US2252441A - Sharp-edge deflection - Google Patents

Description

1941- K. SCHLESINGER 2,252,441

SHARP-EDGE DEFLECTION Filed April 722, 1938 5 Sheets-Sheet 1 def/ecfed Jnvenfop:

1941- K. SCHLESXNGER 2,252,441

SHARP-EDGE DEFLECTION Filed April 22, 1938 3 Sheets-Sheet 2 Fig 5 Jnvemop:

Mull/w 1941- K. SCHLESINGER 2,252,441

SHARP-EDGE DEFLECTION Filed April 22, 1938 Y 3 Sheets-Sheet 3 VOL 7/] GE IVE Fig. 7

JnVen fon- Patented Aug. 12, 1941 SHARP-EDGE DEFLECTION Kurt Schlesinger, Berlin,

Radioaktiengesellschaft D.

Germany, assignor to S. Loewe, Berlin- Steglitz, Germany, a company of Germany 1938, Serial No. 203,487

Application April 22,

In Germany April 26,

7 Claims.

The present invention relates to cathode ray tube arrangements, more particularly for television purposes wherein means comprising at least one pair of deflecting plates are provided for deflecting the cathode ray in two directions perpendicular to one another.

It is known that a large bundle of rays which, when not deflected, is focussed sharply on the screen will not give a sharp image point in the case of deflection beyond a critical angle. It is also known that this critical angle can be increased if the two plates are supplied with reverse phase deflecting voltages so that their potentials oscillate symmetrically with respect to the anode potential. New investigations, however, have shown that even in this case an enlargement of the image point takes place if the beam is deflected beyond an angle of about 17. For several reasons, however, it is desirable to have considerably greater deflections of the ray with full sharpness of Then can be obtained either larger pictures with a given length of tube or shorter tubes with a given size of picture. In the latter case it is also possible, for electron optical reasons, to obtain a smaller image point and a greater density of light.

It is. an object 'of the present invention to perform a wide an'gle'defiection in cathode ray tubes, more particularly for television purposes, and at the same time to maintain an irreproachable sharpness of the picture over its entire area.

According to the invention, in a cathode ray tube arrangement of the above mentioned type, wherein the cathode ray tube comprises an anode which is mounted immediately adjacent to the deflecting plates at their side facing the cathode and is connected to a source of constant potential, and there are provided means for producing the effect of a common bias applied to the deflecting plates, which is positive with respect to the anode and varies in rhythm with the deflecting voltage built up across the deflecting plates, the peak value of the common bias being preferably substantially equal to one half of the peak value of the deflecting voltage.

The invention will be better understood with the aid of, and further features of the invention will be apparent from the following more detailed description and the accompanying drawings in which- Fig. 1 illustrates an experimental circuit used for obtaining the eflects shown by Figs. 2a and 2b,

Figs. 3, 4, 5, '7, and 8, in a purely diagrammatic fashion and by way of example, illustrate cirthe edges of the picture.

cuits for avoiding the effect according to Fig. 2a, whilst Fig. 6 is a graph showing age and an example of a common to the deflecting plates.

The following experiment illustrated by Fig. 1 has been made for investigating the errors of an electro-static deflecting system:

In a cathode ray tube there are provided two deflecting plates 1 and 2 beyond an anode 3.

the deflecting voltbias applied The bundle of cathode rays 4, in thenon-deflected condition, is 'focussed sharply on to the screen 5. The battery '6 supplies to the plates the deflecting potential. In the exampleshown the ray is thus deflected downwards. In parallel with the battery 6 there is connected a potentiometer I, the wiping contact of which is connected with the anode 3. If a certain deflection is adjusted, it can be ascertained that beyond the critical angle of deflection the sharpness of the point "is maintained in full if plate I, which is connected to the negative terminal of the battery, is at the same time connected to the anode and the positive plate exhibits in relation to the ray the full deflecting potential. In Fig. 1 this connection is obtained by displacing the wiper of the potentiometer towards the right. If the opposite adjustment is made,i. e., the positive plate connected to the anode and the negative plate allowed to oscillate in relation to the ray, the sharpness of the edge of the picture will be considerably poorer.

