mm 1HHI Hffitllw AH- IRK Hi ■HOHnHl 9bm| mm SHI LIBRARY OF THE UNIVERSITY OF ILLINOIS AT URBANA-CHAMPAIGN 510.84 I46r no. 679-68+ cop. 2. The person charging this material is re- sponsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Thefl, mutilation, and underlining of books are reasons for disciplinary action and may result in dismissal from the University. UNIVERSITY OF ILLINOIS LIBRARY AT URBANA-CHAMPAIGN NOV 5 OCT 13 RECO JAN 2 m L161 — O-1096 )U Af /nUCDC8-B-7U-68l hf 7^ 7?u^U SCANTRIX: A SCANNED LED MATRIX DISPLAY by SIK KEE YUEN November, 197*+ IHE LIBRARY OF THE FEB 24 1975 UNIVERSITY OF ILLINOIS Digitized by the Internet Archive in 2013 http://archive.org/details/scantrixscannedl681yuen uiucdcs-r-7 1 +-68i coo-li+69-0239 SCANTRIX: A SCANNED LED MATRIX DISPLAY BY SIK KEE YUEN November, 1973 Department of Computer Science University of Illinois Urbana, Illinois 6l801 This work was supported in part by Contract No. US AEC(ll-l) 1U69 and was submitted in partial fulfillment of the requirements for the degree of Master of Science in Electrical Engineering at the University of Illinois. Ill ACKNOWLEDGMENT The author would like to express his gratitude to Professor W. J. Poppelbaum for suggesting this thesis topic. He is also grateful to Professor W. J. Kubitz for his continued support and guidance. Thanks are also due Frank Serio for his help in building this project, Ms. Evelyn Huxhold for typing the thesis, and Mark Goebel for the drawings . IV TABLE OF CONTENTS Page 1.0 INTRODUCTION 1 1.1 Plasma Displays ______________ ____ i 1.2 LEDs .__ 2 2.0 SYSTEM CONSIDERATIONS 10 2.1 Rotating Drum Schemes _________________ iq 2.2 LED Panel with Shift Registers 12 2.3 Scantrix Implementation ________________ 12 3.0 CIRCUIT DESCRIPTION _l8 3.1 Vertical Sync Driver _________________ 18 3.2 Horizontal Sync Driver -___-----_______ 18 3.3 Video Gates and Sampling Clock -___---_____ 23 3.U Horizontal Decoder-Control Addresser - - ■ — 23 3.5 Vertical Decoder-Control Addresser ___--_-___ 23 3.6 The Display Panel 26 U.O CONCLUSION 29 BIBLIOGRAPHY 35 APPENDIX 36 LIST OF FIGURES Figure Page 1.1 Zero Biased Junction --------------------- 3 1.2 Forward Biased Junction -------------------- 3 1.3 Emission Spectrum of GaAsP and GaP -------------- 6 l.k GaP is More Efficient than GaP at Low Current - -- 7 1.5 Human Eye Response to Visible Spectrum ------------ 8 2.1 Rotating Drum With h Lines of LEDs 11 2.2 Side View of the Rotating Drum 11 2.3 Simplified Block Diagram of Scantrix ------------- ±k 2.h Scantrix Block Diagram -------------------- 15 3.1 Vertical Sync Driver --------------------- 19 3.2 Vertical Sync Signal Before Reshaping ------------- 20 3.3 Horizontal Sync Driver -------------------- 21 3.U Unattenuated Horizontal Sync ----------------- 22 3.5 Video Gates /Sampling Clock -------__-------__ 2U 3.6 Horizontal Decoder - Control Addresser ------------ 25 3.7 Vertical Decoder - Control Addresser ------------- 27 3.8 Single Unit of LED with the Driver and Storage 28 U.l Picture of Scantrix 30 k.2 Picture of "Ul" Displayed on Scantrix 31 k.3 Picture of Floating Power Supply Card ------------- 33 k.k A Single Unit of the LED Display Card 3 1 * A.l TV Schematic 37 A. 2 Row-Voltage Level Controller ----------------- 38 A. 3 Floating Power Supply 39 A.k Video Amplifier and Level Shifter --------------- kO VI LIST OF TABLES Table Page 1 Materials for Visible Electroluminescence -__-_-_--_ 5 1 . INTRODUCTION The Cathode Ray Tube (CRT) is undeniably the most popular display device known today. Since its invention in the late 19th century, it has been developed into a sophisticated, mass-producible, reliable, relatively inexpensive, and high resolution display device available in numerous sizes. In addition, it possesses the capability of presenting grey-scale, color, or monochromatic images. Not only is it the most common display device in use today in computer systems, it is almost the only device used in television and radar systems. However, although considerable effort has been invested in reducing the overall length of CRTs, the CRT is nevertheless still very bulky. Out- standing proposals for making flat CRTs were presented by G. D. Gabor and W. R. Aiken in the 1950' s, but they never became popular because of difficul- ties in manufacturing. Besides being bulky, CRTs suffer from a maximum size limitation. The largest CRTs that can be manufactured measure roughly 25 inches diagonally. If a tube giving a larger size presentation is desired, a steel reinforced wall must be employed which makes this approach quite impractical and very expensive. A good deal of research exits nowadays aimed at seeking new forms of display devices which can compete with CRTs, outperform them and eventually replace them. Both plasma display panels and light emitting diode (LED) dis- plays offer many of the desired characteristics making them the most plausible alternatives. 