nw« #: L I B ^AHY OF THE UN IVER.SITY Of 1LL1 NOIS 510.84 iJfcr cop 2- The person charging this material is re- sponsible for its return to the library from which it was withdrawn on or before the Latest Date stamped below. Theft, 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 MAY 3 JUN V MAY MAY 4 19 38 L161 — O-1096 C ■ 6 f /h^if-^C^i Report No, 236 STEERING CIRCUITRY FOR AN ELECTROLUMiNESCENT PANEL by TAKEHIKO KATOH May 18, 1967 toe library of m AUG 1 10. UMIVERSJIY Of ILLINOIS Digitized by the Internet Archive in 2013 http://archive.org/details/steeringcircuitr236kato Report No. 236 STEERING CIRCUITRY FOR AN ELECTROLUMINESCENT PANEL fey Takehiko Katoh May 18, 1967 Department of Computer Science University of Illinois Urbana, Illinois 618OI This -work was supported in part by the Office of Naval Research, Contract US Nonr I83M15) and ™ as submitted in partial fulfillment for a Master of Science Degree in Electrical Engineering,, TABLE OF CONTENTS ACKNOWLEDGEMENT LIST OF FIGURES 1. INTRODUCTION 2. PROCESSES OF LUMINESCENCE 2.1 Introduction 2.2 Conditions with Static and Time Varying Field 2.3 Relation of Brightness to Electric Field 3. ELECTROLUMINESCENT PANEL 3.1 Introduction 3.2 Construction and Operation 3«3 Discrimination Ratio k. DISPLAY UNIT AND CONTROL SYSTEM 4.1 Introduction 4.2 Logic for Cell Selection 4.3 Display System 4.3.1 Clock (Oscillator) 4.3.2 Register 4.3.3 Decoder 4.3.4 Switch Matrix 4.3.5 Driver 4 . 4 Example 5 . CONCLUSION BIBLIOGRAPHY iii iv 1 2 2 3 6 IT IT IT 20 23 23 24 2T 2T 29 29 34 3T 3T 41 43 iii ACKNOWLEDGEMENT I "would like to express my gratitude to my thesis advisor, Professor W. J. Poppelbaum for suggesting this problem and for his interest and help during its solution. Deep thanks also go to Professor Louis Van Biljon for his counsel and suggestions and to Mr. Ai Irwin for his enthusiastic help in all phases of the project. iv LIST OF FIGURES Figure Page 1. Schematic Representation of the Collision Mechanism of Electroluminescence . 7 2. Mott-Schottky Exhaustion Layer. 9 3. Variation of Electrostatic Field Configuration •with Applied Voltage - A Uniformly Doped Crystal. 12 k. Schematic Representation of a Model for Brightness Waves. lh 5. Light Output Waveforms for Electroluminescent Phosphor e l6 6. Brightness vs. Applied Voltage Characteristic of Electroluminescence . 18 7. Configuration of Electroluminescent Cell. - 19 8. Configuration of Electroluminescent Matrix Panel. 19 9. Method of Selection 20 10. Discrimination Ratio for a 28 x 28 Matrix . 22 11. Control System for the Electroluminescent Panel, 28 12. Register. 30 13. Decoder. 31 lU. A Possible Circuit for the Switch Matrix. 33 15. Switch Matrix. 36 16. Driver 38 17. Example of Lighting up the Cells ( 1,2) , (2,3) , (3,3) ho 1. INTRODUCTION In many cases it is desirable to display the output of infor- mation processors by graphical means. One of the ' op contenders in the display area is tlie electroluminescent panel in which matrix steering of all display points is possible, Up to r.ow the highly non-linear and time-variable characteristics of electro Luminescent panels have led to considerable difficulties m building practical display systems. The system described in this thesis is the outcome of the theoretical investigations concerning the mechanism of electroluminescence and uses a very high voltage pulse super position method. It is felt that the uniformity of a 2 x 28 panel is sufficient and r r.at the access circuitry is of not more than average compiicar ■ r, 2. PROCESSES OF LUMINESCENCE 2.1 Introduction Luminescence is a general term describing light emission from matter, in excess of any radiation due to thermal vibration. Examples of luminescence are the narrow bands of radiated light energy from neon lamps or natural lightning, for example. Also, oxidation of certain organic matter "when exposed to air, as seen with glow -worms and fire flies, are instances of luminescent processes. The general term of luminescence may be broadly specified by considering the times involved in the process. If the excitation and emission processes occur in an interval approximating the natural life- _Q time of excited non -me ta stable isolated atoms, i.e., in about 10 seconds, the luminescent