Further detailed investigations have shown that not a marginal field nor a variation of the speed of the ray, but probably a space charge effect is causing the described eiiect.

In Fig. 2a there is shown the wrong connection, the anode 3 being connected with'the positive plate 2, and in Fig. 2b the proper connection. In Fig. 2a the point of intersection of the single rays isdisplaced from the plane of the screen 5 towards the anode to the point 511. The focal distance of the system is shortened and the image loses its sharpness at the edge.

In "the proper connection, Fig. 2b, the anode being connected with the negative plate, the reverse effect occurs. The rays nearer the positive plate are deflected somewhat more strongly than those opposite to the negative plate. The focal distance of the system is extended from 5a to 5b. The image point remains on the screen.

It has been found that any variation of the sharpness of the image point during the whole deflectionperiod can be avoided when both plates are furnished, in addition to the deflectingpotentials, with a common varying bias increasing with the absolute value of the deflecting voltage in such a way that the potential of the deflecting plates is always higher than or at least equal to the potential of the anode. It will be understood from the following that the desired effect, i. e., the effect of a common bias applied to the deflecting plates, can also be obtained by circuit means which do not supply the deflecting plates with a common bias in the strict sense of the word.

The simplest way to realize the desired effect is to provide means connecting that deflecting plate which is instantaneously negative with the anode. That means that the connection between plates and anode must be commutated twice in a complete deflection period from the left to the right and back when push-pull deflection is used. As regards the technical reduction to practice the following circuit illustrated by Fig. 3 would be conceivable in principle:

The two plates I and 2 are connected with the secondary of a deflection transformer 8 the primary of which is fed by a relaxation oscillator 23. The mean point of the secondary is connected by way of a leak resistance 9 with the anode 3, Two rectiflers I (la, lfib (diodes are shown in the drawings) are connected by the cathodewith the plates and by the anodes with the tube anode 3. Neither of the plates is then able: to become negative in relation to the tube anode, whereas the potential of the instantaneously positive plate is able to oscillate with respect to the anode without obstruction.

Consequently each plate carries alternately constant anode potential for one half period of deflection and a positive saw-tooth potential for the next half period, the potentials of both plates having 'a phase difference of one half period. Thus the voltage between both plates has a sawtooth wave form the amplitude of which can easily be made equal to the required deflecting voltage. The efiect is exactly the same as if the plates were oscillating in push-pull and both plates had a common positive bias increasing with the absolute value of the deflection. This results from the fact that the mean potential of the deflecting condenser varies proportional to and with the same frequency as the absolute value of the potential difference produced by the reverse phase voltages which would appear at the terminals of the secondary winding of transformer 8, if ordinary push-pull operation were used.

The problem can also be solved in a similar way by means of grid controlled thermionic tubes according to Fig. 4. Two amplifying tubes l9 and I 9' are via condensers 20 and 20 coupled with the two deflecting plates I and 2. 32 is the common anode battery of the tubes, 33 and 33' are the anode resistances. The grids of the tubes are provided with grid current limiting resistances 2| and 2| and have no bias voltage. Thus the tubes work as class B-amplifiers and produce exactly the desired deflection voltages. Instead of utilizing the grid currents for cutting off the undesired exciting half-wave a special pair of rectiflers, for exampletwo crystal detectors, can naturally also be included on the secondary side of 8, i. -e., in front of the grids of the tubes. in which case the tubes, as normal class A-amplifiers, would then have a purely amplifying function to perform.

A disadvantage of this circuit is that associated with all class B-ampliflers consisting in the fact that in the vicinity of the zero point of deflection there is a departure from the linearity, which can only be avoided with difficulty by careful biassing and the selection of equal tubes. This comparatively harmless zero anomaly in the case of sound amplifiers can be intolerable in television.

The circuit system shown diagrammatically in Fig. 5 and more detailed in Fig. 7 is free of this disadvantage. The deflecting plates are again connected with the secondary 8 of a relaxation transformer the mean point of which, however, is not, as usual connected with the anode 3 directly, a variable bias 1) being included between. The additional voltage 22 must be approximately one-half of the deflecting voltage and traverse a positive maximum twice during one relaxation period.

