JPS6065671A - Cable television receiver - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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.

A conventional cable television receiver will be described with reference to FIG. 1 without considering the configuration of the conventional example and its problems.

A television signal is received from an input terminal 1 of a CATV converter and tuned by a tuner 2. This tuner 2 is controlled by a tuning control device 6 using a signal from an optical remote control light receiving section 5 that receives and decodes an infrared remote control signal from an optical remote control transmitter 4. Can receive signals. The output 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.

However, this device only controls channel selection and cannot control the audio system. Therefore, noise occurs during volume control and channel selection 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 the 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 mute the audio when selecting a channel, and also control the volume on the 7th floor. FIG. 2 is a block diagram showing its basic configuration.

A television signal is input to an input terminal 11 and received by a tuner 12. Similar to the CATV converter, this tuner uses a control signal from an optical remote control receiver 15 that receives and decodes infrared signals from an operating section 13 and an optical remote control transmitter 14 to control the tuning control circuit 1.
6. An intermediate frequency is used as the output of the tuner 12, and is detected by a video detection circuit 18 through an intermediate frequency amplification 17 that amplifies it. When performing this detection, the frequency and level of the signal must be uniform, so the AFC detection device 19 detects the intermediate frequency signal and controls the local frequency of the tuner 12, and the noise remover removes noise from the video detection signal. a removal device 20 and an AG that amplifies it and controls the tuner 12 and intermediate frequency amplification 17;
It has a C amplifying device 21.

Since the video detection output signal contains a video signal and an audio intermediate frequency carrier, there are an audio bandpass filter (BPF) 22 and an audio elimination filter (BEF) 23 that separate the video signal and audio intermediate frequency carrier. 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 subjected to FM detection by an audio detector 25 to become an audio signal. This audio signal is amplified by audio amplifier 26. On the other hand, the video signal output from the audio BEF 23 is amplified by the video amplification 27. The audio signal 28 is connected to a speaker to output sound,
The video signal 29 is processed and output to a cathode ray tube.

The audio signal is controlled by the channel selection control section 16 using the operation section 13 and the audio control means of the optical remote control transmitter 14. The audio amplification circuit 26 has a built-in DC control attenuator, and receives the DC control signal 3 from the channel selection control section 16.
0, this DC control attenuator is activated to control the volume.

On the other hand, since no-signal noise is produced in the same way as in a CATV converter when selecting a station, muting is applied from the station selection control circuit 16 using the control signal 3o. This eliminates noise when selecting a channel.

Focusing on this point, the audio output terminal 28 and the video output terminal 29
There is an example in which a single RF television signal is created by layering the output signal of the RF modulator 31 to create a CATV converter. Although this CATV converter can naturally control the volume, it cannot eliminate noise when selecting a channel. 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 transmitted to the RF modulator 31 and the TV receiver connected to the CATV converter. This is because it is generated in aircraft and can be heard as if it were no-signal noise.

In this way, with conventional cable TV receivers such as CATV converters, either the RF type that outputs the tuner output directly, or the baseband type that demodulates and then modulates the 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 The present invention includes 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 detects the intermediate frequency signal to generate a video signal and an audio signal. A video detection amplification device and an audio detection amplification device that create a signal are provided, and a video mute device and an audio mute device are provided that can mute the video signal and the audio signal, respectively, by a signal from the channel selection control device, and mute each of the video and audio signals. This will be explained by creating an RF television signal by modulating the output signal of the device. 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 (-1) is added between the video amplification 27 and the RF modulator 31, and the mute function works only when the channel selection operation is started and a normal video signal is output. The control signal 33 is outputted from the channel selection control 16 for ease of use.

As a result, d: is not excessively input to the RF modulator 31, and no overmodulation noise is generated. 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 3o of the channel selection control 16 so that the DC control attenuator of the audio amplifier 26 has the maximum attenuation amount. 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 is performed by the operation unit 13 and the optical remote control receiver 1.
It can be detected by signal input from 5, and managed by channel selection control 16. A microprocessor is used in this part,
This control and the tuning control of the tuner 12 are performed. Video muting 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.

FIG. 4 shows a specific circuit that realizes video muting. The output 29 of the video amplifier 27 is received by the emitter follower 01. In the case of FIG. 4, AC coupling is performed by capacitor C1, and bias is supplied to transistor Q1 by bias resistors R1 and R2, but direct current coupling may be used without the bias resistor. Emitter resistor R3 and transistor Q1
A diode D1 is inserted between them, and the signals at both ends thereof are supplied to a current-regulated push-pull circuit consisting of transistors Q2 and Q3 and protection resistors R4 and R5.

