1
`
`Inter Partes Review of RE 43,707
`IPR 2014-00778
`Exhibit 1028
`
`

`

`(19)
`
`JAPANESE PATENT OFFICE (JP)
`(12) Published Patent Application (A)
`(11) Patent Application Publication (Kokai) No. 2000-56737
`(P2000-56737A)
`(43) Publication Date: February 25, 2000
`
`
`(51) Int. Cl.7:
`
`
`
`G09G 3/36
`
`G02F 1/133
`
`H04N 5/66
`
`
`Classification
`Codes
`
`505
`102
`
`FI
`
`G09G 3/36
`G02F 1/133
`H04N 5/66
`
`Theme Codes
`
`(Reference)
`
` 2H093
`
` 5C006
`505
`102B 5C058
`
`Request for Examination: Not requested
`
`Number of Claims: 4
`OL (Total of 9 pages [in original])
`Patent App. No. H10-221901
`August 5, 1998
`000003078
`Toshiba Corp.
`72 Horikawa-cho, Saiwai-ku
`Kawasaki, Kanagawa Prefecture
`Hiroaki Serita
`Toshiba Fukaya Works
`1-9-2 Hatara-cho, Fukaya, Saitama Prefecture
`100076233
`Susumu Ito, Patent Attorney
`
`(21) Application No.:
`(22) Filing Date:
`(71) Applicant:
`
`
`
`(72) Inventor:
`
`
`(74) Agent:
`
`
`(54)
`
`[Title of the Invention]
`
`Continued on last page
`Luminance Irregularity Correction Device of a
`Liquid Crystal Panel
`
`[Abstract]
`(57)
`[Problem]
`To provide a luminance irregularity correction device of a liquid crystal
`panel that is able to suppress the occurrence of luminance irregularity due to liquid crystal
`layer thickness irregularity (gap irregularity) of a liquid crystal panel.
`[Means for Solving] A correction circuit 50 for generating correction signals to correct
`luminance irregularity due to liquid crystal layer thickness irregularity of a liquid crystal
`panel is provided. With this correction circuit 50, gradually changing correction signals
`are generated such that the amplitude grows larger the more toward the center of the
`horizontal direction of the liquid crystal panel, and grows larger the more toward the
`
`2
`
`

`

`center of the vertical direction when this signal is viewed in the vertical direction. After a
`correction signal from the correction circuit 50 is added to the input video signal by the
`adding means 51, signal processing for doing alternating current drive or the like is
`performed, and this is supplied to the liquid crystal panel unit 10. In this way, by using a
`constitution for which the correction signal is superimposed on the input video signal of
`the liquid crystal panel, it is possible to correct luminance irregularity.
`
`
`
`
`
`
`
`2
`
`3
`
`

`

`
`[Claims]
`[Claim 1]
`
`A luminance irregularity correction device of a liquid crystal panel, comprising:
`
`a liquid crystal panel for displaying video based on input video signals,
`
`a timing circuit for generating the timing signals necessary for performing signal
`processing and display processing for displaying the video on the liquid crystal panel,
`
`a correction circuit that is a circuit for generating correction signals to correct
`luminance irregularity due to liquid crystal layer thickness irregularity of the liquid crystal
`panel, that generates gradually changing correction signals such that the amplitude
`becomes larger the more to the center of the horizontal direction of the liquid crystal
`panel, and the amplitude becomes larger more to the center in the vertical direction when
`this signal is viewed in the vertical direction, and
`
`an adding means for adding the correction signal from the correction circuit to the
`input video signal.
`[Claim 2]
`
`A luminance irregularity correction device of a liquid crystal panel, comprising:
`
`a liquid crystal panel for displaying video based on input video signals,
`
`a timing circuit for generating the timing signals necessary for performing signal
`processing and display processing for displaying the video on the liquid crystal panel,
`
`a correction circuit that is a circuit for generating correction signals to correct
`luminance irregularity due to liquid crystal layer thickness irregularity of the liquid crystal
`panel, that generates gradually changing correction signals such that the amplitude
`becomes larger the more to the center of the horizontal direction of the liquid crystal
`panel, and the amplitude becomes larger more to the center in the vertical direction when
`this signal is viewed in the vertical direction, and
`
`an adding means for adding the correction signal from the correction circuit to the
`pixel common electrode voltage (common voltage) of the liquid crystal panel.
`[Claim 3]
`
`3
`
`4
`
`

