US3794876A

US3794876A - Deflection circuit for an electron beam in a cathode-ray tube

Info

Publication number: US3794876A
Application number: US00284966A
Authority: US
Inventors: Alphen W Van
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1971-09-04
Filing date: 1972-08-30
Publication date: 1974-02-26
Anticipated expiration: 1991-02-26
Also published as: FR2151122B1; JPS4837017A; JPS5520431B2; GB1407223A; DE2243217A1; DE2243217B2; NL7112210A; CA983160A; FR2151122A1; DE2243217C3

Abstract

A deflection circuit for an electron beam formed with an electrode system suitable for both focussing and deflection, which system includes an electrode dividend in segments. The electrode segments are incorporated in a bridge circuit built up from resistors while two deflection signal generators are each connected to two bridge connection points. A focussing voltage source is connected to a central connection point of a bridge cross branch so that the source and the generators are mutually decoupled.

Description

[baited-States Patent 11 1 I 1 1 3, 94,876

Van Alphen Feb. 26, 1974 [5 1 DEFLECTION CIRCUIT FOR AN 3,688,156 8/1972 Utsunomiya 335/213 ELECTRON BEAM IN A CATHODE-RAY TUBE FOREIGN PATENTS OR APPLICATIONS Invento eijnde t an A pha, France 3 l 7 Emmasingel, Eindhoven, Netherlands Primary Examiner-Maynard R. Wilbur [73] Assignee: U.S. Philips Corporation, New Assistant Potenza york, Attorney, Agent, or Fzrm-Frank R. Tr1far1 221 Filed: Aug. 30, 1972 [21] Appl. N0.: 284,966 [57] ABSTRACT 1 A deflection circuit for an electron beam formed with [3O] Fore'gn Application Pnomy Data an electrode system suitable for both focussing and Sept. 4, 1971 Netherlands 7112210 deflection, which System includes an electrode divi 1 1 v dend in segments. The electrode segments are incor- [52] U.S. Cl. 315/17, 3l 5/27 R porated in a bridge circuit built up from resistors while [5l 1 II!!- Cl. H01J 29/70 two deflection Signal generators are each connected to [58] held of searchm' 335/213; 161 two bridge connection points. A focussing voltage 315/171 27 R source is connected to a central connection point of a bridge cross branch so that the source and the genera- [56] References Cted tors are mutually decoupled.

UNITED STATES PATENTS 2,911,563 11/1959 Atti et a1 315/17 7 Claims, 4 Drawing Figures 8 =E R 1 1 I! a 9 51 u, +u v H 18 12 V5 V2 5 7 8 810 2 R2 U 1 B V" V P4 R W1 P P 9 11 i:

vvv v 'b'" 5 6 N P P2 1 Up 17 I :53 S I E- F s S 11. R3 411w 16 k (U -U v2 53 1: v 52 v2 PAIENIEBFEMQQH SHEET 1 0F 3 U 2 0 u 2 R w om V H R W 1 U U B P U 2 Z 3 DU 1 2 S Dina R S m 1 R S D! 9 0 5 6 .l V DH .VT S 300B DI B U- m n "r 1111 S d 1 P P 5 U 8 E A 8 S Rh" R m 5 5 5 P 7 S n R 14 S 3 B H H U i.7 U U W m P LW V R) w m N. U on n. v 4 1 P F G DEFLECTION CIRCUIT FOR AN ELECTRON BEAM IN A CATHODE-RAY TUBE The invention relates to a deflection circuit for an electron beam in a cathode-ray tube, which circuit is provided with an electrode system suitable for both focussing and deflecting the electron beam for which purpose the system comprising an electrode divided in segments is connected to a focussing voltage source and to two deflection signal generators for deflection in two transverse directions relative to the tube axis.

