United States Patent [191
`United States Patent
`[19]
`Kalmanash et al.
`Kalmanash et a1.
`
`[11] Patent Number:
`,
`‘ [11] Patent Number:
`[45] Date of Patent:
`[45] Date of Patent:
`
`4,770,500
`4,770,500
`Sep. 13, 1988
`Sep. 13, 1988
`
`Calif.
`
`'
`
`[54] METHOD AND APPARATUS FOR MULTI
`[54] METHOD AND APPARATUS FOR MULTI
`COLOR DISPLAY
`COLOR DISPLAY‘
`[75] Inventors: Michael H. Kalmanash, Los Altos;
`Inventors: Michael H. Kalmanash, Los Altos;
`[75]
`James L. Fergason, Atherton, both of
`James L. Ferguson, Atherton, both of
`cam
`'
`_
`_
`[73] Assrgnee: mrxnglgzilgg’Eéfigomfi
`[73] Asslgnee: comgrxgzfigg?lgilgé?iu?omcs
`[21] APPL N°~= 872,520
`[21] APPL N04 872,520
`[22] Filed.
`Jam 10, 1986
`[22] Filed:
`Jun. 10’ 1986
`_
`’
`4
`_
`' 51
`Cl 4
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`G02F 1/13' G02B 5/30-
`[51]
`Int. Cl.
`.......................... G02F 1/13; C333351//3203,
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`[52] US” CL
`”0/347 1153/5353%335$33858’
`[52] US‘ Cl’ """""""""
`33552733858’
`[53] Field of Search ............... 350/347 R, 347 E, 335,
`[53] Field of Search ............. .. 350/347 R, 347 E, 335,
`350/378 387 388 389 391, 358/242 58
`350/378, 387, 388, 389, 391; 358/242, 58
`’
`’
`’
`’
`’
`’
`References Cited
`References Cited
`U_S_ PATENT DOCUMENTS
`u.s_ PATENT DOCUMENTS
`,
`3,407,017 6/1964 Fleisher et a1.
`..................... 350/388
`3,407,017 6/1964 Flelsher et al. ................... .. 350/388
`3,781,465 12/1973 . Emstoff et al.
`.
`........ 350/335
`3,781,465 12/1913, Ernstoff et al. .
`...... .. 350/335
`
`4,385,806
`5/1983 Fergason ........
`350/347 R
`4,385,806 5/1983 Fergason ...... ..
`350/347 R
`4,582,396 4/1936 Bos et a1.
`........................ 350/347 E
`4,582,396 4/ l986 Bos et al. ...................... .. 350/347 E
`
`[56]
`[56]
`
`-
`
`'
`
`4,674,841 6/1987 Buzak ............................ .. 350/ 347 E
`4,674,841
`6/1987 Buzak .............................. 350/347 E
`Primary Examiner~Stanley D. Miller
`Primary Examiner—Stanley D. Miller
`Assistant Examiner-Huy V. Mai
`Assistant Examiner—Huy V. Mai
`Attorney, Agent, or Firm-Marvin H. Kleinberg
`Attorney, Agent, or Firm—Marvin H. Kleinberg
`[57]
`ABSTRACI‘
`[57]
`ABSTRACT
`An apparatus and method for producing a color display
`An apparatus and method for producing a color display
`from a substantially monochromatic source utilizes a
`from a substantially monochromatic source utlllzes a
`liquid crystal cell combination together with a ple
`liquid crystal cell combination together with a ple-
`chroic ?lter to differentially polarize the light compo
`chroic filter'to differentially Polarize the light compo-
`nents comprising the light emitted from the source. The
`nents comprismg the light emitted from the source. The
`'
`liquid crystal cells are connected in push-pull fashion to
`liquid crystal cells are connected in push-pull fashion to
`individually retard light by one fourth of a wave as a
`individually retard light by one fourth of a wave as a
`function of the control signal applied to them. A fourth
`function of the control signal applied to them. A fourth
`wave Plate f°ll°wed by a 11“” ”lam“ “mm“ the
`Wat‘fe flaw 231°?“ ‘2' ‘ilm‘ilartpdttmelr °°lmP'e{.esd"t‘e
`optical combination. A signal at a first level applied to
`0p ica com 1na 1011.