`

`The luminance irregularity correction device of a liquid crystal panel of claim 1,
`
`wherein when the liquid crystal panel is driven by inverse polarity drive type video
`signals for each horizontal period, at the stage before signal processing that does polarity
`inversion of the input video signal for each horizontal period, a correction signal from the
`correction circuit is added to the input video signal.
`[Claim 4]
`
`The luminance irregularity correction device of a liquid crystal panel of claim 2,
`wherein when the liquid crystal panel is driven by a inverse polarity drive type video
`signal for each horizontal period, polarity inversion is performed for each horizontal
`period also on the correction signals added from the correction circuit to the pixel
`common electrode voltage (common voltage) of the liquid crystal panel.
`[Detailed Description of the Invention]
`[0001]
`[Technical Field of the Invention]
`
`The present invention relates to a luminance irregularity correction device of a
`liquid crystal panel for correcting luminance irregularity due to liquid crystal layer
`thickness irregularity (gap irregularity) of a liquid crystal panel.
`[0002]
`[Prior Art]
`
`In recent years, display devices that use liquid crystal have become popular. For
`example, pocket liquid crystal television receivers, laptop computer display devices,
`liquid crystal projectors and the like have been commercialized.
`[0003]
`
`In particular, along with demand for display devices that have a large screen but
`are compact and light, there has been a great deal of development of liquid crystal
`projectors using liquid crystal panels. Since it is easy to make the screen large with liquid
`crystal projectors, there is also anticipation for these for high definition televisions. With
`liquid crystal projectors, as is well known, it is possible to use a liquid crystal panel as a
`light valve, and display an image by changing the transmittance of the light from the light
`
`4
`
`5
`
`

`

`source according to the video signals, and to expand this image and display it on the
`screen using a projecting lens optical system or the like.
`[0004]
`
`However, for liquid crystal projectors, there is a single panel type that uses one
`liquid crystal panel, and a three panel type that uses three liquid crystal panels. The single
`panel type has a simple structure, and it is possible to reduce costs. However, when
`attempting to colorize by using a color filter on the single panel type, the resolution
`worsens. Because of this, currently, the three panel type is mainstream. With a three panel
`type liquid crystal projector, an active matrix type monochromatic liquid crystal panel is
`used that has a switching element such as a thin film transistor (hereafter referred to as
`TFT) or the like for each pixel.
`[0005]
`
`With the three panel type liquid crystal projector, the constitution is such that the
`light from the light source is split into the three primary colors of R (red), G (green), and
`B (blue), made incident on liquid crystal panels for each color. The three primary colors
`of light that passed through the liquid crystal panels are again synthesized to form a color
`image.
`[0006]
`
`Recently, there has been focus on a liquid crystal data projector as a personal
`computer presentation tool, and for this kind of liquid crystal data projector, when taking
`into consideration adaptation to various use environments, the three panel type structure
`described above was used in light of the points of screen brightness and high resolution.
`[0007]
`
`Normally, with the liquid crystal panel used for the liquid crystal data projector
`noted above, to accurately reproduce video based on input video signals, a liquid crystal
`drive circuit is used that has functions such as amplifying the input video signal up to the
`voltage necessary to drive the liquid crystal panel, performing AC drive to lengthen the
`product life of the liquid crystal and the like.
`[0008]
`
`5
`
`6
`
`