U.S. Pat. No. 2,91 1,563 describes a cathode-ray tube which is formed with a system of electrodes for both focussing and deflecting the electron beam. Since one of the electrodes of the system is divided in segments, different voltages can be applied to the electrode segments. The mean value of these voltages across the electrode segments relative to the voltage across a different electrode in the system determines focussing. The difference between the voltages across the segments yields a field strength at right angles to the axis of the tube so that the electron beam is deflected.

Apart from the extent to which both focussing and deflection according to said patent specification could be effected in a satisfactory manner, which is not quite satisfactory because the specification states that the deflection is only small and can be used for correcting purposes, it is not at all described how the electrode system is to be connected to the focussing source and to the deflection signal generators so as to cause the circuit to fulfil its dual task.

An object of the invention is to provide a deflection circuit with which a satisfactory focussing and a satisfactory deflection can be obtained, while the control of the electrode system is as simple as possible without mutually unwanted influences of the various voltage sources and signal generators.

To this end the deflection circuit according to the invention is characterized in that when a bridge circuit having bridge branches between four bridge connection points is used for the deflection, of which points each facing pair is connected between two connection terminals of each different deflection signal generator and in which the branches include resistors and further connection points focussing is effected by providing at least a cross branch formed with resistors and connection points in the bridge, which cross branch has a central connection point for connection to the focussing voltage source.

It is to be noted that it is known per se from French Patent Specification No. 1.368.473 to supply an electrode system composed of bar-shaped segments and being solely intended for the deflection, from a bridge circuit formed with bridge branches between the four connection points and being provided with resistors and connection points. In this case, however, the problem of focussing to be performed in a combined manner does not at all occur.

The application of the focussing voltage according to the invention to a symmetry point made through the cross branch or branches has the result that ever present segment leakage currents do not cause asymmetrical errors.

The invention will be further described with reference to the following Figures as examples in which FIG. 1 diagrammatically shows a cathode-ray tube, which is provided with a system of electrodes for both focussing and deflecting and with control means therefor,

FIG. 2 shows a schematic circuit diagram of the control means formed according to the invention, suitable for use with an electrode divided in eight segments.

FIG. 3 shows, likewise as FIG. 2, a bridge circuit with which deflection error corrections can be performed, and

FIG. 4 shows, likewise as FIG. 2, a bridge circuit which is suitable for use with an electrode divided in six segments.

Corresponding components in the various Figures are denoted by the same reference numerals in so far as this is useful.

FIG. 1 shows a partial diagrammatic cross section of a cathode-ray tube K,. A so-called target plate is denoted by K in tube K,. The target plate K is scanned by an electron beam not shown which is generated by an electron gun K K, denotes a tube axis of the tube K,. In order to cause the electron beam to scan the target plate K while being satisfactorily focussed, a system of electrodes E consisting of three electrodes E,, E and E is provided. The electrode E, is divided in eight segments S, S, some of which are shown in FIG. 1. In FIG. 2 all segments S, S of the electrode E, are shown in a cross-section which is at right angles to that of FIG. 1. The electrode segments S, S,, are

. located on the circumference of a circle along the wall of the tube K,.

FIG. 1 shows that a voltage U, is applied to the electrodes E and E,,, which voltage is supplied by a direct voltage source (u) denoted by D The electrodes E and B, may alternatively receive different voltages. In case of a more positive voltage across the electrode E the electrons are accelerated between the electrodes E and E3.

The eight segments S, S of the electrode E, are connected to a cable L provided with eight leads L, L All eight leads L, L, are connected to a resistive network N Two deflection signal generators denoted by G and G are connected to network N which generators provide voltages U H and U respectively, varying in accordance with a sawtooth function. Some leads, namely L,, L L, and L, are connected to a resistive network N to which a direct voltage source D applies a focussing voltage Up.

The difference between the voltages U, and Up determines focussing of the electron beam. If the voltages U,, and Up were equal, focussing would not take place and the electrodes E and B, would only be operative as anodes. A satisfactory focussing may be obtained, for example, with U, 500 V and U V.

