DE1058097B - Multi-beam convergence circuit for color television receivers - Google Patents

Description

The invention relates to color television receivers, and more particularly to arrangements that ensure should that the three electron beams converge at all scanned points of a three-beam picture tube.

Shadow mask type color television tubes typically have three beam generating systems, which are arranged in the tube neck. There are means provided by which it is achieved that the three electron beams converge at the multi-pinhole of the screen when the beams are in the center of the area to be scanned, so that they then all three through the same opening in the center step through the multi-hole diaphragm. After passing through the multi-hole diaphragm, the electron beams hit on three phosphor points, each emitting light of a different color. All three However, beams are deflected by a common horizontal and a common vertical deflector deflected so that the rays sweep symmetrically across the screen, but in the process are Deflection from the center of the screen misaligns or diverges the three beams, if not measures for correction, which are to be referred to here as the »convergence system«. The further the three beams are deflected from the center of the image, the greater the misalignment or Separation of the rays when they hit the multi-pinhole diaphragm. It is therefore common for a dynamic Provide convergence system that correct the misalignment as a function of the deflection of the beams target. For this purpose, currents are generally with the horizontal and vertical deflection circles derived from an approximately parabolic time course and fed to three convergence electromagnets, to keep the three beams convergent at every moment so that it scanned over the whole Step through the same opening in the multi-hole diaphragm.

Circuits to achieve such dynamic convergence require very careful adjustment the amplitude and waveform of the currents involved in order to achieve that at all scanned points of the screen a beam convergence is achieved. With the known institutions this kind of the disadvantage that a readjustment of the convergence conditions for a Part of the screen the adjustment made earlier on other parts of the screen impaired again or completely destroyed. The mutual influence of the individual convergence regulators made adjustment difficult and time consuming.

The invention aims to provide an improved device for achieving convergence in a multi-beam convergence dialing
for color television receivers

Applicant:
Radio Corporation of America,
New York, NY (V. St. A.)

Representative: Dr.-Ing. Ε. Sommerfeld, patent attorney,
Munich 23, Dunantstr. 6th

Claimed priority:
V. St. v. America April 24, 1957

James Conrad Schopp, Merchantville, N.J. (V. St.A.) has been named as the inventor

beam color television tube can be specified, which is constant over long periods and at which adjustments the convergence condition at the edges of the screen an adjustment made earlier the convergence condition in the center of the screen is not affected.

According to the invention, a color television receiver that operates with a three-beam picture tube, the Electron beams are supposed to converge on the screen, provided by a deflection system for deflection which contains electron beams above the screen, furthermore a convergence system that the convergence which maintains three beams regardless of the deflection angle. The convergence system according to the invention contains three convergence electromagnets, devices for generating convergence currents from the 'deflection circuits which are fed to the electromagnets and are essentially parabolic in shape, with the tips of the waves during the retrace intervals of each scan and the minima in the middle of each scan interval lie; Furthermore, the circuit according to the invention contains a level maintenance circuit or clamping circuit through which the minimum of the parabolic wave is kept at a reference potential, whereby the circuit for generation of the waveform can be adjusted so that a convergence at the edges of the screen can be adjusted without affecting the adjustment of the convergence in the center of the screen.

909 528/171

In the drawing means

1 shows an embodiment of a circuit according to the invention,

Fig. 2 is a cross section through the neck of a color television tube, which in connection with the circuit can be used according to Fig. 1,

Fig. 3 is a diagram of the current curve for the horizontal convergence and

4 shows a diagram of the current profile for vertical convergence.

In Fig. 1, the horizontal deflection voltages are supplied by a horizontal deflection circle, which is indicated within the dashed rectangle 10 , and then in currents of substantially parabolic shape in the excitation coils 11 G, III? and 11 B of the three convergence electromagnets 12 G, 12 R and 125 are converted. Pulses and sawtooth voltages are supplied by a vertical deflection circuit, which is indicated within the dashed rectangle 14 , and converted into currents with an essentially parabolic course in the further excitation coils 13 G, 13 R and 13 5 on the already mentioned convergence magnet 12 . The magnets 12 can be attached to the tube neck 15 of the picture tube in the manner shown in FIG. 2, so that they interact with pole pieces 16 located inside the tube and generate corresponding magnetic fields for deflecting the electron beams 17 in radial directions.

