KR20020009095A - A circuit for generating a focus signal of a CRT - Google Patents

Abstract

PURPOSE: A circuit for generating a focus signal of a cathode ray tube is provided, the circuit that detects an active region of a video signal to generate a parabolic waveform focus signal whose amplitude and delay are controlled according to the active region. CONSTITUTION: A circuit for generating a focus signal of a cathode ray tube includes a video detector(10) for detecting the starting point and end point of an active region of a video signal to generate a starting point informing signal and an end point informing signal, and a waveform generator(20) that starts to generate a vertical parabolic waveform and a horizontal parabolic waveform when the starting point informing signal is inputted and stops generation of the vertical parabolic waveform and horizontal parabolic waveform when the end point informing signal is inputted. The circuit further has a waveform amplifier(30) for amplifying the parabolic waveforms, a waveform superposition unit(40) for superposing the amplified parabolic waveforms on each other, and a flyback transformer for amplifying the superposed parabolic waveform to provide it to a focus grid of the cathode ray tube.

Description

A circuit for generating a focus signal of a CRT

The present invention relates to a focus signal generation circuit of a cathode ray tube for compensating for a focus shift when scanning an edge of a screen in an image display device.

More particularly, the present invention relates to a focus signal generating circuit of a cathode ray tube which detects an active region of a video signal and generates a horizontal and vertical parabola waveform focus signal whose amplitude and delay are adjusted according to the active region.

In general, a cathode ray tube (CRT) used in an image display device focuses and accelerates hot electrons emitted from R, G, and B guns, and collides with R, G, and B fluorescent surfaces through a point on a shadow mask to form pixels. The sawtooth current flows through the vertical and horizontal deflection coils to form a two-dimensional screen.

In order to operate the cathode ray tube (CRT), a heater voltage of about 6.3 V is applied to the heater, and a focus grid voltage, a screen grid voltage, and the like are required for focusing the emitted hot electrons. High pressure of about 25KV is applied.

In this case, a focus grid for focusing the electron beam emitted from the cathode is divided into a static focus (S.FOCUS) grid and a focus (D.FOCUS) grid, and the focus grid includes a focus signal (a focus signal for dynamic focusing). Is applied).

As is well known, the diameter of an electron beam in a cathode ray tube increases toward the periphery of the screen. That is, since the focus at the edge is wider than the focus formed at the center of the image display device, the sharpness is poor at the edge. In order to compensate for this, a high resolution image display device applies a compensation waveform, that is, the above-described focus signal, so that the focus of the electron beam is accurately formed on the fluorescent surface of the cathode ray tube.

The focus signal depends on the combination of the cathode ray tube and the deflection coil. In general, as the screen of the cathode ray tube becomes larger, the voltage crest required for compensation tends to increase.

Therefore, a focus signal having a function of correcting a difference in focus caused by a difference in distance between a center portion and a periphery of a cathode ray tube requires several hundred volts of power, and such power is usually obtained from a flyback transformer (FBT). Lose.

FIG. 2 is a circuit diagram showing a conventional focus signal generating circuit of a cathode ray tube. As shown in FIG. 2, a conventional focus signal generating circuit generates waveforms for generating horizontal and vertical parabola waveforms by horizontal and vertical synchronization signals. Part 2; A waveform amplifier (3) for amplifying the generated horizontal and vertical parabola waveforms; A waveform superimposing unit (4) overlapping the amplified horizontal and vertical parabolic waveforms; It consists of a flyback transformer (FBT) for amplifying the superimposed parabola waveform and supply it to the focus grid of the cathode ray tube.

The operation of the conventional focus signal generation circuit constructed as described above will be described in more detail with reference to the waveform diagram of FIG. 3.

First, the waveform generating unit 2 generates a horizontal parabolic waveform in which the center portion is concave in the horizontal period as shown in FIG. 3 (b), and a vertical parabola waveform in which the center portion is concave in the vertical period as shown in FIG. 3 (c). do.

The generated horizontal and vertical parabola waveforms are amplified by the waveform amplifying section 3 and then superimposed through the waveform overlapping section 4 to form a waveform as shown in FIG.

