JPH0542870B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a television receiver, and particularly to a television receiver having an improved horizontal AFC circuit provided therein.

[Conventional technology]

A horizontal AFC circuit used in a television receiver is generally constructed as shown in FIG. In the figure, 1 is a horizontal oscillator (VCO), and the oscillation output of the horizontal frequency _H is supplied to the horizontal output circuit 3 via the horizontal drive circuit 2, and the flyback pulse P _F obtained from this horizontal output circuit 3 is integrated. This sawtooth signal P _T is supplied to the phase comparator 6 together with _{the horizontal synchronizing signal P H supplied} to the terminal 5, where the phases are compared, and the phase comparison output is low pass filter 7
By being supplied to the horizontal oscillator 1 via
Horizontal frequency _H is controlled.

By the way, if such a horizontal AFC circuit 10 is used as an IC
In general, a circuit group 9 as shown by a dashed line is integrated.

In addition, in such a television receiver, screen distortion occurs due to changes in screen brightness and, therefore, changes in beam current. Screen distortion caused by this change in beam current includes symmetrical screen distortion in which the screen size expands in bright areas and narrows in dark areas due to changes in the high voltage supplied to the picture tube, and the storage time of the horizontal output transistor. There is asymmetrical screen distortion that occurs due to changes in the flyback pulse waveform, etc.

Fig. 8 shows an example of left-right asymmetric screen distortion, and Fig. 8A shows an image in which there is a black part S _B and a rectangular white part S _W on the screen S.
As shown in Figure B, the white portion _SW is asymmetrically distorted.

[Problem that the invention seeks to solve]

By the way, in order to correct the left-right asymmetric screen distortion component among the above-mentioned screen distortions, it is sufficient to control the horizontal oscillator 1 by superimposing a ripple waveform corresponding to the screen distortion on the phase comparison output shown in FIG. . In this case, as described above, a part of the horizontal AFC circuit 10
When integrated into an IC, an external terminal 8 as shown in the figure must be provided.

However, in the case of an IC 9 that does not take screen distortion correction into consideration, the terminal 8 is not provided, so when such an IC 9 is used, screen distortion cannot be corrected.

Redesigning IC9 for correcting screen distortion is extremely wasteful in terms of cost.

Furthermore, if the horizontal AFC circuit 10 has a digital configuration, the ripple waveform component described above cannot be directly supplied to the digital low-pass filter, so screen distortion cannot be corrected with the current configuration.

Therefore, the present invention solves these conventional problems, and it is possible to correct screen distortion even in a horizontal AFC circuit using an existing IC that does not have the terminal 8 or a horizontal AFC circuit with a digital configuration. It was made so that it could be done.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides a monostable _{multivibrator} 20 as shown in FIG. This monostable multivibrator 20 is supplied with a ripple waveform component (screen distortion correction signal) V _D corresponding to screen distortion.

[Effect]

The pulse width or pulse phase of the monostable multivibrator 20 is modulated by the screen distortion correction signal V _D corresponding to the screen distortion. This modulation is equivalent to a change in the phase of the flyback pulse P _F , so
The AFC control system operates to correct this phase change. As a result, the AFC control system operates in a direction that corrects screen distortion, and asymmetric screen distortion is corrected.

〔Example〕

FIG. 1 shows a television receiver according to the present invention.
In particular, an example will be shown in which the horizontal AFC circuit 10 is applied to the analog horizontal AFC circuit shown in FIG.

In the present invention, as shown, a flyback pulse P _F (FIG. 4A) is supplied to a differentiator circuit 11 to form, in this example, a positive differential pulse P _D (FIG. 4B), which is monostable. multi vibrator 20
is supplied as a trigger pulse. The multi-output P _M (C in the same figure) of the multivibrator 20 is supplied to the integrator 4 and converted into a sawtooth wave output P _T (D in the same figure), which is supplied to the phase comparator 6.

The pulse width of the multivibrator 20 is controlled by the screen distortion correction signal V _D shown in FIG.
FIG. 3 shows an example of this multivibrator 20, and 21 is a pair of transistor circuits constituting the multivibrator, and a resistor R of a time constant circuit 22 consisting of R and C that determines the pulse width controls a control transistor Q. The above-mentioned correction signal V _D is supplied to the base of this transistor Q via a capacitor 23 . 24 is its input terminal.

As shown in FIG. 1, the correction signal V _D is detected by the high voltage generation circuit 15 in this example. FBT indicates a flyback transformer, from which an output terminal 17 for high voltage HV is led out via a diode 16. A detection resistor 18 is connected to the FBT, and a terminal 24 for the correction signal V _D is derived from one end thereof.