For obtaining the deflection of the electron beam a voltage +U and U,, is impressed on, for example, two segments such as S, and S, which are pairwise located and face each other relative to the tube axis K.,, which voltage U has a sawtooth variation with an amplitude of 50 V peak-to-peak. The combination of focussing and deflection then results in, for example, the segment S, conveying a voltage of 100 25 V and the segment 8, conveying a voltage of 100 25 V.

The cathode-ray tube K, according to FIG. 1 is operative with its target plate K which is formed, for example, with photosensitive material, as a television camera tube in which a scene to be picked up is displayed through an objective lens not shown on the target plate K Any other embodiment of the tube K, is possible. The electrodes 15,, E and E shown in the electrode system E may alternatively exchange positions.

In the description of FIG. 1 it has not been shown in detail how the control means shown outside the tube K, are active and particularly not how the electrode E, is controlled; FIG. 2 serves for this purpose. FIG. 2 shows that the resistive networks N and N of FIG. 1 are formed as a combined bridge circuit N. In the bridge circuit N the reference R denotes resistors, B denotes branches and P denotes connection points. P,, P P and P, denote four bridge connection points with the points P, and P and P, and P.,, respectively, facing each other being connected to two connection terminals and of the deflection signal generators G and G respectively. Bridge branches B,, B B and B are provided between the points P, and P P and P P and P P, and P,, respectively, which branches are each provided with two resistors R in series denoted susccessively by R,, R R R The bridge circuit N according to FIG. 2 is provided with two cross branches which are located between points P, and P and P and P,,, respectively, and are denoted by B and B The branches B and B are each provided with four resistors in series R R,, and R R respectively. The branches B, B are provided with connection points P at the areas where two resistors R are connected together. Thus connection points P,,, P,.,, P, and P,,, of the branches 3,, 8-,, B, and B, are connected to the segments 8,, 8,, S and 8,, respectively. Two connection points P,, and P of branch 8, are connected to the segments S, and S respectively, while two connection points P,, and P of branch B are connected to segments 5,, and S,. Central connection points P and P of the branches B and B are connected together and are connected to the connection terminal of the focussing voltage source D which provides the focussing voltage U!)- It is found that the network N according to FIG. 1 corresponds to the resistors R,,,, R,,, R,., and R, of the bridge circuit N. The remaining resistors R of the bridge circuit N are incorporated in the network N The bridge circuit N ensures that a required combination of the voltages provided by voltage source D and by one or both signal generators G and Gy is impressed on each of the electrode segments S, S while the source D and the generators G and G do not influence each other without extra steps being necessary therefor. By connecting source D, to point P P,,, the focussing voltage Up is impressed as a bias on the bridge circuit N, which voltage thus reaches all segments S, 8,, through the resistors R, R Relative to the focussing (bias) voltage 'lUp, the generators G and G decoupled through the bridge circuit N provide sawtooth varying voltages V,, and U whose mean value corresponds to the voltage U The following apllies for the value of the voltages which are to be impressed on the electrode segments S, S, located on the circumference of a circle in FIGS. 1 and 2 in order to obtain a deflection of the electron beam in the tube K, of FIG. 1 as linearly as possible. The starting point is a deflection of the electron beam in which the landing spot on the target plate K, as seen from the axis K, in the tube K, writes a line from the right to the left and in which a television raster corresponds to a deflection from the top to the bottom. Seen from the outside of the tube K, the deflection ofa raster thus commences in the top-left corner of the target plate K,. It is assumed that in order to deflect the electron beam landing spot to the top, a voltage +U,/ across the segment S, is required and U across segment 5,, is required. For the deflection to the right there follows that a voltage +U across the segment 8,, is required and U,,, across segment S, is required.

