JPH0345953B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a cable television receiver that receives any RF television signal and converts it into a single RF television signal.

Configuration of Conventional Example and its Problems First, a conventional cable television receiver will be described with reference to FIG.

A television signal is received from the input terminal 1 of the CATV converter and tuned by the tuner 2. This tuner 2 is controlled by a channel selection control device 6 using signals from an optical remote control light receiving section 5 that receives and decodes infrared remote control signals from an operating section 3 or an optical remote control transmitting section 4. Can receive. The output 7 of the tuner 2 is generally output to one of the VHF low band channels, and a general television receiver is connected to this output 7. However, this device can only control channel selection and cannot control the audio system. Therefore, as the voice carrier is temporarily lost as a transient phenomenon during tuning, noise occurs during the tuning process. The cause of this noise is that although the television receiver is tuned to the output channel of this converter, there is a temporary no signal until tuning is completed, and noise due to no signal can be heard. This was a problem for users because it was unpleasant to the ears. However, it is nearly impossible to eliminate this on the conventional converter side.

On the other hand, recent television receivers perform audio muting when selecting a channel, and also perform volume control. FIG. 2 is a block diagram showing the basic configuration.

A television signal is input to the input terminal 11,
It is received by the tuner 12. This chuyuna
Like the CATV converter, it is controlled by a channel selection control circuit 16 using control signals from an optical remote control light receiving section 15 that receives and decodes infrared signals from an operating section 13 and an optical remote control transmitter 14. An intermediate frequency is used as the output of the tuner 12, and the intermediate frequency amplification 1 amplifies this.
7 and is detected by the video detection circuit 18. When performing this detection, the frequency and level of the signal must be uniform, so the local frequency of the tuner 12 is controlled by detecting the intermediate frequency signal.
It has an AFC detection device 19, a noise removal device 20 that removes noise from the video detection signal, and an AGC amplification device 21 that amplifies it and controls the tuner 12 and intermediate frequency amplification 17.

Since the video detection output signal contains both the video signal and the audio intermediate frequency signal, there is an audio bandpass filter (BPF) 22 and an audio removal filter (BEF) 23 that separate the video signal and the audio intermediate frequency signal. The audio intermediate frequency signal, which is the output signal of the audio BPF 22, is amplified by a limiter amplifier 24, subjected to a limiter, and then processed by an audio detector 25.
It is FM detected and becomes an audio signal. This audio signal is amplified by audio amplifier 26. On the other hand, audio BEF
The video signal output from 23 is amplified by video amplification 27. The audio signal 28 is connected to a speaker to output sound, and the video signal 29 is processed and output to a cathode ray tube.

The audio signal is sent to the channel selection control unit 1 by the audio control means of the operation unit 13 and the optical remote control transmitter 14.
Controlled from 6. The audio amplification circuit 26
Built-in DC control attenuator, channel selection control section 16
This DC control signal 30 is received from
Operate the control attenuator to control the volume.

On the other hand, since no-signal noise is generated during tuning, similar to a CATV converter, the tuning control circuit 16 applies a control signal 30 to mute. This eliminates noise when selecting a channel.

Focusing on this point, the output signals of the audio output terminal 28 and the video output terminal 29 are connected to the RF modulator 31 to create a single RF television signal,
There is an example of creating a CATV converter. this
CATV converters can naturally control the volume, but they cannot eliminate noise when selecting stations. The reason is as follows. That is, when selecting a channel, there is temporarily no signal, so the AGC circuit operates, and the tuner 12 and intermediate frequency amplification circuit 17 attain maximum gain. Therefore, a large amount of noise is generated at the video output terminal 29. Although the time is short, excessive noise is generated at the video output terminal 29, causing the RF modulator 31 to become overmodulated, and the overmodulation buzz is caused by the RF modulator 31 and the
This is because it occurs in the TV receiver connected to the CATV converter and can be heard as if it were no-signal noise.

