JPS60239188A - Television signal demodulator - Google Patents

Abstract

PURPOSE:To use a television receiver, a tuner circuit in a television tuner and a VIF amplifier for CATV reception in common by providing a changeover switch switching long/short two time constants to an AGC circuit provided to a video signal amplifier system and selecting the time constant to the long time constant position at the reception of a television signal applied with scramble or at the connection of an adaptor for descrambling. CONSTITUTION:While the 1st AGC circuit 6 has a comparatively short time constant such as several ms so attain excellent AGC operation at the reception of a general television broadcast, the 2nd AGC circuit 12 has a comparatively long time constant such as several hundreds ms so that the video signal portion is not affected by a rapid AGC at the reception of a television signal subject to scramble. Further, a changeover control circuit 13 detects the reception of the television signal subjected to scramble or the connection of a CATV adaptor 10 to select either the 1st AGC circuit or the 2nd time constant circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention provides a television signal demodulator suitable for receiving scrambled television signals such as television signals in CAT■ pay television services, for example. Regarding.

[Background Art and Problems Therewith] When receiving CATV broadcasting using a general television receiver, a CATV adapter with a built-in descrambler is required. This CATV adapter has a configuration as shown, for example, in FIG. 104. A part of the output signal from this descrambler 104 is sent to the AGC circuit 10.
5 to the AGC terminal of the VIP amplifier 103, and is again subjected to RF signal modulation by the modulator 106 and sent to the output terminal 107 of the CA'rV adapter 100. The output signal from the output terminal 107 is supplied to, for example, a VHF signal input terminal 112 of a general color television receiver via a changeover switch 110. The changeover switch 110 is used to select the RF multiplied signal from the antenna input terminal 111 for receiving normal television broadcasting, and the above CA'T.
This is used to switch the output signal from the V adapter 100.

Here, the descrambler 104 is for restoring a scrambled television signal to the original standard television signal for so-called paid television (pay TV) services.
When the DC level of the synchronization signal portion of the signal supplied to 04 changes randomly due to the above scrambling,
If the gain of the VIP amplifier 103 is rapidly controlled by AGC, it will have a negative effect on the video part of the television signal, so the time constant of the AG'C circuit 105 is partially controlled by the AGC circuit for the VIP amplifier of the television receiver. The time constant is set longer than the time constant.

By the way, such a C'A TV adapter 100
, the cheese circuit 102 and the vIF amplifier 1
03, and the RF signal is converted again in the modulator 106, which not only complicates the structure and makes it expensive, but also has the disadvantage that the signal deteriorates due to extra signal processing. .

Therefore, it has been considered to share the cheese circuit and VIP amplifier in a television receiver or television cheese device when receiving general television broadcasts and when receiving CATV broadcasts. In this case, it is sufficient to provide only the descrambler part as a CATV adapter, which extracts the output signal from the VIP amplifier in the television receiver, descrambles it, and then returns it to the television receiver again. Supply to the next stage circuit.

I can normally receive television signals with Tochi and Star Rumple applied.

However, as mentioned above, when receiving CATV, the VI
It is necessary to set the time constant of the AGC circuit long to control the gain of the P amplifier, but when receiving general television broadcasting, the electric field changes relatively rapidly due to external interference, etc. Therefore, it is desirable to set the time constant of the AGC circuit short.

[Purpose of the invention]

In view of the above points, the present invention provides CA for tuner circuits and VIF amplifiers in television receivers and television tuner devices.
It can also be used for TV reception, and it not only makes it possible to receive CATV broadcasts by simply adding an inexpensive CATV adapter consisting only of a descrambler part, but also enables the above-mentioned VI.
To provide a television signal demodulator capable of receiving both general television broadcasting and CATV broadcasting in the best condition by automatically switching the time constant of an AGC circuit for a P amplifier.

