JPH0367299B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color cathode ray tube, in which the size of a ruster 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 B1 emitted from the in-line electron gun 1 and located in the same plane and a pair of outer electron beams B2 and B3 are deflected horizontally by a deflection device 5 disposed in a funnel-shaped portion of the evacuated glass envelope 2. and is vertically deflected through a shadow mask 3 placed on the top surface of the glass envelope 2 and 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. Form a scanning screen. In order to make this color cathode ray tube a self-convergence type 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 the figure, a pair of outer electron beams B2 and B are formed by these deflecting magnetic fields.
The comatic aberration of 3 is eliminated to form a coincident scanning screen 6 on the fluorescent surface 4. In this case, the scanning screen 7 of the central electron beam B1 is generally smaller both horizontally and vertically than the scanning screen 6 formed by the outer electron beams B2 and B3. 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, an electron gun 1 is attached to the tip of the electron gun 1, which is exposed to the rear leakage magnetic field of the deflection device 5. A magnetic field control element made of a magnetic material with high magnetic permeability is disposed on the bottom surface 11 of the concentrated magnetic pole 10 formed of a non-magnetic material in the shape of a cylinder with a bottom. FIG. 3 shows an example of a magnetic field control element, in which a center electron beam transmission aperture 12 formed in the bottom surface 11 of a concentrated magnetic pole 10 is arranged so as to be sandwiched on the vertical axis Y-Y, which is the short axis of the fluorescent surface 4. It is arranged so as to surround a pair of disk-shaped magnetic enhancement elements 15 and 16 provided therein and both outer electron beam transmission apertures 13 and 14 formed on the horizontal axis XX, which is the long axis of the fluorescent surface 4. It is composed of annular magnetic shielding elements 17 and 18 provided. The magnetic enhancement elements 15 and 16 are connected to the central electron beam B.
1, the deflection sensitivity of the horizontal deflection magnetic field F _H of the deflection device 5 is increased from both outer electron beams B2 and B3, and the annular magnetic shielding elements 17 and 18 The deflection sensitivities of the horizontal and vertical deflection magnetic fields F _H and F _V of No. 5 are lower than those of the center electron beam B1, and the deflection sensitivity of the vertical deflection magnetic field F _V has a greater effect on the center electron beam B1 than 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 B1 is enlarged both horizontally and vertically, and conversely, the scanning screen 6 of the outer electron beams B2 and B3 is reduced, and the coma aberration caused by the deflection magnetic field is removed, and the scanning screen 6, 7 can be completely matched.

On the other hand, recently, so-called display color cathode ray tubes, which are color cathode ray tubes with high resolution characteristics, have been used to display various types of information.This allows alphanumeric characters, symbols, kanji, charts, etc. to be displayed in high density. Ru.

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. This 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 frequency h is increased to more than 15.734 KHz of the current standard color TV system. In this case, horizontal deflection frequency h=
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 deflection 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 h = 15.73KHz is doubled, h = 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 h increases is as follows.

First of all, there is a magnetic flux of a horizontal deflection magnetic field that penetrates the cylinder side part 19 of the bottomed circular concentrated magnetic pole 10 in the screen vertical axis Y-Y direction, and an eddy current is generated in the magnetic flux passing surface, which causes a horizontal deflection. Deflection magnet A magnetic flux is generated that obstructs the magnetic flux change in this field, which attenuates the magnetic flux, reduces the change sensitivity of the center and both outer electron beams B1, B2, B3, and reduces their horizontal deflection amplitude, reducing the magnetic flux. reduces the magnetic shielding effect of the annular magnetic shielding elements 17,18. 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 eddy current becomes impossible to ignore, and as shown in Figure 4, 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 of the horizontal scanning screen, and point b corresponds to the right end position. That is, the left end position of the horizontal scanning screen corresponds to the end of the horizontal retrace time t ₂ , the right end corresponds to the end of the horizontal retrace time t ₁ , and during the horizontal retrace period t ₂ it corresponds to the end of the horizontal retrace time t ₁ . A magnetic field is generated by a current that changes 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 could not be found in reality, 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 shortcomings, and is aimed at increasing the horizontal deflection frequency of a cathode ray tube using a self-convergence type in-line electron gun. This is to prevent displacement due to coma aberration from occurring on the screen.

That is, the cylindrical concentrated magnetic pole with a bottom, which is made of a non-magnetic material and is attached to the tip of the electron beam exit side of the in-line electron gun, has a short length on the cylindrical side.
With this configuration, it is possible to prevent eddy current loss caused by the horizontal deflection magnetic field penetrating the side of the concentrated magnetic pole cylinder, and the scanning formed by the central and both outer electron beams can be prevented regardless of the high horizontal deflection frequency. It is possible to eliminate asymmetric shifts due to screen coma aberration, and the in-line electron gun can be made into an electron gun structure capable of displaying high-density video information.

