United States Patent [191
`Culter et al.
`
`llllllIllllllllllllllllllllllllll|ll|llllllllllllllllllllllllllllllllllllll
`5,457,551
`Oct. 10, 1995
`
`USO05457551A
`[11] Patent Number:
`[45] Date of Patent:
`
`[54] FRAME RESPONSE COMPENSATED, VIDEO
`RATE ADDRESSABLE LIQUID CRYSTAL
`PASSIVE MATRIX DISPLAY SYSTEM
`
`Scheffer, Terry and Nehn'ng, Jiirgen, “Supertwisted Nematic
`(STN) LCDs,” I993 SID International Symposium, May
`16-21, 1993, pp. M 7/l-M 7/63.
`
`[75] Inventors: Robert G. Culter; Keith F. Kongslie,
`both of Beaverton, Oreg.
`
`[73] Assignee: Planar Systems, Inc., Beaverton, Oreg.
`
`[21] Appl. No.: 133,700
`[22] Filed:
`Oct. 8, 1993
`
`[51] Int. Cl.6 ....................... .. G02F 1/1347; G02F 1/137;
`609G 3/36
`[52] U.S. Cl. ............................... .. 359/53; 359/55; 359/73;
`4
`359/103; 345/87
`[58] Field of Search ................................ .. 359/54, 53, 73,
`359/103, 55, 93, 87, 85; 345/87, 94; 348/761,
`766
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,952,036
`
`8/1990 Gulick et a1. ......................... .. 350/335
`
`. . . .. 359/53
`5,035,489
`7/1991 Iijima et al. . . . . .
`359/53
`5,090,794 2/1992 Hatano et a1.
`. 359/53
`5,124,818
`6/1992 Conner et al. .... ..
`5,272,553 12/1993 Yamamoto et a1. .................... .. 359/53
`
`FOREIGN PATENT DOCUMENTS
`
`0379241 7/1990 European Pat. Off. ............... .. 359/53
`507061A2 7/1992 European Pat. Off.
`. G09G 3/36
`0204725 8/1990 Japan ..................................... .. 359/53
`
`OTHER PUBLICATIONS
`
`Conner, Arlie R. and Gulick, Paul E., “High—Resolution
`Display System based on Stacked Mutually Compensated
`STN-LCD Layers,” SID 91 Digest, 1991, pp. 755-757.
`
`Takahashi, Taiju and Saito, Susumu; “Improvement of Mul
`tiplexability of Double-Layered Homogeneously Oriented
`Nematic LCD by Simultaneous Driving Method”; Electron
`its and Communications in Japan, Part II; vol. 74, No. 12;
`1991; PP- 49-58.
`
`Primary Examiner—William L. Sikes
`Assistant Examiner-Tai V. Duong
`
`[57]
`
`ABSTRACT
`
`A display system (10) uses an electrically driven compen
`sator cell (16) not only to improve the color quality of the
`display system but also to solve viewability problems stem
`ming from the frame response effect. The display system
`includes a liquid crystal cell (14) patterned as a matrix
`display device and the compensator cell patterned in a
`row-only fashion. Corresponding row electrodes (26, 32) of
`the matrix display cell and the compensator cell are con
`currently driven from the same row driver circuit (40). The
`cells are constructed and oriented relative to each other so as
`to cancel unwanted polarization state changes resulting from
`the frame response effect. The resulting light transmission
`through the display system in the OFF optical state is
`substantially at a minimum at all times during a frame
`period.
`
`10 Claims, 4 Drawing Sheets
`
`45
`
`FRAME
`BUFFER
`COLUMN
`DATA
`
`COMPENSATOR
`NON-SELECT
`BACKPLANE
`DATA
`
`36
`
`38
`
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`
`Patent Owner’s Exhibit 2002
`IPR2015-00021
`Page 1 of 9
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`

`

`US. Patent
`
`Oct. 10, 1995
`
`Sheet 1 of4
`
`,
`
`5,457,551
`
`FIG. 1
`
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`Patent Owner’s Exhibit 2002
`IPR2015-00021
`Page 2 of 9
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`

`

`US. Patent.
