JPH0690374A - Dynamic focus circuit - Google Patents

Abstract

PURPOSE:To improve the quality of focus by generating digitally a parabolic voltage for a horizontal and a vertical period required for dynamic focus in a cathode ray tube. CONSTITUTION:One horizontal period and one horizontal period are respectively divided into a required number of periods, and a digital level is set to the vertical and horizontal divided periods through adjustment (PLLs 3, 4, adjustment signal generating sections 5, 6 and control circuits 7, 8). Vertical and horizontal digital levels for each set period are respectively D/A-converted by D/A converter circuits 11, 12. Since the analog output is a voltage waveform changing stepwise for each period, a vertical and a horizontal parabolic voltage are obtained through LPFs 13, 14. The horizontal and vertical parabolic voltages are mixed by a mixer circuit 15 and an output circuit 16 amplifies the result to have a required level. The amplified output is superimposed on a DC focus voltage from the FBT via a capacitor C1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention In the so-called dynamic focus of a cathode ray tube, the present invention makes it possible to easily obtain a necessary parabolic waveform by digitally generating parabola voltages of horizontal and vertical periods necessary for the dynamic focus. Dynamic focus circuit.

[0002]

2. Description of the Related Art A conventional dynamic focus circuit is shown in FIG. Further, FIG. 4 is a waveform diagram of the focus voltage for explaining the dynamic focus. Below, FIG.
The conventional dynamic focus will be described with reference to FIG. It should be noted that, as shown in FIG. 4, increasing the focus voltage in a parabolic shape from the central part toward the peripheral part of the screen means that the optimum focus voltage becomes higher toward the peripheral part and the change is parabolic. Because it takes. The vertical sawtooth wave voltage 32 from the vertical output circuit 31 is integrated into the integrating circuit 33.
Integrate with. The vertical parabolic wave 34 is obtained by this integration. Similarly, when the horizontal sawtooth wave voltage 36 from the horizontal output circuit 35 is integrated by the integrating circuit 37, a horizontal parabolic wave 38 is obtained. The vertical parabolic wave 34 and the horizontal parabolic wave 38 are mixed by the mixing circuit 39. Since the output voltage (amplitude) of the mixing circuit 39 is small with respect to the required focus voltage, the output circuit 40 amplifies the phase including the phase to obtain a required parabolic voltage (horizontal and vertical) parabolic voltage. On the other hand, the DC focus voltage is taken out from the high voltage winding (N2) of the flyback transformer (FBT) connected to the horizontal output circuit 35, and the DC voltage is extracted to the required voltage by the focus adjustment volume VR1 and the CRT 42 (CRT) is adjusted. ) Is applied to the focus electrode. The output circuit for the DC focus voltage from VR1
The mixed parabolic voltage from 40 is superimposed via capacitor C1. The focus voltage (VF) on which the parabolic voltage is superimposed is shown in FIG. In the figure, Vf is the VR1
Shows the DC focus voltage from, and the mixed parabolic voltage of the vertical period (1V) and horizontal period (1H) parabolic voltage is superimposed on this Vf. FIG. 4B shows the parabola voltage in the horizontal period.

[0003]

As described above, in order to obtain the best focus in the entire center and peripheral areas on the screen, it is necessary to change the focus voltage in a parabolic shape as shown in FIG. 4 (A). However, the optimum parabolic waveform varies not only with the type of cathode ray tube but also with the same tube type. In this case, the method of generating a parabola by the integrating circuit as shown in FIG. 3 has a limit in obtaining a desired parabolic waveform, and therefore, the focus quality in the entire screen area has a certain limit. The present invention digitally generates horizontal and vertical parabolic voltages and uses this parabolic wave to obtain the focus voltage in order to further improve the focus quality in the entire screen area under the tendency of screen enlargement. It is an object of the present invention to provide a dynamic focus circuit having the above structure.

[0004]

According to the present invention, a digital level is set to be variable by setting a required number of sections evenly divided into a required number of sections within one vertical cycle, and the first level is constituted by each section.
Generating means for generating a digital level signal, a first D / A conversion circuit for converting the first digital level signal generated by the first generating means into a first analog signal, and A first memory unit for storing a signal of a digital level of 1 in association with the section;
The first low-pass filter that outputs the parabolic voltage of the vertical cycle by passing the low-frequency component of the first analog signal from the D / A conversion circuit of No. 1, and the required number of sections are evenly distributed within the period of one horizontal cycle. A digital level is variably set for each of the divided sections, and second generating means for generating a signal of the second digital level for each of the sections, and a second digital level of the second generating level by the second generating means. A second D / A conversion circuit for converting the signal into a second analog signal; a second memory section for storing the signal of the second digital level in association with the section; and the second D / A A second low-pass filter for passing a low-frequency component of the second analog signal from the A conversion circuit to output a parabola voltage having a horizontal period;
A mixing circuit that mixes the vertical-period parabolic voltage from the first low-pass filter and the horizontal-period parabolic voltage from the second low-pass filter, and the mixed parabolic voltage from the mixing circuit is amplified to a required voltage. And a dynamic focus circuit composed of an output circuit for

