Morris, J.E., Martin, A, Weber, L F."Displays The Electrical Engineering Handbook Ed. Richard C. Dorf Boca raton crc Press llc. 2000
Morris, J.E., Martin, A., Weber, L.F. “Displays” The Electrical Engineering Handbook Ed. Richard C. Dorf Boca Raton: CRC Press LLC, 2000
83 Displays 83.1 Light-Emitting Diodes Semiconductor Device Principles. Semiconductor 83.2 Liquid-Crystal Displays Principle of Operation. Interfacing James E Morris 83. 3 The Cathode Ray Tube tate University of New York Monochrome crts· Color Crts· Contrast and Brightness. Measurements on CRTs. Projection Screen Andre martin 83.4 Color Plasma Displays Hughes Display Products troduction. Color Plasma Display Markets.Color Plasma Display Attributes.Gas Discharge Physics. Current Limiting Larry F. Weber Plasma Displays ac Plasma Displays. Color Plasma Display Plasmaco, subsidiary of matsushita Devices.Gray Scale 83.1 Light-Emitting Diodes James e. Morris The light-emitting diode(LED) has found a multitude of roles as the field of optoelectronics has bloomed. Infrared devices are used in conjunction with spectrally matched phototransistors in optoisolation couplers hand-held remote controllers, interruptive, reflective and fiber-optic sensing techniques, etc. Visible spectrum pplications include simple status indicators and dynamic power level bar graphs on a stereo or tape deck. This section will concentrate on digital display applications of visible output devices. Semiconductor Device Principles The operation of an LED is based on the recombination of electrons and holes in a semiconductor. As an electron carrier in the conduction band recombines with a hole in the valence band, it loses energy AE equal to the bandgap E, with the emission of a photon of frequency c/=△E/h (83.1) where n is the radiation wavelength and h is Plancks constant. The incidence of recombination under equilibrium conditions is insufficient for practical applications bu an be enhanced by increasing the minority carrier density. In an LED, this is accomplished by forward biasing the diode, the injected minority carriers recombining with the majority carriers within a few diffusion lengths of the junction edge Figure 83.1 illustrates the process. The potential barrier eV, is reduced by forward bias ev, leading to net forward current and the minority carrier distributions shown on either side of the depletion yer. As the carriers diffuse away from the junction edges, these distributions decay exponentially because of ecombination with the majority carriers. Each recombination event shown on either side of the junction gives off a photon. This process is called injection electroluminescence. c 2000 by CRC Press LLC
© 2000 by CRC Press LLC 83 Displays 83.1 Light-Emitting Diodes Semiconductor Device Principles • Semiconductor Materials • Device Efficiency • Interfacing 83.2 Liquid-Crystal Displays Principle of Operation • Interfacing 83.3 The Cathode Ray Tube Monochrome CRTs • Color CRTs • Contrast and Brightness • Measurements on CRTs • Projection Screen 83.4 Color Plasma Displays Introduction • Color Plasma Display Markets • Color Plasma Display Attributes • Gas Discharge Physics • Current Limiting for Plasma Displays • ac Plasma Displays • Color Plasma Display Devices • Gray Scale 83.1 Light-Emitting Diodes James E. Morris The light-emitting diode (LED) has found a multitude of roles as the field of optoelectronics has bloomed. Infrared devices are used in conjunction with spectrally matched phototransistors in optoisolation couplers, hand-held remote controllers, interruptive, reflective and fiber-optic sensing techniques, etc. Visible spectrum applications include simple status indicators and dynamic power level bar graphs on a stereo or tape deck. This section will concentrate on digital display applications of visible output devices. Semiconductor Device Principles The operation of an LED is based on the recombination of electrons and holes in a semiconductor. As an electron carrier in the conduction band recombines with a hole in the valence band, it loses energy DE equal to the bandgap Eg with the emission of a photon of frequency u = c/l = DE/h (83.1) where l is the radiation wavelength and h is Planck’s constant. The incidence of recombination under equilibrium conditions is insufficient for practical applications but can be enhanced by increasing the minority carrier density. In an LED, this is accomplished by forward biasing the diode, the injected minority carriers recombining