JPS61144979A - Horizontal afc circuit - Google Patents

Abstract

PURPOSE:To obtain a normal display image whose longitudinal lines have no curvature by correcting reversely horizontal pulses which are outputted from a horizontal output circuit to a saw-tooth wave forming circuit and amplitude-modulated with a distortion correcting waveform by using a simple amplitude modulating circuit which uses one FET so that the amplitude becomes constant. CONSTITUTION:Horizontal pulses of the horizontal output circuit 6 are inputted to the saw-tooth waveform forming circuit 7 through the amplitude modulating circuit 9. This amplitude modulating circuit 9 inputs horizontal pulses which are amplitude- modulated with the distortion correcting waveform and a correcting waveform D similar to the distortion correcting waveform A. The amplitude modulating circuit 9 imposes amplitude modulation on the input horizontal pulses B by using the correcting waveform D to generate and output horizontal pulses G having a nearly constant amplitude to the saw-tooth waveform forming circuit 7. The voltage division of a voltage dividing resistance 14 varies with the internal resistance of the FET13 in the amplitude modulating circuit 9, so the input horizontal pulses are divided according to variation in the internal resistance and outputted to a horizontal pulse output terminal 12. For the purpose, the horizontal pulse G having the nearly constant amplitude are obtained by optimizing the amplitude of the correcting waveform through a variable resistance 18.

Description

Detailed Description of the Invention [Field of Application of the Invention] The present invention relates to a horizontal AFC (automatic waste wave number control) circuit in a horizontal deflection circuit of a display device using a cathode ray tube. The present invention relates to a horizontal AFC circuit that reduces distortion of vertical lines in an image that occurs when the image is modulated.

[Background of the invention]

In the horizontal deflection circuit, a horizontal AFC circuit is provided to stably synchronize the horizontal oscillation circuit with a horizontal synchronization signal. This horizontal AFC circuit is a sawtooth AFC circuit, a pulse width AF circuit, and a pulse width AF circuit, depending on the type of phase detection circuit, signal comparison method, etc.
Although there are C circuits, the former is generally used.

A block diagram of a horizontal deflection circuit using a conventional sawtooth AFC circuit is shown in FIG. In the figure, 1 is a horizontal synchronization signal input terminal, 2 is a phase detection circuit, 3 is an integration circuit, 4 is a horizontal oscillation circuit, 5 is a horizontal drive circuit, 6 is a horizontal output circuit, and 7 is a sawtooth wave forming circuit. This circuit forms an AFC circuit. Further, 8 is a distortion correction circuit 0 The basic operation of the AFC circuit will be explained below. The phase detection circuit 2 compares the phases of the horizontal synchronizing signal and the sawtooth wave from the sawtooth wave forming circuit 7, and generates a detection voltage corresponding to the phase difference. Normally, this voltage is in the form of a pulse, so it is added to the integrator circuit 3 and converted into a DC voltage to the horizontal oscillation circuit 4.
is under control. This horizontal oscillation circuit 4 uses a circuit whose oscillation frequency and phase can be controlled by a control voltage.

Further, the horizontal drive circuit 5 is driven by the output of the horizontal oscillation circuit 4, and the horizontal drive circuit 5 drives the horizontal output circuit 6. Furthermore, the horizontal pulse of this horizontal output circuit 6 is input to the above-mentioned sawtooth wave forming circuit 7 to form a sawtooth wave whose phase is compared with the horizontal synchronizing signal. Therefore, the horizontal oscillation circuit 4 is operated so that the horizontal synchronization signal and the horizontal pulse (converted into a sawtooth waveform) match in phase.
is controlled, and the horizontal output circuit 6 is synchronized with the horizontal synchronization signal.

Further, since pulse noise mixed in the horizontal synchronization signal is removed by the integrating circuit 3, stable synchronization without disturbance due to noise can be obtained.

On the other hand, the distortion correction circuit 8 shown in FIG. 6 corrects image distortions such as left-right pincushion distortion, which is one of the deflection distortions of cathode ray tubes, and horizontal keystone distortion, which is one of the projection distortions of projection display devices. Therefore, the magnitude of the horizontal deflection current of the horizontal output circuit 6 is changed. For example, in order to correct the left-right pincushion distortion of the former, the seventh
As shown in FIG. A(1), the power supply voltage of the horizontal output circuit 6 may be changed using a distortion correction waveform of a vertically periodic parabolic wave. In the case of the latter horizontal trapezoidal distortion, a sawtooth wave with a vertical period as shown in FIG. 7A(2) may be used as the distortion correction waveform. Note that although a sawtooth wave is used as the distortion correction waveform in the following 12-light, the operation is the same even if a parabolic wave or other complicated correction waveform is used.