[0005]

According to the present invention, one vertical cycle period and one horizontal cycle period are each divided into a required number of sections, and digital levels are set vertically and horizontally by adjusting each of the divided sections. The vertical and horizontal digital levels for each set section are D / A converted. The D / A
The converted analog output has a voltage waveform that changes stepwise in each section. The D / A conversion output is LP
Vertical and horizontal parabolic voltages are obtained by passing F. The vertical and horizontal parabolic voltages are mixed and amplified to the required level. The amplified output is superimposed on the DC focus voltage from the flyback transformer via the capacitor.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A dynamic focus circuit according to the present invention will be described below with reference to the drawings. 1 is a block diagram of an essential part showing an embodiment of a dynamic focus circuit according to the present invention, and FIG. 2 is an explanatory diagram of parabola voltage generation in FIG. In FIG. 1, 1 is a vertical sync signal or a vertical drive signal of a vertical cycle pulse (VD), 2 is a horizontal sync signal or a horizontal drive signal of a horizontal cycle pulse (HD), and 3 and 4 are synchronized with the VD or HD respectively. The first PLL and the second PLLs 5 and 6 for generating the clock signal are a first adjustment signal generator and a second adjustment signal generator 7 and 8 which are used for vertical parabola wave generation and horizontal parabola wave generation. Is each PL
A first control circuit and a second control circuit for outputting digital level data set for each interval obtained by dividing a vertical period or a horizontal period into a required number from a clock signal from L and an adjustment signal from each adjustment signal generator. Control circuits 9 and 10 for storing digital level data output from the control circuits, respectively.
And 12 are first D / A conversion circuits and second D / A conversion circuits for converting the digital level data from the respective control circuits into analog voltages, respectively, and 13 and 14 are signals from the respective D / A conversion circuits. First, a vertical parabolic voltage and a horizontal parabolic voltage are obtained by extracting only low-frequency components from the signal.
LPF (low pass filter) and a second LPF, 15 is a mixing circuit for mixing the vertical parabolic voltage and the horizontal parabolic voltage from the first and second LPFs, and 16 is a mixing parabolic voltage from the mixing circuit 15. An output circuit that amplifies to a predetermined level. In addition, the same components as those in FIG. 3 are denoted by the same reference numerals.

Next, the operation of the present invention will be described. A feature of the present invention is that the vertical parabola wave and the horizontal parabola wave are digitally generated. For this purpose, one vertical period and one horizontal period are each divided into a required number of sections. Although the number of divisions is arbitrary, it is determined in advance (at the design stage) in consideration of the required accuracy of the parabolic wave and the ease of adjustment. In this embodiment, one vertical cycle is 10
Equal division, 1 horizontal period was made into 20 equal divisions. An example of this division is shown in FIG.
Shown in (A) and (C). (A) is a vertical parabola, (C)
Corresponds to each horizontal dish. Incidentally, FIG. 7B is a vertical parabolic wave corresponding to FIG. 7A, and FIG.
Is a horizontal parabolic wave corresponding to. Although it is considered that this degree of division is sufficient, the number of divisions may be increased to further improve the correction accuracy. As shown in FIGS. 2A and 2C,
Each divided position (vertical (P1 to P10), horizontal (P1 to P10)
P20)] and digitally set the level. This setting is the adjustment of each parabolic wave generation. Specifically, the position is designated, and the level is set for each designated position. Therefore, with the function to specify this position,
An adjustment signal output function for level setting is required. The first adjustment signal generator (vertical) 5 and the second adjustment signal generator (horizontal) 6 are provided with these functions.

The adjustment signal for each position output from each of the first and second adjustment signal generators as described above is input to the first control circuit 7 and the second control circuit 8. On the other hand, a clock signal synchronized with the vertical drive signal (VD) is supplied to the first control circuit 7 by the second control circuit 8.
A clock signal synchronized with the horizontal drive signal (HD) is input to each. Therefore, each control circuit outputs digital data of a level corresponding to the adjustment signal for each position from the clock signal and the adjustment signal. The digital data from the first control circuit 7 is converted by the first D / A conversion circuit 11, and the digital data by the second control circuit 8 is converted by the second D / A conversion circuit from a digital signal to an analog signal. Is converted to.
The output of each D / A conversion circuit is as shown in FIGS.