with the majority carriers within a few diffusion lengths of the junction edge. Figure 83.1 illustrates the process. The potential barrier eVo is reduced by forward bias eV, leading to net forward current and the minority carrier distributions shown on either side of the depletion layer. As the carriers diffuse away from the junction edges, these distributions decay exponentially because of recombination with the majority carriers. Each recombination event shown on either side of the junction gives off a photon. This process is called injection electroluminescence. James E. Morris State University of New York at Binghamton André Martin Hughes Display Products Larry F. Weber Plasmaco, subsidiary of Matsushita
recombination 8888° Recombination Carrier Holes FIGURE 83 1 Light emission due to radiative recombination of injected carriers in a forward-biased pn junction. Energy Indirect Recombination hala p -h≠/{a FIGURE 83.2 (a)Interband recombination in a direct-bandgap semiconductor;( b) recombination in an indirect-gap semiconductor also involves a momentum chan Equation(83. 1) implies that the radiation emitted will be monochromatic, but in practice AE> E, and there is a spectral distribution corresponding to the energy distributions of the carriers in the conduction and valence bands Semiconductor materials Silicon is the most common material used in current semiconductor technologies, but it is not at all suitable for an LED. The reason is that silicon has an indirect bandgap, and a direct bandgap is required for process efficiency. Direct and indirect bandgaps are compared in Fig. 83. 2, where carrier energy is plotted versus momentum for both cases. The photon momentum P=h=hu/c (83.2) e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Equation (83.1) implies that the radiation emitted will be monochromatic, but in practice DE > Eg, and there is a spectral distribution corresponding to the energy distributions of the carriers in the conduction and valence bands. Semiconductor Materials Silicon is the most common material used in current semiconductor technologies, but it is not at all suitable for an LED. The reason is that silicon has an indirect bandgap, and a direct bandgap is required for process efficiency. Direct and indirect bandgaps are compared in Fig. 83.2, where carrier energy is plotted versus momentum for both cases. The photon momentum p = hl = hu/c (83.2) FIGURE 83.1 Light emission due to radiative recombination of injected carriers in a forward-biased pn junction. FIGURE 83.2 (a) Interband recombination in a direct-bandgap semiconductor; (b) recombination in an indirect-gap semiconductor also involves a momentum change. VB CB E Eg eV np pn x p n npO pnO EFn EFp Hole Injection Electron Injection Light Out Holes Depletion layer MinorityCarrier Density Light Out recombination e (V–VO) pnoe pnoe -x/Le -x/Lh recombination Light Output Indirect Transition Energy Change Momentum Change Injected Electron Direct Recombination with Hole VB CB E E Hole -h¹/a 0 h¹/a (a) p VB Hole -h¹/a 0 h¹/a (a) p
ENERGY 1-xPx 085155 23 INDIRECT MINIMUM ENERGY X=0.85 GaP GREEN GaAsP RED CONDUCTION BAND N TRAPPING LEVEL CON DUCTION BAND 一 ZnO TRAPPING LEVEL GREEN RED VALENCE BAND VALENCE BAND MOMENTUM FIGURE 83.3 (a) Plot of momentum versus bandgap energy, and(b)corresponding semiconductor parameters for va compounds of the GaAs/GaP system;(c) plot of momentum versus bandgap energy for indirect GaP materials showing special trapping levels. (Source: S Gage et al, Optoelectronics/Fiber-Optics Applications ManuaL, 2nd ed, New York: Hewlett Packard/McGraw-Hill, 1981, PP. 13-4. With permission. (where c is the velocity of light) is very small, and conservation of momentum can be readily accommodated by small deviations from the vertical transition shown in Fig. 83. 2(a). For the indirect case illustrated in Fig 83. 2(b), the energy change AE defines the photon energy and momentum, again according to Eqs. (83. 1) and(83. 