JPS5942945B2 - cathode ray tube device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in the electron beam focusing method for a cathode ray tube.

In general, in a cathode ray tube, there are two methods for focusing an electron beam from a cathode onto a phosphorescent surface: an electromagnetic focusing method using a magnetic field, and an electrostatic focusing method using an electrostatic field.

In the former case, an electric current is normally passed through a coil to focus the electron beam, and the focusing is adjusted by adjusting the strength of the current.

However, this method has the disadvantage that it requires a highly stable power source for passing current through the coil.

A method using permanent magnets has been attempted as an improvement on this, but it is difficult to adjust the strength of the magnet, and in particular, it is nearly impossible to perform dynamic focusing to focus at each point on the phosphor surface.

On the other hand, in the case of the latter electrostatic focusing, the strength of the focusing effect can be easily controlled by adjusting the voltage applied to the electrodes.

However, cathode ray tubes that require high resolution have the disadvantage that they cannot provide the focusing characteristics required by electrostatic focusing.

There is a method of combining electromagnetic focusing and electrostatic focusing to compensate for these drawbacks, but in this case, the electrostatic focusing is used as an auxiliary and therefore needs to be weakened, and the focus voltage becomes high and the voltage applied from the stem is becomes difficult.

Furthermore, since the virtual object point position of the electron beam changes due to adjustment using electrostatic focusing, there is a drawback that it is difficult to obtain an image point on the screen surface.

This will be explained based on FIG.

Figure 1 shows a cathode ray tube device that combines conventional electromagnetic focusing and electrostatic focusing. 1 is the main body of the cathode ray tube, 11 is its face, and the inner surface is a phosphor (
(not shown) is applied.

Further, an electron gun is arranged inside the neck portion 12.

13 is the cathode, and there is usually a cathode heating heater (
(not shown).

A first grid 14 controls the amount of electron beams emitted from the cathode 13.

A second grid 15 applies a positive potential to the cathode 13 to accelerate the electron beam.

16 is a third grid to which a focus voltage is applied from the stem.

A fourth grid 17 is electrically connected to the conductive film 18 inside the neck.

Thus, the third grid 16 and the fourth grid 17 form an electrostatic lens and the electron beam is prefocused.

Here, 24 is the object-side principal surface of the electrostatic lens, and 25 is the image-side principal surface, and the electron beam is refracted and focused between these bidirectional surfaces 24 and 25.

Without this electrostatic lens, the outermost electron beam of the electron beam emitted from the cathode would spread as shown by the solid line 20, and would be focused on the fluorescent surface by the focusing magnetic field from the magnetic field generator 2.

Here, the "outermost electron beam" refers to an electron beam that passes through the outermost part of the electron beams that enter the object-side main surface 24 of the electrostatic lens.

However, if a potential different from that of the fourth grid 17 is applied to the third grid 16 and an electrostatic lens is formed between them, the outermost electron beam of the electron beam is slightly focused as shown by the dotted line 21, and the magnetic field generator 2 is focused on the fluorescent surface by a focusing magnetic field.

In this case, the virtual object point position 22 of the electron beam moves backward 23.

Here, the "virtual object point position 22" refers to a point where the slope of the outermost electron beam on the object-side main surface 24 of the electrostatic lens is extended in the electron beam incident direction and intersects with the electron beam central axis 26.

The way in which this movement actually occurs is that all the electrons in the electron beam are not uniform, and differ depending on the radial position of the electrons when they pass through the electron lens.

For this reason, the width of the variation in the virtual object point position of the electron beam increases, and the width of the variation in the image point also increases accordingly, so that the beam diameter obtained on the fluorescent surface increases.

In addition, since the electrostatic lens is also weak, the third grid 16
The difference between the potential of and the potential of the fourth grid 17 becomes smaller,
The potential of the third grid 16 becomes high.

Supplying this through the stem has the disadvantage that various problems tend to occur in terms of reliability.

The present invention solves these drawbacks by combining electromagnetic focusing and electrostatic focusing, adjusting the difficulty of adjusting electromagnetic focusing with electrostatic focusing, and solving the poor focusing characteristics of electrostatic focusing by using an electrostatic lens. The present invention provides a cathode ray tube device that takes advantage of the good focusing characteristics of electromagnetic focusing by disposing it at a specific position.

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

FIG. 2 shows a cathode ray tube device of the present invention.

Points different from FIG. 1 will be explained.

The position of the electrostatic lens composed of the third grid 16 and the fourth grid 17 in FIG. 1 is in a special position in FIG.

That is, by forming the second grid 16 short and the third grid 17 long, the main surface 24 on the object point side of the electrostatic lens composed of the third grid 16 and the fourth grid 17 is moved backward (to the left). The electron beam is moved to the position of the virtual object point of the outermost electron beam of the electron beam emitted from the electron gun composed of the cathode 13, the first grid 14, the second grid 15, and the third grid 16.

Since the distance from the geometric lens center plane 27 located between the third grid 16 and the fourth grid 17 to the object point side main surface 24 is a substantially constant value that depends on the grid voltage, as described above, By forming this lens, the geometrical lens center plane 27 is moved further rearward than in the conventional example shown in FIG. 1, and the object point side main surface 24 is moved rearward by that amount.

In this way, the virtual object point position 22 of the electron beam 20 without a lens and the virtual object point position 23 of the outermost electron beam of the electron beam 21 when passing through this lens are almost the same.

Moreover, the outermost electron beam is not affected by lens aberration.

Furthermore, since the magnitude of refraction of the electron beam is proportional to the square root of the potential ratio in the lens space, the above equation is enough (N - potential of the fourth grid 17/potential of the third grid 16). 16 can be used at a considerably lower potential.

In fact, in the conventional example shown in FIG.
, the third grid 16 is 20-35, while the second
In the illustrated invention, the fourth grid 17 and the second grid 15
When the applied voltage of the third grid 16 is the same as that of the conventional example, the applied voltage of the third grid 16 may be 5 to 35.

In other words, the voltage applied to the third grid 16 can be lower than 20, which is the lower limit of the conventional example.

As explained above, according to the present invention, the spread of the electron beam at the electron focusing lens section (the two magnetic field generator sections) can be improved without the various drawbacks caused by adding electrostatic focusing adjustment of the electron beam. It is possible to reduce the aberration of the electromagnetic focusing lens, and to maintain a constant focusing magnetic field, the strength of the electrostatic lens can be adjusted to optimize the electron beam diameter on the fluorescent surface. can be easily done.

Further, in the figure, an electrostatic lens such as a pi potential is used, but it goes without saying that the lens is not limited to this.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory sectional view of a conventional cathode ray tube device, and FIG. 2 is an explanatory sectional view of a cathode ray tube device of the present invention. 1 is the cathode ray tube body, 2 is a focusing coil, 13 is a cathode, 14 to 17 are grids, 22.23 is a virtual object point position,
24 is the main surface on the object point side. Note that the same reference numerals in the figures indicate the same or corresponding parts.

Claims (1)

[Claims] 1. In a cathode ray tube that operates by combining an electrostatic focusing lens and an electromagnetic focusing lens, the electrostatic focusing lens is provided closer to the cathode than the electromagnetic focusing lens, and the main surface on the object point side of the electrostatic focusing lens is the cathode, and the first 1. A cathode ray tube device, characterized in that the cathode ray tube device is disposed near a virtual object point position of an outermost electron beam of an electron beam emitted from an electron gun composed of a grid, a second grid, and a third grid.