CA1233282A - Solid state color display system and light emitting diode pixels therefor - Google Patents

Solid state color display system and light emitting diode pixels therefor

Info

Publication number
CA1233282A
CA1233282A CA000496813A CA496813A CA1233282A CA 1233282 A CA1233282 A CA 1233282A CA 000496813 A CA000496813 A CA 000496813A CA 496813 A CA496813 A CA 496813A CA 1233282 A CA1233282 A CA 1233282A
Authority
CA
Canada
Prior art keywords
pixel
color
signals
display
means
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
CA000496813A
Other languages
French (fr)
Inventor
Brent W. Brown
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
INTEGRATED SYSTEMS ENGINEERING Inc
Original Assignee
INTEGRATED SYSTEMS ENGINEERING Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Priority to US73862485A priority Critical
Application filed by INTEGRATED SYSTEMS ENGINEERING Inc filed Critical INTEGRATED SYSTEMS ENGINEERING Inc
Application granted granted Critical
Publication of CA1233282A publication Critical patent/CA1233282A/en
Priority to US738,624 priority
Application status is Expired legal-status Critical

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Classifications

    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control 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
    • G09G3/22Control 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 using controlled light sources
    • G09G3/30Control 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 using controlled light sources using electroluminescent panels
    • G09G3/32Control 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 using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00Command of the display device
    • G09G2310/02Addressing, scanning or driving the display screen or processing steps related thereto
    • G09G2310/0243Details of the generation of driving signals
    • G09G2310/0259Details of the generation of driving signals with use of an analog or digital ramp generator in the column driver or in the pixel circuit
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00Control of display operating conditions
    • G09G2320/02Improving the quality of display appearance
    • G09G2320/0285Improving the quality of display appearance using tables for spatial correction of display data
    • GPHYSICS
    • G09EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09GARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20Control 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
    • G09G3/2007Display of intermediate tones
    • G09G3/2014Display of intermediate tones by modulation of the duration of a single pulse during which the logic level remains constant

Abstract

ABSTRACT OF THE DISCLOSURE
Solid state color display systems and light emitting diode (LED pixels therefore Each pixel comprises a large number of LED chips arranged compactly to provide a discrete element light source of sufficient output to ye viewed as a point source of light from a substantial distance. The arrays of pixels are placed in a matrix of a type typically used in scoreboards, message centers and other large display systems, although the various combinations, sub combinations, and elements are not limited to such uses. Each pixel is mounted in a molded package which may include a transparent lens covering and sufficient number of connecting leads to provide for the number of colors of LEDs contained in the pixel array. Each pixel is placed in a mounting fixture which also accommodates the necessary electrical connections to multiplexed driving circuitry. The light emitted is determined by the type of LED used in the array, preferably an array of red, green and blue, although amber, green and other color combinations may be used. Using three colors, blue, red, green that are controlled by separate driving circuitry provides the capacity to create any color in the spectrum.

Description

issue Solid Sly` ~lSl'Lr,Y YO-YO Anal i~lG~r ~MlT'rlNG
DIODE PIXELS rho row Field of invention This invention relates generally to display equipment and more particularly to a solid state color display system suitable for a color display and discrete elements therefore each comprising a compact array of light emitting diodes.

Prior Art In the convential construction of a large color display system (for example apparatus for displaying advertising, pictures, or the like at stud, etc.), the words or pictures are formed by selectively turning on or off colored electrical lamps in predetermined pattern (this will produce what is known as cartoon color), or CRT types which are miniature TV screens which then provides the capability to produce true color (any color in the spectrum). Both systems present difficult problems.

The electric lamps have poor color rendition, which results from the fact that the electric lamps bring out colors by having their filaments heated to red heat and assumes a red heat or white orange color. Therefore, in order to produce colors, colored glass filters are used to selectively filter two color desired. Since electric lamps on the order of 7 watts or more have been generally used, a large display (using thousands of lamps) consumes a large amount of electrical power anal 9cnc~rat(!s a Lowry amount Or heat.
A display using Cuts requires a large amount of power also and, although not much electrical power or heat is generated by the CRT, the circuitry required to drive and control the intensity is extensive and is very costly to manufacture and operate.