In Fig. 6 there have been entered the courses of the deflecting voltage (2 and the additional voltage 12. As measurements have shown, the course of 21 requires to be represented, at least in the case of a spherical or plane screen, not by a straight, but by a parabolic curve in order to obtain the best compensation. This fact enables the potential 22 to be produced without the use of rectifying tubes simply by integration of a linear relaxation curve, e. g., by charging a second condenser via a rather high resistance by the voltage of a usual relaxation condenser.

In Fig. '7 there is shown an embodiment of the scheme according to Fig. 5. I6 is the relaxation condenser charged via resistance [1 and discharged by the grid controlled thermionic tube It). The condenser is coupled to an amplifying tube IS the anode circuit of which contains in series the primary coils of the transformers 8 and I2. The transformer 8 for the deflecting voltage at is shunted on the primary side by a relatively low resistance H in order to enable it to yield on its secondary terminals a linear relaxation voltage. The secondary of 8 should have a self-induction which is so small that the natural period of the secondary circuit comprising the deflecting plates and the leads to them is equal to or preferably smaller than the return period of the ray. The transformerl2 for the voltage U is tuned considerably lower than the transformer 8. It has preferably on the primary and secondary side two to three times more windings than 8 and is, like 8, shunted on its primary side by a resistance l3. The exact adjustment of the voltage 11 takes place by varying experimentally the capacity of the integrating condenser !4 or the charging resistance 34. In the case of a 4G0-line image it amounts to approximately 300 m. The voltage arising at the secondary terminals of I2 is already the desired parabolic voltage '1). (The same effect can naturally also be obtained by employing on the primary side a larger condenser.) The secondary terminals of I2 are connected to the anode 3 respectively via a damping resistance 24 of approximately '10 to 10 ohms to the mean point of the secondary of 8 in order to prevent an oscillation of the circuit l3--2 initiated by the return beat and otherwise disturbing the linearity of the deflection.

To enable the transformers 8 and J2 to function independently of each other the tube l5 must be a pentode, 'as otherwise the anode current would be affected by the variable impedances of the transformers and would not be an undistorted reproduction of the purely linear relaxa- *tion potential :resulting cat the storage condens- "81' 1| 6.

Thearrangement described above can be em- .ployedi-alsoin-the case of electrostatic deflection in .both coordinates.

Mixed deflection, however, hasalsobeen found particularly suitable, the slow As comparedwith thetmethod of performing rapid .deflections magnetically, the method according to the invention has .the advantage of requiring aconsiderably.smallerpower input. It'has been carried out up to .angles of approximately 2 25 without any limit having been reached.

The effect of the positive bias of the plates is only suflicient alone if the spacing of the plates does not exceed the thickness of the crosssection of the ray when entering the plates. Even greater angles of deflection can, however, be obtained if, together with the plates, the electronic lens is also controlled by the rectifying potential or by a part of the same in such fashion that the refractive power of the reproducing lens decreases when the angle of deflection increases. This can be performed in the case of both magnetic as Well as electric lenses.

A circuit system for combined plate and lens control is shown in Fig. 8. The linear relaxation potential 23 is amplified by a screening grid tube, preferably a pentode l5. The anode current flows in series through the deflecting transformer 8, which is shunted by the resistance II, The

anode current then traverses a part of the poten-' tiometer 35 the whole resistance of which remains in parallel to the primary of the transformer l2 so that its excitation is able to be adjusted by the slider of 35. By means of the condenser I4 the secondary voltage of I2 is integrated, as described above. At the potentiometer 28 a suitable part-potential, which can be adjusted by observing the effect at the image field, is tapped and is passed via condenser 21 to the lens electrode 26. The lens in this case is shown as an electro-static one. It is furnished via the high resistance 29 with a bias by a tapping on the potentiometer 30 shunting the anode battery 3|. This bias is so chosen that the centre of th picture is sharp.

I claim:

1. In a cathode ray tube arrangement comprising means including a cathode for producing a cathode ray, a screen, means including an anode for focusing said cathode ray on said screen, and means including a pair of deflecting plates for deflecting said cathode ray, said anode being mounted immediately adjacent to said deflecting means at their side facing said cathode and being connected to a source of constant anode potential: means for producing the effect of a common, variable positive bias applied to said deflecting plates with respect to said anode and increasing with the absolute value of the deflection of said cathode ray.