In this way, with conventional cable television receivers such as CATV converters, either the RF type that outputs the tuner output directly, or the baseband type that demodulates and then modulates it to an RF signal using an RF modulator and outputs it. This will generate noise when selecting a station.

OBJECTS OF THE INVENTION It is an object of the present invention to provide a cable television receiving device that prevents the generation of noise during channel selection.

Structure of the Invention In the present invention, a tuner that receives a television signal, a tuning control device that controls it, an intermediate frequency amplification device that amplifies the tuner output signal,
A video muting device that is equipped with a video detection amplification device and an audio detection amplification device that detect the intermediate frequency signal and create a video signal and an audio signal, and can mute the video signal and the audio signal, respectively, according to the signal from the channel selection control device. and an audio mute device, and modulates the output signal of each mute device to create an RF television signal.
It is characterized by being equipped with an RF modulator.

DESCRIPTION OF EMBODIMENTS One embodiment of the present invention will be described below with reference to the block diagram of FIG. In the figure, the same parts as those in the apparatus shown in FIG. 2 are given the same symbols, and the explanation of their operation will be omitted.

Since this device is a baseband type CATV converter, noise during channel selection becomes a problem.

In order to improve this, a video mute device 32 is added between the video amplifier 27 and the RF modulator 31, so that the mute function only works during the period from when the channel selection operation starts until a normal video signal is output. A control signal 33 is output from the channel selection control 16.

As a result, excessive input is not applied to the RF modulator 31, and overmodulation noise does not occur. Naturally, in order to prevent no-signal noise in the audio system, it is necessary to mute the audio during the channel selection operation.

The audio system mute operation is controlled by the volume control signal 30 from the channel selection control 16 so that the DC control attenuator of the audio amplifier 26 has the maximum attenuation. The no-signal time during channel selection can be determined in advance from the operation of the device.
The start of the channel selection operation can be detected by signal input from the operation section 13 and the optical remote control light receiving section 15, and can be managed by the channel selection control 16. A microprocessor is used in this part to perform this control and tuner selection control. Video recording is also performed using this microprocessor. The over-signal time during channel selection can also be determined in advance in the same way as the no-signal time in the audio system.

Figure 4 shows a specific circuit that realizes video muting. The output 29 of the video amplifier 27 is received by the emitter follower _Q1 . In the case of FIG. 4, the capacitor _C1 performs AC coupling, and the bias resistors _R1 and _R2 supply bias to the transistor _Q1 , but direct current coupling may be used without the bias resistor. Diode D ₁ between emitter resistor R ₃ and transistor Q ₁
and connect the signals at both ends to transistor Q ₂ and
Supplied to a current regular push-pull circuit consisting of Q ₃ and protection resistors R ₄ and R ₅ . When the load can be driven only by transistor _Q1 ,
This circuit is unnecessary. But for that,
It is necessary to pass a large amount of current through transistor _Q1 .

In this device, this push-pull circuit is added so that it can drive not only one load but two or more loads. To achieve input matching with the RF modulator, the output of this push-pull circuit is connected to an output resistor _R6 between resistors _R4 and _R5 , and connected to the RF modulator through a DC cut capacitor _C2 . Connect to the collector of the mute control transistor _Q4 through the resistor _R7 between the resistor _R6 and the capacitor _C2 . The emitter of transistor Q ₄ is grounded, and the base and control signal line 3 from channel selection control 16 are connected to the ground.
_A charging diode _D2 and _a resistor _R8 are inserted in series between the transistor _{Q4 and} the ground. Insert charging capacitor _C3 .

