FIG. 8 is a block diagram of a drive circuit
`different from that of FIG. 1;
`
`[0027] FIG. 9 is a graph showing the data value of an
`image signal inputted to the liquid crystal display device of
`FIG. 8 and the change of light transmittance dependent on
`time;
`
`[0028] FIG. 10 is a block diagram of a drive circuit
`different from those of FIGS. 1 and 8;
`
`[0029] FIG. 11 is a graph showing the write operation
`signals of the FIFO memories of FIG. 10;
`
`[0030] FIG. 12 is a graph showing the read operation
`signals of the FIFO memories of FIG. 10;
`
`[0031] FIG. 13 is a block diagram of a drive circuit
`different from those of FIGS. 1, 8 and 10;
`
`[0017] According to the embodiment, at least one piece of
`image data out of the image data supplied at second and
`subsequent times out of the image data supplied the plurality
`of times in one vertical synchronization interval is provided
`
`[0032] FIG. 14 is a graph showing the data value of an
`image signal inputted to the liquid crystal display device of
`FIG. 13 and the change of light transmittance dependent on
`time;
`
`LGD_000499
`
`LGD_000499
`
`

`

`US 2002/0044115 A1
`
`Apr. 18, 2002
`
`[0033] FIG. 15 is a block diagram of a drive circuit
`different from those of FIGS. 1, 8, 10 and 13; and
`
`[0034] FIG. 16 is a graph showing the data value of an
`image signal inputted to the liquid crystal display device of
`FIG. 15 and the change of light transmittance dependent on
`time.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`[0035] The present invention will be described in detail
`below on the basis of the embodiments thereof shown in the
`
`drawings.
`
`First Embodiment
`
`[0036] FIG. 1 is a block diagram of a drive circuit for
`materializing the liquid crystal display device driving
`method of the present embodiment. Digital image signals for
`R, G and B of pixels sequentially read from video equipment
`or the like are inputted as input image signals to a first frame
`memory 1, a second frame memory 2 and a third frame
`memory 3. FIG. 2 shows the write operation signals of the
`frame memories 1, 2 and 3. FIG. 3 shows the read operation
`signals of the frame memories 1, 2 and 3. In FIGS. 2 and
`3, the reference characters “A”, “B”, “C”, “D”, “Y” and “Z”
`show the image data written in the frame memories 1, 2 and
`3.
`
`In the present embodiment, as is apparent from
`[0037]
`FIGS. 2 and 3, while the image data inputted to any one of
`the first frame memory 1, the second frame memory 2 and
`the third frame memory 3 is being written, image data are
`read repetitively two times in one vertical synchronization
`interval from the remaining two memories. When one ver-
`tical synchronization interval of the inputted image signal
`thus ends, the first frame memory 1 in which image data A
`has been written becomes a read frame memory in the next
`one vertical synchronization interval, and the next image
`data B is written in the different second frame memory 2.
`Subsequently, this operation will be sequentially repeated,
`consistently, with one frame memory used for image data
`write and with the remaining two frame memories used for
`image data read. Thus, the two pieces of image data read
`from the two frame memories are transferred to an arith-
`metic unit 4.
`
`[0038] The arithmetic unit 4, which has a look-up table,
`refers to the look-up table on the basis of the data values
`(voltage values) of the image signals inputted from the two
`frame memories and transfers an image signal constituted of
`the obtained data value (voltage value) to a liquid crystal
`display device 5. It is to be noted that the voltage of the data
`value is applied to the pixel electrode (not shown) of the
`desired pixel by the image signal thus transferred to the
`liquid crystal display device 5 although no detailed descrip-
`tion is provided. Then, the orientation of the liquid crystal
`molecules is changed by the applied voltage to change the
`light transmittance, displaying the pixel.
`
`[0039] FIG. 4 shows one example of the look-up table. As
`for this look-up table, in a position of intersection of the data
`value of the previous image signal and the data value of the
`current image signal, a data value of a value greater than the
`data value of the current image signal is written when the
`data value of the current image signal is greater than the data
`
`value of the previous image signal, a data value of a value
`smaller than the data value of the current image signal is
`written when the data value of the current image signal is
`smaller than the data value of the previous image signal, and
`the data value of the current image signal is written when the
`data value of the previous image signal and the data value of
`the current image signal are equal to each other.
`
`[0040] Therefore, upon receiving image data A from the
`first frame memory 1 and image data Z from the third frame
`memory 3, the arithmetic unit 4 transfers the data value of
`the value greater than the data value A of the current image
`signal to the liquid crystal display device 5 when the data
`value A of the current image signal is greater than the data
`value Z of the previous image signal. When the data value
`A of the current image signal is smaller than the data value
`Z of the previous image signal, the data value of the value
`smaller than the data value A of the current image signal is
`transferred to the liquid crystal display device 5. When the
`data value Z of the previous image signal and the data value
`Aof the current image signal are equal to each other, the data
`value A of the current image signal is transferred to the
`liquid crystal display device 5.
`
`[0041] FIG. 5 shows the data value (voltage value) of the
`image signal that is inputted to the liquid crystal display
`device 5 and applied to the pixel electrode of the desired
`pixel and the change of light transmittance dependent on
`time. It is to be noted that the vertical axis represents a
`relative intensity. In FIG. 5,
`the reference character (a)
`represents a (target) data value to be written, the reference
`character (b) represents the data value inputted from the
`arithmetic unit 4, and the reference character (c) represents
`the light transmittance of the display pixel in the liquid
`crystal display device 5. When the image signal inputted to
`the arithmetic unit 4 changes from small image data to large
`image data, as shown in FIG. 5, the data value (b) of the
`value greater than the data value (a) to be written is inputted
`to the liquid crystal display device 5 repetitively two times
`in one vertical synchronization interval. In the above case, it
`can be understood that the step response of the light trans-
`mittance (c) of the display pixel is improved in comparison
`with the case where the data value (b) of the same value as
`the target data value (a) is repetitively inputted three times
`once per vertical synchronization interval, as shown in FIG.
`6.
`
`[0042] FIG. 7 shows quite the same data values (a) and (b)
`as those shown in FIG. 5, where the frequency of inputting
`of the data value (b) is one. In this case, it can be understood
`that the inclination of the rise of the light transmittance (c)
`of the display pixel is worse than in the case shown in FIG.
`5, and this indicates that the repetitive input of the data value
`(b) is effective for the improvement of the rise of the light
`transmittance (c) of the liquid crystal display device 5.
`
`[0043] As described above, the present embodiment has
`the first, second and third frame memories 1, 2 and 3 in
`which the input image signal is written. While the image
`data is written into any one of the frame memories, image
`data are read repetitively two times in one vertical synchro-
`nization interval from the remaining two frame memories
`and transferred to the arithmetic unit 4. This operation is
`executed with the frame memories sequentially changed.
`Then, the arithmetic unit 4 refers to the look-up table on the
`basis of the data values of the image signals inputted from
`
`LGD_000500
`
`LGD_000500
`
`

