JPH08102868A - Dynamic focus circuit - Google Patents

Abstract

PURPOSE: To normally obtain the screen of a sufficient focus over a whole screen by simple adjustment even if the deflection amplitude of the screen, that is, the proportion of the valid display period of the screen as against the deflection period is changed. CONSTITUTION: A rough parabolic focus waveform generated by a horizontal waveform generating part 1 and a vertical waveform generating part 2 is adjusted by a horizontal amplitude adjusting part 9 and a vertical amplitude adjusting part 11 to secure the optimum focus potential difference of a screen central part from a screen peripheral part. At this time, the waveform where the potential difference of a dynamic focus waveform central value from the average value of the whole dynamic focus waveform becomes fixed is added to the dynamic focus waveform by a horizontal waveform adding part 10 or a vertical waveform adding part 12 during a non-display period. Thus, A optimum focus voltage is obtained in the whole screen after passing through a coupling capacitor 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 circuit for a cathode ray tube (hereinafter referred to as CRT) display or the like which is used by changing a deflection amplitude.

[0002]

2. Description of the Related Art In recent years, various video media have been put into practical use, and a single CRT display is often used to display a plurality of types of screens by changing the horizontal and vertical deflection amplitudes. In addition, particularly in CRT displays such as high-definition TV displays and computer terminal displays, which have a large deflection angle and require a high-definition reproduced image,
In order to obtain better focus quality on the entire screen, a dynamic focus circuit synchronized with the deflection waveform is required.

In a conventional dynamic focus circuit, a substantially parabolic dynamic focus waveform created by a waveform generating section is converted into a dynamic focus voltage having a necessary potential difference by a voltage amplifying section, and then this voltage is passed through a coupling capacitor to DC. The bias voltage is superimposed on the bias voltage through a bias addition resistor and applied to the focus electrode of the CRT.

Further, in a CRT display which requires a more accurate focus quality, an amplitude adjusting section is connected to the waveform generating section to adjust the amplitude of the parabolic dynamic focus voltage so that the central part of the screen and the peripheral part of the screen are adjusted. The focus voltage difference of is adjustable.

[0005]

However, when the deflection amplitude is changed and the screen is displayed as described above, the image display period on the signal, that is, the ratio of the display period to the deflection period, changes. Misalignment occurs between each point on the synchronized dynamic focus waveform and the actual electron beam position on the CRT screen. For example, when the deflection amplitude is increased as shown in FIG. 4B, the ratio of the display period to the deflection period becomes small. At this time, since both ends of the image display period correspond to peripheral portions on the CRT screen, the focus voltage of the portion corresponding to the image display period on the dynamic focus voltage waveform is actually the electron beam on the CRT screen. It is applied during the scanning period. As a result, compared to the case where the deflection amplitude shown in FIG. 4A is small, the potential difference of the dynamic focus voltage corresponding to the central portion of the CRT screen and the peripheral portion of the screen becomes smaller. It will be necessary to adjust to that.

However, if the potential difference in the central portion of the dynamic focus waveform is increased, the potential difference of the entire waveform also increases accordingly and the average value of the dynamic focus voltage changes. Therefore, in FIG.
As shown in (a) and (b), the difference between the focus voltage value corresponding to the central portion of the screen during the display period and the average value of the entire dynamic focus waveform is significantly deviated due to the change in the deflection amplitude.

In particular, as shown in FIG. 4B, when the deflection amplitude is large, the display period becomes shorter than the deflection period, so the dynamic focus voltage during the display period becomes extremely lower than the average value. FIG. 4A shows a focus waveform when the deflection amplitude is small. When such a dynamic focus voltage is superimposed on the DC bias voltage, the average value becomes the bias voltage, and the focus voltage in the entire screen becomes low. Therefore, the DC voltage must be readjusted to obtain proper focus. That is, every time the deflection amplitude of the screen is changed, not only the amplitude of the dynamic focus waveform but also the DC voltage has to be readjusted.