`
`Oct. 10, 1995
`
`Sheet 2 of 4
`
`5,457,551
`
`FIG. 2
`
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`DATA
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`Patent Owner’s Exhibit 2002
`IPR2015-00021
`Page 3 of 9
`
`

`

`US. Patent
`US. Patent
`
`Oct. 10, 1995
`0a. 10, 1995
`
`Sheet 3 of 4
`Sheet 3 of 4
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`5,457,551
`5,457,551
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`Patent Owner‘s Exhibit 2002
`|PR2015-00021
`Page 4 of 9
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`Patent Owner’s Exhibit 2002
`IPR2015-00021
`Page 4 of 9
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`

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`US. Patent
`
`Oct. 10, 1995
`
`Sheet 4 of 4
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`5,457,551
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`|PR2015-00021
`Page 5 of 9
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`Patent Owner’s Exhibit 2002
`IPR2015-00021
`Page 5 of 9
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`

`5,457,551
`
`1
`FRAME RESPONSE COMPENSATED, VIDEO
`RATE ADDRESSABLE LIQUID CRYSTAL
`PASSIVE MATRIX DISPLAY SYSTEM
`
`TECHNICAL FIELD
`
`The present invention relates to matrix display systems
`and, in particular, to a matrix display system whose display
`elements are optically compensated to prevent a decrease in
`contrast ratio caused by a frame response e?ect.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`A passive matrix liquid crystal display (“LCD”) is one
`popular type of display whose display elements respond to
`the values of the rms voltages applied across them. A passive
`matrix LCD includes overlapping row electrodes and col
`umn electrodes positioned on opposite sides of a ?lm of
`liquid crystal material. The locations where the row and
`column electrodes overlap de?ne the display elements. The
`portion of liquid crystal ?lm associated with each display
`element is an electro-optic material that responds to a
`change in the value of an rms voltage applied across the
`display element to provide a corresponding change in the
`amount of light passing through it. The liquid crystal device
`most prevalently used in such displays is of a supertwisted
`nematic (“STN”) type. The row electrodes receive address
`ing signals that select the rows at various times, and the
`column electrodes receive data signals that represent the
`information patterns to be displayed.
`There are optimum values of the rms voltages that can be
`applied across the display elements to provide light trans
`mitting (“ON”) and light blocking (“OFF”) optical states.
`For standard addressing, the rows are sequentially selected
`typically with a 2l-volt pulse, and the display system
`requires a 16.7 millisecond repetition period to select all 'of
`the rows one at a time. These row addressing waveforms,
`which are called Alt and Pleshko waveforms, are normally
`used to provide the optimum voltages, but they are of highly
`nonuniform amplitude as a function of time.
`If it can respond within the repetition period of the row
`select waveforms, an LCD will not respond to the true rms
`value of the waveforms. This phenomenon is called a “frame
`response” effect. The frame response causes the transmis
`sion characteristic of the LCD to be different from that
`which is intended. For example, a display element driven to
`remain in the OFF optical state in successive frames will
`leak light during a portion of the frame period. The result is
`a lower contrast ratio for the display element. If an LCD is
`constructed to respond sufficiently fast so that its display
`elements switch at video rates, the frame response effect can
`become so severe that it is difficult to make a passive matrix
`LCD that is capable of displaying video rate images.
`Two approaches have been used to solve the frame
`response effect problem. One approach is to increase the
`frame rate of the Alt and Pleshko waveforms, and the other
`approach is use waveforms whose amplitudes are more
`uniform with time.
`The ?rst approach has two difficulties. One di?iculty is
`that the row and column signal drivers need to operate at
`higher than normal rates, thereby increasing circuit com
`plexity and power consumption. The second dif?culty is that
`signals of higher frequencies are applied to the row and
`column electrodes of the display. Because the row electrodes
`are of high resistance and the row signals drive signi?cant
`capacitance, the use of higher frequency signals makes it
`
`15
`
`25
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`30
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`40
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`45
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`55
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`65
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`2
`di?icult to maintain the desired voltage levels across the
`display elements down the rows and columns of the display.
`The second approach, which is sometimes called “active
`addressing,” requires more complex drive circuit electron
`rcs.
`STN displays are often coupled with compensator cells or
`sheets of compensator material to improve the color quality
`(i.e., by making a black-and-white display instead of a
`blue-and-white or a yellow-and-black display) and improve
`the viewing angle performance. An electrically driven com
`pensator cell includes a second STN liquid crystal cell of
`opposite liquid crystal molecular helical twist direction that
`offsets the birefringence resulting from color dispersion
`effects of the STN display cell. The compensator cell does
`not usually contain patterned row or column electrodes.