`.slg‘na a a 1rst eve app 1e 0
`the cells causes transmission of one component color
`the cells causes transmlsslon of one component color
`and blocks the other. A signal at a second level blocks
`and blocks the other. A signal at a second level blocks
`the onedcomllaoneint ccgllor and trarésn?ts tlhe other} An
`the one component color and transmits the other. An
`mterme late eve sign transmits 0t co ors, resu ting
`intermediate lave} Signal transmits both COIO’S' resumng
`.
`.
`.
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`1“ a thud, °°mbman°n “01°“
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`15 Claims, 3 Drawing Sheets
`15 Claims, 3 Drawing Sheets
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`IVI LLC EXHIBIT 2015
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`XILINX V. IVI LLC
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`Inter Partes Review Case 2013—001 12
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`

`

`US. Patent
`Sep. 13,1988
`US. Patent Sep. 13,1988
`
`Sheet 1 of‘3
`Sheet 1 of3
`
`4,770,500
`4,770,500
`
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`
`Sep. 13,1988
`
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`4,770,500
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`
`Sep. 13,1988
`
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`4,770,500
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`

`1
`1
`METHOD AND APPARATUS FOR MULTI COLOR
`METHOD AND APPARATUS FOR MULTI COLOR
`DISPLAY
`DISPLAY
`
`5
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`The present invention relates to a method and appara-
`The present invention relates to a method and appara
`tus for producing multi color displays and, more partic
`tus for producing multi color displays and, more partic-
`ularly, to a liquid crystal cell combination which acts as
`ularly, to a liquid crystal cell combination which acts as
`an optical switch to display selected colors from an
`an optical switch to display selected colors from an
`apparently monochromatic source.
`apparently monochromatic source.
`It is well known in the prior art that an apparently
`It is well known in the prior art that an apparently
`monochromatic source such as a cathode ray tube
`monochromatic source such as a cathode ray tube
`(CRT) can provide a multi color display. From the
`(CRT) can provide a multi color display. From the
`earliest experiments in color television which used a
`earliest experiments in color television which used a
`rotating color wheel together with a CRT, it was possi
`rotating color wheel together with a CRT, it was possi-
`ble to place images on the screen in synchronism with
`ble to place images on the screen in synchronism with
`the color wheel so that a number of colors could be
`the color wheel so that a number of colors could be
`visualized. This phenomenon was as much a product of
`visualized. This phenomenon was as much a product of
`the persistence of the image in the human eye as the
`the persistence of the image in the human eye as the
`synchronization of certain images to the concurrent
`synchronization of certain images to the concurrent
`presentation of a ?lter of preselected color.
`presentation of a filter of preselected color.
`The development of the shadow mask tube and the
`The development of the shadow mask tube and the
`use of triads of monochromatic phosphors was deemed
`use of triads of monochromatic phosphors was deemed
`preferable to the electromechanical color wheel and, as
`preferable to the electromechanical color wheel and, as
`a result, the color television industry abandoned the
`a result, the color television industry abandoned the
`electromechanical approach. It has been taught in the
`electromechanical approach. It has been taught in the
`past that a polychromatic source which appears to be
`past that a polychromatic source which appears to be
`monochromatic (from the mixing of the colors) can
`monochromatic (from the mixing of the colors) can
`provide images in the principal colors or in colors
`provide images in the principal colors or in colors
`which result from the mixture of the principal colors.
`which result from the mixture of the principal colors.
`PRIOR ART
`PRIOR ART
`An early approach to an electronic ?eld sequential
`An early approach to an electronic field sequential
`color television system was described in the patent to
`color television system was described in the patent to
`Ernstoff et al US. Pat. No. 3,781,465, which issued
`Ernstoff et a1 U.S. Pat. No. 3,781,465, which issued
`Dec. 25, 1973. That patent showed a monochromatic
`Dec. 25, 1973. That patent showed a monochromatic
`CRT with a tri-color liquid crystal assembly that in
`CRT with a tri-color liquid crystal assembly that in-
`cluded red, blue and green cells. Electronic circuitry
`cluded red, blue and green cells. Electronic circuitry
`switches the three cells sequentially to provide a series
`switches the three cells sequentially to provide a series
`of single color images in rapid succession that, to the
`of single color images in rapid succession that, to the
`eye of the human observer, appear to be in full color.
