JPH07118280B2 - Cathode ray tube - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a cathode ray tube, and more particularly to an in-line type electron gun.

2. Description of the Related Art A cathode ray tube, for example, a color picture tube includes a fluorescent screen having a light emitting region of each color formed on the inner surface of the face portion of the picture tube, and a shadow having a large number of through holes and a curved effective surface. A mask and an electron gun for generating a plurality of electron beams are provided, and the electron beam passes through a through hole of an effective surface of the shadow mask so that the electron beam impinges on a predetermined light emitting region of the fluorescent screen. Thus, a color image is displayed.

As such a color picture tube, as shown in FIG. 2, there is a color picture tube using a so-called self-convergence in-line electron gun which does not require dynamic convergence.

In FIG. 2, the central electron beam G and the pair of outer electron beams R and B which are emitted from the in-line type electron gun (1) and are in the same plane are arranged in the funnel-shaped portion of the glass envelope (2). And a fluorescent screen (4), which is deflected horizontally and vertically by the deflecting device (5), is on the top surface of the glass envelope (2), and is internally coated with a plurality of fluorescent pixels for emitting three colors. A scan screen is formed through the color selection electrodes (3) arranged on the top of the scan screen. In order to use this color picture tube as a self-convergence method that does not require dynamic convergence correction, the horizontal deflection magnetic field of the deflecting device (5) is made into a strong pincushion distortion and the vertical deflection magnetic field is made into a strong barrel distortion, and FIG. As shown in FIG. 4, these deflection magnetic fields eliminate the coma aberration of the pair of outer electron beams R and B to form a coincident scanning screen (6) on the phosphor screen (4). In this case, the scanning screen (7) of the central electron beam G is generally smaller than the scanning screen (6) formed by the outer electron beams R and B both horizontally and vertically. This misalignment of the scanning screen is due to the coma aberration of the deflecting device (5), and in order to remove the coma aberration and match the scanning screens, the rear leaking magnetic field of the deflecting device (5) affects the electron gun (1). A magnetic field control element made of a magnetic material having a high magnetic permeability is disposed on the bottom surface (11) of a concentrated magnetic pole (10) formed in a cylindrical shape with a bottom and made of a non-magnetic material attached to the tip.

FIG. 4 shows an example of the magnetic field control element arranged on the bottom surface (11) of the concentrated magnetic pole (10). The central electron beam transmission aperture (12) formed in the bottom surface (11) of the concentrated magnetic pole (10) is arranged so as to be sandwiched on the vertical axis YY 'which is the short axis of the phosphor screen (4). A pair of disc-shaped magnetic enhancement elements (15)
And (16) and the phosphor screen (4) are arranged so as to surround both outer electron beam transmission apertures (13) and (14) formed on the horizontal axis XX 'which is the long axis of the phosphor screen (4). It is composed of annular magnetic shield elements (17) and (18). The magnetic enhancing elements (15) and (16) act to increase the deflection sensitivity of the horizontal deflection magnetic field F _H of the deflecting device (5) with respect to the central electron beam G more than the outer electron beams R and B. On the other hand, the annular magnetic shield elements (17) and (18) are connected to the outer electron beam R
Horizontal and vertical deflection fields of the deflection device (5) for B and B
The deflection sensitivity of F _H and F _V is lower than that of the central electron beam G, and the deflection sensitivity of the vertical deflection magnetic field F _{V with} respect to the central electron beam G is higher than that of both outer electron beams.

Therefore, the magnetic field control elements (15), (16), (17) and (18)
As a result, the scanning screen (7) of the central electron beam G is expanded in both the horizontal and vertical directions, and conversely, the scanning screens (6) of both outer electron beams R and B are reduced, and the coma aberration due to the deflection magnetic field is removed for scanning. It is possible to completely match the screens (6) and (7).

(Problems to be Solved by the Invention) Recently, a so-called color picture tube for display, which has a high resolution in a color cathode ray tube, is used for displaying various kinds of information. The density is displayed. To achieve high-density display, the color cathode ray tube has high resolution and uniform focus characteristics, the frequency band of the video circuit is wide to increase the horizontal resolution of the display screen, and the vertical resolution of the display screen is increased. Requires a large number of scanning lines.