1.1 Plasma Displays Plasma panels consist essentially of tiny localized gas discharges en- closed by two parallel sheets of very thin glass upon which two orthogonal sets of conducting electrodes have been deposited. The discharge takes place at points where two crossing electrodes are activated, giving rise to a glow and thus light emission. Many refinements have been made since its development in 196U for the Plato system at the University of Illinois. The Digivue panel is an AC plasma panel developed under a patent held by the University of Illinois and announced by Owens-Illinois is 1971* It is a much improved version of the original panel which can operate at a much lower drive potential and frequencies. The Self-Scan panel announced by Burroughs Corp in 1970 presented another ver- sion of a plasma display panel. It operates at 250v with three phase 110 volts drive controls signals. Quite satisfactory results have been obtained with both of these plasma panels. Two color panels are developed, three color panels have been prototyped, and grey-scale has been achieved. Safety and structural sturdiness are constantly improving while the desirable flat panel structure is maintained for ever larger panel capability. The life expentancy is roughly two to three times that of CRTs (> 5000 hours). 1 . 2 LEDs LED display technology is not as advanced as that of either CRTs or plasma panels but its potential is overwhelmingly attractive and its charac- teristics are most desirable. LEDs are electroluminescent p-n junction devices. At a zero-bias condition, Figure 1.1, a potential barrier prevents the mobile electrons and holes from diffusing. As a positive voltage is applied across the junction which lowers the potential barrier, electrons and holes begin to diffuse across the junction. These excess minority carriers then begin to recombine, as shown in Figure 1.2, in order to return the minority carrier con- centrations to their equilibrium values, emitting visible electromagnetic radia- tion in the process. It is obvious that not every kind of semiconductor possesses such an electroluminescent characteristic. Radiative recombination occurs only o UJ S2 Barrier T Empty electron states n ^jiA^aM* Empty hole states Figure 1.1 When zero biased, the built in potential at the p-n junction presents a barrier for the motion of holes and electrons. UJ SB c 0> o>j/ Jl*. Barrier T \: 'W^- + + H- + + + + + + + + ++S*" fti'iTltrlrt tl BfaiiiM triniTHTfaiiiaai " +l'l'lt B Figure 1.2 When forward biased, the potential barrier is reduced, allowing some diffusion. Some minority carriers begin to recombine radiatively. when the energy involved in the process of recombination generates photons. Table 1 is a list of the materials being studied and their characteristics. At present, GaAs P is the most widely used. It emits red light with wave- lengths between 6500 and 67OO Angstroms (Figure 1.3), depending on the pro- portions of arsenic and phosphorus used. Higher phosphorus concentration diodes emit shorter wavelengths with higher luminosity but lower power efficiency. Optimum distribution is obtained with x = O.k or k0% phosphorus for which the emission peaks at 6600 Angstroms at about 1+5 lumens/watt. While GaAsP diodes are cheaper and more easily available, GaP diodes are gaining attentions because of their higher quantum efficiency at low currents, Figure 1.4. Red GaP diodes emit at 69OO to 7900 angstroms. Even though their quantum efficiency is higher, the fact that most of the radiation is in the invisible region and they emit light in all directions (isotropic) makes their overall efficiency roughly the same