`eye of the human observer, appear to be in full color.
`A different approach was described by Hilsum et al in
`A different approach was described by Hilsum et al in
`U.S. Pat. No. 4,003,081,
`issued Jan. 11, 1977. Their
`U.S. Pat. No. 4,003,081, issued Jan. 11, 1977. Their
`approach, which is the precursor to the approach of the
`approach, which is the precursor to the approach of the
`present invention, was to select a CRT that produced an
`present invention, was to select a CRT that produced an
`45
`image in at least two colors combined with an electri-
`image in at least two colors combined with an electri
`cally controlled filter element. The filter was a liquid
`cally controlled ?lter element. The ?lter was a liquid
`crystal material capable of transmitting separately dif
`crystal material capable of transmitting separately dif-
`ferent colors depending upon the applied energizing
`ferent colors depending upon the applied energizing
`signals. In a preferred embodiment, video images from
`signals. In a preferred embodiment, video images from
`a first source, such as radar, were to appear in one color
`a ?rst source, such as radar, were to appear in one color
`while video images from a second source, such as a
`while video images from a second source, such as a
`computer, were presented in a second color. Altema-
`computer, were presented in a second color. Altema
`tive embodiments included a field sequential color dis-
`tive embodiments included a ?eld sequential color dis
`play which includes a third filter so that a three color
`play which includes a third ?lter so that a three color
`combination is available.
`combination is available.
`The patent to Fergason, U.S. Pat. No. 4,385,806,
`The patent to Fergason, U.S. Pat. No. 4,385,806,
`which issued May 31, 1983, taught a liquid crystal de
`which issued May 31, 1983, taught a liquid crystal de-
`vice light shutter in combination retardation with re-
`vice light shutter in combination retardation with re
`tarding wave plates to compensate for the retardation in
`tarding wave plates to compensate for the retardation in
`the device operating under a bias. Utilizing a bias, the
`the device operating under a bias. Utilizing a bias, the
`operation of the shutter devices could be speeded up
`operation of the shutter devices could be speeded up
`and the retardation plates compensated for the normal
`and the retardation plates compensated for the normal
`birefringence of the cells.
`birefringence of the cells.
`In a continuation-in-part of Fergason, U.S. Pat. No.
`In a continuation-in-part of Fergason, U.S. Pat. No.
`4,436,376, issued Mar. 13, 1984, a pair of liquid crystal
`4,436,376, issued Mar. 13, 1984, a pair of liquid crystal
`cells were operated in the manner of a push-pull ampli-
`cells were operated in the manner of a push-pull ampli
`fier in that each cell was operated to impart its own
`?er in that each cell was operated to impart its own
`phase shift to a passing optical beam. The application of
`phase shift to a passing optical beam. The application of
`
`4,770,500
`4,770,500
`2
`2
`a bias to the cells aligns the preponderence of the crys-
`a bias to the cells aligns the preponderence of the crys
`tals except for the layers immediately adjacent the elec
`tals except for the layers immediately adjacent the elec-
`trodes. The application of incremental electrical signals
`trodes. The application of incremental electrical signals
`across the conducting surfaces achieves a rapid on-off
`across the conducting surfaces achieves a rapid on-off
`cycle for the cell. The cells thus taught were utilized as
`cycle for the cell. The cells thus taught were utilized as
`a communications link and information was modulated
`a communications link and information was modulated
`on a light beam by means of applied electrical signals to
`on a light beam by means of applied electrical signals to
`the cells. Signals that were 180“ out of phase were ap-
`the cells. Signals that were 180“ out of phase were ap
`plied to the two cells for push-pull operation.
`plied to the two cells for push-pull operation.