Since the output voltage waveform has a stepped shape as shown in the figure, the first LPF is used to remove this stepped shape.
13 and a second LPF 14 are used. Each LPF removes high frequency components from the staircase waveform to pure vertical and horizontal parabolic voltages. The output of the first LPF 13 is shown in FIG. 2 (B), and the output of the second LPF 14 is shown in FIG. 2 (D). In the figure, "1V" means one vertical cycle and "1H" means one horizontal cycle. The cutoff frequency of the first LPF 13 and the cutoff frequency of the second LPF 14 are different because the frequencies to be handled are different. The vertical parabolic voltage from the first LPF 13 and the horizontal parabolic voltage from the second LPF 14 are mixed by the mixing circuit 15. Since the output level of the mixing circuit 15 is lower than the finally required level, the output circuit
Amplify by 16. The amplified voltage is superimposed on the DC focus voltage from the flyback transformer (FBT) via the capacitor C1. The final superimposed focus voltage is shown in Fig. 4.
Needless to say.

The voltage required for dynamic focusing is generated as described above, and the optimum state of the parabolic wave is set by adjustment as described above. Whether or not the setting is optimum may be determined by comparing each parabolic waveform observation with an oscilloscope and the focus quality on the screen. If the optimum state is set by adjustment, the level for each position is the first memory unit 9 and the second memory unit.
Remember 10 each. This storage is performed by operating the first adjustment signal generator 5 and the second adjustment signal generator 6 so that the first control circuit 7 is in the first memory unit 9 and the second control circuit 8 is in the second memory. Each is stored in the section 10. During normal use after storage in each memory unit, stored data is read from each memory unit and a required parabolic voltage is output from the data.

[0011]

As described above, according to the present invention, the parabolic voltage of the vertical and horizontal periods required for the dynamic focusing of the cathode ray tube is generated by digital control, and the parabolic waveform is arbitrarily changed for each point (section). Therefore, compared with the conventional method of generating a parabolic wave by an integrating circuit (FIG. 3), it is possible to partially increase or decrease the correction amount and improve the focus quality. In particular, it is possible to improve the effect on a large CRT having a wide deflection angle.

[Brief description of drawings]

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

FIG. 2 is an explanatory diagram of parabola voltage generation in FIG.

FIG. 3 is a principal block diagram showing an embodiment of a conventional dynamic focus circuit.

FIG. 4 is a focus voltage waveform diagram for explaining dynamic focus.

[Explanation of symbols]

 1 Vertical Drive Signal (VD) 2 Horizontal Drive Signal (HD) 3 First PLL 4 Second PLL 5 First Adjustment Signal Generating Unit 6 Second Adjustment Signal Generating Unit 7 First Control Circuit 8 Second Control circuit 9 First memory unit 10 Second memory unit 11 First D / A conversion circuit 12 Second D / A conversion circuit 13 First LPF (low pass filter) 14 Second LPF (low 15 pass filter 16 output circuit FBT flyback transformer 42 cathode ray tube (CRT)

Claims (1)

[Claims] 1. In a so-called dynamic focus in a cathode ray tube, a digital level is set to be variable by setting a predetermined number of sections equally divided within a period of one vertical cycle, and a first digital signal formed by each section. First generation means for generating a level signal, a first D / A conversion circuit for converting the first digital level signal generated by the first generation means into a first analog signal, and the first
And a first memory section for storing the digital level signal of the first analog signal from the first D / A conversion circuit, and a parabola voltage of a vertical cycle. And a first low-pass filter for outputting a digital level and a digital level that is set by varying the digital level for each section obtained by evenly dividing a period of one horizontal period into a required number of sections. Second generation means for generating a signal, a second D / A conversion circuit for converting the signal of the second digital level generated by the second generation means into a second analog signal, and the second digital level Second memory unit for storing the signal of No. 2 in correspondence with the section and the low frequency component of the second analog signal from the second D / A conversion circuit to output the parabola voltage of the horizontal period. Second row Filter, a mixing circuit that mixes a vertical period parabolic voltage from the first low-pass filter and a horizontal period parabolic voltage from the second low-pass filter, and a mixed parabolic voltage from the mixing circuit. A dynamic focus circuit, which is configured with an output circuit that amplifies the voltage.