US2274098A

US2274098A - Deflecting circuit

Info

Publication number: US2274098A
Application number: US210598A
Authority: US
Inventors: Shore Henry
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1938-05-28
Filing date: 1938-05-28
Publication date: 1942-02-24
Anticipated expiration: 1959-02-24

Description

Feb. 24, 1942.

H. SHORE 2,274,098

DEFLECTING CIRCUIT Filed May 28, 1938 5 Sheets-Sheet 1 IMJ U U T 6 77 Fg'gdfg 0 HENZViJJE A TTORNE Y.

Feb. 24-, 1942. H. SHORE DEFLEGTING CIRCUIT 5 Sheets-Shet 2 Filed May 28, 1938 INV EN TOR. HENRY SHORE ATTORNEY.

Feb. 24, 1942. H. SHORE DEFLECTING CIRCUIT Filed May 28, 1938 5 sheets sheeb 5 INVENTOR. HENRY SHORE 7Y4- A TTORN E Y.

Feb. 24, 1942. SHORE DEFLECTING CIRCUIT Filed May 28, 1938 5 Sheets-Sheet 4 INVENTOR. HEM? Y SHORE wggm II. II||I IIILI ll IIIII I I l l IIL Wm g a \R R\ A TTORN E Y.

Feb. 24, 1942. I H. SHORE DEFLECTING CIRCUIT Filed May 28, 1938 5 Sheets-Sheet 5 INVENTOR. HENRY SHORE ATTORNEY.

Patented Feb. 24, 1942 DEIFLECTING CIRCUIT Henry Shore, Brooklyn, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application May 28, 1938, Serial No. 210,598

11 Claims.

This invention relates to image reproducing systems, and more particularly, to scanning systems such as used in the transmission and reception of images by means of cathode ray tubes, such as television systems.

In using cathode ray tubes in a television system, it is usual to scan the image of the object to be transmitted line by line by means of the cathode ray and to produce from the scanning electrical signals which are transmitted. The transmitted signals upon being received, are then used to modulate a scanning beam of electrons generally impacting upon a luminescent surface to reproduce the image of which the electrical signals are representative, the scanning speed at the receiving point being maintained in substantially exact synchronism with that of the scanning speed at the transmitting point. Among those systems of scanning, the preferred form appears to be that in which the area to be scanned is scanned in one direction only at a linear speed, and to return the scanning beam for the next line at a much higher rate of speed upon completion of one line of scanning. However, even though the speed of the beam on its return path is as high as ten times the speed of scanning, there is still generated signals at the transmitter and a visible trace at the receiver. The visible trace at the receiver is particularly undesirable in view of the fact that it tends to destroy the effective contrast ratio, i. e. the ratio of illumination between the darkest parts and whitest parts of the picture, as well as to cause a destruction of detail by the superimposed faint pattern of the return line trace.

To overcome this it has been proposed to suppress the beam of electrons during the time the beam normally would be retracing its path at high speed and in accordance with this, it has been proposed to supply a cathode ray tube equipped with a control electrode, which control electrode, in addition to being supplied with video signals for controlling the intensity of the focused beam of electrons in a receiving tube, is also supplied with a signal of such magnitude and of such polarity to suppress the flow of electrons from the cathode through the electro-optical system, which serves to focus-the electrons upon the target electrode. However, while this does serve tokeep the return line 0115 the viewing field, the necessity for supplying the signal to the control electrode, which causes the suppression of the beam and consequently the return line, from an auxiliary circuit tends to introduce distortion ponents of the video signals are discriminated against to an extent that they are reduced below their proper value. This, in turn, tends to reduce the amount of detail which can be reproduced on the luminescent screen. The same circuit likewise tends to reduce the effective impedance so that the gain of the amplifier must be increased in order to provide suflicient control potential between the control electrode and cathode to effectively control the intensity of the beam throughout its workable range. Since the video amplifiers must pass frequencies from zero up to and including 3 /2 megacycles for a high detail television system, it will be readily apparent that considerable difliculty is entailed in providing linear response for such amplifiers together with linear phase response in order that distortion shall not be introduced by the amplifier. The addition of the supplementary or auxiliary circuit for suppressing the beam, therefore, increases the difficulties of an already difilcult problem, and accordingly, to overcome this detrimental feature, and at the same time; to perceive the advantages by preventing the return line from appearing on the viewing surface, this invention proposes to deflect the beam off the target surface during the return line by auxiliary circuits which are entirely unconnected with the control electrode of the cathode ray tube. By so doing, the input capacity between the control electrode and cathode of the cathode ray tube is maintained at a minimum, while at the same time the return line is prevented from being visible on the screen so that the problem of providing suitable amplifiers to supply video signals to the control electrode is simplified, and at the, same time, the maximum resolution and details of the image can be provided with a resultant reduction in distortion.