`

`FIG. 9 is a block diagram showing an example of a liquid crystal drive circuit that
`
`can be used for this kind of conventional three panel type liquid crystal data projector.
`[0009]
`
`As shown in FIG. 9, the liquid crystal data projector is equipped, for example,
`with three active matrix type liquid crystal panel units 10, 20, and 30. Each liquid crystal
`panel unit 10, 20, and 30 respectively contains a liquid crystal panel, a horizontal drive
`unit (sample hold circuit and horizontal drive circuit), and a vertical drive unit (vertical
`drive circuit). The liquid crystal panel unit 10 forms red (R) images, the liquid crystal
`panel unit 20 forms green (G) images, and the liquid crystal panel unit 30 forms blue (B)
`images. R color video signals (hereafter R signals) are supplied to the liquid crystal panel
`unit 10 from an input terminal 11, a video processing circuit 12, and an alternating circuit
`13, G color video signals (G signals) are supplied to the liquid crystal panel unit 20 from
`an input terminal 21, a video processing circuit 22, and an alternating circuit 23, and B
`color video signals (B signals) are supplied to the liquid crystal panel unit 30 from an
`input terminal 31, a video processing circuit 32, and an alternating circuit 33. Also, the
`clocks and various timing pulses required for displaying each color video signal are
`supplied from a timing circuit 40.
`[0010]
`
`Video processing circuits 12, 22, and 32 are circuits for respectively doing R, G,
`and B input video signal amplification, gamma correction, and clamp processing. The
`alternating circuits 13, 23, and 33 respectively perform polarity inversion for both the
`alternating current and direct current voltage of the signal for each line (specifically, one
`horizontal period) for the R, G, and B video signals. Specifically, each color video signal
`is polarity inverted with a focus on each direct current level E1, E2, and E3 of pixel
`common electrodes (common terminals) 10a, 20a, and 30a of each liquid crystal panel,
`kept, for example, at +4 V in comparison to the 0 V of the substrate. By doing this,
`changes in the average direct current level by each color video signal for each liquid
`crystal panel are cancelled, and driving is always done at a fixed direct current level. The
`timing circuit 40 generates switching pulses fH of the alternating circuits 13, 23, and 33
`
`6
`
`7
`
`

`

`and timing signals for driving the liquid crystal panel units 10, 20, and 30 from the
`horizontal (H) and vertical (V) synchronization signals input from an input terminal 41.
`[0011]
`
`However, the liquid crystal panel has a structure like that shown in FIG. 10, and
`liquid crystal 100 is sealed between two glass substrates 101 and 102. Seen from a plan
`view, it has a structure like that shown in FIG. 11. It includes a pixel constituted by liquid
`crystal, a thin film transistor (TFT) such as a field effect transistor (FET) for supplying
`sample hold pixel signals from the horizontal drive unit to this pixel, a source line for
`supplying sample-held pixel signals from the horizontal drive unit to this TFT source, and
`a gate line for supplying scanning signals from the vertical drive unit to the TFT gate.
`[0012]
`
`With the liquid crystal structure shown in FIG. 10, if the thickness of the liquid
`crystal is not constant, this will appear as luminance irregularity. The manifestation of the
`luminance irregularity is as shown in FIG. 12 and FIG. 13.
`[0013]
`
`FIG. 12 shows the changes in brightness of the liquid crystal layer, with the input
`voltage shown on the horizontal axis and the brightness (luminance) shown on the
`vertical axis. With the input voltage of the vertical axis as the common voltage, the input
`voltage is changed with this common voltage as the maximum value. Even when the
`same input voltage is supplied to the source line, the brightness differs according to the
`thickness of the liquid crystal layer. When the thickness of the liquid crystal layer is thick,
`the brightness is high, and when the thickness of the liquid crystal layer is thin, the
`brightness is low. This is called luminance irregularity due to gap irregularity.
`[0014]
`
`To eliminate this luminance irregularity, typically spherical supports (called pearl
`beads) of similar diameter to the thickness of the liquid crystal are mixed in the liquid
`crystal to make the thickness of the liquid crystal constant. However, due to non-selection
`of the location of the pearl beads, they also exist on the pixel, so there is the disadvantage
`that the existence of the pearl beads is visible. In particular, with small scale liquid crystal
`panels, the pixel (electrode) size is about 20 µm x 20 µm, and the diameter of the pearl
`
`7
`
`8
`
`