`
`SUMMARY OF THE INVENTION
`
`An object of the present invention is, therefore, to provide
`a matrix LCD that is capable of presenting images at video
`rates.
`Another object of the invention is to provide such a
`system with enhanced viewability properties.
`A further object is to provide such a system that uses
`standard Alt and Pleshko waveforms at normal addressing
`rates.
`The present invention is a display system that uses an
`electrically driven compensator cell not only to improve the
`color quality of the display system but also to solve view
`ability problems stemming from the frame response effect.
`The presence of frame response causes nonuniform light
`leakage through display elements in the OFF optical state
`and nonuniform light transmission through display elements
`in the ON optical state. Thus, during a frame period the
`time—dependent contrast ratio of the ON optical state to the
`OFF optical state varies. (A frame period is de?ned as the
`length of time required for all of the row electrodes to be
`selected one at a time before an addressing cycle repeats.)
`The display system includes a liquid crystal cell patterned
`as a matrix display device and a compensator cell patterned
`in a row-only fashion. The row electrodes of the matrix
`display cell and the compensator cell are driven from the
`same row driver circuit. The compensator cell has its own
`frame response that is equal to the frame response of the
`matrix display cell. The column electrodes of the matrix
`display cell receive drive signal voltages representing dis
`play pattern information stored by the display elements, and
`a back plane common electrode of the compensator cell
`receives a constant nonselect drive voltage throughout the
`frame period. The cells are constructed and oriented relative
`to each other so as to cancel unwanted polarization state
`changes resulting from the frame response effect. The result
`ing light transmission through the display system in the OFF
`optical state is substantially at a minimum at all times during
`the frame period. The display system is, therefore, operable
`with a constant output backlight.
`The present invention greatly improves the performance
`of passive matrix LCDs in a large number of applications
`such as laptop and notebook computers; television; and
`projection, instrumentation, and avionics displays.
`'
`Additional objects and advantages of the present inven
`tion will be apparent from the following detailed description
`of preferred embodiments thereof, which proceeds with
`reference to the accompanying drawings.
`
`Patent Owner’s Exhibit 2002
`IPR2015-00021
`Page 6 of 9
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`

`

`5,457,551
`
`3
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows the timing relationship between selection
`pulses applied to a row electrode and the resulting frame
`response effect for the ON and OFF optical states.
`FIG. 2 is an exploded isometric view of a display system
`showing the electrical drive connections for, and the relative
`orientation of, the matrix display cell and compensator cell
`of the invention.
`FIG. 3 is an exploded side elevation view of the display
`system of the invention showing the relative helical twist
`directions of the liquid crystal directors of the display matrix
`cells in their nonselected conditions.
`FIG. 4 is a diagram showing the progressive optical
`processing of light propagating through the matrix display
`and compensator cells in the ON and OFF optical states.
`
`10
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`20
`
`FIG. 1 shows the timing relationship between a selection
`pulse applied to a row electrode (line A) and the correspond
`ing frame response effect for a display element of a liquid
`crystal matrix display cell with the display element in the
`ON (white) and OFF (black) optical states (line B) during a
`frame period. The frame response interval shown in FIG. 1
`(line B) results from undesired amounts of birefringence
`imparted to light propagating through a liquid crystal cell of
`the variable optical retardation type. The present invention is
`a display system that incorporates a compensator liquid
`crystal cell whose optical retardation produces a second
`frame response effect that offsets that of the matrix display
`liquid crystal cell.
`FIG. 2 shows the electrical connections for, and optical
`components of, a display system 10 designed in accordance
`with the present invention. With reference to FIG. 1, display
`system 10 includes a passive matrix liquid crystal panel 12
`that comprises liquid crystal matrix display cell 14 posi
`tioned face to face to a liquid crystal compensator cell 16.
`Passive matrix panel 12 is positioned between a pair of
`neutral density linear polarizers 18 and 20 whose respective
`transmission axes 22 and 24 are orthogonally aligned.
`Matrix display cell 14 includes multiple, parallel ?rst or row
`electrodes 26 that extend in one direction and multiple,
`parallel second or column electrodes 28 that overlap and
`extend in a direction perpendicular to that of row electrodes
`26. Row electrodes 26 and column electrodes 28 are posi
`tioned on opposite sides of the liquid crystal material, and
`the locations where electrodes 26 and column electrodes 28
`overlap de?ne display elements 30. Compensator cell 16
`includes multiple, parallel third or row electrodes 32 that are
`parallel to and are spatially aligned with row electrodes 26.