2), but conservation of momentum additionally requires that the much greater electron momentum on the order of h/2a be accounted for. For lattice dimensions, a, on the order of 10-10 m and wavelengths, h, on the order of 10-m, it is clearly not possible for both conservation criteria to be met without the participation of a third body, i.e., a phonon. The two consequences of this result are that the indirect transition is inefficient (in that it must transfer momentum and hence thermal energy to the lattice)and less likely to occur than the direct transition(because of the requirement for all three particles to simultaneously meet the energy and momentum conditions). Indirect bandgaps therefore lead to long diffusion lengths and recombination times which produce good transistors but poor LEDs The most common direct-bandgap semiconductor is GaAs, but the photon wavelength calculated for E Ep=1.43 ev as listed in Fig. 83.3(b)is in the infrared. Such a material may be ideal for communications and sory optoelectronic applications but is unsuitable for display purposes. The bandgap may be adjusted, ver, by the substitution of phosphorus for arsenic in the lattice as shown in Fig. 83. 3(a). The color range sted corresponds to the range of LEd colors commonly available: red, yellow, and green. The direct and indirect bandgaps, Ep and Ep of GaAsk-Px vary with x as ED=1.441+1.091x+0.210x2 (83.3) E1=1.977+0.144x+0.211x2 (834) [ Wang, 1989], enabling one to design the material to produce the required LEd color. e 2000 by CRC Press LLC
© 2000 by CRC Press LLC (where c is the velocity of light) is very small, and conservation of momentum can be readily accommodated by small deviations from the vertical transition shown in Fig. 83.2(a). For the indirect case illustrated in Fig. 83.2(b), the energy change DE defines the photon energy and momentum, again according to Eqs. (83.1) and (83.2), but conservation of momentum additionally requires that the much greater electron momentum on the order of h/2a be accounted for. For lattice dimensions, a, on the order of 10–10 m and wavelengths, l, on the order of 10–6 m, it is clearly not possible for both conservation criteria to be met without the participation of a third body, i.e., a phonon. The two consequences of this result are that the indirect transition is inefficient (in that it must transfer momentum and hence thermal energy to the lattice) and less likely to occur than the direct transition (because of the requirement for all three particles to simultaneously meet the energy and momentum conditions). Indirect bandgaps therefore lead to long diffusion lengths and recombination times, which produce good transistors but poor LEDs. The most common direct-bandgap semiconductor is GaAs, but the photon wavelength calculated for Eg = ED = 1.43 eV as listed in Fig. 83.3(b) is in the infrared. Such a material may be ideal for communications and sensory optoelectronic applications but is unsuitable for display purposes. The bandgap may be adjusted, however, by the substitution of phosphorus for arsenic in the lattice as shown in Fig. 83.3(a). The color range listed corresponds to the range of LED colors commonly available: red, yellow, and green. The direct and indirect bandgaps, ED and EI , of GaAs1–xPx vary with x as ED = 1.441 + 1.091x + 0.210x2 (83.3) and EI = 1.977 + 0.144x + 0.211x2 (83.4) [Wang, 1989], enabling one to design the material to produce the required LED color. FIGURE 83.3 (a) Plot of momentum versus bandgap energy, and (b) corresponding semiconductor parameters for various compounds of the GaAs/GaP system; (c) plot of momentum versus bandgap energy for indirect GaP materials showing special trapping levels. (Source: S. Gage et al., Optoelectronics/Fiber-Optics Applications Manual, 2nd ed., New York: HewlettPackard/McGraw-Hill, 1981, pp. 1.3–4. With permission.)
Note the continuous transition from the direct gaas to the indirect gaP. The materials have an indirect bandgap for x>0.4 and have the same problems as light emitters as silicon. The efficiency of an indirect-gap emitter can be greatly enhanced by the introduction of appropriate impurity recombination centers, as shown in Fig. 83. 3(c). In the process shown, an injected minority carrier electron(in p-type material) is first trapped by the localized impurity(which is itself electrically neutral but which introduces a local potential to the lattice which attracts electrons). The center is then negatively charged and attracts a hole to complete the recombination process, which produces the photon. The recombination center solves the momentum transfer problem, because the trapped electron is localized to the impurity lattice site and has a momentum range according to the Heisenberg Uncertainty Principle of △p~h/2πa (83.5) that is, sufficient to include the processes shown in the diagram at p-O. In the cases used as examples,a nitrogen atom substitutes for a phosphorus, or a zinc-oxygen pair substitutes for adjacent gallium-phosphorus atoms in the