JP2637233B2 - Automatic input switching circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an input switching circuit in a magnetic recording / reproducing apparatus (VTR) and the like, and more particularly, to an input switching circuit having an external signal input terminal. The present invention relates to an automatic input switching device that automatically switches between signals.

[Conventional technology]

In video equipment and audio equipment such as VTRs, input switching for signal processing by switching between signals generated inside the equipment (internal input) and signals input from a video camera, BS tuner or other signal source (external input) A circuit is provided (for example, refer to the instruction manual of Hitachi VTR.VT-F410).

FIG. 2 is a block diagram showing an example of this type of input switching circuit according to the above-mentioned prior art.
External left audio signal input terminal 2, External right audio signal input terminal 3
And switch circuits 4 (sSW1), 5 (SW2), 6 (SW3) for switching between internal signals and external signals for each signal,
A switch circuit 7 (SW) for controlling these switch circuits
4).

In the circuit of this configuration, the input signal is switched from the internal 11, 12, 13 side to the external 1, 2, 3 side by switching the switch circuit 7 to the arrow A side. Switching requires two operations, an operation of inserting a plug into each external input terminal and an operation of switching the switch 7.

FIG. 3 is a block diagram showing another example of the input switching circuit according to the prior art, in which plugs are inserted into the external video signal input terminal 1, the external audio left input signal input terminal, and the external audio right input signal input terminal 3, respectively. In this case, the internal signal inputs 11, 12, and 13 are switched from the external signal inputs 1, 2, and 3 to (a) a video signal, (b) a right audio signal, and (c) a left audio signal. Independent plugs are provided for each input of the audio signal.

That is, in this configuration, when no plug is inserted, an internal signal is selected, and when a plug is inserted, an external signal is selected.

Therefore, only the terminal where the plug is inserted switches to the external signal, and the terminal where the plug is not inserted keeps the internal signal selected, so if the external audio signal is monaural,
For example, it is necessary to insert a plug into the left audio signal input terminal 2 for inputting an external audio signal and also insert a dummy plug into another external audio signal input terminal 3.

[Problems to be solved by the invention]

In the former prior art, when an external signal is input, it is necessary to insert an external signal plug and switch the switch. In the latter prior art, a switch is provided for each external signal terminal. Is
Plugs have to be inserted into all the terminals, and the operation is troublesome.

An object of the present invention is to simply insert an external signal plug into an external signal input terminal when inputting an external signal,
An object of the present invention is to provide an automatic input switching circuit capable of switching an input from an internal signal to an external signal.

[Means for solving the problem]

The above object is achieved by using a signal input terminal in which an input contact for an internal signal is released by inserting a plug, and paying attention to the fact that an impedance matching resistor is connected between a video input terminal and a ground, and A resistor having an impedance sufficiently larger than the impedance matching resistor is inserted between the contact and the power supply which is released in step 2, and this contact is connected to the control terminal of each of the switching circuits for the video signal and the left and right audio signals. This is achieved by switching the switch circuit to a low (L) level when a signal is input and to a high (H) level by inserting a plug when an external signal is input.

[Action]

When a plug is inserted into the input terminal for inputting an external signal, the contact which is separated by the insertion of the plug is opened, and the high-level voltage of the power source switches all the switches including the input switch to the external input side.

As a result, an external signal can be input only by inserting the plug, and when the plug is removed, the signal is switched to the internal signal side.

〔Example〕

 Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram of an embodiment of an automatic input switching device according to the present invention, wherein 1 is an external video signal input terminal, 2 is an external left audio signal input terminal, 3 is an external right audio signal input terminal, Is a video signal switching switch circuit, 5 is a left audio signal switching switch circuit, 6 is a right audio signal switching switch circuit, 70
Is a resistor for impedance matching, 71 is a resistor having a sufficiently larger impedance than the resistor 70, 72 is a capacitor for DC cut, 8 is a video output terminal, 9 is a left audio output terminal, 10 is a right audio output terminal, and 11 is an internal left audio. Signal input, 12 is an internal right audio signal input, 13 is an internal video signal input, and 21, 22, and 23 are control terminals of the switching switch circuits 4, 5, and 6.

