JPH0479189B2 - - Google Patents

Description

[Detailed description of the invention] Industrial application field The present invention is a single flyback transformer type
This invention relates to a pincushion distortion correction circuit for stabilizing images on CRT display monitors.

Conventional technology The pincushion distortion that occurs on the cathode ray tube surface as shown in Figure 2 can be solved by passing a horizontal deflection current modulated by a parabolic wave through a deflection coil as shown in Figure 3, and maximizing the horizontal amplitude at the center of the raster. It is known that correction can be made by FIG. 4 shows an example of a correction circuit for a television receiver that corrects such raster distortion. That is, a vertical output a applied to a vertical coil is rectified via a transformer T1 and a diode D1, and integrated by a capacitor C1 to create a parabolic voltage signal b. This parabolic voltage signal b
is added to the base of transistor Q1 and amplified and inverted. The amplitude of this parabolic voltage signal b' is adjusted by a vertical pin adjustment volume VR1, and a DC voltage whose level is adjusted by a horizontal amplitude volume VR2 is superimposed. The parabolic signal c subjected to amplitude adjustment and DC potential adjustment is inverted and amplified by transistor Q2. The parabolic voltage c superimposed on the DC voltage amplified by the transistor Q2 changes the resistance value added to the transistor Q3, and as a result, the capacitor C3 connected to the output side of the transistor Q3 is discharged. controlled. Therefore, the potential V _A of capacitor C3 is the parabolic voltage
The horizontal deflection coil HDY varies according to the change in c′.
A correction current flows between A and B in FIG. 4 by a comparison potential difference with the potential of the capacitor C4 connected to the low potential side of the capacitor C4. To summarize the above constraint method, by constraining the internal resistance value of transistor Q3 with transistor _Q2 , the correction current generated between A and B can be constrained, and as a result, the deflection current flowing in the horizontal deflection circuit can be controlled. You can. More specifically, by adjusting the vertical pin adjustment with the volume VR1 and the horizontal amplitude with the volume VR2, it is possible to obtain a good image without distortion.

Problems to be Solved by the Invention CRT display monitors are used as terminal equipment for computers, and are completely different from equipment such as television receivers, which receive a certain signal, display moving images, and perform overscan operation.
Generally, various signals from a computer are input, and an underscan operation is performed on a still image. In particular, the output signal format differs depending on the type of computer connected. In order to accommodate such differences in signal formats, various design changes may be made to monitors, and in particular, changes in the horizontal oscillation frequency bring about major changes in the design of the horizontal deflection system of CRT display monitors. on the other hand,
The video output signal from a computer changes instantaneously, such as a signal that displays the entire screen or a signal that displays a part of the screen, and the image on the screen fluctuates due to the sudden signal change, especially when the amplitude is fluctuate. However, since the image displayed on the monitor is a still image and is underscanned, the amplitude fluctuation is very noticeable, and the quality of the CRT display monitor is greatly impaired. In addition, as the graphic display and brightness of computers have increased in recent years, the load fluctuation factor due to the input signal from the computer of the CRT display monitor has become larger.
There is a strong demand for image stabilization.

Conventional image stabilization circuits have not been designed to take into account load fluctuations in response to the characteristics of images displayed on CRT display monitors and market demands.

SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to provide a pincushion distortion correction circuit that is inexpensive and has a large image stabilizing effect.

Means for Solving the Problems In order to achieve the above object, the pincushion distortion correction circuit of the present invention receives the vertical deflection output as input, detects fluctuations in the output voltage of the power transformer that supplies the power supply voltage to the flyback transformer, and inputs the vertical deflection output. A comparison signal generation circuit generates a comparison voltage signal indicating the duty ratio of the video signal, and a calculator compares this comparison voltage signal with a reference voltage signal indicating that a video signal with a predetermined duty ratio has been input. The comparison output and the correction parabola signal are superimposed by a computing unit, and the output of the computing unit supplies a parabolically modulated horizontal deflection current to the horizontal deflection coil according to the duty ratio of the input video signal.

Operation With the above configuration, a calculation voltage corresponding to the duty ratio of the input video signal of a CRT display monitor where the duty level of the input video signal changes rapidly is obtained, and this calculation output and a parabolic voltage signal for correction are used. By superimposing the parabolic signal and creating a parabolically modulated horizontal deflection current from this superimposed parabolic signal, it is possible to create a horizontal deflection current with a current value that corresponds to the duty ratio of the video signal. It is possible to realize pincushion distortion correction with a correction amount that corresponds to the duty ratio, and it is possible to realize high-quality images.

Embodiments Hereinafter, embodiments of the pincushion distortion correction circuit of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of a pincushion distortion correction circuit according to an embodiment of the present invention. Components in FIG. 1 that are similar to those shown in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted. In other words, the secondary output voltage of the power transformer T1 to which the vertical deflection output is input is rectified by the diode D1 and the capacitor C1, and the rectified output is sent to the flyback transformer FBT via the chopper power transformer T2.
Supplied to the next side. Chotsupa power transformer T2
1 of the output side of the flyback transformer FBT
The next side is a Zener diode D via a resistor R1.
2. Connected to reverse current prevention diode D3. The anode side of the Zener diode D2 is grounded, while the cathode side of the diode D3 is
It is connected to the horizontal amplitude adjustment volume VR1. The midpoint of volume VR1 is connected to the positive side of operational amplifier OP1. The secondary output of power transformer T1 is connected to diode D4 and capacitor C.
2, and the rectified voltage is supplied as a power source for the deflection system and video system, and is also supplied to the negative side of the operational amplifier OP1 via a resistor R2.
Furthermore, the output of operational amplifier OP1 is
This op amp OP is supplied to the positive side of OP2.
The voltage from the side pink coupling circuit is supplied to the negative side of 2. Its output is fed to the base of transistor Q1, which is a diode modulator circuit.