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south types of displays are subject to short lamp life, on the order ox 8000-10,0()0 hours, which recolors costly m~lint~nance to replace them.
While light emitting diodes (Lids) have been used in displays, they have been used in small installation or devices such as calculators and indicators. Their use in large displays have been rejected as impractical due to the small amount of luminance available for the standard LED. The luminance emitted by an LED
chip over an area of approximately .014" by .014" (0.0002 square inch area) is diffused over an area of approximately 0.0628 square inches. Therefore, the legality is diffused over an area 300 times larger than the source chip and hence the light emitted is unacceptably low.
In those situations, where a discrete LED is used in a matrix, (see Teshima, US. Patent No. 4,271,408) the display would have to use large collimating lens that pick up the luminance from several discrete Lids.
In array uses ox Lids, such as mentioned by Ichikawa (US.
Patent No. 4,445,1~), a flat panel display results. 'Lowe method described by Ichikawa would be useful in small flat panel displays, the density and amount of circuitry required to drive each module would be both costly and prohibitive in a large matrix display used to display alphanumerics and animations.

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BRIEF SUMMARY AND OBJE(,`TS_OF THE I MENTION

In brief summary, the present invention largely overcomes or alleviates the aforementioned problems of the prior art and provides novel and unobvious solid state color display systems, including the large scoreboard type, and light emitting diode pixels forming the discrete legality source elements thereof. A large number of SLED chips typically comprise each pixel and the pixels are placed in a matrix and selectively illuminated under the control of driving circuitry. The light emitted is determined by the type ox Lids usual in the array. Using three colors, blue, red, green that are controlled by separate driving circuitry, accommodates generation of any color in the spectrum.
With the array containing many Leeds spaced at close intervals, the whole array becomes a point source for the light;
hence the effective light output is increased to the point that it becomes possible to have satisfactory contrast. The size of the array is determined by the number of lo chips included to achieve the size of pixel desired.
By using red, blue, green chip combinations on the same array with separate connecting leads, a true color system is created which will reproduce any color.
With the foregoing in mind, it is a primary object of the present invention to provide a novel solid state color display system and related method.
nether paramount o~jcct ox this invention is the provision of a novel solid state discrete pixel, for a color display system, comprising an array of light emitting diodes sleds).
A further dominant object is the provision of novel solid state color display systems, includil1~ but not limited to large scoreboard type displays, weakly systems comprise one or more matrices formed of pixels each comprising an array of closely :

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spaced variously colored Lo which are selectively illuminated.
An additional important object of the present invention is the provision of novel solid state color display systems comprising discrete elements formed ox LED pixels having one or more of the following characteristics: (1) on the order of several times the electric to optical efficiency of a conventional lamp discrete display element; and (2) sufficient light intensity to provide sufficient contrast.
Another valuable object to the present invention is the provision of a solid state color discrete light source element comprising a very compact array of sufficient size to generate a light source of any color in the spectrum having sufficient luminous output to be viewed in high ambient light conditions.
A further significant object is to provide a display system comprising discrete color light source display elements comprising an array of light emitting diodes having at least one of the following features: (1j all LED chips are of the same type connected in parallel or series - parallel, (2) the LED chips comprise a plurality of colors, each separately electrically actuated accommodating change in tile display image from one color to another; and (3) the LED chips comprise red, green and blue colors, each color being mounted as a group of Lids in each array and each differentially electrically controlled to vary the intensity of the output of each color whereby any color in the spectrum may be selectively produced.
These and other objects and features of the present invention will be apparent from the detailed description taken with reference to the accompanying drawings.

