EP0523741A1

EP0523741A1 - Cathode ray tube apparatus

Info

Publication number: EP0523741A1
Application number: EP92112290A
Authority: EP
Inventors: Kouichi c/o Intellectual Property Div. Soneda
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 1991-07-18
Filing date: 1992-07-17
Publication date: 1993-01-20
Also published as: KR960000350B1; CN1069144A; KR930003223A; CN1040934C

Abstract

A cathode ray tube apparatus comprising a cathode ray tube (10), a deflecting device (13), an inverse voltage supply section (14), and a pair of compensating radiators (15). The deflecting device (13), which is mounted outside a funnel (11) of the cathode ray tube (10), deflects electron beam for scanning, emitted from an electron gun in a neck (12) of the funnel (11). The inverse voltage supply section (14) is used to obtain a voltage opposite in polarity to a deflection voltage applied to deflecting coils of the deflecting device (13). The compensating radiators (15), which are arranged individually on the top and bottom of a panel wall, receive the voltage of the opposite polarity from the supply section (14). The compensating radiators (15) are designed so as to generate electric fields which are opposite in polarity to a leakage electric field. Thus, AC electric fields leaked from the cathode ray tube apparatus and a cathode ray tube image display apparatus are suppressed by the compensatory electric fields.

Description

The present invention relates to a cathode ray tube apparatus and a cathode ray tube image display apparatus, and more particularly, to a measure to counter leakage electric fields from the cathode ray tube apparatus and the cathode ray tube image display apparatus.
Modern office automation apparatuses have been remarkably developed and become familiar to us in household use as well as in office use. In these circumstances, a technique for intercepting leakage electromagnetic waves and leakage electric fields is an essential measure to prevent noises of electronic apparatuses or influences of electromagnetic waves upon the human body. In northern Europe, in particular, the influences upon the human body are feared, and allowable values are prescribed for AC magnetic and electric fields. These standards are spreading.
Among wide-use office automation apparatuses, there is a cathode ray tube image display apparatus in which a cathode ray tube apparatus for deflecting electron beams for scanning, emitted from an electron gun, by means of a deflecting device, is set in a cabinet. As shown in Fig. 1, the cathode ray tube apparatus comprises an envelope formed of a panel 1 and a funnel 2, a phosphor screen 3 on the inner surface of the panel 1, the electron gun in a neck 4 of the funnel 2, and a deflecting device 6 mounted outside the funnel 2. The electron gun emits electron beam for exciting the phosphor screen 3. The deflecting device 6 generates a deflecting magnetic field which deflects the electron beam for scanning. It is necessary, therefore, to intercept leakage electromagnetic waves from the cathode ray tube apparatus.
In general, shielding is effected using various processes which include electric shielding, electromagnetic shielding, and magnetic shielding. In the electrostatic shielding process, a material with a low electric resistance is used to prevent lines of electric force from leaking out. In the electromagnetic shielding process, a low electric resistance material is used so that a current flow therein can be utilized for shielding. In the magnetic shielding process, a material with a low magnetic resistance is used to confine lines of magnetic force in a shielding conductor.
To attain this, various methods are used including a method in which the deflecting device is covered by means of a metallic plate formed of stainless steel or the like, a method in which the top, bottom, right- and left-side portions, and rear portion of the cathode ray tube apparatus are covered by means of a metallic plate or the like, and a method in which a see-through electromagnetic shielding plate is provided in front of the screen of the cathode ray tube. However, covering the apparatus by means of a durable metallic plate or forming a film of, e.g., an electrically conductive oxide on the front face of the screen of the cathode ray tube is not an economical method.
These shielding method cannot satisfactorily cope with the leakage of AC magnetic fields from the front face of the screen. Alternatively uses, therefore, are methods in which a permeable ring is arranged on the screen side of the deflecting device, or the leakage magnetic fields are compensated by means of a compensating coil, through which flows a current synchronous with a deflection current so that a magnetic field opposite in polarity to the leakage magnetic fields is generated.
