Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/03—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
  • G09G3/3433—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices
  • G09G3/346—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using light modulating elements actuated by an electric field and being other than liquid crystal devices and electrochromic devices based on modulation of the reflection angle, e.g. micromirrors
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/07—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on electro-optical liquids exhibiting Kerr effect
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N9/00—Details of colour television systems
  • H04N9/12—Picture reproducers
  • H04N9/31—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM]
  • H04N9/3102—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators
  • H04N9/312—Driving therefor
  • H04N9/3123—Driving therefor using pulse width modulation
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2310/00—Command of the display device
  • G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
  • G09G2310/0235—Field-sequential colour display
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G2320/00—Control of display operating conditions
  • G09G2320/02—Improving the quality of display appearance
  • G09G2320/0242—Compensation of deficiencies in the appearance of colours
• • G—PHYSICS
  • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
  • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
  • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
  • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
  • G09G3/2007—Display of intermediate tones
  • G09G3/2018—Display of intermediate tones by time modulation using two or more time intervals

Definitions

• This invention relates to a pulse width modulated light projection system, and more particularly, to a technique for operating a pulse width modulated light projection system to minimize motion contouring.
• DMD Digital Micromirror Device
• a type of semiconductor device comprising a plurality of individually movable micromirrors arranged in a rectangular array. Each micromirror pivots about limited arc, typically on the order of 10-12° under the control of a corresponding driver cell that latches a bit therein.
• the driver cell Upon the application of a previously latched "1" bit, the driver cell causes its associated micromirror cell to pivot to a first position.
• a previously latched "0" bit to the driver cell causes the driver cell to pivot its associated micromirror to a second position.
• each individual micromirror of the DMD device when pivoted by its corresponding driver cell to the first position, will reflect light from the light source through the lens and onto a display screen to illuminate an individual picture element (pixel) in the display.
• each micromirror When pivoted to its second position, each micromirror reflects light away from the display screen, causing the corresponding pixel to appear dark.
• An example of such DMD device is the DMD of the DLPTM projection system available from Texas Instruments, Dallas Texas.
• Present day projection systems that incorporate a DMD of the type described control the brightness (illumination) of the individual pixels by controlling the duty cycle during which the individual micromirrors remain “on” (i.e., pivoted to their first position), versus the interval during which the micromirrors remain “off (i.e. pivoted to their second position).
• DMD-type projection systems use pulse width modulation to control the pixel brightness by varying the duty cycle of each micromirror in accordance with the state of the pulses in a sequence of pulse width segments.
• Each pulse width segment comprises a string of pulses of different time duration.
• the state of each pulse in a pulse width segment determines whether the micromirror remains on or off for the duration of that pulse. In other words, the larger the sum of the widths of the pulses in a pulse width segment that are turned on (actuated), the longer the duty cycle of each micromirror.
• the frame interval i.e., the time between displaying successive images, depends on the selected television standard.
• the NTSC standard currently in use in the United States requires a frame interval of 1/60 second whereas certain European television standards employ a frame interval of 1/50 second.
• Present day DMD-type television projection systems typically achieve a color display by projecting red, green, and blue images either simultaneously or in sequence during each frame interval.
• a typical sequential DMD-type projection system utilizes a motor-driven color wheel interposed in the light path of the DMD.
• the color wheel has a plurality of separate primary color windows, typically red, green and blue, so that during successive intervals, red, green, and blue light, respectively, falls on the DMD.
• red, green and blue light must fall on the DMD at least once within each successive frame interval. If only one red, one green and one blue image is made and each consumes 1/3 of the frame interval, then the large interval between colors will produce perceptible color breakup with motion.
• Present day DMD systems address this problem by breaking each color into several intervals and interleaving the intervals in time, thereby reducing the delay between colors.
• Pulse width modulated projection systems of the type described above that have the ability to make multiple images of each primary color during each frame interval to yield a color picture often suffer from motion contouring on small amplitude transients, such as those associated with motion in a scene or motion of the viewer's eyes. This type of artifact results from changes in the distribution of the light pulses across different portions of the display period.
• U.S. Patent 5,986,640 discloses a scheme for reducing motion contouring by splitting the most significant bits in a sequence of pulse width segments between two or more time-adjacent segments (intervals). While this scheme serves to reduce contouring, it does not eliminate contouring on all transitions. Further, splitting bits in a manner sufficient to reduce contouring will increase the number of times each pixel must be addressed, thereby increasing the bandwidth needed to accomplish such addressing.