`The general idea of using a “black and white” CRT in
`The general idea of using a “black and white” CRT in
`conjunction with liquid crystal cells and color polariz
`conjunction with liquid crystal cells and color polariz-
`ers was described by Brinson et al in IBM Technical
`ers was described by Brinson et al in IBM Technical
`Disclosure Bulletin Vol. 22, No. 5 of October, 1979.
`Disclosure Bulletin Vol. 22, No. 5 of October, 1979.
`Because a full three color capability is desired, a first
`Because a full three color capability is desired, a ?rst
`liquid crystal cell is followed by a ?rst color polarizer
`liquid crystal cell is followed by a first color polarizer
`and a second liquid crystal cell is followed by a second
`and a second liquid crystal cell is followed by a second
`color polarizer. Essentially “white” light is transmitted
`color polarizer. Essentially “white” light is transmitted
`through a linear polarizer and, depending upon the state
`through a linear polarizer and, depending upon the state
`of the first cell, either cyan or red is passed to the sec-
`of the ?rst cell, either cyan or red is passed to the sec
`ond cell. Depending on the state of this cell, either blue
`ond cell. Depending on the state of this cell, either blue
`or yellow is passed. The net output of the combination
`or yellow is passed. The net output of the combination
`is then either blue, red, green, or black at any instant of
`is then either blue, red, green, or black at any instant of
`time. During a presentation, the net colors would be
`time. During a presentation, the net colors would be
`“mixed” by having images persist through more than
`“mixed” by having images persist through more than
`one output color phase to provide a substantially full
`one output color phase to provide a substantially full
`palette of colors.
`palette of colors.
`A slightly different approach was disclosed by
`A slightly different approach was disclosed by
`Shanks et al in US. Pat. No. 4,328,493, issued May 4,
`Shanks et al in U.S. Pat. No. 4,328,493, issued May 4,
`1983. A CRT which emits at least two different colors
`1983. A CRT which emits at least two different colors
`is combined with first and second color selective polar-
`is combined with ?rst and second color selective polar
`izers, a liquid crystal cell and a neutral linear polarizer.
`izers, a liquid crystal cell and a neutral linear polarizer.
`The liquid crystal cell in one condition rotates the plane
`The liquid crystal cell in one condition rotates the plane
`of applied polarized light and in a second condition
`of applied polarized light and in a second condition
`transmits the light without rotation. The cell is then
`transmits the light without rotation. The cell is then
`switched in synchronism with the presentation of the
`switched in synchronism with the presentation of the
`images that are to be seen in color. Because the cells
`images that are to be seen in color. Because the cells
`cannot be switched between states in the time available
`cannot be switched between states in the time available
`during television transmissions, only one half of the cell
`during television transmissions, only one half of the cell
`is switched at a time and the electrodes are driven ac-
`is switched at a time and the electrodes are driven ac
`cordingly.
`cordingly.
`In the recently published U.K. patent application of
`In the recently published U.K. patent application of
`Bos et al No. GB 2 139 778 A, published Nov. 14, 1984,
`Bos et al No. GB 2 139 778 A, published Nov. 14, 1984,
`corresponding to a US. application, Ser. No. 493,106,
`corresponding to a U.S. application, Ser. No. 493,106,
`filed May 9, 1983, now US. Pat. No. 4,582,396, issued
`?led May 9, 1983, now U.S. Pat. No. 4,582,396, issued
`Apr. 15, 1986, a field sequential color system disclosed
`Apr. 15, 1986, a ?eld sequential color system disclosed
`a liquid crystal cell which functioned as a variable opti-
`a liquid crystal cell which functioned as a variable opti
`cal retarder in a polarizing system which included pleo-
`cal retarder in a polarizing system which included pleo
`chroic filters which selectively transmit a first or a
`chroic ?lters which selectively transmit a ?rst or a
`second color, depending upon the polarization of the
`second color, depending upon the polarization of the
`light. A color sensitive polarizing means is placed in
`light. A color sensitive polarizing means is placed in
`front of a CRT which is capable of emitting light of at
`front of a CRT which is capable of emitting light of at
`least two colors. A first absorption axis passes linearly
`least two colors. A ?rst absorption axis passes linearly
`polarized light of the first color and a second absorption
`polarized light of the first color and a second absorption
`axis passes linearly polarized light of the second color.