This circuit is unnecessary when the load can be driven only by the transistor Q1. However, to achieve this, it is necessary to allow a large amount of current to flow through the transistor Q1.

In this device, this bush-pull circuit is added so that it can drive not only one load but two or more loads. The output of this push-pull circuit must be connected to the RF modulator by an output resistor R6.
is connected between resistors R4 and R5, and connected to the RF modulator through a DC cut capacitor C2. Resistance R
6 and the capacitor C2 through a resistor R7 to the collector of the mute control transistor Q4. The emitter of the transistor Q4 is grounded, a charging diode D2 and a resistor R8 are inserted in series between the base and the control signal line 33 from the channel selection control 16, and a discharging resistor is connected in parallel to both ends of the diode D2 and resistor R8. R9
A charging capacitor C3 is inserted between the base of the transistor Q4 and ground.

The mute operation must be performed immediately upon entering the channel selection operation. In other words, it is necessary to complete the mute operation faster than the AGC time constant during channel selection. Therefore, the resistance R8 should be made as small as possible, and the charging time constant R8・C
3 must be made small, but since the output of the channel selection control circuit 16 is expected to be destroyed by the rush current, the protection must be as thick and strong as possible. From both of these, the resistance R
8 can be determined. When the resistance R8 is determined, 03 is determined from the required time constant. This capacitor C3 may seem unnecessary, but since the DC voltages at the eight points change rapidly when muting is canceled, the mute output voltage increases through the capacitor C2. This acts like an oversignal and generates noise. Therefore, the above problem is solved by inserting the capacitor C3 and gradually lowering the base voltage of the transistor Q4. In addition, the time constant for discharging the charge charged in this capacitor C3 is determined by the channel selection control 16.
If the output equivalent resistance of is R1°, then C3・(R9→R10
) is determined. In order to prevent the above-mentioned noise, the discharging time constant needs to be quite long, and the resistor R9 needs to be about 10 times as large as the charging resistor R8.

The diode D2 is designed to be discharged through a resistor R8. The resistor R7 determines the signal amplitude of the output terminal 34 during muting.

The output signal is the RF modulator 310 input resistance and resistor R7.
The voltage is divided by the parallel equivalent resistance and the resistor R6 and output.

If the output signal is not needed when muting the video, use resistor R7.
is not required.

In many cases, it is considered better to have a channel scanning function as a channel selection function, and to be able to see the image at that time. It can produce output to the extent that no modulation bus is generated.

Effects of the Invention As described above, according to the present invention, in a baseband type CATV converter that uses both audio mute and video mute and an RF modulator, it is possible to eliminate noise during channel selection, and the user This has the great effect of improving the user experience by eliminating the need to listen to annoying noises.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a conventional RF type cable television receiver, FIG. 2 is a block diagram of another conventional baseband type cable television receiver using audio mute, and FIG. 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 unit, 4,14...
... Optical remote control transmitter, 5, 15 ... Optical remote control light receiving section, 6, 16 ... Tuning control circuit, 7
, 35...Output terminal, 1T...Intermediate frequency amplification circuit, 18...Video detection circuit, 19...
...AFC detection circuit, 20...Noise removal circuit, 21...AGC amplifier circuit, 22...Audio BPF, 23...Audio BEF, 24... ...
Riminter amplifier circuit, 26...Audio detection circuit, 2
6...-Audio amplification circuit, 2A...Video amplification circuit, 28...Audio output circuit, 29...
...Video output circuit, 30...Volume control circuit, 31...RF modulator, 32...
...Video mute circuit, 33...Video mute control circuit, 34...Video mute output terminal, C1-C3...Capacitor, R1-R9
... Resistor, D1-D2... Teriode, Q1-Q4... Transistor. Figure 1

Claims (2)

[Claims] (1) Equipped with a tuner that receives a television signal and a tuning control device that controls it, an intermediate frequency amplification device that amplifies the tuner output signal, and a video signal and an audio signal that are generated by detecting the intermediate frequency signal. It has a video detection amplification device and an audio detection amplification device, and is equipped with a video mute device and an audio mute device that can respectively mute the video signal and the audio signal by signals from the station selection control device, and output signals of the respective mute devices. A cable television receiver equipped with an RF modulator 1/-ter that modulates an RF television signal. (2) The video mute device is equipped with a mute control transistor whose emitter is grounded by using an output resistor connected to the emitter of a common emitter transistor as a collector resistor, and between the base of the transistor and the channel selection control device. The claim is that a diode and a resistor are connected in series to serve as a charging device, a discharging resistor is connected in parallel between the diode and the resistor, and a charging capacitor is provided between the base and ground. The cable television receiving device according to item 1.