process is called fluorescence. Processes involving longer times, probably indicating the existence of an inter- mediate, trapped electronic state, are normally termed phosphorescence. Electroluminescence involves the excitation of luminescence by electric fields, commonly in some solid. Luminescence produced by cathode rays is not considered true electroluminescence since the excit- ation energy is derived from an electric field external to the lumin- escing material. The process- of electro.lumine.seje.nce is neither a simple, nor in all probability, a single phenomenon. Depending on the energy level structure in different materials, and on local field conditions inside a specific material, the electroluminescent mechanism could, according to current evidence, differ considerably. Theoretically, there are several conceivable mechanisms for the excitation of luminescent solids? 1) The activator system could be field-excited or field- ionized directly -with sufficient applied voltage. 2) Appropriate injected minority charge carriers could be captured by the activator system "which is thereby ionized: Either a p-n junction or suitable surface states are prerequisite to the carrier injection mechanism. 3) Conduction electrons having sufficient kinetic energy could, by impact, excite or ionize the activator system, or ionize the lattice, thereby producing electron-hole pairs which recombine in -cbe activator system. In every case, electric fields play an important role in electroluminescence . 2,2 Conditions with Static and Time Varying Fields. Before discussing the mechanism of electroluminescence, the effect of electric fields in crystals will be outlined. (Crystalline luminescent solids are normally termed "phosphors 7 ') . Let E s active field within the crystal E : applied external field EU : opposing field due to displaced electrical charge One then has E = E - ]L a By calling the conductivity a and the vector J the current density, one has: J = oE Tne total charge of the elementary volume dx.dy.dz increases in the time dt, by the quantity dq, such that dq = - V'J dxdydz.dt or dq = - a*7*E dxdydz.dt On the other hand, by calling the volume charge density £, we have d< l = if dtdxdydz Combining these quations, ~we have 7-B = - i |f a ot However, E n is the field produced by the internal charges, and substitut- ing in Poisson's equation y ^0 £ Where € is the dielectric constant of the crystal, we have t; = -ev*E = - e(7*E - 7°s) and, consequently (2-1) 7 ' E = 1 [fe <**.> - h <**>] By using a phasor notation E = C e jVt a a similarly E = Ce j(wt + «" Therefore fr-fi V • Ce$ = W • C v . ce^ = -i- 7 . c .0 a 7 *' C a 7 • C = — 1 + to 2 and tan = — ew 5 If E n is a constant then from equation (2-l) and ^ 7 • E = 0, ve have |p (? • I) ♦ « v . I = o S7 . E = (v • E )e" € a If E is a sinusoidal function then the relation between peak values Ep, Ql Eap are Ep = _^l f^ 2 and phase difference is -1 a 0. = tan r GW This result shows that the higher the frequency w, and the smaller the conductivity, a, the closer the peak value of the sinusoidal field in the phosphor is to the applied field. In the next section the relation bet-ween the field strength and the brightness of the lumines- cence -will be discussed. 2.3 Relation of Brightness to Electric Field The mechanism -which has been accepted most generally to explain the electroluminescence of zinc sulfide, for example, is one of acceler- ation of electrons in the conduction band followed by collision excitation of luminescent centres. More precisely, a three-step excitation process is assumed, as follows: l) Transfer of electrons from donor levels to the conduction band under the action of the applied electric field and/or temperature. 7 2) Acceleration of these electrons in the conduction band. Carrier multiplication or avalancrie formation may occur . 