as that of GaAsP. However, GaP offers another advantage which cannot be achieved with GaAsP. GaP can be doped to emit green light, or green and red in various proportions, giving colors through yellow and orange. Or, if a green and a red diode are placed close together, they can be tuned to appear from green to red by appropriately varying the input currents. Research is now being conducted with the goal of growing GaP on top of GaAsP in order to improve the overall efficiency of red LEDs. Besides red and green LEDs, blue LEDs made 3 with GaN are being developed at RCA which currently have power efficiencies of about 0.1$, comparable to green LEDs. GaN can also be made to offer two differ- ent colors with the same chip by simply reversing the biasing polarity, provided certain fabrication conditions are satisfied. Figure 1.5 is a diagram of the response of the human eye to the visible spectrum. 1. George E. Smith, "The display job calls the shots in contest between GaP and GaAsp," Electronics , October 25, 1971, pp. 7^-75. 2. Ibid. , p. 75. 3. "Blue LED Display Developed at RCA," Electronics , February 1, 1973, pp. U0-U1. o Ch -p o o> H W fi> •H 03 Ch o •H Ch 03 a co a o •H -p •H a •H O ,r "D cd a p >> h !>> >» a u Ch >h Ch «H 03 o o o O o a p 03 •p -d p h o Ch cd Ih o CJ -P H o Ch o fi O U O S* c cd 03 H 0) r-{ cd H 03 H cd P t> ft -5 ft > ft TJ ft > f> C/J 03 X O X T3 X o X ■s "3 q 03 a J •p > p •H -H P H CJ -H cd £> cu cd Ch P CO •H ^J A o o ■ M P P H cd cd < a a CO 03 Ch •H •H O a a >> CU CU -P o o •H >, •H •H > P -P -P •H >H P -P P H cd cd CJ -H H H cd £> • 9 VO VO • • • • > i/% on OJ CM H CM CM CM CM !>> cu • l 1 • • 1 | 1 1 bD CO CO vo CM CM ^t -sf -=t -=1- Ch • CM o~\ ro -3" _=r CU CM • • • • * C CM H rH H H W Oh rH X cd 1 •H H Ch cd 03 o P a o X pj cd cd •H H cd a C5 CQ <; O 03 Ph (Ih X < « XPh X cd h X 1 c5 , • cd o a 6 GaAsP | I 5 & z til GaAsP HI INFRARED INPUT POWER: 18.5 mA @ 1.62 V > TOTAL RADIATED POWER : 120 »jW < $ 4 '1 II GaP o E c all INPUT POWER: 15mA @ 2 V /l TOTAL RADIATED POWER : 300 pW 3 3 VISIBLE ' > RADIATION II \~-7> TOTAL ►- ^yf RADIATION 3 \ Jl J z HI \1K i v^ o 2 K i\f M HI i 1 i jn H GaP \ \ L y]J, ^1 * . l"*"*--*- 1 600 700 800 900 10 00 WAVELENGTH (NANOMETERS) Figure 1.3* Emission Spectrum of GaAsP and GaP. The solid lines are the real total radiation, the shifted dotted lines represent the visible radiation, taking the human response as a factor. Smith, op.cit. , p. 16. D O UJ < Hi - ^iaA iP (RE 0) GaP (REC » (a) 10 20 30 40 50 60 70 80 90 100 FORWARD CURRENT (mA) Figure l.k GaP is more efficient than GaAsP at low current, Ibid. , p. 77 • 700 /V— G»P (GREEN) 600 es 500 z UJ Z 3 400 - ' •*- ULTRAVIOLET 1 INFRARED — ► LUMINOSir 8 8 § k GaAs 05 P 0S 1 (AMBER) \ GaA$ 06 P 04 \y (RED) V ^-GaP(RED) i . i V^ i ( ) 300 J400 500 |600 700 800 (PURPLE) (GREEN) (RED) WAVELENGTH (NANOMETERS) Figure 1.5 Human Eye Response to Visible Spectrum. Ibid. , p. T5« In addition to offering a variety of colors, LEDs are knovn for their ruggedness and longevity of operation. Some manufacturers claim their LEDs have a lifetime of 10 hours (more than 100 years) under recommended operation conditions "before their brightness drops to half of the original. There are many additional desirable properties for LEDs, some of which include DC excita- tion, fast response, low forward voltage drop, good reverse cutoff characteris- tic, linear brightness to forward current characteristic, high brightness, easy handling, and, very importantly, ease in fabrication. In order to evaluate the effectiveness of LEDs in display panels (with particular emphasis on applications to large screen displays) they were used to build SCANTRIX,a Scann ed M atrix LED Display. Scantrix can display live TV pic- tures or assorted patterns. DIALCO's GaAsP LED #521-9165 was chosen for the elements of the display. It emits red light with its peak wavelength at 6500 Angstrom. The diode is encapsulated in a red diffused plastic case which improves the contrast. 10 2.0 SYSTEM CONSIDERATIONS Cost was a major consideration in building Scantrix. Many schemes of implementation are possible, but the high price of LEDs at the time the project was undertaken made the decision very difficult. This chapter describes four possible schemes that were considered, the last two were financially possible only after the cost of LEDs dropped drastically. 