However, AC electric fields also leak from the cathode ray tube apparatus and the cathode ray tube image display apparatus, and influences of these AC electric fields upon the human body are feared nowadays. A shielding structure used to cover the whole surface of the apparatus, in order to intercept the leakage AC electric fields, entails high cost, and a satisfactory effect cannot be obtained with use of a simple method.
The object of the present invention is to provide a cathode ray tube apparatus and a cathode ray tube image display apparatus capable of effectively suppressing leakage AC electric fields with ease.
In order to achieve the above object, according to the present invention, there is provided a cathode ray tube apparatus which has a deflecting device including a horizontal or vertical deflecting coil for deflecting electron beam for scanning, emitted from an electron gun, the apparatus comprising at least one compensating radiator to which is applied a voltage waveform synchronous with and opposite in polarity to a deflection voltage waveform applied to the horizontal or vertical deflecting coil.
Also, there is provided a cathode ray tube image display apparatus in which a cathode ray tube apparatus, which has a deflecting device including a horizontal or vertical deflecting coil for deflecting electron beam for scanning, emitted from an electron gun, is set in a cabinet, the image display apparatus comprising at least one compensating radiator to which is applied a voltage waveform synchronous with and opposite in polarity to a deflection voltage waveform applied to the horizontal or vertical deflecting coil.
In the cathode ray tube apparatus or cathode ray tube image display apparatus according to the present invention, an electric field generated from the compensating radiator is opposite in polarity to the electric field which varies in synchronism with the deflection voltage waveform, so that the two electric fields cancel each other to intercept and suppress a leakage electric field when they are combined with each other.
This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a sectional view showing an arrangement of a conventional cathode ray tube apparatus;
Fig. 2 is a perspective view showing a cathode ray tube apparatus according to one embodiment of the present invention;
Fig. 3 is a diagram showing an inverse voltage supply section for supplying a voltage which is opposite in polarity to a deflection voltage used in the apparatus of Fig. 2;
Fig. 4 is an equivalent circuit diagram corresponding to Fig. 3;
Fig. 5 is a diagram for illustrating the operation of the invention, showing a leakage electric field generated from a deflecting device;
Fig. 6 is a diagram for illustrating the operation of the invention, showing an electric field which, generated by compensating electrodes, is synchronous with and opposite in polarity to a deflection voltage waveform;
Fig. 7 is a diagram for illustrating the operation of the invention, showing an electric field obtained by combining the electric fields shown in Figs. 5 and 6;
Figs. 8A, 8B and 8C are diagrams for illustrating the operation of the invention, showing potentials at predetermined positions of the electric fields shown in Figs. 5 to 7;
Fig. 9 is a perspective view showing a modification of the compensating radiator according to the invention;
Fig. 10 is a perspective view showing another modification of the compensating radiator according to the invention;
Fig. 11 is a perspective view showing still another modification of the compensating radiator according to the invention;
Fig. 12 is a perspective view showing a further modification of the compensating radiator according to the invention;
Figs. 13A and 13B show distributions of compensated electric fields.
Fig. 14 is a perspective view showing a modification of the inverse voltage supply section according to the invention;
Fig. 15 is a perspective view showing another modification of the inverse voltage supply section according to the invention;
Fig. 16 is a cutaway perspective view showing a cathode ray tube image display apparatus according to another embodiment of the present invention; and
Fig. 17 is a perspective view showing still another modification of the inverse voltage supply section according to the invention.

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.
Referring first to Figs. 2 to 8, one embodiment of the present invention will be described.
