JPH0410693B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving focus characteristics of an in-line color cathode ray tube, and particularly to improving focus deterioration caused by a just focus voltage difference between three guns.

Generally, an electron gun used in a color cathode ray tube has a prefocus type electron lens 1 and a main lens type electron lens 2, as shown in FIG.
As a result, the electron beam of the virtual object point 3 is imaged on the screen 4. Note that 5 is a crossover point.

In addition, in the shadow mask in-line type electron gun, as shown in FIG. 2, the electron gun is arranged on one plane, and the offset of the main lens 2,
Three electron beams are converged at each point on the screen 4 by the STC magnetic pole 6 and the deflection yoke magnetic field. Note that 7 is the focal point of the central electron gun, and 8 is the focal point of the side electron guns.

However, with conventional integrated in-line electron guns,
Except for the final offset electron lens, all three electron guns were designed with the same dimension. Therefore, due to the astigmatism caused by the final offset electrode and the quadrupole magnetic field that corrects the residual offset design, a difference occurs in the focus voltage between the central electron gun and the electron guns placed on both sides, which affects the focus characteristics. It had some influence. In particular, focus adjustment is delicate in color display tubes for OA use, and this is a major hurdle in improving focus. The measures that have been taken in the past are as follows. That is, in the conventional design shown in FIG. 2, if the imaging points of the electron beams on both sides are located in front of the imaging point of the central electron beam, that is,
When the just-focus voltages on both sides are high, the pre-focus lenses on both sides are weakened so that the imaging point coincides with the central imaging point.
However, in this case, the side beams are affected by electrode offset (shifting the centers of opposing electrode holes in the main lens) and astigmatism due to the quadrupole magnetic field due to convergence, which makes the effect of spherical aberration in the main lens more significant. I will receive it.

Contrary to the conventional method, the present invention increases the prefocus lens strength of the side beams to reduce the difference in beam spot diameter between the center beam and the side beams.

In other words, the present invention increases the strength of the prefocus lens on both sides.
By narrowing down the beam diameter of the side beam at the main lens and reducing the influence of spherical aberration at the main lens, the difference in spot diameter between the central beam and the side beam is reduced. Of course, by making the prefocus lenses stronger on both sides, the total lens strength of the prefocus and main lenses will be different between the center and both sides, and the focus points of the center beam and side beams will shift. become. However, the difference in beam spot diameter due to the difference in spherical aberration experienced by the center beam and side beams is larger than the difference in spot diameter between the center beam and the side beams due to the shift of the focus point, so the present invention does not work as a whole. Therefore, excellent effects can be obtained.

FIG. 3 shows an embodiment of the present invention. Regarding the hole diameter of the second grid electrode _G2 , the hole diameters on both sides are made smaller than the hole diameter in the center to strengthen the prefocus. Note that G ₃ is the third grid electrode, and 9 is the main lens surface.

The embodiment of FIG. 4 uses this as the second grid electrode G ₂
This is an example achieved by using a difference in plate thickness. Note that L _S is the side electron lens, and L _C is the center electron lens.

In the embodiment shown in FIG. 5, the incident side of the third grid electrode G ₃ is deflected as shown in the figure to change the electrode spacing l ₁ and l ₂ .
Controls the strength of the pre-focus lens. In this case, it also has the effect of correcting STC deviation due to focus voltage fluctuation.

In the embodiment shown in FIG. 6, prefocus correction is performed by changing the hole diameter on the incident side of the third grid electrode _G3 .

The embodiment shown in FIG. 7 is an example in which a pseudo-multistage prefocus lens is realized. 2nd grid electrode
The diameter of the exit hole on the side of G ₂ is made smaller so that a sufficiently strong lens is constructed at the small entrance hole. By doing this, the prefocus on both sides is made stronger than that in the center. Also in this case, by making the large holes on both sides eccentric to the outside with respect to the small hole, it is possible to provide the function of correcting the STC deviation due to the focus voltage difference.

As explained above, according to the present invention, the focus voltages of each electron gun can be matched by prefocus correction, and a cathode ray tube with extremely high quality and good focus can be obtained in a terminal display or the like.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram for explaining the lens system of an electron gun of a general cathode ray tube, Fig. 2 is an explanatory diagram for explaining the focus voltage difference between the center and both side electron guns, and Fig. 3 is an explanatory diagram for explaining the lens system of the electron gun of a general cathode ray tube. An enlarged sectional view of a main part of one embodiment of the pipe, and FIGS. 4 to 7 are enlarged sectional views of main parts of other embodiments. 1... Prefocus lens, 2... Main lens, 3... Virtual object point, 4... Screen, 7...
Focus of central electron gun, 8...Focus of side electron gun,
9...Main lens surface, _G2 ...Second grid electrode,
G ₃ ...Third grid electrode.

Claims (1)

[Claims] 1. In a color picture tube having an in-line electron gun, the in-line electron gun that generates three electron beams has a prefocus lens formed by a second grid electrode and a third grid electrode. , and a main lens formed on the fluorescent surface side of the prefocus lens, and the prefocus lenses on both sides, which receive the electron beam, have a lens strength higher than that of the central prefocus lens, which receives the electron beam. A color picture tube with an in-line electron gun characterized by strong 2. The color picture tube according to claim 1, wherein the holes through which the electron beams pass through on both sides of the second grid electrode are smaller than the hole through which the electron beams pass through the central hole. 3 The thickness of the second grid electrode in the vicinity of the hole through which the electron beam passes on both sides is greater than the thickness in the vicinity of the hole in the center through which the electron beam passes. A color picture tube according to scope 1. 4. The color picture tube according to claim 1, wherein the holes through which the electron beams pass through on both sides of the third grid electrode are smaller than the hole through which the electron beams pass through the central hole. 5. Claim 1, characterized in that the distance between the second grid electrode and the third grid electrode is smaller in the vicinity where the electron beams on both sides pass than in the vicinity where the central electron beam passes. Color picture tube as described in section. 6 In the second grid electrode, the hole diameters on the electron beam entrance side and the exit side are different, and the hole diameter on the exit side is such that the hole through which the electron beams on both sides pass is larger than the hole through which the electron beam passes through the central hole. 2. The color picture tube according to claim 1, wherein the color picture tube is smaller than .