`

`beads is about 5 µm, so the size of the pearl beads in relation to the pixel (electrode) is
`too large and the pearl beads have to be omitted. This omitting results in structural
`deformation of the liquid crystal panel, and as shown in FIG. 13, the closer to the screen
`center the liquid crystal panel is, the easier it is to have dents (or bulges), and there is the
`problem that this appeared as dark (or bright) luminance irregularity the closer to the
`screen center.
`[0015]
`[Problems the Invention Attempts to Solve]
`
`As described above, with a small scale liquid crystal panel, since it is necessary to
`omit supports (pearl beads), there was the problem that luminance irregularity occurred
`based on structural deformations of the liquid crystal panel.
`[0016]
`
`In light of that, the present invention, taking into consideration the problems noted
`above, has an object to provide a luminance irregularity correction device of a liquid
`crystal panel that is able to suppress the occurrence of luminance irregularity due to liquid
`crystal layer thickness irregularity (gap irregularity) of a liquid crystal panel.
`[0017]
`[Means to Solve the Problems]
`
`The luminance irregularity correction device of a liquid crystal panel of the
`invention according to claim 1 is equipped with a liquid crystal panel for displaying video
`based on input video signals, a timing circuit for generating the timing signals necessary
`for performing signal processing and display processing for displaying the video on the
`liquid crystal panel, a correction circuit that is a circuit for generating correction signals
`to correct luminance irregularity due to liquid crystal layer thickness irregularity of the
`liquid crystal panel, that generates gradually changing correction signals such that the
`amplitude becomes larger the more to the center of the horizontal direction of the liquid
`crystal panel, and the amplitude becomes larger more to the center in the vertical
`direction when this signal is viewed in the vertical direction, and adding means for adding
`the correction signal to the input video signal from the correction circuit.
`[0018]
`
`8
`
`9
`
`

`

`With the invention of claim 1, using a constitution with a correction signal
`
`superimposed on the input video signal of the liquid crystal panel, it is possible to correct
`luminance irregularity.
`[0019]
`
`The luminance irregularity correction device of a liquid crystal panel of the
`invention according to claim 2 is equipped with a liquid crystal panel for displaying video
`based on input video signals, a timing circuit for generating the timing signals necessary
`for performing signal processing and display processing for displaying the video on the
`liquid crystal panel, a correction circuit that is a circuit for generating correction signals
`to correct luminance irregularity due to liquid crystal layer thickness irregularity of the
`liquid crystal panel, that generates gradually changing correction signals such that the
`amplitude becomes larger the more to the center of the horizontal direction of the liquid
`crystal panel, and the amplitude becomes larger more to the center in the vertical
`direction when this signal is viewed in the vertical direction, and an adding means for
`adding the correction signal from the correction circuit to the pixel common electrode
`voltage (common voltage) of the liquid crystal panel.
`[0020]
`
`With the invention of claim 2, using a constitution with a correction signal
`superimposed on the common voltage supplied to the pixel common electrode of the
`liquid crystal panel, it is possible to correct luminance irregularity.
`[0021]
`
`For the invention according to claim 3, with the luminance irregularity correction
`device of a liquid crystal panel of claim 1, when the liquid crystal panel is driven by
`polarity inversion drive type video signals for each horizontal period, at the stage before
`signal processing that does polarity inversion of the input video signal for each horizontal
`period, a correction signal from the correction circuit is added to the input video signal.
`[0022]
`
`For the invention according to claim 4, with the luminance irregularity correction
`device of a liquid crystal panel of claim 2, when the liquid crystal panel is driven by a
`polarity inversion drive type video signal for each horizontal period, polarity inversion is
`
`9
`
`10
`
`

