JP2000092346A - Video output device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the video output device that reduces a drive current of a video output means that detects presence/absence of connection of a transmission cable and supplies an output video signal to a video output terminal not connecting to the transmission cable. SOLUTION: The video output device is provided with a video signal output means 3 that applies impedance conversion to an input video signal 2 and outputs the result, an output impedance setting means 5 that matches an output impedance of the video signal output means 3 with a characteristic impedance of a transmission cable connecting externally with a video output terminal 7 and outputs externally an output video signal 4b, a video output detection means 10 that detects whether or not the output video signal 4b is sent externally based on an amplitude level difference between an output signal 4a of the video signal output means 3 and the output video signal 4b of the output impedance setting means 5, and a control means 8 that controls a drive current of the video signal output means 3 based on a detection signal from the video signal detection means 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video output device for converting an input video signal into an impedance signal so as to efficiently transmit the input video signal to an externally connected transmission cable and outputting the converted signal. The present invention relates to a video output device which controls a video signal output drive current to save power.

[0002]

2. Description of the Related Art Conventional video output devices include, for example, a VTR (video tape recorder) for recording and reproducing video signals,
It is used in video output systems such as video signal generators. Although a plurality of video output terminals are provided in a video output system such as a VTR or a video signal generator, it is often the case that all of the terminals are not used at the same time.

As shown in FIG. 12, a conventional video output device for one system of video output terminals comprises a video signal output means 4.
1 and an output impedance setting means 5. The input video signal 2 input from the video input terminal 1 is
The impedance is converted by the video signal output means 41 and output to the output impedance setting means 5 as an output signal 4a. The video signal output means 41 has a circuit configuration as shown in FIG. Input video signal 2 is input terminal 5
The bias is applied to the transistor 61 whose collector is grounded by the resistors 59 and 60. Transistor 6
At 1, after the emitter current value is set by the resistor 62 and the DC component is removed by the capacitor 63, the output signal 64 a is output from the output terminal 64.

The output impedance setting means 5 converts the output impedance of the video signal output means 41 into an impedance having the same value as the characteristic impedance of a transmission cable (not shown) connected to the video output terminal 7, and outputs the output signal 4a. To the video output terminal 7 as the output video signal 4b.

As a transmission cable connected to the video output terminal 7 when transmitting the output video signal 4b, a coaxial cable having a characteristic impedance of several tens of ohms is generally widely used.

[0006]

However, the conventional video output device cannot determine whether or not a transmission cable is connected to the video output terminal 7, as shown in FIG.

In this video output device, the transmission cable connected to the video output terminal 7 when transmitting the output video signal 4b has a low characteristic impedance of several tens of ohms.
The output drive current of the video signal output means 41 of the single power supply specification is usually several mA to several tens mA per system of the video signal output means 41 irrespective of the connection of the transmission cable, that is, regardless of the presence of the AC load. The DC drive current always flows, and the power is unnecessarily consumed by constantly supplying the DC drive current to the video output terminal 7 to which the transmission cable is not connected among the plurality of video output terminals. is there.

In addition, since the video output terminal cannot instantaneously determine whether or not the transmission cable connected to the video output terminal 7 is properly connected, there is a problem that a trouble such as a disconnection of the transmission cable cannot be easily found. .

For these reasons, it is required to detect the presence or absence of the connection of the transmission cable, to save the power of the video output device, and to detect a trouble such as disconnection of the transmission cable at an early stage. The present invention detects the presence or absence of connection of a transmission cable, reduces the drive current of a video signal output unit that supplies an output video signal to a video output terminal that is not connected to the transmission cable, and prevents transmission trouble of the video signal beforehand. It is an object to provide a video output device.

[0010]

According to the present invention, there is provided a video output apparatus comprising: a video signal output means for converting an input video signal into impedance and outputting the video signal; and a characteristic of a transmission cable to which an output impedance of the video signal output means is externally connected. Output impedance setting means for externally outputting an output signal from the video signal output means as an output video signal in accordance with impedance; and an amplitude level between an output signal of the video signal output means and an output video signal of the output impedance setting means. Video output detecting means for detecting whether or not an output video signal is transmitted from the output impedance setting means to the outside based on the difference.