In the figure, the external video signal input terminal 1 and the external right audio signal input terminal 3 are in contact with each other in the internal signal input state, and the terminals are separated from each other by inserting a plug. Structure.

The external left audio signal input terminal 2 is connected to the input terminals 1, 3
Unlike this, it does not have a contact that opens and closes when a plug is inserted.

The contacts of the input terminals 1, 2, and 3 are contacts for supplying an external signal input to the switch circuits 4, 5, and 6, respectively, and the contacts are ground terminals.

When a high level is applied to the control terminals 21, 22, and 23, the switching switch circuits 4, 5, and 6 switch from the low terminal L to the high terminal H.

The control terminals 21, 22, and 23 are applied with a high-level voltage from the power supply Vcc via the resistor 71, and are connected in the same pattern.

The external audio signal input terminal 2 is used as an audio input terminal when monaural audio is input.
Has no contacts like other input terminals.

That is, the resistor R2 is connected between the contact of the terminal 1 and the ground, the resistor R1 is connected between the contact and the power supply Vcc, and the contact is connected to the control terminals 21, 22, and 23 of the respective switching switch circuits 4, 5, and 6. ing. The contact of the input terminal 2 is connected to the contact of the input terminal 3.

When no plug is inserted in the input terminal 1, the resistor R1
Has a sufficiently higher impedance than the resistance R2, a low-level voltage is applied to the control terminals 21, 22, and 23 of the switching switch circuits 4, 5, and 6, and each switching contact is connected to the L side. The internal signal inputs 13, 11, 12 are output to the output terminals 8, 9, 10.

On the other hand, when a plug is inserted into the input terminal 1, the contacts are separated from each other. As a result, the power supply Vcc (high level) is applied to the control terminals 21, 22, and 23 of the switching switch circuits 4, 5, and 6. The switch circuits 4, 5, and 6 are switched to the H side shown in the figure.

This allows the external video signal and external audio signal to be
The state is output from 8, 9, and 10. Therefore, by inserting an external signal input plug into the input terminals 1, 2, and 3, the internal signal is automatically switched to the external signal.

Also, when inputting an external video signal input and a monaural external audio signal, the plug for external signal input is inserted only into the input terminal 1 and the input terminal 2 and the video output terminal 8 and the monaural audio output terminal are respectively connected. Is output.

[Effects of the Invention] As described above, according to the present invention, an automatic input switching circuit that automatically switches a signal from an internal signal to an external signal only by inserting an external signal input plug into the external signal input terminal is provided. Can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of an automatic input switching circuit according to the present invention, FIG. 2 is a block diagram showing an example of this type of input switching circuit according to the prior art, and FIG. 3 is input switching according to the prior art. FIG. 9 is a configuration diagram illustrating another example of a circuit. 1 ... external video signal input terminal, 2 ... external left audio signal input terminal, 3 ... external right audio signal input terminal, 4 ... video signal switching switch circuit, 5 ... left audio signal switching switch circuit, 6 ... … Right audio signal switching switch circuit, 70… impedance matching resistor, 71… resistor with sufficiently higher impedance than resistor 70, 72… DC cut capacitor, 8… video output terminal, 9… left audio output Terminals, 10 ...
… Right audio output terminals, 21,22,23 …… Switching switch circuits 4,5,
6 control terminals.

Claims (1)

(57) [Claims] An external video signal input terminal, a left external audio signal input terminal, a right external audio signal input terminal, an external input signal input from each of the external signal input terminals, an internal video signal and a left audio signal, A switching means having a control terminal for switching between a right audio signal and a right audio signal, wherein at least one of the external video signal input terminal, the left external audio signal input terminal, and the right external audio signal input terminal is A contact that separates when a plug is inserted, a resistor for impedance matching connected between the video signal input terminal and ground, and a resistor having a value sufficiently larger than the impedance matching resistor connected between the contact and a power supply. And a configuration in which the contact and the control terminal are connected, and the internal video signal and the left audio signal in the contact state of the contact. Enter the right audio signal, the external video signal input and a left outer audio signal input terminal, an automatic input switching circuit, wherein the switch to the right external audio signal input terminal in response to the deviation of the contact.