Fig. 2 is a perspective view of a cathode ray tube apparatus according to the present embodiment. This apparatus comprises a cathode ray tube 10, a deflecting device 13, an inverse voltage supply section 14, and compensating electrodes 15. The deflecting device 13, which is mounted outside a funnel 11 of the cathode ray tube 10, includes a horizontal deflecting coil and a vertical deflecting coil for deflecting electron beams for scanning, emitted from an electron gun (not shown) in a neck 12 of the funnel 11. The inverse voltage supply section 14 is used to obtain a voltage opposite in polarity to a deflection voltage applied to the deflecting coils of the deflecting device 13. The compensating radiators or electrodes 15 receive the voltage of the opposite polarity from the supply section 14. The deflection voltage is applied to the input terminal of the inverse voltage supply section 14. One end of an inverse voltage output terminal of the supply section 14 is connected to the radiators 15, and the other end to the ground potential. In the cathode ray tube, an external conductive coating 17 and a tension band 18 are connected to the ground potential. Thus, the other end of the inverse voltage supply section 14 is connected to the tension band.
The cathode ray tube 10, which is constructed in the same manner as the conventional example, mainly comprises a glass envelope formed of a substantially rectangular panel 16 and the funnel 11 continuous therewith, a phosphor screen on the inner surface of the panel 16, and the electron gun in the neck 12 of the funnel 11. The electron gun emits electron beam for exciting the phosphor screen.
The deflecting device 13, which is mounted outside the funnel 11, is composed of the horizontal deflecting coil for generating a horizontal deflecting magnetic field, which deflects the electron beam in the horizontal direction, and the vertical deflecting coil for generating a vertical deflecting magnetic field, which deflects the electron beam in the vertical direction. Generally, deflecting devices may be classified into two types, a saddle-saddle type and a saddle-toroidal type. In the saddle-saddle type, the horizontal deflecting coil is formed of a pair of saddle-shaped deflecting coils, upper and lower, and the vertical deflecting coil is formed of another pair of saddle-shaped deflecting coils, right and left. In the saddle-toroidal type, the horizontal deflecting coil is formed of a pair of saddle-shaped deflecting coils, upper and lower, and the vertical deflecting coil is formed of a pair of toroidal coils, upper and lower. Voltages of predetermined waveforms, which vary in predetermined cycles, are applied individually to the horizontal and vertical deflecting coils, thereby generating deflecting magnetic fields. Normally, the voltage applied to the horizontal coil is a pulsating voltage ranging from several hundreds of volts to about 1 kV.
An AC electric field leaks from the cathode ray tube apparatus. An investigation made by the inventor hereof revealed that the deflecting device is the cause of this leakage. More specifically, as the deflecting device is supplied with the deflection voltage, which varies with time in synchronism with the deflection frequency, the potential in the deflecting coils undergoes a spatial change from the high-voltage side to the low-voltage side. Since this potential is higher than the ground potential, an alternating electric field is generated between the deflecting device and the ground.
Thus, when the deflection voltage is applied to the deflecting device, the AC electric field, which varies substantially in synchronism with the waveform of the deflection voltage, is generated from the deflecting device. This AC electric field leaks to the region around the cathode ray tube apparatus. Accordingly, the present invention is arranged so that an inverse AC electric field for compensating and suppressing the AC electric field is generated, and these two electric fields are combined to intercept and suppress the AC electric field. The following is a detailed description of an arrangement for this purpose.
In order to compensate the leakage AC electric field, the apparatus of the present embodiment comprise the inverse voltage supply section 14 and the paired compensating radiators 15, upper and lower (lower one is not shown), arranged near the side wall portion of the panel 16, as shown in Fig. 2. In the inverse voltage supply section 14, as shown in Fig. 4, coils 21a and 21b are wound around a ring-shaped core 20, which is a closed magnetic path, and a deflection current flows through the coil 21a. Each end of the coil 21a serves as an input-side terminal. One end 22 of the coils 21b, which constitutes the inverse voltage output terminal, is connected to the compensating radiators 15, and the other end 23 to the ground potential. When the deflecting current flows through the coil 21a, a magnetic flux is generated in the core 20, and an induced electromotive force is produced in the coil 21b. The direction of the electromotive force in the coil 21b depends on that of the magnetic flux flowing through the core 20. This does not guarantee that the compensating radiators can apply a potential opposite in polarity to the deflection voltage, that is, negative potential, when the deflection voltage is positive. Thereupon, a voltage waveform 24b opposite in polarity to a voltage waveform applied to the coil 21a is applied to the compensating radiators by leading the potential at one output-side end, as a reference potential, to the ground potential. Fig. 4 is an equivalent circuit diagram of this arrangement. In Fig. 4, numeral 30 denotes a main deflecting coil, e.g., the horizontal deflecting coil in the case of the present embodiment. The compensating radiators radiate electric fields which, opposite in polarity to the leakage electric field, vary substantially in synchronism with horizontal deflection. In the equivalent circuit diagram shown in Fig. 4, the voltages applied individually to the upper and lower compensating radiators, which are equal in value, are represented by one voltage.