For obtaining a satisfactory linear line deflection in which distortion is left out of consideration the segments 8,, S4, S and SB located on the circumference of a circle are provided and a combination of the voltages U and U is to be impressed on these segments. Calculated from the centre of the circle (at the area of P P of the bridge circuit N) towards, for example, the

centre of segment 5,, an angle of 45 relative to the branches B and B is associated with 'the segment S, and a deflection voltage of U, /2 and U,,/ 2 corresponds thereto. For the combination there applies that U,,+ UH)/ 7 Generally there applies that for an angle (1) between the branch 8, and a direction which varies clockwise, the deflection voltage at that area has the function: U cos 15 U sin 4) l Taking the given polarities of the voltages U and U into account, the

deflection voltages shown in FIG. 2 follow for the segments 8,, S and S In order to realize that the point P,, of branch B, of bridge circuit N connected to segment S conveys the voltage (U u)/ 2 the voltages U VIE and U 2 are to be impressed on the bridge connection points P, and P respectively. In fact, when it is assumed that no voltage from generator G is impressed on point P and that resistors R, and R have equal values, the resistors R, and R, operate as a divide-by-two circuit so that the voltage across point P, must be twice the voltage Uy/ V2 Thus there follows that U, U,-

2. A similar reasoning yields for generator G U,, UH

It is found from the foregoing that the resistors R, and R are equal and may have a value of, for example, k.ohms. The same applies to resistors R R Resistors R and R,,, must have a value such that a voltage division from U \/2 to U, is effected, hence R R 1: V2-l When resistor R,,, is given a value of 65 k.ohms, approximately 27 k.Ohms is the value for resistor R,,. For reasons of symmetry there follows for the cross branch 8,, that R R,, and R R,,. A similar reasoning applies to resistors R R in the cross branch B with R,, R 27 k.ohms and R,., R

= 65 k.ohms.

The focussing voltage +U is impressed onall electrode segments S, S, with the aid of the bridge circuit N and each segment separately receives a different deflection voltage without any mutual unwanted influence taking place. The position of the generators G, and 6,, may be interchanged without further steps. The bridge circuit N ensures in its simplicity a satisfactory focussing and deflection when the electrode system E and the electron gun K, as such do not cause deflection errors. Due to, for example, symmetry errors in the configuration of the system E and the gun K, relative to each other and to the tube axis I(.,, noticeable deflection errors may occur in practice. FIG. 3 shows a bridge circuit N in which some deflection error corrections can be performed while there are no principal deviations relative to the bridge circuit N according to FIG. 2.

In FIG. 3 two cross branches B and B are provided beyond the bridge branches B B. and the two cross branches B and B6. The cross branches B and B provided between the connection points P and P of the bridge branches B and B and P and P respectively, of the bridge branches B and 8, include two resistors R and R and R and R respectively. Thus the segments S S S and S are connected to both a bridge branch B B B or B and to a cross-branch B, or B Unlike the bridge circuit N according to FIG. 2, the points P and P in FIG. 3 are not directly connected together but are connected together through a potentiometer R Furthermore the points P and P are connected together through two series-arranged resistors R and R while the junction of resistors R and R is connected to ground through a resistor R Branches B and B have connection points P and P respectively, between the resistors R R and R R As described with reference to points P and P 21 ptentiometer R two resistors R and R in series and a resistor R to ground are provided near points P and P The wipers on potentiometers R and R are both connected to the output terminal of the focussing voltage source D The potentiometers R and R form part of a bridge circuit R R R and R R R respectively.

Since the potentiometers R and R produce a similar effect, this effect will be described with reference to the potentiometer R When the wiper on potentiometer R occupies its central position, points P and P convey the same positive voltage which is active as a focussing voltage. Relative to this focussing voltage of, for example I00 V, the points P and P convey, for example, a more positive and a less positive voltage, respectively, of 25 V which are brought about by voltages +U and -U The same applies to, for example, points P and P which under the influence of the voltages +U' and 'U,, convey the voltages 125 V and 75 V respectively.