In this way, since the magnitude of the horizontal deflection current of the horizontal output circuit 6 is modulated by the distortion correction waveform, the horizontal pulse input from the horizontal output circuit 6 to the sawtooth wave forming circuit 7 also changes as shown in FIG. As shown, the amplitude is modulated using a distortion correction waveform (a sawtooth waveform with a vertical period). For this reason, the above-mentioned horizontal AF
Since the distortion correction waveform is superimposed on the output of the integrating circuit 3 of the C circuit (the control voltage of the horizontal oscillation circuit 4) as shown in FIG. arise. At this time, the displayed image becomes very difficult to see with curved vertical lines. Also, if the time constant of the integrating circuit 3 is made very large, the influence of the distortion correction waveform can be removed, but since this time constant affects the horizontal AFC synchronization pull-in time, it is possible to remove the distortion correction waveform of the vertical period. It is not possible to increase the time constant until

Examples of patents for horizontal AFC circuits that address problems caused by waveform distortion of horizontal pulses include JP-A-55-20011;
JP-A-56-90679, JP-A-56-1328
No. 70, JP-A-57-18166, etc.

[Purpose of the invention]

An object of the present invention is to provide a horizontal AFC in which the phase of the horizontal synchronizing signal and the horizontal pulse does not change even if the horizontal pulse of the horizontal output circuit is amplitude-modulated by a distortion correction waveform, and therefore the vertical line does not curve in the displayed image. The purpose is to provide circuits.

[Summary of the invention]

In the present invention, a horizontal pulse amplitude-modulated with a distortion correction waveform, which is output from a horizontal output circuit to a sawtooth wave forming circuit, is fixed in amplitude by using a simple amplitude modulation circuit using one field effect transistor. It is characterized in that it is reversely corrected so that

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a horizontal deflection circuit using a horizontal AFC circuit according to the present invention, and the same parts as in the conventional example are given the same reference numerals and explanations will be omitted.

In FIG. 1, the difference from the conventional example is that the horizontal pulse from the horizontal output circuit 6 is inputted to the sawtooth wave forming circuit 7 through amplitude variation #1 #I9.

The amplitude modulation circuit 9 receives a horizontal pulse B amplitude-modulated with a distortion correction waveform and a correction waveform similar to the distortion correction waveform A shown in FIG. However, the polarity of the direction of change in the correction waveform and the direction of change in the amplitude of the horizontal pulse B differ depending on the configuration of the amplitude modulation circuit 9. The amplitude modulation circuit 9 modulates the amplitude of the inputted horizontal pulse B using a correction waveform, converts it into a horizontal pulse G having a substantially constant amplitude as shown in FIG. 4, and outputs it to the sawtooth waveforming circuit 7. Therefore, unlike the conventional example, the distortion correction waveform is not superimposed on the control voltage of the horizontal oscillation circuit 4, and the synchronization of the horizontal output circuit 6 does not change, so that a normal display image can be obtained.

Next, the amplitude modulation circuit 9 will be explained in detail using FIGS. 2 to 4. FIG. 2 shows an example of the configuration of the amplitude modulation circuit 9, where 10 is an input terminal for a horizontal pulse amplitude-modulated with a distortion correction waveform, 11 is an input terminal for the above-mentioned correction waveform, and 12 is an input terminal whose amplitude is corrected to be almost constant. horizontal pulse output terminal, 1
3 is a junction field effect transistor (hereinafter abbreviated as FET) that functions as a variable resistance element, 14 is a voltage dividing resistor, 15 and 16 are resistors and capacitors for applying bias voltage vB to the FET, and 17 is a correction A coupling capacitor 18 that blocks the DC component of the waveform is a variable resistor that adjusts the amplitude of the correction waveform applied to the gate of the FET 13 by iW so that the amplitude of the output horizontal pulse is constant.

The operation of the amplitude modulation circuit having such a configuration will be explained below. The horizontal pulse applied to the input terminal 1o is divided by the internal resistance of the resistor 14 and the FET 13 and output to the output terminal 12. Therefore, as the internal resistance increases, the amplitude of the output horizontal pulse also increases; The lower the resistance, the lower the amplitude of the output horizontal pulse. Furthermore, the internal resistance of the FET 13 can be controlled by the value of the gate-source voltage Vas. Therefore, if the gate-source voltage VGS is changed so that the internal resistance of FET 13 is decreased when the amplitude of the horizontal pulse is large, and conversely, the internal resistance is increased when the amplitude is small, the horizontal Pulses can be obtained from output terminal 12.

Here, the relationship between the internal resistance and the gate-source voltage VGS of FBTls is shown in FIG.

In the figure, the vertical axis represents the internal resistance, the horizontal axis represents the gate-source voltage VGS, and 19 is a characteristic curve representing the change in internal resistance with respect to the gate-source voltage V()S. Note that the FET 13 has a gate-source voltage VaS
It is necessary to operate in the negative region. Therefore, as shown in Fig. 2, the period of the distortion correction waveform (
The bias voltage vB is obtained by connecting a parallel circuit of a resistor 15 and a capacitor 16 having a time constant sufficiently larger than the vertical period) and integrating horizontal pulses.

