US2227020A - Cathode ray deflecting means - Google Patents

Description

31, 1940- K.'SCHLESINGER 2 CATHODE RA Y DEFLECTING MEANS I Filed Aug. 10, 1937 2 Shee ts-Sheec 1 Dec. 31', 1940. I K. SCHLESINGER 2,227,020 I CATHODE RAY DEFLECTING MEANS Filed Aug. 10, 1957 2 Sheets-Sheet 2 [/70 en far.-

Patented Dec. 31, 1945 PATENT OFFlCE CATHODE RAY DEFLECTING MEANS Kurt SchlesingenBerlin, Germany, assignor, by mesne assignments, to Loewe Radio, Inc.,. a

corporation of-New York 5 Application Augustlii, 1937, Serial No. 158,389

. V In Germany August 12, 1936 1 Claim. (Cl. 250-27) The object of .the present invention is to provide an improved method of electrostatic-ally deflecting cathode rays at large angles in a manner such that any .lack of sharpness of the. image point occurring at the edge of the image is avoided. The method consists in the combination of the deflecting plates with an electrical front lens, this front lens being supplied, by the deflecting potentials, with alternating potential by way of a special integrating coupling which is a'feature of 1 the invention. The front lens then compensates the lack of sharpnessat theedge of the picture. 1

In order that the invention may be fully understood, reference will hereinafter be-made to the accompanying drawings, of which I Fig. 1, showing a pair of electrostatic cathode ray deflectors and a few essential electrode and circuit elements associated therewith, illustrates in a diagrammatical fashion the production of the fault which the invention serves to eliminate,

and also one mode of eliminating this fault,

Fig. 2, being of a similar type as Fig. 1, illustrates a modified way of eliminating said fault,

Fig. 3 is a diagram of potentials plottedagainst time as abscissa and serving to'e'xplain certain considerations involved in the invention, and Fig. 4 shows the essential parts of the electrode system of a cathode ray tube-and the circuits associated therwith and designed according to the invention.

Referring now to Fig. 1, let a bundle of cathode rays I, the thickness of which is comparable with the distance between the two deflecting plates 2 and 3, be supposed to be deflectedupwards. For this purpose plate 2 is maintained positive relatively to plate 3 by an appropriate voltage source or biasing means 4. Let the anode 5 be grounded or assumed to be earthed. The sharpness of the edge of the picture then depends to a very large extent on where the grounding point 6 is connected withthe potentiometer 1.

Case A.-Plate 3 is directly earthed; the plate 2 then possesses the potential e1+ez in relation to the cathode '8, e1 being the anode to cathode voltage and c2 the. voltage between the plates 2 and 3. The electrons then have, in the vicinity of plate 2, a maximum speed, which will be referred to as v+Av, v being the velocity. of the electrons after having been accelerated by the anode to cathode voltage. This applies to the upper stratum i of the bundle; The upper stratum I is, therefore, the least deflected. The resulting focal distance of the system is accordingly the longest when the pulling plate 2 is free and the pushing plate 3 is earthed (see fa in Fig. 1).

Case B.-Pulling plate 2 is earthed, pushing plate 3 is free. The stratum I" then has the speed v-Av. The deflection is stronger than normal. The focal distance is is shortened.

If the earth point 6 is connected to the middle of the potentiometer l (push-pull deflection) the focal error assumes an intermediate value, the focal distance in the case of large-angle deflection beingtoo short and then toolong. According to the invention a remedy against this shifting of the focus is obtained by avoiding as far as possible the speed variation Av. The applicant has experimented with a successful method consistingin the provision of a wire grid it, formed by wires parallel to the plate surfaces and perpendicular to the direction of movement of the electrons, and earthed. A disadvantage, however, of'this method according to the invention resides in a certain reduction of the sensitivity of deflection in the ratio inwhich the penetration of the deflecting field through the wire grid is reduced. Another method consists in increasing the distance between the plates, but is attended by the same disadvantage. The technical object must consist in eliminating the focal displacement without impairing the sensitivity of deflection.

The lack of sharpness at the edge of the images may be eliminated by sharply readjusting the refractive power through an adaptation of the reproducing lens of the electron-optical system in a weakening sense. These alterations to the main lens must be performed, however, in accordance with the varying cathode ray deflection. They must be controlled by the two pairs of de fleeting plates of the tube in a certain manner which is described in connection with Fig. 4. This method of the oscillating lens potential will accordingly be exactly described with reference to Fig. 4 at the end of this application.

Alternatively, the procedure may be such that each deflecting system corrects its marginal error separately. This is achieved according to the invention by the following arrangement (Fig. 2)

The deflecting plates 2 and 3 are operated in push-pull by the deflecting voltage from 4. The rays must traverse, before entering the plate field, a front lens 8 according to the invention. This front lens is connected with a correcting alternating potential e The curves of the potentials are to be seen from Fig. 3. If the potential e3 increasesfrom negative to positive values, whilst the potential 62 is mirror-reversal thereto,

measurement of the potentials e which are required for the adjustment of an evenly sharp image point, results in the peculiar form of curve e as shown in Fig. 3. The marginal unsharpness is negligible in the zone a. In the zones b it appears in a quickly increasingamount, andv must be corrected by positive auxiliary potentials eq. tive in relation to the anode 5, the effect of a dispersion lens, which counterbalances the undesired positive lens eifect of the deflecting plates.