3) Collision of electrons "with luminescent centres -which are thereby excited or ionized, or with the basic crystal lattice itself and the consequent production of electron-hole pairs B A schematic representation of the collision mechanism of electroluminescence is shown in Figure 1. Electrons from donor levels in the surface barrier region are liberated by the action of the high electric field and/or temperature (l) in Figure 1. They are then accelerated by the field, (.2), to acquire energies higher than the bottom of the conduction band, and collide with activator centers whereby they lose their energy (3) and the activator centre is ionized, (h) , or excited. Emission may occur immediately, or later in the cycle when the applied potential is reversing « CONDUCTION BAND DONORS ACTIVATOR CENTRE VALENCE BAND Figure 1. Schematic Representation of the Collision Mechanism of Electroluminescence. 8 Considering the free path lengths of the accelerated electrons, it is required that an electron attain an energy equal to, or greater than, W = hv from the electric field in traveling a path iL in the direction of the field, i.e., W = hv = e^E It is known, however, from kinetic theory, (7), that in a gas the fraction of particles having path lengths which equal or exceed a certain value JL is given simply by exp {-£/!) since - W/W = f|§ = ,g/l where (I is the mean free path. The amount of light emitted, i.e., the brightness B, of the crystal, will be a function of the energies involved as well as the number of transitions made in a certain time interval. Combining the equations above, leads to an expression for its brightness B, as: or B a exp(" W /e E) = exp (-b/E) B = a exp (-b/E) (2-2) where a and b are constants. Wow a brightness B is expressed as a function of an active field, E, within the crystal. In the above argument a Mott-Schottky exhaustion barrier has been assumed (6). This type of surface barrier is shown in Figure 2. WIDTH OF THE--H ELECTRODE (b) THICKNESS OF THE __ EXHAUSTION LAYER --SURFACE OF THE CRYSTAL Figure 2. Mott-Schottky Exhaustion Layer, (a) Fotential Configuration, (b) Distribution of Electrostatic Charge Density!") „ For mathematical simplicity consideration will be confined to the case of a single crystal phosphor in intimate contact with plane parallel electrodes. The thickness of the crystal is small compared to the electrode dimensions so that edge effects may be neglected. If the electric potential difference is applied between the electrodes, an exhaustion layer will form next to the cathode. 10 Let V n = the applied potential which is large compared to the difference of work functions. e = the dielectric constant of the crystal. d = the width of the exhaustion layer . x = distance into the crystal. N = N,-N = K. the density of electron donors since I\L»N d a ' d da In the exhaustion region the positive space charge density will he N,ej no space charge will exist in the bulk of the crystal. Substituting in Poissoni' s equation dE/dx = Ne/e and integrating E(x) = (Ne/e)x + C. 1 Substituting the boundary condition E(d) = and defining A = (2Ne/e)2 where x = is at the surface of the crystal and x = d is the oxher end of the barrier E(x) = | A 2 (x-d). (2-3) If an electron at the cathode has a potential energy of V , with respect to the anode, then od V(x) E(s)dx=- i A 2 (x-d) 2 Combining (2-3) and (2-h) then and the width of the exhaustion region Therefore the brightness, B, from Equation (2-2) is: where a and b are constants 11 1 A 2 / *\ 2 + r A (x-d) (2-k) E(x) = AV(x)2 (2-5) d = 2V 2/A (2-6) n = a exp (b/^/v) (2-7) The barrier is particularly effective when close to a conduct- ing electrode. In an n-type semiconductor, electrons from donor levels are swept through the crystal from the region near the cathode. As the applied potential difference across the crystal is increased, the exhaustion region broadens and the field in the barrier increases as the square root of the applied voltage for a uniformly doped crystal. These 12 changes in field configuration are shown in Figure 3, 2/V^ DISTANCE FROM INTERFACE Figure 3« Variation of Electrostatic Field Configuration "with Applied Voltage in a Uniformly Doped Crystal* Figure k is a schematic representation of a model in which the variable width of the barrier is responsible for the excitation as a function of the applied voltage. When voltage is applied (Figure h-b) the cathode barrier widens and the anode barrier disappears . During this period luminescent centers in the barrier are emptied by impact of electrons entering from the cathode and recombination of some of the incoming electrons produces the