Accordingly, the purpose of this invention'is to provide a new and improved system of scanning with cathode rays.

Another object of the invention is to provide a system of scanning in" which substantially linear scanning in one direction at a predetermined speed is efiected, and deflecting the scanning beam ofi the viewing surface during the time required for the return of the beam to the position necessary for the next line of scanning- Still another object of my invention is to provide a scanning system wherein a beam of. electrons traverses a target surface line by line and upon the completion of each line, is deflected entirely off the target surface and returned to the starting point of a following line, while ofi the target surface.

A further object of the invention is to provide a scanning system wherein an area is scanned line by line in one direction and at the completion of each line of scanning,"the" ray is deflected to the edge of the scanned area and traverses the edge portion of the area until itis brought to the position for starting a following line.

Other methods and means of the invention will become apparent upon reading the following description, together with the drawings in which:

Fig. 1 shows graphically the paths taken by a scanning beam in accordance with my invention;

Fig. 2 shows graphically the scanning pattern according to a modification of the scanning pattern shown in Fig. 1;

Figs. 3a-3g show graphically wave formations of voltage or magnetic fields for explaining the invention;

Figs. 4 and 5 show two embodiments'in block diagram form of the apparatus in accordance with my invention; while Figs. 6 and 7 show diagrammatically details of certain portions of the apparatus shown in Figs. 4 and 5 respectively.

Referring to Fig. 1, there is shown an area I which is to be scanned by a cathode ray beam. The paths of the cathode ray beam during the scanning process beginning at A follow along the line 3 to a point B just outside of the area. At

point B the beam follows along the line i I to the point C, from point C along the line 3;. to point D and from point D along 'the line l3 to point E where the beam is now ready to commence a second line of scanning along the path 5. To cause the beam to traverse such a path as I have shown, there is provided a cathode ray tube equipped with a conventional electromagnetic deflecting system, or alternatively an electrostatic deflecting system. Such a system is supplied with a saw-tooth wave which wave produces substantially linearly increasing fields with respect to time so that the beam of electrons under the influence of this increasing field is deflected across the screen. Simultaneously a second set of electromagnetic deflecting coils or electrostatic deflecting plates has impressed thereon a saw-tooth wave of different frequency but similar in shape to that of the first system so that as the beam moves across the area to be scanned, it is also moved downward. Under the simultaneous influence of the two fields, therefore, there is produced a scanning pattern of parallel lines, which lines however, are not parallel to the top and bottom of the scanned area. This much .is conventional and well known in the prior art. However, upon completing a line of scanning, for example, when the scanning beam reaches the point B in Fig. 1 in the prior art, the beamwould be deflected back along the line which would be substantially parallel to the top and bottom edges of the scanned area I. However, in acccordance with the invention, the beam is substantially instantaneously deflected to the point C upon reaching the point B and the deflection and magnitude of the deflection from B to C is made at least twice as great as the distance A to R, and

' preferably somewhat greater than twice the distance from A to R. Simultaneously, with this vertical deflection, the return line deflection is effective to deflect the beam along the path 3' to the point D, where the beam is immediately deflected in a vertical direction to the point E, whereupon the horizontal deflecting circuit now causes the beam to follow path 5 to the path F. At point F the beam is again deflected in a vertical direction to the point G and the deflection along the path II FG is made equal to the deflection along path ll BC'and the operation is repeated until the entire area l is scanned, whereupon the beam is caused. to rescan the

paths

3, 5, 1, 9, etc.