The pulse width of the multi-output P _M output from the multi-vibrator 20 is set to be equal to the pulse width of the flyback pulse P _F when there is no screen distortion. When an image is projected and the screen becomes brighter by tracing the position of the white part S _W , the beam current increases and the high voltage HV decreases accordingly, resulting in a voltage across the resistor 18. The voltage value of the correction signal V _D decreases.

Therefore, a correction signal V _D as shown in FIG. 2 is obtained at both ends of the resistor 18. If this correction signal V _D is supplied to the transistor Q, the screen S
The voltage decreases in the white part _SW , and the time constant circuit 2
Since the voltage applied to the multivibrator 20 decreases, the pulse width of the multivibrator 20 increases (FIG. 4F).

As a result, the sawtooth signal P _T becomes
As shown in , the retrace period _TR becomes longer, and the phase comparison output V ₂ with the horizontal synchronizing pulse P _H becomes lower than when screen distortion does not occur (V ₂ <V ₁ ). Along with this, the horizontal oscillator 1 is controlled to increase the horizontal frequency, the phase of the screen advances compared to when there is no screen distortion, and the screen distortion is corrected.

In this way, the correction signal V _D has a voltage value corresponding to the screen distortion as shown in _FIG . , the screen distortion is corrected as shown by the broken line in FIG. 8B, and a correct screen S as shown in FIG. 8A is displayed.

The correction signal V _D is supplied through a detection resistor 18 in series with a focus adjustment resistor 19, as shown in FIG.
The correction signal V _D may be detected by connecting the

Furthermore, in the above description, the leading edge of the flyback pulse _PF is detected to form the differential pulse _PD , but the trailing edge may also be detected. However, in this case, since the trace period T _T is controlled by the correction signal V _D , the phase of the multi-output P _M is once inverted to make it have the polarity as shown in FIG. need to be supplied.

FIG _. 6 shows a case where the present invention is applied to a digital _horizontal AFC circuit.
0 is provided, and its output is 1/1 at the counter 31.
The frequency is divided into N and supplied to the horizontal output circuit 3 via the horizontal drive circuit 2. Also, the flyback pulse P _F obtained from this horizontal output circuit 3
is connected to the multivibrator 20 via the differentiating circuit 11
The multi-output P _M is supplied to the digital phase detector 32 and is pulse width modulated by the correction signal V _D.
The _phase comparison output is supplied to the digital low-pass filter 33, and the frequency division ratio N of the counter 31 is controlled according to the phase comparison output.

The frequency division ratio N is determined in advance so that the horizontal frequency _H is supplied to the horizontal drive circuit 2 when no screen distortion occurs.

Therefore, when the correction signal V _D is supplied, the pulse width of the multi-output P _M is controlled and the frequency division ratio N is changed in the same way as described above, so the screen distortion can also be corrected in this configuration. It will be controlled in the direction in which it will be carried out.

Further, in each of the embodiments described above, screen distortion can also be corrected by providing two or more multivibrators 20 and modulating the phase of their multi-outputs with the correction signal V _D.

Furthermore, the analog horizontal AFC circuit 10 is not limited to a sawtooth AFC circuit.

〔Effect of the invention〕

As explained above, according to the present invention, a flyback pulse is supplied to a phase comparator via a monostable multivibrator, and the pulse width or pulse phase of the monostable multivibrator is modulated by a waveform corresponding to screen distortion. Therefore, screen distortion can be reliably corrected.

Further, according to the present invention, since a multivibrator is provided, the present invention can be applied to both analog and digital horizontal AFC circuits. Since it can be used, it is extremely convenient for practical use.

[Brief explanation of the drawing]

1 and 6 are system diagrams of essential parts showing an example of a television receiver according to the present invention, FIG. 2 is a waveform diagram of a screen distortion correction signal, and FIG. 3 is an example of a monostable multivibrator. 4 is a waveform diagram for explaining the correction operation, FIG. 5 is a connection diagram showing another example of the correction signal detection system, and FIG. 7 is a system diagram showing an example of a conventional television receiver. , FIG. 8 is a diagram for explaining its operation. 10 is a horizontal AFC circuit, 1 is a horizontal oscillator, 3 is a horizontal output circuit, 6 is a phase comparator, 11 is a differentiation circuit, 20 is a monostable multivibrator, 15 is a high voltage generation circuit, 18 is for detection of correction signal V _D It is a resistor.

Claims (1)

[Claims] 1 Input the horizontal synchronization signal to the phase comparator, control the phase of the horizontal oscillator with the output of this phase comparator,
It has a horizontal AFC circuit that supplies the flyback pulse obtained from the latter stage of the horizontal oscillator to the phase comparator as a comparison signal, and supplies the flyback pulse to the phase comparator via the monostable multivibrator, and A television receiver that corrects screen distortion by modulating the pulse width or pulse phase of a monostable multivibrator with a waveform that corresponds to screen distortion.