Usually, in order to increase the number of scanning lines as one means of high-density display, the horizontal deflection frequency _{h is set} to that of the current standard color TV system.
It is being increased to 15.75KHz or higher. In this case, when the horizontal deflection frequency _h = 15.75 KHz, there was no problem at all. The horizontal deflection magnetic field generated a horizontal aberration on the scanning screen formed by the outer electron beam and the central electron beam, and a core aberration was generated. As shown in FIG. It is slightly enlarged by '(horizontal scanning screen 6) of both outer electron beam to the screen (7)', and the ratio of enlargement are different in the left and right of the phosphor screen (4), expanding the size of the left l ₁ Causes an asymmetry that is larger than the enlarged dimension l ₂ on the right side. This deviation of the scanning screen is a convergence error, which significantly deteriorates the quality of the image receiving screen. For example, in a 20-inch 90-degree deflection type color picture tube, when the horizontal deflection frequency _h = 15.75 KHz is doubled to _h = 31.5 KHz, the above deviations l ₁ and l ₂ are l ₁ ≈ 0.2 mm, l near the effective phosphor screen. ₂
≈0.05 mm, and when _h = 64 KHz, l ₁ ≈0.4 mm, l ₂ ≈0.1 mm
Becomes

The cause of the shift of the scanning screens (6 ') and (7') formed by the outer electron beam and the central electron beam in the horizontal direction due to the coma aberration with the increase of the horizontal deflection frequency _h is as follows. First of all, a horizontal magnetic field component penetrating the side surface of the final accelerating electrode causes an eddy current on the side surface of the final accelerating electrode, which causes a magnetic flux that interferes with the magnetic flux of the normal horizontal deflection magnetic field component to reduce the magnetic flux. The loss of magnetic flux due to this eddy current was completely negligible at the conventional horizontal deflection frequency of _h = 15.75 KHz, but as the frequency increased, the loss of magnetic flux due to eddy current became non-negligible. The scanning screen (6 ') of (1) spreads in the left-right direction with respect to the scanning screen (7') of the central electron beam.

On the other hand, the waveform of the current flowing through the horizontal deflection coil of the deflection device (5) for performing the horizontal scanning is the sawtooth wave shown in FIG. In FIG. 5, the time t ₁ from the point a to the point b is the horizontal scanning time, the time t ₂ from the point b to the point c is the horizontal retrace time, and normally t ₂ is about 1 / t of t _1. It is set to about 5.
Point a or point c corresponds to the left end of horizontal scanning, and point b corresponds to the right end. That is, the position of the left end 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 scan time t ₁ , and the horizontal scan time t ₁ during the horizontal retrace time t _2. A magnetic field is generated by an electric current that changes at a speed that is about five times as fast.

This is because the amount of change in magnetic flux when moving from horizontal scanning to horizontal retrace is the same as the amount of change in magnetic flux when moving from horizontal retrace to horizontal scan, but in the former case, the television signal is cut when horizontal retrace is performed. Therefore, it does not affect the screen at all. Therefore, the left edge of the screen where horizontal scanning starts is greatly affected. Therefore, the change in magnetic flux due to the eddy current loss due to the high-frequency component magnetic field is larger on the left side of the phosphor screen than on the right side. For this reason, as shown in FIG. 5, the lateral expansion width of the scanning screen (6 ') of both outer side electron beams with respect to the scanning screen (7') of the central electron beam is larger on the left side l ₁ than on the right side l _2. Therefore, asymmetry occurs in the coma aberration in the horizontal direction. At the horizontal deflection frequency _h = 15.75 KHz used in the conventional standard color TV system (NTSC system), about t ₁ = 51 to 53 µsec, t ₂
= 10 to 12 μsec, the eddy current loss due to this is completely negligible, and therefore the above-mentioned coma aberration and its asymmetry cannot be found substantially. However, the horizontal deflection frequency _h
The difference between t ₁ and t _{2 as well as} the effective scanning time t ₁ are increased, the retrace time t ₂ is set as small as possible, and the asymmetry of the eddy current loss becomes a non-negligible amount and the above phenomenon occurs. Come on.

As a means for confirming this phenomenon digitally, the horizontal direction of the deflecting device (5) is provided by a minute search coil that can be inserted inside the aperture diameter of the electrode forming the main lens for focusing the electron beam of the electron gun on the phosphor screen. Focusing on the phase difference between the magnetic field generated by the deflection coil and the magnetic field generated inside the central electron gun and inside both outer electron guns, paying attention to the part a of the horizontal deflection current waveform in FIG. 7, it is measured as shown in FIG. It can be seen that there is a difference between the internal magnetic field of the gun and the internal magnetic fields of both outer electron guns.

The present invention has been made in view of the above-mentioned drawbacks.
An in-line electron gun that prevents the coma aberration from occurring in the scanning screen formed by both outer electron beams and the central electron beam by increasing the horizontal deflection frequency of the color cathode ray tube using the convergence type in-line electron gun. It is intended to be provided.

