KR960009150B1 - Tv signal converting apparatus - Google Patents

Abstract

None.

Description

TV signal converter

1 is a principle explanatory diagram of a television signal conversion device according to the present invention;

2 is an overall configuration diagram of a CATV system under the premise of the present invention;

3 is a circuit diagram for explaining an embodiment of the present invention;

4 is a circuit diagram of a conventional television signal converter;

5 is a frequency array diagram of a two-carrier voice multiplexing scheme,

6 is an enlarged detail view of a voice carrier frequency.

* Explanation of symbols for main parts of the drawings

1: demodulator (demodulation means) 2: separate adjustment part (separation adjustment means)

3: adding unit (adding means) 4: AM modulating unit (modulating means)

11: converter 12: descrambler

13: Split Out (SPL OUT) terminal 14: Tap-off

15: BPF 21 ₁ , 21 ₂ : resistance

22 ₁ , 22 ₂ , 27 ₁ , 27 ₂ : Buffer amplifier 23 ₁ , 23 ₂ , 26 ₁ , 26 ₂ : Filter

25 ₁ , 25 ₂ : limiter 28 ₁ , 28 ₂ : variable resistor

[Industrial use]

The present invention relates to an improvement of a television signal converting apparatus suitable for a CATV terminal apparatus installed on a receiving side of a community antenna television or common antenna television (CATV) system, in particular, for two-carrier voice multicasting or stereo broadcasting reception. will be.

[Prior art]

4 shows a schematic circuit configuration of a television signal conversion device used in a conventional CATV terminal device. As the two-carrier method, the Korean method and the West German method are known, and as an example, frequency arrays of voice multiplex (or stereo) broadcasts according to the Korean method are shown in FIGS.

As shown in this FIG. 5 and FIG. 6, multiplex broadcasts of two-carrier method (or a stereo broadcast), in addition to conventional audio carrier (first audio carrier) signal F _A1, the first sound carrier signal F _A1 In this system, an additional voice carrier (second voice carrier) signal F _A2 is added and transmitted at a higher frequency.

In this case, the first sound carrier signal F _A1, the main audio (stereo broadcasts in the L + R signal), a second audio carrier signal F _A2, the sub-audio (in the LR stereo broadcast signals) are assigned, respectively. First voice carrier signal Is 4.5MHz, the second voice carrier signal F _A2 is 4.7252MHz and is FM-modulated by each voice signal.

The levels of the first audio carrier signal F _A1 and the second audio carrier signal F _A2 are specified to be -13 dB and -20 dB, respectively, compared to the level of the video carrier.

In FIG. 4, in the conventional television signal conversion apparatus, a multi-channel television signal from a broadcasting center (not shown) is input to the converter 11 through a common transmission cable and the converter 11 is input to the television signal. The TV signal of the desired channel is tuned and frequency-converted to output an intermediate frequency signal IF.

The intermediate scan signals IF, the baseband video signal V by the AM modulated video intermediate frequency signal IF _V respective image intermediate frequency (45.75MHz) to the first audio signal A ₁ and the second audio signal by the A _second IF signal _V FM modulated first and second intermediate frequency signals IF _A1 and IF _A2 with frequencies lower than 4.5 MHz and 4.7242 MHz are included.

The intermediate frequency signal IF is input to the descrambler 12 to be descrambled and input to the demodulator 1. In the demodulator 1, the main function thereof has recently been one-chip IC. This IC is widely used for video detection and audio detection in TVs, and has integrated functions such as intermediate frequency amplification, video detection, AGC, AFT, and voice detection, which are necessary for them.

In the demodulator 1, the baseband video signal V and the first audio signal A ₁ are demodulated and output. However, since the demodulation IC targets the one-carrier type audio such as the NTSC system, the original signal cannot be obtained directly with respect to the second audio signal A ₂ . A middle frequency signal (including F _A1 and F _A2 ) obtained from a split out terminal 13 installed in the apparatus, and the band having the band of the second voice carrier F _A2 The second audio carrier F _A2 is extracted through a pass filter (BPF) 15 and provided for addition to the video signal V described later.

The first audio signal A ₁ is FM modulated by a FM modulator 40 to a carrier having a local oscillation frequency fa ₁ (eg 4.5 MHz) and then added to the video signal V by an adder 33.

Furthermore, the second voice carrier signal F _A2 is added to the adder 34 to the added video signal V and output to the AM modulator 41.

