1、I 3 - EIA TEB24 BL 3234600 0007LO O m /- -7 NOVEMBER 1981 EIA ENGINEERING BULLETIN No. TEB24 * THE EFFECT OF PULSE SHAPE IN RASTER DOT ALPHA-NUMERIC CRT PRESENTATIONS ON SPOT LUMINANCE AND LUMINANCE DISTRIBUTION FORMULATED BY EIA/TUBE ENGINEERING PANEL ADVISORY COUNCIL Published by ELECTRONIC INDUCT
2、RIES ASSOCIATION Engineering Department 2001 Eye Street, N.W. Washington, D.C. 20006 Printed in U.S.A. EIA TEB24 81 W 3234600 0007192 4 , E- -1 TEPAC ENGINEERING BULLETIN No. 24 CRT APPLICATION AND REFERENCE NOTES THE EFFECT OF PULSE SHAPE IN RASTER DOT ALPHA-NUMERIC CRT PRESENTATIONS ON SPOT LUMINA
3、NCE AND LUMINANCE DISTRIBUTION Prepared by Frederick G. Oecs Member, TEPAC JT-20 Committee on Opto Electronic Devices -1- EIA TEB24 82 W 3234600 0007293 b 4 - O TEPAC Engineering Bulletin No. 24 Page 1 THE EFFECT OF PULSE SHAPEIN RASTER DOT ALPHA-NUMERIC CRT PRESENTATIONS ON SPOT LUMINANCE AND LUMIN
4、ANCE DISTRIBUTION TABLE OF CONTENTS Section Paqe A. B. C. D. E. F. G. H, PURPOSE 2 PRELIMINARY NOTES, EQUATIONS AND ASSUMPTIONS 3 THEORETICAL DISCUSSION 6 NUMERICAL ANALYSIS OF A TRIANGULAR PULSE 10 COMPARISON OF THE EFFECTS ON THE SPOT DISTRIBUTION 18 IN RECTANGULAR AND TRIANGULAR PULSING PULSES OF
5、 ARBITRARY FORM 21 CONCLUSIONS 22 REFERENCES 23 ,- e I EIA TEB24 A3 3234600 0007394 A - A. PURPOSE e These notes provide means of analyzing the effect of pulse shape on the written spot configuration and its relative brightness in raster-dot displays. The observ- ations noted and the application of
6、the methods described will provide the equipment designer with better insight into pulse shape limitations, observed spot size, spot shapes and their luminance distributions as well as variations resulting from changes in the applied drive- voltage levels in a particular tube design. The subject dis
7、cussed is becoming increasingly important due to the demands for higher resol ution and increased writing speeds. It will be shown that after the luminance and line width characteristics of a given CRT design in terms of the drive voltage have been established, the spot shape and its luminance distr
8、ibution can be synthesized for any pulse shape at a given set of operating conditions. e EIA TEB24 81 9 3234600 0007195 T ! - B. PRELIMINARY NOTES, EQUATIONS AND ASSUMPTIONS It has previously been demonstrated (Ref 1) that if ideal rectangular drive pulses are applied the highlight luminance of a wr
9、itten spot can only approach, that of a written line (in a given tube under identical operating conditions) if spot roundness is sacrificed. Under con- ditions of constant writing speed., complete spot round- ness is theoretically only possible with an infinitesimal pulse width which would reduce th
10、e highlight luminance essenti al ly to zero. Reference 1 suggested a compromi se pulse equivalent of a 2.5 width of the written line at the same drive level. It was shown that this would reduce the highlight luminance by about 20% and provide a reason- ably round written spot under conditions of pro
11、per spot separation. In generals pulses used in raster dot writing are not rectangular and as a result more sophisticated analytical approaches become necessary. The following material will first treat the theoretical equations applicable to arb- itrary pulse shapes for isolated spots. A triangular
12、pulse shape will then be used to illustrate the method suggested and to provide performance comparisons between rectangular and triangular pulse shapes. To simplify the discussiondhe following assumptions and conditions are made: 1. The spatial beam current density distribution at the screen is a So
13、lid Gaussian Distribution. 2. There is little or no phosphor saturation. 3. The luminance response to beam current density is assumed to be instantaneous rather than possessing finite rise and decay times. This assumption does not affect the validity of the analysis. -3- I- 7 - 4. 5. 6. 7. 8. 9. 10.