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BRIEF DESCRTPTTON OF Tile DRAWINGS
_ _ _ _ _ _ _ _ _ . _ . _ . _ _ . _ , . . . . _ _ _ _ _ _ . _ _ . . . _ , _ _ _ _ _ _ _ _ _ _ _ . _ _ Figure 1 is a cross scion ox an lo of an array or pixel in accordance with the present invention mounting to substrate;
Figure 2 is an enlarged front view of a tricolor trod, green, blue (RUB)] LED array or pixel in accordance with the present invention;
Figure 3 is a reduced scale cross section of the LED array or pixel taken along lines 3-3 of Figure 2;
Figure 4 is a front view of a typical series-parallel cathode/anode printed circuit board forming a part of the illustrated LED pixel;
Figure 5 is a series-parallel anodc/cathode circuit diagram for LED pixels according to the present invention;
Figure 6 is an exploded cross section of a typical electrical connection arrangement for an LED pixel in accordance with the present invention;
Figure 7 is a rragl11cnLary frill view of a matrix display using LED pixels according to the present invention;
Figure 8 is a schematic block diagram of an eight color RUB
digital display system driven by a computer controlled massage center;
Figure 9 is a schematic of a typical RUB driver circuit forming part of the system of Figure 8;
: Figure 10 is a schematic block diagram of another RUB 4096 color digital display system optionally driven by either a computer : : controlled message center or a video digitizer;
Figure 11 is a schematic ox a driver circuit forming a part of the display system of ~igurc 10;
Figure 12 is a schematic block diagram of a RUB analog : display system which processes composite video to the LED pixel : display of the present invention;

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Figure 13 is a schematic of analog RUG driver circuitry used in conjunction with the display system of Figure 12; and Figure 14 is an enlarged fragmentary circuit diagram of part of the circuit of Figure 13 my which selected Lids ox any pixel are turned on and off and the brightness thereof controlled.

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DETAILED DISCRETION Old Toll tI.L.USTR~TED EMBODIMENTS

Reference is now made to the drawings wherein like numerals are used to designate like parts throughout. In genera], the Figures illustrate presently preferred color embodiments of solid state display systems and light emitting diode pixels therefore Each pixel light source comprises a large number of LED chips arranged compactly to provide a discrete element light source of sufficient output to be viewed Clairol from a substantial distance (on the order of 300-600 feet or greater). The arrays or pixels of Lids are placed in a matrix suitable for use in large scoreboard displays, message centers and other large, intermediate and small display systems. Each pixel comprises a sufficient number of connecting leads to provide for each color of Lids contained in the specific pixel array. Each pixel also accommodates the necessary electric connections to multiplex driving circuitry. The light emitted by each pixel is determined by the type or types of-LEDs used in the array. Use of Lids which produce the three primary colors, red, green and blue, controlled by drive circuitry, provides the capacity to create any one Or a plurality of colors.
I; Discrete elements or pixels in accordance with the present invention provide a light source having satisfactory contrast. The size of each pixel is a function of the number of Lowe chips ; included for the type of display needed.
As mentioned heretofore, the actual dimensions of each ; discrete LED pixel or light source, generally designated 18 in Figure 1, may vary. Once the dimensions have been selected for a qiven~d1splay, an appropriately dimensioned substrate 20 layer is provided. In the illustrated embodiments, the substrate layer 20 can be comprised of glass epoxy printed circuit (PC) board or dielectric ceramic upon which conductive areas are created using ::

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thin or thick film tecl1nology currently available.
The utilization of such technology produces alternate cathode and anode conductive strips or fingers 22 and 24, respectively. See riguKes 1 end 4. The manner in which the conductive layers or strips 22 and 24 are produced creates an integral bond at the two interfaces 26 (Figure 1 ) between the substrate 20 and each conductive strip 22 and 24. The cathode conductive layers 22 may be joined electrically and an exposed conductive cathode connection terminal provided. Likewise, the anode conductive layers 24 may be electrically joined and an exposed conduct; Ye Natalie connect i on tory i no 1 rove i clod .
LED chips 40 are superimposed upon a layer of commercially available conductive epoxy I at predetermined spaced intervals along each cathode conductive layer 22. It is presently preferred that the Lids be spaced it proximate hornet ~nc1 vertical intervals of about 0.050 to 0. 10 of one inch to insure that the entire array appears to the eye of the viewer as a point source of light. After all Lids are in place, the substrate is heated sufficient to malt thought conductive epoxy under okay- kid chip. I~ftcr the conductive epoxy has cured, the chip is thereby bonded in place. A conductive wire 46 is connected from the anode of each LED
chip 40 to the ad jacent common node conductor or strip 24. The process of bonding each connecting wire or conductor 46 to the anode of each Lo chip 40 and Lo the adjacent anode conductor I is well known and need not be described in this specification.
It is presently preferred, as illustrated in Figure 2, that each discrete LED pixel or l ig11t source 18 comprise red, green and blue Lids arranged in a pattern, such as alternate rows and driven so that the intensity or brightness of each color may be select-lively varied between cry end my i mum i tens fly whereby! when the three primary colors arc in~c~rale(1, any desired color may be displayed by the pixel I