`

`US 2002/0044115 A1
`
`Apr. 18, 2002
`
`the two input frame memories and transfers to the liquid
`crystal display device 5, for example, the data value of the
`value greater than the data value A of the current image
`signal when the data value A of the current image signal
`from the first frame memory 1 is greater than the data value
`Z of the previous image signal from the third frame memory
`3, the data value smaller than the data value Awhen the data
`value A is smaller than the data value Z and the data value
`
`A of the current image signal when the data value A is equal
`to the data value Z.
`
`[0044] Therefore, when the image signal inputted to the
`arithmetic unit 4 changes from small image data to large
`image data, as shown in FIG. 5, the data value (b) of the
`value greater than the target data value (a) is inputted to the
`liquid crystal display device 5 repetitively two times in one
`vertical synchronization interval. As a result, the response
`characteristic of the light transmittance (c) of the liquid
`crystals is improved in comparison with the case where the
`data value (b) of the same value as the target data value (a)
`is repetitively inputted three times once per vertical syn-
`chronization interval, as shown in FIG. 6. Moreover, the rise
`of the light
`transmittance (c) of the liquid crystals is
`improved in comparison with the case where the frequency
`of inputting of the data value (b) is one, as show in FIG. 7.
`
`the
`the present embodiment enables
`is,
`[0045] That
`improvement of the response characteristic of the liquid
`crystal display device 5, the attainment of the transmittance
`corresponding to the input image signal in a short period, the
`achievement of high-speed image display and the improve-
`ment of the dynamic image display quality.
`
`[0046] Although the read from the frame memories 1, 2
`and 3 is executed repetitively two times in one vertical
`synchronization interval of the image input signal in the
`aforementioned embodiment, the frequency of repetition is
`not limited to two. The step response characteristic of the
`liquid crystal display device 5 is more improved as the
`frequency of repetition increases, enabling higher-speed
`image display. However, in the above case, it is required to
`improve the abilities of the liquid crystal drive elements and
`the like so that the liquid crystals are charged with electric
`charges in a short period.
`
`[0047] Moreover, in the aforementioned embodiment, the
`arithmetic unit 4 adopts the look-up table system in which
`the data value outputted to the liquid crystal display device
`5 is obtained by referring to the look-up table on the basis
`of the two pieces of image data transferred from the two
`frame memories. However, it is not always required to adopt
`the look-up table system. According to another method, an
`arithmetic circuit
`for executing the operation of,
`for
`example, “A+(A—Z)><ot” or the like based on the data value
`A of the current image signal and the data value Z of the
`previous image signal is mounted on the arithmetic unit.
`Then, an output from the arithmetic circuit may be outputted
`as a new image signal to the liquid crystal display device 5.
`
`Second Embodiment
`
`[0048] FIG. 8 is a block diagram of a drive circuit for
`materializing the liquid crystal display device driving
`method of the present embodiment. A first frame memory
`11, a second frame memory 12, a third frame memory 13 and
`a liquid crystal display device 15 have the same construc-
`tions as those of the first frame memory 1, the second frame
`
`memory 2, the third frame memory 3 and the liquid crystal
`display device 5, respectively, shown in FIG. 1.
`
`[0049] The arithmetic unit 4 of the first embodiment
`outputs the data value obtained by referring to the look-up
`table two times out of the data values outputted two times in
`one vertical synchronization interval. In contrast to this, the
`arithmetic unit 14 of the present embodiment outputs a data
`value obtained by referring to the look-up table with regard
`to a first-time data value out of the data values outputted two
`times in one vertical synchronization interval, similarly to
