US2274366A

US2274366A - Television scanning

Info

Publication number: US2274366A
Application number: US259194A
Authority: US
Inventors: Hansen Siegfried
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1939-03-01
Filing date: 1939-03-01
Publication date: 1942-02-24
Anticipated expiration: 1959-02-24
Also published as: FR863581A; BE438172A

Description

S. HANSEN TELEVISION SCANNING 74W 7007 GEIYE/FdTfl/l Hg. 2. A B

HR. Z m M M6 L/IVE FREQUENCY 204 Irwvento 1":

fried Hansen JV Sieg PUL SE GENERATOR Aug o SUPERSYNCHRON/ZING MFL IFIER DEO MPLIFIER GENERATOR AMPLITUDE.

SAW TOOTH GENERATOR DETECTOR A DE TECTQR A Ll/VE FREQUENCY 2/6 SOUND u. AMPLIFIER v/nso I.F.

nPuF/ER SEPARATUR MASTER V OSCILLATOR CONVERTER OSCILLATOR TIME.

Patented Feb. 24, 1942 TELEVISION SCANNING Siegfried Hansen, Schenectady, N. Y., assigno'r to General Electric Company, a corporation of New York 7 Application March 1, 1939, Serial No. 2 59,194

14 Claims.

My invention relates to the art of television and particularly to the scanning of the screen of a cathode ray tube employed therein.

A television system well known at the present time employs double interlaced scanning and has a frame frequency of 30 per second. Such a frame frequency is much higher than is necessary to preserve continuity of motion in the reproduced picture, hence the system is wasteful of band width. Efforts have been made in the past'to reduce the frame frequency, namely, the number of pictures per second, without introducing flicker or impairing continuity of the re- Q improved method of scanning in a cathode ray Because of the great difficulty, if not the impossibility of constructing a patent drawing with which one could trace the movements of the beam in a cathode ray tube in scanning a frame or picture comprising several hundred lines, .I have chosen to describe my invention first as applied to an extremely simple form embodying only a few lines which are widely spaced apart. Having explained the principle by means of this simple example its application to a commercial form will be readily apparent.

As is well known to those skilled in the art the electron beam of a cathode ray television tube is made to scan the tube screen or' target whether the tube is of the transmitting type or the receiving type by causing the beam to move simultaneously in two directions substantially at right tube and an improved apparatus for carrying out that method whereby the excessive band width may be materially reduced without the addition of an objectionable amount of crawl.

In accordance with my invention, I move-the electron beam of the cathode ray tube or tubes in a television system in a manner-to cause the beam to scan the screen thereof'succes'sively in a plurality of spaced parallel lines and thereafter to scan the screen intermediate said lines in a plurality of interlaced lines. As a result I have found that the frame frequency may be greatly reduced without producing an objectionable flicker or lack of continuity of motion. The reduction of the frame frequency permits a corresponding reduction in the band width of frequenciesrequired for the transmission of the picture.

Because of the interlaced interlace scannin which I employ the amount of crawl produced I is not objectionable.

My invention will be better understood from the. following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram illustrating by way of example, one form angles to each other, one being in the direction of the scanning lines, usually horizontal, and the other substantially at right angles thereto, hence, usually vertical. In accordance with one form of my invention, I cause the beam first to scan successively every fifth line, that is, it successively

scans lines

1, 6, 11, 16, etc. to the end of the picture and then to scan the intermediate lines in an interlaced manner. This system of scanning I have termed, interlaced quintuple interlace.

' This may be more readily understood by referring to Fig. 2A where the

scanning lines

1, 6, 11 and 16 are shown by a full black line, the horizontal fly backs being shown bylighter full lines. Since

lines

1, 6, 11 and 16 divide the total scanning lines into groups of five it is convenient to consider every fifth line as having the same number, such being shown in Fig. 2A by the second column of numbers. In this figure it will be seen that the number of lines called 1, shown by a solid line, is 3%, the first line 1, beginning at the point 1 and the last lin 1 terminating at the point 2, its length being /5 the length of a full line. Vertical fly back then occurs taking the line to the point 3 at the top of the picture where a new line starts which is line 3, represented by dashes. The last portion of line 3 terminates at the point 4 whence fiy back takes it to the point 5 at the top of the picture. Line 5 represented by a dash and two dots, now begins, terminating at the point 6. Fly back carries the line to the point 7 where line 2, represented by dots, begins. Line 2 terminates at 8, fly back carries it to 9 where line 4, represented by a dot and a dash, begins, .Line 4 terminates at 10. At this point the scanning is complete and the line returns to the starting point 1. Thus the picture crawl.

