Note: Descriptions are shown in the official language in which they were submitted.
BACKGROUND
Field of Invention
This invention relates generally to clisplay equipment and
more particularly to a solid state display system suitable for a
large monochrome and/or color display and discrete elements therefor
each comprising a compact array of light emitting diodes.
Prior Art
In the conventional construction of a lar~e display system
(for example baseball fields, apparatus for displaying advertising,
pictures, or the like), the words or pictures are formed by selec-
tively -turning on or off colored electric lamps in a predetermined
pattern. Such display systems have presen-ted many difficult problems.
The color re-tention is poor, 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 or glass plates
are used to selectively Eilter the color desirecl.
Since electric lamps on the orcler of 10 watts or more have
been generally employed, a large display ~which may include several
thousand of such lamps) consumes a lar~e amount of power and generates
a large amount of heat.
A certain amount of time is required to turn on the electric
lamps of such a display. Approximately 20 milliseconds are required
for the filament o become heated to produce light and approximately
the same amount of time to turn the filament off. This causes what
is known as "trail off" as a picture o~ word is moved from one lamp
to the next.
The expected liEe of such an electric lamp is on the order
of 5000-8000 hours, which requires constant rnaintenance to replace
the lamps which exceeded their use~ul life.
LEDs have been used in the construction of small indoor
installations and on numerical displays on hand-held calculators. Hereto-
fore, the use of LEDs in an outdoor display has been reiected as ~
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impractical. This has been due largely to the small amount of lumi-
nance available from the standard LED. The luminance emitted by
the .010" X .010" (0.0001 square inch area) LED chip is diffused
over an area of approximately 0.0305 square inches; therefore the
light is diEfused over an area 300 times larger than the source
chip and hence the actual light emitted is very low. This makes
the d~screte LED unreadable.in direct sunlight.
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BRIEF SUMMARY AND OBJECTS OF THE INVENTION
In brief summaryl the present invention largely overcomes
the aforementioned problems of the prior art and provides novel
and unobvious solid state monochrome and color display systems,
including the large scoreboard type, and light emitting diode pixels
forming the discrete light source elements thereof. A large number
of LED 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 of LEDs used
in the array. Using three colors, bluel red, green that are controlled
by ~eparate driving circuitry accommodates generation of any color
in the spectrum.
The electric lamp generally has an efficiency oE up to 40
lumens/watt for converting ~lectrical to optical energy. LEDs in
accordance with the present invention have an efficiency of from
150 to over 600 lumens/watts. Therefore, the LED array in accordance
with the present invention has a better efficiency fQr converting
electrical to optical energy by an order ~f magnitude of five.
The present LED array responds ~turns on and off) much quic-
ker, i.e. on the order of 20 nanoseconds which is a million times
faster than the electric lamp. Another characteristic of the present
LED array is its ability to respond to a pulse type of signal which
allows the LED chip array to actually be turned on with a relatively
low du~y cycle, typically less than 6%. This results ln a very low
power consumption for the display.
The electric lamp has a relatively short life expectancy.
The present LED has a life expectancy of 100,000 hours or greater.
Replacement seldom if ever occurs.
.. ~
With the array containing many LEDs spacecl 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 even when irradiated with
sun in .he daytime. The size of the array is determiend by the number
of LED chip included to achieve the size of pixel desired.
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By using red, blue, gr~en chip combinations on the same
array with s~parate connecting leads, a true color system is created
which will reproduce any color.
With the foregoing in mincl, it is a primary object of the
present invention to provide a novel solid state display system
and related method.
Another paramount object of this invention is the provision
of a novel solid state discrete light source, for a display system,
comprising an array!of light emitting diodes.
A further dominant object is the provision of novel solid
state monochrome and color display systems, i.ncluding but not limited
to large scoreboard type displays, which systems comprise one or
more matric~s formed of pixels each comprising a cluster of closely
spaced light emitting diodes which are selectively illuminated.
An additional important object of the present invention
is the provision of novel solid state display systems comprisiny
discrete elements formed of LED pixels having one or more of the
following characteristics: (1) on the order of several times the
electric to opitcal efficiency of a conventional discrete display
element; (2) a response time essentially infinitely faster than
t~hat oE a conventional discrete display element~ ~3~ a much lower
duty cycle than that of a conventional discrete display element;
and (4) sufficient light intensity to provide sufficient contrast
even when irradiated by the sun.
