JPS6190586A - Video signal generating circuit - Google Patents

Abstract

PURPOSE:To obtain always without adjustment a pair of compound signals where the size (polarity) only is different with a level of a level indicating signal as a center by using a level indicating signal showing standards of a luminance level of the video signal included in the scrambled compound signal, and controlling to generate automatically a video signal level of the compound signal E of the same polarity and a video signal level of the inverted compound signal D to the same. CONSTITUTION:A differential amplifier 4 is constituted so that an illustration level indicating voltage in correspondence to a level indicating signal extracted out of the scrambled compound signal can be supplied as a reference voltage. Consequently, the video signal level in the compound signal E of the same polarity sent from a terminal E and a terminal D, and the video signal level in the inverted compound signal D are always preserved automatically to the same level. For this reason, when either of them is selectively changed over and the scrambled compound signal is generated, the compound signal having the high quality without a level fluctuation can be obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a video signal generation circuit, particularly for descrambling a scrambled composite video signal (hereinafter referred to as composite signal) for viewing, for example, a CATV pay TV channel. At the same time, the level indication signal present in the scrambled composite signal is used to generate a composite signal in which the scrambled composite signal is inverted with respect to the level of the level indication signal, and a composite signal in a non-inverted form. The present invention relates to a video signal generation circuit configured to automatically generate the same levels.

[Prior art and problems to be solved by the invention] - Conventionally, in order to prevent CATV pay channels from being wiretapped, video signals in a composite signal to be transmitted are transmitted every horizontal scanning line or at a predetermined horizontal scanning line. A so-called scrambled composite signal, in which white and black are inverted, is transmitted at regular intervals.

As a method of descrambling (restoring) the scrambled composite signal to the original viewable composite signal, for example, a composite signal of the same polarity (hereinafter referred to as composite signal E) and an inverted form of the scrambled composite signal may be used. There is a method in which a composite signal (hereinafter referred to as composite signal) is prepared, and one of the two composite signals is sequentially selected using an electronic switch and descrambled. At this time, it is necessary that the video signal level of the composite signal E of the same polarity and the video signal level of the inverted composite signal are always constant. If the video signal levels of the two do not match, the image quality will deteriorate. Particularly in the case of color images, due to their nature, the DC component of the video signal is also necessary to reproduce the image, so not only does the image quality deteriorate in the form of brightness differences, but the color tone also deteriorates. Even as a difference, the image quality deteriorates.

In order to prevent the image quality from deteriorating, conventionally, as shown in FIG. was supplied to the other input terminal of the differential amplifier 5. and,
A composite signal E and an inverted composite signal having the same video signal level are obtained from the illustrated terminal and terminal E, which are the respective output terminals of the differential amplifier 5. In this way, conventionally, in order to match the video signal level of the same-extreme composite signal E with the video signal level of the inverted composite signal for the scrambled composite signal, a semi-fixed resistor or the like is used. They were individually adjusted at the time of shipment from the factory. Therefore, when the user uses the device, it may be affected by fluctuations in the DC level of the received input composite signal, fluctuations in the amplitude of the input composite signal, or fluctuations in the bias voltage of the circuit that generates the inverted composite signal. □As a result, the video signal level of the composite signal E with the same polarity and the video signal level of the inverted composite signal with respect to the scrambled composite signal will deviate, making it impossible to obtain a high-quality image. There was a problem.

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention provides, for example, CAT
When descrambling a scrambled composite signal for viewing a paid TV channel etc. of V, the level instruction signal included in the scrambled composite signal By adopting a configuration in which the video signal level of the polar composite signal E and the video signal level of the inverted composite signal are automatically set, composite signals of different polarities having the same video signal level can be combined. , E are obtained without adjustment.

Therefore, the video signal generation circuit of the present invention inverts a composite video signal transmitted including a level instruction signal indicating the signal level of the video signal with respect to the level of the level instruction signal. In a video signal generation circuit that generates a composite video signal of the same type and a non-inverted composite video signal, a level detection circuit detects the signal level of the level instruction signal included in the composite video signal; The level indicated by the input signal is given as the input level of one of the transistors constituting a differential amplifier, and the composite video signal is output from the output of the differential amplifier into a composite video signal that is inverted with respect to the level of the level indication signal and a composite video signal that is not inverted. and a video signal generation circuit that generates a composite video signal.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a configuration diagram of one embodiment of the present invention, and FIG. 2 is a waveform diagram illustrating the operation of the configuration of one embodiment of the present invention shown in FIG.

In the figure, l represents an electronic switch, 2 represents an integrating circuit, 3 represents an impedance conversion circuit, and 4 represents a differential amplifier.

In FIG. 1, a differential amplifier 4 uses a scrambled composite signal inputted from a terminal B shown in the diagram to generate a composite signal E of the same polarity having the same level and a composite signal E of the inverted form from a terminal E and a terminal 1, respectively. It is used to send out signals. At this time, since the differential amplifier 4 is configured to be supplied with the indicated level indication voltage corresponding to the level indication signal extracted from the scrambled composite signal as a reference voltage, The video signal level in the composite signal E of the same polarity and the video signal level in the inverted composite signal are always automatically maintained at the same level.

Therefore, when a descrambled composite signal is generated by selectively switching either the video signal in the composite signal of the same polarity or the video signal in the inverted composite signal, the level A composite signal with a good quality image without fluctuations can be obtained. A detailed explanation will be given below using FIGS. 1 and 2.