The difficulty now only resides in the simple and technically readily practicable generation of the correcting potential a; from thede'fl'ecting potentials 22 or 63. The applicant has found that the curve of e can be obtained by integrating the curve of an ideal saw tooth relaxation oscillation voltage with positive derivative'with re'- spect to time I Of the two deflecting voltages es and 62, only ea has the requisite positive derivative. The integration of saw tooth voltages is effected in very simple and cheap manner by a chargingresistance I I3 and condenser II. It results in the course e (Fig. 3). In thezone a, the curve e sags into negative ascompared with the intended curve q(Aq). This is unimportant in practice, as the undesirable refractive power of Ae.; is compensated by weakening the refractive power of the main reproducing lens, through simply adjusting the sharpness regulator to give sharpness of the image element at the centre of the image. The time constant depends on the frequency of the deflection. For periods image change it amounts for example, to 1 megohm/1,000 cm. The desired disposal of the curve is preferably adjusted experimentally with the aid of oscillographic observation. If the time constant has the correct value, the resulting curve is symmetrical with respect to the mean potential when the time constants of the charge and the discharge are equal. In practice the resistance I t and condenser I I are structurally united with the deflecting condenser. The resistance will always be of one order larger than the internal resistance of the relaxation oscillation generator 4, whereby a distortion of the actual deflection is avoided.

In the case of tubes having two pairs of deflecting plates the method is employed in exactly analogous fashion, in each of the two pairs or coordinates; only the time constant of the resistor I 0 and condenser II is, in the case of the line scanning deflection, smaller by a factor equal to the number of lines.

The front lens 8 may, alternatively, be provided with a separate lead-in conductor and the correcting potentials may be supplied from the outside by separate potential sources. The stated integration method applies only to deflections of the time base type having a sawtooth curve, 1. e., for oscillographic and television purposes. 'The provision of the front lenses 8 also has the additional advantage that such a lens acts as screening means between the different pairs of plates and the surroundings and thus prevent distortions of the image.

Another very convenient method of overcoming the marginal sharpness error consists in applying suitable alternatingpo-tentials to the electrostatic lens of the tube.

The front lens 8 possesses, if biassed posi-.

The oscillation potential of the lens must then be'such as indicated in Fig. Ii -and.

should act in such a direction that when the image point approaches the edge the refractive power of the lens is reduced. Since the lens is connected with a less positive potential than the anode the lens potential must oscillate into positive, as indicated in Fig, 3. In this case no special deflecting plate constructions are required. A connection system for producing the correct oscillating potential at the lens is illustrated in Fig. 4. The television cathode ray tube is represented diagrammatically by its anode 5, its tubular lens ,memberIi-i and its cathode 8.

It operates with the pairs of deflecting plates 2, 3 for horizontal andZ, v3' for vertical deflection. The deflecting voltag'elsupply is shown by relaxation oscillation transformers I4 and I5, which act in push-pull onthe plates and the middles of which are connected to the anode 5. No special correction lenses are provided in front of the deflecting plates. In place thereof the tubular lens member is blessed from the potentiometer I! by way of a working resistance I6. The integration circuit I0/ I I is connected with that phase of the framing deflection which has a positive At the condenser N there is formed the desired distorted potential curve with positive peaks, Which'is represented in Fig. 3 by e This potential-is coupled by way of a condenser I9 to the tubular member. The time constant of the transmission unit I 6, I1 must be greater than all periods occurring in the operation of the tube.

To be able to perform a corresponding correction also in the direction of the lines a second integration system with correspondingly smaller time constant of the resistor I0 and condenser II may be connected with the corresponding phase having a positive de El and amixture of the two correction potentials may be taken from a potentiometer I8 and impressed on the lens I3. The correct phase is found simply by changing the polarity of the primary Windingof' the transformers I4 and I5.

It is obvious that other methods of coupling betweenthe potential formed at I8 and the tubular member are possible. If the potential is not sufficient, it may be amplified by a resistance amplifier stage or it may be transformed; the deflecting. transformer may, for example, be pro .vided with an auxiliary winding Ida, which suphave the curve form e (Fig. 3), which is readily I possible by causing the potential obtained at I8 to control the grid of an amplifying tube, the anode circuit of which includes the exciting Winding of the magnetic lens.

I claim:

An electric circuit comprising a cathode ray tube having included therein an electron emitting cathode and an anode and a target, means to apply a voltage of predetermined magnitude between the anode and cathode to form the released electrons into a beam and move the beam toward the target element within th tube, a beam focusing electrode intermediate the cathode and anode, means to supply a normally substantially constant voltage to said focusing electrode to cause the electron beam in its normal undeflected state 1 to focus at the plane of the tube target, two mutually perpendicular pairs of deflecting plate electrodes intermediate the tube anode and target, means for applying voltages to each of the pairs of deflecting plates in push-pull to defiect the electron beam to cause it to traverse the target according to a predetermined pattern, the deflection in one direction being relatively rapid and in the other direction being relatively slow, integrating circuits each comprising a series resistor and condenser connected to be energized by the voltage applied to one deflecting electrode of such pair, the integrating circuits having time constants of substantially the same relative order as the ratio of the rapid and slow deflections, a potentiometer having its end terminals connected to like terminals of the condensers of each integrating circuit, and a connection from the variable terminal of the potentiometer to the focusing electrode, whereby compensating voltages of magnitudes proportional to the integrated deflection energy in each of the two directions of deflection are applied through a common circuit to the focusing electrode to alter the voltage thereon in accordance with the beam deflection and thereby maintain the electron beam in focus at the target plane independently 'of the deflected state thereof.

KURT SCHLESINGER.

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