NO130137B - - Google Patents

Description

Photo tube for television in three colours, with deflection coils.

The invention relates to a picture tube for

television in three colours, with deflection coils and an approximately flat and perpendicular to

tube axis vertical screen, three electron beams originating from three electron sources arranged at the corners of a three-edge lying in a parallel plane

with the image screen and lies opposite this, as the electron beams can be deflected in half

approximately perpendicular to each other standing

directions.

As you know, for color television purposes the three beams are controlled so that each

beam hits a specific phosphor element,

which is placed on or behind the image screen,

as each element lights up with a different colour.

This happens with the so-called mask tubes

in such a way that the three rays pass through an opening in the mask at mutually different angles of incidence and thereby hit

point-shaped on a plate lying behind, on which blue, red and green are placed

phosphorus elements. By picture screen is understood

here the above-mentioned mask that must

is hit by the three rays in approximately the same place. It is known that although there

using static convergence it is ensured that

the three rays hit the mask in just one

place, when no deflection current flows

through the deflection coils, the beams by deflection cannot cover in any way

each other on the mask as a result of occurring imaging errors.

With known systems, this disadvantage is overcome by using dynamic

convergence, so that using extra

deflection coils and additional convergence

currents, each individual beam is affected regardless of the degree of deflection, so that the three beams are always brought to cover each other on the mask. In this case, three separate convergence couplings and three additional deflection coil sets must therefore be arranged, which is expensive and difficult to set.

It has therefore already been proposed to produce picture tubes where the three electron sources lie in a plane containing the tube axis, and the deflection of the three rays takes place in one of the two directions parallel to this plane. In this way, it is possible with correctly constructed coils to have the three electron beams approximately cover each other over the entire mask of the picture tube. Such an arrangement of the electron sources, however, means that the configuration of the plate behind the mask, which is equipped with the phosphor elements, must be such that the image that is reproduced has a line-like structure, and that the space in the neck of the picture tube must also be larger than usual when three electron sources are arranged at the corners of an equilateral triangle.

The picture tube according to the invention eliminates this disadvantage and is characterized by two of the three electron sources lying in a plane that is parallel to the deflection direction for which the meridional picture plane approximately coincides with the picture screen, and that by means of dynamic convergence, i.e. by means of an additional deflection coil and deflection current, which is exclusively exerted on the electron beam produced by the electron source which lies outside the plane in which the two other electron sources lie, this electron beam is brought during the deflection over the entire screen into coverage with the other two electron beams on the screen, the latter electron beams being brought to cover each other on the screen in that the said image planes coincide with the image screen regardless of the degree of deflection.

An embodiment of a picture tube according to the invention will be explained in more detail with reference to the drawing. Fig. 1 schematically shows a deflection system in which the incident locations of the electron beams and the obtained images are shown. Fig. 2 schematically shows an embodiment of deflection coils for deflection in the vertical direction. Fig. 3 shows in curve form the field strength which is achieved by means of the coils in fig. 2. Fig. 4 shows an embodiment of a deflection coil for deflection in the horizontal direction. Fig. 5 shows in curve form the field strength which is achieved by the coils according to fig. 4. Figs 6, 7 and 8 show further embodiments of coils for deflection in horizontal and vertical directions. Fig. 9 and 10 show connection diagrams for connecting the coils according to fig. 7 and 8.

In fig. 1 shows a right-angled coordinate system in which the z-axis coincides with the axis of the picture tube, and the positive z-direction is the direction in which the electrons move, while the x- and y-axes indicate the directions in which the electrons are deflected. In this figure, it is assumed that the electron beams B, R and G originating from three electron sources hit blue, red and green phosphor elements at z = Z0, when they have not yet been deflected. Furthermore, it is assumed that during focusing and static convergence the three rays are adjusted so that they hit the same spot on the picture tube mask, namely the spot x = 0, y = 0, z = Z, when no current flows through the deflection coils.

