JPH0367298B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color cathode ray tube, in which the size of a raster formed on a fluorescent surface by a central and a pair of outer electron beams emitted from an in-line electron gun is determined by a common deflection magnetic field. In particular, this invention relates to a self-convergence type in-line electron gun that can make the horizontal deflection frequency equal regardless of the horizontal deflection frequency.

FIG. 1 is a longitudinal cross-sectional view of a conventional color cathode ray tube using a so-called self-convergence in-line electron gun that does not require dynamic convergence correction.

A central electron beam B 1 emitted from the in-line electron gun ₁ and located in the same plane and a pair of outer electron beams B ₂ and B ₃ are deflected into a funnel-shaped part of an evacuated glass envelope 2 by a deflection device. 5, and is located on the top surface of the glass envelope 2, and is placed opposite to the phosphor surface 4 on which a plurality of phosphor pixels that emit light in three colors are deposited on the inside. Shadow mask 3
to form a scanning screen. In order to make a color cathode ray tube a self-convergence system that does not require dynamic convergence correction, the horizontal deflection magnetic field of the deflection device 5 is made to have a strong pincushion distortion, and the vertical deflection magnetic field is made to have a strong barrel distortion, as shown in FIG. As shown in , these deflecting magnetic fields eliminate the comatic aberration of the pair of outer electron beams B ₂ and B ₃ and form a scanning screen 6 that coincides with the fluorescent surface 4.
form. In this case, the scanning screen 7 of the central electron beam B ₁ is generally horizontally and vertically spaced by both outer electron beams.
It is smaller than the scanning screen 6 formed by B ₂ and B ₃ .
This misalignment of the scanning screens is due to the comatic aberration of the deflection device 5. In order to remove the comatic aberration and make each scanning screen consistent, the deflection device 5 is attached to the tip of the electron gun 1, which is exposed to the rear leakage magnetic field. The bottom surface 11 of the concentrated magnetic pole 10 is formed of a non-magnetic material into a cylindrical shape with a bottom.
A magnetic field control element made of a magnetic material with high magnetic permeability is disposed in the magnetic field. FIG. 3 shows an example of a magnetic field control element, in which a central electron beam transmission aperture 12 formed in the bottom surface 11 of the concentrated magnetic pole 10 is sandwiched between the vertical axis Y-Y, which is the short axis of the fluorescent surface 4. A pair of disk-shaped magnetic enhancement elements 15 and 16 arranged opposite to each other and both outer electron beam transmission apertures 13 and 14 bored on the horizontal axis XX, which is the long axis of the fluorescent surface 4, are surrounded. It is composed of annular magnetic shielding elements 17 and 18 arranged. The magnetic enhancement elements 15 and 16 increase the deflection sensitivity of the horizontal deflection magnetic field F _H of the deflection device 5 with respect to the central electron beam B ₁ compared to both outer electron beams B ₂ and B ₃ , and the annular magnetic shielding elements 17 and 18 Both outer electron beams B ₂ ,
For B ₃ , the horizontal and vertical deflection magnetic fields of the deflection device 5
It functions to lower the deflection sensitivity of F _H and F _V than that of the central electron beam B1, and to increase the deflection sensitivity of the vertical deflection magnetic field F _V with respect to the central electron beam B ₁ compared to both outer electron beams.

Therefore, the magnetic field control elements 15, 16 and 17, 1
8, the scanning screen 7 of the central electron beam B ₁ is horizontal,
Both the vertical direction is expanded, and conversely, both outer electron beams B ₂ ,
The scanning screen 6 of _B3 is reduced, coma aberration due to the deflection magnetic field is removed, and the scanning screens 6 and 7 can be made to coincide completely.

On the other hand, in recent years, so-called display color cathode ray tubes, which are color cathode ray tubes with high resolution characteristics, have been used to display various information, and alphanumeric characters, symbols, kanji, charts, etc. can be displayed with high density. .

In order to achieve high-density display, the color cathode ray tube must have high resolution and uniform focus characteristics, the video circuit must have a wide frequency band to increase the horizontal resolution of the display screen, and the vertical resolution of the display screen must be increased. requires a large number of scanning lines.