14、 11. EIA TEB24 BL 3234b00 0007196 1 I The tem “instantaneous luminance values“ as used in these notes designates the integrated instantaneous luminance values at the given repetition rate and writing speed and for the drive level and location relative to the beam center applying at that instant. Val
15、ues used may be expressed relative to the time or the spacial domain. Variations due to phosphor or glass surface granularities are ignored. The spot motion is horizontal at a constant writing speed. The CT val ues given are those associated with the perpendicular luminance cross-section of a fully
16、written line at a given drive level. The os val ues are normal i zed val ues corresponding to the perpendicular luminance cross-section of a fully written line at the maximum drive level used in the applied pulse. Undeflected spot grid cut-off reference is used. Deflection defocusing phenomenon are
17、neglected. The analysis applies to the center of the tube face. . Because of its basic importance to this subject. the maximum or highlight luminance across a single, well separated CRT line as given in Reference 1 is repeated here: fi (I-=-) N PoEkTs S .67726 r N= Jir LH = p E Tos - 1)- ovs s (e-)
18、where : is the highlight luminance in F1. is the maximum beam current density within the beam in A/cm2. screen voltage relative to the cathode minus the screen breakthrough vol tage). T _-, is the transmission of the glass faceplate as a decimal fraction. LH - Po - E _ is the effective view screen v
19、oltage in Volts (actual view vc - is the phosphor screen ef fi ci ency in Fi /Watt/cm2. 1, s - is the writing speed in inches/sec. r (e-9 - is the spot radius at the e- level of the Gaussian in un. is the shrinking raster spot radius in cm. 1 -e- 1 N- i s the repetition rate in Hz. n the same for al
20、l consistent dimensional Equation 1 will yema systems. O -4- EIA TEB24 81 3234600 0007397. 3 1 The minimum pulse width necessary to duplicate the full lum- inance of the written line using a rectangular pulse is 60 (Ref. In the time domain, this value is given by: = (3.132 d/S) sec T1 I Y ss -I O P
21、IL W 2 10- . - n I -1.0 -0.5 0.0 . 0.5 - 1.0 1.5 c *o -1.5 # A X- SCALAR VALUES - os A V. HEASURED FROM SPOT CUT-OFF-(Vcs) A SCALAR VALUES IN TERMS OF THE YIDTH OF A FULLY URITTEN LINE A7 V, 30 V O FIGURE 3: TRIANGULAR PULSE SHAPE TO BE APPLIED TO TUBE TYPE CE727M12P4 - lO-r“ EIA TEB24 81 m 3234600
22、0007203 5 m I The first step involves the adjustment of the focus voltage to the maximum grid drive voltage called for by the pulse in Figure 3. The resultant value will then become the standard for all sub- sequent measurements in the analysis. If the system in which the tube is to be used has some
23、 dynamic means of focus adjustment for drive conditions, then these should be, set for the drive range of the pulse. In step 2 the SRM line width and highlight luminance are evaluated using a full width 252 line 60 Hz raster with retrace blanking. The results are then plotted and an average curve is
24、 drawn through both sets of data as shown in Figures 4 and 5. It will be noted that deviations from the average line are relatively small. -11- f 7 100 EIA TEB24 Bl m 3234600 0007204 7 = 80 x. W. 40 a Y O 5 - 10 15 20 25 30 32.5 DRIVE VOLTAGE (V,) -32.5 (VOLTS) FIGURE 5: DRIVE VOLTAGE VS HIGHLIGHT L
25、UMINANCE Step 3 requires the listing of the drive voltage (V,), values of line width (SRM,) and highlight luminance (L, d the average ) of the written line at a reasonable interval of x in os units of the line width corresponding to the maximum drive level of the pulse. This is shown in Table 2. Sin