When the wiper on potentiometer R is moved towards point P the result is that the voltage across point P increases and the voltage across point P decreases by the same extent. It is assumed that a variation of 2.6 V is present, hence a voltage of 102.6 V at point P and a voltage of 97.4 V at point P Assuming that there applies in FIG. 3 that R R R R 68 k.ohm and R R R R 50 k.ohm, there follows that the voltage increase of 2.6 V across point P yields a voltage increase of 50/50 68 X 2.6 1.1 V across both points P and P due to the voltage division across the resistors R and R and R and R respectively. For points P and P a voltage decrease of 1.1 V follows. The result is that the segments S, and S and S and S which prior to the displacement of potentiometer R corresponds to two equal electrical poles of opposite polarity have now acquired an extra positive and negative pole, respectively. This corresponds to a constant electrical quadripolar field which is superimposed on the two deflection fields varying in accordance with the sawtooth function. Such an electrical quadripolar field produces a given distortion of the electron beam landing spot on the target plate K in the tube K, according to FIG. 1 dependent on the intensity and the polarity, hence the extent and the direction of the displacement of the wiper on potentiometer R This distortion caused by'the quadripolar field corresponds to the static astigmatism caused by tolerances in the tube K so that its correction is possible by causing the quadripolar. field to produce an equally large, oppositely directed distortion.

It is found that the potentiometer R of FIG. 3 generates a quadripolar field as a function of the displacement from the centre, while the polar axes of this field are located in the direction of the segments 8,, S and of the segments S S (FIG. 2). The intensity of the quadripolar field and the polarity is dependent on the magnitude and the direction of the displacement of the wiper on potentiometer R To realize an error correction which is performed in an entirelt correct manner it may be desirable to modify also the direction of the polar axes of the quadripolar field. To this end the branches 8, and B and the bridge circuit R R R are provided in FIG. 3. In the same manner as described with reference to potentiometer R a second quadripolar field with the polar axes in the direction of the segments 8 S and S S can be generated therewith (FIG. 2). By superimposition of the two quadripolar fields having 45 shifted polar axes, any quadripolar field for which given polar axis directions are required may be realized dependent on the direction and the extent of the displacement of potentiometers R and R It is found that the potentiometer R and the resis tors R R and R constitute a distributing circuit R R with which the focussing voltage across points P and P may be made different, while the mean value remains the same. There is also a distributing circuit R R By giving the resistors R and R unequal values, whereas the others have equal values, a voltage may occur between points P and P which is different from the voltage occurring between points P and P in case of an equally large displacement of the wipers on the potentiometers R and R The distributing circuits R R and R R then have a difference in sensitivity.

The provision of the cross branches B and B according to FIG. 3 has a further advantage when a correction is required for a barrel or pincushion distor tion which may occur in a raster shown on the target plate K of FIG. 1. For reasons of symmetry one and the same value of, for example, 68 k.ohms has been taken for resistors R, R R R and R As already de scribed a value of 50 k.ohms has been taken for resistors R R R and R It follows from calculations that the voltages given in FIG. 2 occur in the segments S if the resistors R R likewise have a value of 50 k.ohms. By taking a value differing from 50 k.ohms for resistors R R the voltage across the segments S S and S 5,, may be modified in such a manner that the distortion which becomes clearly manifest in the corners near the segments S S S and S is influenced. In case of pincushion distortion the deflection near the corners is to be attenuated relative to the linear deflection i.e., the segments S S S and S are to receive less voltage which may be satisfied by giving the resistors R R a lower value than resistors R R R and R The opposite applies in case of barrel distortion.