The present invention has been made to solve the above-mentioned conventional problems, and provides a dynamic focus circuit such as a CRT display in which the entire screen is always in good focus by a simple adjustment with respect to a change in deflection amplitude. To do.

[0009]

A dynamic focus circuit according to the present invention includes a waveform generating section for generating a substantially parabolic focus waveform, an amplitude adjusting section for adjusting the amplitude of the focus waveform, and the focus in a non-display period. And a waveform adding section for adding a predetermined waveform to the waveform.

[0010]

With this configuration, the amplitude of the dynamic focus waveform is changed by the amplitude adjusting unit in response to the change in the deflection amplitude, and the amplitude of the parabolic voltage waveform within the display period, that is, the focus voltage between the screen central portion and the screen peripheral portion is changed. Even if the difference is fixed, by adding an appropriate waveform to the non-display period that does not affect the screen, the potential difference between the median value of the dynamic focus waveform and the average value of the entire dynamic focus waveform can be kept constant. Therefore, the focus voltage superimposed on the DC bias voltage can always be optimized for the entire screen.

[0011]

FIG. 1 shows a dynamic focus circuit which is an embodiment of the present invention. In FIG. 1, a horizontal parabolic generator 1 and a vertical waveform generator 2 generate a substantially parabolic dynamic focus waveform. The amplitude of the waveform is adjusted by the horizontal amplitude adjusting unit 9 and the vertical amplitude adjusting unit 11 to be optimum. At this time, by the horizontal waveform adding unit 10 and the vertical waveform adding unit 12,
During the blanking period that is not displayed on the screen, a waveform is added to the focus waveform such that the potential difference between the median value of the dynamic focus waveform and the average value of the entire dynamic focus waveform is constant. These optimized horizontal dynamic focus waveform and vertical dynamic focus waveform are amplified by the voltage amplifying section 3 to a predetermined voltage, synthesized, and obtained by the bias power supply 6 via the coupling capacitor 4 and the bias addition resistor 5. Superimposed on the bias voltage. This superimposed voltage is applied to the focus electrode 7 of the CRT 8.

In FIG. 1, Hp indicates a horizontal synchronizing signal and Vp indicates a vertical synchronizing signal. Next, details of the dynamic focus circuit will be described by taking a horizontal dynamic focus waveform as an example. FIG. 2 shows one of the above embodiments.
It shows a horizontal dynamic focus circuit unit.

In FIG. 2, the horizontal waveform adding section 10 comprises a detecting means for detecting the display period and a generating means for generating a waveform to be added in the non-display period. The detection means includes an AND circuit 13 that detects only the blanking period when the deflection amplitude is a predetermined value based on the signal from the horizontal amplitude adjustment unit 9, and the analog switch 14 that operates in conjunction with the AND circuit 13. The generating means includes a DC power supply 15 that generates a predetermined voltage.

Since it has the above configuration, it is shown in FIG.
Retrace line that is a non-display period as shown by the focus voltage waveform
Predetermined voltage E during the period₁In the screen by applying
The focus potential difference a between the central part and the peripheral part of the screen is
Focus waveform in the display period even if adjusted for changes
The potential difference b between the median value and the average value of the entire focus waveform is
Can be kept constant. That is, the focus of CRT8
Voltage V applied to electrode 7₆Dynamic focus
Waveform voltage V_FourIs the voltage V amplified by the voltage amplifier 3. _FiveIs joined
Superposed on the voltage E of the DC bias power supply 6 via the capacitor 4.
The DC bias power source 6 and the bias are added.
Resistor 5 and average dynamic focus waveform voltage
The value becomes E. Therefore, the focus voltage of the central portion of the screen = E−b which is actually applied = the focus voltage of the peripheral portion of the screen = E−b + a does not change under the conditions of the deflection amplitudes A and B.