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It is also presently preferred, as illustrated in figure 3, that provision be made at each pixel for avoiding loss of light intensity. More specifically, a reflector plate 48 may be continuously superimpose, at the back surface 49 thereof, upon the front surface of the layer 22 comprising the cathode and anode conductors. Reflector plate 48 comprises a plurality of tapered apertures 50 arranged for each to receive, at the base thereof, one of the pixels in visually exposed relation. The apertures 50 are illustrated as being circular and as providing an outwardly divergent tapered reflective surface 52. A transparent lens 56 is continuously superimposed, at the flat back surface 54 thereof, upon the flat forward surface 53 of the reflector 48. The forward surface 58 of the lens 56 has a curved shape or is crowned.
Individual collimating lenses may also be molded over individual Lids.
Each pixel pa comprises an anode pin 60 for each color and a cathode pin 62 for each color. ice Figure 3. Itch RUB pixel 18 thus has separate red, green and blue cathode pins 62R, 62G and 62B, and separate red, green and blue anode pins 60R, 60G and 60B. The red, green and blue cathode conductors 22 are respectively connected to the red, green and blue cathode pins 62. All red, green and blue anode conductors 24 are respectively connected to the red, green and blue anode pins 60. A presently preferred arrangement of red, green and blue cathode and anode conductors 22R, 22G and 22B and 24R, 24G and 24B is illustrated in logger I Red, green and blue Lids are respectively designated OR 4~G and 40B, in logger 4.
The serles-parallel printed circuit of Figure 4 is shown schematically in Figure 5. Application of a separate voltage pulse having a predetermined voltage to easily ox the respective groups of red, green and blue anode connectors of a pixel provides the capacity to produce any one of a plurality of colors ranging across the entire spectrum. Resistors RR, IT and RUB are respectively used in series with the KGB anode terminals, respectively to cause all Lids forming any one of the three RUG circuits to have a selected Jo _ -123328~
uniform brightness. The collective red, green and blue LED circuits of each pixel are designated 25R, 25G and 25B, respectively in Figure 5.
Reference is now made to Figure 6 which show presently preferred structure for connecting etch discrete To light source arrays 18 to driving circuitry. Specifically, each anode conductive pin 60 (one each for red, green and blue), mounted to substrate backing 20, is inserted into a matching conductive female receptacle 72 of a driving circuitry anode conductor 70. One such anode conductor 70 is provided for each of the three RUB pins 60.
The three anode pins 60 are respectively aligned with and are releasable press fit into female electrical receptacles 72 of the driving circuitry. The three ~emalc receptacles 72 for each pixel are firmly carried by a mounting display printed circuit board 74. Similarly, the three cathode pins 62 of each pixel 18 aye respectively aligned with and are releasable press fit into conductive electrical receptacles 76 of the driving circuitry. Each of the three receptacles 76 is electrically connected to its own .
separate cathode conductor 78.
When all of the pixels 18 of a given display system have been mounted to the board 74, as described, the display configure-lion of Figure 7 is created.
One typical multi-color matrix driving circuit 100 is shown n Figure 8. Circuitry 100 uses an available computer controlled message controller 102. The message controller 102 is convention-all~y~proqramed to produce a series of red, green and blue digital signals so that a corresponding visual image is presented on the fa~cé~of~a~score~oard or like display 104. Display 104 is thus-trated~a~s comprising OllC hutldrc~d twenty eight (128) columns and forty (:40) rows of pixels 18, made up of five (5) panels 106 each comprising one hundred twenty eight (128) columns and eight (rows) of pixels 18. Displays of other sizes can I used as desired.

