1、L .I I. 1 EIA TE821 79 3234b00 0007121 3 9 -i APRIL 1979 TEPAC ENGINEERING BULLETIN N.O. 21 CRT CONSIDERATIONS FOR RASTER DOT ALPHA NUMERIC PRESENTAT IONS .- FORMULATED BY IA TUBE ENGINEERING PANEL ADVISORY COUNCIL f I EIA TEB23 79 3234600 0007322 5 s * NOTICE EIA Engineering Standards and Publicati
2、ons are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating intecchangeabili ty and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need
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4、e other than EIA members, whether the standard is to be used either domestically or internationally. Recommended Standards and Publications are adopted by EIA without regard to whether or not their adoption may involve patents on articles, materials, or processes. By such action, EIA does not assume
5、 any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Recom- mended Standard or Publication. Published by ELECTRONIC INDUSTRIES ASSOCIATION Engineering Department 2001 Eye Street, N,W. Washington, D.C. 20006 Published in U.S.A. EIA TEB23 79 3234600 00
6、07323 7 = d TEPAC ENGINEERING BULLETIN NO21 CRT CONSIDERATIONS FOR RASTER DOT ALPHA NUMERIC PRESENTATIONS FREDERICK G. OESS Member, TEPAC JT-20 Committee -1- CRT CONSIDERATIONS FOR RASTER DOT ALPHA NUMERIC PR ES EN TAT I ON S Frederick G. Oess, Dir. of Display Tube Engineering C1 inton Electronics C
7、orporation, Rockford, Ill. . ABSTRACT The purpose of this article is to describe some of the major CRT para- meters and haw they relate to each other, as well as the data presentation method provided by Clinton Electronics Corporations tube data sheets. The stress is on optimization of raster-dot, a
8、lpha-numeric displays, based on tubes using unipotential focus lenses and magnetic deflection. PREi IMINARY NOTES 0 I. The general forms of CRT data sheets, as they have evolved over the years:, provide the monitor designer with very useful information on mechanical dimensions of the tube, maximum e
9、lectrical operating levels for the various electrodes .inter-electrode capacitance values , etc. Their shortcoming, however, lles in the failure to describe more fully the total operating conditions in terk of spot Size and light output over the useful operating range of the tube. What is kffered, a
10、t best, is a typical set of operating conditions at some single fixed Grid #2 voltage (VG2) and final anode voltage (ivs). Under given conditions of writing speed, repetition rate and drive, the tube is specified to provide a certain minimum value of integrated raster luminance at a given maximum li
11、ne width, usually measured in terms of EIA TEB23 79 3234600 0007325 O F shrinkfng. raster values. by most monitor designers: without any attempt to optimize the tube performance in terms of the desired dis p? ay. great deal of performance varfation from unit to unit due to the normally expected cuto
12、ff variations from tube to tube. The design of systems on the basis of a few sampie tubes from a single tube run, and the resulting bitter disappointment in the operating parameters when the full range of tube variabi 1 i ty is experienced during subsequent production, additional Information from th
13、e tube designer. This has resulted in the following types of actions 1. Straightforward use of the stated “typical“ operating conditions 2. The blind acceptance of a fixed Grid #2 voltage, and thereby a 3, 4. A conscientious effort, at some design-time expense, to obtain Further difficulties arise w
14、hen such specifications are copied and subsequently cent out for quotation by other tube manufacturers. *. It should be noted that it is quite possible to develop a great number of tube designs which will meet such a speeification at the given “typical“ operating cnditions, but all of these designs
15、will deviate considerably hm the original tube (and each other) once thes.e “typical“ conditions are changed, If an, identical tubenerally grown out of the less expensive standard manochrome TV tubes and associated circuit technology. for improved performance have forced a considerable degree of ,.