According to the present invention, it is possible to obtain a video output device capable of detecting whether or not a transmission cable is connected.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention according to claim 1 of the present invention provides a video signal output means for converting an input video signal into an impedance and outputting the converted output signal, and a transmission cable to which the output impedance of the video signal output means is externally connected. Output impedance setting means for externally outputting an output signal from the video signal output means as an output video signal in accordance with the characteristic impedance of the output signal, and an output signal of the video signal output means and an output video signal of the output impedance setting means. A video output device provided with video output detection means for detecting whether or not an output video signal is transmitted from the output impedance setting means to the outside based on the amplitude level difference; and Can be detected.

According to a second aspect of the present invention, there is provided a video signal output means for converting an input video signal into an impedance and outputting the converted output video signal, and converting the output impedance of the video signal output means into a characteristic impedance of a transmission cable connected to the outside. An output impedance setting unit adapted to externally output an output signal from the video signal output unit as an output video signal, and the output based on a change in a DC voltage component superimposed on the output video signal of the output impedance setting unit. A video output detecting means for detecting whether or not an output video signal is transmitted from the impedance setting means to the outside, wherein the transmission cable is connected only with the output video signal of the output impedance setting means. Can be detected.

According to a third aspect of the present invention, in the first or second aspect, control means for controlling a drive current of the video signal output means based on a detection signal from the video output detection means is provided. It is possible to detect the presence or absence of the connection of the transmission cable and reduce the drive current of the video signal output means for supplying the output video signal to the video output terminal to which the transmission cable is not connected.

According to a fourth aspect of the present invention, there is provided a display means for displaying whether or not a transmission cable in a proper use state is connected to an output impedance setting means based on a detection signal from a video output detection means. Claim 1 provided with
Alternatively, a video output device according to claim 2 can be used to instantly grasp troubles such as poor contact or disconnection of a transmission cable, and prevent a video signal transmission trouble from occurring.

According to a fifth aspect of the present invention, the image output detecting means is provided with a processing means for performing a predetermined operation when the image output detecting means detects that the transmission cable is connected to the output impedance setting means. The video output device according to item 2, wherein the drive current of the processing means when the transmission cable is not connected can be reduced.

According to a sixth aspect of the present invention, there is provided the video output device according to the fifth aspect, wherein the processing means is an on-screen generator for superimposing character information on the video signal. The drive current of the on-screen generator when not connected can be reduced.

Hereinafter, a video output device according to the present invention will be described based on specific embodiments. (Embodiment 1) As shown in FIG. 1, a video output device according to a first embodiment of the present invention includes a video signal output unit 3 that converts an input video signal 2 into impedance and outputs the input video signal 2; Output impedance setting means 5 for externally outputting the output signal 4a from the video signal output means 3 as the output video signal 4b by adjusting the output impedance to the characteristic impedance of the transmission cable externally connected to the video output terminal 7, Video output detection for detecting whether or not the output video signal 4b is transmitted from the output impedance setting means 5 to the outside based on the amplitude level difference between the output signal 4a of the means 3 and the output video signal 4b of the output impedance setting means 5. Means 10 and control for controlling the drive current of video signal output means 3 based on the detection signal from video output detection means 10 It is provided with a stage and 8.

The video signal output means 3 has a circuit configuration as shown in FIG. Input video signal 2 is input terminal 1
The bias is applied to the base of the transistor 17 whose collector is grounded by the resistors 15 and 16. In the transistor 17, after the first emitter current value is set by the resistor 18 and the DC component is removed by the capacitor 21, the output signal 14 is output from the output terminal 14. Further, a control signal 9 from a control means 8 described later is input to an input terminal 13, and
When the control signal 9 is at the Hi level, the transistor 20 with a built-in resistor is turned on, a current flows through the resistor 19, and the second emitter current value of the transistor 17 is set. Second
The values of the resistors 18 and 19 are set so that the emitter current value becomes larger than the first emitter current value. When the control signal 9 is not output, the built-in resistor type transistor 20 is turned off, no current flows through the resistor 19, and the second emitter current value is not set.

The output impedance setting means 5 has a circuit configuration as shown in FIG. The output signal 4a is input to the input terminal 21, and after the DC component is removed by the capacitor 23 through the resistor 22 having the same value as the characteristic impedance value of the transmission cable to be connected to the video output terminal 7, the output signal 24a The output video signal 4b is output.

The video output detecting means 10 has a circuit configuration as shown in FIG. The output signal 4a is input terminal 25
The output video signal 4b is input to the input terminal 26. The reference DC potential is determined in advance by the resistors 28 and 29 and the capacitor 30 and the diodes 31 and 3 are set.
2 to each of the anodes. The resistor 35 is connected to the cathode of the diode 31 and sets the forward current of the diode 31. Similarly, the resistor 36 sets the forward current of the diode 32, and the forward current values of the diode 31 and the diode 32 are substantially equal.