The superimposed parabola waveform is applied to the focus signal input terminal of the flyback transformer (FBT) and amplified again, and then applied to the focus grid of the cathode ray tube, thereby correcting the focus of the cathode ray tube (CRT). Improves the disadvantages of focus coming from

At this time, the focus signal input to the focus terminal of the flyback transformer (FBT) becomes a parabolic waveform concave down as shown in FIG. 3 (d), and a horizontal focus signal for compensating the left and right edges of the screen. Is a parabolic waveform signal in which the center portion generated by the horizontal period (1H) is concave, and a vertical focus signal for compensating the upper and lower edges of the screen is a parabolic waveform signal in which the center portion is generated by the vertical period (1V). to be.

However, since the conventional focus signal generation circuit as described above generates a parabola waveform by triggering a synchronization signal as shown in FIG. 3 (a), the active region or the back and front porch of the video signal are different at the same frequency. Even in this case, there was a problem in that the horizontal and vertical parabola waveforms of the same amplitude and delay were generated.

That is, since the same waveform is generated even though the video signal is different, a waveform having no exact voltage and delay is generated in one video signal, and a voltage difference and delay is generated in another video signal. There was a problem of not losing.

In addition, since the conventional focus signal generation circuit as described above generates a parabola waveform by triggering a synchronization signal as shown in FIG. 3 (a), amplifying it also amplifies voltages other than the active region, thereby unnecessarily high voltage. Since a device having specifications is used, there is a problem that optimal focus is not achieved.

Accordingly, the present invention has been made to solve the above problems of the prior art, to detect the active area of the video signal to generate a horizontal and vertical parabola waveform focus signal whose amplitude and delay are adjusted according to the active area. It is an object of the present invention to provide a focus signal generating circuit of a cathode ray tube.

In order to achieve the above object, the circuit of the present invention includes a video detection unit for detecting a start point and an end point of an active area of a video signal input from the outside and outputting a start point notification signal and an end point notification signal; A waveform generator for starting the generation of a horizontal parabola waveform and a vertical parabola waveform when the start point notification signal is input, and stopping the generation of the horizontal parabola waveform and the vertical parabola waveform when the end point notification signal is input; A waveform amplifying unit configured to amplify the generated horizontal parabola waveform and vertical parabola waveform; A waveform superimposition unit overlapping the amplified horizontal parabola waveform and the vertical parabola waveform; It is characterized by consisting of a flyback transformer for supplying to the focus grid of the cathode ray tube by amplifying the superimposed parabola waveform.

1 is a view showing a typical cathode ray tube,

2 is a circuit diagram showing a focus signal generating circuit of a conventional cathode ray tube;

3 is a waveform diagram of each part of FIG. 2;

4 is a circuit diagram showing a focus signal generating circuit of a cathode ray tube according to the present invention;

5 is a waveform diagram of each part of FIG. 4.

* Explanation of symbols for the main parts of the drawings

10: video detector 20: waveform generator

30: waveform amplifying unit 40: waveform superimposing unit

50: waveform correction unit FBT: flyback transformer

Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

4 is a circuit diagram showing a focus signal generating circuit of a cathode ray tube according to the present invention.

As shown in FIG. 4, the circuit of the present invention includes a video detection unit 10 which detects a start point and an end point of an active area of a video signal input from the outside and outputs a start point notification signal and an end point notification signal; When the start point notification signal is input, the generation of the horizontal parabola waveform and the vertical parabola waveform is started, and when the end point notification signal is input, the generation of the horizontal parabola waveform and the vertical parabola waveform is stopped, and the waveform is delayed by the correction signal. Generation unit 20; A waveform correction unit (50) which receives the parabola waveform from the waveform generator (20) and compares the voltage of the start point and the end point of the parabola waveform video signal active region and outputs a correction signal to the waveform generator (20); A waveform amplifying unit 30 for amplifying a horizontal parabolic waveform and a vertical parabola waveform generated from the waveform generating unit 20; A waveform superimposing unit 40 overlapping the horizontal parabola waveform amplified by the waveform amplifying unit 30 and the vertical parabola waveform; It consists of a flyback transformer (FBT) for amplifying the parabolic waveform superimposed from the waveform overlapping portion 40 to be supplied to the focus grid (G3, G4) of the cathode ray tube (CRT).

