JPH01138852A - Dynamic focus phase controller - Google Patents

Abstract

PURPOSE:To prevent focus deterioration due to phase shift by detecting a phase difference between a phase pulse and a reference pulse and controlling the phase of generation of a driving pulse so as to make the phase difference zero. CONSTITUTION:When a horizontal period driving pulse (a) is inputted to a monostable multivibrator 15, a reference pulse (b) is generated from the output. A sinusoidal voltage detected by a resistor 22 at a zero cross comparator 20 is converted into a rectangular wave (h) and given to the comparator input terminal of a phase comparator 16. The output of the comparator 16 decreases the output of an LPF 17 and the generating timing of the output pulse (c) of the VCO 18 is delayed. The is equal to the delay of the driving pulse (d) of a power MOS 6, then the switching pulse (e) is delayed and the phase of voltage/current of the correction coil 2 is retarded. Thus, the leading edge of the output waveform (h) of the comparator 20 and the leading edge of the pulse (b) are made coincident to bring the state the same as the state of phase at optimum focus.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a dynamic focus circuit for a picture tube, that is, a dynamic focus circuit that can obtain optimum focus over the entire screen.

[Conventional technology]

As an electromagnetic focusing type dynamic focus circuit, there is a method in which a switching circuit and an LC resonant circuit are combined, an auxiliary coil used for dynamic focusing is connected as an inductor of the resonant circuit, and a correction current is caused to flow. In addition, related devices of this type include, for example, Japanese Patent Application Laid-open No. 5
No. 5-79573.

Publications such as Japanese Unexamined Patent Publication No. 56-98970 can be cited.

[Problem that the invention seeks to solve]

In general, for high-definition displays that require images with a high degree of resolution, it is more advantageous to use a magnetic focusing lens than to use an electrostatic focusing lens as a means for forming an electron beam.

FIG. 3 is a sectional view of a cathode ray tube for explaining the outline of the magnetic focusing method. In the figure, l is a focusing coil (or permanent magnet), 2 is an auxiliary coil, 3 is a magnetic focusing lens, and 4
is a deflection yoke, and 5 is a screen.

As shown in Figure 3, in order to achieve the magnetic focusing method, a focusing coil (or a permanent magnet may be used) 1 is installed around the neck of the cathode ray tube, and a focusing lens system 3 is installed inside the neck. Form.

Generally, the magnetic field for obtaining optimal focus at a point on the screen 5 is not constant, and the magnetic field strength differs between the center and the periphery of the screen.

Therefore, in order to obtain optimum focus over the entire surface of the screen 5, it is necessary to change the magnetic field strength depending on the point on the screen. This is what is called dynamic focus. For this purpose, the auxiliary coil 2 inside the focusing coil (or permanent magnet) l has a parapolar wave pattern (
By flowing a correction current (or a sinusoidal waveform), the magnetic field strength is changed depending on the point (position) on the screen to achieve dynamic focus.

Next, the problems will be explained using the conventional dynamic focus circuit.

FIG. 4 shows a conventional dynamic focus circuit. In the figure, 6 is a power MO8 (switch), 7 is a damper diode, 8 is a capacitor, 9 is a choke coil, 10 is a capacitor, 11 is a variable inductor, 12 is a resonance capacitor, 2 is an auxiliary coil, and 14 is a resistor. .

FIG. 5 is an operational waveform diagram of each part of FIG. 4.

The circuit operation will be explained with reference to FIGS. 4 and 5.

First, a horizontal periodic drive pulse 1 is input to the gate of the switching power MO86. At this time, the power MOf
96 repeats ON and OFF, and a switching pulse b is generated by series resonance between the choke coil 9 and the capacitor 8. This switching pulse b generates a horizontally periodic sinusoidal waveform in the LCR series-parallel auxiliary circuit constituted by the capacitor 12 and the two-coil resistor 14, and a horizontally periodic sinusoidal correction current flows through the auxiliary coil 2. If the resonant frequency of this circuit matches the horizontal scanning frequency, the phase of the horizontal period drive pulse 1 and the correction current match as shown by the solid line in FIG. 5C, and optimum focus can be obtained at all points on the screen. However, since the Q of the resonant circuit is high, even if there is a slight change in the horizontal scanning frequency or the element value of the resonant circuit, the phase shifts as shown by the dotted line in FIG. 5C, and all points on the screen become out of focus. Normally, this phase shift is adjusted by the variable inductor 11. Although this adjustment can deal with variations in the elements, it is necessary to readjust the phase in response to changes in temperature and aging, or changes in the horizontal scanning frequency.

SUMMARY OF THE INVENTION An object of the present invention is to provide a dynamic focus circuit that can compensate for the above-mentioned drawbacks and prevent focus deterioration due to phase shift.

[Means for solving problems]

The dotted line in FIG. 5C shows a state in which the phase of the correction current is ahead of the horizontal period drive pulse. At this time, in order to correct the phase lead of the correction current, it is sufficient to delay the generation timing of the switching pulse b by the amount of the phase lead. Conversely, if the phase of the correction current is delayed, the timing of generation of the switching pulse b may be advanced by the amount of the phase delay. Therefore, when performing phase compensation, it is sufficient to provide a circuit that controls the generation timing of the teswitching pulse according to the phase shift.