`There are no separate column electrodes provided on com
`pensator cell 16, but there is a common electrode 34
`covering a back plane of compensator cell 16. A continuous
`illurnination light source 36 is positioned adjacent a surface
`38 of polarizer 18 and functions as a continuous backlight
`for display system 10.
`To address display system 10, a row driver circuit 40
`concurrently provides to row electrodes 26 of matrix display
`cell 14 and row electrodes 32 of compensator cell 16 drive
`signals of the standard Alt and Pleshko waveform type to
`sequentially select corresponding pairs of all of row elec
`trodes 26 and 32 one pair at a time during a frame period.
`Thus, for a display matrix cell 14 and a compensator cell 16
`each having N total number of rows, row driver circuit 40
`
`35
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`45
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`55
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`60
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`65
`
`4
`selects at the nth time interval the nth pair of row electrodes
`26 and 32, where n=l, 2, .
`.
`. , N.
`During the selection of each pair of row electrodes 26 and
`32, a column driver circuit 42 provides to column electrodes
`28 drive signals whose voltages represent display pattern
`information stored by the display elements 30 de?ned by the
`selected row 26 of matrix display cell 14 and spatially
`aligned with the selected row electrode 32 of compensator
`cell 16. A voltage driver 44 applies to common electrode 34
`a constant nonselect data voltage throughout a frame period.
`The image data presented for display by display elements 30
`are stored in an image data frame buffer 46, whose contents
`are continually updated by a host computer or other image
`data source (not shown). Frame buffer 46 and row driver
`circuit 40 communicate to synchronize ' the delivery to
`column electrodes 28 image data signals corresponding to
`the selected electrodes 26 of matrix display cell 14 and
`selected row electrodes 32 of compensator cell 16.
`The present invention uses a row electrode-only
`addressed compensator cell 16 of perpendicular alignment
`direction to that of matrix display cell 14 to rotate the
`unwanted polarization direction resulting from the frame
`response effect to achieve high contrast during the entire
`frame period. The row signals applied to compensator cell
`16 are the same as those applied to matrix display cell 14.
`(It will be appreciated, however, that the row signals applied
`to matrix display cell 14 may be phase-displaced by 180
`degrees relative to the row signals applied to compensator
`cell 16.) Compensator cell 16 also thermally tracks tempera‘
`ture-related changes in matrix display cell 14 so as to
`provide thermal compensation.
`FIG. 3 shows a side view of display system 10 with the
`interior sections of display matrix cell 14 and compensator
`cell 16 expanded to depict the rotational direction of the
`liquid crystal directors in their nonselected condition (as
`indicated by V,“ applied across each of cells 14 and 16).
`Matrix display cell 14 and compensator cell 16 are of a
`supertwisted nematic type. Matrix display cell 14 comprises
`a nematic liquid crystal material 50 contained between
`optically transparent electrode structures 52, and compen
`sator cell 16 comprises a nematic liquid crystal material 54
`contained between optically transparent electrode structures
`56.
`A suitable matrix display cell 14 can be adapted from a
`Tektronix Part No. HTD-256l HypertwistTM Flat Panel
`Display, which includes an STN matrix having a ZSO-degree
`molecular helical twist along its thickness dimension 58.
`The molecular twist angle is determined by the relative
`alignment directions of electrode structures 52 and the type
`and amount of chiral additive to liquid crystal material 50.
`A suitable compensator cell 16 would require appropriate
`modi?cation of the STN matrix in the HTD-256l display to
`have along its thickness dimension 60 a 250-degree molecu
`lar helical twist of opposite rotational sense to that of matrix
`display cell 14 and preferably to include not separate column
`electrodes but a common back plane electrode 34. Matrix
`display cell 14 and compensator cell 16 are alike in all other
`respects.
`With reference to FIG. 3, in display system 10, matrix
`display cell 14 and compensator cell 16 are oriented so that
`their optic axes established by their alignment directions are
`set at a 90 degree angle relative to each other and at 45
`degree angles relative to the transmission axes 22 and 24 of
`the respective polarizers 18 and 20. Directors 62 of liquid
`crystal material 50 of matrix display cell 14 are depicted to
`have a right-handed molecular helical twist along its thick
`
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`ness dimension 58, and directors 64 of liquid crystal material
`54 of compensator cell 16 are depicted to have a left-handed
`molecular helical twist along its thickness dimension 60.