GaAs P, lattice. The GaAs -P, system is well established, but can only produce wavelengths defined by the range of energy p widths, i.e., down to green. Blue LEDs require higher band-gap materials (a)SiC technology is well developed for high temperature semiconductor applications, but it has an indirect band gap, so its emission efficiency is very poor [Pierret, 1996 (b) Gan (and In/Al GaN alloys)is a direct band gap material system producing successful blue and blue green devices [iles, 1994; Nakamura, 1995; Pierret, 1996 (c)II-IV compounds such as ZnS and ZnSe possess direct band gaps in the 1.5-3.6eV range, offering the possibility of full spectrum LEDs within the single materials system iles, 1994] Device Efficiency In considering LED efficiencies, it is convenient to consider the emission process to consist of three distinct steps: (a)excitation,(b)recombination, and(c)extraction. These will be discussed with reference to Fig 83.4 (a) Photons created by minority electron recombination on the p-type side of the junction are more likely be successfully emitted from the surface of the device, for the structure shown in Fig. 83. 4(a)and(b)if the p-type region is a thin surface layer. For a given total LED current, I, made up of electron, hole, and space charge region recombination components, In,Ip and I, respectively, the electron injection efficiency( which provides the excitation)is Yn=I(I++1) (83.6) In principle, all the physical processes described above apply equally to both electrons and holes. However, the electron mobility, H,, is greater than that of a hole, Hp, and since p=Naμn/Nap (83.7) (where No N are n-type donor and p-type acceptor doping densities, respectively) greater Y, is attainable for a given doping ratio than hole injection efficiency, Yp Consequently, LEDs are usually p-n' diodes constructed (b)Some of the recombinations undergone by the excess electron distribution, An, in the p-type region will ad to radiation of the photon desired, but others will not, because of the existence of doping and various impurity levels in the bandgap. The total recombination rate, R, can be written in terms of the radiative and R + r (838) where n/t 83.9) e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Note the continuous transition from the direct GaAs to the indirect GaP. The materials have an indirect bandgap for x > 0.4 and have the same problems as light emitters as silicon. The efficiency of an indirect-gap emitter can be greatly enhanced by the introduction of appropriate impurity recombination centers, as shown in Fig. 83.3(c). In the process shown, an injected minority carrier electron (in p-type material) is first trapped by the localized impurity (which is itself electrically neutral but which introduces a local potential to the lattice which attracts electrons). The center is then negatively charged and attracts a hole to complete the recombination process, which produces the photon. The recombination center solves the momentum transfer problem, because the trapped electron is localized to the impurity lattice site and has a momentum range according to the Heisenberg Uncertainty Principle of Dp ~ h/2pa (83.5) that is, sufficient to include the processes shown in the diagram at p ~ 0. In the cases used as examples, a nitrogen atom substitutes for a phosphorus, or a zinc–oxygen pair substitutes for adjacent gallium–phosphorus atoms in the GaAs1–xPx lattice. The GaAs1-xPx system is well established, but can only produce wavelengths defined by the range of energy gap widths, i.e., down to green. Blue LEDs require higher band-gap materials: (a) SiC technology is well developed for high temperature semiconductor applications, but it has an indirect band gap, so its emission efficiency is very poor [Pierret, 1996]. (b) GaN (and In/Al GaN alloys) is a direct band gap material system producing successful blue and bluegreen devices [Jiles, 1994; Nakamura, 1995; Pierret, 1996]. (c) II-IV compounds such as ZnS and ZnSe possess direct band gaps in the 1.5–3.6eV range, offering the possibility of full spectrum LEDs within the single materials system [Jiles, 1994]. Device Efficiency In considering LED efficiencies, it is convenient to consider the emission process to consist of three distinct steps: (a) excitation, (b) recombination, and (c) extraction. These will be discussed with reference to Fig. 83.4. (a) Photons created by minority electron recombination on the p-type side of the junction are more likely to be