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The computer generated I~GB digital data (in raster scan format), describing the "on", "off" and intensity of each LED of each tricolor pixel and representative of the image to be displayed, is transmitted in a known and suitably modulated serial data format from the computer controlled message controller 102 along RUB conductors 108, 110 and 112, respectively, to a serial receiver apparatus 114. Controller 102 can be any suitable commercially available computer controlled message controller. For example, a model 1000 HO contrary with three display interfaces [part no. 11231 available from integrated Systems Engineering, Inc.
of Loran, Utah]. Three data bits are required to define the desired state of each pixel 18. One bit its, therefore, assigned to control each of the three colors of the pixel 18. To this manner, each pixel 18 can be directed to emit any one of eight colors. This type of color rendering is known as cartoon color.
The receiver 114 may be a single integrated device for the signals for all three colors or separate receivers, one for the signals for each of the three colors. Suitable serial receivers are also available from Integrated Systems Engineering, Inc. For example, part no. 10003 may be used for each of the three receivers. The receivers 114 de-multiplexes, respectively distributes or switches the RUB data and routes 8 rows of said data via three RUB independent cable conductors to an 8 row driver 116R, 116G, 116B. Five drivers of each type, i.e. five 116R, five 116G
and five 116B arc required, one Or eclcll or equal 8 row display panel 106. Each driver 116R, 116G, 116B may comprise part no. 10000 available from Integrated Systems Engineering, Inc.
A power source 122 supplies electrical energy to the drivers 116R, 116G and 116B and to the pixels 18 of the display 104. If desired, more than one power source may be substituted for source 122. One suitable power source is part no. 10025 available from Integrated Systems Engineering, Inc.

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The details ox one of the RUB driver circuits 116R, 116G, 116~ for an 8 cool digital lo dozily is illustrated in Logger 9.
Specifically, the red driver circuit 116R is illustrated and described, it being understood that the 116G and 116B are structural and functionally the same.
In the driver circuit 116R, red rows of digital data, issued from the receiver 114, are communicated serially to a conventional shift register 126, where the 8 serial bits of input data are converted to a parallel word, all from thence the parallel data are addressed and written to a loam memory 1~8 using the eight input conductors, preferably during a frame update.
An output control logic signal, issued by the logic 132, is communicated to input control logic 130 which enables a write cycle to occur in a conventional fashion, with switch 131 connecting logic 130 and memory 128 for correct addressing of data.
The RAM memory 128 uses a time shared process for outputting the data to the multiplexed display in such a lesion that each discrete element image and the color thereof are periodically refreshed.
With the address switch 131, positioned as shown in Figure 9, and with output control logic 132 disabling input control logic 130 and shift register 126 so that temporarily no further red data are written into RAM memory 128. Red data are properly addressed and caused to be output, using the eight output conductors 134, from RAM memory 128 to a 1 of 8 selector or demultiplexer 135, which selects one of eight rows of data and communicates the same along conductor 137 to red shift register 136 and from thence across latch circuit 138 alollg anode conductors 70R to the columns .~:
of red LED circuits 251~ of tl1c display. ~ufrcrs 140 supply current across cathode conductors 78R to the red Lids on a row by row sequential basis. Selector 135 may be dcmultiplexer part no. ICKY
and decoder part no. 11C237, available from Motorola, '1'cxas Instruments, among others.

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While only red pixel diodes are illustrated in Figure 9 and while only the operation thereof has been described for one 8 row display panel, it is to be appreciated that the remainder of the red and all of the green and blue pixel diodes are identically connected and utilized.
Thus, the driver circuits 116R, 116G, 116B buffer the data and, using conventional LIE) multiplexing techniques, drives rows and columns of LOU pixels. In tl1is way, three independent sets of outputs are utilized to drive the rows and columns.
Another typical multi-color matrix driving circuit 150 is shown in Figure 10. Circuitry 150 comprises an available computer controlled message controller 152, which is comparable to controller 102, but conventionally programmed to produce four digitized bits of red, green and blue data, respectively ~12 bits/pixel). In this way, any one of 4096 colors may be selected and displayed at any pixel 18 Or an LED pixel display 154. Display 154 is illustrated as comprising sixty-four (64) columns and forty (40) rows of pixels 18, made up of five I panels 156 each comprising sixty-four (64) kimonos and eight (8) rows of pixels 18.
Displays of other sizes may be used.
Circuitry 150 comprises an additional or alternative source of data, i.e. a video digitizer 158, which receives video signals across switch 160 from any suitable source of video signals such as a video camera 162, a VCR 164 or broadcasted video (TV) signals via antenna 166 and tuner 168.
A switch 170 allows the user to select between controller tS2 and digitizer 158 as a source of video input. In either case, data digitized into 12 bits/pixel are transmitted, across twelve conducts (4 each for RUB data, respectively), to a serial receiver 172. This data is in row-by-row raster scan format and describes the on, off and intensity level for each color of each LED ouch tricolor pixel. The data, collectively represents the image to be illuminated at the display 154.