For example, if the video output signal from a computer is a signal that requires a larger current to flow through the deflection system of a CRT display monitor than a normal signal (for example, if the entire display area of the CRT display has a duty ratio (In the case of a 100% white solid signal) The load on the deflection system of the CRT display monitor increases, the secondary output current of the flyback transformer FBT increases, and the secondary voltage decreases. Due to the single flyback type circuit configuration, when the secondary voltage of the flyback transformer FBT decreases, the amplitude of the raster on the monitor screen changes significantly. At the same time, the output voltage of the chopper power transformer T2 connected to the primary winding of the flyback transformer FBT increases, working to further increase the raster amplitude change.

The output side of chopper power transformer T2 is resistor R.
The cathode side of the Zener diode D2 is connected to the Zener diode D2 via the
Always kept at a constant voltage V _Z. This voltage V _Z is connected to the diode D3 and the horizontal amplitude adjustment volume VR1.
The level is adjusted by the volumes VR2 to VR4, and the adjusted voltage is supplied to the positive side of the operational amplifier OP1. This adjusted voltage is the op amp
This is the operating reference voltage for OP1. This operating reference voltage is the voltage that occurs at the cathode of Zener diode D2 when there are no volumes VR1 to VR4 when a character signal with a duty ratio of 30% is input.
Let it be V _a .

Next, the secondary output of the power transformer T1 is rectified by a diode D4 and a capacitor C2, and the rectified output voltage is supplied as a power supply to the deflection system and video system. Therefore, when the above-mentioned all-white solid signal is supplied, the currents in the deflection system and the video system increase, and as a result, the rectified output voltage decreases.
The rectified output voltage is divided by resistors R2 and R3 and is supplied to the negative side of operational amplifier OP1.
The voltage fluctuation of the rectified output described above is transmitted to the operational amplifier OP1. Now, assuming that the voltage on the positive side of operational amplifier OP1 is V _a and the voltage on the negative side is V _b , when a video signal with a duty of 30% or more is supplied, the secondary side voltage of power transformer T1 decreases, and voltage V _b As a result, the relationship of voltage V _a > V _b is established, and a DC output voltage is generated at the output of operational amplifier OP1. Its output voltage goes to the positive side of operational amplifier OP2,
A parabolic voltage from the side pink coupling circuit is supplied to the negative side, and a parabolic voltage on which a DC voltage is superimposed is obtained at the output terminal of the operational amplifier OP2. This parabolic voltage is applied to the base of transistor Q1 to raise the base potential and increase the internal resistance value of transistor Q2. Therefore, the discharge current from capacitor C3 becomes smaller, and the current flowing through coil L becomes larger than the current flowing through deflection coils H and DY, which reduces the horizontal deflection current and works to reduce the horizontal amplitude. .

As described above, according to this embodiment, since the horizontal amplitude is adjusted in accordance with load fluctuations, image stabilization suitable for display monitors with many load fluctuation factors can be realized.

Effects of the Invention According to the present invention, a sudden signal change (change in duty ratio) of a video output signal from a computer
is detected as a change on the load side of the CRT display monitor, especially as a change in the output voltage of the chopper power supply and a change in the secondary side voltage of the power transformer.
These fluctuating voltages are compared and detected using a calculator, and by superimposing the output voltage corresponding to the load fluctuation and the correction parabolic voltage, the distortion correction amount of the horizontal deflection current flowing through the horizontal deflection coil is automatically changed. It is possible to effectively provide stable images at all times.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a pincushion distortion correction circuit according to an embodiment of the present invention, Fig. 2 is a plan view showing raster distortion generated in a cathode ray tube, and Fig. 3 is a waveform showing the waveform of a horizontal deflection current modulated by a parabolic wave. 4 are circuit diagrams of a conventional pincushion distortion correction circuit. T1...power transformer, T2...chopper power transformer, FBT...flyback transformer,
H・DY...Horizontal deflection coil, R2, R3...Resistor for voltage fluctuation detection, VR1...Volume for horizontal amplitude adjustment, VR2 to VR4...Auxiliary horizontal amplitude volume, OP1, OP2...Operation amplifier.

Claims (1)

[Claims] 1. A power transformer that receives the vertical deflection output as input and outputs the power supply voltage to the flyback transformer, and the secondary side ends are electrically coupled to the secondary high voltage side of the power transformer and the primary high voltage side of the flyback transformer, respectively. a chopper power transformer that stabilizes the voltage supplied to the flyback transformer; and a reference signal creation circuit that creates a reference voltage signal indicating that a video signal with a predetermined duty ratio has been input from the secondary output of the chopper power transformer. a comparison signal creation circuit that rectifies the secondary side output of the power transformer to create a comparison voltage signal indicating the duty ratio of the input video signal; It is equipped with an arithmetic unit that superimposes and outputs a voltage signal corresponding to a voltage difference and a parabolic signal for correction, and creates a parabolically modulated horizontal deflection current according to a duty ratio of an input video signal from the output of the arithmetic unit. A pincushion distortion correction circuit characterized in that the pincushion distortion correction circuit supplies a horizontal deflection coil.