Normally, in order to increase the number of scanning lines as a means of high-density display, the horizontal deflection frequency fh is increased above the 15.734 KHz of the current standard color TV system. In this case, horizontal deflection frequency fh=
At about 15.734 KHz, there was no problem at all, but coma aberration occurs in the scanning screens 6' and 7' formed by the outer and central electron beams due to the horizontal magnetic field, and as shown in Figure 4, the scanning screen 7' of the central electron beam. In contrast, the scanning screen 6' of both outer electron beams is slightly expanded in the horizontal direction, and the rate of expansion is different on the left and right sides of the fluorescent surface 4, with the enlarged dimension _d1 on the left side being larger than the enlarged dimension on the right side.
An asymmetry occurs that is larger than d ₂ . This shift in the scanning screen results in a convergence error that depends on the horizontal deflection frequency, which significantly deteriorates the quality of the image received on the fluorescent surface. For example, in a 20-inch 90 degree polarization color cathode ray tube, if the horizontal deflection frequency fh = 15.73KHz is doubled, fh = 31.5KHz, the above-mentioned deviations d ₁ and d ₂ will be d near the outermost part of the effective fluorescent surface. ₁ = 0.7mm, _d2 = 0.3
mm. The reason why the scanning screens 6' and 7' formed by both outer electron beams and the central electron beam are shifted in the horizontal direction due to coma aberration as the horizontal deflection frequency fh increases is as follows.

First of all, due to the magnetic flux of the horizontal deflection magnetic field that penetrates the cylinder side part 19 of the bottomed cylindrical concentrated magnetic pole 10 in the screen vertical axis Y-Y direction, an eddy current is generated in the magnetic flux passing surface, which causes horizontal deflection. A magnetic flux is generated that obstructs the magnetic flux change of the magnetic field, which attenuates the magnetic flux, reduces the deflection sensitivity of the central and both outer flux electron beams B ₁ , B ₂ , B ₃ and reduces their horizontal deflection amplitude, and the magnetic flux A decrease in the magnetic shielding effect of the annular magnetic shielding elements 17, 18 is reduced. The loss of magnetic flux due to this eddy current could be completely ignored at the conventional horizontal deflection frequency h = 15.73KHz, but as the frequency increases, the loss of magnetic flux due to the eddy current becomes impossible to ignore, and as shown in Figure 4, the loss of magnetic flux becomes impossible to ignore. The scanning screen 6' of the outer electron beam is expanded in the horizontal direction with respect to the scanning screen 7' of the central electron beam.

On the other hand, in order to perform horizontal scanning, the deflection device 5
The current waveform flowing through the horizontal deflection coil is a sawtooth wave shown in Figure 5, where the time t1 from point a to point b in the figure is the horizontal scanning time, and the time _t2 from point b to point c is the horizontal _scanning time. This is the horizontal retrace time, and _t2 is usually set to about 1/5 of _t1 . Point a or point c corresponds to the left end position of the water seal scan on the screen, and point b corresponds to the right end position. On the other hand, the left end position of the horizontal scanning screen corresponds to the end of the horizontal retrace time _t2 , the right end corresponds to the end of the horizontal retrace time _t1 , and the position during the horizontal retrace time _t2 corresponds to the end of the horizontal retrace time _t1 . A magnetic field is generated by a current that changes about five times faster,
Therefore, the annular magnetic shielding elements 17, 18 due to a decrease in magnetic flux due to eddy current loss due to the harmonic component magnetic field.
The magnetic shielding effect loss is larger on the left side of the fluorescent surface than on the right side, and as shown in FIG. d ₁ becomes larger than d ₂ on the right side, causing asymmetry in coma aberration in the horizontal direction. At h = 15.734KHz used in the conventional standard color TV system (NTSC system), t ₁ = 51~
53 μsec, t ₂ = 10 to 12 μsec, the eddy current loss caused by this can be completely ignored, and the above-mentioned coma aberration and its asymmetry were not found substantially, but as h increases, the difference between t ₁ and t ₂ Furthermore, in order to increase the effective scanning time t ₁ , the retrace time t ₂ is set to be as small as possible, and the asymmetry of the horizontal deflection magnetic flux reduction due to eddy current loss becomes a non-negligible amount. This phenomenon is becoming more noticeable.

The present invention has been made in view of the above-mentioned drawbacks, and the scanning screen formed by both outer electron beams and the central electron beam is improved by increasing the horizontal deflection frequency of a color cathode ray tube using a self-convergence type in-line electron gun. This is to prevent deviations due to coma aberration from occurring.

On the side, there are three in-line array holes drilled in the bottom surface of the bottomed cylindrical concentrated magnetic pole made of non-magnetic material attached to the tip of the electron beam exit side of the in-line electron gun, and the vertical tube side part is locally located. It is a notch. This configuration prevents eddy current loss in the horizontal deflection magnetic field penetrating the side of the concentrated magnetic pole tube, and reduces coma aberration in the scanning screen formed by the central and both outer electron beams regardless of the increase in horizontal deflection frequency. As a result, asymmetrical deviation can be eliminated, and the in-line type electron gun can be made into an electron gun assembly capable of displaying high-density video information.

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 6 shows a concentrated magnetic pole 2 according to an embodiment of the present invention.
FIG.

