JP2002290768A - Television set - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the disturbance of an image even when a deteriorated video signal exists. SOLUTION: The television set has an A/D converter 32 for supplying a demodulated video signal, a sampling pulse generation means 36 for the A/D converter, a variable oscillator 34 for oscillating a reference signal, a deflecting circuit 22 for supplying the oscillation output of variable oscillation as a horizontal drive signal, and a control part 38 for supplying A/D conversion output and controlling a variable oscillation frequency. The variable oscillator is controlled so as to be synchronized with a horizontal cycle detected by the A/D conversion output. The minimum value is detected from the A/D conversion output of a video signal, and the minimum value out of the A/D conversion output before and after one horizontal cycle is detected. When the minimum value is detected, the variable oscillator is controlled so as to correspond to an interval (cycle) obtaining the two minimum values before and after it, and the horizontal oscillation frequency is controlled. Even the deteriorated video signal can generate a horizontal drive signal having the oscillation frequency related to the input video signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a television receiver having a circuit for generating a horizontal drive signal. More specifically, by detecting the vicinity of the horizontal synchronizing signal from the A / D converted output of the demodulated video signal and predicting the next horizontal cycle based on the detected horizontal synchronizing signal to generate a horizontal drive signal, even in a weak reception environment. This is to minimize the disturbance of the image as much as possible.

[0002]

2. Description of the Related Art As shown in FIG. 4A, a television signal is a synchronization signal (horizontal synchronization signal) obtained at regular intervals.
Since the video signal SV is superimposed between the HD signals and where the reception level (electric field intensity) is strong, the waveform of the horizontal synchronizing signal is also a rectangular wave. Therefore, as shown in FIG. Since the horizontal synchronization signal HD can be accurately separated and supplied to the deflection circuit system, a synchronized image can be reproduced on the screen.

On the other hand, as the reception level becomes weaker,
Since the waveform of the television signal becomes dull, the sync signal and the video signal may not be clearly distinguished as shown in FIG. 4B in some cases. Even in such a case, the synchronization signal can be separated by performing amplification processing of the input signal in the circuit system.

[0004] However, there is a limit to this, and when the reception level is considerably weak, the synchronization signal is significantly increased, so that the synchronization signal may not be accurately separated in terms of level. In such a case, the separated synchronization signal HD
4C is disturbed as shown in FIG. 4C, and if the deflection circuit system is driven based on the disturbance, the image is disturbed.

[0005]

Conventionally, even when the reception electric field strength of a television signal is extremely poor, the synchronization signal HD is separated or cannot be separated after the video signal is amplified. In such a case, the self-propelled frequency of the synchronizing signal is used to overcome the emergency. For this reason, it was not possible to project an image without much synchronization disorder.
Therefore, the present invention has solved such a conventional problem, and particularly, even when the reception electric field strength is weak,
An object of the present invention is to provide a television receiver capable of correctly reproducing a synchronization signal as much as possible and eliminating image disturbance.

[0006]

According to a first aspect of the present invention, there is provided a television receiver, comprising: an A / D converter to which a demodulated video signal is supplied;
A sampling pulse generating means for generating a sampling pulse supplied to the A / D converter, a variable oscillator for oscillating a reference signal serving as a basis of the sampling pulse,
A deflection circuit to which the oscillation output of the variable oscillation is supplied as a horizontal drive signal; and a control unit to which the A / D conversion output is supplied and which controls the oscillation frequency of the variable oscillator. The variable oscillator is controlled so as to be synchronized with the horizontal period detected from the converted output.

In the present invention, the video signal is A / D converted,
A minimum value is detected from the A / D conversion output. When the video signal is A / D converted, the horizontal synchronization signal section takes the minimum value among the A / D conversion outputs. Even when the received electric field strength is weak, the minimum value may correspond to the horizontal synchronization signal.