FIG. 4 shows the waveforms of each part, and a horizontal pulse B whose amplitude has been modulated by a distortion correction waveform is input to the horizontal pulse input terminal 10. Further, a correction waveform similar to the distortion correction waveform A input to the correction waveform input terminal 11 has direct current cut off by the coupling capacitor 17, and is adjusted to a desired amplitude by the variable resistor 18. This correction waveform is superimposed on the bias voltage VB described above to form a gate-source voltage waveform E.

When such a gate-source voltage waveform E is applied to the FET 13, the internal resistance of the FET 13 increases when the gate-source voltage VGS is low and decreases when the voltage VGS is high, as shown in FIG. , F. Due to this internal resistance change F, the voltage dividing resistor 14
Since the voltage division ratio between the horizontal pulses and the horizontal pulses changes, the input horizontal pulses are divided according to the change in internal resistance F and are output to the horizontal pulse output terminal 12. Therefore, by optimally adjusting the amplitude of the correction waveform with the variable resistor 18,
It is possible to obtain a horizontal pulse G whose amplitude is approximately constant as shown in FIG.

As explained above, a horizontal pulse with constant amplitude can be obtained with a simple circuit configuration using one FET, eliminating malfunctions of the horizontal AFC circuit due to distortion correction, and displaying a normal display image without synchronization disturbance. can get.

Further, FIG. 5 shows another configuration example of the amplitude modulation circuit 9, and the same parts as in the above-described configuration example are denoted by the same reference numerals, and a description thereof will be omitted. The input horizontal pulse, which is amplitude-modulated by distortion correction, is transmitted to the diode 20. By inputting the signal to an envelope detection circuit 23 consisting of a capacitor 21 and a resistor 22, a correction waveform similar to the distortion correction waveform is formed. The other operations are exactly the same as those in the above configuration example, and therefore the same effects as in the above structure N can be obtained.

〔Effect of the invention〕

According to the horizontal AFC circuit of the present invention, even if the horizontal pulse of the horizontal output circuit is amplitude-modulated with a distortion correction waveform, the phase of the horizontal synchronization signal and the horizontal pulse can be kept constant, so that vertical lines in the image do not curve. A normal display image can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a horizontal deflection circuit showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing an example of the configuration of an amplitude modulation circuit,
Figure 3 is a characteristic diagram showing the characteristics of a field effect transistor, Figure 4 is a waveform diagram showing operating waveforms, Figure 5 is a circuit diagram showing another example of an amplitude modulation circuit, and Figure 6 is a conventional sawtooth waveform diagram. A
FIG. 7 is a block diagram of a horizontal deflection circuit using an FC circuit, and a waveform diagram showing operating waveforms. Description of symbols 1...Horizontal synchronization signal input terminal, 2...Phase detection circuit, 3...Integrator circuit, 4...Horizontal oscillation circuit, 5...Horizontal drive circuit, 6...Horizontal output circuit , 7... Sawtooth wave forming circuit, 8... Distortion correction circuit, 9... Amplitude modulation circuit, 10... Horizontal pulse input terminal, 11... Correction waveform input terminal, 12...
Horizontal pulse output terminal, 13... Field effect transistor, 14... Voltage division resistor, 23... Envelope line detection circuit. Representative Patent Attorney Akio Takahashi Figure 1 Figure 4 Figure 6 Figure 7

Claims (1)

[Scope of Claims] 1) A horizontal output circuit that generates a horizontal pulse to be supplied to a horizontal deflection coil of a picture tube, and a sawtooth wave generation circuit that receives the horizontal pulse from the circuit and generates a sawtooth wave. , Compare each phase of the sawtooth wave with a horizontal synchronizing signal included in the video signal to be displayed on the picture tube, and control the frequency of the horizontal pulse generated from the horizontal output circuit so that the two coincide. a horizontal AFC circuit further comprising a distortion correction circuit for supplying a distortion correction signal to the horizontal output circuit and modulating horizontal pulses therefrom in order to correct image distortion in the picture tube; A modulation circuit for shaping the horizontal pulse modulated by the distortion correction signal into the original horizontal pulse and outputting the same is provided on the input side of the sawtooth wave generation circuit, and the horizontal pulse is converted to the sawtooth wave generation circuit through the modulation circuit. A horizontal AFC circuit characterized in that an input signal is input to the circuit. 2) In the horizontal AFC circuit according to claim 1, the modulation circuit applies a horizontal pulse modulated by the distortion correction signal to the drain through a resistor, and has a bias voltage generating circuit between the source and ground. A horizontal AFC comprising a field effect transistor connected to a parallel circuit of a resistor and a capacitor, the distortion correction signal being applied to the gate of the transistor, and an output being obtained from the drain of the field effect transistor. circuit. 3) In the AFC circuit according to claim 2, instead of the distortion correction signal applied to the gate of the transistor, a horizontal pulse modulated by the distortion correction signal is obtained by envelope detection. A horizontal AFC circuit characterized in that it uses a correction signal.