Next, the operation and effects of the circuit according to the present invention configured as described above will be described with reference to FIG. 5.

First, as illustrated in FIG. 5A, the video detector 10 detects a start point and an end point of an active area of a video signal input from the outside, and outputs a start point notification signal and an end point notification signal.

When the start point notification signal is input, the waveform generator 20 starts to generate the horizontal parabola waveform and the vertical parabola waveform. When the end point notification signal is input, the waveform generator 20 stops the generation of the horizontal parabola waveform and the vertical parabola waveform.

That is, the waveform generator 1 includes a horizontal parabolic waveform in which the center portion is concave at the horizontal period as shown in FIG. 5 (b), and a vertical parabola waveform in which the center portion is concave at the vertical period as shown in FIG. 5 (c). Create

In this case, the waveform corrector 50 receives a horizontal parabolic waveform and a vertical parabola waveform from the waveform generator 20, and compares the voltage of the start point and the end point of the video signal active region of each parabola waveform to the waveform generator 20. Output the correction signal with).

That is, the waveform corrector 50 detects whether the voltage of the start point and the end point of the video signal active region is constant, and if a voltage difference occurs, outputs a correction signal according to the voltage difference to the waveform generator 20. Accordingly, the waveform generator 20 delays and outputs the horizontal and vertical parabola waveforms according to the correction signal.

Meanwhile, the waveform amplifier 30 amplifies the horizontal parabola waveform and the vertical parabola waveform generated from the waveform generator 20, and the waveform overlap unit 40 amplifies the horizontal parabola amplified from the waveform amplifier 30. The waveform and the vertical parabola waveform are superimposed to form a waveform as shown in Fig. 5 (d).

The parabola waveform superimposed from the waveform superimposing unit 40 is applied to the focus signal input terminal of the flyback transformer (FBT) and amplified once more, and then applied to the focus grids G3 and G4 of the cathode ray tube. By correcting the focus of, the disadvantage of the focus coming from the cathode ray tube (CRT) structure is improved.

At this time, the focus signal input to the focus terminal of the flyback transformer (FBT) becomes a parabolic waveform concave down as shown in FIG. 5 (d), and a horizontal focus signal for compensating the left and right edges of the screen. Is a parabolic waveform signal in which the center portion generated by the horizontal period (1H) is concave, and a vertical focus signal for compensating the upper and lower edges of the screen is a parabolic waveform signal in which the center portion is generated by the vertical period (1V). to be.

As described above, the circuit according to the present invention detects an active region of a video signal and generates a horizontal and vertical parabola waveform focus signal whose amplitude and delay are adjusted according to the active region. Even if it is possible to generate a horizontal and vertical parabola waveform focus signal with amplitude and delay adjusted according to the active area or the back / front pitch, it is effective in accurately correcting the upper, lower, left and right focus of the cathode ray tube screen.

Claims (3)

A video detector for detecting a start point and an end point of an active area of a video signal input from the outside and outputting a start point notification signal and an end point notification signal; A waveform generator for starting the generation of a horizontal parabola waveform and a vertical parabola waveform when the start point notification signal is input, and stopping the generation of the horizontal parabola waveform and the vertical parabola waveform when the end point notification signal is input; A waveform amplifying unit configured to amplify the generated horizontal parabola waveform and vertical parabola waveform; A waveform superimposition unit overlapping the amplified horizontal parabola waveform and the vertical parabola waveform; And a flyback transformer for amplifying the superimposed parabola waveform and supplying it to a focus grid of the cathode ray tube. The method of claim 1 And a waveform correction unit for receiving the parabolic waveform from the waveform generator and outputting a correction signal by comparing the voltage of the start point and the voltage of the active region of the video signal of the parabola waveform. . The waveform generator of claim 2, And a parabolic waveform delayed by the correction signal.