Therefore, the minimum value obtained first from the A / D conversion output is detected, and the A / D after one horizontal cycle is detected.
Detect conversion output. Then, a minimum value near one horizontal cycle is detected. When the minimum value is detected, the variable oscillator is controlled so that the horizontal oscillation frequency is controlled so as to correspond to the interval (period) at which the two preceding and following minimum values are obtained. In this way, a horizontal drive signal having an oscillation frequency related to the input video signal can be generated.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a television receiver according to the present invention will be described in detail with reference to the drawings. FIG. 1 shows an embodiment of a television receiver 10 according to the present invention. A desired channel among television signals received by an antenna 12 is selected by a tuner 14. The television signal of the selected channel is demodulated by the demodulation circuit 16, and the demodulated video signal is supplied to the video output circuit 1.
The video of the channel supplied to and received by a monitor, for example, a cathode ray tube (CRT) via the CRT 8 is reproduced. The outputs of the horizontal and vertical deflection circuits 22 are supplied to the corresponding horizontal and vertical deflection coils 24 as horizontal and vertical deflection signals, respectively.

In the present invention, the video signal itself output from the demodulation circuit 16 is supplied to the horizontal drive signal generation circuit 30. The horizontal drive signal generation circuit 30 exerts its power especially in an area where received radio waves are weak.

The horizontal drive signal generation circuit 30 has an A / D converter 32, which performs A / D conversion processing including a synchronization signal. The A / D conversion output is output from the control unit 3 composed of a microcomputer.
8 is supplied. A sampling pulse generated based on the oscillation frequency from the variable oscillator 34 is supplied to the A / D converter 32. The oscillation frequency at the center of the variable oscillator 34 is the horizontal frequency fh (15.734 Hz).

The oscillating frequency is once supplied to a sampling pulse generating circuit 36, and is converted into an n-times frequency to form a sampling pulse. In this embodiment, n = 100 is selected for ease of measurement. Therefore, the video signal is sampled and quantized at the sampling frequency of 100 fh.

The control unit 38 detects the minimum value of the A / D conversion output and detects one horizontal cycle. The detection output SC is supplied to the control circuit 40 for the variable oscillator 34, and is controlled so that the oscillation frequency matches the horizontal period of the input video signal.

There is no particular problem when the horizontal synchronizing signal HD is correctly generated as shown in FIG. 2A. However, when the horizontal synchronizing signal HD cannot be completely extracted as shown in FIG. The position (front edge portion) of the horizontal synchronizing signal HD superimposed on the video signal SV and its cycle are predicted. Therefore, the control unit 38 exerts its power in the reception mode using a weak electric field.

That is, in the case of FIG. 2B, the minimum value Emin obtained first from the A / D conversion output is detected.
This is because the first obtained minimum value is considered to correspond to the leading edge of the horizontal synchronization signal HD. The value at that time is defined as En.

When the sampling pulse is 100 fh, the sampling pulse after one horizontal cycle is after 100 clocks. Therefore, 100 clocks after the sampling pulse SPa when the minimum value Emin is detected should correspond to the beginning of the next horizontal cycle.

Therefore, the level of the A / D conversion output around 100 clocks is determined based on the sampling pulse SPa. The minimum value En + 1 of the A / D conversion output after one horizontal cycle is 1 counting from the sampling pulse SPa.
Although it should be obtained after 00 clocks, if the number of clocks deviates from 100 clocks, the period of the horizontal synchronizing signal of the input video signal HD also deviates, so that it is adjusted to the input environment.

Therefore, the control signal SC from the control unit 38 is supplied to the control circuit 40, and the oscillation frequency of the variable oscillator 34 is controlled so as to match the detection cycle.
For example, when it is determined that the interval at which the minimum value of the A / D conversion output is obtained as a result of the detection by the control unit 38 is, for example, (SPa + 101 clocks) later, it can be determined that the sampling cycle is longer than the reference. In this case, the oscillation frequency is kept low to make the horizontal period extremely short but longer than the reference. As a result, an oscillation frequency suitable for the input video signal is obtained. This oscillation frequency is supplied as a horizontal drive signal in the deflection circuit 22 described above.

Conversely, when the interval at which the minimum value of the A / D conversion output is obtained is, for example, (SPa + 99 clocks) later, by controlling the oscillation frequency to be higher by that amount, the deteriorated video signal is controlled. Can be generated.

FIG. 3 shows a specific example of the variable oscillator 34 and the control circuit 40. In this example, the oscillator 34 is provided with a crystal oscillator 44 in the oscillation amplifying section 42, a capacitor 46 and a variable capacitance element (for example, a varicap) 48
Constitutes the oscillation control unit 50, and the oscillation frequency is determined here. Then, by finely adjusting the value of the variable capacitance element 48, the oscillation frequency fh is varied based on the horizontal frequency (15.734 Hz).