`Cells 14 and 16 are of the same thickness and therefore have
`the same molecular pitch.
`FIG. 4 shows the progressive optical processing of light
`propagating through a display element 30 of matrix display
`cell 14 and corresponding region of compensator cell 16 in
`the ON optical state (line A) and the OFF optical state (line
`B). Compensator cell 16 is set to impart nearly zero retar
`dation to light propagating through it in the ON and OFF
`optical states of display system 10.
`Line A shows the frame response effect that occurs when
`the voltage across the selected display element 30 of matrix
`display cell 14 is suf?ciently small that the molecules of
`liquid crystal material 50 impart to light exiting polarizer 18
`an amount of retardation causing an effective polarization
`direction rotation of 90 degrees. The overall quantity of light
`exiting polarizer 20 is diminished by an amount correspond
`ing to the amount of retardation associated with the frame
`response of the selected row electrode 32 of compensator
`cell 16. This is so because the effect of compensator cell 16
`is to contribute an amount of negative retardation corre~
`sponding to the OFF optical state of matrix display cell 14
`to impart to the light striking polarizer 20 a net effective
`polarization direction rotation of nearly 90 degrees. Thus,
`minor and major quantities of light propagating through
`compensator 16 are, respectively, absorbed and transmitted
`by polarizer 20.
`Line B shows the frame response effect that occurs when
`the voltage across the selected display element 30 of matrix
`display cell 14 is su?iciently large that the molecules of
`liquid crystal material 50 impart to light exiting polarizer 18
`an amount of retardation causing an e?ective polarization
`direction rotation of nearly zero degrees. If compensator cell
`16 were not present, the effective polarization direction
`rotation would result in a quantity of light exiting polarizer
`20. The quantity of light exiting polarizer 20 is, however,
`zero because matrix display cell 14 and compensator cell 16
`develop equal but opposite amounts of retardation and
`therefore impart to the light striking polarizer 20 a zero
`degree net polarization direction rotation. Thus, no light is
`transmitted by polarizer 20.
`FIG. 4 shows that in the preferred embodiment, compen
`sator cell 16 corrects for the frame response elfect only in the
`OFF optical state. Skilled persons will appreciate that com
`promising the contrast ratio achieved by compensating the
`frame response effect in the OFF optical state could improve
`the frame response effect in the ON optical state but at the
`expense of an overall decrease in contrast ratio. This could
`be done by causing driver 44 to apply a constant select data
`voltage to common electrode 34 and thereby compensate
`display panel 10 to the white state.
`As an alternative, compensator cell 16 need not have the
`same number of row electrodes 32 in one-to-one correspon
`dence to the number of row electrodes 26 in matrix display
`cell 14. For example, compensator cell 16 could include
`multiple electrode bars, each of which of a width equal to the
`total width of, for example, 8, 16, or 32 row electrodes, and
`be driven in spatial alignment with corresponding row
`electrodes 26 of matrix display panel 14. The phase differ
`ence between a selected row electrode 26 and compensator
`bar must be su?iciently small to obtain the necessary spatial
`association that achieves frame response effect compensa
`tron.
`Skilled persons will appreciate that the invention may be
`
`45
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`60
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`6
`implemented in dual scan panels in a manner that renders
`more homogeneous the effect of the frame response com
`pensation. For example, the scan of the display elements
`may proceed from top to bottom of one panel and bottom to
`top of the other panel or from the middle toward the top of
`one panel and from the middle toward the bottom of the
`other panel. These alternative techniques for scanning
`toward or away from the middle of the dual scan panels
`would help prevent incidental compensation of one panel by
`compensation intended for the other panel.
`It will be obvious to those having skill in the art that many
`changes may be made to the details of the above-described
`preferred embodiments of the present invention without
`departing from the underlying principles thereof. For
`example, the row drive waveforms need not strictly obey the
`equations governing Alt and Pleshko waveforms. The scope
`of the present invention should, therefore, be determined
`only by the following claims.