in-phase peak. While the applied voltage is decreasing (Figure ^-c) electrons recombine with the empty centres in the diminishing (but still 13 present) cathode barrier region and cause the secondary peak, When the voltage (Figure h-d) is reversed this barrier disappears and recombination in the region immediately adjacent to the electrode produces the primary peak? at the same time the barrier at the other end of the crystal is growing and in-phase emission occurs later in time. Up to this point sinusoidal voltages have been assumed . Before closing this section one should discuss excitation by a square-wave unidirectional field and by an alternating square-wave field „ In Figure 5 are shown some results for a phosphor for both unidirectional pulses and pulses of alternating polarity. In the former case very little light is emitted when the voltage is applied. Most of the emission occurs in the absence of the voltage and the decay is very slow. When the same phosphor, however, is excited by alternating pulses of the same peak-to-peak amplitude and frequency, the output is more than twice that for unidirectional pulses „ The two half -cycles are identical and decay of the emission is much faster than in the previous case. After reversal of the voltage the field is in such a direction as to aid return of electrons to the center empcied during the previous half -cycle, while for unidirectional pulses this return occurs under nearly field-free conditions and therefore is slower. From Figure h in the former case, states (b) and (c) are repeated, therefore there are only in-phase peaks and secondary peaks but no primary peaks. On the other hand in the latter case states (b) and (c) are repeated and there are only in-phase peaks and primary peaks and they occur at the same instance but there are no secondary peaks. ].h do d [ o u o F (a) ^ L 2 do \do 1 — Li L 3 hH Figure 4. Schematic Representation of a Model for Brightness Waves 15 The drawings on the left indicate the barrier widths (dotted lines) and area of ionized luminescence centers (shaded) at four points during the voltage cycle as indicated. The drawings on the right indicate the potential distribution across the crystal. L and L.. correspond to the in-phase peak, L p to the secondary, and L, to the primary peak. The "in-phase" peaks, which occur when the voltage and current are maximum, disappear if a sufficiently thick insulating layer is inserted between the crystal and the metal electrode so that carriers cannot enter the crystal. 16 -OF-PHASE PEAK IN-PHASE PEAK ZERO . VOLTAGE (a) ZERO VOLTAGE (b) Figure 5. Light Output Waveforms for Electroluminescent Phosphor. 17 3. ELECTROLUMINESCENT PANEL 3.1 Introduction A prototype matrix electroluminescent panel is on the market. It is about one inch square and contains 78^ (= 28 x 28) intersections. The brightness vs. applied voltage characteristic curve is as shown in Figure 6. The panel will be used as a display/storage device. In this section will be discussed the construction of an electroluminescent cell and panel, and the relation between wanted and unwanted signals, i.e., the so-called "discrimination ratio". 3.2 Construction and Operation A typical electroluminescent cell is shown in Figure 7= When an alternating voltage is applied to the electrodes, light is emitted, and it emerges through the transparent bismuth-oxide/gold layer. Contact is made to the electrodes by soldering directly to the silver strips baked into the glass substrate . To make a matrix of cells, the single electrodes are replaced by narrow conducting strips, as shown in Figure 8. The strips are produced by a photo-etching process, and each has two silver contact "flags". 18 E o o o li. CD I0 3 0.06 0.07 0.08 H h h- -1/2 Vrms 102 -\ -\ \ \ \ \ \ 10' \ • \ • — i v \ \ X \ \ \ 10° in-l 1 1 1 300 250 200 Volts (rms) 150 Figure 6. Brightness 7s, Applied Voltage Characteristic of Electrolumin- escence. 19 Figure 7> Configuration of Electroluminescent Cell, Figure 8. Configuration of Electroluminescent Panel, 20 3. 