The present invention pertains to displays. More particularly, the present invention relates to a method and apparatus for a LED (light emitting diode) based display.
Displays are an integral part of conveying information. Many different technologies are being utilized for electronic color displays. CRT (Cathode Ray Tube) based displays are very commonly used in the home (for television and computer monitors) as well as in offices, factories, commercial establishments, and public places (such as airports and shopping malls). However, CRT's are big, bulky, and consume large amounts of power. This may present a problem.
LCD based displays are extensively used in very portable devices such as cell phones, mobile PCs, mobile games, and portable televisions. Recently LCD based display screens have been taking a much bigger role as display devices in offices and homes as monitors for computers and are replacing the ubiquitous CRT as a display of choice. Large thin flat screen displays based on plasma technology, and backlit LCD displays are becoming very popular although they are relatively expensive at present. This expense may present a problem.
Projection displays using SLM (spatial light modulators such as LCDs, Digital Mirror Devices or LCOS devices) are used in front projection mode. These devices may require a high power light source such as a projection lamp. This may present a problem.
Rear view projection devices, such as very large screen televisions may be based on power hungry CRTs. This may present a problem.
LEDs are now available and many large outdoor displays are built with LEDs. This requires the use of a very large number of red, green and blue LEDs.
Thus all these displays present a problem.
The invention is illustrated by way of example and not limitation in the figures of the accompanying drawings in which:
This design, as exemplified in various embodiments of the invention, illustrates how LEDs (light emitting diodes) may be used to create a display. There are a variety of light emitting diodes, for example, light emitting diodes (commonly referred to as LEDs), resonant cavity light emitting diodes (RCLEDs), organic light emitting diodes (OLEDs), electroluminescent diodes (ELDs), photon recycling semiconductor light emitting diode, etc.
The phenomena of electroluminescence caused by carrier injection in semiconductors was discovered by Round (in 1907) who injected carriers into silicon carbide from a metal contact and observed a yellowish light. The red LED was invented by Holonyak and Bevacqua (in 1962) and soon saw widespread use in instruments and consumer products such as calculators and watches. The early LEDs were not very bright and it was difficult to produce bright blue and green LEDs. Improvements in the manufacturing processes and better understanding of the mechanisms of producing light in solid state devices as well as the minimization of losses is leading to brighter devices every year. There are several advantages to using LEDs in displays. Very good quality emissive displays may be built using LEDs. Emissive displays typically use less power than non-emissive type displays such as backlit LCDs or projection displays using SLMs. This is due to the fact that in a typical frame that is displayed only a fraction of the screen, say, between 10 to 20% is displayed at maximum power. On the other hand, to get maximum brightness, a backlit display has the backlight turned up to the maximum all the time. This also leads to a better contrast ratio for emissive displays because when an area of the screen is not to be displayed the light for that portion of the screen is not created. It is impossible to completely shut off the light in backlit displays thus leading to lowered contrast ratios.
Another advantage of using bright red, green, and blue LEDs for displays is that it is possible to build color displays with a larger color gamut than the NTSC standard, for example, using inexpensive and readily available Red (626 nm using AlGaInP LED), Green (525 nm using GaInN LED), and Blue (450 nm using GaInN LED) devices. Additionally, Haitz's Law which has held true for more than 30 years predicts a doubling in LED luminous output every 18 to 24 months.
In one embodiment of the invention 400, as illustrated in
Another input from the outside is power 533 for the drive and display electronics. The digital video information 503 is fed into the controller 504. A clock 535 at a high frequency (for example, from 40 MHz to 200 MHz) is provided to the controller 504. The controller 504 interfaces (via 511) to nonvolatile memory 510 and interfaces (via 513) to random access memory 512. The RAM (random access memory) 512 is used to store a complete frame of information. The nonvolatile memory 510 is used to store various parameters required in the running of the system. For example, when the RGB LED arrays are assembled, testing is performed on them to check the uniformity of the brightness of the LEDs. The slight differences in brightness (5-10%) are stored in the nonvolatile memory 510, such as flash, to allow for compensation. The actual distance between the columns is found during the testing as well and is stored in the nonvolatile memory 510.