The points of incidence of the rays at the location z = Zn are in fig. 1 likewise marked with B, R and G, and from this figure it is clear that when calculating with polar coordinates the incidence coordinates in the plane z = Z0 can be written:

The mask is shown schematically by lines 1, 2, 7 and 10 and lies in a plane z = Zs. If the three rays are deflected, then a claim is made

that when passing through the mesh they always pass through approximately only one point, regardless of the degree of deflection.

It is assumed, e.g. that the beam is deflected towards the point x = Xs, y = -Ys, z = Zs. Rays B, R and G must then all pass through this point, but as a result of imaging errors they pass through the points:

If there is deflection in the x-direction, and the error in this direction is brought down to zero (that is, AxR — AxR = AxG = 0), then a line appears instead of a point, and this line is defined as the meridional image or focus line , and the plane in which the meridional focal line lies is called the meridional image plane.

If, on the other hand, deflection in the x-direction causes the error to be reduced to zero in the y-direction (i.e. AyR<=> A<y>H<=> A<y>G = 0), then instead of the point a line arises which is de- defined as the sagittal image or focal line, and the plane in which the sagittal focal line lies is called the sagittal image plane.

Likewise, when the error is reduced to zero in the x direction by deflection in the y direction, this is a sagittal focal line, and with an error equal to zero in the y direction, a meridional focal line.

Thus, in fig. 1, for the sake of clarity, a fourth beam emanating from the point P is also shown, and the situation then becomes as

following. For deflection in the positive x-direction, line 5 is the meridional focal line

(or 5 it is in the meridional picture plane

lying place for the rays B, R, G and P) and 6 is the sagittal focus line (or 6 is the lying place for the rays B, R, G and P in the sagittal image plane) while in the case of deflection in the negative y direction the line forms 8 the sagittal focal line and line 9 the meridional focal line.

One can therefore say:

1. In the sagittal image plane, the focal line lies in the direction of the deflection. 2. In the meridional image plane, the focus line is perpendicular to the deflection direction.

Usually the sagittal and meridional image planes are curved, not coincident surfaces. In the following, it will be demonstrated that when according to the invention for deflection in the x direction, which occurs parallel to the plane in which the red and green electron sources are located, will:

1. the curvature in the meridional image plane is reduced to zero, 2. the meridional image plane is brought to coincide with the mask, and 3. the so-called coma errors are reduced as much as possible.

The red and green rays then hit, regardless of the deflection in the x-direction, always at the same place on the mask, so that only the blue ray has to be brought into coverage with the red and green rays by means of dynamic convergence.

Likewise, it can be demonstrated that when, according to the invention, the deflection occurs in the y direction: 1. the curvature of the sagittal image plane is reduced to zero, 2. the sagittal image plane is brought to

coincide with the mask, and

3. the so-called coma errors are reduced the most

possible.

The red and green rays then hit, regardless of the deflection in the y-direction, always at the same place on the mask, so that only the blue ray with the help of

dynamic convergence must be brought to coverage with the red and the green beam.

When deflected in a magnetic field, so-called astigmatic errors occur which can be determined using the formulas:

(for derivation of these formulas see Haant-jes, J. and G. J. Lubben, Philips Research Report 12, pages 46-48, Feb. 1957). Here, An and Bn (n = 4, 5, 6) are integral functions of the field strength and the deflection, Xs is the degree of deflection in the x direction at the location z = Zs, and Ys is the degree of deflection in the y direction at the location z = Zs.

Z0, Z., r and tp are those in fig. 1 specified coordinates. If one substitutes the incident coordinates for the blue ray in formulas (3) and (4), one finds an aberration of formulas (la) and (2a), namely:

In the same way, by substituting the incident coordinates for the I red and green rays, the other aberrations are found, namely:

If only the deflection in the y direction is considered, then Ys =fj= 0 and Xs == 0, so that formulas (5) and (6) turn into:

From the formulas (5') and (6') it appears that when B5 = 0, the aberration in the x-direction becomes zero, and there is only an aberration in the y-direction. According to the above definition, this is the sagittal focal line, and as the radius of curvature for the sagittal image plane lies in this sagittal focal line, it is given by the formula

and hence

follows that when B5 approaches zero, the sagittal image plane transitions into a flat plane that coincides with the mask of the picture tube.