3 Discrimination Ratio The 'discrimination ratio' is the ration between a wanted signal and an unwanted signal, let the excitation voltage pulses, of magnitude shown in Figure 9 be applied to the conductors of the matrix , V/x -V/2 V/x selected cell Figure 9, Method of Selection, Thus,, the selected-row conductor receives a pulse which rises from to +7/2 with respect to ground, and the pulse on the selected column goes from to -V/2 with respect to ground. All the non-selected row conductors are connected together and thus also receive pulses which go from to -7/X, and the non-selected columns, ones which go from to V/Xo Therefore the selected cell has a pulse of amplitude V across it. The 2(n-l) cells along the selected row and column have pulses of (V/2 - V/X) . The remaining (n-l) 2 cells have pulses of (2V/x) . The special cases are: 21 (i) X -» oo i.e., the non-selected conductors are all grounded, There are then 2(n-l) unselected cells "with pulses of amplitude V/2, and 2 (n-l) have no voltage across them- p (ii) X -» 6, when all (n -l) unselected cells have pulses of amplitude V/3« Each cell 'will emit a light pulse which has a maximum intensity given by equation (2-7) . B = A exp (-b//V) (2-7) If V is the 'wanted' signal, i.e., the output from the photo-multiplier w resulting from the light emitted by a selected '1', V^ = A'exp (-b/Yv) (3-D The 'unwanted' signal, i.e., the output which would result from all 2 (n -l) unselected 'l's when a '0' is selected, is Vu = 2(n-l)A'exp(-|| r f2-) + (n-ljVexp (- £ §) (3-2) fi4 « v|v Thus, the ratio of wanted to unwanted signals is Vw Vu 2(n-l) exp -V / x-2 J7 +(n-l) exp l-D (5-3) 22 Using equation (3 _ 3) curves of Vw/Vu as a function of X, drawn for b s /y varying from +0.5 to +U.5; -with n = 28 are shown in Figure 10. Observed values of b/yV ranged from about ho to ^5 for n - 28 which gives a usable value of Vw/Vu. The optimum value of X is close to 6, log V u 10 - 9 - 8 - 6 - 4.0 b//v~ = 44.0 b//v"=43.0 b//vr=42.0 b//V=4l .0 5.0 6.0 7.0 8.0 Figure 10. Discrimination Ratio for a 28 x 28 matrix 23 h. DISPLAY UNIT AND CONTROL SYSTEM 4.1 Introduction This section deals "with two problems » Firstly, how to select the cell which is wanted. Secondly, how to generate a field which is high enough to light up the cell. For the former case a cyclic counter is used. For the latter case high voltage power transisters or a transformer could be used. However, transformers and sinusoidal waves are not easily compatible with discrete level logic circuits. Fower transistors using square waves would be more easily matched to the digital circuitry. The latter combination will in general also be the cheaper one, thus making its adoption an obvious choice. As has been discussed in Chapter 3 > Section 3> "the optimum value of X is 6. However since the constant b is large enough to say expC-b/Jv) » exp (-b/JT/2) and as has been discussed at the end of Chapter 2., alternating square waves are more effective than unidirectional square waves, X can be assumed to be infinite. The human eye cannot detect the difference between B("v/2) and B(0) . This property of vision simplifies the system. 2k 4.2 Logic for Cell Selection Name the columns of the matrix X~, X. , . ... X and the rows 1 n Y~, Y-, .... Y for an n x n matrix. 0' 1' n Suppose a cell has coordinates (i,j). Let the columns and rows be "1" when they are selected. Then "the cell (i,j) is selected" means (X ± , Y.) = (1,1). The cell (i,j) lights up if and only if (X,, Y ) = (1,1) If only ori e cell in the matrix were chosen, this system would •work. What happens -when more than two cells having no common rows nor columns are selected? Call these two cells (i,j) and (k,x) tfhere i \ k and J =j=jg. Then (X ± , Yj) = (1,1) (X v Y £ ) - (1,1) 25 This implies X = 1, X. = 1, Y. = 1, and Y = 1. 1 K (X ± , i ) - (1,1) and (X k , Yj) = (1,1). i.e., two other unwanted cells light up. To solve this problem another variable is needed; namely time. Consider a cyclic counter modulo m 'where m > n, and divide the cycle time into m equal sized intervals, At. Name the times t.,, t_, ,.., t = t_. Then 1 m t, - t. + At, t = t~ + 2 At . . . t = t. + mAt 10 2 m Define X. = 1 for t . < t < t . + At ■ t. , . i i — i i+1 Then "the cell (i,j) is selected" means (1,1) for t, < t < t. +1 {x ± , r^j .=< (Q ^ or £ ^ otherwise Therefore, only cell (i,j) lights up When cells (i,«j) and (k, ) are selected, then 26 Y = <* t. < t. . 