successfully emitted from the surface of the device, for the structure shown in Fig. 83.4(a) and (b) if the p-type region is a thin surface layer. For a given total LED current, I, made up of electron, hole, and spacecharge region recombination components, In, Ip, and Ir , respectively, the electron injection efficiency (which provides the excitation) is gn = In/(In + Ip + Ir) (83.6) In principle, all the physical processes described above apply equally to both electrons and holes. However, the electron mobility, mn, is greater than that of a hole, mp, and since In/Ip = Nd mn/Na mp (83.7) (where Nd, Na are n-type donor and p-type acceptor doping densities, respectively) greater gn is attainable for a given doping ratio than hole injection efficiency, gp. Consequently, LEDs are usually p-n+ diodes constructed as in Fig. 83.4, with the p-layer at the surface. (b) Some of the recombinations undergone by the excess electron distribution, Dn, in the p-type region will lead to radiation of the photon desired, but others will not, because of the existence of doping and various impurity levels in the bandgap. The total recombination rate, R, can be written in terms of the radiative and nonradiative rates, Rr and Rnr, as R = Rr + Rnr (83.8) where Rr = Dn/tr , Rnr = Dn/tnr, R = Dn/t (83.9)
Absorbed Light Output GaAs Transparent Encapsulation GaAs FIGURE 83.4 Effect of(a)opaque substrate, (b)transparent substrate, and(c)encapsulation on photons emitted at the pn Junction and where t, and t, are the minority carrier lifetimes associated with the radiative and nonradiative recombi nation processes, and t is the effective lifetime. The radiative efficiency is defined as n=R/(R1+Rm)=t/τ (83.10) and the internal quantum efficiency is ni= ny 83.11) (c) It is clear from Fig. 83. 4 that many of the photons generated on either side of the junction will pass through sufficient bulk semiconductor to be reabsorbed. In fact the photon energy may be ideally suited to reabsorption if it exceeds the semiconductor direct bandgap. It is obvious, then, why GaAs is opaque and Gap transparent to photons from Ga(As: P) junctions. Clearly, a greater efficiency might be expected from the transparent substrate with reflecting contact [Fig. 83. 4(b) The photon must strike the LED surface at an angle less than the critical angle for total internal reflection, 1/n (83.12) and next, nLED are the external and internal refractive indices, respectively. For air, next=1, but critical angle loss be reduced by encapsulating the device in an epoxy lens cap[ Fig 83. 4(c)] to increase both nat >1 and the angle of incidence at the air interface. Even within angles less than 0, there is Fresnel loss, with transmission ratio T=4n/(1+n)2 (83.13) The total external quantum efficiency is then the fraction of photons emitted [Neamen, 1992], given by n。=1/(1+v/AT e 2000 by CRC Press LLC
© 2000 by CRC Press LLC and where tr and tnr are the minority carrier lifetimes associated with the radiative and nonradiative recombination processes, and t is the effective lifetime. The radiative efficiency is defined as h = Rr/(Rr + Rnr) = t/tr (83.10) and the internal quantum efficiency is hi = hg (83.11) (c) It is clear from Fig. 83.4 that many of the photons generated on either side of the junction will pass through sufficient bulk semiconductor to be reabsorbed. In fact the photon energy may be ideally suited to reabsorption if it exceeds the semiconductor direct bandgap. It is obvious, then, why GaAs is opaque and GaP transparent to photons from Ga(As:P) junctions. Clearly, a greater efficiency might be expected from the transparent substrate with reflecting contact [Fig. 83.4(b)]. The photon must strike the LED surface at an angle less than the critical angle for total internal reflection, qc, where sin qc = next /nLED = 1/n (83.12) and next, nLED are the external and internal refractive indices, respectively. For air, next = 1, but critical angle loss can be reduced by encapsulating the device in an epoxy lens cap [Fig. 83.4(c)] to increase both next > 1 and the angle of incidence at the air interface. Even within angles less than qc, there is Fresnel loss, with transmission ratio T = 4n/(1 + n)2 (83.13) The total external quantum efficiency is then the fraction of photons emitted [Neamen, 1992], given by [Yang, 1988] he = 1/(1 + avo/AT) (83.14) FIGURE 83.4 Effect of (a) opaque substrate, (b) transparent substrate, and (c) encapsulation on photons emitted at the pn junction. A Absorbed Photons Graded Alloy GaAs1-y Py (y=0 0.4) Graded Alloy GaAs1-y Py Reflective Contact Emitted Photons Emitted Photons Predominantly Electron Injection Transparent Plastic Encapsulation Al Top Contact Light Output Insulating Layer Al Back Contact GaAs GaAs P GaAs1-yPy Ga P B n p n n p (a) (b) (c) qc p