There is thus again an aberration in the y direction, but this is the same for

the red and green rays, so that these rays, regardless of the value of B4 and Y,, everywhere hit the same place on the mask. When affected by the blue beam in a proportional relationship with Ys2, this beam will likewise hit the same place on the mask as the red and green beams. One can thus manage with a single set of extra placed deflection coils which are flowed through by a parabolic current with image frequency (when Y.. is the deflection in the vertical direction), as the field for this coil exclusively affects the blue beam and is directed parallel to the x-axis.

For the x direction, Ys = 0 and X, ^ 0

so that the aberrations become:

When A4 = 0, the aberration in the x direction is again brought to zero, and despite deviation in the y direction, the red and green rays hit the same point on the mask, regardless of the value of A5 and X,. The blue beam can again be brought into coverage with the red and the blue beam, a parabolic current of line frequency (when Xs is the deflection in the horizontal direction) is sent through another set of additional deflection coils, the field being directed parallel to the x- the axis must be provided by these coils. Since in both cases the produced field is parallel to the x-axis, only one set of extra coils is needed, and through these coils must flow a current that is proportional to both X 2 and Ys2.

Since in this last case only an aberration remains in the y direction, while there is deflection in the x direction, a meridional focal line applies here. The radius of curvature of this meridional image plane in which the meridional focal line lies can

1

is indicated approximately with om = so that also 2 A4

this meridional image plane turns into a flat plane now A4 O, as this flat plane coincides with the mask of the picture tube.

If there is deflection in the x-direction as well as in the y-direction, then everything described above remains valid, but both in the x-direction and in the y-direction an aberration is added as a result of the rightmost term in the formulas ( 3) and (4). This aberration can always be made equal to zero when the term Ac -f- B(i = 0.

In the event of a deflection, so-called coma errors also occur, which can be determined using the formulas:

in that An and Bn (n = 7,8) are integral functions of the field strength and deflection and the other symbols have the same meaning as in formulas (3) and (4).

From (7) and (8) you get that when the blue, red and green beam do not coincide as a result of coma error, this can only be remedied when A7 = As = B- = B8 = 0.

In order to be able to produce the coils that are necessary for this deflection system, the conditions found above must be worked out.

To overcome astigmatism in the y direction, B5 = 0 or:

H, and H,, are coefficients in the power spectrum, where Hx is the field strength in the x direction in the plane x = 0. HIo along the z-axis and between the values Z2 = Zu and Z2 = Z1( has the same sign (here assumed positive) while the sign of Hl2 between the same functions changes as a function of z. Thus z = Zn is the beginning and z., ~ Z, the end of the deflection coil system. k is a proportionality constant and the terms Y and Y' indicate the degree of deflection and variations in this in the y direction and is given by the ratio:

when z = Zn. The first two terms in (9) together give a positive quantity, so that the third term must give a negative quantity. For a positive H^, in the direction of movement of the electrons chosen here, Y is negative, so that the size of the deflection at the end of the coil is then greater, and the size H|2 at the end of the coil must also be negative.

To overcome the astigmatism in the x direction, A4 = 0 or: HIs a coefficient of the power series

where Hy is the field strength in the y-direction in the plane y = 0. For <H>I]o, under the same conditions as for H, n, the sign along the z-axis remains the same (also here assumed positive) and applies under the same conditions as for H, 9, that the sign of HI12 changes as a function z, X and X' being the degree of deflection and its change in the x direction and is given by X = X(z)

The conditions Au + BG = 0 are met when:

= Z0. The first term in (11) gives a positive quantity, so that the second term must give a negative quantity. For a positive Hv, the direction X chosen here is positive, so that HIP at the end of the coil must be positive.