1 — i+I otherwise t. < t < t. . k — i+I otherwise Then (X., Y.) (1,1) (0,0) t. < t < t. . i - i+1 otherwise i\, Y .; (1,1) (0,0) t. < t < t. . k — k+l otherwise and (1,0) t, < t < t 1+1 (X., Y ) =1 (0,1) t. < t < t. ,, k - k+l (0,0) m otherwise f (o,i) t . < t < t . . i — i+I (X k , Y.) = , (1,0) t.. < t < t. ,, k — k+l (0,0) otherwise 27 Therefore only cells (i,j) and (k,,^) light up but cells (i,jt) and (k,j) do not. This system "works for the general case. The number of columns, n, is 28, and usually m = 2 , -where s is a positive integer. Recalling that m > n, the best choice of s is 5 and m = 32 . 4,3 Display System A control system for the electroluminescent panel is as shown in Figure 11. 4,3.1 Clock (Oscillator) As -was discussed in Section 2, if only the cell (i,j) is selected then X. = 1 only t. < t < t. . 1 " 1 — l+l Y . = 1 only t . < t < t . J 1 - i+l That is, the duty cycle is l/m = l/32. Because of the build-up pheno- menon in the panel luminescence there should be at least 8 ^ 10 square ■waves in At, and to prevent flickering there should be at least 30 cycles/sec in the counter cycle. 28 Ul > cr q 7r- UJ \- O UJ cr or uj o o o UJ Q _x X 5 X o or UJ > cr o i!: I uJ £c/)UJ P^UJZ *-! = Q. UJ-J H 0) 03 m ■p c 0) U ca H O Sh •P UJ .a ■p o 0J •P .' >j H M -P o o 0J g> P<4 29 8 square waves . 32 At . 30 cycles At counter cycle sec = 8 . 3 2 -30 sq < uare ^ aves = lOKHz sec Therefore at least 10 kHz square waves are needed for the clock. h.3.2 Register If there are 8 square waves in At and 32 At's in one cycle of the cyclic counter,, 8 hits of binary counter are required since o 8° 32 = 2 , An integrated J-K flip-flop circuit is used as a binary counter . As shown in Figure 12 the output of the most significant bit is labelled A, and the second is B, etc. ^.3 '3 Decoder Suppose 2 input AND gates with a maximum fan-out of 10, are used for a decoder. Input for the decoder is 5 binary digits, namely A, B, C, D, and E. Then 28 outputs (including h extra which are not used right now) are labelled f , f , . .., f , and f Q = A'B'OD'E = "1" t Q < t < t f = A°B o C\J or CVI_ 0_ < 00 z z a. a. "©—I A a -5 O * T K§> A. O KJ 27?.. IO IO -3 o * -^ o *: r 1 31 ED ED ED ED B C B l-^k^-j- — -j- — -j- — 3. ■ ' KDr KDt KD? l ®? Figure 13 •> Decoder 32 f = A-B-C-D-E = "1" t < t < t, d d — 9 f 2? = A-B-CD-E = "1" t 2? < t < t 2Q They are also -written as 3'C)j f Q = -| A(B-C)J- (D-E) f i |a(b.c)| (d-e) 3-C)l (D-E) f 2T H A < E Since most of the integrated circuits on the market have a final output with NAIQ, instead of 2 input A3!D gates, 2 input EA'/m'D gates are used for the decoder, The maximum number of fan-outs is 10 for NA1NFD gates, too. The logic with a minimum number of 2 input NASTD's and a max- imun of 10 fan-out's is as shewn in Figure 13. In this logic two input NAM) gates are also used as an inverter with one of the two inputs floating, the maximum fan-out required here being 7- Since f.. or f . requires a maximum of 29 fan-outs, namely ore for x. (i column) and at most 28 rows, an emitter follower is needed ^ for each f . « Nov there are two alternatives" Either f. s or f. 's 1 11 can be used for the switch matrix « When f . ! s are applied to the switch matrix AM) diode gate circuits rather than integrated NAM) gate circuits will be used. Each row of switch matrix is kept at -5 volts unless a signal from the emitter follower pulls it up to volto Every output of the row of the switch matrix is followed by a NAND gate integrated circuit. For "0" state 3 input current to a NAM) gate is -1.6 ma at -k .6 volts ^ -5 .0 volts and for ,: 1 ' it is -kO |ia at volts / "^-2.6 volts o The way to keep voltage of the row -5 volts is shown in Figure 1^. Then another -10 volt voltage source is needed. -5 -^ yi -^-^n) ^2 *27 .* r~® © 27 y 27 Figure 15 , Switch Matrix 37 If the input of the inverter is an open circuit, then the integrated inverter circuit recognizes the input signal as "1", and then the output signal of the inverter is '"0". Therefore there is no need to fix the line at some voltage level. This is one of the main advantages of using integrated circuit gates* U»3»5 Driver The largest problem for the drive is that the driving voltage to the electroluminescent panel is relatively higho The required volt- age of 270 volts poses several problems „ However, there are several ■ways to accommodate this voltage, the simplest being the use of an NPN silicon high voltage power transistor, for example R.C.A. U0321, R.C.A. ^0327, or MJ ^21. The driver circuit is shown in Figure l6. As discussed in Chapter 1 and Chapter 2, the applied fields o must be 180 out of phase, therefore clock pulses for X. 