JPS6238822B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to cathode ray tubes, and more particularly to cathode ray tube displays comprising a dynamic focusing correction circuit.

[Conventional technology and its problems]

Conventional electromagnetic deflection cathode ray tubes (hereinafter simply referred to as CRTs) for displaying images, such as characters and graphics, use a single electron lens means to focus the electron beam. In other words, there are unipotential electron lenses (hereinafter referred to as UPL) in which the entrance and exit electrode potentials are equal to each other, and bipotential electron lenses (hereinafter referred to as UPL) in which the entrance and exit electrodes have different potentials.
(referred to as BPL). In these CRTs, especially when the display screen area is large (for example, 19 inches), the display screen is relatively flat and there is a large deviation from the spherical surface with the center of deflection as a reference, so the optimal focusing is at the center of the display screen. If adjusted to , the convergence state in the peripheral area will be incomplete, that is, the focus will be out of focus. In order to solve this problem, it is conceivable to adopt a so-called dynamic focusing correction technique in which the focusing electrode voltage is corrected according to the deflection signal of the electron beam.

A CRT for displaying character and graphic information requires extremely high resolution over the entire display screen. CRTs for this purpose generally use BTL, whose average focusing voltage is approximately 3 kV or higher when the electron beam is at the center of the screen. Use such BPL
To perform dynamic focusing correction on the CRT and obtain proper focusing of the electron beam across the entire screen,
It is necessary to further apply a large-amplitude correction voltage of about 500V to this voltage of about 3kV or more. The reason why this correction voltage has a large amplitude is that because the average voltage of the focusing electrode is high (approximately 3 kV or more), the change in the focusing position relative to the voltage change, that is, the sensitivity is low. Therefore, the focusing amplifier that adds this correction voltage to the BPL is approximately
Must be isolated from high operating voltages above 3kV,
The configuration is complicated, expensive, and maintenance services are inconvenient. Furthermore, amplification devices that can amplify large amplitude signals of about 500V are difficult to obtain, and have the drawbacks of not only being expensive but also lacking in reliability.

[Purpose of the invention]

It is therefore an object of the present invention to provide a CRT with low voltage control means for dynamically correcting the focus of the electron beam across the screen.

[Summary of the invention]

The CRT of the present invention forms a first crossover of the electron beam by a triode section consisting of a cathode, a control grid and a first anode;
A second crossover is formed in the second electron lens section using a first electron lens means of the UPL and a second electron lens means of the UPL or BPL, and the central electrode of the first electron lens means is operated at approximately a reference potential. The output of the focusing amplifier is applied to move the position of the second crossover in the direction of the tube axis, so that an electron beam image properly focused over the entire display screen is formed by the second electron lens means.

〔Example〕

FIG. 1 is a longitudinal cross-sectional view of one embodiment of a CRT according to the present invention, and the CRT 10 has a glass tube 12 comprising a neck portion 14 and a funnel portion 16.
Also within the clock bulb 12 are a triode section consisting of a cathode 18, a control grid 20 and a first anode 22, a generally cylindrical entrance electrode 24 coaxially disposed along the tube axis, a central (or focusing) electrode 28, and a triode section consisting of a cathode 18, a control grid 20 and a first anode 22; first electron lens means of the UPL consisting of an exit electrode 26;
The second electron lens means of the BPL comprises an electrode 26 that is part of the UPL, a conductive layer 30 on the inner surface of the funnel 16, and a fluorescent screen 48. Further, a deflection coil 42 is fixed to the outer periphery of the bulb 12, which substantially corresponds to the second electron lens means of the CRT 10.

The cathode 18 has a reference potential or ground potential, has a heater coil 32 therein, and emits thermoelectrons. The control grid 20 is connected to a power source with a negative bias voltage, for example -50V, with respect to the cathode 18, and has an aperture 34 through which the electron beam 36 emitted from the cathode 18 passes, and shapes the electron beam 36 with the aperture 34. Determine its electron density.
Control grid 20 acts on and focuses electron beam 36 to form a first crossover C ₁ between control grid 20 and first anode 22 .

The first anode 22 is connected to a power source at a positive potential, for example 1 kV, with respect to the cathode 18, and the electron beam 3
6 has a beam-forming aperture 38 through which it passes. The electric field created by this first anode 22 acts on the electron beam 36 and diverges as it moves through the entrance electrode 24 of the UPL means. The same voltage is applied to the central electrode 24 and the exit electrode 26 of the UPL means,
For example, apply 2kV. Entrance electrode 24 has a beam-forming aperture 40 through which electron beam 36 passes.
The electron beam 36 passes through this electrode 24 and diverges as it approaches the central (focusing) electrode 28 .

Horizontal and vertical deflection coils 42 of conventional design are provided around the outer periphery of bulb 12, and conventional X and Y deflection circuits 44 are provided.
It is driven by the deflection signal generated by. A focusing correction signal obtained by performing necessary waveform conversion from the deflection circuit 44 is input to the focusing amplifier 46, and its amplified output is applied to the focusing electrode 28. Since no high voltage is applied to the focusing electrode 28, the output voltage of the focusing amplifier 46 is a low voltage and low amplitude, for example, 0 to 100 V, and the voltage level is equal to the deflection given to the electron beam 36 by the deflection coil 42. Note that it is degree dependent. That is, as the electron beam 36 deviates from the tube axis due to deflection, the focusing electrode 28
The voltage at is also changed, thereby changing the electric field of the UPL and moving the position of the second crossover C ₂ of the electron beam 36 to a different tube axis position within the exit electrode 26 of the UPL.