It will be appreciated, of course, that in Fig. 1 only 4 lines of a scanning pattern are shown with considerable space between lines, merely to facilitate the explanation of the method of scanning. Of course, in actual practice, for high definition scanning systems 400 lines more or less would be scanned with each line closely adjacent to the preceding and succeeding lines. But for purposes of illustration, it is believed to attempt to show scanning patterns of such a system on a true scale would be more confusing than helpful. Alternatively, in accordance with the invention, the

'. scanning pattern shown in Fig. 2 may be provided.' In this figure the scanning pattern runs along the line 2 3 to 3i, where it is deflected vertically to the point V and along the line to point W, and then down to trace the line 25. Upon the completion of line 25, the beam is again deflected to the point V and along the same line 35 to W, and then down along line 33 to scan line 2'7. It will be noted in this figure that the return line is always along the same path, i. e. line 35.

In Fig. 4 I have shown in block diagram for purposes of illustration, a cathode ray tube used as a part of a television receiver to reproduce transmitted images together with the apparatus for providing a scanning pattern such as shown in Fig. 1. In Fig- 4 a video receiver ml receives signals comprising the video signals together with vertical and horizontal synchronizing signals. The video receiver may be of a sort well known in the prior art, and supplies video signals to the electron gun and control electrode I23 of the cathode ray tube H9. The synchronizing signals together with the video signals are supplied to a separating circuit H13 such as well known in the art, which separates the vertical synchronizing signals from the horizontal signals, as well as separating both of these signals from the picture signals. The separated synchronizing signals are then supplied to the saw-tooth oscillators Hi5 and I25. The saw-tooth oscillators maybe of any of the types well known in the art, such as the blocking grid type or the gaseous discharge type. The vertical saw-tooth oscillator is generally set at a lower frequency than that of the horizontal saw-tooth oscillator, and generally the two oscillators have an integer relationship, or in cases of interlaced scanning systems, a non-integer ratio of frequencies The wave shape of the energy produced by these oscillators is shown in Fig. 3, where Fig. 3a represents graphically the wave shape of the horizontal saw-tc--th oscillator I25, while Fig. 3c shows the wave shape of the vertical oscillator I05.

In accordance with the invention, the sawtooth wave furnished by the oscillator I25 is fed through a wave shaping circuit I21 and which serves to convert the saw-tooth wave into a wave shape shown in Fig. 3b for purposes which will be explained later. The wave shaping circuit may be of the type shown and disclosed in copending application of Arthur W. Vance, Serial No. 544,959, filed June 1'1, 1931, entitled Methods and apparatus for communication by television]? and allowed May 5, 1938. The output of the wave shaping circuit I21 is fed to an amplifier I29, which in turn has its output connected to the magnetic deflecting coils I31. The purpose of the saw-tooth wave shown in Fig. 3a to the shape shown in Fig. 3b is to provide a flow of current through the magnetic coils I31 which shall have the same shape as that shown in Fig. 30., so that substantially linearly increasing fields at a relatively slow rate are provided with a sharply decreasing field upon reaching the maximum predetermined magnetic field strength. The wave shaping circuit I01 and amplifier I09 are similar to the circuits I21 and I29 and serve to provide vertical magnetic scanning fields by the coils II1, which shall also be saw-tooth wave in shape. A portion of the output of the amplifier I29 is fed to a circuit I I I which I havecalled a square wave amplifier and which serves to convert the wave shape shown in Fig. 3b to square top, square sided pulses having a duration equal to that shown as 41 in Fig. 3b. This is brought about by limiting the signal both as to its threshold value and maximum value, and a suitable square wave amplifier of this type may be that shown in United States Patent No. 2,005,111 to Henry Shore, which issued June 18, 1935, and entitled Amplifier. The output of the square wave amplifier III is, therefore, a short pulse having substantially vertical sides at a horizontal top, which when fed to the amplifier II3 serves to permit current to flow through the amplifier only during the time that the square wave impulses are produced, and a pair of auxiliary coils I I are connected to the output of the amplifier II3, so that the short square Wave pulses produced by the amplifier II3 produces a magnetic field which suddenly increases to its maximum value, which maximum value is maintained for a duration equal to the duration of the square wave pulse and upon the cessation of this pulse, the magnetic field immediately collapses to zero. The current which flows through the auxiliary coils H5 is chosen so that the magnetic field produced by these is at least twice that produced by the maximum value of current which flows through the main vertical deflecting coils II1.