[Summary of the invention]

That is, the feature of the television signal demodulator of the present invention is that the AGC circuit provided in the video signal amplification system is provided with a changeover switch for switching between long and short time constants, and the output from the AGC circuit is connected to the video intermediate. Frequency amplifier AGC
The descrambler is supplied to a terminal, and includes control means for switching the changeover switch to the long time constant side when receiving a scrambled television signal or when connecting a descrambling adapter. Therefore, the above-mentioned video signal amplification system can also be used for CA'l'V broadcast reception, and there is no need to provide an amplification circuit such as a video intermediate frequency amplifier on the CATv adapter side, which simplifies the configuration of the CATV adapter. , the user can always receive some television broadcasts and CATV broadcasts in the best condition without having to be conscious of switching the descrambler. .

〔Example〕

Preferred embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a partial circuit of a television receiver or television tuner device as a television signal demodulator according to an embodiment of the present invention, and a CATV adapter 10.
1 is provided.

In FIG. 1, a general television broadcast signal and a CATV broadcast signal are supplied to an RF signal input terminal 1 of a television receiver or a television tuner device. The signal from this input terminal 1 is passed through a tuner circuit 2 to a video intermediate frequency amplification circuit (VI
P amplifier) 3. The output signal from the VIP amplifier 3 is sent to the video detection circuit 4 and subjected to video detection.
After amplification and trapping of the 4.5 MHz audio carrier wave component, etc., the signal is sent to one selected terminal a of the changeover switch 5. The output signal from the common terminal of the changeover switch 5 is sent to a luminance/chroma signal processing circuit (Y/C processing circuit) or the like.

Further, the output signal from the video detection circuit 4 is transmitted to the first AGC
The signal is sent to one selected terminal a of the selector switch 7 via the circuit 6. Furthermore, the output signal from the video detection circuit 4 is sent to the descrambler 11 of the CATV adapter 10, and the output signal descrambled by the descrambler 11 is sent to the other selected terminal of the changeover switch 5 and the second selected terminal. The signals are sent to the AGC circuit 12, respectively. Second
The output signal from the AGC circuit 12 is sent to the other selected terminal of the changeover switch 7, and the output from the common terminal of the changeover switch 7 is sent to the A()C terminal of the vIF amplifier 3. There is.

Here, the first AGC circuit 6 is operated for several ms so that good AGC operation can be performed when receiving general television broadcasting.
The second AGC circuit 12 has a relatively short time constant of several hundred seconds, while the second AGC circuit 12 has a relatively short time constant of several hundred It has a relatively long time constant of about ms.

Then, the switching control circuit 13ζ detects that a scrambled television signal is received or that the CATV adapter 10 is connected, and the switching control circuit 13 controls the switching switch 7. , either the first AGC circuit 6 or the second time constant circuit 12 is selected.

By the way, various configurations are possible for the switching control circuit 13, but for example, in order to detect reception of a scrambled television signal, the output signal from the video detection circuit 4 is taken out and the synchronization signal is , the DC potential, or the presence or absence of scrambling.

Specifically, for example, a configuration as shown in FIG. 2 may be used. In FIG. 2, as part of the configuration of a normal television receiver, near the output stage of the video detection circuit 4, an emitter-follower transistor 21 receives the video-detected output signal. A circuit is provided in which the signal is received again by the emitter follower transistor 23 via the trap circuit 22 that removes the audio signal component, and then sent to the next stage circuit section. This transistor 2
P of the switching control circuit 13.
The bottom level of this output signal is held by the transistor 24 and the capacitor 25 connected to the emitter of the transistor. The terminal voltage of this capacitor 25 is received by an emitter follower transistor 26, and then passed through a smoothing circuit 27 consisting of a resistor and a capacitor.
is converted into a DC signal by

In the circuit having the configuration shown in FIG. 2 as described above, when a general television broadcast signal is received.