's and Y °s must also be 180 out of phase . h „U Example As an illustration of the principles described above | a 3x3 matrix and a switching signal having 2 square waves per At, is analyzed below. In Figure 18 D(X.) ' s and D(Y.) 's are directly connected to the electroluminescent panel. For the selected cells, for example (l,2), the drivers output for column X n and row Y-, are D(X n ) and D(Y-) respectively, and these two square waves are 180 out of phase. Therefore voltage applied to the cell (l,2), the difference of D(X Q ) 38 il s* > + in u CO > •H p VD H a; u w •H P4 o -J a: o o 39 and D(Y-) are square waves with peak-to-peak 5^0 volts for t Q < t < t-. For the unselected cells (unwanted cells) for example (l,l), (1,3), in a part of a cycle or whole cycle the cells are driven by unidirectional square waves with peak value 270 volts. ko — II 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 _ |«-At-«>|«-AI-4«-At-«| fo i I r~ * i 4- T7- i _ r _i l fo f| F fi y \jT j* y y y »0 »2 Figure 17. Example of Lighting up the cells (1,2), (2,3), and (3,3). hi 5 . CONCLUSION The system described above illustrates a successful and practical method for the selective display of coordinates on an electroluminescent panel, Previous efforts in this field have been less successful than the present one for two main reasons, Firstly the panels used exhibited large variations in brightness at different points on the panel. Secondly the electroluminescence was not sufficiently voltage - dependent to provide adequate discrimination between selected and non-selected points. Although the present panel eliminates much of the above mentioned drawbacks other unique difficulties have been introduced. The most significant of these is the relatively long lighting up time required by points near the centre of the panel, as compared with those around the edges. This larger build up phenomenon is directly related to the field in the phosphor. It could be eliminated by apply- ing from five to ten volts higher potentials to the rows and columns when points near the centre are to be energized. This will, however, complicate the logic . Another problem which may arise in similar electroluminescent panels is that of flicker. The present panel has a 28 x 28 matrix and the 10 kHz square wave drive is fast enough to prevent flicker . Larger arrays will require higher frequencies for comparable access times, but this will decrease the brightness of the selected point. U2 Both problems mentioned above are obviously directly related to the properties of the phosphors employed. Should brighter phosphors with longer decay times become available, most of these problems will disappear. As the system stands at present it uses a 28 x 28 matrix of toggle switches. Should the switches be replaceable by some logic circuitry, this system could well serve as an input to Paramatrix. ^3 BIBLIOGRAPHY (1) Destriau, G., ''The Nev Phenomenon of Electrophotoluminescence and its Possibilities for the Investigation of Crystal Lattice", Phil. Mag. 38, p. 700, p. 800 (19^7). (2) Destriau, G., and Ivey, H. F M "Electroluminescence and Related Topics", Proc. IPE 1+3, p. 1911, (1955). (3) Piper, W. W., and Williams, F. E., " ; i'he Mechanism of Electrolumin- escence of Zinc Sulphide", British J, of Appl. Phys., Suppl. No. k, 39, (1955). ' (h) Curie, Do, "Sur Le Mecanisme de L'electroluminescence: I Considerations Theoriques, and II Applications aux Faits Experimentaux", J. Phys. Radium, ih, p, 510, p. 672, (1953)° (5) Ivey, E. P., Electro luminescence and Relat ed Effects, Academic Press, (l9b3) (6) Piper, Wo Wo, and Williams, F. E., ""Electroluminescence 5 ", Solid State Physics, Vol. 6, p. 95* (1958). (7) Henisch, H. K., Electroluminescence, International Series of Monographs on Semiconductors, Pergamon Press, (1962) . (8) Kilburn, T., Hoffman, G. K., and