Referring now to Figs. 5 to 8, the operation of the apparatus of the present embodiment will be described. Fig. 5 diagrammatically shows an electric field for a certain time, among other AC electric fields generated by the deflecting device of the cathode ray tube apparatus. Fig. 5 is diagrammatic because it illustrates a typical potential distribution formed between the deflecting device and the ground (ground potential) with the electric field approximated simply. In the case shown in Fig. 5, equipotential lines 40a spread radially from the center of a deflecting device 41, and the potential becomes lower with distance from the center. Electric force lines 42a are directed radially from the center. Fig. 6 diagrammatically shows an electric field for a certain time, among other AC electric fields generated by upper and lower compensating radiators 43, upper and lower. In the case of Fig. 6, equipotential lines 40b spread from the upper and lower compensating radiators 43, and a voltage opposite in polarity to the deflection voltage is applied to the radiators 43. Accordingly, electric force lines 42b are directed to the compensating radiators in the regions above and below the cathode ray tube apparatus, and to the screen in the region in front of it. Fig. 7 shows a combination of the leakage AC electric field shown in Fig. 5 and the compensatory electric field shown in Fig. 6. As seen from Fig. 7, the leakage electric field, which spreads around the cathode ray tube apparatus, especially in front of the screen, as the compensating radiators 43 are arranged as aforesaid, can be suppressed. Figs. 8A, 8B and 8C show potentials on sections A-A', B-B' and C-C' of Figs. 5, 6 and 7, respectively. Each electric field can be calculated as an inclination of each corresponding potential. As also seen from Fig. 8, the electric fields generated from the cathode ray tube apparatus are suppressed.
The compensating radiators must be insulated from those portions on the outer surface of the cathode ray tube which are connected to the ground potential for example, outer conductive layer or implosion protection band. The reason is that the compensatory electric field cannot be generated unless the compensating radiators are kept insulated from the portions connected to the ground potential.
Figs. 9 to 12 individually show modifications of the compensating electrode according to the present invention. In the modification shown in Fig. 9, a pair of compensating radiators 61, right and left, are arranged on the side wall of the panel 16 of the cathode ray tube 10. In the modification shown in Fig. 10, a compensating radiator 62 is arranged throughout the periphery of the side wall of the panel 16 of the cathode ray tube 10. In this case, the radiator 62, which may be formed by passing a conductor around the whole periphery of the side wall of panel 16, can enjoy a simple construction. In this arrangement, as compared with the example shown in Fig. 2, the radiator 62 covers the right- and left-hand side portions of the side wall of the panel 16. It is advisable, in this case, to arrange the radiator 62 so that its potential is uniform throughout the periphery. In the modification shown in Fig. 11, compensating radiators 63 are arranged individually at the four corners of the panel 10 of the cathode ray tube 10. In the modification shown in Fig. 12, a compensating radiator 64 is arranged on a screen-side flange portion of the deflecting device 13 of the cathode ray tube apparatus. The compensating electrodes are not limited in shape to the above-described embodiment and modifications, and may alternatively be disk-shaped, rectangular, etc.
