Classifications

• • 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
  • G09G3/3406—Control of illumination source
  • G09G3/3413—Details of control of colour illumination sources
• • 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
  • H04N9/3111—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators for displaying the colours sequentially, e.g. by using sequentially activated light sources
  • H04N9/3114—Projection devices for colour picture display, e.g. using electronic spatial light modulators [ESLM] using two-dimensional electronic spatial light modulators for displaying the colours sequentially, e.g. by using sequentially activated light sources by using a sequential colour filter producing one colour at a time
• • 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]
  • H04N9/3141—Constructional details thereof
  • H04N9/315—Modulator illumination systems
• • 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
  • G09G2310/00—Command of the display device
  • G09G2310/02—Addressing, scanning or driving the display screen or processing steps related thereto
  • G09G2310/0237—Switching ON and OFF the backlight within one frame
• • 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
  • G09G2310/06—Details of flat display driving waveforms
  • G09G2310/066—Waveforms comprising a gently increasing or decreasing portion, e.g. ramp
• • 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
  • G09G2320/06—Adjustment of display parameters
  • G09G2320/0613—The adjustment depending on the type of the information to be displayed
  • G09G2320/062—Adjustment of illumination source parameters
• • 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
  • G09G2320/06—Adjustment of display parameters
  • G09G2320/0626—Adjustment of display parameters for control of overall brightness
• • 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
  • G09G2320/06—Adjustment of display parameters
  • G09G2320/0626—Adjustment of display parameters for control of overall brightness
  • G09G2320/064—Adjustment of display parameters for control of overall brightness by time modulation of the brightness of the illumination source