2.1 Rotating Drum Schemes In the first scheme, 512 LEDs are used to form one TV line. TV signals are scanned along this line of LEDs, a point at a time, from appropriate drivers. An optimum number of mirrors are mounted on a rotating drum to project the images of the LEDs onto a screen on which the rotating movement of the mirrors are being converted into the vertical scanning action. The mirrors on the drum are arranged so that the first line of the signals would be projected onto the top of the screen, and the last line onto the bottom. Several mirrors share the pro- jection function in order to allow slower rotation frequencies. A similar alter- native would be to mount the LEDs directly on the drum. This would demand one line of LEDs for each mirror being replaced. The principle remains the same, except that delicate optics are eliminated while the LEDs must now project di- rectly onto the screen. Figures 2.1 and 2.2 are used to illustrate the principle. There are several obvious drawbacks with these two schemes. First, there is no storage of signals at all so that flickering cannot be avoided. Secondly, as the images have to travel from the LEDs to the screen, either directly or indirectly via the mirrors, sharp images are impossible because of the divergence effect unless appropriate optics are incorporated into each source to correct the prob- lem. Brightness is also a problem since only one LED is on at a time. 11 512 LED'S/LINE DIRECTION OF ROTATION Figure 2.1 Rotating Drum with k Lines of LEDs, SCREEN LED'S DIRECTION OF ROTATION Figure 2.2 Side View of the Rotating Drum 12 2.2 LED Panel with Shift Registers To improve the system, though unfortunately at the expense of real time display capability, TV signals can be first changed into digital signals and stored in shift registers. These signals are then converted back into analog signals simultaneously to drive one whole line of LEDs all at the same time. While this is going on, another series of shift registers can be used to store the incoming TV signals. The signals on this second line of shift registers are again converted back into analog signals to drive the LEDs when the next TV line comes in. At this time, the contents of the first line of shift registers is already cleared, ready to store this incoming signal. These alternating shift registers enable the system to have one line storage, enhancing brightness at the same time. Obviously, if the system is further modified to allow the images of several lines (say, N lines) of LEDs to be displayed at the same time, twice that number (2N) of shift registers can be used to alternatively store the signals and drive the LEDs. This allows even longer storage, enhancing the overall brightness even further. As a limit to the scheme just discussed, one can use 512 lines of LEDs with 512 elements on each line. This corresponds to full TV raster resolution. The overall brightness is now much greater, since storage time is one picture (~ 32 msec.) though delay time is unfortunately the same as the storage time. 2.3 Scantrix Implementation If one retains the entire LED panel but abandons the shift registers, there is a straight forward approach to building a real time TV display. This is the approach adopted for Scantrix even though the prototype panel is on a much smaller scale for economic reasons. Scantrix consists of a 60 x 6U LED-element display panel. Behind each LED is a sample-and-hold circuit which has a storage time of at least l6 msec, (the frame frequency of commercial TV). The analog video signal is sampled one 13 point at a time, first horizontally across the grid, then proceeding downward to the next line and across it in a similar fashion, just as is done for the scanning scheme of a TV raster. The sampled signals are stored in the holding circuits which activate the FET drivers, turning on the LEDs accordingly. In order to control the scanning of the panel, there is a horizontal decoder and a vertical decoder to keep track of the sync signals from the TV. The decoders supply information to the horizontal controller which has 6k outputs and the vertical controller which has 60 outputs forming a 60 x 6U crossed