16、sophi stication, In recent years, however, demands applying increased pressure on both circuit and tube designers. Since today monitors of the raster-dat type represent, by far, the largest share of the market for dsplay CRTs, the need for better engineering communications between tube and monitor d
17、esigner is essential. The establishment of a meantngful specification fovmat is one form such communication can -take. - ., II . . y-= - * The other important factor irvolves co.nveyance by the tube designer of come very basic information about tube operating theory. THEORETICAL AND DESIGN CONSIDERA
18、TIONS This article will explain the advantage of a means of describing the operating parameters of any common type of CRT, in terms of its most basic form. parameters relationships, thereby providing a clearer understanding of what can be done to maximize tube performance. and brevlty, the discussio
19、n will be mainly based on tubes using gun designs with a preaccelerator or buffer anode (GZ), a unipotential and no limiting apertures. cribed are generally applicable to magnetic and electro-static deflection tubes, using either unipotential , bipotential or magietic. focus, with or without limitin
20、g apertures. Figure 1 shows .a schematic of a gun with typical electrode voltage ranges. The general form of the electron beam is indicated in Figure 2. Also noted are the parameters which shall subsequently be referred to. In the latter figure the radial dimensions are greatly exag- gerated to bett
21、er illustrate the relationships involved. Furthermore, the writer wi 11 attempt to clarify some fundamental tube For the sake of clarity foc.using lens However, the methods ”. of data presentation dec- -. . e To simplify the theoretical discussion, this analysis of CRTs uses the cathode as the refer
22、ence. potential. source of electrons whjck form a space charge cloud in front of the emitter surface. The emitted electrons have Maxwellian thermal velocity distributions in both axial and radial directions. These distributions limit the attainable spot size in any CRT. penetration of Grid #Z (62).
23、into the cathode space, thereby permitting the amount of current drawn from the space.charge cloud to be controlled. The combination of the aforegoing elements consti tutes the triode generator, or simply the triode. on the G1 necessary to provide viiual extinction of the undeflected spot is called
24、the spot cutoff. be readily calculated from one of the following formulae: The cathode (K) provides a continuous The purpose of Grid #i (Gl) is to constrict the field For a given 62 voltage (VG2), the negative voltage In any CRT, the optimum cathode current, IC, can Figure 1 EIA TEE21 79 = 3234600 0
25、007327 4 -4- DEFLECTXON YOKE CRT Scheinatic . . .I . SCHEMATIC OF ELECTRON RAY DIVERGING FROM THE CENTER OF THE CRnSSOVER. (TOP) (Equivalent th-in lenses assumed. Ray : distortion in focus region omitted fur C?ari.ty.) SCHEMATTC OF BEAM ENVELOPE. (6OT.TOM) ELECTRON VE LO CI T Y A TRIODE AREA LOK 1 C
26、ATHODE B CRIO 2 DRIFT SPACE INCREASED 2 CkOSSOVER : :3 G2-GJ LENS C GRID 5 DRIFT SPACE HIGH D FOCUS AREA LOWER 4 . FOCUS LEkS E ANODE DRIFT SPACE HIGH 5 OEFL. CEkTER F DEFLECTION REGION .HIGH G ANODE ,DRIFT, SPACE HIGH , , D.ES C R r P T I 0.N STAT1 ON DESCRI P.T.I.0 N SECTOR VIEW SCREEN 6 Figure 2
27、Electron Beam C e EIA TEB21 79 m 3234b00 0007128 b m -5- 3.0 -1.5 IC = KV, Vc 3 5 -2.0 IC KVD Vc W I U Y r O O I I- a z= W z -I Y Y 17 15 13 11 9 7 -35 - 17 - LINE WIDTH VS. CUT-OFF VOLTAGE AT CONSTANT CATHSDE CURRENT“ (SHRINKING RASTER METHOD) -45 - 55 -65 -75 Vc VOLTS (RASTER CUT-OFF) - 95 .a5 Fig
28、ure 7 HIGHLIGHT LUWINANCE VS. CUT-OFF VOLTAGE AT CONSTANT CATHODE CURRENT* ( S H R I M K I N G RAST E R EIETH OD ) -35 mure 8 - -45 -55 -65 -75 -85 V, VOLTS (RASTER CUT-OFF) -q -95 S EIA TEBZL 79 m 3234600 0007l141 9 m 2 4 - 18 - .- Radical divergence from theoretically. expected trends are generall
29、y due to excessive aberration in the various lens or deflection systems, saturation effects or, in rare cases, space charge repulsion within the beam. The latter defect is not normally a factor unless tubes are operated well outside of their intended design ranges. minimal over the recommended opera
30、ting conditions. Lens aberration on well designed tubes are also PERFORMANCE CHARACTERI ST ICs 1 The graphs of Figures 7 and 8 represent typical experimental data for the type of design under discussion. Physically, the particular characteristics are those of a 12” diagonal, 900 deflection, small ne
31、ck diameter (2mm) tube. It was not selected for the qual ty of its operating characteristics. Measurements on several hundred different tube types have been performed, uti1 izing many different designs. though line width, light output values and their rates of change with cutoff may show appreciable
32、 differences. The general forms of the curves do not vary greatly, even The resolution and light output measurements are based on the Shrinking Raster Method (SRM). This technique represents the simplest, most practical and most widely acc pted means of taking extensive data of the type required for