It will be evident that not only the described static corrections but also dynamic deflection error corrections are possible. These corrections may be dependent for image field curvature and anisotropic astigmatism on the deflection voltages U v and U,,, and may comprise sum and difference terms or product terms of the deflection voltages. Such corrections may be applied as voltages superimposed on the focussing voltage between the points P and P and P and P FIG. 3 shows that dependent on a given construction of, for example, the deflection signal generator G a provision may be included to cause a direct current to flow through the branches B B and B, of the bridge circuit N for shift purposes in the vertical direction. The generator G, in FIG. 3 is formed with two generators G and G which are connected to ground with terminals of opposite polarity, while the remaining terminals are connected with respect to alternating current through capacitors C, and C to the bridge connection points P, and P A series arrangement of two resistors R and R is arranged in parallel with the generator G, to whose junction the voltage U is applied. A direct voltage source which includes a direct voltage source D and a potentiometer R is connected in parallel with resistors R and R A displacement of the wiper on the potentiometer R;,, which is connected to the resistor R provides the shift direct current through the branches B B and B A direct current is not produced by the bridge circuit configuration in the branch B, as is evident in a simple manner from FIG. 2. By connecting in a similar manner an adjustable direct voltage source (D R R in parallel with the bridge connection points P and P.,, a horizontal shift direct current through the branches B B and B may be obtained while no direct current is produced through branch B Instead of the embodiment of the adjustable direct voltage source D R R shown the required direct voltage may alternatively be derived directly from the focussing voltage Up.

FIG. 3 shgwsth atcapagitors Q C, are arranged in parallel with the resistors R R R,,, R R, and R,,,. These capacitors C C are not principally required for the invention, but they are to be provided when, as is shown in FIG. 1, the cable L is used. The leads L, L, of the cable L have their own capacitance which together with the capacitance of the segment S connected thereto in tube K, may yield a composite capac itance of approximately 50 pF. Since as shown in FIG. 2 the generator G provides a low frequency sawtooth voltage of, for example, 50 or 60 Hz for the deflection in the vertical direction, the influence of the composite capacitance at this low frequency is negligible. This, however, does not apply to the line deflection in the horizontal direction to which end the generator 6,, provides a high frequency sawtooth voltage of 15625 or 15750 Hz. Since the composite capacitance of the lead L, and of the segment 8, is present in parallel at the bridge resistor R,., and calculated for example from point P,,,, the capacitor C-, is to be arranged in parallel with resistor R,,, for the sake of a satisfactory bridge equilibrium. The same reasoning applies to all capacitors C C In that case there applies that the said composite capacitors per segment S and the associated lead of cable L need not all have the same value so that the capacitors C C, are to be adapted and may for this purpose be formed in an adjustable manner.

For obtaining a low dissipation in the bridge circuit N it is favourable to give the resistors R, R a high value. The result is that charging and discharging of the said composite capacitors is effected through a long RC-time constant. For the sweep in the high frequency sawtooth voltage U' the time constant does not provide difficulties, but in case of a short-lasting flyback discharging of the said capacitors cannot be effected as fast as possible. For realizing a sufficiently fast discharge of the capacitors the use of capacitors C C is most desirable.

If the cable L of FIG. 1 were to have a negligibly low capacitance or if it were absent because, for example, the bridge circuit N shown in FIG. 2 is provided in an integrated form on or neae the tube I(,, capacitors C, C of FIG. 3 could be omitted.

In case if integration of the resistors R of the bridge circuit N they may be provided in or outside the tube K, on its wall near the electrode E,.

FIG. 4, likewise as in FIG. 2, shows a bridge circuit N which is, however, suitable for use with an electrode E, which is built up from six segments S. As compared with FIG. 2 it is found that the segments S and S, are omitted and the remaining six segments 5,, S S S S and S, as seen along the circumference of a circle have a longer form. Since the segments 8,, and S of FIG. 2 are absent, the cross branch 8,, is likewise absent.

Calculated from the centre of the circle which corresponds to the connection point P of the cross branch 8,, to which the focussing voltage U, is applied an angle 4) of 60 (point P, is associated with segment S in FIG. 4.