• a pulse width modulated display system such as a pulse width modulated display system that incorporates a Digital Micromirror Device (DMD), to selectively reflect light from a light source through a projection lens and onto a display screen.
• DMD Digital Micromirror Device
• the illumination of each pixel for a given color is controlled responsive to pulses within a sequence of pulse width segments. The state of each pulse in each segment determines whether the pixel becomes illuminated during the interval associated with that pulse.
• pixel brightness is increased by actuating selected pulses such that within a first range of brightness levels between first and second pixel brightness boundaries, a first large- duration pulse (or combination of pulses) becomes actuated to reach the second pixel brightness boundary.
• a first large- duration pulse or combination of pulses
• the first large duration pulse or combination of pulses
• the second large duration pulse or combination of pulses
• a second large duration pulse also becomes actuated, with the first large duration pulse remaining actuated.
• thermometer code pulse Because once actuated, that pulse (or combination of pulses) remains actuated upon further increases in pixel brightness above that brightness boundary in a manner analogous to a temperature level on a mercury thermometer.
• a given segment can include more than one such thermometer code pulse.
• thermometer code pulse changes state (i.e., becomes actuated). Conversely, when the pixel brightness is decreased to a given pixel brightness boundary, only a single thermometer code pulse that had been actuated becomes now de-actuated, with the other thermometer code pulses that have yet to be de-actuated thus remaining actuated.
• FIGURE 1 depicts a block schematic diagram of a present-day pulse width modulated display system
• FIGURE 2 depicts a frontal view of a color wheel comprising part of the display system of FIG 1;
• FIGURES 3-7 collectively illustrate a pulse map depicting each of a plurality of sequences of pulse width segments that control the brightness of one of the pixels within the display system of FIG. 1 for a given color to reduce motion contouring in accordance with the present principles.
• FIGURE 1 depicts a present-day pulse width modulated display system 10 of the type disclosed in the Application Report "Single Panel DLPTM Projection System Optics” published by Texas Instruments, June 2001 and incorporated by reference herein.
• the system 10 comprises a lamp 12 situated at the focus of a parabolic reflector 13 that reflects light from the lamp through a color wheel 14 and into an integrator rod 15.
• a motor 16 rotates the color wheel 14 to place a separate one of red, green and blue primary color windows between the lamp 12 and the integrator rod 15.
• the color wheel 14 has diametrically opposed red, green and blue color windows 17 ⁇ and 17 4 , 17 2 and 17s, and 17 3 and 17 6 , respectively.
• the motor 16 rotates the color wheel 14 of FIG. 2 in a counterclockwise direction, red, green and blue light will strike the integrator rod 15 of FIG. 1 in an RGBRGB sequence.
• the motor 16 rotates the color wheel 14 at a sufficiently high speed so that during a frame interval of a 1/60 second, red, green and blue light each strikes the integrator rod five times, yielding 15 color images within the frame interval.
• Other mechanisms exist for successively imparting each of three primary colors. For example, a color scrolling mechanism (not shown) can perform this task as well.
• the integrator rod 15 concentrates the light from the lamp 12, as it passes through a successive one of the red, green and blue color windows of the color wheel 14, onto a set of relay optics 18.
• the relay optics 18 spread the light into a plurality of parallel beams that strike a fold mirror 20, which reflects the beams through a set of lenses 22 and onto a Total Internal Reflectance (TIR) prism 23.
• TIR prism 23 reflects the parallel light beams onto a Digital Micromirror Device (DMD) 24, such as the DMD device manufactured by Texas Instruments, for selective reflection into a projection lens 26 and onto a screen 28.
• DMD Digital Micromirror Device
• the DMD 24 takes the form of a semiconductor device having a plurality of individual mirrors (not shown) arranged in an array.
• the DMD manufactured and sold by Texas Instruments has a micromirror array of 1280 columns by 720 rows, yielding 921,600 pixels in the resultant picture projected onto the screen 28.
• Other DMDs can have a different arrangement of micromirrors. As discussed previously, each micromirror in the DMD pivots about a limited arc under the control of a corresponding driver cell (not shown) in response to the state of a binary bit previously latched in the driver cell. Each micromirror rotates to one of a first and a second position depending on whether the latched bit applied to the driver cell, is a "1" or a "0", respectively.