Similarly a portion of the vertical energy is fed through a similar square wave amplifier I3I, the output of which amplifier is connected to amplifier I33 and the auxiliary coils I35 are connected to the output of the amplifier I33. Again, the action is the same as above described in connection with amplifiers I II and H3, and the maximum flow of current from the amplifier I35 through the coils I33 is so chosen that the magnetic field set up by the coils I35 is equal to at least twice the magnetic field set up by the coils I31 when maximum deflecting current flows therethrough. The coils H5 and their connection to the amplifier II3 are so poled as to produce magnetic fields in the opposite direction to the fields set up by the amplifier I09 and the coils II1. Likewise the coils I35 are so poled and connected to the amplifier I33 as to produce a r .agnetic field opposite to that set up by the coils I31 when fed by current for deflecting the beam horizontally at its relatively low speed.

It will be readily apparent, therefore, that at the termination of the forward sweep produced by the current increasing along the path 15 in a horizontal direction, there is produced a very strong Vertical pulse in the coils II5 which is sufficient to deflect the beam off the screen I2I of the tube II9. During the interval 41, therefore, when the beam is on its return stroke, the return path of the beam will be off the screen. The sudden collapse of the current through the coils I I5 at the termination of the return stroke places the beam at a point where it is ready to scan the next adjacent line. This will readily become apparent by considering curves 3c, 3d and 3e.

In Fig. 3c the magnetic field strength set up in the coils H1 is shown to follow th line 43. The magnetic fields set up by the coils II5 are shown in Fig. 3d and are normally at zero along the path 5I corresponding to the forward sweep of the horizontal saw-tooth Wave shown in Fig. 311. During the return line period of the horizontal sweep the short duration pulse of high magnitude is produced, producing a magnetic field of amplitude 53 in the opposite direction to that shown in Fig. 30. Since the cathode ray beam produces a deflection which is the sum of these two deflecting fields, the resultant deflecting field effective upon the beam is shown in Fig. 3e, and it will be readily appreciated that the application of such a vertical deflecting field produces the scanning pattern shown in Fig. 1.

Similarly the portion of the energy from the amplifier I09 fed through the square wave amplifier I3I and the amplifier I33 through the coils I35 serves to maintain the beam to the left hand side of the picture area I shown in Fig. 1 during the time that the vertical sweep circuit is executing its return path along I3 from R to A. Since the operation of this portion of the circuit is identical with that described above in connection with amplifiers III and H3, it is believed unnecessary to redescribe the steps in the operation.

It will thus be seen that in this embodiment of the invention there has been supplied an effective deflecting field for the cathode ray which increases linearly with time at a predetermined rate and the increasing field is periodically abruptly decreased to a negative value under the control of the oscillator which provides energy for deflecting the beam in a mutually perpendicular direction. That is to say that the effective deflecting field has magnitudes as indicated in Fig. 3e where the

portions

55, 65, 61 and 69 comprise the linearly increasing magnetic field, while 51, 59, BI and 63 indicate the abrupt reversal of the field during the time intervals corresponding to the return time of the horizontal saw-tooth oscillator.

Referring now to Fig. 6, certain details of the embodiments shown in Fig. 4 are illustrated more completely, and these will be described in order that even those not skilled in the art will be able to practice the method of scanning above disclosed. In Fig. 6 numerals which are identical to those of Fig. 4 indicate the same apparatus as shown in Fig. 4. Only a portion of one deflecting system will be described in view of the fact that the deflecting system for causing the ray to be deflected in a mutually perpendicular direction is substantially the same, except for minor changes of resistance capacity and inductance values. i

