JPH06205235A - Dynamic focus circuit - Google Patents

Abstract

PURPOSE:To obtain an optimum focus characteristic even left and right ends in the horizontal direction in a television receiver employing a CRT whose aspect ratio is 16:9 by slicing a voltage component over a prescribed voltage of a parabolic wave voltage. CONSTITUTION:A parabolic wave of a negative polarity generated by a parabolic wave generating circuit comprising a choke coil L1 and a capacitor C1 is divided by resistors R6, R7 and a voltage portion over a prescribed voltage is sliced by a resistor R8 and a diode DI connected to a DC voltage source Vcc 1. Then the waveform is inversely amplified by an inverting amplifier circuit comprising resistors R9-R11 and an NPN transistor(TR) Q1 connected to a DC voltage source Vcc 2 and the resulting signal is fed to a low voltage winding being a secondary winding of a boosting transformer T1 connected to ground via a capacitor C3 and a resistor R12. Then a sliced waveform is superimposed onto a basic positive parabolic wave at a secondary side of the boosting transformer T1 and the resulting waveform is optimum to the television receiver employing a CRT whose aspect ratio is 16:9.

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 used in a television receiver using a cathode ray tube (CRT).

[0002]

2. Description of the Related Art In recent years, television receivers have become larger and larger, and the deflection angle has been widened in order to improve the focus characteristics of CRTs. Further, in high-vision, wide-vision, etc., the aspect ratio is 16: 9. CRTs have come into use. Along with this, the number of television receivers using a dynamic focus circuit in order to improve the focus characteristic of the peripheral portion of the CRT is increasing.

FIG. 3 is a circuit diagram showing an example of a conventional dynamic focus circuit of a transformer boosting method. In FIG. 3, a horizontal pulse synchronized with a horizontal synchronizing signal output from a flyback transformer (not shown) is converted into a negative (convex upward) parabolic wave by a parabolic wave generation circuit including a choke coil L1 and a capacitor C1. It This parabolic wave is input to the primary side of the step-up transformer T1 via the resistor R1, and a boosted positive (convex downward) parabolic wave is generated on the secondary side. Here, the step-up transformer T
When the number of turns on the primary side of 1 is n1 and the number of turns on the secondary side is n2, the input parabolic wave is multiplied by n2 / n1 and output.

Then, the boosted positive parabolic wave is passed through a resistor R2 and a capacitor C2 to generate a high voltage HV generated by a flyback transformer (not shown) through resistors R3 and R.
It is superimposed on the focus DC voltage divided by 4 and R5 and applied to the focus electrode of the CRT (not shown). As a result, as shown by the solid line in FIG. 4, the focus voltage becomes high in the peripheral portion of the CRT in the horizontal direction, and the focus characteristic is corrected.

[0005]

Such a conventional dynamic focus circuit is a CR with an aspect ratio of 4: 3.
In the case of a television receiver using T, the optimum focus characteristic can be obtained as described above. However, in the case of a television receiver using a CRT with an aspect ratio of 16: 9, the originally required focus voltage is as shown in FIG.
In the waveform shown by the solid line in FIG. 4, the correction voltage at the left and right ends in the horizontal direction is insufficient due to the widening of the horizontal deflection angle as shown in FIG. There was a problem. Therefore, the present invention has been made in view of the above problems, and in a television receiver using a CRT with an aspect ratio of 16: 9, optimum focus characteristics can be obtained even at the left and right ends in the horizontal direction. An object of the present invention is to provide a dynamic focus circuit that can be used.