`

`performed for each horizontal period also on the correction signals added from the
`correction circuit to the pixel common electrode voltage (common voltage) of the liquid
`crystal panel.
`[0023]
`[Embodiments of the Invention]
`
`We will describe an embodiment of the present invention while referring to the
`drawings. FIG. 1 shows a block diagram of the luminance irregularity correction device
`of a liquid crystal panel of an embodiment of the present invention. With the liquid
`crystal drive circuit used for the three panel type liquid crystal data projector, as shown in
`FIG. 9, three drive circuit systems, for R, G, and B, are required as shown in FIG. 9, but
`since the R, G, and B drive circuit system have the same constitution, to abbreviate the
`description, with this embodiment, we will describe only the R liquid crystal drive circuit
`system.
`[0024]
`
`With this embodiment, the point that differs from the prior art example of FIG. 9
`is that the constitution has an adder 51 and a correction circuit 50 provided between the
`video processing circuit 12 and the alternating circuit 13, and the constitution is such that
`correction signals are added from the correction circuit 50 to video signals supplied to
`one of the input terminals of the adder 51.
`[0025]
`
`The R video signal input to the input terminal 11 is supplied to one input terminal
`of the adder 51 via the video processing circuit 12. The video processing circuit 12 is a
`circuit for doing amplification, gamma correction, and clamp processing of the R input
`video signal. Correction signals from the correction circuit 50 described later are made to
`be supplied to the other input terminal of the adder 51.
`[0026]
`
`The correction circuit 50 is a circuit for generating correction signals to correct
`luminance irregularity due to liquid crystal panel thickness irregularity of the liquid
`crystal panel unit 10, and generates gradually changing correction signals such that the
`amplitude becomes bigger the closer to the center of the horizontal direction of the liquid
`
`10
`
`11
`
`

`

`crystal panel, and the amplitude becomes bigger the closer to the center in the vertical
`direction when this signal is viewed in the vertical direction.
`[0027]
`
`With the adder 51, the correction signal is added to the video-processed input
`video signal as shown in FIG. 2, and the video signal to which this correction signal has
`been added is made to be input to the alternating circuit 13.
`[0028]
`
`The alternating circuit 13 performs polarity inversion for both the alternating
`current and direct current voltage of the video signal corrected for each horizontal period
`for the R video signal, and performs alternating current drive of the liquid crystal.
`Specifically, the corrected video signal is polarity inverted in relation to the direct current
`level E1 of the common electrode 10a of the liquid crystal panel, kept, for example, at +4
`V in comparison to the 0 V of the substrate. The polarity inversion for each horizontal
`period with the alternating circuit 13 is performed using the switching pulse fH from the
`timing circuit 13. Then, the video signal output from the alternating circuit 13 that was
`polarity inverted for each horizontal period is input to the liquid crystal panel unit 10.
`[0029]
`
`The liquid crystal panel unit 10 is constituted from a sample hold circuit that
`inputs and does sample holding of signals from the R alternating circuit 13 polarity
`inverted for each horizontal period, a horizontal driver circuit that amplifies the sample
`held circuit to the voltage necessary to drive the liquid crystal panel, and supplies that to
`the signal line (source line) of each pixel of the liquid crystal panel, and a liquid crystal
`panel that forms the R video, and among the three primary color RGB signals, the R
`video signals are supplied from the R alternating circuit 13 to this liquid crystal panel unit
`10. Also, the clocks and timing pulses required to display output signals from this R
`alternating circuit 13 are supplied from the timing circuit 40.
`[0030]
`
`The timing circuit 40 generates switching pulses fH to the alternating circuit 13
`and the clocks and timing pulses for driving the liquid crystal panel 10 from the
`horizontal (H) and vertical (V) synchronization signals input from the input terminal 41,
`
`11
`
`12
`
`

`

`and meanwhile, generates the timing signals for matching the timing of the correction
`signal generated by the correction circuit 50 to the video period of the input video signal.
`[0031]
`
`FIG. 3 shows an example of the constitution of the alternating circuit 13 noted
`above. The video signal to which the correction signal from the adder 51 has been added
`is supplied to inverting amp Q1 and non-inverting amp Q2, and two types of video
`signals, positive polarity and negative polarity, are formed by the inverting amp Q1 and
`the non-inverting amp Q2. These formed video signals are supplied to the input terminals
`a and b corresponding to a switching means SW. Then, the switching means SW switches
`the input terminals a and b for each horizontal period based on the switching signal fH
`supplied from the timing circuit 40, and by doing this, the output of the output terminal c
`becomes a video signal switched to positive polarity and negative polarity for each
`horizontal period. In other words, it is possible to obtain a video signal corresponding to
`the 1H polarity inversion drive method of the liquid crystal panel unit 10.
`[0032]
`
`Next, we will describe the operation of the device of the constitution noted above
`while referring to FIG. 4. In FIG. 4, (a) is the input video signal of the input terminal 11,
`(b) is the correction signal from the correction circuit 50, (c) is the addition output for
`which the correction signal of (b) is added to the signal for which the signal of (a) was
`amplified or the like, (d) is two types of video signals, positive polarity and negative
`polarity, respectively generated by the inverting amp Q1 and the non-inverting amp Q2
`with the alternating circuit 13, (e) is the switching pulse fH of each horizontal period
`from the timing circuit 40, and (f) respectively shows the alternating output for which the
`two types of video signal Q1 and Q2 of (d) were switched using the switching pulse fH of
`(e) by the switching means SW.
`[0033]
`
`The input video signal (a) undergoes video processing such as amplification or the
`like by the video processing circuit 12. With the correction circuit 50, the correction
`signal (b) is generated for each horizontal period based on the horizontal and vertical
`synchronization signals from the input terminal 41. With the adder 51, the signal (c) for
`
`12
`
`13
`
`