26、ce relative values are used, SRM values need not first be transposed to o levels. The intervals are chosen to provide an adequate number of points to permit reason- ably accurate numerical integration at later stages of the pro- cedure by either the Trapezoidal or the Simpson rule. In the example gi
27、ven Ax=2.50aS/30= .O8330 was the interval chosen. - 12- EIA TEB24 BL m 3234600 0007205 9 m I) 1 (os) 9 .- VD(V0LT) o 2 4 6 8 io 12 14 16 18 20 22 24 26 ze 30 SRHa(HIL) 2.95 3.15 3.35 3.55 3.80 4.00 4.20 4.40 4d62 4.88 5.22 5.42 5.72 6.10 6.50 7.00 1, (FL) 0.0 0.0 0.0 0.0 0.0 0.15 1.0 3.1 7.0 1225 19
28、.5 29.5 40.0 51.5 63.0 74.5 L TABLE 2: CORRESPONDING .V,ALUES OF DRIVE SPOT SIZE AND HIGHLIGHT LUMINANCE AS A FUNCTIONOF x OBTAINED FROM THE GRAPHS OF FIGURES 3,4 AND 5 The conversion of absolute to equalized values of line width (U,) by means of Equation 8, the normalization of highlight luminance
29、amplitude .(K,) arrived at by Equation 7 and values for -.5U2 are shown in Table 3, (Step 4) I 1 (OS) a 1-25 I 1-17 I 1-08 I 1.00 I -917 1 -833 1.750 i .667 I .583 t .m I -417 1 -333 1 -250 I -167 1.083 I ,000 -. 2.37 2.22 2.09 1.97 1.84 1.75 1.67 1.59 1.52 1.43 j;M 1.29 1.22 1.16 1.08 1.00 .suaa 2.
30、82 2.47 2.18 1.94 1.70 1*53 1.39 1.27 1.15 1.03 0.90 0,a3 0.75 0.66 0.58 0.50 TABLE 3: VALUES FOR THE CALCULATION OF THE RELATIVE AMPLITUDE u, 0.00 0.00 0.00 0.00 0.00 0.00 0.O1 0.04 0.09 0.16 0.26 0.39 0.53 0.69 0.84 1.00 i DISTRIBUTION OBTAINED BY EQUATIONS 6 AND 7 AND TABLE 2 The evaluation of th
31、e spot profile along the beam center fine or X-axis is executed in step 5. For this purpose Equations 4 and 6 simplify to: 4 a 2 a(x,y=)= K, exp (-.SU, xr for the instantaneous amplitude at any point on the X-axis for the integrated amplitde at any point on the X-axis. Table 4 provides a systematic
32、method for accomplishing the eval- uatlon. The central matrix shows both the calculated “xrt values and the. “a values. Beam center positions below -1.000 have been omitted since the values for “a“ at these locations are zero. O EIA TEB24 A1 m 3234b00 0007206 O m . a e !I + 8 ci1 - N ? y!. $+ no 19
33、P CI :I I y u: I-: ?Y 44 bOO 0007207 2 9 . . l I I -1 8 9 In m 9 O ? z 9 8 9 - m Pl 3 a 8 I I I EIA TEB2i.I 83 = 323i.IbOO 0007208 i.I The upper values in the central matrix are the distances from the center of the Snstantaneous distrlbution to the point of integration “xrl and are obtained from Equ
34、ation 5 (x,=x -x). The lower values represent the relative instantaneous Gaussian amp1 itudes “a“ derived from Equation 4a. P It is of interest to note that the amplitude values in the columns of the central matrix represent portions of instantaneous Gaussions each with different Kx and U, values. S
35、ince the function on the two sides of the pulse centerline are mirror images, only the negative half of the pulse is given. The numerical integration was performed us.ing the Trapezoidal rule. The results are plotted in Figure 6. RELATIVE LUHINANCE t LEVELS t. .I 3 2 1 O 3 2 1 O 1 CRCSS-SECTION Y CR
36、OSS SCTION X OR V- os VALUS X DIRECTION- as VALES i) LUHINANCE PLOT 6) LUHINANCE CONTOUR PLOT (WLF-SECTIONS) . (PURTER-SECTION) FIGURE 6: NORMALIZED SPOT SHAPE FOR A TRIANGULAR PULSE AT 2.50, PULSE WIDTH FOR TUBE TYPE CE727M12P4 The ampljtude distribution in the y-direction of the pulse center is ar
37、rived at in a similar manner. For this case Equation 6 remains unaltered. However, since x is zero for all conditions, x =xr. The integrated y values are given in Table 5 and the distribution is plotted in Figure 6. P EIA TE824 81 m 3234600 0007209 6 m 1 An examination of Figure 6 shows that the spo