Another valuable object of the present invention is the
provision of a solid state discrete light source element comprising
a very compact array of sufficient size to generate a light source
of sufFicient output luminous to be viewed in a direct sunlight
condition from distances of 300 to 600 fee-t or greater.
It is also a paranlount object of this invention to provide
discrete light source display elements compr.ising an array of light
emitting diodes which can be used in either new display or to retrofit
existing displays.
A further significant object is to provide a display system
comprising discrete light source display elements comprising an
array of light emitting diodes having at least one of the following
features: (1) all LED chips are of the same type connected in parallel
series - parallel, or series to produce images; (2) the LED chips
comprise two or more colors, each separately electri.cally actuated
accommodating change in the 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 I.~Ds in each array and each dif-
ferentially electrically controlled to vary the intensity of the
output of each color whereby any color in the spectrum may be selec-
tively 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 DESCRIPTION OF THE DRAWINGS
Figure 1 is a sid~ view elevation of an LED oF an array
in accordance with the present inventioll mounting to sukstratej
Figure 2 is a front view of an LED array in accordance with
the present invention;
Figure 3 is a side plan view of the LED array of Figure
2;
Figure 4 is a plan view of an LED monochrome array mounted
on substrate and showing electrical conductors;
Figure 5 is a side cross sectional view taken along lines
5-5 of Figure 4;
Figure 6 is a plan view similar to Figure 4 r except an array
arrangement of two different colors of LEDs is illustrated;
Figure 7 is a plan view similar to Figure 4, except an array
arrangement of red, green and blue ~EDs is i].lustrated;
Figure 8 is a schematic representation of a parallel chip
LED array;
Figure 9 is similar to F'i~ure 8, except a series-resistor
is included for each LED of the array;
Figure 10 is similar to Figure 8, except a series-parallel
configuration is shown;
Figure 11 is similar to Figure 9, except a series connection
is shown;
Figure 12 is a side elevational view of a typical electrical
conenction arrangement for LED arrays in accordance with the present
invention;
Figure 13 is a fragmentary plan view of a matrix display
using LED array according to the present invention;
Figure 14 is a side elevation of an LED array according
to the present i.nvention encapsulated in a bulb with threaded fitting
from retrofit utiilization;
Figure 15 is a side elevation view similar ~o Figure 1 Eur-ther
illustrating use of a reflective shield in conjunction with each
LED of the array; and
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Figure 16 is an electrical schema-tic of drive circuitry
by which display systems in accordance with the present invention
and specfically the LED arrays thereof are selectively controlled.
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DET~ILED DESC~I~TION OF TIIE ILLUS~TLD EMBOVIM~NTS
Reference is now made to the drawings wherein like numerals
axe used to designate like parts throughout. In general, the Figures
illustrate monochrome, combination monochrome and color embodiments
of solid state display systems and light emitting diode pixels therefor.
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 cl~arly from a substantial distance (on the
order of 300-600 feetox greater) even when irrad.iated by direct sun-
light. The arrays or pixels of LEDs are placed in a maxtrix suitable for
use in large scoreboard displays, messag~ c~nters and other large,
intermediate and small display systems. Preferably, each pixel is
mounted in a shape retaining mol~ed encapsulation which preferably
includes a transparent lens. Each pixel comprises a sufficient number
of connecting leads to provide for each color of LEDs contained
in the specific pixel array. Each pixel envelope 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. All red, all green, all blue, all yellow,
all amber may be used or any combination of such colors as well.
Use of the three primary colors, blue, red and ~reen, each controlled
by separate drive circuitry, provides the capacity to create any
color in the spectrum.
LED pixels in accordance with the present invention provide
an electrical to optical energy efficiency on the order of five
times better than available from conventional discrete light source
elements. LED arrays in accordance with the present invention respond
(turn on and off) on the order of one millon times faster than conven-
tional discrete light source elements and require on]y a pulse having
a duty cycle of on the order of six percent (6~) to turn on an LED
array. As a result, the power consumption for a display in accordance
with the present invention is very low.
In addition, the life expectancy of discrete light source
elements in accordance with the present invention is on the order
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of 100,000 hours instead of the 5,000-8,000 hours provided by conven-
tional discrete light source elements of the prior art.
Discre~e elements in accordance with the present invention
provide a point light source having satisfactory ~ontrast even when
irradiated with direct sunlight during the daytime. The size of
each pixel is determined by the number of LED chips inclùded for
~he type of display needed.