• each micromirror When pivoted to its first position, each micromirror reflects light into the lens 26 and onto the screen 28 to illuminate a corresponding pixel. While each micromirror remains pivoted to its second position, the corresponding pixel appears dark. The interval during which each micromirror reflects light through the projection lens 26 and onto the screen 28 (the micromirror duty cycle) determines the pixel brightness.
• the individual driver cells in the DMD 24 receive drive signals from a driver circuit 30 of a type well known in the art and exemplified by the circuitry described in the paper "High Definition Display System Based on Micromirror Device", R.J. Grove et al. International
• the driver circuit 30 generates the drive signals for the driver cells in the DMD 24 in accordance with sequences of pulse width segments applied to the driver circuit by a processor 31.
• Each pulse width segment comprises a string of pulses of different time duration, the state of each pulse determining whether the micromirror remains on or off for the duration of that pulse.
• the shortest possible pulse i.e., a 1 -pulse
• LSB Least Significant Bit
• each pulse within a pulse width segment corresponds to a bit within a digital bit stream whose state determines whether the corresponding pulse is turned on or off.
• a "1" bit represents a pulse that is actuated (turned on), whereas a "0" bit represents a pulse that is de-actuated (turned off).
• each color primary is displayed in a sequence of five pulse width segments.
• Each pulse width segment has a total pulse width of 51 LSBs, so each sequence of five pulse width segments has a total pulse width of 255 LSBs, thus enabling each pixel to have one of 256 brightness levels for a given color
• Each LSB (1-pulse) typically has a duration of 15 microseconds.
• each 51 LSB pulse width segment has a duration of 765 microseconds.
• Table 1 illustrates an illustrative arrangement of LSBs in each of the five segments comprising a pulse width sequence.
• Motion contouring is minimized in accordance with present principles by minimizing the number and width of pulses that become de-actuated when one or more other pulses become actuated for a consecutive one-Least Significant Bit (i.e., a 1-pulse) change in brightness.
• a consecutive one-Least Significant Bit i.e., a 1-pulse
• selected pulses in one or more segments are actuated such that at each successive pixel brightness boundary, a yet un-actuated large duration pulse (i.e., a 13 -pulse in the illustrative embodiment, or a combination of pulses, such as the 7-pulse and 6- pulse) becomes actuated.
• a yet un-actuated large duration pulse i.e., a 13 -pulse in the illustrative embodiment, or a combination of pulses, such as the 7-pulse and 6- pulse
• each large duration pulse (or combination of pulses) that was previously actuated upon reaching the preceding pixel brightness boundary remains
• thermometer code Each large duration pulse (or combination of pulses) that becomes actuated to reach a given pixel brightness boundary is referred to as a "thermometer code" pulse because once actuated, each such thermometer code pulse remains actuated upon further increases in pixel brightness above that pixel brightness boundary in a manner analogous to the mercury in a mercury thermometer. (Upon reaching a particular temperature level, the mercury continues to rise above that level responsive to a temperature increase.)
• a given pulse width segment can have multiple thermometer code pulses.
• FIGURES 3-6 collectively illustrate a pulse map of the sequences of pulse width segments that illuminate a corresponding pixel for a given color at each of brightness levels #0- #255.
• Segment 3 is chosen as the first segment whose thermometer code pulses are actuated, with each thermometer code pulse that had been actuated to reach pixel brightness boundary remaining actuated as the pixel brightness increases above that boundary.
• reaching brightness level #1 requires actuation of a 1-pulse. Since Segment 3 has no 1-pulse in this example, the 1-pulse in Segment 2 is actuated.
• the 2-pulse in Segment 3 becomes actuated with the 1-pulse in Segment 2 de-actuated at this brightness level.
• the 1-pulse in Segment 2 and the 2-pulse in Segment 3 become actuated.
• Brightness level #13 (which constitutes a first pixel brightness boundary) is reached by actuating the 13-pulse (first) in Segment 3 with all the other pulses de-actuated at this pixel brightness level.
• the 1-pulse in Segment 2 is actuated with the 13-pulse (first) in Segment 3 remaining actuated.
• the 13-pulse (first) within Segment 3 remains actuated.
• the 13- pulse (first) in Segment 3 constitutes the first thermometer code pulse in that segment that becomes actuated.