In this case the angle d) relates to formula (1) given with reference to the description of FIG. 2. Angles which are an integral multiple of 60 are associated with the subsequent segments 5,, S S and 8,. While using the manner shown in FIG. 2 of calculating the required various voltages in the bridge circuit N at which the voltage U is fictitiously present, because the segments 8,, and S, are absent in FIG. 4, it follows for the segment 8, that: U cos 60 U sin 60 /2U,- /zU,,. n. By drawing a tangent in point P,,, to the circumference of the circle on which the segment S2 is located, the voltages can be calculated which are to be impressed on the points P, and P so as to obtain the desired voltages across the segments S. Starting from +U on segment S, a voltage of +U 2 U follows for point P,. When assuming the fictitious voltage +U to be present at the area between the segments S and 8,, it follows for point P2 thaiiy 2 y/ 3 AS shown in FIG. 2 the voltages across the other points P are found in FIG. 4 by including the and polarities.

Since the bridge branches 8,, B B and B, are identical, two resistors are denoted by R and R of the bridge branch B, only. Since the cross branch 3,, is identical on either side of point P two resistors are denoted by R and R which are located between the points P,, P and P Since the resistors R are to have a ratio which is the same as the length of the line sections of the bridge circuit N in which they are shown it follows that R R and it follows from R R vsa 1/ fithatR 3 R,,,,.

In the manner as described in FIGS. 2 and 4 the required ratios of the resistors R in the bridge circuit N can be calculated in a simple manner, dependent on the number of segments S of the electrode E,.

Likewise as in FIG. 4 the segments S, and S of FIG. 2 are absent, the segments S, and 8;, might be omitted in FIG. 2 although the deflection will be effected less linearly even when enlarging the remaining segments 5,, S S and S Dependent on the imposed requirements this may be allowed. When the segments 5,, S.,. S, and S, are present the cross branches B, and B, are

omitted and instead the cross branches B-,- and B P P and P P The focussing voltage U is again applied to the central connection points P and P in this case.

As compared with a conventional arrangement of four deflection electrodes located in the two transverse deflection directions which correspond to the use of only the segments 8,, S S and S according to FIG. 2, the use of only the segments S S S and S which are located between the said deflection directions has the advantage that at the area where the greatest problems for a linearly varying deflection field occur, namely in the corners, the presence of the segments at that area reduces the problems.

What is claimed is:

1. An electrostatic deflection and focussing circuit for a cathode ray tube including a plurality of opposite electrode segments symmetrically arranged about a central axis, comprising in combination, a bridge circuit having two pairs of opposite junctions connected to assigned pairs of electrode segments, two sources of deflection signals each connected to a pair of said junctions, a crossed connection of four resistances having a common point and four terminal points connected to said junctions, respectively, and a source of a focusing voltage having a terminal connected to said common point.

2. A circuit as claimed in claim 1, characterized in that a distributing circuit to which the focussing voltage source is connected is provided between the common point of the said crossed connection, which distributing circuit causes an inequality in the voltages applied to the common point.

3. A circuit as claimed in claim 2, characterized in that the distributing circuit is formed with a bridge circuit including a potentiometer which is arranged between the said common point, while a wiper on the potentiometer is connected to the focussing voltage source.

4. A circuit as claimed in claim 1, charachterzied in that a deflection signal generator having output terminals coupled by capacitors to the bridge junctions and an adjustable direct voltage source connected in parallel to said junctions for supplying a shift direct current.

5. A circuit as claimed in claim 4, characterized in that capacitors are arranged in parallel with the resistors which are connected to those bridge junctions and are connected to the deflection signal generator which provides a volrage of a higher frequency.

6. A circuit as claimed in claim 1, characterized in that the bridge circuit is provided with resistors in integrated form mounted on the cathode ray tube.

7. A cathode-ray tube provided with a deflection circuit as claimed in claim 6, characterized in that the resistors are provided in an integrated form on the wall of the cathode-ray tube.