In one embodiment of the present invention, any gamma corrections, if necessary, are made on the data, for example in the controller 504. The nonvolatile memory 510 has information on the characteristics of the motion as produced by the motion device 514 which is communicated via 515 to the LED array 506. This allows the controller 504 to calculate the time when a particular column is turned on and the width of the pulse for a particular pixel. The controller 504 receives position information 517 from the position sensors 516. In one embodiment of the invention, a linear encoder is used to determine position. In another embodiment, a VCSEL is used as a very narrow beam precision light source (such as optical signal 509) at, for example, 850 nm mounted on the moving substrate (such as 506) and photo-detectors (such as at 516) covered with a high pass filter in wavelength (cutoff at 800 nm) filters at fixed positions. The photo-detector signals 517 are sent to the controller. When the display device is being assembled (in manufacturing) tests for calibrations are made to get precise distance information of the fixed position mounted detectors. This data is stored in the nonvolatile memory 510. The advantage of this approach is that the position information is obtained in a “weight-less” way from the substrate; using the linear encoders on the substrate would require many more connections (such as 505) from the substrate (which may hold LED array 506) to the controller 504. It is important to minimize the number of signals (such as 505) from the substrate (such as 506) to the controller (such as 504). The LED array 506 produces an optical output 507 which is communicated to an optical system 508 such as a screen for display.
In one embodiment of the present invention, the operation of an LED based display device is as follows:
One of skill in the art will notice an advantage for this approach compared to the fixed M×N display in that the individual red, green, and blue LEDs are not distinguishable by the human eye. In the fixed display when white is displayed, for example, one can notice the white color with spots of red, green, and blue. With this embodiment of the invention, the red, green, and blue LEDs are organized in columns, however because of the motion of the substrate the excitation of the LEDs is designed so that although the columns are spaced physically apart, the excitation is made sequentially in time so that the colors coincide in space.
In one embodiment of the present invention, the majority of the energy required to form the display is that required for lighting up the LEDs and that required for moving the substrate (mechanical energy). The kinetic energy of a moving carriage and substrate of mass m (in kg) and moving at a fixed velocity v (in m/sec) is given by Equation 1:
Kinestic Energy=½ mv2 (Equation 1)
In one embodiment of the invention, to minimize energy, we minimize m and especially v. The time required to scan a full frame is usually fixed and so the velocity v can be reduced by reducing the total excursion of the carriage and substrate. This may be done by using multiple columns of RGB spaced a fixed known distance apart.
In one embodiment of the present invention, linear motion of the substrate is used. Linear motion of the substrate is now discussed. For example, if we are creating 50μ pixels and the pitch of the LEDs is 50μ, the LED column has to move 1024×50μ (51.2 mm) for a 1024 pixel display with one set of columns of LEDs. With 4 sets of columns of RGB LEDs the total motion is 51.2/4 mm (12.8 mm). The motion is over a time period of 10 ms. The average velocity is 5.12 m/sec with 1 column and 1.28 m/sec with 4 equally spaced columns.
It is not necessary to have pure linear motion to create the image for the display. As long as the motion characteristics are precisely known, it is possible to create an image accurately by changing the time for which a particular pixel column is energized. For example, If di is the distance traveled to create pixels for the ith column, then to create equal size pixels,
di=d, a constant.
di=∫vdt (Equation 2)
In one embodiment of the present invention, sinusoidal motion is used. This is shown in
The distance x(t) (802) is given by:
x(t)=a sin(ωt) (Equation 3)
The velocity v(t) (804) is given by:
At time zero, the substrate 806 is in the middle i.e. x(0)=0. The substrate starts moving to the left, in a negative direction, until it reaches the extreme leftmost end. At that point the velocity is zero. The substrate starts moving to the right and goes past the zero position and to the right until it reaches the extreme right position.
In one embodiment of the invention, some numbers are:
From the equations above (Equations 2-5) it is possible for the controller to know the values of ti and ti-1 since all the other quantities are known. The product of time and velocity is constant, so to have the same apparent size column width, when the velocity is the highest the time interval for the column energizing is the lowest. Conversely, if the velocity is low, the time interval is large. However, the longer the time interval of energizing the brighter the column may appear. Therefore, a correction that depends on the column position may have to be applied.
In one embodiment of the present invention an electronic projection display 900 is created using the above approach with projection optics as shown in
The projector type approach as illustrated above may be used in another embodiment of the present invention to create a flat panel display. Two such flat panel embodiments 1002 and 1004 of the present invention are illustrated in
One of skill in the art will appreciate that the present invention as a LED projection engine may be used with other screen technologies, such as, screen waveguide technologies to create LED based flat panel displays.
The discussion above, for sake of discussion has used three LEDs; Red, Green, and Blue. The invention is not so limited. For example, to increase the color gamut of an LED display more than three LEDs may be used as well as different colors of LEDs.
For example in one embodiment of the present invention by using columns of 4 or more LEDs at suitable wavelengths in the display system described here, the color gamut may be increased.
Additionally, one of skill in the art will appreciate that the techniques described above may be used with non-visible light sources as well. For example, infrared range LEDs may be used. These may be useful in fluorescing apparatuses as well as a source of radiation for other purposes, for example exposing photoresist, film, stereo lithography, etc.