The mute operation must be performed immediately when entering the channel selection operation. In other words, when selecting
It is necessary to complete the miute operation earlier than the AGC time constant. Therefore, it is necessary to make the resistance _R8 as small as possible and the charging time constant _R8・_C3 small, but since the output of the tuning control circuit 16 is expected to be destroyed by the rush current, the protection must be as large as possible. Must not be. From both of these, resistance
_R8 can be determined. Once resistance R ₈ is determined, C ₃ is determined from the required time constant. This capacitor
_C3 may seem unnecessary, but since the DC voltage at point a changes rapidly when mute is released, the mute output voltage increases through capacitor _C2 .
This acts like an oversignal and generates noise. Therefore, by inserting capacitor _C3 and gradually lowering the base voltage of transistor _Q4 ,
Solve the above problem. Also, this capacitor C ₃
The time constant for discharging the charge charged in the channel selection control 1
If the output equivalent resistance of 6 is R ₁₀ , then C ₃・(R ₉ + R ₁₀ )
It is determined by The discharge time constant needs to be quite long to prevent the above noise, and the resistor _R9 is the charging resistor _R8.
Approximately 10 times as much is required.

Diode _D2 is designed to prevent discharge through resistor _R8 . The resistor _R7 determines the signal amplitude at the output terminal 34 during muting.

The output signal is voltage-divided by the input resistance of the RF modulator 31, the parallel equivalent resistance of the resistor _R7 , and the resistor _R9, and then output.

If the output signal is not required when muting the video, the resistor _R7 is not required.

In many cases, it has a channel scanning function as a channel selection function, and it is considered better to be able to see the image at that time, so in that case, it is necessary to
By inserting _R7 , the output can be output to the extent that no overmodulation bus occurs even when the AGC is at its maximum.

Effects of the Invention As described above, according to the present invention, in a baseband type CATV converter that uses audio mute and video mute in parallel and uses an RF modulator, it is possible to eliminate noise during channel selection, which is troublesome to the user. This means that you do not have to listen to noise, which has a great effect in improving the usability.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional RF type cable television receiver, Figure 2 is a block diagram of another conventional baseband type cable television receiver using audio mute, and Figure 3 is a block diagram of a baseband type cable television receiver using audio mute. The figure is a block diagram of a baseband type cable television receiver according to an embodiment of the invention, and FIG. 4 is a circuit diagram of a video mute circuit used in the same apparatus. 1, 11... Input terminal, 2, 12... Tuner, 3, 13... Operation section, 4, 14... Optical remote control transmitter, 5, 15... Optical remote control light receiving section, 6,
16... Tuning control circuit, 7, 35... Output terminal,
17...Intermediate frequency amplification circuit, 18...Video detection circuit, 19...AFC detection circuit, 20...Noise removal circuit, 21...AGC amplification circuit, 22...Audio
BPF, 23...Audio BEF, 24...Limiter amplification circuit, 25...Audio detection circuit, 26...Audio amplification circuit, 27...Video amplification circuit, 28...Audio output circuit, 29...Video output circuit, 30... Volume control circuit, 31... RF modulator, 3
2...Video mute circuit, 33...Video mute control circuit, 34...Video mute output terminal, _C1 to _C3 ...Capacitor, _R1 to _R9 ...Resistor,
_D1 to _D2 ...diode, _Q1 to _Q4 ...transistor.

Claims (1)

[Claims] 1. A tuner that receives a television signal, a tuning control device that controls it, an intermediate frequency amplification device that amplifies the tuner output signal, and a video detector that detects the intermediate frequency signal and creates a video signal and an audio signal. A video mute device and an audio mute device each include an amplifier device and an audio detection amplification device, and can mute a video signal and an audio signal, respectively, according to a signal from the channel selection control device. a transistor for mute control, an output resistor connected to the emitter of the first transistor, and a second transistor for mute control whose collector is coupled to the output resistor and whose emitter is grounded; A charging diode and a resistor are connected in series between the base of the transistor and the channel selection control device, a discharging resistor is connected in parallel to the charging diode and the resistor, and the base of the second transistor is connected to the ground. A cable television receiver comprising a charging capacitor in between and an RF modulator that modulates the output signals of the respective mute devices to create an RF television signal.