`

`which the signal from the video processing circuit 12 and the correction signal (b) are
`added is output. With the alternating circuit 13, the video signal (f) for which the signal
`(c) underwent polarity inversion for each horizontal period using the switching pulse (e)
`is generated, and this is supplied to the liquid crystal panel unit 10.
`[0034]
`
`FIG. 5 corresponds to the luminance irregularity due to the gap irregularity that
`occurs on the liquid crystal panel, and is a drawing for describing the manifestation of the
`correction signal for cancelling that.
`[0035]
`
`In FIG. 5, (a) shows liquid crystal layer thickness irregularity (gap irregularity)
`with the liquid crystal panel. The manifestation of the gap irregularity is more indented
`the more it is toward the center in the drawing. (Alternatively, the gap irregularity is more
`bulged the more it is to the center). (b) shows the luminance irregularity that occurs on
`the screen due to the gap irregularity of (a). It is darker the more to the center of the
`screen. (Alternatively, it can be brighter the more to the center of the screen.) (c) shows
`the manifestation of the correction signal by the correction circuit 50. At approximately
`the center of the screen, the kind of correction signal shown in FIG. 4 (b) is generated and
`supplied to the adder 51, but at the upper part and lower part of the screen, since there is
`no luminance irregularity, corrected signals are not specifically generated. Therefore, as
`the correction circuit 50, it is necessary to have a circuit that generates gradually changing
`correction signals such that the amplitude becomes larger the more toward the center of
`the horizontal direction of the liquid crystal panel, and the amplitude becomes larger the
`more toward the center in the vertical direction when this signal is viewed in the vertical
`direction. For generation of the correction signal, by generating this so as to be adapted as
`much as possible to the gap irregularity format, in other words, the luminance irregularity
`format, it is possible to cancel the luminance irregularity at a higher level of precision.
`[0036]
`
`FIG. 6 is a block diagram of the luminance irregularity correction device of a
`liquid crystal panel of another embodiment of the present invention. Here as well, the
`
`13
`
`14
`
`

`

`drive circuit system for R, G, and B is the same, so only the drive circuit system for R is
`shown, and a description for the drive circuit system for G and B is omitted.
`[0037]
`
`With this embodiment, the constitution for correcting luminance irregularity with
`common voltage is shown, and the common voltage E1 shown in the prior art example of
`FIG. 9 is corrected every horizontal period by the correction signal (f) generated by a
`correction circuit 60 and an alternating circuit 61. The remainder of the constitution is the
`same as in FIG. 9.
`[0038]
`
`The R video signal input to the input terminal 11 is supplied to the alternating
`circuit 13 via the video processing circuit 12. The video processing circuit 12 is a circuit
`for doing amplification, gamma correction, and clamp processing of the R input video
`signal. The alternating circuit 13 does polarity inversion for both the alternating current
`and direct current of the video signal for each horizontal period for the R video signal,
`and performs alternating current drive of the liquid crystal. Specifically, the video signal
`that underwent the video processing noted above is polarity inverted in relation to the
`voltage of the pixel common electrode 10a of the liquid crystal panel kept, for example, at
`+4 V in comparison to the 0 V of the substrate. The polarity inversion at the alternating
`circuit 13 is performed using the switching pulse fH from the timing circuit 13. The video
`signal that underwent polarity inversion for each horizontal period from the alternating
`circuit 13 is supplied to the liquid crystal panel unit 10.
`[0039]
`
`The correction circuit 60, the same as the correction circuit 50 in FIG. 1, is a
`circuit for generating correction signals to correct luminance irregularity due to liquid
`crystal layer thickness irregularity of the liquid crystal panel unit 10, and generates
`gradually changing correction signals such that the amplitude becomes larger the more
`toward the center of the horizontal direction of the liquid crystal panel, and the amplitude
`becomes larger the more toward the center of the vertical direction when this signal is
`viewed in the vertical direction. With the correction circuit 60, a correction signal of one
`polarity of either positive polarity or negative polarity is generated, so to correlate this
`
`14
`
`15
`
`

