JPH0441667Y2 - - Google Patents

Description

[Detailed description of the invention] (a) Industrial application field The present invention relates to a mute circuit for reproduced video signals in a video tape recorder (VTR).

(b) Prior Art Television signal recording devices such as VCRs that receive and record television signals are required to avoid unnecessary radio waves other than those from regular television in areas with strong electric fields, such as West Germany, where there is a lot of interference due to telecommunication regulations. They are required to have rejection capability, and are required to mute the audio when receiving signals other than regular television signals.

For this reason, the television signal recording devices in the aforementioned regions are equipped with means for determining whether or not the received radio waves are regular television signals, and means for muting the audio using this output.
FTZMUTE circuit. For example, the device disclosed in Japanese Patent Application Laid-Open No. 57-202186 is preferred.

The above-mentioned conventional technology detects a horizontal synchronization signal in a video signal, determines whether or not the received radio wave is a regular television signal, and mutes the audio signal if it is not a regular television signal. It is a digital signal recording device.

(C) Problems to be Solved by the Invention In the prior art described above, dedicated discrimination means and muting means are required to mute the reproduced video signal immediately after starting reproduction and when reproducing a non-recorded portion.

(d) Means for solving the problem The present invention is a video mute circuit that detects the presence or absence of a synchronization signal in a television signal received by a tuner, and uses the detection output to detect the audio signal of the television signal. A detection circuit that cuts off the supply to the recording circuit detects the presence or absence of a synchronization signal in the reproduced video signal, and if there is no synchronization signal,
It is characterized in that the passage of the reproduced video signal is blocked by the output thereof.

(E) Effect Since the present invention is constructed as described above, it is necessary to mute the reproduced video signal immediately after starting playback and during non-recording playback, and to mute the received television signal when a regular television signal is not being received. It is possible to use one discrimination circuit for determining gender.

(f) Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit block diagram of this embodiment. A reproduced video signal obtained by the reproduction circuit 1 is amplified by the video amplifier 2 and sent to the reproduction side fixed contact 3P of the changeover switch 3. On the other hand, the video signal of the broadcast television signal of the desired selected channel received by the tuner circuit 4 is led to the fixed contact 3R on the playback tuner side of the changeover switch 3.

The movable contact piece 3A of the changeover switch 3 is connected to the input side of a synchronous separation circuit 5, and the synchronous separation output is one input of a phase comparison circuit 6. This phase comparison circuit 6 is a low-pass filter (LPF) in the subsequent stage.
7. A loop is formed with a voltage controlled oscillator (VCO) 8, and the oscillation output of the voltage controlled oscillator 8 becomes the other input, forming a PLL (phase lock loop) circuit, in which the phase of the synchronized separated output and the oscillation output are always compared. Accordingly, the voltage controlled oscillator 8 is controlled.

In addition, the synchronization separation output is mono multi 9 and
It serves as an input to the EXOR circuit 11. Said
The other input of the EXOR circuit 11 is the monomulti 9 inverted by the NOT circuit 10.
The mono multi 11 is a retriggerable mono multi that is triggered at the rising edge of the synchronous separation output.
The metastable period is set longer than the horizontal scanning period (IH). The output of the EXOR circuit 11 is
NAND whose one input is the voltage controlled oscillator 8 output inverted by NOT circuit 12
It serves as the other input of the circuit 13.

The output of the NAND circuit 13 passes through the LPF 14 and becomes the positive input of a comparator circuit 15 to which a constant DC voltage V _O is previously applied to the negative input. 17 movable contact piece 17A. Fixed contacts 17P and 17R of the changeover switch 17 are connected to a reproduced video signal mute circuit 18 and an audio mute circuit 19, respectively.
The movable contact piece 17A is connected to the fixed contact 17P,
17R, the inverted output of the comparator circuit 15 becomes the mute signal of both the mute circuits 18 and 19. Further, the changeover switch 17 is interlocked with the changeover switch 3, and during playback, the movable contact pieces 3A, 17A are connected to the playback side fixed contacts 3P, 7P.
During recording, the recording side fixed contacts 3R and 17R are switched. Here, when the reproduced video signal mute circuit 18 is at H level, the video amplifier 2
The audio mute circuit 19 mutes the reproduced video signal obtained through the tuner circuit 4 and prevents it from being sent to the output terminal 21, and the audio mute circuit 19 mutes the audio signal of the broadcast television signal obtained from the tuner circuit 4 and outputs it to the recording circuit ( This prevents the terminal 20 from being led out to the terminal 20 (not shown). In addition, capacitors 22 and 23
have separate capacitances, and a fixed contact 17 is used to smooth each mute signal and remove high-frequency components.
It is inserted between P, 17R and ground.