Referring now to Figs. 13A and 13B (enlarged views), the angle dependence of the leakage electric field generated with use of the aforementioned various compensating radiators will be described. These drawings show the results of measurement of the leakage AC electric field with the cathode ray tube apparatus of the present invention incorporated in a chassis in a cabinet. It is possible to evaluate an actual use of the cathode ray tube apparatus, when the cathode ray tube is received in the chassis and the leakage AC electric field from the chassis is measured. According to the embodiment and modifications (Figs. 2, 9 and 10) in which the compensating radiator or electrodes are arranged on the front face of the screen, the leakage electric field can be halved. In the case of the compensating radiator 64 of Fig. 12, the same applied voltage for the other compensating radiators is used, so that the amount of suppression of the leakage electric field is small. Since the angle dependence varies depending on the correlation between the location of the compensating radiator and a chassis in the cabinet, which incorporates the cathode ray tube apparatus, the radiator position should preferably be determined as required. If the compensating radiator is located near the deflecting device, the distribution of the compensatory electric field can be approximated to that of the leakage electric field. If the compensating radiator is thus located, however, the inverse potential to be applied to the radiator must be increased substantially to the level of the deflection voltage, which ranges from several hundreds of volts to about 1 kV. In consideration of the dielectric properties, another measure for insulation is needed. Actually, the cathode ray tube apparatus is mounted in the chassis, and the leakage electric field can be suppressed to some degree, in all the area except the region in front of the screen, by means of the chassis. Thus, a measure to counter the leakage electric field is to suppress the electric field leaked to the front of the screen. Since the voltage to be applied to the compensating radiator can be lowered (substantially to half the deflection voltage or less) as the front face of the screen is approached or with distance from the deflecting device, moreover, the compensating electrode should preferably be situated near the screen.
Figs. 14 and 15 individually show modifications of the inverse voltage supply section. The modification shown in Fig. 14 utilizes an induced electromotive force produced by a magnetic flux from a main deflecting magnetic field of a deflecting device 70. In this arrangement, the loop plane of coils 72 is positioned in the tube axis direction so that the magnetic flux leaked to the region near a screen-side flange portion 71 of the deflecting device 70 penetrates the loop plane. Leakage magnetic field compensating means 73 are used in the modification shown in Fig. 15. In order to suppress a leakage magnetic field generated from the cathode ray tube apparatus, each compensating means 73 is formed of a core 75 wound with a coil 74, through which a current synchronous with a deflection current flows so that a magnetic field directed opposite to the leakage magnetic field is generated. A coil 76 connected to the compensating radiator is wound around the same core 75 having the coil 74 thereon, whereby an induced electromotive force is utilized. In this case, no current flows through the compensating radiators themselves, so that no substantial loss is incurred, and the compensation effect of the leakage magnetic field is lowered by only a small margin. Thus, both the leakage electric field and the leakage magnetic field can be effectively suppressed.
Since the leakage electric field synchronous with deflection can be easily suppressed by arranging the compensating electrodes in the manner described above, the screen front face of the panel need not be provided with any special electromagnetic shielding plate. Accordingly, the screen front face can be furnished with means for non-glare properties or other essential properties without giving consideration to electromagnetic shielding.
According to the present invention, moreover, the leakage electric field should only be suppressed by means of the compensating radiators to which is applied the voltage opposite in polarity to the deflection voltage. Also, the number, location, shape and size of the compensating radiators should be suitably set in consideration of the size of the cathode ray tube apparatus, to which the present invention is applied, the distribution of the leakage electric field, the level of suppression, etc. More specifically, the positional relationships between the compensating radiators and the ground-potential regions should be taken into consideration. Further, the level of the voltage applied to the compensating radiators need not always be equal to that of the deflection voltage, and should only be suitably adjusted depending on the position, length, etc. of the compensating radiators. The applied voltage can be easily adjusted by regulating the number of turns of the coils shown in Fig. 3. Furthermore, different voltages may be applied individually to the upper and lower compensating radiators shown in Fig. 2 or the right- and left-hand compensating radiators shown in Fig. 9.
In the embodiment described above, the voltage opposite in polarity to the voltage applied to the horizontal deflecting coil is applied to the compensating radiators, in order to cope with VLF (Very Low Frequency: 2 kHz to 400 kHz) which is attributable to horizontal deflection. However, the present invention is not limited to the above embodiment. Alternatively, a voltage opposite in polarity to the voltage applied to the vertical deflecting coil may be applied to the compensating radiators, in order to cope with ELF (Extremely Low Frequency: 5 Hz to 2 kHz) which is attributable to vertical deflection, or independent compensating radiators may be arranged to cope with the VLF and ELF simultaneously.