`the first embodiment. However, with regard to a second-time
`data value, the data value of the current image signal out of
`the image signals inputted from the two frame memories is
`outputted.
`
`[0050] FIG. 9 shows the data value of the image signal
`inputted to the liquid crystal display device 15 and the
`change of light transmittance dependent on time. In FIG. 9,
`the reference character (a) represents a target data value, the
`reference character (b) represents a data value inputted from
`the arithmetic unit 14, and the reference character (c)
`represents the light transmittance of the display pixel. When
`the image signal inputted to the arithmetic unit 14 changes
`from small image data to large image data, as shown in FIG.
`9, a data value (b1) of a value greater than the target data
`value (a) is inputted to the liquid crystal display device 15
`once in the first half of one vertical synchronization interval.
`Next, a data value (b2) of the current image signal, i.e., the
`target data value (a) is inputted once in the latter half of the
`same vertical synchronization interval.
`
`In the above case, the response characteristic of the
`[0051]
`light transmittance (c) can be improved in comparison with
`the case where the data value (b) of the same value as the
`target data value (a) is repetitively inputted three times once
`per vertical synchronization interval, as shown in FIG. 6.
`Moreover,
`the rise of the light transmittance (c) can be
`improved in comparison with the case where the frequency
`of inputting of the data value (b) is one, as shown in FIG.
`7. Furthermore, as shown in FIG. 9, by setting the data value
`(b1) inputted at a first time to an appropriate value slightly
`higher than the data value (b) inputted at a first time in the
`first embodiment shown in FIG. 5, the time for the attain-
`ment of the target data value (a) can be made shorter than in
`the case of the first embodiment.
`
`[0052] As described above, in the present embodiment, the
`arithmetic unit 14 refers to the look-up table on the basis of
`the data values of the image signals inputted from the two
`input frame memories and outputs the first-time data value
`in the first half of one vertical synchronization interval to the
`liquid crystal display device 15. On the other hand, with
`regard to the second-time data value in the latter half of the
`same vertical synchronization interval, the data value of the
`current image signal out of the data values inputted from the
`two input frame memories is outputted to the liquid crystal
`display device 15.
`
`[0053] Therefore, by setting the data value (b1) inputted at
`a first time to an appropriate value slightly higher than the
`data value (b) inputted at a first time in the first embodiment,
`the time for the attainment of the target data value (a) can be
`made shorter than in the case of the first embodiment, and
`the dynamic image display quality can further be improved.
`
`It is to be noted that the frequency of repetition of
`[0054]
`read from each of the frame memories 11 through 13 is, of
`
`LGD_000501
`
`LGD_000501
`
`

`

`US 2002/0044115 A1
`
`Apr. 18, 2002
`
`course, not limited to two in the case of the present embodi-
`ment, similarly to the case of the first embodiment. The step
`response characteristic of the liquid crystal display device 15
`is more improved as the frequency of repetition increases,
`enabling higher-speed image display. However, in the above
`case,
`it is required to improve the abilities of the liquid
`crystal drive elements and the like so that the liquid crystals
`are charged with electric charges in a short period. The
`operation of the arithmetic unit 14 is not required to conform
`to the look-up table system. An arithmetic circuit for execut-
`ing the operation of, for example, “A+(A—Z)><ot” or the like
`based on the data value A of the current image signal and the
`data value Z of the previous image signal may be mounted
`on the arithmetic unit.
`
`[0055] Furthermore, when the display operation is
`repeated two times in one vertical synchronization interval,
`a FIFO (First-In First-Out) memory whose input a