' the present-standard number of lines.

is scanned with a quintuple scanning and the lines comprising each group of flve are scanned with an interlaced scanning, hence I have applied the term interlaced quintuple interlace.

The advantage of the above-described system of interlacing is that the number of frames or pictures per second may be very materially reduced without sacrificing continuity of motion or producing flicker and without objectionable I have found, for example, that whereas the number of frames or pictures per'second common heretofore has been 30, by employing my invention, I can reduce that number by the factor, 2.5, namely, to 12 frames per second and still obtain equally good results. The important result of such a material reduction in the frame frequency required is that it obviously permits a the horizontal and the vertical deflections of the ter oscillator 25 which, in the form of my invencorresponding reduction in the band width of tain the 4 megacycle band width but increase the number of lines.

The interlaced quintuple interlace system of scanning which I employ is obtained by supplying the proper frequencies to-the beam deflecting means of a cathode ray tube of a well known form employed in television. In the case of the simplified form illustrated by Fig. 2A where the picture comprises only 18 lines, the lineor horizontal frequency may be 2l6-cyclesper second and the field or vertical frequency may be 60 cycles per second. A 216 cycle frequency repre sented at 12 will therefore be applied to the horizontal deflecting means of the tube ,and a 60 cycle frequency represented at 13 will be applied to the vertical deflecting means thereof. The combined effect of the two electric fields resulting from these two frequencies operating at right angles to each other is to cause the cathode beam to make a trace on the screen approximately of the form shown by Fig. 2A. For convenience in making the drawing I have not attempted to show the various lines, particularly the fly backs, exactly as they would actually appear since an approximate showing is ample. for the purpose of disclosing my invention. It will be noted that the ratio of the line frequency, 216 cycles, to the vertical frequency 60 cycles, is 3%, namely an integer plus This corresponds with the total numberof each of

lines

1, 2,. 3, 4 and 5 in Fig. 2A as pointed out above which was 3%. ,The number of complete pictures per second is equal to 60 divided by 5 namely 12, there being 5 fields "to each frame or picture.

, Having described th simplified form of my invention, I shall now re er to the more practicable form illustrated by Fig. 1 and applied to a system having 448 scanning lines, approximately In this figure the cathode ray tube I5 is shown as a tion represented by Fig. 1, produces a frequency of 26,880 cycles per second. This frequency is supplied to the'multivibrator 26 which, having a ratio of 5, reduces the frequency to 5376 cycles per second. It is also supplied to the chain of

multivibrators

21, 28 and 29 which, having ratios respectively of 8, 8 and 7, reduce the frequency respectively to 3360 cycles, 420 cycles and 60 cycles per second. The deflecting windings 20 and I9 are supplied with saw tooth waves havin frequencies respectively of 5376 cycles and 60 cycles per second from the

saw tooth generators

30 and 3| which may be of any common and well 7 known construction. The generator 30 is controlled in a well known manner by the 5376 cycle frequency supplied to it from the multivibrator 26 and likewise the generator 3| is controlled by the 60 cycle frequency supplied to it from the multivibrator 29. The ratio of the line -.freqiiency, 5376 cycles, to the vertical frequency, 60 cycles, in this case is 89%; thus, as in the previously described example, this ratio is an integer.

plus The frame frequency or number of complete pictures per second is equal to 60 di vided by 5, namely 12, rather than 30, the number common at present.

For radio transmission of the output of the cathodetray tube and the synchronizing signals I have shown the "radio transmitter 34 connected toreceivethe output of the tube l5 "and to receivethe output of the supersynchronizing pulse generator 35 which may be of any suitable and well known form, the generator being controlled by connections with the

multivibrators

26 and 29 whereby the line and framing synchronizing pulses may be transmitted to the receiver.