`

`correction signal (e) to polarity inversion by the alternating circuit 13 of the video signal
`side, polarity inversion of the correction signal (e) is performed for each horizontal period
`by the alternating circuit 61 provided at the back stage of the correction circuit 60.
`[0040]
`
`This alternating circuit 61 can be constituted in the same way as the alternating
`circuit 13 of the video signal side (see FIG. 3), and it is possible to constitute it with an
`inverting amp, a non-inverting amp, and switching means for switching these amps for
`each horizontal period.
`[0041]
`
`With the adder 62, as shown in FIG. 7, the correction signal (f) that underwent
`polarity inversion is added to the direct current common voltage E1. Then, the common
`voltage (g) to which the correction signal (f) has been added is made to be supplied to the
`pixel common electrode (common terminal) 10a of the liquid crystal panel unit 10.
`[0042]
`
`The liquid crystal panel unit 10 is constituted with a sample hold circuit that
`inputs and does sample holding of the R signal from the R alternating circuit 13 polarity
`inverted for each horizontal period, a horizontal driver circuit that amplifies the sample-
`held R signal to the voltage necessary to drive the liquid crystal panel, and supplies that to
`the signal line (source line) of each pixel of the liquid crystal panel, and a liquid crystal
`panel that forms the R image. Therefore, among the three primary color RGB signals, the
`R video signal is supplied to this liquid crystal panel unit 10 from the alternating circuit
`13. Also, the clocks and timing pulses necessary for displaying the output signals from
`this R alternating circuit 13 are supplied from the timing circuit 40.
`[0043]
`
`The timing circuit 40 generates the switching pulse fH to the alternating circuit 13
`and the alternating circuit 61 and the clocks and timing pulses for driving the liquid
`crystal panel unit 10 from the horizontal (H) and vertical (V) synchronization signals
`input from the input terminal 41, and meanwhile, generates timing signals to match the
`timing of the correction signal generated by the correction circuit 60 to the video period
`of the input video signals.
`
`15
`
`16
`
`

`

`[0044]
`
`Next, we will describe the operation of the device of the constitution noted above
`while referring to FIG. 8. In FIG. 8, (a) is the input video signal of the input terminal 11,
`(b) is two types of video signals, positive polarity and negative polarity, respectively
`generated by the inverting amp Q1 and the non-inverting amp Q2 at the alternating circuit
`13, (c) is the switching pulse fH for each horizontal period from the timing circuit 40, (d)
`is the output from the alternating circuit 13, (e) is the correction signal generated by the
`correction circuit 60, (f) is the correction signal for which the correction signal of (e)
`undergoes polarity inversion for each horizontal period by the alternating circuit 61, (g) is
`the common voltage corrected by the adder 62 adding the correction signals of (f) to the
`direct current voltage E1, and (h) is the relationship between the video signal (d) supplied
`to the liquid crystal panel unit 10 and the common voltage (g).
`[0045]
`
`The input video signal (a) undergoes video processing such as amplification or the
`like at the video processing circuit 12, and at the alternating circuit 13, the signal after
`video processing undergoes polarity inversion for each horizontal period using the
`switching pulse fH and is output as the video signal (d), and this is supplied to the liquid
`crystal panel unit 10.