One of skill in the art will appreciate that moving or positioning a substrate having LEDs may be done by a variety of methods, including but not limited to, a rail system, a cantilever system, a pendulum approach, a rotary pivot approach, etc.
Thus a method and apparatus for a light emitting diode based display have been described.
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For purposes of discussing and understanding the invention, it is to be understood that various terms are used by those knowledgeable in the art to describe techniques and approaches. Furthermore, in the description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be evident, however, to one of ordinary skill in the art that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention. These embodiments are described in sufficient detail to enable those of ordinary skill in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical, and other changes may be made without departing from the scope of the present invention.
Some portions of the description may be presented in terms of algorithms and symbolic representations of operations on, for example, data bits within a computer memory. These algorithmic descriptions and representations are the means used by those of ordinary skill in the data processing arts to most effectively convey the substance of their work to others of ordinary skill in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of acts leading to a desired result. The acts are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the discussion, it is appreciated that throughout the description, discussions utilizing terms such as “processing” or “computing” or “calculating” or “determining” or “displaying” or the like, can refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage, transmission, or display devices.
An apparatus for performing the operations herein can implement the present invention. This apparatus may be specially constructed for the required purposes, or it may comprise a general-purpose computer, selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer readable storage medium, such as, but not limited to, any type of disk including floppy disks, hard disks, optical disks, compact disk-read only memories (CD-ROMs), and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), electrically programmable read-only memories (EPROM)s, electrically erasable programmable read-only memories (EEPROMs), FLASH memories, magnetic or optical cards, etc., or any type of media suitable for storing electronic instructions either local to the computer or remote to the computer.
The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct more specialized apparatus to perform the required method. For example, any of the methods according to the present invention can be implemented in hard-wired circuitry, by programming a general-purpose processor, or by any combination of hardware and software. One of ordinary skill in the art will immediately appreciate that the invention can be practiced with computer system configurations other than those described, including hand-held devices, multiprocessor systems, microprocessor-based or programmable consumer electronics, digital signal processing (DSP) devices, set top boxes, network PCs, minicomputers, mainframe computers, and the like. The invention can also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network.
The methods of the invention may be implemented using computer software. If written in a programming language conforming to a recognized standard, sequences of instructions designed to implement the methods can be compiled for execution on a variety of hardware platforms and for interface to a variety of operating systems. In addition, the present invention is not described with reference to any particular programming language. It will be appreciated that a variety of programming languages may be used to implement the teachings of the invention as described herein. Furthermore, it is common in the art to speak of software, in one form or another (e.g., program, procedure, application, driver, . . . ), as taking an action or causing a result. Such expressions are merely a shorthand way of saying that execution of the software by a computer causes the processor of the computer to perform an action or produce a result.
It is to be understood that various terms and techniques are used by those knowledgeable in the art to describe communications, protocols, applications, implementations, mechanisms, etc. One such technique is the description of an implementation of a technique in terms of an algorithm or mathematical expression. That is, while the technique may be, for example, implemented as executing code on a computer, the expression of that technique may be more aptly and succinctly conveyed and communicated as a formula, algorithm, or mathematical expression. Thus, one of ordinary skill in the art would recognize a block denoting A+B=C as an additive function whose implementation in hardware and/or software would take two inputs (A and B) and produce a summation output (C). Thus, the use of formula, algorithm, or mathematical expression as descriptions is to be understood as having a physical embodiment in at least hardware and/or software (such as a computer system in which the techniques of the present invention may be practiced as well as implemented as an embodiment).
A machine-readable medium is understood to include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computer). For example, a machine-readable medium includes read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.); etc.
As used in this description, “one embodiment” or “an embodiment” or similar phrases means that the feature(s) being described are included in at least one embodiment of the invention. References to “one embodiment” in this description do not necessarily refer to the same embodiment; however, neither are such embodiments mutually exclusive. Nor does “one embodiment” imply that there is but a single embodiment of the invention. For example, a feature, structure, act, etc. described in “one embodiment” may also be included in other embodiments. Thus, the invention may include a variety of combinations and/or integrations of the embodiments described herein.
Thus a method and apparatus for a light emitting diodes based display have been described.
This patent application claims priority of U.S. Provisional Application Ser. No. 60/584920 filed Jul. 01, 2004 titled “Method and Apparatus for LED Based Display”, which is hereby incorporated herein by reference. This patent application is related to U.S. application Ser. No. 10/810300 filed Mar. 26, 2004 titled “Method and Apparatus for Light Emitting Devices Based Display”, which is by the same inventor as this application.
Number | Date | Country | |
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60584920 | Jul 2004 | US |