JPH06350865A - Focus adjustment circuit for flat type picture receiving tube - Google Patents

Abstract

PURPOSE:To attain the focus adjustment of a whole screen in a flat type picture receiving tube. CONSTITUTION:The parabolic wave focus correction signal (b) of a horizontal period is modulated by the trapezoidal wave distortion correction signal (a) of a vertical period, and the trapezoidal wave distortion correction signal (a) is superposed on this modulated focus correction signal (c), and a dynamic focus correction signal (f) is formed, and the focus adjustement of the flat type picture receiving tube 1 is executed by this dynamic focus correction signal (f). Since the dynamic focus correction signal (f) is a correction signal based on the trapezoidal wave distortion correction signal (b), focus can be adjusted correctly extending over the whole screen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus adjusting circuit suitable for application to a flat type picture tube or the like.

[0002]

2. Description of the Related Art A flat type picture tube (flat type cathode ray tube) 1 having a fluorescent screen formed so as to be inclined at a relatively small angle with respect to a central axis of an electron gun is a flat CRT shown in FIG.
As described above, the electron gun 2 and the image receiving surface 4 arranged in the tube are arranged in the same plane, and the fluorescent surface 3 is formed on the inner surface of the panel facing the image receiving surface 4.

Horizontal and vertical deflecting devices (not shown) are arranged on the neck side of the picture tube 6, and the electron beam emitted from the electron gun 2 is deflected as shown by the broken line to reach the fluorescent screen 3. Then, the fluorescent screen 3 emits light. An image (color image or the like) obtained by this light emission is observed from the image receiving surface 4 side.

Even if a flat type picture tube is used, focus adjustment is necessary, and a normal picture tube (image receiving surface 4
And the electron gun 2 are arranged in a vertical plane), the focus on the left and right of the screen deteriorates, so that a parabola-shaped focus correction signal is used as the focus adjustment signal.

[0005]

Since a flat type picture tube produces a trapezoidal distortion larger than that of an ordinary picture tube, a means for correcting the trapezoidal distortion is adopted. Further, the deflection state of the electron beam is corrected so that the focus error is eliminated. However, if the focus adjustment is performed using the same focus correction signal having the same waveform and amplitude on the upper surface side and the lower surface side of the screen (image receiving surface), insufficient focus adjustment occurs especially on the upper side of the screen.

Therefore, the present invention has solved such a conventional problem, and even if a flat type picture tube in which the degree of deflection of the electron beam is different in the upper and lower parts of the screen is used, the focus thereof is entirely covered. We propose a focus adjustment circuit that allows correct adjustment over the entire range.

[0007]

In order to solve the above problems, in the present invention, a horizontal period parabolic wave-shaped focus correction signal is modulated by a vertical period trapezoidal wave distortion correction signal, and this modulated focus correction signal is obtained. The above-mentioned trapezoidal wave distortion correction signal is superimposed to form a dynamic focus correction signal, and the focus adjustment of the flat type picture tube is performed by this dynamic focus correction signal.

[0008]

As shown in FIG. 2, a trapezoidal wave distortion (keystone distortion) correction waveform a is used as a correction waveform approximate to the dynamic focus curve required in the flat type picture tube 1, and a horizontal period parabolic wave shape is obtained. The focus correction signal c is modulated to deflect the electron beam. In this case, the electron beam is deflected by the focus correction signal c modulated by the trapezoidal wave distortion correction signal a and the trapezoidal wave distortion correction signal a further superimposed thereon.

In this way, since the trapezoidal wave distortion correction waveform approximates the dynamic focus curve, proper focus adjustment can be performed at each vertical position on the image receiving surface 4, and the focus can be adjusted correctly over the entire image receiving surface 4. You can

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a case where an example of a focus adjusting circuit for a flat type picture tube according to the present invention is applied to the flat type picture tube having the above-mentioned structure will be described in detail with reference to the drawings.

As the flat type picture tube 1, a case where a picture tube having a structure as shown in FIG. 7 is used will be exemplified. As shown in FIG. 1, a trapezoidal wave distortion correction signal a output from a trapezoidal wave generation circuit 9 used to correct trapezoidal wave distortion (keystone distortion) is supplied to a horizontal output circuit 11.

As shown in FIG. 2A, the trapezoidal wave distortion correction signal a has a correction waveform which has a vertical cycle and is approximate to a sawtooth wave. The power supply voltage of the horizontal output circuit 11 is modulated by this correction waveform and the modulated horizontal deflection is performed. The signal (current) b (FIG. 2B) is supplied to the horizontal deflection device (horizontal deflection coil) 7 to correct the trapezoidal wave distortion of the screen.

Here, as shown in FIG. 3A, the screen (image receiving surface 4)
8a to 8 as measurement points in the same horizontal direction of
When a total of 7 points are taken up to g, the focus voltage for just focusing at the specific vertical measurement points 9a to 9e shown in FIG.

Thus, in order to achieve just focus, it is necessary to dynamically control the focus voltage both in the horizontal direction and in the vertical direction, and the optimum focus voltage at the same vertical position becomes a parabolic wave as shown in FIG. This parabolic waveform can be approximated by an inverted waveform of the trapezoidal wave distortion correction waveform of FIG. 2A.