The output signal 4a input to the input terminal 25 passes through the capacitor 33, and is output by the diode 31 to the output signal 4a.
Is reproduced (hereinafter referred to as a sync tip clamp) and input to the plus terminal of the comparator 37. Similarly, the output video signal 4 input to the input terminal 26
b is passed through the capacitor 34, is sync-tip clamped by the diode 32, and is input to the minus terminal of the comparator 37. The output signal 4a and the output video signal 4b that have been subjected to the sync tip clamp processing are compared by the comparator 37 based on the DC voltage component of the same sync tip.

When the output signal 4a is larger than the output video signal 4b, the output of the comparator 37 becomes Lo level, the transistors 39 are turned on by the resistors 40 and 38, and the Hi level is output to the output terminal 27.

In the comparator 37, the output signal 4
a is equal to the output video signal 4b, or
When a is smaller than the output video signal 4b, the output becomes Hi level, the transistor 39 is turned off by the resistor 38, and the output terminal 27 becomes high impedance.

FIGS. 5 and 6 show waveforms in each state of the input terminal of the comparator 37. FIG. Waveform 4 of output signal 4a
2 and the waveform 43 of the output video signal 4b are aligned with the sync tip potential 45.

When nothing is connected to the video output terminal 7 and no video signal flows to the output impedance setting means 5, for example, when the output signal 4a has the waveform 42 shown in FIG. As shown in FIG. 5B, the waveform 43 of 4b is a waveform aligned with the sync tip potential 46, and the waveform 42 and the waveform 43 are equal.

On the other hand, when the transmission cable is connected to the video output terminal 7, since the video signal flows through the output impedance setting means 5, the waveform 44 of the output video signal 4b is shown in FIG. As shown, the waveform has a waveform whose video amplitude level is attenuated by about 6 dB while being kept at the sync tip potential 46.

Here, the operation of the video output device will be specifically described. The input video signal 2 is input to the video signal output means 3 via the video input terminal 1, and the video signal output means 3 converts the input video signal 2 to low impedance and outputs an output signal 4a.

The output impedance setting means 5 receives the output signal 4a from the video signal output means 3 and has a required impedance, that is, a transmission cable (not shown) to be connected to the video output terminal 7. After being converted into the characteristic impedance value, the output video signal 4 b is output from the video output terminal 7.

The output signal 4a and the output video signal 4b are also input to the video output detection means 10, and the video output detection means 10 sets the output signal 4a and the output video signal 4b based on the sync chip level of the video signal. The video signal levels are compared to detect whether the output video signal 4b is transmitted from the output impedance setting means 5 to the outside, and the detection signal 11 is output to the control means 8.

For example, when a transmission cable is connected to the video signal output terminal 7, a video signal current flows through the output impedance setting means 5, and the output signal 4a attenuates the video signal level by about -6 dB from the output video signal 4b, it is detected. Signal 11
Output Hi level. Conversely, when the transmission cable is not connected to the video output terminal 7, the output signal 4a
And the output video signal 4b have substantially the same value, and the detection signal 1
1 is not output.

In the control means 8, the input detection signal 11
The control signal 9 is output to the video signal output means 3 based on When the transmission cable is connected to the video signal output terminal 7, the video signal output means 3 increases the DC drive current based on the control signal 9 and outputs the output video signal 4b.
Is transmitted further without distortion, so that the impedance is further reduced.

The transmission cable is connected to the video signal output terminal 7.
Is not connected, the control signal 9 is not input, and the video signal output means 3
Is attenuated to make only the minimum necessary DC drive current, and the power consumption of the video signal output means 3 is suppressed.

With this configuration, it is possible to detect whether or not the transmission cable is connected to the video signal output terminal 7 with a normal load impedance, and to output the output video signal 4b to the video output terminal 7 not connected to the transmission cable. The drive current of the supplied video signal output means 3 can be reduced, and the power consumption of the video output device can be reduced.

(Embodiment 2) As shown in FIG. 7, a video output device according to a second embodiment of the present invention is similar to the video signal output unit 3 according to the first embodiment except that
In addition, the control means 8 is replaced with the display means 6, respectively.

The display means 6 is adapted to display, based on the detection signal 11 from the video output detection means 10, whether or not a transmission cable in an appropriate use state is connected to the output impedance setting means 5. . The display means 6 has a circuit configuration, for example, as shown in FIG. The detection signal 11 is supplied to an input terminal 54.
The input terminal 54 is connected to the anode of an LED (light emitting diode) 56 through a resistor 55, and the cathode of the LED 56 is grounded.