Definitions

• the present invention is related to the field of image projection.
• a number of projection systems designed to render images, or more specifically, an image frame, by successively turning on and off selected ones of a number of light emitting devices have been proposed.
• each of the light emitting devices emits light in a primary color, e.g. red, green or blue.
• each of the light emitting devices is driven in accordance with its drive current design point, which is often selected to enable the light emitting device to have a reasonable chance of having a reasonably lengthy operational life.
• many of these projection systems employ light valves to control the color of each pixel of the image frame being rendered.
• a light valve e.g. may be a micro-mirror device, (for example DLP® device from Texas Instruments, Dallas, Texas) and the color of a pixel may be controlled by controlling the on or off state of one or more micro-mirrors of the micro-mirror device through pulse width modulation of the micro-mirror device in synchronization with colored illumination light. Due to the responsiveness (response time) limits of some of the micro-mirrors (in the light valves), many of these projection systems have difficulty effectively imaging dark scenes, where discernment between the lowest gray levels are desired. An example is night scenes in a movie. Typically, temporal and/or spatial dithering is required.
• Temporal dithering refers to the effectuating of a color (and grayscale) effect through color controls that span different frame periods
• spatial dithering refers to the effectuating of a color (and grayscale) effect through color controls that span different pixels.
• practice of either or both of these dithering techniques adds to operational complexity and cost (since a high compute power image processing ASIC is required to implement spatial and/or temporal dithering).
• these dithering techniques result in image artifacts: the appearance of noise or "snow" or lack of image detail in darker images and blurring of moving objects.
• Another problem suffered by non-CRT projection systems is their inability to provide "peak white" to a small area of an image frame like CRT displays can.
• Figure 1 is a block diagram illustrating a number of function blocks of a projection system, in accordance with one embodiment
• Figure 2 illustrates the light source and the projection optics in further details, in accordance with one embodiment of the present invention
• Figures 3a-3d illustrate various schemes for driving the light emitting devices of the light source of Fig. 1, in accordance with various embodiments
• Figure 3e illustrates an example complementary control of a light valve, in accordance with one embodiment
• Figure 4 illustrates a portion of the operational flow of the controller of Fig.
• Embodiments of the present invention include but are not limited to methods for driving light emitting devices of a light source of a projection system, and projection systems incorporated with logic to practice the methods.
• various aspects of embodiments of the present invention will be described. However, it will be apparent to those skilled in the art that other embodiments may be practiced with only some or all of the described aspects. For purposes of explanation, specific numbers, materials and configurations are set forth in order to provide a thorough understanding of the embodiments. However, it will be apparent to one skilled in the art that other embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the description.
• projection system 100 includes light source 102 and projection optics 104, optically coupled to each other.
• light source 102 optically cooperates with projection optics 104, by providing light, to jointly effectuate rendering of desired images, which may be image frames of a video.
• desired images which may be image frames of a video.
• a still image may be considered as a degenerate or special video where there is only one frame. Accordingly, both still image and video terminologies may be used in the description to follow, and they are not to be construed to limit the present invention to the rendering of one or the other.
• a frame is typically comprised of a number of lines of pixels, which are rendered by controlling provision of light of selected colors in a time period, referred to as a frame period.
• the colors may be primary colors, and may be sequentially provided in portions of the frame period, also referred to as a sub- period.
• light source 102 may include a number of light emitting devices. More specifically, in various embodiments, the light emitting devices may be primary color light emitting devices designed to output light in corresponding primary colors. In particular, in various embodiments, the light emitting devices may be light emitting diodes (LED). Further, in various embodiments, projection optics 104 may include a light valve. More specifically, in various embodiments, the light valve may be a micro- mirror device having a number of micro-mirrors to facilitate control of the colors of the various pixels of an image frame being rendered. For the embodiment of Fig. 1 , projection system 100 also includes controller 106, which is electrically coupled to light source 102 and projection optics 104.
• controller 106 which is electrically coupled to light source 102 and projection optics 104.
• Controller 106 may receive e.g. a video signal as input, and control light source 102 and projection optics 104 accordingly, to effectuate rendering of the image frames of the video signal.
• controller 105 drives the light emitting devices of light source 102 in a selected or derived one of a number of advantageous driving schemes, and optionally, controls a light valve of projection optics 104 in a complementary manner. Resultantly, light emitting devices of light source 102 may have the desired longer operational life, and yet, projection system 100 may also render an image frame with improved gray levels and/or improved peak white.
• Figure 2 illustrates the light source 102 and projection optics 104 in further detail, in accordance with one embodiment.
• light source 102 may include light emitting devices 202R, 202G and 202B, which may be red, green and blue light emitting diodes (LED) respectively, for emitting light in various primary colors, e.g. red, green and blue, when driven (i.e., when currents are applied).
• Projection optics 104 may include a dichroic combiner 204, light integrator 206, mirror 208 and micro-mirror device 210, optically coupled to each other and to light emitting devices 202R, 202G and 202B as shown.
• Micro-mirror device 210 may include in particular a number of micro-mirrors.
• light emitting devices 202R, 202G and 202B, and micro-mirror device 210 are electrically coupled to, and controlled by controller 106, to control the colors of the various pixels of an image frame being rendered, during operation.
• controller 106 advantageously controls the operation of light emitting devices of light source 102 and a light valve of projections optics 104
• projection system 100 represents a broad range of projection systems.
• light source 102 and projection optics 104 may be provided with light emitting devices and light valves of other types respectively, to facilitate control of the colors of the various pixels of an image frame being rendered.
• FIGS. 3a-3d illustrate various schemes controller 106 may drive the light emitting devices of light source 102, in accordance with various embodiments.