Saw-tooth wave energy from the horizontal saw-tooth oscillator I is impressed across the terminals I99 so that between the cathode ray and grid of tube 203 there is a potential impressed which varies linearly with time to a predetermined maximum value, and thereafter decreases to zero in a time interval which is relatively small compared to the length of time it takes to reach the predetermined maximum value of potential. The voltage, however, which appears across the serially connected inductance 201 and resistance 203 is not instantaneously produced due to the time lag introduced by the inductance, and by supplying the potential produced across these serially connected constants through the condenser 2H to the resistor 2I3, there is produced across the grid cathode circuit of tube 2I1 a potential wave having the form shown in Fig. 3b as described in more detail in the allowed application to Vance referred to above. The output of tube 2I'I coupled to the electromagnetic deflecting coils I31 produces a current in the coils I31 which is substantially identical in wave shape to that of the impressed voltage across the terminals I99 for horizontal deflection. A portion of the output energy appearing across the inductance 22I is fed to the square wave oscillator I II being impressed across the resistor 225. The polarity is so chosen that the short negative pulse 31 of the wave shown in Fig. 3b is in a direction to drive the grid of the tube 221 negatively with respect to the cathode of this tube so that the grid which is normally maintained is zero, or a slight positive value is abruptly driven negatively beyond the cut-off point so that the plate current flowing in the resistor 233 changes from a relatively large value to zero. This is brought about by the fact that any change in potential of the grid of tube 221 is amplified by the tube MI and returned through the condenser 263 to augment the change in potential and this regenerative action being accumulative, causes the current flowing through tube 221 to have either zero value or a predetermined maximum value as is explained in more detail in the above referred to patent to Shore. A portion ofthe potential drop appearing across the resistor 233 is fed to the tube 249, in whose output circuit the auxiliary deflecting coils II5 are connected. It will thus be clear that as the distorted saw-tooth wave shown in Fig. 3b is impressed on the resistor 225 for the positive values of potential represented by in Fig. 3b, substantially saturation plate current flows through the resistor 233, producing a large potential drop, which potential drop being impressed on the grid cathode circuit of the tube 249 is sufiicient to maintain the tube in cut-ofi condition, so that no current flows through the coils I I5. However, upon the abrupt change in potential which occurs during the return time of the horizontal wave, so that a decrease in potential is impressed across the resistor 225, the tube 221 has its plate current changed abruptly from its predetermined maximum value to zero.' The potential drop, therefore, across the portion 231 of resistor 233 becomes zero and under such conditions, the grid cathode circuit of the tube 249 being zero, maximum plate current abruptly flows through the coil II5 to produce the auxiliary field for deduring the time increase in current is flowing through the coils II1 fed from amplifier I29. A similar set of circuit connections is supplied for actuating the horizontal deflecting circuit under the control of the vertical oscillator comprising the vertical saW-tooth oscillator I05, the wave shaper I01, the amplifier I09, the square wave amplifier I3I, and the amplifier I33.

Further in accordance with the invention, where it is desired to do away with the necessity of supplying auxiliary deflecting coils since, in general, this introduces further problems of shielding and complexity, the arrangement shown in Fig. 5 may be used. In Fig. 5 the reference numerals which are the same as that shown in Fig. 4 refer to substantially the same apparatus. in Fig. 5 from that of Fig. 4 is that different amplifiers I5I, I53 are fed from the wave shapers I31 and I 21, respectively, and further, the square wave amplifiers III, I 3i instead of actuating the separate amplifiers H3 and I33, actuate amplifiers I53 and I5I respectively. The square wave amplifiers serve to bias the amplifiers driving the deflecting coils to cut-ofi during the return line time of the oscillators, so that there is produced a deflecting field which increases linearly with time but is periodically reduced to zero during the time it is increasing from zero to a predetermined maximum value. By supplying such a deflecting field, the area 2I is scanned in a pattern as shown in Fig. 2.

