JPH0617386Y2 - Oscillation prevention device for no signal in video tape recorder - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention is a video tape recorder (hereinafter referred to as VTR).
When a TV receiver (hereinafter referred to as a TV) is used in combination with the VTR, oscillation occurs due to the noise signal of the feedback loop formed between the VTR and the audio signal input / output terminal of the TV. The present invention relates to a device for preventing oscillation when there is no signal in a video tape recorder in which an audio signal conversion circuit is formed inside a VTR.

[Problems to be solved by the conventional technology and the invention]

Generally, a TV is connected to a VTR by a cable and the TV is used as a monitor. That is, as shown in FIG.
The audio signal input / output terminals 24, 25 of 21 are connected to the audio signal input / output terminals 22, 23 of the TV 20 with a cable, and
The TV 20 is used as a monitor.

However, such a device has a VTR as shown in FIG.
When the TV 20 is set to the TV mode with the tuner line changeover switch 26 of No. 21 changed over to the contact b side in the line state, the contact b of the tuner line changeover switch 26, VTR2
1 through the amplifier 27 and the audio signal output terminal 25, the audio signal input terminal 22 of the TV 20, the audio circuit 28 and the audio signal output terminal 23, and the audio signal input terminal 24 of the VTR 21,
Since a feedback loop is formed, a noise signal is generated from the feedback circuit, the noise signal is amplified and oscillated through the amplifier 27, and the oscillating sound is generated even when the VTR 21 and the TV 20 are in a no signal state. It was supposed to be output by the speaker of TV20.

Such a conventional technique has a problem in that a noise signal oscillates to make a viewer uncomfortable, and excessive oscillation causes deterioration of internal elements of the device.

Therefore, the present invention was devised to solve such problems.

[Means for solving problems]

In the present invention, a capacitor (C ₂ ), a tuner line changeover switch (1), an amplifier (between the audio signal input terminal (12) and the output terminal (9) of the video tape recorder are connected so as to be connected to a television. 2) and a capacitor (C ₄ ) are connected to each other, the capacitor (C ₁ ), the buffer (3), and the buffer (3) between the audio signal input terminal (12) and the output terminal (9) of the video tape recorder. A capacitor (C ₃ ) is connected, and a power source (B ⁺ ) is connected so as to be applied to the power source input side of the buffer (3) and the amplifier (2) via the switch units (4) and (5), The output signal of the sync signal detection circuit (8) for detecting the vertical sync signal (V _S ) is the switch part (5).
The synchronizing signal detection circuit (8) is connected to the ON / OFF control signal by applying an ON / OFF control signal to the ON / OFF control.
The signal output from the inverter and passed through the inverter (7) and the line high signal (L _H ) are applied to the switch section (4) through the AND gate (6) as ON / OFF control signals. There is provided a device for preventing oscillation in a video tape recorder when there is no signal, which is characterized by being connected.

That is, between the VTR audio signal input / output terminals, a transmission line for a buffer operated by an emitter follower is formed separately from the transmission line passing through the tuner line changeover switch and the amplifier, and the vertical sync signal is normally detected. In the state, a feedback loop is formed through the transmission line passing through the tuner line changeover switch and the amplifier, and in the no signal state where the vertical synchronizing signal is not detected, the feedback loop is formed through the transmission line of the buffer. Therefore, even if a TV is connected to the VTR to form a feedback loop, when there is no signal, self-oscillation due to amplification of the noise signal does not occur, so that noise that touches the ear is output from the speaker. Can be prevented.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram of a device for preventing oscillation when there is no signal of the present invention, FIG. 2 is a detailed circuit diagram of one embodiment of FIG. 1, and FIG. 3 is a diagram showing a conventional type device, which is a video tape recorder. Of the audio signal input / output terminal of the television receiver and the audio signal input / output terminal of the television receiver in a schematic configuration diagram, FIG. 4 shows the video tape recorder of FIG. 3 and the inside of the television receiver. In the diagram showing the outline, as shown in FIG.
As the audio signal input terminal 12 of R is, the contact b of the capacitor C ₂ and the tuner line change-over switch 1, through an amplifier 2 and a capacitor C ₄ is connected to the audio signal output terminal 9 of the VTR, it is connected using a TV In the above device, the audio signal input terminal 12 of the VTR is connected to the audio signal output terminal 9 of the VTR through the capacitor C ₁ and the buffer 3 and the capacitor C ₃ operated by the emitter follower, and the power source B ⁺ Is applied to the buffer 3 and the amplifier 2 via the switch units 4 and 5, respectively,
The output signal of the sync signal detection circuit 8 for detecting the vertical sync signal V _S is applied to the switch section 5 and connected so as to control the on / off state of the switch section 5. The signal output and passed through the inverter 7 and the line high signal L _H are applied to the switch unit 4 through the AND gate 6 and are connected so as to control the on / off state of the switch unit 4, The sync signal detection circuit 8 is configured to detect, when the vertical sync signal V _S of a certain period is input to the input side thereof, to detect it and output a high potential signal to the output side thereof.

Then, as shown in FIG. 2, the buffer 3 has a resistance R
₁ -R ₃ and constituted by the transistor _{Q 1,} the switch section 4, the resistor _R 4 -R ₇ and is composed of a transistor _Q 2 · _{Q 3,} the switch unit 5, the resistor _R 8 _{-R 11} and transistor Q It is composed of ₄ and Q _5, and the operation of the present invention configured as described above is as follows.

That is, in the state of being switched to tuner line change-over switch 1 in the VTR to the contact b side of the line state, since the vertical synchronizing signal V _S is not generated, the output side of the synchronizing signal detection circuit 8, a low potential signal is outputted , The low potential signal is inverted by the inverter 7 into a high potential signal, and the AND gate 6
Applied to one side input terminal.