grid matrix. Only one point is activated at a time across the matrix which is responsible for the sampling action at that point. A simplified block diagram is shown in Figure 2.3 to illustrate the above scheme. Since the analog video signal is utilitized directly in this scheme, it is not necessary to have any form of data conversion. The brightness of each LED element is controlled by the amplitude of the video signal at that particular instant so that the brightness varies over a continuous spectrum rather than by discrete steps. In addition, the storage circuits greatly enhance the overall brightness of the display panel. With a total of 38U0 elements, the average brightness is enhanced by a factor of 381+0 as compared to the point at a time scheme without storage thus making this special point-at-a-time approach possible, Figure 2.k is a more detailed block diagram of Scantrix. It consists of a small black and white television set from which audio, composite video, hori- zontal sync and vertical sync signals are obtained. The audio naturally goes to a speaker which serves as the sound for the system. The sync signals obtained from the TV are on the order of tens of volts so that they must be appropriately attenuated in order for them to be TTL compatible. They then go through the re- shaping circuits whose functions are two-fold. They eliminate extraneous spikes on the one hand and regenerate better defined sync pulses on the other. The two sync signals, which are now TTL compatible, next go to the "video-gate and Ik UJ O o o Z o N (Z O X 7H 5 < o Q UJ tn (0 £ o CD K s< d3110d!N03 1V0I1U3A cr z uj >■ > co < o: H O CC O UJ UJ > Q -p a u w

u. cc «n _j "x - 1 tf) - V. DECO -CONT a ADORES I CD < z UJ t 1 i Crt z UJ UJ 1- 4 X /o \ / Ul 0-> cO -J / 22 / >< IDEO s. C J i > > in 318VN3 A _ i 1 / 1 _! 2 4 or UJ z 1- O Z UJ f- »- >-' (/> c/> z O >- HORIZ LI SELE 1 O l- CC X (- K < < O § CO z |«Z UJ 0. UJ 0. 1- < t- < K I H- X < - >- UJ V) Q > X >' z S P >- uj £ V7 v 2a ! So- r^ *K 1 /~\ ^ u 2 1 £J * > y u bD •H Q o H PP •H -P cd o C\J a; u g, •H En 16 system clock generator" where they are used to generate a train of 6k pulses for each horizontal line. The start of the pulse train is delayed slightly from the trailing edge of the horizontal sync pulse. These pulses, with a 50% duty cycle, have a period of approximately 0.8 ysec each. The pulse trains, which start after each sync signal, but stop before the next one, function as the sam- pling clock for the system. In order to properly control the raster size, hori- zontal and vertical enables are produced by the video gate circuitry through the use of the sync signals and the clock pulses generated earlier. The vertical enable pulse goes high during the useful horizontal lines period while the hori- zontal enable goes high only for that portion of each horizontal line from which desirable information is extracted. To derive the logic for controlling the scanning raster, the horizontal enable and the sampling clock signals are wired to the "horizontal decoder control and addresser" circuit. The outputs from this circuit include four-bit binary numbers which keep track of the sampling clock pulses and four strobes which control the action of the decoder. With this information, the l-out-of-6U decoder is able to output strobes serially in accor- dance with the clock sequence, turning ON or OFF the sixty-four analog switches, all of which have a common input — an amplified and properly DC level shifted video signal. These switches are turned on only one at a time, giving rise to the scanning action of LED panel. The vertical scanning scheme is very similar to the horizontal scanning scheme. Since only one of every four horizontal TV lines can be used (there are 2^2 horizontal lines/frame for the TV as compared to 60 for Scantrix), a horizontal line selector, actually a divide by four divider, selects the desired horizontal lines. The selected sync signals, with the verti- cal enable , both now go through a process similar to that used for the horizontal enable and the sampling clock. The result is strobes activated one at a time vertically along the 1-out-of 60 vertical decoder. These strobes, instead of controlling the analog switches, are responsible for lowering the LED row