Next, the operation of the circuit of this embodiment will be explained. If a normal playback video signal is obtained during playback when the changeover switches 3 and 17 are switched to the fixed contacts 3P and 17P side, the playback video signal from the playback circuit 1 passes through the changeover switch 3 and is sent to the synchronization separation circuit 5. Then, a horizontal synchronizing signal is extracted as shown in FIG. 2a. on the other hand,
The voltage controlled oscillator 8 generates an oscillation output as shown in b by constant phase comparison. In addition, since the monomulti 9 is triggered again at the next rising edge of the horizontal synchronization signal during the metastable period, which is longer than the horizontal scanning period (IH),
An H level output is always generated as shown in c. By EXORing the inverted output of the monomulti 9 with the horizontal synchronizing signal, an output like d, which is the same as the original horizontal synchronizing signal, can be obtained.

This EXOR circuit 11 output and e's _VCO inverted output
When NAND is used, an L level output f is obtained by the phase difference between the horizontal synchronizing signal and the oscillator output. this
The output of the NAND circuit 13 is smoothed by the LPF 14 and becomes an output that is always considered to be at H level. When this is compared by the comparator 15 whose reference voltage is set to the value V _O shown by the dashed line g, the output of the comparator 15 becomes H level. This output is NOT circuit 16,
The reproduced video signal is supplied as a mute signal to the mute circuit 18 via the changeover switch 17,
Since it is inverted by the NOT circuit 16 and becomes L level,
The reproduced video signal is not muted.

Next, immediately after starting the playback operation, if the playback video signal is not normal or if a blank tape is being played, the horizontal synchronization signal will not be extracted from the synchronization separation circuit 5 and the monomulti 9 will not be triggered. figure,
The EXOR circuit 11 output is always at H level. On the other hand, if there is no horizontal synchronization signal, the voltage controlled oscillator 8 will also be at the L level, the output of the NAND circuit 13 will also be at the L level, and the reference voltage V _O of the comparator 15 will be at the L level.
As the level becomes lower, the output of the comparator 15 becomes L level, and after this is inverted, the reproduced video signal mute circuit 18 is activated, the reproduced video signal is muted, and the abnormal reproduced video signal is sent to the terminal 21. transmission is prevented.

Next, when recording, that is, when the changeover switches 3 and 17 are switched to the fixed contacts 3R and 17R, the broadcast television signal from the tuner circuit 4 is transferred to the changeover switch 3.
The signal is supplied to the synchronization separation circuit 5 via the synchronous separation circuit 5. Below, if the broadcast television signal is a regular signal,
It operates in the same way as when reproducing a normal reproduced video signal, the audio mute circuit 19 does not operate, and the audio signal of the broadcast television signal is not muted.
Furthermore, if the broadcast television signal is not a regular signal, a mute signal is emitted from the comparison circuit 15 in the same way as when inputting an irregular reproduced video signal or when playing back a non-recorded tape, and the audio mute signal of the broadcast television signal is output. will be done.

That is, during this recording, the synchronization separation circuit 5
The detection circuit 30 constituted by each circuit up to the NOT circuit 16 is used as a discrimination circuit for the FTZ-MUTE circuit. Here, FTZ−
MUTE means that when receiving television signals, in areas with strong electrical fields where there is a lot of interference such as West Germany, it is required by telecommunications regulations, etc. to be equipped with the ability to eliminate unnecessary radio waves other than official television signals. This refers to muting the audio when receiving signals other than television signals.

For this reason, the television signal recording apparatus in the above-mentioned areas must be equipped with means for determining whether or not the received radio waves are regular television signals, and means for muting the audio by the output of this. In this embodiment, the detection circuit 30 constitutes the determining means.

(g) Effects of the invention As mentioned above, according to the invention, a reproduced video signal is input to the conventionally used FTZ-MUTE circuit,
The reproduced video signal is muted immediately after the start of the reproduction operation and during reproduction of the non-recorded tape, and the circuit configuration can be extremely simplified and has high practical value.

[Brief explanation of the drawing]

The drawings all relate to one embodiment of the present invention, with FIG. 1 being a circuit block diagram and FIG. 2 being a waveform diagram. 3...Switching switch (switching means), 4...Tuner circuit, 18...Playback video signal mute circuit (second mute circuit), 19...Audio mute circuit (first mute circuit), 30...Detection circuit.

Claims (1)

[Scope of utility model registration request] a detection circuit that detects the presence or absence of a periodic signal in the television signal received by the tuner; and a first mute circuit that cuts off the supply of the audio signal of the television signal to the recording circuit at the output of the detection circuit. A video mute circuit comprising: switching means for switching the television signal input to the detection circuit to a reproduced video signal from a reproduction circuit; A video mute circuit comprising: a second mute circuit that blocks passage of a video signal.