Referring now to Fig. 16, another embodiment of the present invention will be described. Fig. 16 is a cutaway perspective view of a cathode ray tube image display apparatus according to the present embodiment. In the display apparatus 80, a cathode ray tube apparatus 82 is set in a cabinet 81. In the cabinet 81, moreover, a compensating radiators 83 are arranged individually at regions near the top and bottom of the side wall of a panel of the cathode ray tube apparatus. A voltage opposite in polarity to the deflection voltage is applied to the electrodes 83.
The voltage opposite in polarity to the deflection voltage is applied to the compensating radiators 83 by means of an inverse voltage supply section 84, which is constructed in the same manner as that of the first embodiment shown in Fig. 3. The inverse voltage supply sections shown in Figs. 14 and 15 may be also used for this purpose. In the cathode ray tube image display apparatus, moreover, a flyback transformer for generating the deflection voltage is provided at the bottom of the cabinet 81. Thus, the inverse voltage supply section may be also formed by winding a coil 91 around a flyback core 90, as shown in Fig. 17. Also, a voltage waveform synchronous with and opposite in polarity to the deflection voltage waveform can be obtained directly from a substrate in the cabinet. Furthermore, the compensating radiators may be modified variously, as shown in Figs. 9 to 12 for the first embodiment.
Basically, as shown in Figs. 5 to 8 for the first embodiment, the present embodiment is arranged so that the leakage electric field is suppressed by combining an electric field conventionally leaked from the deflecting device of the cathode ray tube apparatus and an electric field generated by means of the compensating radiators to which is applied the voltage opposite in polarity to the deflection voltage. Since the cathode ray tube is set in the cabinet, however, the state of the ground potential is somewhat different from the state for the first embodiment, although there is no difference in basic principle. Although the compensating radiators are arranged on the side wall of the panel of the cathode ray tube apparatus in the cabinet according to the present embodiment, the invention is not limited to this arrangement. More specifically, the compensating radiators may be arranged on the inside of the front face of the cabinet, or formed integrally with a degaussing coil which is arranged in a conventional cathode ray tube image display apparatus. It is necessary only that the compensating radiators be located individually in suitable positions for the generation of an inverse electric field which can compensate the leakage electric field. When arranging the compensating radiators on the inside of the front face of the cabinet, the radiators must only be located on that wall surface of the cabinet which is not in contact with the cathode ray tube apparatus, so that they can be easily insulated from those portions of the apparatus which are connected to the ground potential.
Since the leakage electric field synchronous with the deflection can be easily suppressed by arranging the compensating radiators in the manner described above, the screen front face of the panel need not be provided with any special electromagnetic shielding plate. Accordingly, the screen front face can be furnished with means for non-glare properties or other essential properties without giving consideration to electromagnetic shielding.
According to the present invention, moreover, the leakage electric field should only be suppressed by means of the compensating radiators to which is applied the voltage opposite in polarity to the deflection voltage. Also, the number, location, shape and size of the compensating radiators should be suitably set in consideration of the size of the cathode ray tube image display apparatus, to which the present invention is applied, the distribution of the leakage electric field, the level of suppression, etc. More specifically, the positional relationships between the compensating radiators and the ground-potential regions should be taken into consideration. Further, the level of the voltage applied to the compensating radiators need not always be equal to that of the deflection voltage, and should only be suitably adjusted depending on the position, length, etc. of the compensating radiators. The applied voltage can be easily adjusted by regulating the number of turns of the coils shown in Fig. 3. Furthermore, different voltages may be applied individually to the upper and lower compensating radiators shown in Fig. 2 or the right- and left-hand compensating radiators shown in Fig. 9.