38、tis essential13 round except for some minor devitions in the central amplitude range where a slight elongation in the x-direition. exists. The maximum. amplitude *of the pulse is however only about 22% of that of a* fully written line at the maximum drive of the pulse or about 28% of a rectangular p
39、ulse of identical width. As- can-beappreciated from the massive calcu3ations shown., the.,uce of a computer is vital in obtaining al full so1utionq:for non-reet- angular pulses in a reasonable time frame particularly if off-axis . ,. points are to be included in the evaluation. r*. c A ;y=- 1 - 17-
40、7 EIA TEB2V 81 m 3234600 0007210 2 m * ,. - E. COMPARISON OF THE EFFECTS ON.THE SPOT DISTRIBUTION IN RECTANGULAR AND TRIANGULAR PULSING In the last chapter it was already indicated that in com- paring rectangular with triangular pulses of identical width and maximum amplitudes, the highlight luminan
41、ce of . the latter will be very significantly lower. If the drive at maximum instantaneous highl ight 1 uminance is al ready adjusted (as it should be) to the optimum cathode loading level, then the only means available to increase luminance short .of changing the view screen voltage rests in increa
42、s- ing the pulse width.* The effect of increased pulse width can be observed in Figure 7, In comparing the curves with corresponding values-of the pulse width shown in Figure 8 the following becomes apparent: 1, . The highlight luminance of the rectangular pulse or the fully written line can never b
43、e approached using a triangular pulse. 2. The pulse shape ovality deteriorates much more rap-. idly for triangular pulses with increasing highl ight . 1 uminances. 3. At the 1.80 half-pulse width of a triangular pulse spot roundness is reasonable and comparable to that of a rectangular pulse at 1.25
44、0 half-pulse width; however, the comparable highlight -luminance is still only at 38% of the rectangular pulse. *Some questions exist as to whether it may be possible to increase cathode. loading and therefore drive in the triangular case since the duty cyle at high drive level is significantly lowe
45、red. If this is done the instantaneous spot size growth at increased drive would however produce a deterioration in the integrated luminance distribution of the written spot. e EIA TEB2Y 81 323Yb00 00072LL Y 1 lkG NO RMA .- TRIANGULAR PULSE. AT VARIOUS PULSE WIDTHS _- 5PO.T- SHAPE _- OF - - A _- 5-
46、_. . .: , . .I -_ 1- . - . :. A. . x - VVALInS . ,- . b) CROSS-SCCT1OM a) X CSS-SECTIONS .a . HALF SECTIOHS) (HALF SECTIQIU) I. I- .! PULS E WIDTHS - 19 - - Y- 3 EIA TEB24 83 m 3234600 0007232 6 J - Under assumed conditions of a Gaussian beam distribution it is of interest to note that the cross-bea
47、m sections using a rectang- ular pulse remain Gaussian while those of other pulse shapes dev- iate from this condition. .This can be readily understood by an examination of Equations 4 and 6. Sin-ce the so called “roll-off constant“ (.uX) is a ccnstant in rectangular puises for ail cross-beam sectio
48、ns of the instantaneous luminance distribution, the summation of such distributions must also be Gsussian. With non-rectangular pulses the value of U, is variable and therefore the summation cannot be Gaussian. The relatively smaller deviation of spot roundness of triangular pulses at low width and
49、the low integrated highlight luminances are due mainly to the shape of the volltage drive characteristic relative to beam current which is roughly a 7/2 power exponential. The other factor which tends to emphasize this is due to the fact that the cutoff reference is taken from the undeflected spot level and therefore a drive of about 10 volts is required to obtain measurable raster 1 uminance values. e The long tails obtained by increasing the pulse width of triangular puls