vol- tages for appropriate time intervals, one row at a time. In other words, if any 17 particular row's voltage level is lowered "by the vertical controller, that par- ticular row, and that row only, can respond to the video signals being passed to it "by the scanning analog switches. To understand how the display panel works, first imagine the first usable line of the TV video is applied to the LED panel. The top row of the panel is allowed to turn on first by lowering its voltage level. The first analog switch is then turned on so that the video sig- nal at that particular instant lights up the first LED accordingly. Then the second LED of the row is lighted up through the second analog switch. Then the third one and so on along the row. As the next line of usable video comes along, the second row of LEDs is enabled, and the analog switches are allowed to turn on successively as for the first line. This process is repeated each time for every usable video line until the whole picture is displayed on the display panel. 18 3.0 CIRCUIT DESCRIPTIONS Some circuit diagrams with brief analysis are presented in this chapter. Please refer to Appendices for circuits not appearing here. 3.1 Vertical Sync Driver The Vertical Sync Driver shown in Figure 3.1 consists of the attenuator and the reshaping unit. The vertical sync signal extracted from the TV has a peak to peak value of approximately 30 volts so that a high impedance voltage divider is used to attenuate the signal to about three volts which then goes through a LM 302 High Impedance Voltage Follower. A comparator then compares this signal with an adjustable reference voltage in order to eliminate most of the higher frequency, small amplitude spikes (the horizontal sync) from the vertical sync. Figure 3.2 shows the sync signal obtained before reshaping. Then a one-shot with a very long time constant is triggered by the comparator. This serves to eliminate the several spikes left that go beyond the reference which might still trigger the comparator. Another one-shot with ~ 27 ysec time, constant then is triggered off of the rising edge of the previous one-shot to give a smooth, accurate, vertical sync signal. 3.2 Horizontal Sync Driver The Horizontal Sync Driver (Figure 3.3) is very similar to the vertical sync driver. It attenuates the extracted horizontal sync (- 10 V ), compares XT IT the signal with a reference voltage and regenerates through a one-shot again. Since the horizontal sync (Figure 3.M is much "cleaner" than the vertical sync, the first one-shot is not necessary. The reshaped horizontal sync has an approxi- mate pulse width of 5 ysec. If) + sTl^ > A IS 4 10 C2IW.NS ^ 7^; > *3 4.. N - 1- ^ IO l2It»ZNS 7~\ -V\Ar— ||l ' — ^AA, — *-|| 2« 19 t> •H *H Q a C >» CO ■d o •H -P 0) > •H a > 20 3 CJ o -p bO CJ •H & W « o 0) m CJ •H CO o !>> w ■d CJ •rl -P U d) > CM •H CO 1 •H CO en I ■H O UJ 6 -I XjJJ 5 22 o a >> CO & o tsl •H o w a> g -p s CO W) •H 23 3.3 Video Gates and Sampling Clock In Figure 3-5, section A of the circuit represents the sampling clock generator. A small adjustable delay is imposed on the horizontal sync signal by the one-shot SN7U123. The cross-coupled multivibrators are triggered by the trailing edge of the delayed sync signal to generate sixty-four pulses as the sampling clock before the next horizontal sync occurs. Two SNT^+193 four- bit counters determine the number of pulses. The carry output at the end of the 6Hth pulse changes the state of the SN7^107 J-K Flip-Flop giving the Horizontal Enable output . Section B of the circuit (Figure 3*5) has two counters which can be pro- grammed by eight toggle switches to skip any appropriate number of horizontal lines before starting the picture. Section C counts 2U0 horizontal sync pulses after which the carry out- put triggers the SNT^107 which, in conjunction with the SN7^7^ in section B, gives the Vertical Enable strobe. 3.1+ Horizontal Decoder-Control Addresser This circuit, shown in Figure 3.6, is made up of a four-bit counter, a delay circuit, and a four-bit ring counter. The four-bit counter counts the sampling clock pulses and its outputs provide the address input to the demul- tiplexers (SN7U15U). Since it takes four SN7 i +15 1 + l-out-of-l6 demultiplexers to make up the l-out-of-6i+ decoder, the carry output from the SN7^l63 is needed to drive the ring counter whose outputs activate only one SN7^15^ at a time. The SN7U15I+ is used to provide a small delay so that none of the outputs from the demultiplexers are skipped. 