JPH023258B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a multi-stage focusing electron gun in which a main focusing lens system includes a bipotential lens (BPF lens) and a unipotential lens (UPF lens).

In general, bipotential electron guns have small spherical aberrations, and since the final anode is the only electrode to which high voltage is applied, they have good beam spot characteristics (high resolution) and good high voltage resistance characteristics. It is mainly used in color picture tubes. However, when trying to obtain the best beam spot characteristics by using a large diameter lens, there is a drawback that the electron gun length becomes large.

Therefore, a multi-stage focusing electron gun was devised in which a unipotential lens was placed just before a bipotential lens. In this case, the main focusing lens system is
4 grids as shown in Figure 1 a or b
Consisting of G ₃ , G ₄ , G ₅ , and G ₆ , it is possible to shorten the electron gun length. In the electrode configuration shown in Figure 1a,
Although it has the advantage that only two supply voltages, V _L and V _H, are sufficient, the high voltage V _H (final anode voltage) is applied to the fourth grid _G4 , so the high voltage withstand characteristics are
The drawback is that it is worse than a BPF lens alone. Further, although the electrode configuration shown in FIG. 1b has good high voltage quality, it has the inconvenience of requiring three voltages, V _L , V _M , and V _H , to be supplied to the four grids.

In the electrode configuration shown in FIG. 1b, focus adjustment is performed by changing the value of _VM . Variable range is UPF
The closer the lens is to the BPF lens, the wider it becomes.
When the UPF lens is brought closer to the BPF lens, the electron beam diameter inside the UPF lens increases. To explain this with reference to Fig. 2, the lens arrangement shown in Fig. 2a is as follows:
Compared to the lens arrangement shown in figure b (θ ₂ /θ ₁ = constant), the focus variable range is (P ₁ to P ₁ ')/(P ₂ to
P ₂ ′) times wider, but the electron beam diameter inside the UPF lens becomes larger by r ₁ /r ₂ times, and the aberrations caused by the UPF lens become larger. Therefore, UPF
It is desirable to place the lens as far away from the BPF lens as possible, and the focus adjustment should be done using the BPF lens.
It is best to do this by changing the voltage V _M on the low voltage side of the lens. Note that changing the voltage V _L on the low voltage side of the UPF lens causes a change in the divergence angle and beam diameter of the electron beam entering the BPF lens, so the variable range is restricted.

The present invention has been made with the above-mentioned points in mind.Next, the electron gun of the present invention will be explained together with the embodiment shown in FIG.

K is the cathode, G ₁ is the first grid, G ₂ is the second grid, G ₃ is the third grid, G ₄ is the fourth grid,
G ₅ indicates the fifth grid, G ₆ indicates the sixth grid, and G ₇ indicates the seventh grid (final anode). The second grid _G2 , the third grid _G3 , and the _fifth grid G5, which are accelerating electrodes, are all made of plate-shaped bodies, and the fourth grid _G4 and the sixth grid _G6 are both made of cylindrical bodies. It has end plates with holes at both ends in the axial direction. The second grid G ₂ is connected to a 450V power supply,
The third grid G ₃ and the fifth grid G ₅ have a common
It is connected to a 600V variable power supply, the fourth grid _G4 and the sixth grid _G6 are connected to a common 9kV power supply, and the seventh grid _G7 is connected to a 27.5kV high voltage power supply. And the second and third grid G ₂ ,
G ₃ and one end plate of the fourth grid G ₄ produce a prefocus lens l ₁ ; the other end plate of the fourth grid G ₄ , the fifth grid G ₅ and the sixth grid G ₆ One end plate of the sixth grid G6 produces a UPF lens _l2 , and the other end plate of the sixth grid _G6 and the seventh grid _G7 produce a BPF lens _l3 . In other words, the main focusing lens system is BPF
The lens is composed of the lens _l3 and the UPF lens _l2 in front of it as before, but the focus adjustment is performed by adjusting the intermediate low potential of the UPF lens _l2 to the third grid.
This is accomplished by varying the voltage of _G3 .

When the voltages of the third and fifth grids G ₃ and G ₅ are changed, both the strength of the pre-focus lens l ₁ and the strength of the UPF lens l ₂ change, and as a result of the multiplication of both lens actions, the pre-focus lens Compared to the case where the strength of l ₁ is constant, the variable range of focus adjustment by varying the low potential becomes larger. Also,
Not only can the necessary focus adjustment be achieved with a slight voltage change, but the electron gun length can also be shortened without sacrificing the features of the BPF lens.

[Brief explanation of drawings]

Figures 1a and b are schematic diagrams showing the electrode configuration of a conventional multistage focusing electron gun, and Figures 2a and b are diagrams showing the relationship between the distance between lenses and the electron beam diameter of a conventional multistage focusing electron gun, respectively. 3 are diagrams showing an electrode structure of an embodiment of the multi-stage focusing electron gun of the present invention.
G ₃ ... 3rd grid, G ₄ ... 4th grid, G ₅
...5th grid, G ₆ ...6th grid, G ₇ ...
...7th grid.

Claims (1)

[Claims] 1 third and fifth grids to which a common variable voltage V _L is applied, a seventh grid to which a high voltage V _H is applied, and an intermediate voltage V _M that is higher than the low voltage V _L and lower than the high voltage V _H The second grid, the third grid, and the fifth grid, which are acceleration grids, are all made of plate-shaped bodies, and the fourth and sixth grids are both made of cylindrical bodies. , has end plates with holes at both ends in the axial direction, and the pre-focus lens is attached to the end plate of one of the second, third and fourth grids, and the other end plate of the fourth grid is attached to the pre-focus lens. , producing a unipotential lens by one end plate of the fifth grid and the sixth grid, and producing a bipotential lens by the other end plate of the sixth grid and the seventh grid, respectively. A multi-stage focusing electron gun.