In the above-described embodiment, the waveform adding section is configured to detect the fluctuation of the deflection amplitude and the non-display period by the AND circuit and apply the predetermined DC voltage by the analog switch 14 interlocked with the AND circuit. As a method of detecting the period, other than using a blanking pulse, a method of detecting a potential difference from the minimum value of the dynamic focus voltage and determining that the potential is a non-display portion when the potential difference exceeds a certain value may be adopted. . However, in this case, it is necessary to newly create a determination unit, which complicates the circuit configuration, increases cost, and lacks stability. In this respect, since the blanking pulse is generated from the normal deflection pulse on the set side regardless of whether the dynamic focus circuit of the present invention is adopted, this existing blanking pulse is used. Is more preferable. Further, not only the AND circuit can detect the input and switch the analog switch, but also the predetermined voltage value generated by the generating means can be controlled according to the adjustment degree in the amplitude adjusting section.

Further, the adjustment voltage applied during the non-display period need not be a DC voltage and can be obtained by inverting the dynamic focus waveform. However, a circuit for inverting the dynamic focus waveform, which is an AC waveform, is easily affected by peripheral circuits and lacks stability, and it is difficult to obtain a predetermined voltage value accurately. Further, the generated waveform itself may adversely affect peripheral circuit elements. Therefore, a DC voltage that can be easily adjusted to an arbitrary voltage by the volume and does not adversely affect the peripheral circuit elements is practically desirable.

Although the horizontal dynamic focus circuit section has been described in the above embodiment, the configuration of the vertical dynamic focus circuit section is the same as that of the horizontal dynamic focus circuit section described above.

The dynamic focus waveform formed by the dynamic focus circuit of the present invention is
It can be formed separately according to the horizontal deflection cycle and the vertical deflection cycle. As shown in FIG. 1, a general dynamic focus circuit is a circuit in which two parabolic voltage waveforms of a horizontal deflection period and a vertical deflection period are added, and therefore, as in the circuit configuration shown in FIG. The waveforms may be separately manipulated and combined. Further, when the deflection amplitude is switched only one of horizontal and vertical, it is sufficient to perform the waveform operation only on the side where the deflection amplitude is switched.

[0019]

As described above, the dynamic focus circuit of the present invention can keep the average value constant even if the amplitude of the dynamic focus waveform is changed. Even if the amplitude is changed, the necessary focus voltage can be obtained on the entire screen of the CRT. As a result, it is possible to realize a CRT display capable of displaying an image with excellent focus by simple adjustment even if the amplitude of the image is changed.

[Brief description of drawings]

FIG. 1 is a diagram of a dynamic focus circuit according to an embodiment of the present invention.

FIG. 2 is a horizontal dynamic focus circuit diagram in the same circuit.

FIG. 3 is a waveform diagram of a focus voltage generated by the same horizontal dynamic focus circuit.

FIG. 4 is a waveform diagram of a focus voltage by a conventional dynamic focus circuit.

[Explanation of symbols]

 1 Horizontal Waveform Generator 2 Vertical Waveform Generator 9 Horizontal Amplitude Adjuster 10 Horizontal Waveform Adder 11 Vertical Amplitude Adjuster 12 Vertical Waveform Adder

Claims (3)

[Claims] 1. A waveform generator that generates a substantially parabolic focus waveform, an amplitude adjuster that adjusts the amplitude of the focus waveform, and a waveform adder that adds a predetermined waveform to the focus waveform during a non-display period. A dynamic focus circuit characterized by having. 2. A waveform in which the predetermined waveform in the waveform adding section maintains a constant potential difference between the output waveform median value and the average value of the entire output waveform even when the focus waveform amplitude is changed by the amplitude adjusting section. The dynamic focus circuit according to claim 1, wherein: 3. The dynamic focus circuit according to claim 1, wherein the waveform adding section has a detecting means for detecting a non-display period and a generating means for generating a waveform to be added in the non-display period. .