Note: Descriptions are shown in the official language in which they were submitted.
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.
--1--
i23328;~
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.
::
.~., .
~23328~
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
:
~233Z8~
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.
::
.
:
I
lZ33Z8;~
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;
'
:
-5
i2332~
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.
,
.
6-
, . .. .
Jo
~;~33~8~
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
::
-7-
::
1233Z~3~
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
._
~Z3328'~
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.
- 1 0-
:
lZ33Z8~
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.
l'Z33Z8'~
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.
-12-
:,
1233'~8~
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.
-15-
.,
~Z3328~
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.
18
. ,
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--
