JPS6017972Y2 - television receiver - Google Patents

Description

[Detailed Description of the Invention] This invention relates to the structure of a video signal input circuit for a television receiver.

Conventionally, when using a television receiver by connecting the video output of a video tape recorder (hereinafter abbreviated as VTR) to the video signal input terminal, a direct current (DC) signal superimposed on the video signal is transmitted, and the television There was a type that automatically switched the signal source displayed on the receiver screen.

The disadvantage of this type of device is that the V
When you turn on the power switch (SW) of the TR, the display on the television receiver changes to V even though it is not in playback mode.
This has the drawback of causing a malfunction in which it switches to the TR side.

This invention was devised in view of these conventional drawbacks, and is intended to prevent the above-mentioned malfunctions.

FIG. 1 is a circuit diagram showing the configuration of a video signal input circuit of a conventional television receiver.

In the drawings, 1 is an output circuit such as a VTR, 2 is a television receiver, and 3 is a signal transmission wire connecting both the output circuit 1 and the receiver 2.

Further, 11 is an output transistor, 11a is an input terminal of the output transistor 11, and 12 is a resistor of the output transistor 1.
The signal input to 1 is taken out as an emitter follower.

13 is a DC blocking capacitor, 14 is a resistor, 15 is a switch, 16 is a DC power supply, and 17 is an output terminal.

By closing the switch 15, the DC power source 16 is connected to the resistor 1.
4 to be superimposed on the video signal.

In the television receiver 2, 21 is a video signal input terminal, 22 is a DC blocking capacitor, 23 is a video signal amplification transistor, 24 is a transistor, 30 is a switch circuit, and 30a and 30b are each a switch circuit 3.
0 is a switching terminal, 30c is an output terminal, and 40 is an intermediate frequency amplification/detection circuit connected to one end 30b of the switch circuit 30.

50 is a video amplification circuit.

The switch circuit 30 is controlled by the DC voltage at the terminal 21 via the transistor 24, and is connected to the 30a side when the DC voltage is present, and to the 30b side when there is no DC voltage.

This output is displayed as an image on a CRT via an output terminal 30c and an image amplification circuit 50.

In the above connection, when the power switch (not shown in the drawing) is turned on with the switch 15 open in the output circuit 1 of the VTR, the 10B voltage from the transistor 11 charges the capacitor 13.22. Ten voltages are applied to the terminal 21, the transistor 24 is turned on, the relay circuit indicated by the arrow in the figure is activated, and the switch 30 is switched to the 30a side even though it should be connected to the 30b side.

Since this is against the user's wishes and is an undesirable phenomenon, it is necessary to eliminate this drawback from a circuit perspective.

Therefore, the circuit of this invention was devised as a countermeasure to eliminate this drawback.

FIG. 2 is a circuit diagram showing an embodiment of this invention.

The control transistor 24 is connected from the video signal input terminal 21 to the transistor 27 via a differentiating circuit consisting of a capacitor 25 and a resistor 26, and via a discharge circuit consisting of a capacitor 28 and a resistor 29.31, with the transistor 32 interposed therebetween.
It is connected to the.

In such a configuration, the moment a positive voltage is applied to the terminal 21, the transistor 27 is turned on and the capacitor 28 is turned on.
The transistor 32 is on until it is charged and discharged.

Therefore, the charge in the capacitor 22 is instantaneously discharged via the transistor 32.

Therefore, even if the switch 30 malfunctions, the switch 30
It is connected to side b and becomes normal.

Further, the charge of the capacitor 22 is discharged via the transistor 32, and the capacitor 13 is discharged via the transistor 32.
Since the transistor 24 is discharged through the transistor 24, the transistor 24 maintains a cut-off state in a steady state after a transient state when the video output device such as a video tape recorder is turned on.

When the switch 15 is closed, a DC voltage is applied to the terminal 21, and during the rising transition period, the capacitor 28 is charged by the 25°26 differential circuit and the transistor 27.
Transistor 32 is turned on, but when capacitor 28 discharges through resistor 29.30, transistor 32 is turned off, so switch 15 is connected to the base of transistor 24.
, while the DC voltage is applied through the terminal 21, the switch 30 is connected to the 30a side.

As described above, according to this invention, it is possible to prevent signal switching malfunctions that often occur at transient times, and is therefore effective in increasing the reliability of equipment.

For example, while receiving a television broadcast, there are many occasions when a video tape recorder is turned on in an attempt to record what appears to be a broadcast. After switching to the video path, the state returns to the state of receiving television broadcasting, and this invention can prevent such signal switching malfunctions and prevent interference with reception during reception of television broadcasting.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a connection between a conventional video device and a television receiver, and FIG. 2 is a circuit diagram showing a video input section of a television receiver showing an embodiment of this invention. In the figure, 1 is a VTR output circuit, 2 is a television receiver, 3 is an electric wire, 11 is an output transistor, 12 is a resistor, 13 is a capacitor, 14 is a resistor, 15 is a switch,
16 is a power supply, 17 is an output terminal, 21 is a video signal input terminal, 22 is a capacitor, 23 is a video signal amplification transistor, 24 is a transistor, 25 is a capacitor, 26 is a resistor, 27 is a transistor, 28 is a capacitor, 29.31
is a resistor, 32 is a transistor, 30 is a switch circuit, 4
0 is an intermediate frequency amplifier, and 50 is a video amplification circuit. Note that the same reference numerals in each figure represent the same or corresponding parts.

Claims (1)

[Scope of utility model registration request] In a television receiver that may be used in connection with a video output device such as a video tape recorder, the video signal changeover switch is operated by a DC signal that is transmitted superimposed on the video signal from the video output device. A television comprising: a differentiator circuit connected to a video signal input terminal from a video output device; and a circuit that is controlled by the output voltage of the differentiator circuit and grounds the input terminal when the output voltage rises. receiver.