3.5 Vertical Decoder-Control Addresser This circuit is almost identical to the "Horizontal Decoder-Control Addresser" except for the addition of a divide-by- four circuit. The purpose of 2k o o H O 9< w CO CD O o CD •H > CO 25 IO f o CLEAR SN7474 IO K u o _J u M IO 6 1 Q CLEAR Q SN7474 IO ■ u o 3 u u 1 1 s< i IO A a: Q SN74123 ■ 5 w J o a CLEAR Q SN7474 IO ►- w ■ H ■ K O e 3 u a On CM p4 Alo* n z '4 T« T" i u a c • 1 1 IO id ■ ■ 4. ■ il e j u 2 ! 2 ' ■ I o o ■ < ; 1- o o o o « t i > i 5 M J : u 5 >° i u > *~ < ' 1 ' 1 ' 1 ' i < ■ — Ph V) a) UJ CO -1 w CD 0) < Jh z tJ UJ t* < cc UJ H X O UJ Fh _l a. -P K o _l o 3 2 1 UJ Q U *-* a> t3 O O 0) Q 1 -P a o n •H Jh O W VD • on V ENABLE O- CLEAR ^T -eg r itf-M L^C ■°7r 20K i+rr ^> P 0. T 0. CLOCK C SN74163 CARRY CLEAR TO VERTICAL DECODER xO 1 W 1SK 5K/ pj l-4-^SA^r— ^r DELAY CLOCK i ->0 S -»S, ->o, DECODER CONTROL Figure 3.7 Vertical Decoder - Control Addresser. 28 if) (D »-H CVJ 0> »— » 1 ro 1— 1 1^ CVJ CVJ If) If) O UJ Li- en 3 < 5 ii 1- < or UJ o 5 CL Q n O LU li 9 Q. 3 UJ 1 u. c > in ^ Q UJ UJ CVJ >— «v CVJ > oo If) ^— WAr + ^ or CO i— i o GO I— I o T > > O if) i— i + + ^EH' bB aJ O -P CO > •H Q •H CO CO oo so 3 Q_ Z H 29 1* . CONCLUSION Figure k.l is a picture of Scantrix. The display panel measures ~ ik" x lV corresponding approximately to a 19" diagonal measurement. The resolution of the panel severely limits the sharpness of the picture so that complicated scenes are sometimes hard to recognize. However, this is not a fundamental limitation since theoretically its size and its resolution can "be expanded with- out bound by simply adding more elements and expanding the logic. Since its overall brightness increases proportionally with its surface area (assuming the point density constant) the larger the display, the brighter it will be. Non- uniformity of brightness among the LEDs was very much of a problem at an early stage of the design. The FET drivers were sorted at the factory in order to control the variation in threshold voltage of each FET. This does not eliminate all of the problems however. To be complete, the different ON resistances of the FETs should be compensated externally and the LEDs should be sorted also. Due to budget limitations on the project, the LEDs were not sorted. However, the non-uniformity is not that pronounced on the completed display. It is par- tially compensated by the grey-scale effect since the LEDs are not simply ON or OFF, allowing a good reference for comparison. In addition, in live television programs, rapidly changing scenes and moving objects simply do not allow us to examine the display closely for variations in brightness. Moving objects help improve recognition of the pictures also. Figures h.2 is a picture obtained from Scantrix. On the whole, the display is quite staisfactory even though its resolu- tion is only roughly k.Q% of that of a regular TV. The red nature of the LEDs does not seem to disturb the viewer. The system consumes a maximum of 300 watts of 30 Figure k.l Picture of Scantrix 31 Figure U.2 Picture of "Ul" Displayed on Scantrix (The pattern was generated from a mask by a flying spot scanner). 32 power which is very low compared to CRTs or plasma displays. It has an average brightness of 12 ft-L/spot. The whole display is actually very simple in structure compared to most currently available displays. It does not require any high voltage source or possess any fragile structure. It does not emit any harmful radiation. The currents that drive the LEDs are supplied by 60 floating 5 v, 1.5A power sup- plies each of which supplies the power for the entire row. Figure U.3 is a picture of the power supply card which actually houses four independent power supplies. A single unit of the LED display card consisting of four rows of 6U LEDs each and the drivers for all these LEDs is presented in Figure h.k. The card measures ~ lV x 10 1/2" x l" . However, it is not entirely incon- ceivable that with modern monolithic techniques, the LEDs and the drivers can be built in pluggable modulus, with much better controlled characteristics, desirable compactness and ruggedness. Then, a truly solid state, easily ser- viceable large screen display that hangs on a wall will be easily realized. Recently, green LEDs became available on the market. Monsanto already has the MV5^91 available containing both a red LED and a green LED in one pack- age. Blue LEDs, though not available yet, have been produced in research labo- ratories. According to RCA, blue LEDs can be made with efficiencies similar tc those of green LEDs. With the availability of red, green and blue LEDs, color, solid state, large screen displays will soon be reality. 