33、 this task. is the, 1-e- or 63% level. SRM line width can be translated to width at the e-l level by multip ying by 1.477. The l-ight output measurements obtained are proportional to the highlight luminance of the written line. The Gaussian amplitude at the point of line width measurement The indivi
34、dual data points Sn Figures 7 and 8 are actual measured values. Data deviations from the Smooth curves have been drawn through these points. averaged curves tend to provide confidence in the reliability of the measurements. Some reasons for the manner in which measurements are normally made and Sinc
35、e prime interest is in the effects of parameter changes are noteworthy. comparison of various tubes, the following general testing rules are followed: 1) To eliminate yoke variables, all. measurements are made at the -5 - . 5) EIA TEB2L 79 m 3234b00 0007342 O m - 19 - center of the tube. Deflection
36、defocusing is evaluated by another test, using high quality yokes and deflection systems and noting the difference between center and edge focus voltages. The width of the raster is held, as closely as possible, to the design width of the raster for the particular tube. The drive is D.C. voltage wit
37、h retrace blanking. A standardized video ras ter i s appl i ed wi thout i nterl ace i n order to avoid flicker problems since tubes with diverse types of phosphors aFe measured. Except for saturation effects, changes in repetition rates at. a constant writing speed cause proportional changes in high
38、l ight luminance with negligible effect on line width. from a noninterlaced to an- interlaced raster (i.e. from 60 to 30Hz) doubles the number of 1 ines and decreases 1 ine highl ight luminance by about 50%. remains of course constant. linearly related to line highlight luminance and method of data
39、adjustments are obvious. In writing dots the square-wave pulse-width requires careful balancing by design and adjustment to avoid highlight luminance reduction at the low end or horizontal spot elongation at the other extreme. Spot size cannot be improved by pulse shortening below the point of full
40、spacial spot integration even at reduced luminance. tain highl ight luminance and therefore result inevitably in spot size increases. The View Screen Voltage is normally adjusted to the higher oper- ational values for the tube. Lower values will tend to slightly I affect spot size, deflection defocu
41、sing and the “highl ight“ beam Thus, going The large scale integrated raster light output Changes in writing speed are also Such procedure will call for drive increases to main- density at the screen in accordance with the trends previuosly descri bed. The bombardmert energy of el ectrons produces t
42、he expected linearly related change in highlight luminance if sat- uration effects are negligible. estimates of light output, the break-through voltage of about 2KV To obtain reasonably close EIA TEB2L 79 M 3234600 0007343 2 - 20 - must be taken into account. this amount from both EVS values and the
43、n applying the proportionality. Very close values for both highl ght luminance and resolution data at altered Evs conditions can be obtained by measuring a single point on an actual tube at the revised conditions and applying the pro- portional variations relative, to Figures 7 and 8 over the entire
44、 characteri s t i cs. 6) The cutoff data fori Figures 7 and 8 may be based either on raster cutoff or on undeflected spot cutoff. the former. abscissa would generally be 3 to 10 volts more negative with the precise value depending on raster operating conditions such as size, repetition rate and writ
45、ing speed and to a very minor extent, on the operating voltage of the tube. The advantage of raster cutoff rests mainly on the 1 esser 1 i kel i hood of screen damage by inexperienced operators. theoretical basis and a more direct means of utilizing the test data for diverse operating conditions. ev
46、ident 1) The level of highlight luminance is measured simultaneously with the shrunken raster width. When measuring highl ight luminance in this manner the resulting values must be reduced by 24% to obtain the corresponding levels for a single wjdely spaced line measured with a very narrow acceptanc
47、e angle spot photometer. This can be done by subtracting The examples given illustrate For spot cutoff the corresponding points on the Undeflected spot cutoff provides a somewhat better Means of conversion are self For practical purposes, changes in the type of phosphor used will have minor impact o
48、n the ljne width curves. Unless saturation effects become dom- inant, the graphs of highlight luminance will change by a constant which is dependent on the luminous efficiencies OP the phosphors compared. Again, the breakthrough voltage corrections need to be applied, unless the phosphor data is giv
49、en for aluminized screens. In evaluating tubes of the same design, operating at constant VG2, their i- -2 EIA TEB23 i9 3234600 0007344 4 = - 21 - corresponding 1 ine widths and highl ight luminances can be read directly from their raster cutoff values. For the characteristics illustrated in Figures7 and 8, a tube having a -35 volt raster cutoff would possess a. line width of approximately .Oll“ at 50pa beam current. or 16 volts. Another tube operating at -75 volts cutoff and the same beam current would exhibit a spot size of ,0078 at a drive of 20 v