Fig. 7 shows in detail connections of the wave shaper I01 and the amplifier I5I, the square Wave'amplifiers III and I3I, as well as thewave shaper I21 and amplifier I53. The operation of the amplifiers I01 and I21 is identical with that described in connection with Fig. 6. It will be noted likewise, that the sole change takes place in the amplifiers I5I, I53. In these amplifiers an auxiliary resistance 263 and 363 respectively are supplied and across the resistor 263 there is supplied from the square amplifier I3I potential drops to cut the plate current of the tube 2I1 to zero during the time intervals when the horizontal saw-tooth oscillator is supplying decreasing potentials. Normally the tube 2I1 operates with such bias as to be a linear amplifier, so that the potentials appearing across the resistor 2I3 are amplified by the tube 2I1 to supply across the deflecting coils,II1 saw-tooth wave current. The short pulses from the amplifier I3I, however, are of such magnitude and are so poled as to impress the grid cathode circuit of tube 2I1 such a large negative potential that the grid is placed in the plate current cut-off condition 'to reduce the current flowing through the coils III abruptly to zero. Thus it will be noted that the linearly increasing vertical cur- --rent is abruptly reduced to zero periodically unoscillator.

der the control of the horizontal saw-tooth wave Similarly, the current flowing through the coils I31 is abruptly reduced to zero during the time the vertical saw-tooth wave oscillator is supplying decreasing potentials since at this time the square wave ampli- It will be noted that the only difference 1 fier Ill impresses cut-off potentials across the tube 3H so that zero current will flow through the coils Ill. It will thus be appreciated that this arrangement requires two tubes less than the arrangement shown in Fig. 6 and at the same time dispenses with the need of auxiliary defleeting coils while still accomplishing the desired result of preventing return lines of either the vertical or horizontal scanning motions from appearing upon the scanned area, thus providing a scanning system having improved contrast range with freedom from frequency distortion to provide improved images.

It is to be noted that both embodiments of the scanning method and apparatus described above are, of course, applicable to any interlaced scanning system, as well as the sequential line scanning system described in connection with the invention. While for purposes of explaining the invention, sequential line scanning was assumed, it is clear that inasmuch as it is only the return line portion of the scanning wave that is deflected off the screen, this deflection is independent-of the particular scanning pattern used and the invention is applicable to those types of scannings known as interlaced, either odd line or even, as well as to sequential frame scanning. Of course, other modifications of applicants circuit may be used. For example, where electrostatic scanning is preferred, the saw-tooth wave developed by the oscillator may be supplied directly to the deflecting plates without passing it through the wave shaping circuit.

Applicant, therefore, does not limit himself to the specific embodiments shown in the drawings and described in the specification, but believes himself entitled to make and use any and all modifications which fall fairly within the spirit and scop of the foregoing disclosure as it is defined by the hereinafter appended claims.

Having described my invention, what I claim is: l. The method of scanning a target surface positioned within a cathode ray tube by a beam produced within said tube, which comprises the steps of deflecting the beam of electrons horizontally across the target surface, producing a horizontal return deflection of said beam of electrons, simultaneously deflecting the beam of electrons vertically, producing a vertical return deflection of the beam, producing auxiliary d'eflecting fields, and superimposing the produced auxiliary deflecting fields upon said vertical and horizontal return deflections, whereby the beam of electrons is moved by the produced auxiliary deflecting fields off of the target area during both the horizontal and vertical return deflections of the beam.

2. The method of scanning a target surface positioned within a cathode ray tube by a beam of electrons produced within said tube, which includes the steps of producing a deflecting field whose value increases linearly with time for deflecting the beam of electrons, periodically superimposing upon deflecting fields of opposite polarity the" produced deflecting field whereby the beam of electrons is deflected by the superimposed deflecting fields.

3. The method of scanning a target surface positioned within a cathode ray tube by a beam of electrons produced within said tube, which includes the steps of producing a deflecting field, whose value increases linearly with time, period1- cally superimposing upon the produced deflecting field a deflecting field of opposite polarity and of a magnitude equal to the magnitude of the produced linearly increasing field at the time of superpositioning of the second named field, whereby the beam of electrons is deflected by the superimposed fields.

4. The method of scanning a target surface positioned within a cathode ray tube by a beam of elecrons produced within said tube, which includes the steps of producing a deflecting field whose value increases linearly with time having a predetermined maximum value, periodically superimposing upon the produced deflecting field a deflecting field of opposite polarity and of a magnitude at least twice as great as the predetermined maximum value of the produced deflecting field at the time of superpositioning of the second named field, whereby the beam of electrons is deflected by the superimposed fields.