, issue The receiver 172 de-multiplexes and distributes or switches the 12 bits of RUB data and routes 8 rows of data via independent conductors to the drive electronics ox I~GB drivers 173, 174 and 175. Each driver 173, 174 end 175 contains red, green and blue electronics, respectively.
A power source 176 supplies electrical energy to the drivers 173, 174 and 175 and to the pixels 18 of the display 154.
In each RUB driver circuit 173, 174 and 175, RUB rows of digital data (four bits/color), issued from the receiver 172, are respectively communicated to real, green and blue latch circuit. One such latch circuit 180 for red driver !73 is shown in Figure 11.
The latch 180 captures and retains data until the input logic is allowed to process it into the memory, i.e. -the latch 180 is a temporary buffer.
Apart from the control logic 182 of inure 11, which lo common to the driver circuits 173, 174 and 175 for each 8 row panel 156 of the display 154, each color has its separate 7 although identical 8 row driver electronics. Accordingly, only one driver circuit needs to be described, i.e. circuit 173, illustrated in Figure 11.
An input clock pulse, issued by the receiver 172, is communicated to input control logic 184 Jo cor1trol or enable the transfer of data into the red RAM memory 186 in a conventional fashion, with Switch 188 connecting logic 184 and red memory 186 for correct addressing of data under the timing control of master clock 190. Input control Luke 18~ causes newly received data to be written into RAM memory. RAM memory 186 holds the digital image of the current display. Master- clock 190 establishes system timing requirements.
The RAM memory 186 uses a time shared process Lo outputting the data, under the timing control of master clock 190 and output control logic 192, to the red pixel [TED multiplexed display in such a fashion that eke image and toe color thereof are periodically 1233i~8i~
refreshed. output control logic causes the current contents ox the RAM to be read out for display processing.
With the switch positioned as shown in Figure if and with output control logic 192 disabling input control logic 184 so that temporarily no further data is written into EM memory 186, red data, for example, are caused to be output from RAM memory 186 along four conductors to one side of a comparator 194. Four conductors also connect the other side of comparator 194 to a PAM
Prom 196. Comparator 194 compares the output of the RAM to the output of the PAM Prom looking for conditions when data in the RAM
should cause the associated Lids to be turned on. PAM 196 is a programmable Read Only Memory, which contains the look-up table which causes the RAM data to conform to a pulse width modulated brightness scheme containing 16 different intensities.
The PAM Prom 196 is a decoding pulse width modulation permanently programed Read Only Memory which uses a window technique to control when and for how long pixel color data is output from RAM 186 through comparator 194 to shift register 198, i.e. so long A input is greater than B input. The Prom look-up table is customized to match the fight output characteristics Or the three different color LED dice.
As an example, a single row of data may be processed from RAM 186 to column drive shift register l98 sixty four (64) times in 1.0 millisecond. Thus, all 8 rows are reseized in 8 milliseconds.
Continuous scanning of all 8 rows every 8 milliseconds yields a refresh rate of 125 frames per second (fops). This is sufficient to reduce flicker and make the image appear solid to an observer.
nuder control of logic 1'~2, column data stored in register 198 is communicated across latch driver 200 along anode terminals 70 to the columns of red LED circuits 25R of one panel of the display. Buffers 140 supply current to the cathode terminals 78 of the red LIDS of one panel, on row-by-row sequential bests, under control of logic 192 and row counter and decode logic 202.