Contact N GaALoz Asos 2.1 ev P GaAs P GaAlos Asoa GaAs FIGURE 83.5 A GaAlAs heterojunction LED: (a)cross-sectional diagram;(b) energy-band diagr OPEN COLLECTOR GATES ACTIVE PULLUP. TOTEM POLE GATE MAY BE R LOGIC LOGIC SERIES SWITCHING SERIES SHUNT WITCHING CURRENT TO LED FIGURE 83.6 Digital logic can interface directly to LED lamps. Source: S Gage et al, Optoelectronics/Fiber-Optics appli- cations Manual, 2nd ed, New York: Hewlett-Packard/McGraw-Hill, 1981, P. 2. 20. With permission. where a is the average absorption coefficient, v, is the LED volume, and A is the emitting area In considering LED effectiveness for display purposes, one must also include radiation wavelength in relation to the spectral response of the human eye [Sze, 1985]. Although the Gap green LED is intrinsically less efficient than the GaAsP red LED, the eye compensates for the deficiency with a greater sensitivity to green. More recently developed heterojunction LEDs(Fig. 83.5)offer two mechanisms to improve LED efficiencies [Yang, 1988]. The electron injection efficiency can be enhanced, but, in addition, absorption losses through the wider 2. 1-ev bandgap n-type layer are essentially eliminated for photons emitted by recombination in the lower 2.0-ev bandgap p-type region. Interfacing In circuit design applications, the LEd may be treated much as a regular diode, but with a much greater forward voltage, V, Since one usually seeks maximum brightness from the device, it is usually conducting heavily and VE approaches the contact potential. As one moves from GaAs to GaP [Fig 83.3(a), VE varies from about 1.5 to around 2.0 V. The variation in VE with temperature(at constant current)follows similar rules as apply to conventional diodes, but radiant power and wavelengths also change [Gage et al, 1981 Single LEDs are commonly driven by logic gates, perhaps as status indicators, and some of the simplest interface circuits are shown in Fig. 83. 6. In many cases, the gate output will not be able to source or sink sufficient current for visibility, and an amplifier will be required, as in Fig. 83. 7. Bar graph displays are commonly
© 2000 by CRC Press LLC where a is the average absorption coefficient, vo is the LED volume, and A is the emitting area. In considering LED effectiveness for display purposes, one must also include radiation wavelength in relation to the spectral response of the human eye [Sze, 1985]. Although the GaP green LED is intrinsically less efficient than the GaAsP red LED, the eye compensates for the deficiency with a greater sensitivity to green. More recently developed heterojunction LEDs (Fig. 83.5) offer two mechanisms to improve LED efficiencies [Yang, 1988]. The electron injection efficiency can be enhanced, but, in addition, absorption losses through the wider 2.1-eV bandgap n-type layer are essentially eliminated for photons emitted by recombination in the lower 2.0-eV bandgap p-type region. Interfacing In circuit design applications, the LED may be treated much as a regular diode, but with a much greater forward voltage, VF. Since one usually seeks maximum brightness from the device, it is usually conducting heavily and VF approaches the contact potential. As one moves from GaAs to GaP [Fig. 83.3(a)], VF varies from about 1.5 to around 2.0 V. The variation in VF with temperature (at constant current) follows similar rules as apply to conventional diodes, but radiant power and wavelengths also change [Gage et al., 1981]. Single LEDs are commonly driven by logic gates, perhaps as status indicators, and some of the simplest interface circuits are shown in Fig. 83.6. In many cases, the gate output will not be able to source or sink sufficient current for visibility, and an amplifier will be required, as in Fig. 83.7. Bar graph displays are commonly FIGURE 83.5 A GaAlAs heterojunction LED: (a) cross-sectional diagram; (b) energy-band diagram. FIGURE 83.6 Digital logic can interface directly to LED lamps. (Source: S. Gage et al., Optoelectronics/Fiber-Optics Applications Manual, 2nd ed., New York: Hewlett-Packard/McGraw-Hill, 1981, p. 2.20. With permission.) N GaAl0.7 As0.3 P GaAl0.6 As0.4 N GaAl0.7 As P GaAl0.6 As0.4 p GaAs P GaAs Contact Contact 2.1 eV 2.0 eV 1.42 eV Eƒ