The bottom 1 novel has the potential at the tip of the sync pulse (so-called sync tip), and the terminal voltage of the inductor 25 reaches the sync tip level (more precisely, the level of the VBE of the transistor 24 added) due to the sync pulse every horizontal scanning period. While the output signal from the smoothing circuit 27 is a predetermined low-level DC signal, when a scrambled television signal is being received, the synchronization pulse of the television signal is a random DC signal. Since the terminal voltage of the capacitor 25 is superimposed, it is extremely rare for the terminal voltage of the capacitor 25 to drop to the above-mentioned normal sync tip level, and the output signal from the smoothing circuit 27 (or a level higher than the above-mentioned predetermined low level) is extremely rare. Therefore, by sending the output signal from the smoothing circuit 27 to, for example, a level discrimination circuit and detecting whether it is at the predetermined low level, reception of general television broadcast signals is possible. It is possible to determine whether it is the time when a scrambled television signal is being received, and the selector switch 7 can be controlled accordingly.

Next, FIG. 3 shows another specific main part of the switching control circuit 13, and as shown in FIG. 2, the output from the transistor 23 provided near the output stage of the video detection circuit 4 The signal is extracted and sent to a synchronization separation circuit 31 which is part of the switching control circuit 13. This synchronous separation circuit 3
1 uses a PNP transistor 32 to extract only the synchronizing signal portion by amplitude separation, but when a scrambled television signal is being received, the amplitude separation of the synchronizing signal portion can hardly be performed. Therefore, the transistor 32 of the synchronous separation circuit 31
For example, by converting the output signal from the smoothing circuit 33 into a DC signal, a constant DC level can be obtained from the smoothing circuit 33 when receiving a general television broadcast signal, and
When receiving a scrambled television signal, the output level of the smoothing circuit 33 becomes approximately zero. By level-discriminating the output signal from this smoothing circuit 33 using, for example, a level discrimination circuit, it can be determined whether or not a scrambled television signal is being received, and the selector switch 7 can be controlled accordingly. good.

In addition, the channel selection signal etc. from the channel selection circuit 8 provided for the cheese circuit 2 shown in FIG. The ζ changeover switch 7 may be automatically changed over when this occurs.

In addition, if the CATV broadcast is an addressable system for each viewer's device, the changeover switch T is controlled to be forcibly switched to O by a control signal from the broadcasting station. Good too.

All of the above are examples in which the selector switch 7 is automatically switched when receiving general television broadcasting and when receiving scrambled television signals.
The changeover switch 1 may be automatically switched by detecting whether or not the adapter 10 is connected. In this case, for example, by detecting the presence or absence of an output signal from the descrambler 11 of the CATV adapter 10, or by detecting the connection state of the connector, the CA TV receiver, etc.
It is possible to detect whether the TV adapter 10 is connected.

Note that the present invention is not limited to the above-mentioned embodiments. For example, instead of providing two AGC circuits, only one AGC circuit is provided.
The circuit may be configured to have two time constants that can be switched.

〔Effect of the invention〕

According to the television signal demodulation device of the present invention, the tuner circuit, VIP amplifier, etc. in the television receiver and television tuner device can be used for CATV reception, so an inexpensive CATV adapter consisting only of a descrambler can be used. Not only is it possible to receive CATV broadcasts just by adding it, but the time constant of the AGC circuit that controls the gain of the vIF amplifier can be switched between long and short, allowing both some television broadcasts and CATv broadcasts to be optimally received. Moreover, it is convenient to use because the reception in the optimum state is automatically performed without the user being conscious of switching the tescrambler.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing a main part of an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific example near the switching control circuit shown in FIG. 1, and FIG. The circuit diagram shown in FIG. 4 is a block circuit diagram for explaining a conventional example. 2...Tuner circuit, 3...VIP amplifier, 6...
・First AGC circuit, 7... changeover switch, 10...
・CATV adapter, 11...Descrambler, 12
...Second AGC circuit, 13...Switching control circuit. Patent applicant Sony Corporation representative Patent attorney Kodo Koike 1) Sakae Mura −

Claims (1)

[Claims] For the AGC circuit installed in the video signal amplification system,
A switch is provided to switch between two short time constants, and the output from the AGC circuit is supplied to the AGC terminal of the video intermediate frequency amplifier. A television signal demodulator comprising control means for switching the changeover switch to a long time constant side when connected.