`We claim:
`1. A driving method for a passive matrix display system
`including a display device of an optically retarding type
`having an optic axis and overlapping ?rst and second
`electrodes positioned on opposite sides of a supertwisted
`nematic liquid crystal material to de?ne an array of display
`elements, the ?rst electrodes receiving corresponding ?rst
`drive signals during a frame period to cause sequential
`selections of the ?rst electrodes during the frame period, the
`second electrodes receiving corresponding second drive
`signals during the selections of the ?rst electrodes to provide
`a desired information pattern on the display elements, and
`the supertwisted nematic liquid crystal material instanta
`neously responding to the ?rst drive signals and thereby
`resulting in a transient change in display element transmit
`tance before returning to a quiescent state corresponding to
`a lower rrns voltage over the remainder of the frame period,
`the method comprising:
`providing a compensator device of an optically retarding
`type having ?rst electrodes and a reference electrode
`structure positioned on opposite sides of a supertwisted
`nematic liquid crystal material, the compensator device
`having an optic axis;
`positioning the compensator device in optical association
`with the display device so that the ?rst electrodes of the
`display device and the ?rst electrodes of the compen
`sator device spatially overlap and are parallel to one
`another and so that the optic axis of the display device
`"and the optic axis of the compensator device intersect
`at a predetermined angle;
`applying the ?rst drive signals concurrently to the ?rst
`electrodes of the display device and to the ?rst elec
`trodes of the compensator device, the compensator
`device and display device producing offsetting chang
`ing amounts of retardation during the frame period to
`prevent a signi?cant decrease in contrast ratio;
`applying the second drive signals to the second electrodes
`of the display device to provide the desired information
`pattern on the display elements; and
`applying a reference signal to the reference electrode
`structure.
`2. The method of claim 1 in which the optic axes of the
`display device and the compensator device intersect at an
`angle of 90 degrees.
`3. The method of claim 1 in which each of the display and
`compensator devices includes a liquid crystal material hav
`ing directors and a thickness dimension, the directors in the
`direction of the thickness dimension of the display device
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`Patent Owner’s Exhibit 2002
`IPR2015-00021
`Page 8 of 9
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`8
`of the liquid crystal material of the matrix display cell;
`a ?rst drive circuit applying ?rst signals concurrently to
`select the ?rst electrodes of the matrix display cell and
`the spatially associated ?rst electrodes of the compen
`sator cell; and
`second drive circuits applying a reference signal to the
`reference electrode and second signals to correspond
`ing second electrodes of the matrix display cell during
`the selections of the ?rst electrodes to provide a desired
`information pattern on the display elements, the liquid
`crystal materials of the matrix and compensating cells
`instantaneously responding to the ?rst signals and
`producing offsetting changing amounts of retardation
`that prevent a resultant transient change in display
`element transmittance.
`7. The system of claim 6 in which the optic axes of the
`matrix display and compensator cells are set at 90 degrees
`relative to each other.
`8. The system of claim 6 in which the liquid crystal
`material in the display matrix and compensator cells have
`the same helical pitch.
`9. The system of claim 6 in which the ?rst signals are of
`an Alt and Pleshko sequential waveform type.
`10. The system of claim 6 in which the number of ?rst
`electrodes of the display matrix cell is equal to the number
`of ?rst electrodes of the compensator cell.
`
`* * *
`
`* *
`
`5,457,551
`
`7
`being of opposite rotational sense to that of the directors in
`the direction of the thickness dimension of the compensating
`device.
`4. The method of claim 1 in which the ?rst drive signals
`are of an Alt and Pleshko sequential waveform type.
`5. The method of claim 1 in which the number of ?rst
`electrodes of the display device is equal to the number of
`?rst electrodes of the compensator device.
`6. A frame response-compensated passive matrix display
`system, comprising:
`a matrix display cell of an optically retarding type having
`an optic axis and overlapping ?rst and second elec
`trodes positioned on opposite sides of a supertwisted
`nematic liquid crystal material to de?ne an array of
`display elements, the liquid crystal material having a
`thickness dimension and directors to which a twist
`angle is imparted along the thickness dimension;
`a compensating cell of an optically retarding type having
`an optic axis, a reference electrode, and ?rst electrodes
`positioned adjacent a supertwisted nematic liquid crys
`tal material, the optic axes of the matrix display and
`compensating cells being set at a predetermined angle,
`the ?rst electrodes being spatially associated with and
`oriented parallel to the ?rst electrodes of the matrix
`display cell, and the liquid crystal material having a
`thickness dimension and directors to which a twist
`angle is imparted along the thickness dimension, the
`twist angle of the liquid crystal material of the com
`pensator cell being of opposite rotational sense to that
`
`10
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`35
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`40
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`50
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`55
`
`60
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`65
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`Patent Owner’s Exhibit 2002
`IPR2015-00021
`Page 9 of 9
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