The concentrated magnetic pole 20 has a cylindrical shape made of non-magnetic metal and has a bottom surface 21 and a cylindrical side portion 29, and a central electron beam transmission aperture 22 formed in the bottom surface 21 is aligned with the vertical axis Y, which is the short axis of the fluorescent surface. A pair of magnetic enhancement elements 15, 16 placed opposite each other on -Y, and both outer electron beam transmission apertures 23, 24 bored on the horizontal axis XX, which is the long axis of the fluorescent surface. Annular magnetic shielding elements 17 and 18 are disposed surrounding the magnetic shielding elements 17 and 18. The cylindrical side part 29 having a height _h1 has three in-line array apertures drilled in the bottom surface in the Y-Y direction perpendicular to the line-up direction X-X, and both outer electron beam apertures 23, 24. A notch 25 is formed in a rectangular shape with a width w having a length equal to or greater than the distance between the central magnetic poles 20 and a height _h2 from the upper edge of the concentrated magnetic pole 20. That is, the cylindrical side part of the concentrated magnetic pole 20 through which the three in-line array holes in the Y-Y direction can be seen is cut away leaving a height of (h ₁ - _{h 2} ).
Although not shown, a valve spacer is attached to this part, and this is fixed inside the cathode ray tube neck of the electron gun assembly, and high voltage is supplied from the funnel-shaped part of the cathode ray tube to the electron gun assembly from the internal conductive coating applied to the inner wall of the neck. A getter support is attached which holds a getter container necessary to maintain a high vacuum inside the cathode ray tube.

Due to the concentrated magnetic pole 20 having the above-described configuration, the magnetic flux of the horizontal deflection magnetic field penetrating the cylinder side part 29 in the Y-Y direction of the vertical axis of the screen passes through the notch 25, so that eddy currents are not generated in the magnetic flux penetrating surface as in the conventional case. , This prevents the generation of magnetic flux that interferes with changes in the magnetic flux of the horizontal deflection magnetic field. Therefore, the horizontal deflection frequency h is
Even if the frequency is increased from 15.75KHz to 31.5KHz or higher than 64KHz, which has been put into practical use in recent years, there will be no reduction in deflection sensitivity or the magnetic field control action of the magnetic field control element disposed in the concentrated magnetic pole 20, and both The scanning screen of the outer electron beam no longer deviates from the scanning screen of the central electron beam, which means that the convergence error between the two can be minimized to 0.1 mm or less. Even if there is asymmetry at the left and right ends, it can be ignored.

As described above, according to the embodiment of the present invention, even if the horizontal deflection frequency is increased from 15.75 KHz to 64 KHz or higher, the convergence error of both outer electron beams and the center electron beam at the left and right edges of the screen can be ignored. Even if the horizontal deflection frequency of the color cathode ray tube is increased to perform high-density display, there will be no deterioration in image quality due to color shift. Furthermore, since the dependence of the convergence error on the horizontal deflection frequency is eliminated, it is possible to use the same magnetic field control element for all horizontal deflection frequencies without changing the magnetic field control element installed in the concentrated magnetic pole to the one optimized for each horizontal deflection frequency. It also has the advantage of simplifying the cathode ray tube manufacturing process, and its practical industrial value is extremely high.

[Brief explanation of drawings]

Figure 1 is a vertical cross-sectional view of a color cathode ray tube that uses a conventional self-convergence type in-line electron gun, and Figure 2 shows the central and both outer electron guns on the fluorescent surface of this color cathode ray tube. Fig. 3 shows the magnetic field control element for correcting coma aberration of the scanning screen and its effect on the horizontal and vertical deflection fields, and Fig. 4 shows the scanning screen formed by the electron beam as the horizontal deflection number wave number increases. Figure 5 shows the current waveform flowing through the horizontal deflection coil, and Figure 6 shows the current waveform flowing through the horizontal deflection coil. 3A and 3B show perspective views of concentrated magnetic poles showing one embodiment, respectively. DESCRIPTION OF SYMBOLS 1... In-line electron gun, 2... Glass envelope, 4... Fluorescent surface, 5... Deflection device, 6, 6'...
...Scanning screen formed by both outer electron beams, 7,
7'... Scanning screen formed by the central electron beam, 1
0,20...Concentrated magnetic pole, 12,22...Central electron beam transmitting aperture, 13,14,23,24...Both outer electron beam transmitting apertures, 19,29...Cylinder side part, 15,16... ...Magnetic enhancement element, 17, 18...
...Annular magnetic shielding element, t ₁ ...Horizontal scanning time, t ₂ ...
...Horizontal retrace time, 25...notch.

Claims (1)

[Claims] 1. In an in-line electron gun assembly, which is equipped with a bottomed cylindrical concentrated magnetic pole made of a non-magnetic metal material at the tip of the electron beam exit side of the electron gun, the bottomed cylindrical concentrated magnetic pole has three inline arrays drilled in the bottom surface. An in-line electron gun assembly characterized in that a cylinder side part in a direction perpendicular to the direction in which the openings are lined up is notched leaving a height from the upper edge for attaching a valve spacer.