On the other hand, since the line high signal L _H is applied to the other input terminal of the AND gate 6, the high potential signal is output to the output terminal thereof. This high potential signal is applied to the resistance R of the switch unit 4.
Through _6, it is applied to the base of the transistor Q _3, since turning on the transistor Q _3, transistor Q
_{2 is} also turned on. Therefore, the power source B ⁺ passes through the transistor Q ₂ of the switch unit 4 and is applied to the buffer 3 to put the buffer 3 into an operating state.

Further, the low potential signal output from the synchronization signal detection circuit 8 passes through the resistor R ₁₀ of the switch unit ₅ to turn off the transistor Q ₅ and turn off the transistor Q ₄ .
The power supply B ^{+ to} the amplifier 2 is cut off, and the amplifier 2
Does not work.

Therefore, the signal input to the audio signal input terminal 12 of the VTR cannot pass through the transmission line of the capacitor C ₂ and the tuner line changeover switch 1, the amplifier 2, the capacitor C _4, etc., and the capacitor C ₁ and the buffer 3, through the transmission line of the capacitor C _3, VTR the audio signal output terminal 9
Be transmitted to.

However, in this case, VTR audio signal input / output terminal 1
When the VTR and TV are in the no signal state when the input and output terminals of the audio signal of the TV are connected to each other and the audio signal input / output terminals of the TV are connected to each other, the buffer prevents the oscillation. Three
This is because the amplification degree of is smaller than 1.

That is, since the buffer 3 is operated by the emitter follower and its amplification degree is smaller than 1, the output signal of the buffer 3 is gradually reduced every time the feedback loop is passed, and oscillation does not occur. .

On the other hand, in the VTR recording mode and the VTR recording mode, the vertical synchronizing signal V _S is input to the input side of the synchronizing signal detection circuit 8, and thus a high potential signal is output to the output side thereof. The potential signal is oscillated into a low potential signal by the inverter 7 and applied to one input terminal of the AND gate 6, and the low potential signal is output to the output terminal of the transistor Q _{2 of the} switch unit 4. · Q ₃ so turn off the. Therefore, since the power supply B ⁺ is not supplied to the buffer 3, the signal input to the audio signal input terminal 12 of the VTR cannot pass through the transmission line of the capacitor C ₁ and the buffer 3 and the capacitor C ₃ .

However, at this time, the high potential signal output from the synchronization signal detection circuit 8 turns on the transistors Q ₄ and Q ₅ of the switch unit 5 and the power source B ⁺ is supplied to the amplifier 2, so that the VTR
The audio signal input signal input to the terminal 12, the contact b of the capacitor C ₂ and the tuner line change-over switch 1, an amplifier 2, through a capacitor C _4, is outputted to the audio signal output terminal 9 of the VTR.

[Effect of device]

According to the present invention, according to each mode of the VTR used by connecting to the TV, the transmission line of the audio signal output to the outside is automatically formed separately, and when the VTR and the TV are in the no signal state, the feedback is performed. It is possible to prevent the oscillation caused by the noise, prevent the noise that touches the ear from being output from the speaker, prevent the internal elements from being heated due to the oscillation, and improve the reliability of the product.

[Brief description of drawings]

FIG. 1 is a block diagram of an oscillation preventive device when there is no signal of the present invention, FIG. 2 is a detailed circuit diagram of one embodiment of FIG. 1, and FIG.
FIG. 4 is a diagram showing a conventional device, which is a diagram showing an outline of a connection state of audio signal input / output terminals of a video tape recorder and audio signal input / output terminals of a television receiver, and FIG.
FIG. 3 is a diagram showing an outline of the inside of a video tape recorder and a television receiver of the apparatus. 1 ... Tuner line selector switch, 2 ... Amplifier, 3 ... Buffer, 4, 5 ... Switch section, 6 ... AND gate, 7 ...
Inverter, 8 ... Synchronous signal detection circuit, 9 ... Audio signal output terminal, 12 ... Audio signal input terminal.

Claims (2)

[Scope of utility model registration request] 1. A capacitor C ₂ , a tuner line changeover switch 1, an amplifier 2, and a capacitor between an audio signal input terminal 12 and an output terminal 9 of a video tape recorder (VTR) for use in connection with a television receiver. A first circuit in which C ₄ is connected in series; a second circuit in which a capacitor C ₁ , a buffer 3, and a capacitor C ₃ are connected in series between the audio signal input terminal 12 and the output terminal 9; the buffer 3 and the above First and second switch parts 4, 5 for energizing the amplifier 2 from the power source B ⁺ ; Detects a vertical synchronizing signal V _S of the television, and outputs an output signal to the second switch part 5 for on / off control. A synchronizing signal detection circuit 8 connected to apply a signal and also connected to the inverter 7; and a signal output from the synchronizing signal detection circuit 8 and passed through the inverter 7; An AND gate for inputting an in-high signal L _H and applying an ON / OFF control signal to the first switch unit 4 is provided, and in a normal state where the vertical synchronization signal is detected, the transmission line of the first circuit forms a feedback loop. In the non-signal state where the vertical sync signal is not detected, the transmission line of the second circuit forms a feedback loop to automatically form the transmission line of the audio signal output to the outside according to each mode of the VTR. And then
Even when the VTR and the television receiver are in a non-signal state, the above-mentioned buffer contributes to the prevention of oscillation due to the feedback because the amplification factor is less than 1 due to the emitter follower operation and also prevents the internal element from overheating due to the oscillation. A device for preventing oscillation in a video tape recorder when there is no signal. 2. A utility model registration claim characterized in that the buffer (3) is composed of a resistor (R ₁ -R ₃ ) and a transistor (Q ₁ ) so as to operate as an emitter follower. The apparatus according to item 1.