As mentioned heretofore, the actual dimensions of each dis-
crete LED light source, generally designated 1~, may vary. Once
the dimensions have been selected for a given display, an appropriate-
ly dimensioned substrate 20 layer is provided. In the illustrated
embodiments, the substrate layer 20 is preferably a conventional
dielectric ceramic upon which conductive areas are created using
thin or thick film technology currently available.
The utillzation of such technology produces alternate cathode
and anode conductive strips or fingers 22 and 24, respectively.
The manner in which the conductive strips 22 and 24 are produced
creates an integral bond ~t interface 26 (Figure 1) between the
substrate 20 and the conductive strips 22 and 24. The cathode conduc-
tive fingers 22 are joined electrically by a bridge 28 which ter-
minates in an exposed conductive cathode connection terminal 30
in the monochrome embodiment 18 illustrated in Figures 1, 4 and
5. Li~ewise, the anode conductive fingers ~4 are electrically joined
one to another by bridge 32 which terminates in an exposed conductive
anode connection terminal 34.
~ ontinuin~ the description of the monochrome embodiment
18, LED chips 40 are superimposed upon a layer of commercially avail-
a~le conductive epoxy 42 at predetermined spaced intervals 44 along
each cathode conductive fin~er ~2. It is presently preferred that
the LEDs be spaced at approximate hori20ntal and vertical intervals
44 of about 0.050to 0.10 of one inch to insure that the entire array ap-
pears to the eye of the viewer as a point source of light. After all L~Ds
are in place, the suhstrate is heated suEficient to melt the corlduc
tive epoxy under each LED chip. After the conductive epoxy has cured,
the chip is thereby bonded in place. A conductive wire 46 is thPn~P
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connected from the anode of each I,ED chip to the adjacent common
anode conductor or finger 24. The process of bonding each connec-ting
wire or conductor 46 to the anodeof each LED chip 40 and to the
adjacent anode conductor 24 is well known and need not be deseribed
in this speciEieation.
If greater light intensity is desired, a dish-shaped LED
reflector 180 (Figure 15) of conductive material may be used a-t
the back or cathode side of eaeh LED. Conduetive epoxy layers 4~
and 42' are used to secure the reflector 180 to cathode conductor
22 and to the cathode face of the LED, respectively.
It is presently preferred that each LED array 18 be eneapsu-
lated within a glass or plastic envelope at least the faee of whieh
is transparent. One such envelope is illustrated in Figure 5 and
comprises a filter lens 50 secured to the substrate 2Q by bonding
or the liXe at sites 52 and 54. The lens 50 keeps dirt and debris
from reaehing the LED array 18 thereby preserving a high degree
of light transmission therethrough.
Another form of encapsulation is illustrated in Figures
2 and 3 with the envelope again comprising transparent shape retaining
synthetic resinous material which defines a front lens 56, top and
bottom walls 58 and 60 (to which the substrate 2Q is bonded at sites
62 and 64) and rear wall 66 which provides apertures 68 and 70 for
conduetors 72 and 74. The walls of the envelope 55 are integral
one with another at corners 76. Conductors 72 and 74 are secured
by solderingor the like to cathode terminal 30 and anode terminal
34, respectively. The described encapsulated arrangements are intended
for use in new solid state display systems being fabricated from
serateh.
In those cases where it is desired to retrofit an existing
display system by replacing conventional discrete light source ele-
ments with discrete light source elements in aceordance with the
present invention, the configuration 80 of Figure 14 may be used.
Configuration 80 generally resembies a light bulb externally and
comprises the previously described discrete LED light source element
18 enelosed within a transparent glass or plastie envelope 82 com-
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prising a front lens 84, the substrate 20 of the discrete element
18 being secured to the envelope by bonding or the like a-t sites
8~.
The glass or plastic envelope 82 is necked down at site
88 and there receives a conventional threaded conductor 90. Male
threaded conductor 90 is sized and shaped so as to be capable of
being electrically threaded into an existing display system to replace
a conventional light source~ Conductors 92 and 94 conventionally
connect to the threaded collar 96 of the fitting 90 and the central
ground conductor 98 also of the male fitting 90 whereupon electricity
of relatively high voltage is communicated to transformer 100 con-
tained within the envelope 82. Transfoxmer 100 reduces the voltage
of electricity to a level compatible with the LEDs of the discrete
element 18 which low voltage elecricity is communicated alon~ con-
ductors 102 and 104 to a current limiting diode bridge 106 and from
~hence along previously described conductors 72 and 74 to discrete
light source element 1~.