LED 2N2907A ve- (a) For use when LSTTL drives an LED (b) For use when a logic high is needed to drive an LED FIGURE 83.7 LED interfacing for(a)low-power transistor-transistor logic,(b)logic high drive, and(c)CMOS ( Source: M. Forbes and BB Brey, Digital Electronics, Indianapolis: Bobbs-Merrill, 1985, P. 242. With permission. +Vcc NATIONAL L-- LED2 立=LED1 BAR GRAPH DISPLAY POSITION INDICATOR DISPLAY FIGURE 83.8 Operational amplifiers or voltage comparators used to decode an analog signal into a bar graph or position dicator display.( Source: S. Gage et al, Optoelectronics/Fiber-Optics Applications Manual, 2nd ed, New York: Hewlett Packard/McGraw-Hill, 1981, P. 23.3. With permission. used to indicate signal level on audio equipment, with a modification of the position indicator seen in Fig. 83.8 to guide fine tuning. Matrix LED arrays can be used for flexible, high-density panel displays [Fig 83.9(a)] and are conventionally controlled by row or column strobing[ Fig 83.9(b)] controlled by a microprocessor interface. Multiple LEDs are commonly packaged together in a single integrated device, organized in one of the standard display fonts Fig 83. 10(a)l, with decoding often included within the package [Fig. 83. 10(b)]. The 7-segment e 2000 by CRC Press LLC
© 2000 by CRC Press LLC used to indicate signal level on audio equipment, with a modification of the position indicator seen in Fig. 83.8 to guide fine tuning. Matrix LED arrays can be used for flexible, high-density panel displays [Fig. 83.9(a)] and are conventionally controlled by row or column strobing [Fig. 83.9(b)] controlled by a microprocessor interface. Multiple LEDs are commonly packaged together in a single integrated device, organized in one of the standard display fonts [Fig. 83.10(a)], with decoding often included within the package [Fig. 83.10(b)]. The 7-segment FIGURE 83.7 LED interfacing for (a) low-power transistor-transistor logic, (b) logic high drive, and (c) CMOS. (Source: M. Forbes and B.B. Brey, Digital Electronics, Indianapolis: Bobbs-Merrill, 1985, p. 242. With permission.) FIGURE 83.8 Operational amplifiers or voltage comparators used to decode an analog signal into a bar graph or position indicator display. (Source: S. Gage et al., Optoelectronics/Fiber-Optics Applications Manual, 2nd ed., New York: HewlettPackard/McGraw-Hill, 1981, p. 23.3. With permission.)
■口口 ■自日口 口口口 口口口 日口 日口 口口口 百口 口■ 口口口 百日口口口口口 日口■口口 口 X1×2X3 自口口口口 (a 口 口口 FIGURE 83.9 Matrix displays. (a)One LEd will be turned on by applying the proper signal to one x axis and one y axis. (b) Character generation using column strobe methods. Source: S. Gage et al., Optoelectronics/Fiber-Optics Applications Manual, 2nd ed, New York: Hewlett-Packard/McGraw-Hill, 1981, pp 2.25, 5.44. With permission 图 日日口 FONT A: 7-SEGMENT FONT C: 16-SEGMENT FONT E: 5x7 DOT MATRIX FONT GLASS WINDOW ATED CIR NTRAST 接 ETIC SEAL AT EXTERNAL L BACK CERAMIC SUBSTRATE URE 83.10(a)Display fonts used in LED displays.( b) Construction features of a hermetic LED display.( Source: S iage et al, Optoelectronics/Fiber-Optics Applications ManuaL, 2nd ed, New York: Hewlett-Packard/McGraw-Hill, 1981, Pp 5.3, 5.6. with permission. display is adequate for hexadecimal applications, but the 16-segment is required for alphanumerics. To limit pin-out requirements, the LEDs of a single package are connected in either the common anode or commor cathode configuration Fig 83. 11(a)), with multiple display digits multiplexed as illustrated in Fig. 83. 11(b) e 2000 by CRC Press LLC
© 2000 by CRC Press LLC display is adequate for hexadecimal applications, but the 16-segment is required for alphanumerics. To limit pin-out requirements, the LEDs of a single package are connected in either the common anode or common cathode configuration [Fig. 83.11(a)], with multiple display digits multiplexed as illustrated in Fig. 83.11(b). FIGURE 83.9 Matrix displays. (a) One LED will be turned on by applying the proper signal to one x axis and one y axis. (b) Character generation using column strobe methods. (Source: S. Gage et al., Optoelectronics/Fiber-Optics Applications Manual, 2nd ed., New York: Hewlett-Packard/McGraw-Hill, 1981, pp. 2.25, 5.44. With permission.) FIGURE 83.10 (a) Display fonts used in LED displays. (b) Construction features of a hermetic LED display. (Source: S. Gage et al., Optoelectronics/Fiber-Optics Applications Manual, 2nd ed., New York: Hewlett-Packard/McGraw-Hill, 1981, pp. 5.3, 5.6. With permission.)