The conductive layer 30 is connected to a high voltage power source, for example 18 kV, and engages a conventional fluorescent screen 48 formed of, for example, the well-known P4 type phosphor, such that 18 kV is also applied to the fluorescent screen 48. do. The second crossover C ₂ of the electron beam 36 is
BPL ensures proper focus at all display positions on the fluorescent screen 48. Incidentally, the fluorescent screen 48 is made by laminating a plurality of fluorescent layers of different emission colors, and the high voltage power source is set to 18 kV by a switch 54, for example.
It may be a well-known beam penetration type that changes the emission color by switching at 12 kV. It is particularly suitable for high-density character or graphic display devices, as it is possible to improve the discrimination of information displayed on the fluorescent screen 48 by switching the luminescent color.

In the CRT display device of this embodiment, the position of the second crossover C2 of the electron beam ₃₆ is controlled within the exit electrode 26 by changing the voltage of the focusing (center) electrode 28 constituting the UPL in accordance with the deflection signal. By doing so, deflection and focusing distortion is corrected. This focusing distortion correction is performed using a focusing electrode 28 that operates at approximately a reference potential.
Since this is done by controlling the voltage of , the change in the position of the second crossover C ₂ of the electron beam 36 due to this dynamic correction voltage is large. That is, it has high sensitivity and the required correction voltage amplitude is lower (approximately 100V) than in the conventional case (approximately 500V). For that purpose, the focusing amplifier 4
6 does not need to be a high voltage type or an insulated type, and can be constructed easily and inexpensively using conventional elements, and has low power consumption, high reliability, and easy maintenance service.

FIG. 2 shows a CRT according to another embodiment of the present invention.
Elements similar to those of the embodiment of FIG. 1 have been given like reference numerals. In FIG. 2, a second UPL is used as the second electron lens means instead of the BPL in FIG. 1.
The first UPL is the entrance electrode 24, the center (focusing) electrode 28
and an exit electrode 26, and an entrance and exit electrode 24-
26 are both connected to an 18kV high voltage power supply.
The focusing electrode 28 is connected to the output of the focusing amplifier 46 and varies from 0-200V for dynamic focusing distortion correction. The second UPL shares the exit electrode 26 of the first UPL as an entrance electrode, and is composed of a central electrode 52 of about 0V and an exit electrode 50.

The CRT in the embodiment shown in Figure 2 is basically the same as in Figure 1.
Since it is similar to CRT, detailed explanation will be omitted.
Here, due to the output voltage of the focusing amplifier 46, a second crossover of the electron beam formed approximately in the exit electrode 26 is moved along the tube axis, and is properly imaged on the fluorescent screen 48 by the second UPL. .
In the case of the CRT shown in FIG. 2, the fluorescent screen 48 may have a single luminescent color, but it may also be one in which phosphors of red, green, blue, or other desired luminescent color are laminated or each fluorescent particle is coated in multiple layers. It may be a conventional penetration type phosphor. In that case, switch means 54 selectively applies 18 kV or 12 kV to fluorescent screen 48. For example, information can be displayed in red when the voltage is 12kV and green when the voltage is 18kV. Further, by arbitrarily selecting the voltage of the fluorescent screen 48, a continuously changing emission color is obtained between red, orange, yellow and green. Furthermore, when the voltage of the conductive layer 30 is changed, the generated electric field also changes, so in order to obtain the optimum focusing state, the input and exit electrodes 24 of the first UPL are
-26 voltage is also switched by switch 54.

〔Effect of the invention〕

As is clear from the above description, the CRT of the present invention
In place of the BPL commonly used in conventional large electromagnetic deflection CRTs, the present invention employs two electron lens means: a first electron lens means of UPL and a second electron lens means of BPL or UPL. The first electron lens means causes a second crossover of the electron beam into the electrode 26 forming part of the first and second electron lens means, which is imaged onto a fluorescent screen by the second electron lens means. I'm letting you do it. The second crossover position is moved along the tube axis by controlling the central (focusing) electrode of the first electron lens means, operating at approximately the reference potential, by the output voltage of the focusing amplifier in response to the deflection signal; Optimal focusing is achieved over the entire area of the fluorescent screen. Moreover, the focusing amplifier does not require any insulation, and its correction voltage is a low voltage of about 100 to 200V, so it can be easily realized using commercially available inexpensive elements, and it is highly reliable and requires no maintenance service. It has various remarkable effects such as being easy to use.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view of one embodiment of the CRT according to the present invention, and FIG. 2 is a longitudinal cross-sectional view of another embodiment of the CRT according to the present invention. In the figure, 18 is a cathode, 20 is a control grid,
22 is a first anode; 24, 26, 28 are first electron lens means; 26, 30 or 26, 50, 52
42 is a second electron lens means; 42 is a deflection coil; 44 is a deflection coil;
indicates a deflection circuit, and 46 indicates a focusing amplifier.

Claims (1)

[Scope of Claims] 1. A cathode that emits an electron beam, a control grid located near the cathode to which a negative potential is applied, and a control grid located near the control grid to which a positive potential is applied to the cathode. a first anode, the potential of the first anode and the control grid creating a first crossover between the control grid and the first anode; a unipotential first electron lens having generally cylindrical entrance, center and exit electrodes arranged to form an electric field of sufficient strength to cause a second crossover at different tube axial positions within the exit electrode section; means and said first
a second part of which the exit electrode of the electron lens means is included;
electron lens means; a display screen on which the electron beam from the second crossover is focused by the second electron lens means; A cathode ray tube comprising: a focusing amplifier for applying voltage to the central electrode of the first electron lens means to change the second crossover position and correct deflection distortion.