`axis passes linearly polarized light of the second color.
`The liquid crystal cell is followed by a linear polarizer.
`The liquid crystal cell is followed by a linear polarizer.
`When the liquid crystal cell is driven by a first signal,
`When the liquid crystal cell is driven by a ?rst signal,
`it provides a half wave retardation to applied light.
`it provides a half wave retardation to applied light.
`When driven by a second signal, substantially no retar-
`When driven by a second signal, substantially no retar
`dation is experienced by the impinging light. With sub
`dation is experienced by the impinging light. With sub-
`stantially no retardation of light, only light of one of the
`stantially no retardation of light, only light of one of the
`colors can pass through the linear polarizer. With half
`colors can pass through the linear polarizer. With half
`wave retardation, only light of the other of the colors
`wave retardation, only light of the other of the colors
`can pass through the polarizer.
`can pass through the polarizer.
`A specially designed liquid crystal cell functions as
`A specially designed liquid crystal cell functions as
`the variable retarder. A nematic liquid crystal cell is
`the variable retarder. A nematic liquid crystal cell is
`designed to be disclination-free and to switch in a
`designed to be disclination-free and to switch in a
`“bounce-free” manner as it is switched between two
`“bounce-free” manner as it is switched between two
`
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`states which alter the orientation of the surface noncon-
`lated to the magnitude of the applied voltage. The turn
`states which alter the orientation of the surface noncon
`lated to the magnitude of the applied voltage. The turn
`tacting directors of the liquid crystal material in the cell.
`tacting directors of the liquid crystal material in the cell.
`on of a cell is largely independent of temperature.
`on of a cell is largely independent of temperature.
`When the voltage on a cell is removed, the cell “re-
`When the voltage on a cell is removed, the cell “re
`SUMMARY OF INVENTION
`SUMMARY OF INVENTION
`laxes” to the “off" state. However, the time required for
`laxes” to the “off’ state. However, the time required for
`It has been deemed desirable to find a suitable vari-
`turn off is dependent upon temperature and if tempera-
`turn off is dependent upon temperature and if tempera
`It has been deemed desirable to find a suitable vari
`able retarder which can be operated at higher speeds
`tures are reduced below 20" C., the time required is
`tures are reduced below 20n C., the time required is
`able retarder which can be operated at higher speeds
`than those attributable to the structure of the 805 et al
`markedly increased. Of course, if a cell need only relax
`markedly increased. Of course, if a cell need only relax
`than those attributable to the structure of the 80s et al
`from fully “on” to partially “on” with a quarter wave
`from fully “on” to partially “on” with a quarter wave
`application. Accordingly, there has been developed a
`application. Accordingly, there has been developed a
`retardation, the time required is much less than if it had
`retardation, the time required is much less than if it had
`?eld sequential color display system comprising, a
`field sequential color display system comprising, a
`to relax to the half wave retardation condition.
`to relax to the half wave retardation condition.
`source of light of at least two different wavelengths,
`source of light of at least two different wavelengths,
`Because the present invention employs two cells in a
`Because the present invention employs two cells in a
`light polarizing means in optical communication with
`light polarizing means in optical communication with
`“push-pull” con?guration, when one cell is being
`“push-pull” configuration, when one cell
`is being
`said source, including a color selective polarizing filter
`said source, including a color selective polarizing ?lter
`driven “on”, the other cell is relaxing from “on” to a
`driven “on”, the other cell is relaxing from “on” to a
`having ?rst and second substantially orthogonally ori
`having first and second substantially orthogonally ori-
`quarter wave retardation condition. The response of the
`quarter wave retardation condition. The response of the
`ented absorption axes, the ?rst absorption axis passing
`ented absorption axes, the first absorption axis passing
`one cell is therefore independent of temperature and the
`one cell is therefore independent of temperature and the
`linearly polarized light of a ?rst color and the second
`linearly polarized light of a first color and the second
`other cell is only slightly affected by temperature. As a
`other cell is only slightly affected by temperature. As a
`absorption axis passing linearly polarized light of a sec
`absorption axis passing linearly polarized light of a sec-
`ond color.