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

In Figure 6, the horizontal axis represents the side length h of the concentrated magnetic pole tube, and the horizontal deflection frequency h is used as a parameter.
FIG. 3 is a diagram showing the above-mentioned horizontal coma aberration d ₁ of the center and both outer electron beams at the upper left end of the screen of a 90-degree deflection cathode ray tube. As is clear from Figure 6, h = 8.0
When it exceeds mm, _d1 increases rapidly to 0.1 mm or more for h=31.5 to 64 KHz. When h=8.0mm h=
For 31.5KHz, d ₁ = 0.09mm, for h = 64KHz, dmm =
0.18mm, and when h=6.0mm and h=31.5KHz, d ₁
= 0.05, and when h = 64KHz, d ₁ = 0.1mm.

In general, if the convergence error is 0.2 mm or more, it becomes noticeable and degrades the image quality, but if it is 0.1 mm or less, color shift is virtually unnoticeable.

On the other hand, a plurality of valve spacers are attached to the cylinder side of the conventional concentrated magnetic pole, and these spacers fix the electron gun assembly inside the neck of the cathode ray tube, and are connected to the internal conductive film applied from the funnel-shaped part of the cathode ray tube to the inner wall of the neck. Since the getter support is attached with a getter container that has the function of supplying high voltage to the electron gun structure or that is necessary to maintain a high vacuum inside the cathode ray tube, the tube side length is usually selected to be sufficiently large, approximately 15 to 25 mm. has been done.

In the present invention, the length of the cylinder side part is limited to 6.0 mm or less in order to maintain the occurrence of the above-mentioned convergence error in the concentrated magnetic pole cylinder side part at a level that does not deteriorate the image quality by increasing the horizontal deflection frequency. FIG. 7 shows a perspective view of the concentrated magnetic pole 20. The concentrated magnetic pole 20 includes a pair of magnetic enhancement elements 15, which are arranged oppositely to sandwich the central electron beam transmission aperture 22 formed in the bottom surface 21 on the vertical axis Y-Y, which is the short axis of the fluorescent surface, as in the conventional case. 16, and annular magnetic shielding elements 17 and 18 are disposed surrounding both outer electron beam transmission apertures 23 and 24 formed on the horizontal axis XX, which is the long axis of the fluorescent surface. However, the cylinder side part 2
Although the height h of 9 is set to 6.0 mm or less, it is possible to fix a plurality of valve spacers and funnel getter supports (not shown) to the cylinder side part 29 as in the conventional case.

As described above, according to the embodiment of the present invention, even if the horizontal deflection frequency h is increased from 15.75 KHz to 64 KHz, the convergence error at the left and right edges of the screen for both outer electron beams and the center electron beam can be kept below 0.1 mm. In addition, by reducing the amount of error, the asymmetry can be ignored, and even if the horizontal deflection frequency of the color cathode ray tube is increased to perform high-density display, the image quality will not deteriorate due to color shift. . Furthermore, since the dependence of the convergence error on the horizontal deflection frequency is eliminated, the same magnetic field control element can be used without having to change the magnetic field control element installed in the concentrated magnetic pole to one optimized for each horizontal deflection frequency used. It has the advantage of simplifying the cathode ray tube manufacturing process, and its practical industrial value can be said to be 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. Figure 3 shows the magnetic field control element that corrects the coma aberration of the scanning screen and its effect on the horizontal and vertical deflection magnetic fields, and Figure 4 shows the scanning screen formed by the electron beam. A diagram explaining the deviation of the scanning screen formed by the electron beams of the central and both outer electron guns appearing on the fluorescent surface. Figure 5 shows the current waveform flowing through the horizontal deflection coil, and Figure 6 shows the horizontal deflection frequency as a parameter. FIG. 7 is a diagram showing the relationship between the side length of a concentrated magnetic pole cylinder and a convergence error, and FIG. 7 is a perspective view of a concentrated magnetic pole showing an embodiment of the present invention. 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.

Claims (1)

[Claims] 1. A self-convergence type in-line electron gun equipped with a magnetic field control element for concentrating the electron beam on the bottom surface of a bottomed cylindrical concentrating magnetic pole made of a non-magnetic metal material attached to the tip of the electron beam exit side of the electron gun. An in-line electron gun structure characterized in that the length of the tube side of the bottomed cylindrical concentrated magnetic pole is limited to 6.0 mm or less.