[Effect]

As a method for changing the generation timing of switching pulses according to a phase shift, there is a method using a PLL (phase locked loop). A PLL is composed of a phase comparator, a low-pass filter, and a voltage-controlled oscillator.The output voltage of the low-pass filter determines the phase of the output pulse of the voltage-controlled oscillator, and this output pulse operates the controlled @path to change the phase of the desired signal. Comparator comparison input hef 4
- Control the phase of the desired signal by docking.

〔Example〕

An embodiment of the present invention is shown in FIG. 1 below, and its operation will be explained using the waveform diagram shown in FIG. 2.

In Figure 1, 15 and 19 are monostable multi, respectively.
16 is a phase comparator, 17 is a low pass filter (LPF)
, 18 is a voltage controlled oscillator (VCO), 2 is an auxiliary coil,
22 is a resistor, 20 is a comparator, and other components that are the same as in FIG. 4 are given the same reference numerals.

In FIG. 2, T indicates a horizontal retrace period, and T indicates a horizontal scanning period. Now, when the horizontal periodic drive pulse a is input to the monostable multi 15, the reference pulse b is generated from its output. The falling edge of this reference pulse is made to coincide with the falling edge of the horizontal periodic drive pulse b, and the monostable multi 15 is arranged so that the pulse width is 1/2 of the horizontal retrace period. Set. Further, the monostable multi 19 is a circuit that generates a drive pulse d for switching the switching power MO 86 of the dynamic focus circuit.

This monostable multi 19 is set so that the falling edge of its output, the drive pulse d, coincides with the falling edge of the output pulse C of the voltage controlled oscillator 18. Diode 7 is a damper diode. A series resonant circuit is formed by the capacitor 8 and the choke coil 9, and a switching pulse e is generated by switching the resonant circuit and the power M086. The energy generated by this switching pulse e is extracted from the tap of the choke coil 9, and then a series-parallel resonant circuit consisting of a capacitor 10°12, coils 21, 2, and resistors 14, 22 is connected to help flow a correction current. A sinusoidal correction current is passed through the coil 2. The resistor 22 is a resistor that converts the current of the auxiliary coil 2 into a voltage and detects the phase of the correction current g as the phase of the voltage f across the auxiliary coil. Further, the zero-cross comparator 20 converts the sine wave voltage detected by the resistor 22 into a rectangular wave and inputs it to the comparison input terminal of the phase comparator 16. Now, assuming that the phase of the correction current g is ahead of the drive pulse d, the auxiliary
The phase of the voltage f across the four coils is also advanced, and the phase of the output waveform of the zero cross comparator 20 is also advanced. Therefore, the output of the phase comparator 16 is LP F 17
The timing of generation of the output pulse C of the voltage controlled oscillator 18 is delayed. This is the same as the drive pulse d of the power MO 86 being delayed, so the switching pulse d is also delayed, the phase of the voltage and current of the correction coil 2 is also delayed, and the rising edge of the output waveform of the zero cross comparator 20 and the reference pulse b are delayed. The rising edges match. In this state, this phase control circuit converges. That is, the phase of the voltage and current of the correction coil becomes the same as the phase state at the time of optimum focus as shown in FIG.

〔Effect of the invention〕

As described above, according to the present invention, the efficiency of focus adjustment can be improved by automating the phase adjustment in the dynamic focus circuit, and the correction current phase can always be optimized.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram of each part of the operation, Fig. 3 is a cross-sectional view of the inner tube for explaining the outline of the magnetic focusing method, and Fig. 4 is FIG. 5 is a circuit diagram showing a conventional dynamic focus circuit, and FIG. 5 is a waveform diagram of each part for explaining the operation of the circuit. 6... Power MO87... Damper diode 9.
...Choke coil 2...Auxiliary coil 22...
Resistor 15... Monostable multi 16...
Phase comparator 17...Low pass filter 18...
...Voltage controlled oscillator 19... Monostable multi 20.
... Comparator Liu Figure 1 Sf Part 2 Figure 3 Procedural amendment (method) Indication of the case 1988 Patent Application No. 183402 Title of the invention
Relationship between persons who perform dynamic focus phase control device correction Patent applicant name: r5101 Tsuji Tsuji Co., Ltd. Hitachi Manufacturing Co., Ltd. Agent: Hitachi Video Engineering Co., Ltd. Correction. Subject: Correction of the title of the invention in the specification. Content
The statement in the title of the invention column of the specification is amended as follows.

Claims (1)

[Claims] 1. A correction current in the form of a parapolar wave (sine wave) having the same period as the horizontal scanning period is passed through an auxiliary coil provided in conjunction with a magnetic field generating means for focusing the electron beam on the screen, so that the entire surface of the screen is In the dynamic focus circuit of the picture tube, which achieves optimal focus over a wide range of periods, there is a circuit that generates a reference pulse that is synchronized with the horizontal retrace period of the video signal and has the same phase, and a circuit that generates a reference pulse that is synchronized with the horizontal retrace period of the video signal and a drive pulse that has the same period as the horizontal scanning period. a correction current creation circuit that synchronously creates the parapolar wave (sine wave) correction current and causes it to flow through the auxiliary coil; a circuit that generates a phase pulse representing the phase of the correction current that flows through the auxiliary coil; and the phase pulse. A dynamic focus circuit comprising: a comparison circuit that detects and outputs a phase difference between the drive pulse and the reference pulse; and a circuit that controls the generation phase of the drive pulse so that the phase difference becomes zero.