`result, the operating speed of the combination of the
`result, the operating speed of the combination of the
`ond color.
`present invention can be markedly higher than systems
`present invention can be markedly higher than systems
`Variable optical retarding means are disposed be-
`Variable optical retarding means are disposed be
`of the prior art.
`of the prior art.
`tween said color selective polarizing filter and a circular
`tween said color selective polarizing ?lter and a circular
`The first and second liquid crystal cells are oriented
`The ?rst and second liquid crystal cells are oriented
`polarizing means for selectively tranmitting light of a
`polarizing means for selectively tranmitting light of a
`with their optic axes at right angles to each other, and at
`with their optic axes at right angles to each other, and at
`color determined by the amount by which the light
`color determined by the amount by which the light
`forty ?ve degrees with respect to the polarizing axes
`forty five degrees with respect to the polarizing axes
`emitted by said source is optically retarded in said re-
`emitted by said source is optically retarded in said re
`such that upon the application of a potential at said ?rst
`such that upon the application of a potential at said first
`tarding means. Control means coupled to said variable
`tarding means. Control means coupled to said variable
`level, one of said cells converts linearly polarized light
`level, one of said cells converts linearly polarized light
`optical retarding means regulates the amount of optical
`optical retarding means regulates the amount of optical
`to right hand, circularly polarized light, which passes
`to right hand, circularly polarized light, which passes
`retardation imposed by said retarding means upon light
`retardation imposed by said retarding means upon light
`through the circular polarizer with a net retardation of
`through the circular polarizer with a net retardation of
`transmitted therethrough. Accordingly, said retarding
`transmitted therethrough. Accordingly, said retarding
`one half wave (ninety degree rotation), and the other of
`one half wave (ninety degree rotation), and the other of
`means are capable of at least first and second retarda-
`means are capable of at least ?rst and second retarda
`said cells imposes substantially no retardation on im-
`said cells imposes substantially no retardation on im
`tions, resulting in the emission of light of at at least ?rst
`tions, resulting in the emission of light of at at least first
`pinging light. Upon the application of a potential at said
`pinging light. Upon the application of a potential at said
`and second colors.
`and second colors.
`second level, the ?rst of said cells imposes substantially
`second level, the first of said cells imposes substantially
`In a preferred embodiment, the light emitted from
`In a preferred embodiment, the light emitted from
`no retardation, and the second of said cells converts
`no retardation, and the second of said cells converts
`said source is modulated in synchronism with said con-
`said source is modulated in synchronism with said con
`linearly polarized light to left hand circularly polarized
`linearly polarized light to left hand circularly polarized
`trol means to produce images appearing to have a multi
`trol means to produce images appearing to have a multi
`light which passes through the circular polarizer with a
`light which passes through the circular polarizer with a
`colored appearance. This is accomplished through the
`colored appearance. This is accomplished through the
`net retardation of substantially zero or no rotation.
`net retardation of substantially zero or no rotation.
`use of variable optical retarding means comprising ?rst
`use of variable optical retarding means comprising first
`In the preferred embodiment, the two liquid crystal
`In the preferred embodiment, the two liquid crystal
`and second liquid crystal cells and control means in-
`and second liquid crystal cells and control means in
`cells are placed “back-to-back” with adjacent elec
`cells are placed “back-to-back” with adjacent elec-
`cluding a source of electric potential at first and second
`cluding a source of electric potential at ?rst and second
`trodes commonly connected to a source of signal volt-
`trodes commonly connected to a source of signal volt
`levels and means for applying to each of said cells said
`levels and means for applying to each of said cells said
`age. The remaining electrodes are connected between a
`age. The remaining electrodes are connected between a
`electric potential levels for determining the amourit of
`electric potential levels for determining the amourit of
`potential source and a source of common reference
`potential source and a source of common reference
`40
`optical retardation imposed by each of said cells.