回回回回 MULTI PLEXINO FIGURE 83.11 (a)generalized drive circuits for strobed operation. ( b)Block diagram of a strobed (multiplexed) six-digit LED display. (Source: S. Gage et al, Optoelectronics/Fiber-Optics Applications Manual, 2nd ed, New York: Hewlett-Pack ard/McGraw-Hill, 1981, Pp 5.25, 5. 23. with permis Defining Terms External quantum efficiency: The proportion of the photons emitted from the pn junction that escape the device structure(but sometimes alternatively defined as nine) Injection electroluminescence: Electroluminescence is the general term for optical emission resulting from the passage of electric current; injection electroluminescence refers to the case where the mechanism involves the injection of carriers across a pn junction Internal quantum efficiency: The product of injection efficiency and radiative efficiency corresponds to the ratio of power radiated from the junction to electrical power supplied. Related Topic 22 1 Physical Properties References J. Allison, Electronic Engineering Semiconductors and Devices, 2nd ed, London: McGraw-Hill, 1990 M. Forbes and B. B Brey, Digital Electronics, Indianapolis: Bobbs-Merrill, 1990. S. Gage, D. Evans, M. Hodapp, H. Sorensen,R Jamison, and R. Krause, Optoelectronics/Fiber-Optics Applications Manual, 2nd ed. New York: Hewlett-Packard/McGraw-Hill, 1981 D Jiles, Introduction to the Electronic Properties of Materials, London: Chapman Hall,1994 S. Nakamura, " A bright future for blue/green LEDs, " IEEE Circuits Devices, 11(3),19-23, 1995 D. A. Neamen, Semiconductor Physics and Devices: Basic Principles, Boston: Irwin, 1992 R. E Pierret, Semiconductor Device Fundamentals, New York: Addison-Wesley, 1996. S. M. Sze, Semiconductor Devices: Physics and Technology, New York: Wiley, 1985 S. Wang, Fundamentals of Semiconductor Theory and Device Physics, Englewood Cliffs, N J. Prentice-Hall, 1989 E S. Yang, Microelectronic Devices, New York: McGraw-Hill, 1988 e 2000 by CRC Press LLC
© 2000 by CRC Press LLC Defining Terms External quantum efficiency: The proportion of the photons emitted from the pn junction that escape the device structure (but sometimes alternatively defined as hi he). Injection electroluminescence: Electroluminescence is the general term for optical emission resulting from the passage of electric current; injection electroluminescence refers to the case where the mechanism involves the injection of carriers across a pn junction. Internal quantum efficiency: The product of injection efficiency and radiative efficiency corresponds to the ratio of power radiated from the junction to electrical power supplied. Related Topic 22.1 Physical Properties References J. Allison, Electronic Engineering Semiconductors and Devices, 2nd ed., London: McGraw-Hill, 1990. M. Forbes and B. B. Brey, Digital Electronics, Indianapolis: Bobbs-Merrill, 1990. S. Gage, D. Evans, M. Hodapp, H. Sorensen, R. Jamison, and R. Krause, Optoelectronics/Fiber-Optics Applications Manual, 2nd ed., New York: Hewlett-Packard/McGraw-Hill, 1981. D. Jiles, Introduction to the Electronic Properties of Materials, London: Chapman & Hall, 1994. S. Nakamura, “A bright future for blue/green LEDs,” IEEE Circuits & Devices, 11(3), 19–23, 1995. D. A. Neamen, Semiconductor Physics and Devices: Basic Principles, Boston: Irwin, 1992. R. F. Pierret, Semiconductor Device Fundamentals, New York: Addison-Wesley, 1996. S. M. Sze, Semiconductor Devices: Physics and Technology, New York: Wiley, 1985. S. Wang, Fundamentals of Semiconductor Theory and Device Physics, Englewood Cliffs, N.J.: Prentice-Hall, 1989. E. S. Yang, Microelectronic Devices, New York: McGraw-Hill, 1988. FIGURE 83.11 (a) Generalized drive circuits for strobed operation. (b) Block diagram of a strobed (multiplexed) six-digit LED display. (Source: S. Gage et al., Optoelectronics/Fiber-Optics Applications Manual, 2nd ed., New York: Hewlett-Packard/McGraw-Hill, 1981, pp. 5.25, 5.23. With permission.)