Reference is now made to Figure 6 which illustrates a two
color or combination monochrome embodiment o~ the present invention.
The discret~ LED light source element of Figure 6 is generally desig-
nated 118. Discrete element 118 is identical or substantially identi-
cal in certain respects to the previously described discrete element
18~ Those parts of discrete element 118 which are common to previously
described parts of discrete element 18 have been so numbered and
no further description thereof is deemed necessary at this point.
Discrete element 118 is formed in a fashion and of materials as
heretofore described in conjunction with discrete element 18.
Discrete element 118 utilizes alternating rows of red LEDs
120 and green LEDs 122. Red and green L~Ds have been chosen arbri~
trarily and, therefore if desired, other colors can be used. LEDs
120 and 122 are secured in the illustrated positions as heretofore
described at close intervals as men~ioned previously.
Also provided are red LED anode conductive fingers 124 and
green anode conductive fingers 126. As can be seen from inspection
of Figure 6, every other anode conductor interposed between cathode
conductors comprises red anode conductor ~24 and green anode conductor
126. The red anode conductive ~ingers or strips 124 are commonly
joined by a conductive bridge 128 which provides a red anode conduc-
tive terminal 130. The green anode conducting fingers or strips
126 are respectively joined by conductors 132 to a green anode conduc-
tive bridge 134, which comprises a green anode conductive terminal
136. Further in respect to discrete element 118, the anode of each
red LED is connected to the adjacent red anode conducting strip
124 by a looped connecting wire or conductor 138. By the same token,
the anode of each green LED is connected by a connecting wire or
conductor 140 to the adjacent green anode conducting strip 126~
Discrete element 118 may be encapsulated in any satisfactory
way including but not limited to the aforementioned ways to provide
an encased discrete element for installation in display systems
being newly created or for retrofit purposes in existing display
systems.
As can be appreciated, when no electricity whatever is deli-
vered to any of the conductive strips of discrete element 118, the
visual appearance of the element is dark. When low voltage electricity
is communicated at the red anode conducting fingers 124, the discrete
element 118 displayed light having a red hue or color, the illuminated
LEDs of the element has the appearance to an observer of being a
point light source. When electricity is delivered to the green anode
conducting fingers 126, the green LEDs become luminous causing the
viewer to see the color green as a point source of light. If both
the red and green LEDs are illuminated simultaneously, a third color
will result, the hue of which may be varied depending upon the nature
of electrical power delivered to the red and green LEDs, respective}y.
Reference is now made to Figure 7 which illustrates an in-
finite color discrete LED light source element, generally designated
158. Those portions of discrete element 158 common to previously
described discrete element 118 are correspondingly numbered and
no further description is here deemed necessary.
At every third gap be-tween cathode conducting strips 22
is disposed a red anode conductive strip 124, a green anode conductive
:~2~31
strip 126 (both heretofore disclosed) and a blue anode conducting
strip 160, respectively. Evexy third cathode conducting strip 22
respectively conductively supports red, green and blue LEDs 120,
122 and 162 at predetermined intervals as heretofore mentioned.
At every third conducting finger 22 is disposed a plurality of spaced
blue LEDs 162 in electrical communication with the adjacent blue
anode conducting finger 160 via connecting wires or conductors 164.
Each conducting strip 160 is in electrical communication with a
conducting bridge 166 by a connecting wire or conductor 168. Bridge
166 comprises anode connection terminal 170.
It should be readily apparent that by selectively controlling
electricity delivered to the redr green and blue LEDs and controlling
the magnitude thereof, the discrete element 158 may either be dark
or consist of any color within the spectrum at any desired point
in time.
Notwithstanding the heretofore described connections to
the various LEDs, it is to be appreciated that each discrete LED
light source array in accordance with the present invention may
be connected in parallel, in series-parallel and in series as illu-
strated in F'igures 8, 10 and 11. For causing each LED which is illumi-
nated to have uniform brightness, a resistor Rl is used in series
with the anode of each LED, as shown in Figure 9.
The operation of an LED, including light generation and
the output luminance are well known and will not be treated here.
The operation LED arrays in accordance with the present invention
is discussed hereinafter.