[0006]

In order to solve the above-mentioned problems of the prior art, the present invention provides a parabolic wave generating circuit for generating a negative parabolic wave voltage from a horizontal pulse synchronized with a horizontal synchronizing signal, and In a dynamic focus circuit that includes a step-up transformer that steps up the parabolic wave voltage, and applies the parabolic wave voltage output from the step-up transformer to the focus DC voltage by superimposing it on the focus DC voltage, outputs from the parabolic wave generation circuit. A slice circuit for slicing a predetermined constant voltage or more of the parabolic wave voltage thus generated, and an inverting amplifier circuit for inverting and amplifying the voltage output from the slice circuit and superimposing it on the parabolic wave voltage output from the step-up transformer are provided. The present invention provides a dynamic focus circuit characterized by the above.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A dynamic focus circuit according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a circuit diagram showing an embodiment of the dynamic focus circuit of the present invention, and FIG. 2 is a waveform diagram for explaining the dynamic focus circuit of the present invention. In FIG. 1, the same parts as those in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 1, what is newly added by the present invention is a portion surrounded by a broken line. Choke coil L1,
The parabolic wave of negative polarity shown in FIG. 2a generated by the parabolic wave generation circuit including the capacitor C1 has resistances R6 and R.
Resistor R divided by 7 and connected to DC voltage Vcc1
8 and the diode D1 slices a voltage equal to or higher than a predetermined voltage to obtain the waveform shown in FIG. 2b. This waveform shows the resistance R9, resistance R10, resistance R1 connected to the DC voltage Vcc2.
The waveform is as shown in FIG. 2c by being inverted and amplified by the inverting amplifier circuit including the NPN transistor Q1. This waveform is applied to the low voltage side of the secondary side of the step-up transformer T1 which is grounded via the capacitor C3 and the resistor R12.

On the secondary side of the step-up transformer T1,
The waveform shown in FIG. 2c is superimposed on the basic positive parabolic wave shown in FIG. 2d, and a waveform as shown in FIG. 2e is obtained.
The waveform shown in FIG. 2e is an optimum waveform for a television receiver using a CRT having an aspect ratio of 16: 9 as shown by the broken line in FIG. In the present invention, 1 of the step-up transformer T1
From the parabola wave shown in FIG. 2a obtained on the next side, the basic parabola wave shown in FIG.
Since the waveform shown in d is generated, the target waveform shown in FIG. 2e can be obtained without the mutual phase shift. Further, since the load impedance on the secondary side of the step-up transformer T1 is generally as high as several tens of MΩ, waveform distortion can also be improved by superimposing a waveform containing a relatively high frequency component on the secondary side of the step-up transformer T1.

[0010]

As described above in detail, in the dynamic focus circuit of the present invention, the slicing circuit slices a predetermined fixed voltage or more of the negative parabola wave voltage, and this waveform is inverted and amplified by the inverting amplifier circuit. Since it is configured to be superimposed on the positive polarity parabolic wave voltage output from the step-up transformer, when the dynamic focus circuit of the present invention is used in a television receiver using a CRT with an aspect ratio of 16: 9, the horizontal left and right Optimal focus characteristics can be obtained even at the edges, and the image quality is improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment.

FIG. 2 is a waveform diagram for explaining an example.

FIG. 3 is a circuit diagram showing a conventional example.

FIG. 4 is a waveform diagram for explaining a conventional example.

FIG. 5 is a diagram for explaining the problems of the conventional example.

[Explanation of symbols]

 C1 to C3 capacitor D1 diode L1 choke coil R1 to R12 resistance T1 step-up transformer

Claims (1)

[Claims] 1. A parabola output from the step-up transformer, comprising a parabola wave generation circuit for generating a parabola wave voltage having a negative polarity from a horizontal pulse synchronized with a horizontal synchronizing signal, and a step-up transformer for stepping up the parabola-wave voltage. In a dynamic focus circuit that superimposes a wave voltage on a focus DC voltage and applies it to a focus electrode of a cathode ray tube, a slice circuit that slices a predetermined constant voltage or more of the parabolic wave voltage output from the parabolic wave generation circuit,
A dynamic focus circuit, comprising: an inverting amplifier circuit for inverting and amplifying the voltage output from the slice circuit and superimposing it on the parabolic wave voltage output from the step-up transformer.