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While only red pixel diodes for 8 rows of the display are illustrated in Figure 11 and while only the operation thereof has been described, it is to be appreciated that the remainder of the red as well as all of the green and blue pixel diodes are identically connected and it'll iced.
Restated, the system of Figures 10 and 11 utilizes the digital approach of the light color method, and a digital form of pulse width modulation to drive each color within a pixel at any desired one of sixteen different intensities. Thus, 4 bits are used to define each LED s brightness level, and 12 bits define the entire pixel. This yields 4096 different color combinations. This large number of color combinations is sufficient to reproduce a video image so that an observer will experience realistic color reproduction.
The system Or Figures 10 . no 11 is operated in a manner similar to the eight color of Figures 8 and 9. In addition lo the computer, a video source is added as an input alternative.
The receiver functions essentially the same as in the eight color system of Figures 8 and I
The driver also functions similar to the eight color system;
however, the separation of the color signals into independent buffers produces the dozier ruttiness b sod of 4 bit data analysis.
To keep flicker to a minimum and accomplish pulse width modulation within the time periods of the normal refresh cycle, the data rates from the buffer to the output sl1ift registers must be greatly increased over the eigl1t color method. The encoded data from the Ram 186 is compared to the output of a PAM Prom. The output of this Prom determines the length of 15 on states or conditions for each of the 16 losable brightness levels. (State zero, the Thea state, is an off state). Comparing the pixel color data to the PAM prom output will let either a 1 or 0 shift out to turn on or off a color within a pixel. The longer the value of -lo-lZ33;~8~
the pixel data exceeds the value produced by the PAM Prom, tile higher will be the apparent brightness of the LED.
Another multi-color matrix driving circuit 220, suitable for converting an NUTS SAL or SLAM composite video into a contain-usual variable RUB display using analog data and tricolor LED
pixels, is shown in Figure 12-14. Circuitry 220 comprises a source of NTSC, PAL or SEAM composite video 222. See Figure 12.
Using known techniques, a synchronized separator 224 and a color demodulator 226, with output amplifiers 228, are used whereby the NTSC signal is broken into its live primary components, i.e.
horizontal synch (If), vertical sync (V), a continuously varying signal proportional to the amount of red in the picture (R), a continuously varying signal proportional to the amount of green in the picture (G), and a continuously varying signal proportional to the amount of blue in the picture (s).
The H signal is applied to a PULL (phase lock loop) 230 which produces a high frequency clock pulse. This clock pulse determines, in conjunction with horizontal timing circuit 232, the start of each video line, and establishes how often the video is sampled.
The V signal is used, in conjunction with the vertical timing circuit 234, to determine the start of frame tiring. V and H, in conjunction with data strobe timing circuit 236, select which rows of video will go to the LED pixel display.
The final outputs, as a result of the described processing of the H and V signals will: (l) sat a start bit sequentially into each row of column sample shirt rogistcr 238 Figure 13); (2) shift the bit from left to right within shift register 236 as each successive pixel is sampled; I output a strobe pulse to each row of pixels as such is updated; and (4) produce a rcfcrcncc wafcorm of sufficiently high frequent to reduce the flicker that would otherwise result if the Lids were pulsed at normal video rates.

~2;~328~

Each pixel color rulers a .seL)aratc pulse width modulation decoder to establish the desired elements brightness. This is accomplished with a sample and hold circuit voltage comparator circuit, shown in Figures 13 an 14 and hereinafter drscrihed.
With referrals to Err 13, the set, skill clock and row strobe signals, emanating as described above, are delivered to a column sample shift register 238, while the RUB sequential pixel-signals are respectively communicated to toe positive terminal of separate GO comparators 24n, 242 and 24~. 'Icky rercrcncc waveform, amplified at 246, is communicated to the negative terminal of each comparator 240, 242 and 244.
The video is sampled in succession my the action of the shift register 238 and the row strobe pulse. The valve of the video is stored in the sample and hold comparator circuit 239. Using one field of a video frame, this value is updated 30 times per second.
With specific reference to Figure 14, which is an enlarge-mint of one comparator circuit 239, the video signal is sampled when transistor Q is stroked "on", and stored in capacitor C. A
reference waveform voltage is compared to the voltage stored in capacitor C. So long as the volta<3c in capacitor C is greater than the value of the reference, the output, across driver 248, will turn the associated LED's on. When the reference is greater than the voltage stored in capacitor C, the Lids are "off". Thus, the longer any LED is "on" within tile pcrio(l, the greater the brightness and vice versa.
An update rate of 30 Liz is too slow to prevent flicker, so the reference waveform with a repetition rate in excess of 120 Ho is compared to the stored video. This comparison will yield a pulse the width of which will be in proportion to the stored analog voltage. Thus each LED is pulse width modulated to yield the desired brightness.