Referring back, to Fig. 2A it will be remembered that

lines

1, 2, 3, 4 and 5 ofeach group h were interlaced so that scanning took place in the

order

1, 3, 5, 2, 4, this, order being the result of there being 3% lines of each number or, what is'the same thing, of choosing a line frequency and a'vertical frequency having the ratio of 3 My invention is not limited to this particular form of interlacing of the lines in each group but applied equally well if they are interlaced such that scanning occurs in the

order

1, 4, 2, 5, 3. For that order of scanning there will be 3% lines of each number or, what is the same thing, the ratio of the line frequency to the vertical frequency will be 3%. Such an arrangement is represented by Fig. 23 where the lines are represented in the same manner as in Fig. 2A, the line frequency is 204 cycles per second, and the vertical frequency is 69 cycles as before. Obvi= ously, 3 plus equals 4 minus Since in Fig.

- 2A the ratio is 3 plus, and in Fig. 23 it is 4 television camera or transmitting tube havin minus it will be seen that in accordance with my invention the ratio of the line frequency to the vertical frequency may be expressed broadly as difleringfrom an integer by F If the system of interlace disclosed in Fig. 28 I beemployed in the more practicable system illus-' trated by Fig. 1 in which the number of lines is approximately standard the master oscillator will have a frequency of 25920 cycles per second, the multivibrator 26 will have a frequency of 5184 cycles per second and the chain of-multifrequency respectively to 23040, 3840, 480 and cycles per second. The deflecting windings 20'

vibrators

27, 28 and 29 will have frequencies respectively of 4320, 540 and 60 cycles per second. The saw tooth generator 3.0 in that case will have a frequency of 5184 cycles per second. Thus if the above-mentioned frequencies be employed in the circuit shown by Fig. 1, the number of scan! ning lines will be 432 and the ratio of the line frequency to the vertical frequency will be 86 plus which is the same as 8'7 minus in other words, the ratio is a number, which differs from an integer by The interlaced quintuple interlace system which I have devised and described above is not limited to the frequency numbers mentioned above, but may be employed for the production of pictures having a number of lines equal to any number which ends in 2, 3, '7 orB. Inasmuch as 45 is controlled by the 60 cycle frequency sup-' plied to it by the multivibrator 43. As in Fig. 1 the output of the tube and the synchronizing signals are shown supplied to the radio transmitter 34', the latter through the super synchronizing multivibratorsgare at present found necessary for No. of lines Multivibrator of picture ratios 343 7, 7, 7 378 6, 7, 9 392 7, 7, 8 432 6, 8, 9 448 7, 8, 8 512 8, 8, 8 567

Y

7, 9, 9 588 3, 4, 7, 7 648 8, 9, 9 672 4, 4, 6, 7 768 4, 4, 6, 8 882 3, 6, 7, 7 972 3, 6, 6, 9 l, 008 4, 6, 6, 7 l,

l52

3, 6, 8, 8

In the above table,

rows

1, 2, 5, 7, 8, 10 'and 13 apply where the ratio of the line frequency to the vertical frequency is an integer plus the other rows apply where that ratio is an integer plus That part of the above description describing what is shown in Fig. 1 is an example of a picture having 448 lines and the modified form of that figure employing different frequencies is an example of a picture having 432 lines.

In Fig. 3 I have illustrated a completesystem involving my invention including both the transmitting and the receiving apparatus and employing my interlaced quintuple interlace scanning for a 1152 line picture.

The transmitter comprises the cathode ray tube l5 similar to that shown in Fig. 1 and provided with the screen l6 and the optical system H which in this case is represented as being arranged to project a view on the screen, The tube is also provided with the horizontal and pulse generator The ratio of the line frequency, 13824 cycles in this case, to the vertical frequency, 60 cycles, is 230 thus as in the previously described examples this ratio is an integer plus As before the frame frequency, being 60 divided by 5, is 12. Since the ratio is an integer plus the fraction /5 the lines are scanned in the

order

1, 4, 2, 5, 3, just as in Fig. 2B.