[Structure of Invention]

(Means for Solving Problems) In the present invention, a gap common to the central electron gun and both outer electron guns is provided in at least one place of the final acceleration electrode of the in-line type electron gun, and the final acceleration electrode divided by this gap is It is characterized in that it is electrically conducted and kept at the same potential. With this configuration, it is possible to prevent the magnetic flux loss due to the eddy current generated by the horizontal deflection magnetic field that conducts on the side surface of the final accelerating electrode, and the scanning screen formed by the central and outer electron beams despite the high horizontal deflection frequency. Since the asymmetrical shift of the scanning screen due to the coma aberration can be eliminated, a cathode ray tube capable of displaying high-density image information can be obtained.

(Operation) According to the present invention, by dividing the final accelerating electrode of the electron gun of the cathode ray tube into a plurality of final accelerating electrodes, it is possible to suppress the eddy current generated therein and prevent the magnetic flux loss of the horizontal deflection magnetic field. . Since the final accelerating electrodes divided here are kept at the same potential, the action of the main lens is not affected.

Embodiment An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a final focusing electrode of the electron gun part of the cathode ray tube of the present invention and a main focusing electrode forming a main lens. First
In the figure, the final accelerating electrode (20) has an intermediate gap (23), is divided, has a gap width W, and is electrically conductive, so that the gap (23) has an electron lens effect. I don't. A phase difference between the central deflection electron beam and the outer electron beam passage holes of the in-line type electron gun having the final accelerating electrode of the present embodiment and the horizontal deflection magnetic field was compared by a search coil with that of the conventional final electrode having no gap. Then, the 8th
As shown in the figure, it can be seen that the phase difference is significantly relaxed in the gap portion of the final acceleration electrode (23). This is because an eddy current due to the horizontal deflection magnetic field is divided by the main gap due to the presence of a gap in the intermediate portion of the final accelerating electrode (23), and a normal horizontal deflection magnetic field passes through the gap.

In this embodiment, the width W of the gap was changed and the maximum phase difference inside the central and outer electron beam passage holes was measured. As shown in FIG. There was not much change at> 1.0 mm. Therefore W
= 1.0 mm, the present invention is applied to a 20-inch 90-degree deflection type color cathode ray tube, and the convergence error between the scanning screen of the central electron beam and the scanning screens of both outer electron beams at the horizontal deflection frequency _h = 64 KHz is 0.1 on the left side of the screen. It can be minimized to less than mm or almost 0 on the right side.

〔The invention's effect〕

As described above, according to the present invention, the horizontal deflection frequency is 15.7.
Even if the frequency is increased from 5 KHz to 64 KHz or more, the convergence error at the left and right edges of the screen between the outer electron beam and the central electron beam can be reduced to a negligible level, and the horizontal deflection frequency of the color cathode ray tube is increased to achieve high density display. Even if it does, the image quality will not be deteriorated due to the color shift. Further, since the dependency of the convergence error on the horizontal deflection frequency is eliminated, its industrial practical value is extremely high.

[Brief description of drawings]

FIG. 1 is a schematic view showing the vicinity of a final accelerating electrode of an electron gun of a cathode ray tube showing an embodiment of the present invention, FIG. 2 is a schematic sectional view of a conventional color cathode ray tube, and FIG. 3 is this color cathode ray tube. FIG. 4 is a diagram showing a scanning screen formed by the electron beams of the central and outer electron guns on the phosphor screen, and FIG. 4 describes a magnetic field control element for correcting coma aberration of the scanning screen and its action on the horizontal and vertical deflection magnetic fields. FIG. 5 is an explanatory view for explaining the shift of the scanning screen formed by the electron beams of the central and outer electron guns which appear on the phosphor screen when the horizontal deflection frequency becomes large, and FIG. 6 is a horizontal view. FIG. 7 is a diagram showing a waveform of a current flowing through a deflection coil, FIG. 7 is a diagram showing a phase difference between magnetic fields in both outer electron beam transmitting holes with respect to a magnetic field in a central electron beam transmitting hole of a conventional electron gun, and FIG. Central electron of the electron gun Figure electrode arrangement diagram corresponding thereto indicating the phase difference between the two outer electron beam passage holes in the field for over beam transmission hole in a magnetic field, FIG. 9 is a diagram showing the relationship between the phase difference and the gap width. (1) ...... In-line type electron gun, (2) ...... Glass envelope (4) ...... Phosphor screen (6), (6 ') ...... Scanning screen formed by both outer electron beams (7), (7 ') ... Scanning screen formed by central electron beam (23) .. Gap width

Claims (1)

[Claims] 1. A cathode ray tube equipped with an electron gun having at least electrodes and a plurality of electrodes having electron beam passage holes, wherein the final accelerating electrodes of the electron gun section are 1.0 mm in at least two in a plane perpendicular to the tube axis. A cathode ray tube, which is divided at the above intervals, and the divided final accelerating electrodes are kept at the same potential.