The first two terms give a positive magnitude so that the last two terms must give a negative value.

Now Y and Y_„ are negative at the end of the coil, while Xs is positive. According to the preceding, Hn 2 must be positive there, so that the entire magnitude of the third term is positive. For the fourth paragraph, X and XH are positive, Ys is negative, while H, as explained above, is negative. The fourth term thus gives a negative quantity, and if the sum of the third and fourth terms is to be negative, then | H, 2| > | <H>n 2 |.

To overcome the •coma error, it is necessary and sufficient that the terms A7 = As = B7 = Bs = °-

Now is:

The condition B7 = Bs = 0 can thus never be fulfilled, but a good result is achieved when:

If a function is chosen for H, 2 as shown in fig. 3, then the above-mentioned condition is fulfilled, since H, 2 at the end of the coil (z = Z,) gives a negative value.

A similar progression of the field strength can be achieved with the coil set according to fig. 2. These coils only serve for deflection in the y direction and for deflection in the negative direction must carry a current whose direction is indicated by the arrow. An Hx field is produced as indicated by the formula (10) and an Ht2 field as indicated in fig. 3 and with great approximation you get:

lp, are the sizes shown in fig. 2.

[ q1 — constant, ^ = ip, (z) ].

In the foregoing, it was already noted that if Hj 0 is positive, so that when H,, must correspond to that in fig. 3 form shown, must h,>0 in the vicinity of z = Z0, while hj<0 in the vicinity of z = Z1; while ht = 0 for z midway between Z0 and Zv The latter condition is fulfilled when a|>, = 30°.

When z — >. Z, is ip, > 30° and for z near Z0 \ pl < 30°.

In a similar way one finds of

that the condition A7 = As = 0 cannot be fulfilled, but it is sufficient when:

In addition, a function must be selected for HII2 according to fig. 5, and then the latter's integral becomes zero, and furthermore, Hn2 at the end of the coil (z = Z,) gives a positive quantity.

That in fig. 5 showed the course of the field strength

is achieved with a coil set according to fig. 4.

For this coil set, the same applies as for the coils in fig. 2. An Hv field according to formula (12) and an HTI2<-> field according to fig. 5 and then applies with great approximation: where qu and are the sizes shown in fig. 4. The conditions are met when

Here i|j„= 30° applies in the middle,

\|j„ < 30° when z^ Zl and ipn < 30° for z near Z0. At the same time, the condition I H, 2 I <>> I H„ 2 |, which is achieved when at approximately equal H, 0 and Hn0, the angle ip, and \\ >n is chosen so that | h| > | Mr. |

For the sake of completeness, it should be noted that the shape of the coil halves depends on the radius q, the length of the coil Zl - Z() and the distance to the mask Z, - Z0.

If one calls ip, at the site Z0 for \\ >n and at the site Z, for i|)r 2 and the angle \ pn at the site Z0 for \ pu t and at the site Z2 for y u 2, then each coil half gets for the vertical of -bending (the y direction) at a distance Zs - Z0 = 44 cm from the tube screen, the dimensions:

Z, - Z0 = 12.5 cm; q, = 3 cm.

ip, ! = 11°30'; ap, 2 = 36°30'.

And for the horizontal (x direction) becomes:

Z, - Z0 = 12.5 cm; g„ = 3 cm.

aj,, = 34°30'; ap,,, = 27°30'.

A further embodiment is shown in Figures 6, 7 and 8.

In these figures, 11 and 12 denote ferromagnetic, ring-shaped cores which are threaded over the neck of a picture tube, not shown, and on which the coils 13-20 are wound toradially, and serve for deflection in the vertical direction, and the coils 21-28 serve for deflection in horizontal direction. The ring 12 is located at a shorter distance from the screen than the ring 11. In fig. 6, the z-axis is also the axis of the picture tube and only the coils 13, 14, 17 and 18 are shown with solid lines, while the coils 21, 22, 25 and 26 are shown with dashed lines.

