JPS58201468A - Synchronizing signal detector - Google Patents

Abstract

PURPOSE:To absorb the frequency drift of a tuner, by supplying a video carrier extracted from a tuner output to an automatic frequency controlling and detecting circuit, and controlling a local oscillating frequency of the tuner with this detected output. CONSTITUTION:The tuner output is divided into two; one is given to a descrambling modulator 13 and the other is divided further into two at a two-distributor 15. One output of the two-distributor 15 is given to a BPF10, where a sound carrier is extracted, and a descrambling control signal is formed at a decoder 12 to control a descrambling modulator 13. The other output of the two-discributor 15 is extracted for a video carrier at a BPF17, detected at an AFC detecting circuit 19 and its detected output controls the 2nd local oscillating circuit of the tuner. Thus, the frequency drift of the tuner is absorbed completely.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a synchronization signal detection device in a pay TV (hereinafter referred to as pay TV) decoder of a 3ATV converter.

In recent years, with the development of ATV in the United States, pay television has rapidly developed. 0As the number of ATV channels increases, the number of pay TV channels also tends to increase. Pay Channel performs signal processing (this is called scrambling, hereinafter referred to as scrambling) so that it can be viewed only by specific subscribers. among them,
Synchronization suppression scrambling, which suppresses the synchronization signal of a video signal to make the synchronization signal smaller than the video signal, is often used. There are two methods for this; one is a gate synchronization suppression method that attenuates only the synchronization signal period by 6 (iB), and the other is a sine wave 16.76
This is a sine wave synchronization suppression method that performs amplitude modulation at kHz. Both of these decodings (called descrambling) perform the opposite of signal processing. In the gate synchronization suppression method, only the video signal period excluding the synchronization signal is attenuated by 6 (IB), and in the sine wave synchronization suppression method, amplitude modulation is performed using a sine wave of 15.76 kJh with an opposite phase to that of the scrambling. back to the TV RF signal.

In order to perform this descrambling, it is necessary to accurately detect the timing of scrambling and perform descrambling based on it. Therefore, the CATV center sends information to ensure accurate timing. When there were few pay channels, they had their own carrier waves and tried to detect them.
With the increase in pay channels, in-band transmission began. In many cases, the method is to amplitude-modulate timing information on an audio carrier wave and send it. Accurately detecting that timing information is one of the important tasks of descrambling.

Before explaining the present invention, the tuner section of the 0ATV converter will first be explained with reference to FIG. The signal from the 0ATV enters the input terminal 1, controls the first local oscillation circuit 2 according to the signal to be received, and is converted into the same intermediate frequency signal (UHF band in most cases) by the input filter 3 and first mixer 4. Convert once,
After being amplified by the intermediate frequency amplification circuit 6, the second local oscillation circuit 6 and the second mixer 7 convert it into a specific VHF low band (CH3° in most cases) signal, and output it through the output filter 8. When there is no descrambler, this output is input to the television receiver, the television receiver is tuned to the output channel of this tuner, and the output is read. Therefore, the -C1ATV signal is selected by controlling the first local oscillation circuit 2 of the tuner shown in FIG.

On the other hand, when there is a descrambler, the output of the tuner having the configuration shown in FIG. 1 is input to the pay TV decoder shown in FIG. Only the audio carrier wave is extracted, and the next block 11 amplifies it and performs amplitude detection to detect scramble timing information.Based on this, a descrambling control signal is generated by a decoder 12, and its output is sent to a descrambling modulator. 13 to descramble. When it is not scrambled, there is no timing information, so
Descrambling modulator 13 does not operate.

What is important here is the characteristic of the BPF 10 for extracting the audio carrier wave. The scrambling timing information is amplitude modulated onto the audio carrier. On the other hand, adjacent channel transmission is common in CATV signals.

Therefore, as shown by the spectrum in FIG. 3, the interfering signals include the video carrier (fv) of its own channel, the color subcarrier (fc), and the upper adjacent video carrier (fv++). The color subcarrier fc times signal is more than 16 dB smaller than the video carrier fv, and the audio carrier signal is 13 to 20 dB smaller than the video carrier fv.
i B, smaller than the video carrier fv. Also, the video carrier wave f
v and the upper adjacent video carrier fv+ are considered to be at the same level. To remove amplitude modulated signals from interference, it is necessary to reduce the interference signal by 20 dB or more at the detection level. Therefore, as BPFlo, fv and fV+
It is necessary to use an audio carrier extraction BPF that secures an attenuation of 40 dB or more at 1 and 24 dB or more at fc.