Hayes, R. E., "An Accurate Electroluminescent Graphical- Out put Unit for a Digital Computer", Proceedings I.E.E., Paper So. 2^1 M, October, 1951, (105B, p. 136j. (9) Hoffman, G. R., Smith, Do H., and Jeffreys, D. C, "High-Speed Light Output Signals from Electroluminescent Storage System", Proceedings I.E.E., Paper No, 3217 M, February i960, (108E, p. 599) . (10) Oberbeck, P. E. R., ''Hybrid Circuit Design of the Artrix Graphical Processor", Report No. 220, Department of Computer Science, University of Illinois, Urbana, Illinois, 618OI, January 7, 19&7- (11) Esch, J. Wo, "System Design for Artrix Graphical Processor", Report No, 219, Department of Computer Science, University of Illinois, Urbana, Illinois, 618OI, January h, 1967. (12) Chu, I., Digital Com puter Design Fund amentals-. McGraw Hill, (1962). Ot j j.. j . hk (13) "Quarterly Technical Progress Report", (Hardware Systems Research), Department of Computer Science, University of Illinois, Urbana, Illinois. January - March 1966. (l*0 "Quarterly Technical Progress Report", (Hard-ware Systems Research), Department of Computer Science, University of Illinois, Urbana, Illinois o July - September 1966. (15) "Quarterly Technical Progress Report", (Hard-ware Systems Research), Department of Computer Science, University of Illinois, Urbana, Illinois. October - December 19660 (16) "Quarterly Technical Progress Report", (Hardware Systems Research), Department of Computer Science, University of Illinois, Urbana, Illinois. January - March 1967. Unclassified Security Classification DOCUMENT CONTROL DATA - R&D (Security classification of title, body of abstract and indexing annotation must be entered when the overall report is classified) I ORIGINATIN G ACTIVITY (Corporate author) Department of Computer Science University of Illinois Urbana, Illinois 6l801 2a REPORT SECURITY CLASSIFICATION Unclassified 2b GROUP 3 REPORT TITLE Steering Circuitry for an Electroluminescent Panel 4- DESCRIPTIVE NOTES (Type of report and inclusive dates) Thesis 5 AUTHORfS.) (Last name, first name, initial) Katoh, Takehiko « REPORT DATE May 18, 1967 7a TOTAL NO. OF PAGES 7 b. NO OF REFS |l CONTRACT ,OB GR.ANT NO. . C ON T R A CT O R GR.J NONR 185H15) 9a. ORIGINATOR'S REPORT NUMBERfSJ b. PRODUCT NO Report No. 236 9b OTHER REPORT NO(S) (A ny other numbers that may be assigned this report) None 10 AVAILABILITY/LIMITATION NOTICES Send requests to: Department of Computer Science, University of Illinois Urbana, Illinois 0I0OI 11 SUPPLEMENTARY NOTES None 12 SPONSORING MILITARY ACTIVITY Office of Naval Research 219 South Dearborn St. Chicago, Illinois 6o6oh 13 ABSTRACT In many cases it is desirable to display the output of infor- mation processors by graphical means. One of the top contenders in the display area is the electroluminescent panel in "which matrix steering of all display points is possible. Up to now the highly non-linear and time-variable characteristics of electroluminescent panels have led to considerable difficulties in building practical display systems. The system described in this thesis is the outcome of the theoretical investigations concerning the mechanism of electroluminescence and uses a very high voltage pulse super position method. It is felt that the uniformity of a 28 x 28 panel is sufficient and that the access circuitry is of not more than average complication. DD FORM 1 JAN 84 1473 Unclassified Security Classification 14 KEY WORDS LINK A ROLE LINK B LINK C 3 Electroluminescence INSTRUCTIONS \, ORIGINATING ACTIVITY: Enter the name and address of the contractor, subcontractor, grantee, Department of De- fense activity or other organization (corporate author) issuing the report. 2a. REPORT SECURITY CLASSIFICATION: Enter the over- all security classification of the report. Indicate whether "Restricted Data" is included. Marking is to be in accord- ance with appropriate security regulations. 26. GROUP: Automatic downgrading is specified in DoD Di- rective 5200. 10 and Armed Forces Industrial Manual. Enter the group number. Also, when applicable, show that optional markings have been used for Group 3 and Group 4 as author- ized. 3. REPORT TITLE: Enter the complete report title in all capital letters. 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