• Each of brightness levels #14-#25 is achieved by maintaining the 13-pulse in Segment 3 actuated and by actuating selected ones of the 4-pulse, 2-pulse and the 6-pulse (first) within Segment 3 and the 1-pulse in Segment 2.
• the 13-pulse (second) in Segment 3 become actuated, with the 13-pulse (first) in the same segment remaining actuated.
• both the 13-pulses (first and second) in Segment 3 remain actuated, with the 1-pulse in Segment 2 now actuated at this brightness level.
• the 13-pulse (second) in Segment 3 constitutes the second thermometer code pulse that in segment that becomes actuated.
• Each of brightness levels #28-#61 is achieved by maintaining the two 13 -pulses (first and second) in Segment 3 actuated, and by actuating selected ones of the 7- ⁇ ulse, 4-pulse, 2-pulse and the 6-pulses (first and second) in Segment 3 and selected ones of the 7-pulse, 1-pulse and 4- pulse in Segment 2.
• both the 7-pulse and the 6-pulse (second) in Segment 3 are actuated, and both of these pulses remain actuated as the pixel brightness level increases.
• the 7-pulse and the 6-pulse (second) in Segment 3 collectively constitute a combination thermometer code pulse. Note that at pixel brightness level #51, all of the pulses in Segment 3 become actuated. With the exception of the 2-pulse in Segment 3, all of the other pulses in that segment remain actuated as the pixel brightness level increases above brightness level #51.
• the 13-pulse (first) in Segment 2 becomes actuated, along with all of the pulses in Segment 3 except the 2-pulse.
• the 1-pulse in Segment 2 is actuated, with the 13-pulse (first) in Segment 2 and all of the pulses in Segment 3 except the 2- pulse remaining actuated.
• the 13-pulse (first) in Segment 2 becomes the first thermometer code pulse in that segment which is actuated.
• each large pulse e.g., the 13-pulses
• a combination of pulses e.g., the 7-pulse and the 6-pulse (second) in Segment 3
• each such pulse constitutes a thermometer code pulse in accordance with the present principles.
• each thermometer code pulse has the property of being sufficiently large (i.e., of a sufficiently long duration) so that once actuated to reach a pixel brightness boundary, the pulse remains actuated at brightness levels above that pixel brightness boundary while limiting the total number of pulses in a segment.
• a single thermometer code pulse (or a combination of such pulses that comprise a thermometer code pulse) become actuated and remains actuated as the pixel brightness increases above that boundary.
• a single thermometer pulse becomes de-actuated with the thermometer code pulses not yet de-actuated remaining actuated until a next successively lower pixel brightness boundary is reached.
• each thermometer code pulse within each segment should not be so large so that when actuated or de-actuated, there is noticeable transient for an incremental change in pixel brightness (i.e., an increase in pixel brightness to a next higher level or decrease in pixel brightness to a next lower level).
• the selection of thermometer code pulses should serve to confine to substantially a singe pulse width segment the "swapping" of pulses (i.e., the selection of pulses which are actuated) to reach a particular brightness state.
• the swapping of pulses that occur to reach a particular brightness level could occur among several segments so long as a single thermometer code pulse (or combination of pulses) in a single segment become actuated or de-actuated between successive pixel brightness boundaries.

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• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• Engineering & Computer Science (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Theoretical Computer Science (AREA)
• Ceramic Engineering (AREA)
• Crystallography & Structural Chemistry (AREA)
• Chemical & Material Sciences (AREA)
• Computer Hardware Design (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Control Of Indicators Other Than Cathode Ray Tubes (AREA)
• Projection Apparatus (AREA)
• Transforming Electric Information Into Light Information (AREA)
• Video Image Reproduction Devices For Color Tv Systems (AREA)

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• 2003
  • 2003-08-11 AU AU2003265408A patent/AU2003265408A1/en not_active Abandoned
  • 2003-08-11 WO PCT/US2003/025119 patent/WO2004015981A2/en active Search and Examination
  • 2003-08-11 JP JP2004528034A patent/JP2006508378A/ja active Pending
  • 2003-08-11 KR KR1020057002532A patent/KR101015029B1/ko active IP Right Grant
  • 2003-08-11 CN CNB038191946A patent/CN100396105C/zh not_active Expired - Fee Related
  • 2003-08-11 MX MXPA05001668A patent/MXPA05001668A/es active IP Right Grant
  • 2003-08-11 EP EP03785185A patent/EP1546794A4/en not_active Withdrawn

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