Since this processing is performed in the VHF low band (CH3° of 60 to 6611 in most cases), which is the output of the tuner, it is inevitably a narrow band BPF, which has the characteristics shown by a in FIG. 3.

However, when the scramble timing information is detected as described above, if the output of the tuner fluctuates due to temperature and aging, the frequency shifts, making it impossible to accurately detect the timing information. Recently, due to advances in tuning methods, the first local oscillation circuit of the tuner has become a PLL synthesizer system, which has become more stable, but the second local oscillation circuit is still self-oscillating, which poses a problem.

The present invention has been devised to stably detect timing information even if there is drift in the second local oscillation circuit, etc. An embodiment of the present invention will be described below with reference to the block diagram of FIG. 4 and the characteristic diagram of FIG. 6.

The output of the tuner shown in FIG. 1, that is, the input of the descrambler, is divided into two parts, one of which is input to a descramble modulator 13 as in the conventional art, where the scrambled signal is descrambled and output. On the other hand, the other input of the descrambler is further divided into two parts by a two-way divider 16, and one of them is sent to B as before.
In addition to PFlo, only the audio carrier wave is extracted and amplified by the MEC amplifier circuit 16 in the first stage, and the amplitude detection circuit 11
Detects the timing information after detection, and based on it, generates a descramble control signal in the kitecoder 12, and uses this descramble control signal to generate the descramble modulator 13.
control. Everything up to this point is the same as before. This audio extraction BPFlo has the characteristics shown in FIG. 5a, and is the same as FIG. 3a.

Then, the other output of the 2-way divider 15 is applied to the BPF 17 having the characteristics shown in b in FIG. The AFC detection circuit 19 having S-curve characteristics detects the signal, and its output controls the second local oscillation circuit 6 of the tuner to stabilize the frequency of the input signal of the descrambler. This makes it possible to completely absorb the frequency drift of the tuner and to accurately detect timing information. AFC control range is ±1~
It becomes possible to calculate two times, and there is no practical problem.

It is desirable that the characteristics of the BPF 17 for extracting the video carrier wave be narrow in order to eliminate distortions such as interference with adjacent channels and cross-modulation, but if the band is narrowed too much, the pull-in range of the FO will be narrowed, so it cannot be narrowed too much. As mentioned above,
For C, a method of multiplying the MFC (H) using the audio carrier without adding the BPF 17°M GO amplifier circuit 18 is also considered, but the width of the MFC must be at least t I M, and the BpFIQ for extracting the audio carrier is Since the band is narrow and the adjacent upper video carrier wave fv++ is thicker than the audio carrier wave to which the mu FC is applied, the adjacent upper video carrier wave fv++
This is a problem because it takes 5 FC to operate properly and may not operate properly. In this respect, there is no problem in this example, which uses the video carrier wave fv of its own channel and adopts a method of extraction using a wideband BPF.

As described above, according to the present invention, the output of the tuner is divided into two, one output signal is input to the video carrier extraction filter, the output is input to the automatic frequency control detection circuit, and the detected output is used to localize the tuner. By controlling the oscillation frequency, the frequency drift of the tuner can be completely absorbed, making it possible to accurately detect timing information.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the tuner of the OA T V = FIG. 5 is a block diagram of a synchronization signal detection device in FIG. 5, which is a characteristic diagram of an audio carrier extraction BPF and a video carrier extraction BPF. 10...Audio carrier wave extraction filter, 11...
... Amplitude detection circuit, 12 ... Tecoder, 13
... Descramble modulator, 16... 2-way divider, 17... Video carrier wave extraction filter, 19...
Indo/Mu FO detection circuit. Name of agent: Patent attorney Toshio Koo (1st person)
Figure 3 4 6 7 Shio 1111 Figure 2/3 1 1 1 /ρ ///2 Figure 4 3 Figure 5 jA-t jy kJ4 fnt 3IfI
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Claims (1)

[Claims] A tuner that converts the frequency of a television signal that is transmitted with synchronization information of a synchronization suppression method superimposed on the audio carrier wave of its own channel by amplitude modulation, and a two-way divider that divides the output signal of this tuner into two; a first filter for extracting the audio carrier wave from one output of the two-way divider; a means for amplitude-detecting the audio carrier wave from the first filter to detect synchronization information; and an output of the other side of the two-way divider. a second filter that extracts a video carrier wave from the second filter; and an automatic frequency control detection circuit that inputs the video carrier wave from the second filter, and automatically adjusts the local oscillation frequency of the tuner using the detection output signal of this detection circuit. Synchronous signal detection device to control.