In fig. 7 and 8 are cross-sections of the cores 11 and 12, and in these cross-sections the orientation of the coils and the directions of the current are shown.

Thus (x) indicates that the current there flows in the direction of the positive z-axis, while (.) denotes that the current there flows in the direction of the negative z-axis.

The formulas also apply to these coils:

where aj) is half of the acute angle between two coils with the same current direction.

In fig. 7a is ap, ^ = 25° and in fig. 7b is ap, 2 = 43°, while in figures 8a and 8b the various angles are indicated by ap,, = 33° and ap„ 2 <=> 20°.

For these values, the condition h, j > I h„ I is again fulfilled, and the functions H, g and H|,2 are obtained as shown in figures 3 and 5. Since the cores 11 and 12 contain all coils, for this deflection system g , = g„ = q, where g is the mean radius of the nucleus.

A possible connection method for the different coils for deflection in the vertical direction is shown in figures 9 and 10.

In fig. 9, the coils 13-16 placed on the core 11, like the coils 17-20 placed on the core 12, are connected in series. The two series connections are connected at the lower end to the clamp 32 and at the upper end via a variable inductance 30 connected to the clamp 29.

By displacing the core 31, the saw-tooth current supplied to the clamps 29 and 32 can be arbitrarily distributed between the two branches. Of course, the connection of the coils must be such that the current direction in each part has the correct sign in the direction of the z-axis. The coil 30 must be arranged in such a way that it does not affect the beam deflection.

In fig. 10 shows another connection method for the same coils. Here the two series connections are connected in series, with an outlet between the coils 16 and 17 via a wire 36 being connected to an outlet on the variable inductance 34. The sawtooth current is supplied to the terminals 33 and 37 and by displacement of the core 35 the current can arbitrarily distributed to the different branches, so that the correct number of ampere turns is provided in each branch.

The connection of the coil sets for deflection in the horizontal direction can be done accordingly in both cases.

It should be noted that in the present example the red and green beams are always brought to cover each other, and the blue beam is affected by means of dynamic convergence. However, it is obvious that two other beams can also be brought to cover each other in accordance with the arrangement of the deflection coils. It is only necessary that the deflection in one of the two directions occurs parallel to the plane in which two of the three electron sources are located.

Furthermore, it is obvious that when errors in the x-direction cannot be brought completely to zero, dynamic convergence must also be used for red and green beams. In that case, however, three additional deflection coils are needed, but the energy required for convergence of the red and green beam can be considerably less than when the deflection coils according to the invention are not used.

Claims (6)