The AM modulator 41 AM-modulates a carrier of the local oscillation frequency Fo by the added video signal V, and outputs it to the receiver TV (not shown) from the output terminal 4 _OUT .

[Problems that the invention tries to solve]

The conventional television signal converter is configured as described above. After the main voice (L + R signal) A ₁ modulates the first voice carrier fa ₁ to become the first voice carrier signal F _A1 , the adder 33 Is added to the video signal V, sub-negative (LR signal) A ₂ uses the first second voice carrier signal F _A2 which has already been FM-modulated, and directly by the adder 34 without FM modulation. Since it is added to the signal V, the delay time is different between the first and second voice signals due to the FM modulation operation and the presence or absence of filtering. Therefore, the separation cannot be performed in the case of stereo broadcasting. Have

As described above, although the first voice carrier signal has a video signal-to-audio signal power ratio of -13 dB, the second voice carrier signal has a video signal-to-audio signal power ratio of -20 dB. In the configuration, it is difficult to maintain or adjust this level difference.

Accordingly, there is a problem that performance such as separation such as stereo broadcasting is degraded due to the level difference of the power ratio.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to propose a television signal converting apparatus capable of accurately performing separation such as stereo broadcasting and voice multiple broadcasting.

[Means for solving the problem]

1 shows a principle explanatory diagram of the present invention.

In the figure, the television signal conversion apparatus according to the present invention is a television signal conversion apparatus for receiving a television signal including a video signal, a first audio carrier signal and a second audio carrier signal on one channel, wherein the television signal And demodulating means for generating a baseband video signal and outputting the first and second voice carrier signals, and separating the output first and second voice carrier signals. Separation adjusting means for adjusting and outputting at least one level, adding means for adding the separated and adjusted first and second audio carrier signals to the detected video signal of the baseband, and the first and second means. And a modulating means for modulating and outputting a carrier having a frequency corresponding to a predetermined channel by the video signal to which each of the two voice carrier signals is added.

[Action]

In the present invention, the first and second voice carrier signals which are FM-modulated and the video signal demodulated in the base band are output from the demodulation means, and the first and second voice carrier signals are separated by means of separate adjustment means. And the first and second audio carrier signals after the adjustment are added to the baseband video signal by means of an adding means so as to modulate and output them to the modulation means. The delay error and power ratio error between the second voice carrier signals can be eliminated, and the separation of the stereo broadcast can be made completely.

In addition, since the first voice carrier signal is output without being demodulated from the demodulator, it is not necessary to perform FM modulation again as in the prior art, and a local oscillator for FM modulation is unnecessary, and thus modulation characteristics due to the adjustment or drift There is no deterioration of accuracy.

EXAMPLE

Next, a preferred embodiment of the present invention will be described with reference to the drawings.

(i) Overview of CATV System

First, an overview of the CATV system to which the television converting apparatus of the present invention is applied will be briefly described to help understanding of the present invention.

2 shows a general configuration of a CAVT system. The broadcast center 300 receives and relays a commercial broadcast program by the BS antenna 301, the BS converter 302, or the TV antenna 303, or by the TV camera 304 or the VTR 305. The self-produced broadcast program is distributed to each demand through a transmission cable 306.

In general, the distribution service is carried out in a contract with each demand and is in euros.

At each demand price, the TV signal of the CATV to be transmitted is received by the CATV terminal apparatus 100 _{1 to} 100 _n , and the TV signal 200 _{1 is} descrambled after the television signal subjected to the scramble processing for preventing the city. To 200 _n .

The present invention relates to an improvement of the television signal conversion apparatus 100 _{1 to} 100 _n used in the CATV terminal apparatus 100 _{1 to} 100 _n and the like.

(ii) CATV terminal equipment

3 shows an embodiment of a television signal converter according to the present invention.

In Fig. 3, TV input of multiple channels (for example, 50 to 500 MHz as a range) from the broadcasting center 300 (refer to Fig. 2) is input to the input terminal 11 _in . do. The converter 11 selects one desired channel from among the input television signals, frequency-converts the television signal of the selected channel, and outputs an intermediate frequency signal IF. The intermediate frequency signal IF is given to the descrambler 12.

The descrambler 12 extracts the scrambled data superimposed as the in-band data in IF _A1 , for example, the voice carrier signal in the intermediate frequency signal FI by AM detection, and the intermediate frequency signal IF _V scrambled by the extracted scrambled data. Descramble. The descrambled intermediate frequency signal IF is input to the demodulator 1.