The horizontal deflection circuit 10 contains a transformer 16 with the output lines 17 for connecting the horizontal deflection coil of the picture tube. The transformer 16 also has the output terminals 20 and 20 ' for the convergence system. The connections 20 supply a voltage pulse wave to ground which has the line frequency. The output terminals 20 ' supply two voltages in phase opposition with respect to ground.

Between the output 20 and the respective excitation coils HG, IlR and IIB of the three convergence magnets 12 , three circles are switched on for the horizontal convergence. Each of these circuits includes an adjustable inductor, capacitor and variable resistor, all three of which are connected in series, and a connection from the corresponding excitation coil in parallel with the capacitor and variable resistor. The green convergence circle contains the series-connected inductors 21 and 22, the capacitor 23 and the resistors 24 and 25. The red convergence circle contains the inductors 21 and 26, the capacitor 27 and the resistors 28 and 25. The inductors and resistors in the green and red convergence circles are arranged in a type of push-pull or differential circuit to facilitate adjustment of the convergence, the green and red beams being moved towards each other at the same time to establish a point of convergence to which the blue beam is then adjusted. The blue convergence circle is also connected to the output terminals 20 and contains an inductance 31. a capacitor 32 and a resistor 33. Generally speaking, the variable inductances control the amplitude of the wave (30 in Fig. 3) flowing in the respective convergence coils 11, while the adjustable resistors allow the phase, slope or waveform of the coil currents to be adjusted.

The horizontal deflection circuits each contain a switch 35, ie the switch 35 G, 35 R and 355, to selectively connect the respective

Convergence coils 11 to be connected to ground or via the lines 36 to the output connections 20 ' in the horizontal deflection circuit 10 . By the switches 35 G and 35 R , the SpulenllG and III? to voltages of opposite polarity at the terminals 20 ' . This happens when the picture tube used tends to draw a line on the screen as a green and red line with different inclinations, so that it is in the center

ίο of the screen cross. With the switch 355 , one side of the convergence coil 115 can be connected to the terminal 20 ' , which supplies a voltage which is in phase opposition to the voltage applied to the terminal 20. This switchover is made when the blue part of a line has a slope that cannot be compensated for by setting the variable resistor 33.

In each horizontal convergence circuit there is a level maintenance circuit with a resistor 39 G,

ao 39 R or 39 5 and a rectifier 40 G, 40 R or 405 connected in parallel to the corresponding horizontal convergence coil 11. Since the lower connections of the coils 11 are connected by the switch 35 either directly to ground or via the lines 36 and the connections 20 ' to ground, each level holding circuit with the corresponding resistor 39 and rectifier 40 provides a connection between the corresponding coil 11 and a In this way, the level of the parabolic oscillation 30 in FIG. 3 is stabilized so that the central part or the current minimum 42 is at a reference level 43 or the value zero. The value of the resistors 39 is chosen so that the rectifier 40 does not clipping and that the curve shape of the oscillation 30 is somewhat improved by being somewhat flattened in the region 44. The rectifiers 40 can be selenium rectifiers or any other suitable rectifier, such as e.g. B. a crystal diode or a vacuum diode. Selenium rectifiers have the advantage of being cheap and being able to process high currents.

As a result of the stabilization of the central part of the respective convergence current oscillations by the resistor 39 and rectifier 40 in each horizontal convergence circle to zero, the adjustment of the convergence conditions is considerably simplified. In order to adjust the convergence in the line deflection, a measuring transmitter can be connected to the television receiver, which generates the corresponding horizontal and vertical lines on the screen. B. adjustable permanent magnets, which are provided in the receiver, adjusted until all three beams converge in the center of the screen. Normally it will then be found that the three rays diverge from one another to an increasing extent the further one moves away from the center of the screen.

To correct these deviations, ie to achieve dynamic convergence, the adjustment can then be carried out in the following order: inductance 21, push-pull coil 22-26, resistor 25, adjustment resistor 24-28, inductance 31, resistor 33. This shows that in principle the convergence on the right side of the screen is done by setting the series inductance in 21, 22-26 and 31 and the convergence on the left side by setting the parallel resistors 24., 25, 28 and 33. If the convergence then still