The control circuit 40 has an operational amplifier 42, and its non-inverting terminal (+) is supplied with a power supply voltage + B. The zener diode 54, which is a constant voltage element connected to the connection point q, is for preventing a voltage higher than a certain level from being applied to the operational amplifier 52.

A frequency control voltage corresponding to the detection cycle is supplied to the inverting terminal (-) of the operational amplifier 52. Therefore, the voltage obtained at the connection point q is stepped down by the resistor 58 and then applied to the terminal N of the changeover switch 56. The power supply voltage + B is applied to the terminal L in a state where the voltage is lowered by the resistor 60. And another terminal H is installed.

The changeover switch 56 is controlled by a control signal SC generated by the control section 38 from a terminal 38a. A circuit 62 composed of a constant voltage element and a capacitor connected to the feedback path of the operational amplifier 52 functions as a voltage limiting circuit that limits the upper and lower limits of the oscillation frequency.

Since a horizontal synchronizing signal is usually obtained at a reference horizontal cycle, the control signal S at this time is obtained.
It is assumed that the changeover switch 56 has been switched to the terminal N side by C.

As described above, when it is determined that the sampling period is longer than the reference, the control signal S
The switch C is switched to the terminal L by C. As a result, the voltage applied to the inverting terminal of the operational amplifier 52 becomes higher than the reference voltage, and the output voltage of the operational amplifier 52 eventually decreases. When the output voltage decreases, the capacitance of the variable capacitance element 48 increases, so that the frequency is controlled so that the oscillation frequency fh decreases.

When it is determined that the sampling period is shorter than the reference, the switch 56 is switched to the terminal H by the control signal SC.
As a result, the voltage applied to the inverting terminal of the operational amplifier 52 becomes the ground potential and becomes lower than the reference value, whereby the output voltage of the operational amplifier 52 increases. When the output voltage increases, the capacitance of the variable capacitance element 48 decreases, so that the frequency is controlled so that the oscillation frequency fh increases.
Therefore, since the horizontal drive signal HD that follows the horizontal cycle of the input video signal can be supplied to the deflection circuit 22, a stable image can be displayed on the screen even when a deteriorated video signal is input. Although the cathode ray tube 20 is exemplified as a monitor in the above-described embodiment, the present invention can be applied to other image display means.

[0027]

As described above, according to the present invention, the period of the horizontal synchronization signal is predicted after digitizing the demodulated video signal, and a new horizontal drive signal can be generated from the predicted result. is there.

According to this, even when the input video signal is deteriorated and the horizontal synchronizing signal cannot be separated accurately, the horizontal period of the input video signal can be predicted almost accurately. However, stable images can be projected.

Therefore, the present invention is extremely suitable for application to a television receiver or the like which uses a television signal in a region where the reception electric field intensity is extremely weak.

[Brief description of the drawings]

FIG. 1 is a system diagram of a main part showing an embodiment of a television receiver according to the present invention.

FIG. 2 is an explanatory diagram of an input video signal.

FIG. 3 is a connection diagram showing a specific example of a variable oscillator and its control circuit.

FIG. 4 is an explanatory diagram of a video signal used to explain a conventional operation.

[Explanation of symbols]

 Reference Signs List 10 television receiver 16 demodulation circuit 18 video output circuit 20 CRT 22 deflection circuit 30 horizontal drive signal generation circuit 32 A / D converter 38 control unit 34 variable oscillator 36 sampling pulse generation circuit 40 control circuit

Claims (3)

[Claims] An A / D to which a demodulated video signal is supplied
A converter; a sampling pulse generating means for generating a sampling pulse to be supplied to the A / D converter; a variable oscillator for oscillating a reference signal based on the sampling pulse; A deflection circuit that is supplied as a signal, and a control unit that supplies the A / D conversion output and controls the oscillation frequency of the variable oscillator. A television receiver, wherein the variable oscillator is controlled so as to synchronize. 2. When the horizontal drive signal is fh, n
The television receiver according to claim 1, wherein a sampling pulse based on fh is generated. 3. A minimum value of the A / D conversion output is detected.
The A / D conversion output one horizontal cycle after this detection timing is detected. If the A / D conversion output is not the minimum value, the minimum value is detected from the preceding and following A / D conversion outputs. 2. The television receiver according to claim 1, wherein the oscillation frequency of the variable oscillator is controlled based on a horizontal cycle of the television receiver.