Inasmuch as my invention is applicable not only to television transmitting apparatus but to television receiving apparatus I have included in Fig. 3 a diagrammatic representation of suchapparatus including a cathode ray receiver of well known form. In ,this figure the radio signals transmitted by the transmitter 34' and picked up by the antenna 50 are amplified by the radio frequency amplifier 5| and then passed to the converter 52 to which is also connected the oscillator 53 as in well known superheterodyne radio receivvertical deflecting windings 20' and I8 respectively asin Fig. 1. The master oscillator 38 in this case produces a frequency of 69120 cycles per second. This frequency is supplied to the multivibrator 39 which having a ratio of 5 reduces the frequency to 13824 cycles persecond It is also supplied to the chain of multivibrators 40, ll, 42 and 43 which, having ratios respectively of 3, 6, 8 and 8, reduce the master oscillator Hence such a receiver may be used to receive-a ing apparatus. The output of the converter is supplied to the video intermediate frequency amplifler' 54 and, assuming'that sound is being transmitted as well as pictures, is also supplied to the sound intermediate frequency amplifier 55. This amplifier connects through the detector 56 and the audio frequency amplifier 57 with the loud speaker 58 in the usual manner. The output of the video intermediate frequency amplifier 54 is supplied through the detector 59 and the video amplifier 60 to the cathode of the cathode ray receiving tube 8|. The horizontal beam deflecting winding 64 of the tube is supplied from the horizontal sweep frequency generator 63 which produces 13824 cycles per second or approximately ard 441 line pictures having double interlace inasmuch as the horizontal or line frequency, namely 13824, of my transmitter is so close to the horizontal line frequency, 13230, of those receivers that their horizontal sweep frequency generators are readily pulled in step at the end of each line.

picture transmitted in accordance with my invention and comprising 1152 lines without alterat on therein or'change in adjustment.

With the modification shown by Fig. 3 one ob of requiringa band width of approximately 26 megacycles for the 1152 "line. picture using the standard double interlace and -with 30. pictures per second I can, by employing my invention, re-

duce the number of pictures to 12 and thus reduce the band width by the factor 2.5 to approximately 10.4 megacycles.

For-the purpo'se of assisting the reader in obtaining a clear understanding of my invention the above detailed description has been confined to what I have termed an interlaced quintuple interlace system. My invention, however, is not limited to that particular system although for various reasons I prefer it to the modifications which I shall now describe. Inasmuch as the systems comprising these other modifications differ from that already illustrated only in the frethe electron beam of the tube in one direction at a certain single frequency and simultaneously moving it in a direction substantially at right angles thereto at a single frequency having a ratio to' said certain frequency equal to an integer plus a fraction whose denominator is an odd number and whose numerator differs by onehalf' from being equal to one-half of the denominator.

3. In television the method of scanning lines in a cathode ray tube which comprises moving quencies employed, it would seem to encumber addition to the illustration already provided.

quencies whose ratio is an integer plus or I may e ploy frequencies whose ratio is an in.-'

the drawing unnecessarily to illustrate each in- 3 Instead of employing line andvertical freteger plus various other. fractions such for ex- 1 ample as 2/7, 3/7, 4/7, 5/7, 3/8, 5/ 5/9, 7/9, 3/1Q,'1/10, 2/11, 3/11, 4/11, 5/11, 6/11,

'9/14, 11 14, 2 15, 4 15, 7/15, 8 15, 11/15 and 13/15. Moreover, I may,' if desired, employ frequencieshaving a ratio whichincludes a fraction whose denominator is astill higher number. In

the-,quintuple.arrangement illustrated by thedrawing, it will be noted that in no case did the fraction added to the integer to express the ratio of the two frequencies comprise either -1/5' or 4 4/5.. The reason is that a ratioincluding such fractions would not producethe desired interlacing. A broad statement of my invention therefore is that the ratio of the line and vertical frequencies is equal to an integer plus a fraction which, expressed in its lowest terms hence is prime, hasa numerator that is more than one and. is less than the denominator minus one.

