JPH05199428A - Dynamic focus circuit - Google Patents

Abstract

PURPOSE:To obtain an optimum focus even on a cathode-ray tube having a high curvature by using a multiplier to set the horizontal parabolic focus voltage amplitude in the central part and the peripheral part of a picture to an arbitrary value. CONSTITUTION:The horizontal parabolic focus voltage is multiplied by vertical parabolic focus voltage in a multiplier 5 to set the horizontal parabolic focus voltage to an arbitrary amplitude in the peripheral part. The horizonal parabolic voltage has DC cut by a coupling capacitor 2 and is converted into a current by a resistance 4 and is inputted to the multiplier 5. At this time, the resistance value of the resistance 4 is varied to adjust the horizontal amplitude. The vertical parabolic focus voltage which controls the horizontal parabolic focus voltage has DC cut by a coupling capacitor 1 and is converted into a current by a resistance 3 having the variable resistance value to adjust the horizontal amplitude in the peripheral part. Thus, the voltage resulting from addition in an adder 9 of the output voltage of the multiplier 5 and the vertical parabolic focus voltage is used as a synthesized parabolic focus voltage.

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 supplying a dynamic focus voltage to a cathode ray tube.

[0002]

2. Description of the Related Art In a conventional device, a slice level circuit is added to a dynamic focus circuit as described in Japanese Patent Laid-Open No. 62-283779 to slice a voltage near the center. As a result, the focus of the central portion is apparently slightly shifted upward, and the shift amount of the peripheral portion is corrected by the amount of the shift.

[0003]

In the above-mentioned prior art, since the waveform at the central portion is sliced, the focus is deteriorated at this portion and the optimum focus cannot be obtained on the entire screen.

According to the present invention, the optimum focus waveform is obtained even in the peripheral portion without slicing the focus voltage waveform, so that the focus voltage can be adjusted to an arbitrary amplitude in the center portion and the peripheral portion of the screen. This makes it possible to optimize the focus of the peripheral portion without deteriorating the focus of the central portion.

[0005]

In order to achieve the above object, a multiplier is used in the dynamic focus circuit so that the horizontal parabola focus voltage amplitude can be set to an arbitrary amplitude in the central portion and the peripheral portion of the screen.

The multiplier controls the horizontal parabola focus voltage amplitude by multiplying the horizontal parabola focus voltage by the vertical parabola focus voltage. Therefore, by adjusting the vertical parabola focus voltage, the horizontal parabola focus voltage can have an arbitrary amplitude in the peripheral portion.

[0007]

According to the present invention, the horizontal parabola focus voltage is multiplied by the vertical parabola focus voltage by the multiplier to control the horizontal parabola focus voltage in the peripheral portion of the screen.

Therefore, by adjusting the vertical parabola focus voltage, an arbitrary voltage can be obtained as the horizontal parabola focus voltage in the peripheral portion. Further, the vertical parabola focus voltage is added to the horizontal parabola focus voltage waveform, and this waveform is amplified by the output circuit and applied to the focus electrode. Therefore, the center, horizontal, vertical, and peripheral portions of the screen can be adjusted, and optimum focus can be obtained on the entire screen.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The circuit of FIG. 1 is roughly divided into three parts: a multiplier, an adder, and an output part. The following description will be divided into these three blocks.

The multiplier 5 multiplies the horizontal parabola focus voltage by the vertical parabola focus voltage and controls the horizontal parabola focus voltage so that an arbitrary amplitude can be obtained in the peripheral portion. The horizontal parabola focus voltage is DC-cut by the coupling capacitor 2, converted into a current by the resistor 4, and input to the multiplier 5. At this time, the horizontal amplitude is adjusted by setting the resistance 4 to VR. The vertical parabola focus voltage that controls the horizontal parabola focus voltage is also DC-cut by the coupling capacitor 1 and converted into a current by the resistor 3.
At this time, the amplitude of the horizontal parabola focus voltage in the peripheral portion is adjusted by changing the resistance 3.

The sum of the output voltage of the multiplier 5 and the vertical parabola focus voltage by the adder 9 becomes the combined parabola focus voltage. The output voltage of the multiplier 5 is input to the operational amplifier 9 through the input resistor 7. The vertical parabola focus voltage is DC cut by the capacitor 1 and is input to the operational amplifier 9 through the input resistor 6. By changing the input resistance 6, the amount of superposition of the vertical parabola focus voltage can be changed. The resistor 8 is a feedback resistor and determines the output gain by the ratio with the input resistors 6 and 7.

The output voltage of the adder is amplified by the transistor 12 of the output circuit and applied to the focus electrode. The gain of the output circuit is determined by the emitter resistance 10 and the collector resistance 11. The collector voltage waveform of the transistor 12 is DC-cut by the coupling capacitor 13, the bias is given by the resistor 14, and the bias voltage is applied to the focus electrode. This bias is varied to adjust the focus of the central part.

[0013]

According to the present invention, an optimum focus voltage can be applied to a cathode ray tube whose curvature is expected to increase in the future.

[Brief description of drawings]

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

[Explanation of symbols]

 1, 2 ... Coupling capacitor 3 ... Peripheral focus VR 4 ... Horizontal focus VR 5 ... Multiplier 6 ... Vertical focus VR 7, 8 ... Summing resistor 9 ... Operational amplifier 10 ... Emitter resistor 11 ... Collector resistor 12 Output transistor 13 Coupling capacitor 14 Dynamic focus VR

Claims (1)

[Claims] 1. A parabola focus voltage combining section in a dynamic focus circuit for applying a parabola focus voltage waveform to a focus electrode of a cathode ray tube, in which a horizontal parabola focus voltage amplitude is controlled by a vertical parabola focus voltage, and a central portion and a peripheral portion of the screen are controlled. The dynamic focus circuit is characterized in that a circuit that can set the horizontal parabola focus voltage to any amplitude is provided.