. , i2~3328~
. The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Jo v ' 1 g--

Claims (12)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
1. A matrix display comprising:
a plurality of multi-color solid state LED pixels arranged in a pattern;
each multi-color pixel comprising a plurality of differently colored sets of LEDs;
each set of differently colored LEDs of each pixel being electrically interconnected by separate conductor means;
a source of separate but coordinated series of signals representative of the desired color intensity to be obtained at each point in time from each set of differently colored LEDs of each pixel of the display, said source comprising pulse width signal modulating means which control the color intensity;
means simultaneously communicating said series of signals separately to each set of differently colored LEDs of each pixel whereby (a) the color of each pixel displayed to an observer at each point in time is a composite integration of the separate intensity level signals simultaneously delivered to the differently colored sets of LEDs of the pixel, (b) the composite color displayed to an observer of all pixels of the display will at each point in time comprise an integrated image comprising many colors across the spectrum, and (c) the image and many colors thereof will change from time to time as the intensity level signals of the series change.
2. The display according to Claim 1 wherein the simultaneously communicating means comprise driver circuit means which systematically and sequentially drive the differently colored LEDs of each pixel of the display via the series of signals.
3. The display according to Claim 2 wherein the driver circuit means comprise memory means for temporarily storing said signals and means selectively outputting the stored signals to the LEDs in a scan format.
4. The display according to Claim 2 wherein the driver circuit means comprise means for refreshing the color of the LEDs of each pixel during the time interval of each image by recommunicating the current series of data from storage to the LEDs.
5. The display according to Claim 2 wherein the drive circuit means comprise control logic means which cause the demultiplexed signals to be output to scan means from which each series of signals is repeatedly communicated on a sequential basis to the LED pixels.
6. The display according to Claim 1 wherein said source comprises video digitizer means.
7. The display according to Claim 1 wherein said source comprises computer means.
8. The display according to Claim 1 wherein said source comprises means issuing NTSC, PAL, or SECAM television signals.
9. The display according to Claim 1 wherein sample and hold means are interposed between standardized value means and each output signal to retain the intensity of each color of each LED for each pixel for extended periods of time.
10. The display according to Claim 1 wherein the pulse width signal modulating means comprise means by which image flicker is minimized.
11. A matrix display comprising:
a plurality of tri-color solid state LED pixels arranged in a pattern;
each tri-color pixel comprising three differently colored sets of LEDs;
each set of tri-colored LEDs of each pixel being electrically interconnected by separate conductor means;
a source of three separate but coordinated series of signals representative of the desired color intensity to be obtained at each point in time from each set of differently colored LEDs of each pixel of the display, said source comprising a data source and further comprising means by which the data are delivered to the sets of differently colored LEDs in a refreshing modulated scan data format, the rate of which substantially exceeds the rate at which data is issued for the data source;
means simultaneously communicating said three separate series of signals independently to each set of differently colored LEDs of each pixel hereby (a) the color of each pixel displayed to an observer at each point in time is a blended integration of the intensity level signals simultaneously but independently delivered to each of the three sets of LEDs of the pixel, (b) the composite color displayed to an observer of all pixels of the display collectively will at each point in time comprise an integrated image comprising many colors across the color spectrum, and (c) the image and many colors thereof of the display will change from time to time as the signals representing the intensity level of each set of LEDs of each pixel changes.
12. A method of displaying images of varying colors within the spectrum of a matrix display comprising:
providing an array of a large number of juxtaposed multi-color solid state integrated pixels arranged in a close matrix pattern, each pixel comprising sets of differently colored compactly arranged LEDs so that each pixel is an apparent composite point color light source to an observer of the array;
separately controlling and selectively electrical communicating from a source of video signals or computer signals several separate coordinated series of signals respectively to the sets of LEDs of each color;
in such a manner that each pixel will, at any point in time, display only one composite color comprising a visual integration of the plurality of coordinated signals delivered to the differently colored Lids of each pixel and said one composite color each pixel will change from time to time as said plurality of coordinated signals changes whereby successive images each comprising varying array of composite colors across the spectrum are sequentially visually illuminated on the matrix display.
CA000496813A 1985-05-28 1985-12-04 Solid state color display system and light emitting diode pixels therefor Expired CA1233282A (en)

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JPS61273590A (en) 1986-12-03
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