`optical retardation imposed by each of said cells.
`potential or ground. The signal voltage source then
`potential or ground. The signal voltage source then
`40
`The purity of the displayed colors is enhanced by the
`The purity of the displayed colors is enhanced by the
`swings between two intermediate voltages, one of
`swings between two intermediate voltages, one of
`use of a first filter means in the optical path between said
`use of a ?rst ?lter means in the optical path between said
`which places a substantial voltage drop across the first
`which places a substantial voltage drop across the ?rst
`source and light polarizing system and a second filter at
`source and light polarizing system and a second ?lter at
`cell but not the second and the other of which places the
`cell but not the second and the other of which places the
`the output of said circular polarizing means for limiting
`the output of said circular polarizing means for limiting
`substantial voltage drop across the second cell but not
`substantial voltage drop across the second cell but not
`45
`emitted light to said first and second colors at said color
`emitted light to said ?rst and second colors at said color
`the first. This can be accomplished by setting the refer-
`the ?rst. This can be accomplished by setting the refer
`45
`selective polarizing means which eliminates unwanted
`selective polarizing means which eliminates unwanted
`ence level to equal the sum of the signal levels.
`ence level to equal the sum of the signal levels.
`colors from the output of said system.
`colors from the output of said system.
`If a signal at the first, or “lower” level is applied, the
`If a signal at the ?rst, or “lower” level is applied, the
`The contrast of the displayed scene is also enhanced
`The contrast of the displayed scene is also enhanced
`cell across which the lower potential exists will be a
`cell across which the lower potential exists will be a
`through the use of the filter means in that incident ambi-
`through the use of the ?lter means in that incident ambi
`quarter-wave retarder while the other cell across which
`quarter-wave retarder while the other cell across which
`ent light in spectral regions where CRT phosphors emit
`ent light in spectral regions where CRT phosphors emit
`the higher potential exists will be a “zero” retarder.
`the higher potential exists will be a “zero” retarder.
`no light is absorbed. For maximum benefit in contrast
`no light is absorbed. For maximum bene?t in contrast
`When a signal at the second, or “higher” level is ap-
`When a signal at the second, or “higher” level is ap
`improvement, the ?lters are located at the “output side”
`improvement, the filters are located at the “output side”
`plied, the cell which had previously experienced the
`plied, the cell which had previously experienced the
`of the combination, a placement that is not critical if
`of the combination, a placement that is not critical if
`lower potential will now be subjected to the higher
`lower potential will now be subjected to the higher
`improved color purity were the only goal.
`improved color purity were the only goal.
`potential and will now be a “zero” retarder while the
`potential and will now be a “zero” retarder while the
`To enable an increase in the speed of operation of the
`To enable an increase in the speed of operation of the
`other cell, previously the “zero” retarder will experi
`other cell, previously the “zero” retarder will experi-
`variable optical retarding means, each said liquid crystal
`variable optical retarding means, each said liquid crystal
`ence the lower potential and become the quarter-wave
`ence the lower potential and become the quarter-wave
`cell is capable of optically retarding light by one fourth
`cell is capable of optically retarding light by one fourth
`retarder. In one experimental set up, a signal voltage
`retarder. In one experimental set up, a signal voltage
`of a wave upon application of a potential at said first
`of a wave upon application of a potential at said ?rst
`swung between 8 and 32 volts and the reference voltage
`swung between 8 and 32 volts and the reference voltage
`level and ot imposing no retardation upon the applica
`level and ot imposing no retardation upon the applica-
`level was set at 40 volts. With the signal voltage at 8
`level was set at 40 volts. With the signal voltage at 8
`tion of a potential at said second level.
`tion of a potential at said second level.
`volts, one cell had a 8 volt potential difference across its
`volts, one cell had a 8 volt potential difference across its
`electrodes while the other cell had a 32 volt difference.
`To better understand why the arrangement of the
`To better understand why the arrangement of the
`electrodes while the other cell had a 32 volt difference.
`present invention provides a marked advantage both in
`present invention provides a marked advantage both in
`When the signal voltage switched to 32 volts, t