Inasmuch as the rate 'of crawl upward and down-;

ward becomes more nearly the same as the fraction approaches 1/2, I-prefer in those cases where one may choose between several fractions and particularly where the fractions'have small de- 'nominators' to employ those-frequencies whose the electron beam of the tube in one direction at a certain frequency and moving it simultaneously in a direction substantially at right angles thereto at a frequency which diiiers from an exact multiple of said frequency by '1. In television the method of scanning lines in a cathode ray tube which comprises moving the electron beam of the tube in one direction at a certain frequency and moving it simultaneously in a direction substantiallyat right angles thereto at a frequency having a ratio to said certain frequency equal to an integer plus '5. In'television the method of scanning lines in a cathode ray tube which comprises moving the electron beam of the tube in one direction at a certain frequency and moving it simultaneously in a direction substantially at right angles thereto at a frequency having a ratio to said certain frequency equal to an integer plus Television apparatus comprising a cathode ray tube having a screen, -beam'deflecting means and energizing means connected therewith for causing the beam to scan the-screen successively in a plurality of spaced parallel lines, said means including means for causing the beam to scan the screen intermediate said lines in a plurality of interlaced lines.

7. Television apparatus comprising a cathode ray tube having a screen arranged to be scanned by thebeam thereof in a plurality of lines and means for causing the beam to move in the. direction of said lines and in a direction substantially at right angles thereto, said means including means for causing the ratio of the frequency of movement of the beam in the direction of the lines to the frequency of its movement in the other direction to equal an integer plus a fraction ratio is an integer plus a fraction which is close spirit andscope of my invention which modifications 1 am to cover by the appendedv claims.

-What I claim as new and desire to secure by Letters I'atent of the United States is:

which, in its lowest terms, has a numerator that is more than one and is less than the denominator minus one.

' 8. Television apparatus comprising a cathode ray tube having a screen arranged to be scanned by the beam thereof in a plurality of lines and means for causing the beam to move in the direction of said lines and in a direction substantially at right angles thereto, said means including means for causing the ratio of the frequency of movementof the beam in the direction of. the

lines to the frequency of its movement in the other direction to equal an integer plus a fraction whosezdenominator is an odd number and 1. In television the method of scanning lines I in a cathode ray. tube which comprises moving the electron beam of the tube in one direction at a certain frequencyand simultaneously moving it in a direction substantially at right angles thereto at a frequency having a ratio to said certain frequency equal to an integer plus a fraction which in its lowest terms has a numerator that is more than one and is less than the denominator minus, one.

2. In television the method of scanning lines in a cathode ray tube which comprises movin whose numerator differs by one-half from being equal to one-half of the denominator.

ray tube having a screen arranged to be scanned by the beam thereof in a plurality of lines and means for 'causing the beam to move in the direction of said lines and in a direction substantially at right angles thereto, said meansincluding means for causingwthe ratio of the frequency ofmovement of the beam in the direction of the lines to the frequency of its movement in the other direction to d er from an integer by 10. Television apps tus comprising a cathade 9. Television apparatus comprising a cathode ray tube having a screen arranged to be scanned by the beam thereof in a plurality of lines and means for causing the beam to move in the direction of said lines and in a direction substantially at right angles thereto, said means including means for causing the ratio of the frequency of movement of the ray in the direction of the lines to the frequency of its movement in the other direction to equal an integer plus ll. Television apparatus comprising a cathode ray tube having a screen arranged to be scanned by the beam thereof in a plurality of lines and means for causing the my to move in the direction of said lines and in a direction substantially at right angles thereto, said means including means for causing the ratio of the frequency of V movement of the ray in the direction of the lines to the frequency of its movement in the other direction to equal an integer plus "25.

12. Television apparatus comprising a cathode ray tube having a screen arranged to be scanned for producing a plurality of deflection frequencies whose ratio diiiers from an integer by and means for supplying said frequencies each to one of said deflecting means.

13. Television apparatus comprising a cathode ray tube having a screen, and'means for causing the beam of said tube to scan said screen in a of groups of flve lines each, said means including by the beam thereof in a plurality of lines, means for deflecting the beam in the direction of the lines, means for deflecting the beam in a direction substantially at right angles thereto, means means for causing the beam to scan successively corresponding lines of said groups and including means for causing the ray to scan successively lines 1, 3, 5, 2 and 4 of said groups in the order named. a

SEGFRIED HANSEN.