• each of the light emitting devices is assumed to have a drive current design point (Hoc) 306b selected to allow the device to have a reasonable chance of having a reasonably lengthy operational life.
• controller 106 successively drives the light emitting devices in successive sub- periods 302a-302c/302d of a frame period 302. As illustrated in Fig.
• controller 106 causes a drive circuit (not shown) to apply (hereinafter, simply “applies") a level of current (H af j j ) during sub-period 1 (sp1 ) 302a of frame period 302 to drive (304B) a light emitting device to emit the primary blue color.
• controller 106 "applies" a level of current (H ad j) during sub-period 2 (sp2) 302b and sub-period 3 (sp3) 302c of frame period 302 to drive (304R and 304G) two other light emitting devices to emit the primary red color and the primary green color respectively.
• current level Ha d j is the drive current design point Hoc adjusted in view of the size of each of the sub-periods (sp1-sp3, 302a- 302c) relative to the size of frame period 302. More specifically, for the embodiment, since each of the sub-periods (sp1-sp3, 302a-302c) is about 1/3 the size of frame period 302, current level H ac ij is about 3 times that of Hoc- In alternate embodiments, depending on the desired tradeoff between brightness and LED lifetime, H af jj may be somewhat higher or lower than 3 times that of Hoc. For ease of understanding, the embodiment of Fig.
• each of the light emitting devices has been described with each of the light emitting devices as having the same drive current design point HDC > and each of the sub-periods (sp1-sp3, 302a-302c) as having the same size.
• the drive current design point of each of the light emitting devices, and/or the size of each of the sub-periods may be different.
• the applied current for the embodiment, is the drive current design point adjusted in view of the size of the particular sub-period relative to the size of the frame period and the specific properties of the LED.
• Figure 3b illustrates another scheme for driving the light emitting devices of light source 102, in accordance with another embodiment.
• the embodiment in Fig. 3b is similar to the embodiment of Fig.
• controller 106 in addition to successively driving the light emitting devices to emit the primary colors in 3 sub-periods 302a-302c, applies. current to drive all light emitting devices at the same time in a fourth sub-period 302d to provide white light.
• the embodiment advantageously enables projection system 100 to provide improved peak white for an image frame.
• the additional sub-period 302d is included only when the content of the image frame has a need for peak white illumination.
• the applied current is the drive current design point adjusted in view of the size of two of the sub-periods 302a-302d relative to the size of the frame period 302.
• H af jj is about 2 times of Hoc (since two of the sub-periods 302a-302d is about one-half of the frame period 302).
• Figures 3c-3d illustrate yet two other schemes to drive the light emitting devices of light source 102, in accordance with two embodiments.
• the embodiments of Fig. 3c and Fig. 3d are similar to the embodiment of Fig. 3a, except, controller 106, in lieu of applying current to the light emitting devices at a constant rate, applies current in a variable manner during a sub-period.
• the variable application of current has the form factor of a step function (with one step), whereas for the embodiment of Fig.
• variable application of current has the form factor of varying linearly over time.
• variable application of current may have a form factor of a step function with two or more steps, a sawtooth function with a number of sawtooth, or other functions that vary linearly or non-linearly.
• the light valve of a pixel is held in the "on" state for the length of time required to achieve the desired pixel brightness.
• the pixel brightness is the time integral of the pixel brightness from the time the light valve of the pixel is turned on to the time the light valve of the pixel is turned off.
• the average applied current during each sub- period is the drive current design point adjusted in view of the average power applied to the light source over the frame period.
• average H adj is about 3 times of Hoc in the case of square wave current pulse at 1/3 duty cycle.
• each of the embodiments of Fig. 3c and 3d may also be practiced in combination with the embodiment of Fig. 3b.
• Figure 4 illustrates a portion of the operational logic of controller 106, in accordance with one embodiment.
• controller 106 may be implemented employing a general purpose controller or an application specific integrated circuit (ASIC) with the logic being implemented in firmware. In yet other embodiments, the logic may be implemented via combinatorial circuits. Regardless, the portion of operational logic begins with controller 106 determining whether the image frame should be rendered with a standard 3 sub- period frame period, or a frame period with a white sub-period, block 402. In various embodiments, controller 106 may make the determination based on whether the video signal includes a request for the peak white period for a frame. In other environments, controller 106 with sufficient computing resources may analyze a frame in real time to determine whether a peak white period should be provided.
• ASIC application specific integrated circuit
• controller 106 proceeds to the operations of blocks 406- 408. However, if it is determined that the image frame is to be rendered with a frame period with a white sub-period, controller 106 dynamically modifies the size of each sub-period, block 404, before proceeding to perform the operations of blocks 406-408. At blocks 406-408, controller 106 causes the appropriate level of current
• controller 106 may also turns a light valve, such as micro-mirrors of a micro-mirror device, of projection optics 104, on and off, as appropriate, to provide the desired gray scale.

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• Engineering & Computer Science (AREA)
• Multimedia (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• Computer Hardware Design (AREA)
• General Physics & Mathematics (AREA)
• Theoretical Computer Science (AREA)
• Control Of Indicators Other Than Cathode Ray Tubes (AREA)
• Projection Apparatus (AREA)
• Transforming Electric Information Into Light Information (AREA)
• Circuit Arrangement For Electric Light Sources In General (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (2)

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Family Applications (1)

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Cited By (2)

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Citations (4)

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• 2004
  • 2004-04-30 US US10/835,672 patent/US7408527B2/en not_active Expired - Fee Related
• 2005
  • 2005-04-27 JP JP2007510948A patent/JP2007535709A/ja active Pending
  • 2005-04-27 CN CN200580021024.4A patent/CN1985523B/zh not_active Expired - Fee Related
  • 2005-04-27 EP EP05741333A patent/EP1754092A2/en not_active Withdrawn
  • 2005-04-27 WO PCT/US2005/014510 patent/WO2005111691A2/en not_active Ceased
  • 2005-04-29 DE DE202005006910U patent/DE202005006910U1/de not_active Expired - Lifetime
  • 2005-04-30 CN CN200520011877.7U patent/CN2935207Y/zh not_active Expired - Lifetime

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