Claims (3)

is not completely perfect, the adjustment can be repeated again in the same order. This adjustment method is relatively simple and uncomplicated, compared to the methods that were necessary in the known circuits, since each adjustment in the arrangement according to the invention is relatively independent of other adjustments and none of the adjustments affects the static adjustment that was previously carried out by the static means for centered on the screen. Furthermore, an adjustment of the convergence on one side of the screen does not significantly affect the adjustment of the convergence on the other side of the screen. These advances come from the level holding circuit 39, 40 in each of the three convergence circles, which holds the current minimum 42 of each oscillation of the convergence currents 30, which corresponds in time to the central part of the screen for each scan, at a fixed reference potential. 3Q The scanning in the vertical direction is carried out by a vertical deflection circuit 14 which has output lines 46 for connecting a vertical deflection coil for the picture tube; it has proven to be very expedient and desirable to also compensate for the deterioration in convergence that this causes. The circuit 14 includes a vertical deflection tube 48 and output terminals 50 which provide oscillations in antiphase with respect to ground, and an output terminal 50 'which provides a sawtooth voltage at the raster frequency. The end connections of three potentiometers 53, namely the potentiometers 53 G, 53R and 535, are connected to the antiphase output connections 50 of the vertical deflection circuit 14; the wipers of these potentiometers are connected to a connection of the corresponding vertical convergence coils 13 on the three convergence magnets 12. Three potentiometers 54, namely the potentiometers 54 G, 54 R and 545, are practically connected to the output connection 50 'of the vertical deflection circuit 14; 13 G, 13 R and 135 are connected to a voltage pulse wave from the terminals 50, which gives a sawtooth voltage through the convergence coils. The other connection of the vertical convergence coils is connected to a sawtooth voltage at connection 50 ', which results in an essentially parabolic current course through the convergence coils. A capacitor 51 is provided to derive undesired signals at the line frequency. A choke coil 60 with a high alternating current resistance is also connected in parallel to the output terminal 50 'of the vertical deflection circuit 14. The direct current resistance of the choke 60 is dimensioned such that the direct current from the vertical deflection tube 48 is divided by the total resistance so that about two thirds flow through the choke 60 and one third through the resistors 54. Of course, the resistance of the inductor branch can be provided entirely by the inductor winding, on the other hand it can also contain an additional resistance element. The current flowing from point 61 to ground can be represented approximately by the parabolic wave 62 in FIG. The direct current component of this oscillation is given by the position of the line 63 in relation to the current zero line 66. The wave 67 then represents the current through the resistors 54 after approximately two thirds of the direct current component has been diverted through the choke coil. It can be seen that the current minima 64 'of the wave 67, which are assigned to the center of the vertical deflection, correspond to the current zero through the resistors 54. In other words, the vertical convergence currents from the potentiometers 54 are stabilized by the throttle 60 shown practically at the middle of the vertical deflection to the value zero or some other fixed potential value. When adjusting the vertical convergence circuit it is found that the potentiometers 53 affect the inclination or slope of the upper part of a vertical test pattern with respect to the lower part. The potentiometers 54 control the amplitude of the parabolic currents which are fed to the vertical convergence coils 13. Due to the level holding effect of the throttle 60, an adjustment of the vertical inclination by the potentiometer 53 and the potentiometer 54 for the vertical amplitude does not affect the convergence initially adjusted by the static means in the central part of the screen. The adjustment is therefore very convenient and uncomplicated compared to previous arrangements, where the individual adjustment options strongly influenced one another. The level maintenance circuit with the throttle 60 also ensures that the adjustment of the convergence in the vertical direction is maintained over long periods, since the main part of the direct current, which can change due to tube aging, is diverted. Patent claims: 1. Color television receiver with a three-beam picture tube with three electron beams on the screen need to converge at one point, and with a deflection circuit and a convergence system to maintain the convergence of the three beams during beam deflection, which the latter three electromagnets and circuits for generating a convergence current from the Deflection circuits for the coils of the electromagnets contains, the coil currents approximately parabolic course with shoulders within the return intervals and minima in the middle the sampling period, characterized by level holding circuits in the individual circuits to generate the convergence flows through which the flow minimum of the convergence flows is kept at a certain level, so that the circuits for adjustment the convergence at the edges of the screen can be adjusted without affecting the convergence in the middle of the screen. 2. Color television receiver according to claim 1, characterized in that the convergence system Includes circuitry for generating horizontal convergence currents, with a horizontal coil is coupled to a horizontal deflection circuit in the receiver on each of the electromagnets, and that the level holding circuits each contain a rectifier and a resistor which each connected to the circuits for generating the horizontal convergence currents, and so on are polarized that said stabilization of the level takes place. 3. Color television receiver according to claim 1 or 2, characterized by a deflection circuit with a horizontal deflection circle, the output terminal