In the second embodiment described above, the voltage opposite in polarity to the voltage applied to the horizontal deflecting coil is applied to the compensating electrodes, in order to cope with VLF (2 kHz to 400 kHz) which is attributable to horizontal deflection. However, the present invention is not limited to the above embodiment. Alternatively, a voltage opposite in polarity to the voltage applied to the vertical deflecting coil may be applied to the compensating electrodes, in order to cope with ELF (5 Hz to 2 kHz) which is attributable to vertical deflection, or independent compensating electrodes may be arranged to cope with the VLF and ELF simultaneously.
According to the cathode ray tube apparatus and the cathode ray tube image display apparatus of the present invention, as described herein, the leakage electric field can be easily suppressed by arranging at least one compensating radiator to which is applied a voltage waveform synchronous with and opposite in polarity to the deflection voltage waveform.

Claims

A cathode ray tube apparatus characterized by comprising:
means (5) for emitting a electron beam;
an envelope (2) for receiving the electron beam emitting means;
a phosphor screen (3) formed on the envelope (2) and adapted to generate light rays when the electron beam is landed thereon;
means (13, 70) for deflecting the electron beam for scanning, emitted from the electron beam emitting means (5), the deflecting means (13) generating a leakage electric field;
means (9) for generating a deflecting signal to energize the deflecting means (13);
means (14, 72, 73, 84, 91) for generating a compensatory signal opposite in polarity to the deflecting signal in synchronism with the deflecting signal; and
a first compensating radiator (15, 61, 63, 64, 83) connected to the compensatory signal generating means (14, 72, 73, 84, 91), the compensating radiator (15, 61, 63, 64, 83) radiating a compensatory electric field which substantially cancels the leakage electric field.
A cathode ray tube apparatus according to claim 1, characterized in that said deflecting means (13, 70) includes a vertical deflecting coil for vertically deflecting the electron beam and a horizontal deflecting coil for horizontally deflecting the electron beam.
A cathode ray tube apparatus according to claim 1, characterized by further comprising a second compensating electrode (15, 61, 63, 64, 83) arranged on the envelope (2) in symmetrical relation to the first compensating radiator (15, 61, 63, 64, 83), connected to the compensatory signal generating means (14, 72, 73, 84, 91), the second compensating radiator (15, 61, 63, 64, 83) radiating a compensatory electric field which substantially cancels the leakage electric field.
A cathode ray tube apparatus according to claim 1, characterized in that said first compensating radiator (15, 61, 63, 64, 83) is arranged on the outer periphery of the envelope (2) so as to surround the screen (3).
A cathode ray tube apparatus according to claim 1, characterized by further comprising second, third, and fourth compensating radiators (63, 64) arranged on the envelope (2) in symmetrical relation to the first compensating radiator (63, 64), the second, third, and fourth compensating radiators (63, 64) generating compensatory electric fields which substantially cancel the leakage electric field.
A cathode ray tube apparatus according to claim 1, characterized in that said compensatory signal generating means (14) includes
magnetic core (20),
a first coil (20a) wound around the core (20) and receive the deflecting signal, and
a second coil (21b) wound around the core (20), one end of the second coil (21b) is connected to the compensating radiator (15) and the other end to the ground potential.
A cathode ray tube apparatus according to claim 1, characterized in that said deflecting means (13, 70) generates a deflecting magnetic field for deflecting the electron beams in the envelope (2), and generates a leakage magnetic field outside the envelope (2).
A cathode ray tube apparatus according to claim 7, characterized in that said compensatory signal generating means (73) includes a coil (74, 76) linked to the leakage magnetic field, the coil (74, 76) generating the compensatory signal by electromagnetic induction.
A cathode ray tube apparatus according to claim 1, characterized in that said compensating radiator (15, 61, 63, 64, 83) is arranged on the envelope (2).
A cathode ray tube apparatus according to claim 9, characterized by further comprising a housing (81) containing the envelope (2) and the deflecting means (70).
A cathode ray tube apparatus according to claim 1, characterized in that said deflecting signal generating means (9) includes a flyback transformer, and said compensatory signal generating means includes a coil (9) arranged in the flyback transformer.