. 5. A cathode ray tube having a target surface and means for producing a beam of electrons within the tube, means for deflecting the beam of electrons horizontally across the target surface, means for producing a horizontal return deflection of said beam of electrons, means for simultaneously deflecting the beam of electrons vertically, means for'producing a vertical return deflection of the beam, means for producing auxiliary deflecting fields and means for deflecting the beam of electrons by said auxiliary defleeting fields off of the target area during both the horizontal and vertical return deflections of the beam.

6. A cathode ray tube having a target surface and means for producing a beam of electrons within the tube, means for producing a deflecting field whose value increases linearly with time for deflecting the beam of electrons, and means for periodically super-imposing upon the produced deflecting field deflecting fields of opposite polarity and for deflecting said beam of electrons.

7. A cathode ray tube having a target surface and means for producing a beamof electrons within the tube, means for producing a field whose value increases linearly with time, and means for periodically superimposing upon the produced deflecting field a deflecting field of opposite polarity and of a magnitude equal to the magnitude of the produced linearly increasing field at the time of superpositioning of the second named field and for deflecting said beam of electrons.

8. A cathode ray tube having a target surface and means for producing a beam of electrons within the tube, means for producing a deflecting field whose value increases linearly with time having a predetermined maximum value, and means for periodically superimposing upon the produced deflecting field a deflecting field of opposite polarity and of a magnitude at least twice as great as the predetermined maximum value of the produced deflecting field at the time of superpositioning of the second named field and for deflecting said beam of electrons.

9. In combination, a cathode ray tube having a target surface, means for producing a beam of electrons focused upon the target surface, means for horizontally deflecting the beam across the target surface in a predetermined direction, auxiliary means for deflecting the beam horizontally in a direction opposite to the predetermined direction, means for vertically deflecting the beam across the target surface in a predetermined direction, and auxiliary means for deflecting the beam vertically in a direction opposite to the predetermined direction.

10. In combination, a video receiver for receiving video signals combined with horizontal and vertical scanning synchronizing signals, a cathode ray tube having a target surface, means for producing a focused beam of electrons to impact upon the target surface, means to supply video detected signals from the receiver to the cathode ray tube for controlling the intensity of the beam of electrons, means to separate the vertical and synchronizing signals from the picture signals and from each other, means for producing a first saw-tooth wave oscillation of a predetermined frequency, means to produce a second saw-tooth wave oscillation of a frequency lower than the predetermined frequency of the first produced saw-tooth oscillation, means to'control thev first and second produced oscillations by the separated horizontal and vertical synchronizing signals respectively, means to deflect the beam of electrons by the first produced saw-tooth wave oscillation, means to deflect the beam of electrons in a mutually perpendicular direction by the second produced saw-tooth wave oscillation, means for deflecting the beam of electrons off of the target surface under the control of the second produced oscillation at a predetermined point of deflection produced by the first produced saw-tooth wave oscillation, and means to deflect the beam off of the target surface by the first produced sawtooth oscillation at a predetermined point of the mutually perpendicular deflection.

11. In combination, a cathode ray tube having a target surface and means within the tube for producing a beam of electrons focused upon the target surface, a first deflecting means comprising a saw-tooth oscillator of predetermined frequency, means for amplifying oscillations from the saw-tooth oscillator, wave distorting means connected between the saw-tooth wave oscillator and amplifier, deflecting means connected to the amplifier, a second deflecting means comprising a saw-tooth wave oscillator having a predetermined frequency difierent from the saw-tooth wave oscillator of the first deflecting means, means for amplifying oscillations from the sawtooth wave oscillator, a wave shaping circuit connected between the saw-tooth wave oscillator and amplifying means, deflecting means supplied with signals from the amplifier, a square wave amplifier supplied with energy from the amplifier of the first deflecting means to control the second deflecting means, and a square wave amplifier supplied with signals from the second deflecting means for controlling the first deflecting means.

HENRY SHORE.