1. Picture tube for television in three colours, comprising deflection coils, a picture screen that is approximately flat and perpendicular to the tube axis, and three electron sources arranged in the corners of a triangle, with the plane of the triangle parallel to the picture screen and lying opposite it, the electron beams being deflected in two directions which are approximately perpendicular to each other and so that for the two deflection directions the meridional or the sagittal image plane approximated together with the image screen, k a r a k- t e r i s e r t in that two of the three electron sources lie in a plane that is parallel to the deflection direction for which the meridional image plane approximately coincides with the image screen, and that by means of dynamic convergence, i.e. by means of an additional deflection coil and deflection current, which exclusively is exerted on the electron beam produced by the electron source which lies outside the plane in which the two other electron sources are located, this electron beam is brought during the deflection over the entire screen to overlap with the other two electron beams on the screen, the latter electron beams being brought to cover each other on the screen in that the aforementioned image planes coincide with the image screen regardless of the degree of deflection. 2. Car tubes with deflection coils according to claim 1, where the tube axis approximately coincides with the Z axis in a right-angled coordinate system and where the deflection occurs in the directions of the X and Y axes, the plane in which two of the three electron sources lie is parallel with the X axis, and where the y components of the deflection field when deflected in the direction of the X axis and measured in the plane x = 0, are given by the power series: while the x components of the deflection field when deflected in the direction of the Y axis and measured in the plane y = 0, is given by the power series as the coefficients H, 0 and Hu 0 have a positive sign, and the coefficients Ht2 and H„ 2 have a z-dependent sign, characterized in that the value of given by the coils for deflection in the direction of Y- axis, is predominantly negative in one of the coils facing the screen, and predominantly positive in the opposite end of the coils, and that the value of which is given at the coils for deflection in the direction of the X-axis, likewise at the end of the coils facing the screen is predominantly positive and predominantly negative at the opposite end of the coils, so that at the end of the coils facing the screen is both for one and for the other deflection field, the integrals: is approximately equal to zero, Zn being the coordinate for the end of the deflection coils facing away from the screen, and Z„ denotes the screen's position in the coordinate system. 3. Photo tube according to one of claims 1 or 2 with a deflection coil system comprising a first pair diametrically opposite each other, coil halves lying around the tube neck for deflection in a direction parallel to the plane in which two of the three electron sources lie, and an approximately 90° in relative to the first pair of turns, lying around the pipe neck, another pair of diametrically opposite coil halves for deflection in a direction approximately perpendicular to the first-mentioned direction, characterized in that the coil halves in the first pair are so shaped that when they are flowed through by the relevant deflection current , is the size predominantly positive, measured at the end of the coil halves facing the screen and predominantly negative at the opposite end, and that the coil halves in the other pair are shaped in such a way that when they are flowed through by the deflection current for the other deflection direction, the size predominantly negative measured at the end of the coil halves facing the screen and predominantly positive at the opposite end, where rj,, is equal to the radius vector of the first coil pair and \\ >u is the angle between this radius vector and the X-axis, and g , is equal to the radius vector for the second coil pair and \jj, is the angle between this radius vector and the Y axis. 4. Image tube with a deflection system according to one of claims 1 or 2, where the tube neck is surrounded by a first and a second ring of ferromagnetic material and the second ring is located at a shorter distance from the image screen than the first, and where the part of the deflection system for deflection in a direction parallel to the plane in which two of the three electron sources lie comprises a first set of four coils wound toroidally on the first ring and a second set of four coils wound toroidally on the second ring, where further the part of the deflection system for deflection in the other direction comprises a third set of four coils wound toroidally on the first ring and a fourth set of four coils wound toroidally on the second ring, and where each set of four coils is arranged diametrically opposite each other in pairs on the relevant ring, as the deflection currents in two diametrically lying coils in a coil pair flow in mutually opposite directions, and as the Z axis in the aforementioned coordinate system passes through about the center of the rings, characterized in that the first and second sets of four toroidally wound coils produce a field which can be determined by the size that this magnitude is predominantly negative for the first set and predominantly positive for the second set, that the third and fourth sets of four toroidally wound coils produce a field that can be determined by the magnitude: and that this quantity is predominantly positive for the third set and predominantly negative for the fourth set, i|,n being the angle between the radius vector of a coil's center for the first and second sets and the X-axis, and a|,r is the angle between the radius vector of a coil's center for the third and fourth sets and the Y-axis, and <q>{ <=>Qn is the mean radius of the ring. 5. Coupling for a picture tube with a deflection coil system according to claims 1-4, characterized in that a set of further deflection coils are provided which are fed with a first current which is approximately proportional to the square of the current for deflection in one direction, and another current which is approximately proportional to the square of the current for deflection in the other direction, and that the direction of the field produced by these additional coils is approximately parallel to the plane in which two of the three electron sources lie, and that this field exclusively affects the beam originating from the electron source which is not in the plane of the other two electron sources. 6. Coupling according to claim 5, where the deflection in the X direction provided by a sawtooth current with line frequency is the horizontal deflection, and the deflection in the Y direction provided by a sawtooth current with image frequency is the vertical deflection, characterized knowing that the first current through the additional set of deflection coils is a parabolic current with line frequency, and the second current is a parabolic current with frame frequency.