The electronic switch 1 in FIG. 1 uses the level indicating voltage/sampling signal supplied from the illustrated terminal C to extract the indicated level indicating signal from the scrambled composite signal supplied from the illustrated terminal B described above. It is for. The extracted level instruction signal is transmitted from the broadcasting station so as to always maintain an amplitude corresponding to, for example, the APL50% level of the video signal, that is, the intermediate (50%) level between the white level and black level of the video signal. It is of a nature that is Therefore, if the polarity of the scrambled composite signal is inverted around the level instruction voltage corresponding to the level of the extracted level instruction signal, as will be described later with reference to FIG. It is possible to obtain a composite signal in the form of

The intermediate integration circuit 2 is for extracting (sampling) the level of the level instruction signal extracted by the electronic switch 1, and is for performing so-called sample and hold. The integrating circuit 2 having the illustrated configuration detects the level by charging a capacitor with a voltage corresponding to the so-called peak voltage value of the level instruction signal through a resistor.

The impedance conversion circuit 3 in the figure is for converting the impedance of the level indication signal sampled and held by the integration circuit 2 from a high value to a low value. For the input section of the impedance conversion circuit 3, a so-called high input impedance operational amplifier or the like is used, which has a high input impedance and a low output impedance. Due to the impedance conversion, the detected level indicating voltage has a sufficiently low impedance to be supplied to the differential amplifier 4.

The differential amplifier 4 in the figure is for differentially amplifying the scrambled composite signal supplied from the terminal B described above, using the level indication voltage whose impedance has been converted by the impedance conversion circuit 3 as a reference point. be. That is, a so-called inverted composite signal and a composite signal E of the same polarity are sent out from the terminals 1 and 2, respectively, with the level indicating voltage in the scrambled composite signal as the center. As a result, the video signal level in the composite signal E of the same polarity as the video signal level in the inverted composite signal sent from the terminal E and the terminal E is included in the scrambled composite signal. The level always automatically matches the level of the level instruction signal.

Figure 2 (A) shows the waveform of the composite signal before being scrambled, Figure 2 (B) shows the waveform of the scrambled composite signal, and Figure 2 (C) shows the waveform of the level indication voltage/sampling signal. Figure 2 (d) shows the waveform of the composite signal E of the same polarity sent from the terminal E in Figure 1;
FIG. 2(E) shows the waveform of the inverted composite signal sent from the terminal in FIG. 1. In the figure, the vertical axis shows voltage and the horizontal axis shows time.

Figure 2 (a) ■ indicates a horizontal synchronization signal, ■ in the figure indicates a color burst signal, ■ in the figure indicates a video signal,
Each of these signals has a waveform that conforms to, for example, the NTSC system, the PAL system, etc., and only an outline is shown in the figure for convenience of explanation.

2 (b) is a level indication signal included in the scrambled composite signal, and the AP of the video signal is
A signal transmitted from a broadcasting station that always indicates the amplitude corresponding to the level of L50%, and a second
Figure (B) ■ and ■ in the figure indicate a non-inverted video signal and an inverted video signal, respectively. The inverted video signal (2) is transmitted from the broadcasting station in a form in which the magnitude is inverted with respect to the level specified by the level instruction signal (2). Therefore, by detecting the level of the cough level indication signal ■ and inverting the magnitude of the video signal in the scrambled composite signal around the detected level, a descrambled composite signal in a viewable format is generated. Obtainable.

In FIG. 2(c), symbol (2) is a level indicating voltage/sampling signal, which is used to extract the level indicating signal (2). The level indication voltage/sampling signal is
For example, it is extracted from an FM-modulated audio signal used in the NTSC system, and is used to extract the level instruction signal (2) from the horizontal synchronization signal (2).

The composite signal shown in FIG. 2(d) is a composite signal E having the same polarity as the scrambled composite signal and is sent from the terminal E of the differential amplifier 4 in FIG.

The illustrated inverted composite signal in FIG. The video signal level of the inverted composite signal shown in FIG. 2 (D) and the video signal level of the composite signal E shown in FIG. Since the input level is applied to one of the transistors, the magnitude is inverted and automatically controlled so as to always maintain the same level. Therefore, even if the DC level of the scrambled composite signal fluctuates, the power supply voltage fluctuates, or the video signal level changes significantly, the reference level indication signal sent from the broadcasting station will always remain the same. Level (m, tha A P L 50
% level), it is possible to obtain a composite signal with an extremely stable and high quality image, and there is no need to adjust the level, achieving so-called 1-free adjustment. becomes possible.

〔Effect of the invention〕

As explained above, according to the present invention, when descrambling a scrambled composite signal for viewing, for example, a CATV pay TV channel, the luminance level of a video signal included in the scrambled composite signal automatically generate the same video signal level of the composite signal E of the same polarity and the video signal level of the inverted composite signal with respect to the scrambled composite signal using a level instruction signal indicating the standard of the scrambled composite signal. Because of this control, it is possible to always obtain a set of composite signals that differ only in magnitude (polarity) around the level of the level instruction signal without any adjustment. Moreover, there is no difference in level between sets of composite signals of different magnitudes (polarity) due to fluctuations in the DC component of the video signal.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of one embodiment of the present invention, FIG. 2 is a waveform diagram illustrating the operation of the configuration of one embodiment of the present invention shown in FIG. 1, and FIG. 3 shows a conventional video signal generation circuit. In the figure, l represents an electronic switch, 2 represents an integrating circuit, 3 represents an impedance conversion circuit, and 4 represents a differential amplifier.

Claims (1)

[Claims] A composite video signal obtained by inverting the composite video signal with respect to the level of the level designation signal from a composite video signal transmitted including a level instruction signal that indicates the signal level of the video signal, and a composite video that is not inverted. a level detection circuit that detects the signal level of the level instruction signal included in the composite video signal, and a transistor forming a differential amplifier that detects the level detected by the level detection circuit; video signal generation for generating a composite video signal in a form inverted from the level of the level instruction signal and a composite video signal in a non-inverted form from the output of the differential amplifier. A video signal generation circuit comprising a circuit.