Each ~ED in the array, when illumination is desired, is
pulsed with approximatley 200 milliamperes of current for a duration
of essentially 200 microseconds with a duty cycle of six percent
(6%) or lessO The amount of current supplied to the LEr array is determin-
ed by the size of the array and the number of LEDs. Therefore, the
size and thickness of the conductors used on the substrate are selec-
ted to be capable of handlin~ the current pulse~ without adding
excessive resistance or degrading the conductor. Sufficient heat
sink to dissipate the heat thereby maintaining temperatures that
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are in an acceptable range for proper LED operation is also important.
Referring ts Figure 8, applying a pu]se of +8 volts to all
or some of the LEDs of the array will cause the LE3s to illuminate.
The amount of luminance of the array is determined by the number
of LEDs illuminated in the array. If e~ual ouput or intensity of
each LED is desired, a resistor R1 is placed in series with the
LED, causing uniform brightness of each LED. See Figure 9.
When the number of LEDs in the array reaches a practical
limit for heat dissipation, a series-parallel circuit, as shown
in Figure l0, can be utilized to further increase the number of
LEDs in the array. In this way, the total current density is decreased
by the amount of parallel banks of LEDs in series. For example,
if 64 LED were used, a pulse current of 12.8 amperes is needed with
the circuitry of Figure 8. If array were divided into four banks
of 16 LED and connected in series, as illustrated in Figure l0,
the total current required would be reduced by 3/4, i.e. to 3.2
amperes. However, the applied voltage would have to be increased
by four times. Once again, if uniform output is re~uired, a resistor
R1 is needed.
For those applications where a very low current is needed
and a high voltage is available, the LEDs in the array can be in
series as shown in Figure ll. Here, the current can be pulsed at
the 200 milliamperes or the current reduced at 20 milliamperes and
applied in a continuous manner.
Reference is now made to Figures 12 and 13 which show pre-
sently preferred structure for connecting the discrete LED light
source arrays 18 to driving circuitry. Specifically, each array
18 is equipped with conductive pin 200 and 202 mounted to backing
198 and respectively electrically connected to the cathode and anode
terminals 30 and 34.
Pins 200 and 202 are aligned with and are releasably press
fit into female electrical receptacles 204 and 206 of the driving
circuitry 208. Female receptacles 204 and 206 are firmly carried
by a mounting display board 210. Thus, the cathode oE each LED 40
of pixe] 18 is electrically connected to pin 202, fitting 206 and
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wire 212 oE the driving circuitry. The anode of each LED 40 of pixel
18 is electrically connected to pin 200, fitting 204 and wire 214
of the driving circuitry.
When all of the pixels 18 of a given display system have
been mounted to the board 210, as described, the display configuration
of Figure 13 is created.
Typical matrix driving circuitry 208 is shown in Figure
16. In operation, the data of Row 1 is clocked into the bit one
register of shift register U1 on the positive transition of the
clock pulse. On the next positive transistion of the clock pulse
the first data bit is shifted one position to the xight and the
next bit is entered into bit one register. Data is continued to
be shifted and entered until 256 data bits have been entered and,
therefore, all of Row 1 data is now contained in the Ul shift regis-
ters. After the 256th bit has been entered, the multiplexer generates
a positive STROBE pulse which transfers the data in the shift regis-
ters to the storage registers of U1. The OUTPUT ENABLE signal is
enabled by a high level logic signal as long as data is being sent
by the multiplexer and, thus, the data in the storage registers
appear at the outputs of U1 and are applied to the driver U~ which
either apply a ground or lamp supply to the anode of Row 1 LED
arrays. At the same time the Strobe Signal appears, a counter in
the multiplexer is incremented and a logic low Row 1 siynal is gener-
ated which turns on Q1 transistor and applies lamp supply to all
the LED arrays in Row 1. During the time that Row 1 is "on", data
for Row 2 is next clocked into the shift registers and after 256
data bits have been shifted ir-, a strobe pulse is generated to trans-
fer data to the storage registers again presenting data to drivers
U2. At the same time, the counter has been lncremented to "turn
off" Row 1 and "turn on" Row 2. This same procedure continues until
all 16 Rows have been turned "off" and "on". Then the procedure
starts all over with Row 1. The "on" time for each row is approxi-
mately 200 microseconds.
Since a large amount of current is drawn only during six
percent ~6%) of the time, the effectlve or average power consumption
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is decreased remarkably.
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 illustratlve and not restrictive, the scope of the invention
being indicatea by the appended claims rather than ~y 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.