33 Figure U.3 Picture of Floating Power Supply Card 3U Figure k.k A Single Unit of the LED Display Card Consisting of Four Rows of LEDs and their Drivers 35 BIBLIOGRAPHY 1. Ahrous, Richard W. , "In Strobed LED Displays, How Bright is Bright?" Electronics, Vol. UU, November 22, 1971, pp. 78-80. 2. "Blue LED Display Developed at RCA." Electronics, Vol. U6, No. 3, February 1, 1973, pp. UO-Ul. 3. Davis, Samuel, Computer Data Displays , Prentice-Hall, 1969- h. Forman, Jan, "Gas Discharge Display as an Alternative to CRTs," Computer Design, Vol. 12, No. k a April 1973, pp. 77-83. 5- Luxenberg, H. R. , and Rudolph L. Kuehn , Display Systems Engineering , McGraw Hill, 1968. 6. Nettle, Victor, Jr., and R. Gregory, "A Scanned Light Emitting Diode Dis- play," Proceeding of the S.I.D., Vol. 13/U, Fourth Quarter 1972, pp. 182-18U. 7. Nuese, C. J., H Kressel, and I. Ladany, "The Future for LEDs," Solid State, IEEE Spectrum, Vol. 9, No. 5, May 1972, pp. 28-38. 8. Sherr, Sol, Fundamentals of Display System Design , Wiley-Interscience , 1970. 9- Smith, George E. , "The Display Job Calls the Shots in Contest Between GaP and GaAsP, "Electronics, Vol. UU , No. 22, October 25, 1971, pp. 7^-77. 10. "Which LED is Best?", Electronic Design, Vol. 20, No. 19, September lU, 1972, pp. 120-12U. 11. Yuen, S. K. , "Quarterly Technical Progress Reports," Department of Computer Science, University of Illinois, starting July 197-1 to March 1973. 36 APPENDIX Figure Page A.l TV Schematic --. 37 A. 2 Row-Voltage Level Controller -38 A. 3 Floating Power Supply . 39 A.U Video Amplifier and Level Shifter ----------- kO 5 m i .1 ' 37 a 1 ^1 aSsse iifrOr 14 j ! « i: HH(-H(-» I ■■'./ S 7. +SS "So IHh > I s I § #^C?* \s ♦♦?s 5S ■a *■ v_r " f t( • vv ' • • • * '■ m ?• + I. 5? I -3^18 / £»• 5~r* & •!i — trrrt*— t -~fc 1 if Is T"2 / NH* J + it] 43M^ if! u Tgl$ i — ► i i'i_iLi_ ; :»-i_ i r€)i ©Us te ffi' | ^D | H fTT 1 ii L. -?<£ A itf* BH o •rH Id a Xi O 0) 3> •H 2* 38 +10 i — \w- 5.1K ^O VW— <► / SN7406 300pf HI— ♦ — vw- 51 ?€) 2N2905 D> ^ET© 2N2219 300 pf +5 Figure A. 2 Row-Voltage Level Controller 39 < cvi o 5 o o ft ft 0) > o ft ■H o 0) ft Uo R 9 >- > > — ^AA#— (|i m 0) -p •H -C CO <1J > u 0) •H Cm I O CiJ •H > •H O uj Ui X Q K > 2 O (T U. BIBLIOGRAPHIC DATA SHEET 1. Report No. UIUCDCS-R-7U-681 3. Recipient's Accession No. I. Title and Subtitle SCANTRIX: A SCANNED LED MATRIX DISPLAY 5. Report Date November, 1973 6. I Authors) Sik Kee Yuen 8. Performing Organization Rept. No. L Performing Organization Name and Address Department of Computer Science University of Illinois at Urb ana-Champaign Urbana, Illinois 6l801 10. Project/Task/Work Unit No. 11. Contract/Grant No. US AEC(ll-l) 1U69-P 12. Sponsoring Organization Name and Address Atomic Energy Commission Chicago Operations Office 9800 South Cass Avenue Argonne, Illinois 60^+39 13. Type of Report & Period Covered 14. 15. Supplementary Notes 16. Abstracts A real-time television display consisting of 6U x 6k red light -emitting diodes. A completely solid state display system. 7. Key Words and Document Analysis. 17a. Descriptors Television display Light-emitting diodes Solid State display system 7b. Identifiers /Open-Ended Terms 7c. COSATI Fie Id /Group & Availability Statement unlimited distribution 19. Security Class (This Report) UNCLASSIFIED 20. Security Class (This Page UNCLASSIFIED 21- No. of Pages U6 22. Price CRM N TIS-35 ( 10-70) USCOMM-DC 40329-P71 i? ** Q- UJ CO UNIVERSITY OF ILIINOIS-URBANA 110 84U6Rno C002 no 6?9 684(1974 Ripofl / 12 0884015 MM --r-l ■m ' ' MJ Rfflyffli ■ m H bob 1BH BBS] ■VI nut *y ,* » ■■ Hi ■ rani ■■ rr-'A ■ ■1 B ^| ■ ■■■■ . ■ I I HI ■■■ ■■■■ B St^'iVI ■1 b n