JPH04253476A - Dynamic focus device for cathode ray tube - Google Patents

Abstract

PURPOSE:To realize a dynamic focus device for a cathode ray tube to apply a dynamic focus voltage efficiently to a dynamic focus electrode to increase the accuracy of a focus at peripheries of a fluorescent screen of a cathode ray tube in the focus device to focus the electron beam from the cathode ray tube onto the fluorescent screen. CONSTITUTION:A parabolic voltage synchronously with a deflection circuit 1 is outputted from a parabolic waveform generating circuit 2 and an overscan part of deflection of the parabolic voltage is eliminated by a limiter circuit 6. The dynamic focus device for a cathode ray tube has an output circuit 3 to apply the output of the limiter circuit 6 to the dynamic focus electrode 5 of the cathode ray tube 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic focus device for a cathode ray tube, which improves the focus of a display device using a cathode ray tube, such as a television receiver.

0002

[Prior Art] In recent years, display devices such as television receivers using cathode ray tubes (hereinafter referred to as CRT) have been equipped with dynamic focus devices that correct the focus shift of the electron beam spot due to the difference in deflection distance between the center and the periphery. It has come to be used. An example of a conventional dynamic focus device will be described below with reference to the drawings.

FIG. 3 shows a block diagram of a conventional dynamic focus device. As shown in FIG. 3, the components are 1 a deflection circuit, 2 a parabolic waveform generation circuit,
3 is an output circuit, 4 is a CRT, and 5 is a dynamic focus electrode.

The operation of the dynamic focus device configured as described above will be explained below. First, horizontal and vertical reference signals (H pulse from horizontal deflection and vertical sawtooth wave from vertical deflection) are extracted from the deflection circuit 1 and input to the parabolic waveform generation circuit 2. The parabolic waveform generating circuit 2 shapes the waveform from this reference signal to create horizontal and vertical parabolic waveforms, and adds them together. This waveform is a parabolic waveform shown in FIG. Output circuit 3
Now, the dynamic focus electrode 5 of the CRT 4 is driven by adding a DC component. This allows for better focus on the entire screen.

[0005]

[Problems to be Solved by the Invention] However, in the conventional configuration, the amplitude of the parabolic waveform input to the dynamic focus electrode 2 is up to the deflection overscan portion, which is unnecessary because it does not appear on the screen. C is limited by the input tolerance of the dynamic focus electrode 5.
If the parabolic waveform amplitude is lower than the focus characteristic of RT4, the overscan voltage does not function as a dynamic focus, resulting in a loss.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a dynamic focus device for a cathode ray tube that can effectively use the amplitude of a parabolic waveform for dynamic focus to the fullest input permissible value.

[0007]

[Means for Solving the Problems] In order to achieve the above object of the present invention, a dynamic focus device for a cathode ray tube according to the present invention generates a parabolic voltage synchronized with the output of a deflection circuit that deflects an electron beam of a cathode ray tube. It is equipped with a parabolic waveform generation circuit and a limiter circuit that limits the amplitude of the output voltage of this parabolic waveform generation circuit, and the output voltage of the parabolic waveform generation circuit is cut by this limiter circuit, and the output is applied to the dynamic focus electrode of the cathode ray tube. 1 is a dynamic focus device for a cathode ray tube having means.

[0008]

[Operation] According to the above-described structure, the present invention applies a limiter to the overscanned portion of the parabolic waveform, thereby eliminating the parabolic voltage in the overscanning portion and applying the limiter to the cathode ray tube's allowable input value at the periphery of the screen. It can take full amplitude and improve peripheral focus.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of a dynamic focus device for a cathode ray tube according to an embodiment of the present invention. As shown in FIG. 1, the constituent elements 1 are a deflection circuit;
2 is a parabolic waveform generation circuit, 3 is an output circuit, and 4 is a CRT.
, 5 is a dynamic focus electrode, and 6 is a limiter circuit. The operation of the dynamic focus device for a cathode ray tube configured as described above will be explained below.

First, the horizontal and vertical reference signals (horizontal pulse for horizontal deflection, vertical sawtooth wave for vertical deflection) are supplied from the deflection circuit 1.
is taken out and inputted to the parabolic waveform generation circuit 2. The parabolic waveform generation circuit 2 performs waveform shaping on this reference signal to create horizontal and vertical parabolic waveforms. The upper overscan portion of this parabolic waveform is limited by a limiter circuit 6, and the horizontal and vertical parabolic waveforms are added together. FIG. 2 shows a waveform obtained by applying a limiter to a parabolic waveform. The output circuit 3 adds a DC component to this waveform and outputs it to the dynamic focus electrode 5.

As described above, according to this embodiment, by applying a limiter to the upper part of the parabolic waveform, unnecessary voltages of overscan are cut off, and the amplitude of the input voltage standard value of the CRT can be obtained at the periphery of the screen. Can be done.

0012

As is clear from the above description, the present invention provides a limiter circuit for the dynamic focus voltage for the cathode ray tube and applies a limiter to the overscan portion, thereby reducing the allowable input voltage of the cathode ray tube at the periphery of the screen. The full amplitude can be obtained, the amount of dynamic focus correction can be increased, and the focus in the peripheral area can be improved, which has great practical effects.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a dynamic focus device for a cathode ray tube, which is an embodiment of the present invention.

[Figure 2] Output waveform diagram of the limiter circuit of the dynamic focus device for cathode ray tubes of the same example

[Figure 3] Block diagram of a conventional dynamic focus device

[Figure 4] Output waveform diagram of the parabolic waveform generation circuit of the conventional dynamic focus device

[Explanation of symbols]

1 Deflection circuit 2 Parabolic waveform generation circuit 3 Output circuit 4 Cathode ray tube 5 Dynamic focus electrode 6 Limiter circuit

Claims (2)

[Claims] 1. A deflection circuit for deflecting an electron beam of a cathode ray tube, a parabolic waveform generation circuit for generating a parabolic waveform voltage synchronized with the deflection circuit, and limiting the amplitude of the output voltage of the parabolic waveform generation circuit. A dynamic focus device for a cathode ray tube, comprising: a limiter circuit, and output means for applying an output of the limiter circuit to a dynamic focus electrode of the cathode ray tube. 2. The dynamic focus device for a cathode ray tube according to claim 1, wherein the output means has an output obtained by superimposing a DC voltage on the output of the limiter circuit.