2. In a cathode ray tube arrangement comprising means including a cathode for producing a cathode ray, a screen, means including an anode for focusing said cathode ray on said screen, and means including a pair of deflecting plates for deflecting said cathode ray, said anode being mounted immediately adjacent to said deflecting means at their side facing said cathode and being connected to a source of constant anode potential: means for producing the effect of a com- .mon, variable .positive bias applied -to-said deflectingzplateswith respect to said "anode andincreasing with'the absolute value of the deflection of;sa'id "cathode :ray, said last mentioned means comprising "a circuit connecting the instantaneously negativeof said plates to said anode.

3; In a cathode ray tube arrangement comprising means including a cathode for producing a cathode ray, a screen, means including an anode for focusing said cathode ray on said screen, means including a pair of deflecting plates for deflecting said cathode ray, said anode being mounted immediately adjacent to said deflectingzmeans at their side facing said cathode and being connected to a source of constant anode potential, and a deflecting voltage transformer the secondary winding of which is "connected to said deflecting plates: a circuit additionally connecting each of said plates via a rectifier to said anode so that the instantaneously negative of said plates is raised to anode potential.

In a cathode ray tube arrangement comprising means including a cathode for producing a cathode ray, a screen, means including an anode for focusing said cathode ray on said screen, means including a pair of deflecting plates for deflecting said cathode ray, said anode being mounted immediately adjacent to said deflecting means at their side facing said cathode and being connected to a source of constant anode potential, and a deflecting voltage transformer: a circuit comprising two leakage resistances each connecting one of said plates to said anode, and two thermionic tubes each being provided with cathode, control grid, anode, a high grid resistance and an anode resistance, the cathodes of said thermionic tubes being connected to the mean point of the secondary of sa d deflection transformer, said grids via said grid resistance to th terminals of said secondary, and the anodes of said thermionic tubes each to one of said plates.

5. In a cathode ray tube arrangement comprising means including a cathode for producing a cathode ray, a screen, means including an anode for focusing said cathode ray on said screen, means including a pair of deflecting plates for deflecting said cathode ray, said anode being mounted immediately adjacent to said deflecting means at their side facing said cathode and being connected to a source of constant anode potential, and means for connecting said deflecting plates with a relaxation generator adapted to produce reverse phase deflecting potentials symmetrical to the potential of said anode: means for producing the effect of a common bias applied to said deflecting plates, which is positive with respect to said anode and varies in rhythm with the deflecting voltage built up across said deflecting plates, the peak value of said bias being substantially equal to one half of the peak value of said deflecting voltage.

6. In a cathode ray tube arrangement comprising means including a cathode for producing a cathode ray, a screen, means including an anode for focusing said cathode ray on said screen, means including a pair of deflecting plates for deflecting said cathode ray, said anode being mounted immediately adjacent to said deflecting means at their side facing said cathode and being connected to a source of constant anode D tial, and means for connecting said deflecting plates with a relaxation generator adapted to produce reverse phase deflecting potentials metrical to the potential of said anode: means for producing the effect ofa common bias of linear wave form applied to said deflecting plates, which is positive with respect to said anode and varies in rhythm with the deflecting voltage built up across said deflecting plates, the peak value of said bias being substantially equal to one-half of the peak value of said deflecting voltage.

'7. In a cathode ray tube arrangement comprising means including a cathode for producing a cathode ray, a screen, means including an anode for focusing said cathode ray on said screen, means including a pair of deflecting and being connected to a source of constant anode potential, and means for connecting said deflecting plates with a relaxation generator adapted to produce reverse phase deflecting potentials symmetrical to the potential of said anode: means for producing the efiect of a common bias of linear wave form applied to said deflecting plates, which is positive with respect to said anode and varies in rhythm with the deflecting voltage built up across said deflecting plates, the peak value of said bias being substantially equal to one-half of the peak value of said deflecting voltage, said last mentioned means consisting of a circuit adapted to suppress the plates for deflecting said cathode ray, said anode 5 actually negative wave of said deflecting voltage.

being mounted immediately adjacent to said deflecting means at their side facing said cathode KURT SCHLESINGER.

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