The horizontal deflection signal b is applied to the parabolic wave conversion circuit 12
And the sawtooth wave signal having a horizontal period is converted into a parabolic wave signal. The focus correction signal c (FIG. 2C) converted into the parabolic wave shape is supplied to the modulation circuit 13 and is modulated by the trapezoidal wave distortion correction signal a (whose amplitude is B).

At this time, the modulation rate α is determined so that the output waveform (amplitude is A) of the focus correction signal c matches the optimum focus voltage waveform shown in FIG. The modulation rate α is adjusted by the variable resistor 14. Focus correction signal d shown in FIG. 2D modulated by trapezoidal wave distortion correction signal a
(= A × αB) is supplied to the waveform synthesis circuit 15 and added to the trapezoidal wave distortion correction signal a (FIG. 2E).

Waveform synthesis signal e (= B + A) which is the addition result
The focus correction signal f (F in the figure) is the grid electrode provided in the electron gun 2 and the deflection signal for dynamic focus is applied to the third grid electrode G3 in this example. Supplied as.

The final dynamic focus correction signal f thus formed is first a sawtooth wave signal having a horizontal period modulated by the trapezoidal wave distortion correction signal a, and is therefore characteristic of a flat type picture tube. Corrects trapezoidal wave distortion. Secondly, since the horizontal deflection signal b is further modulated by the trapezoidal wave distortion correction signal a having a modulation rate of α, the focus is corrected particularly at the center portion of the screen to be just focus.

Thirdly, since the trapezoidal wave distortion correction signal a is added to the focus correction signal d, the focus state at the corner portion of the screen is corrected to just focus or a state close thereto.

FIG. 6 shows a focus adjusting circuit 10, particularly a modulating circuit 13, a waveform synthesizing circuit 15, and an inverting amplifier 16.
A specific example of

In the figure, the modulation circuit 13 is composed of transistors Q1 to Q3. The focus correction signal c supplied to the terminal 13a is inverted and amplified by the transistor Q1 and then input to the gate of the transistor (FET) Q2.

The terminal 9a is connected to the drain of the transistor Q2.
The trapezoidal wave distortion correction signal a supplied to is supplied via the variable resistor 14. At this time, since the resistance between the drain and the source changes depending on the gate voltage, a current in which the parabola-shaped horizontal deflection signal b is modulated by the trapezoidal wave distortion correction signal a flows on the source side.

Since the source current of the transistor Q2 flows through the emitter-collector path of the transistor Q3, a voltage corresponding to the modulation current is generated across the resistor Ra. The modulated focus correction signal d converted into the voltage is supplied to the waveform synthesizing circuit 15 including the transistors Q4, Q5 and Q6. The focus correction signal d supplied to the buffer transistor Q4 and the trapezoidal wave distortion correction signal a also supplied to the buffer transistor Q5 are supplied to the emitter of the transistor Q6 and combined (wired OR).

The combined output voltage (waveform composite signal e) obtained at the collector of the transistor Q6 is inverted and amplified by the transistor Q7 constituting the inverting amplifier 16 and supplied to the above-mentioned third grid electrode G3 as a dynamic focus correction signal. To be done.

[0025]

As described above, in the focus adjusting circuit according to the present invention, the focus is dynamically adjusted by using the trapezoidal wave distortion correction waveform in both the horizontal and vertical scanning directions. It was done.

According to this, in addition to being able to correct the trapezoidal wave distortion peculiar to the flat type picture tube, the focus can be adjusted not only on the center of the screen but also on the corners of the screen, so that the image quality can be greatly improved. .

[Brief description of drawings]

FIG. 1 is a system diagram showing an example of a focus adjustment circuit for a flat type picture tube according to the present invention.

FIG. 2 is a waveform diagram for explaining focus adjustment.

FIG. 3 is an explanatory diagram of focus adjustment.

FIG. 4 is a diagram showing a relationship between a vertical position and a focus voltage.

FIG. 5 is a diagram showing an optimum focus voltage.

FIG. 6 is a connection diagram showing a specific example of a main part of a focus adjustment circuit.

FIG. 7 is a view of a flat type picture tube.

[Explanation of symbols]

 1 Flat-type picture tube 9 Trapezoidal wave generation circuit 10 Focus adjustment circuit 11 Horizontal output circuit 12 Parabolic wave conversion circuit 13 Modulation circuit 15 Waveform synthesis circuit Q3 Grid electrode

Claims (2)

[Claims] 1. A horizontal period parabolic wave-shaped focus correction signal is modulated by a vertical period trapezoidal wave distortion correction signal, and the trapezoidal wave distortion correction signal is superimposed on the modulated focus correction signal to form a dynamic focus correction signal. Then, the focus adjustment circuit for the flat type picture tube is characterized in that the focus of the flat type picture tube is adjusted by the dynamic focus correction signal. 2. The focus adjusting circuit for a flat-type picture tube according to claim 1, wherein the amplitude of the trapezoidal wave distortion correction signal is matched with the dynamic focus characteristic of the flat-type picture tube.