The demodulator 1 synchronously detects the input intermediate frequency signal IF _V , outputs the baseband video signal V to the adder 3, and simultaneously intercepts the first and second voice carrier signals IF _A1 and IF _A2 . The carrier is detected and the first and second voice carrier signals F _A1 and F _A2 are mixed and output from the split out terminal 13 to the separation adjusting unit 2.

Further, the outputting of the video intermediate frequency signal IF _V as the video signal V of the base band is to cause a muting process (not shown) to prevent a disturbance of the screen occurring at the time of channel switching or the like.

The separation adjusting unit 2 separates the input first and second voice carrier signals F _A1 and F _A2 and adjusts the power levels of the separated first and second voice carrier signals F _A1 and F _A2 .

That is, the input voice carrier signal is adjusted to a predetermined power level by the resistors 21 ₁ and 21 ₂ of the separation adjusting unit 2, and after the power level is amplified by the buffer amplifiers 22 ₁ and 22 ₂ , the filter 23 ₁ and 23 ₂ are used to separate the first and second voice carrier signals F _A1 and F _A2 .

Each of the separated first and second voice carrier signals F _A1 and F _A2 is constantly adjusted in amplitude by the limiters 25 ₁ and 25 ₂ , and the filter 26 ₁ and 26 ₂ is again used for signal selection. The high frequency is removed by doing.

Each of the first and second voice carrier signals F _A1 and F _A2 output from the filters 26 ₁ and 26 ₂ is output by lowering the output impedance to the buffer amplifiers 27 ₁ and 27 ₂ , and the variable resistor 28 is further reduced. ₁ , 28 ₂ ) to adjust the voltage level and output to the adder 3 at the rear stage, respectively.

The adder 3 adds the separately adjusted first and second voice carrier signals F _A1 and F _A2 to the adder 31 and simultaneously adds the first and second voice carrier signals F _A1 and F to each other. _A2 is added to the baseband video signal V by the adder 32.

In order to FM modulate the _first voice A ₁ input as in the prior art from the first and second voice carrier signals F _A1 and F _A2 as added and modulated as described above, This is because there is no need to install an oscillator, and the deterioration of modulation characteristics due to the adjustment and drift of the oscillator is eliminated.

The video signal V added to this adder 3 is output to the AM modulator 4 at a later stage.

The AM modulator 4 localizes a carrier frequency corresponding to an empty channel, for example, a second channel, of a television receiver (corresponding to 200 _{1 to} 200 _{n shown} in FIG. 2 and not shown in FIG. 3). The oscillation frequency Fo is amplitude modulated and is output as a high frequency signal from the output terminal 4 _OUT to the television receiver.

Further, in the above embodiment, the modulation method of the audio and video signals is made into the FM method and the AM method, respectively, but other methods may be applied.

The television signal converting apparatus according to the present invention has a function of converting and outputting various apparatuses other than the CATV terminal apparatus shown in the above embodiments, for example, a received television signal or a reproduced television signal into a television signal suitable for a predetermined channel. It can also be used for a VTR etc.

[Effects of the Invention]

As described above, in the present invention, the first and second voice carrier signals and baseband video signals which are FM-modulated by the demodulation means are output, and the first and second voice carrier signals are separated and adjusted. And the first and second audio carrier signals after the adjustment are added to the video signal by means of an adder to modulate and output the modulated means. Second, the delay error and power ratio error between the respective voice carrier signals are eliminated, and the separation of the stereo broadcast can be completely taken.

In addition, since the first voice carrier signal output without being demodulated from the demodulator is used as it is, there is no need to perform FM modulation again as in the prior art, and since a local oscillator is unnecessary for FM modulation, modulation due to the adjustment or drift It has an effect which can prevent deterioration of characteristics or ignition degree.

Claims (1)

A television signal converting apparatus for receiving a television signal including a video signal, a first audio carrier signal and a second audio carrier signal for stereo broadcasting in one channel, and converting the television signal into a television signal of a predetermined channel, A demodulation means for detecting the television signal to generate a baseband video signal and outputting the first and second audio carrier signals, and separating the output first and second audio carrier signals. And at least one level adjusting means for adjusting and outputting at least one level, adding means for adding the separated and adjusted first and second voice carrier signals to the detected baseband video signal, and the first means. And modulating a carrier having a frequency corresponding to the predetermined channel by the video signal to which the respective second voice carrier signals are added. And a modulating means.