Here, the operation of the video output device will be specifically described. The input video signal 2 is input to the video signal output unit 41 via the video input terminal 1, and the video signal output unit 41 converts the input video signal 2 to low impedance and outputs an output signal 4a.

The output signal 4a is input to the output impedance setting means 5 and converted into a required impedance, that is, a characteristic impedance value of a transmission cable to be connected to the video output terminal 7, and then converted to a video output terminal. 7
Then, an output video signal 4b is output.

The output signal 4a and the output video signal 4b are also input to the video output detecting means 10, and the video output detecting means 10 sets the output signal 4a and the output video signal 4b based on the sync chip level of the video signal. The video signal levels are compared to detect whether the output video signal 4b is transmitted from the output impedance setting means 5 to the outside, and the detection signal 11 is output to the display means 6. When a transmission cable is connected to the video output terminal 7, a Hi-level detection signal 11 is output to the display means 6, and when no transmission cable is connected to the video output terminal 7, the detection signal 11 is output to the display means 6. Not done.

As shown in FIG. 8, the display means 6 turns on the LED 56 when the Hi-level detection signal 11 from the video output detection means 10 is input.
When the transmission cable is not supplied, the LED 56 is turned off and the output impedance setting means 5 indicates whether or not a transmission cable in an appropriate use state is connected.

With this configuration, it is possible to detect whether or not a transmission cable is connected to the video signal output terminal 7, and to visually check whether or not the transmission cable is connected by displaying the display means 6. This makes it possible to instantly grasp troubles such as contact failure and disconnection of the transmission cable, and prevent transmission troubles of video signals.

(Embodiment 3) As shown in FIG. 9, an image output apparatus according to Embodiment 3 of the present invention uses the on-screen generator means 47 instead of the display means 6 of Embodiment 2 described above.
Is replaced by

This on-screen generator means 47
Is for superimposing character information on a video signal. Here, the operation of the video output device will be specifically described.

The input video signal 2 is input to the video signal output means 41 via the video input terminal 1, and the video signal output means 41 converts the input video signal 2 to low impedance and outputs an output signal 4a.

The output signal 4a is input to the output impedance setting means 5 and converted into a required impedance, that is, a characteristic impedance value of a transmission cable to be connected to the video output terminal 7, and then converted to a video output terminal. 7
Then, an output video signal 4b is output.

The output signal 4a and the output video signal 4b are also input to the video output detecting means 10, and the video output detecting means 10 sets the output signal 4a and the output video signal 4b based on the sync chip level of the video signal. The video signal levels are compared to detect whether or not the output video signal 4b is transmitted from the output impedance setting means 5 to the outside.
Outputs 1. When a transmission cable is connected to the video output terminal 7, the Hi-level detection signal 11 is output to the on-screen generator 47, and
Is not connected to the transmission cable, the detection signal 11 is not output to the on-screen generator 47.

The on-screen generator 47 turns on / off the power supply for driving the on-screen generator 47 based on the detection signal 11 to supply / stop the power supply. Specifically, the detection signal 11
Is Hi level, the power supply is turned on, the power is supplied, the on-screen superimposition function which is character information on the video signal is activated, and when the detection signal 11 is not supplied, the power supply is turned off and the power supply is stopped and turned on. The screen superimposition function is configured to stop.

With this configuration, it is possible to detect whether or not a transmission cable is connected to the video signal output terminal 7. When the transmission cable is not connected and the on-screen superimposition function is not required, the on-screen generator can be used. The drive current of the means 47 can be reduced,
Power saving of the video output device can be achieved.

In the third embodiment, when the video output detecting means 10 detects that the transmission cable is connected to the output impedance setting means 5, a specific on-screen generator means 47 is used as a processing means for performing a predetermined operation. However, other than the on-screen generator means 47, even if the processing means uses an active element which does not need to operate when the transmission cable is not connected, the power can be supplied / stopped, and the same effect can be obtained. Have.

(Embodiment 4) A video output device according to a fourth embodiment of the present invention is such that the video output detection means 10 of the first embodiment is replaced with a video output detection means 65 as shown in FIG. is there.

The video output detecting means 65 transmits the output video signal 4b to the outside from the output impedance setting means 5 based on the change of the DC voltage component superimposed on the output video signal 4b of the output impedance setting means 5. Is configured to detect if Specifically, the video output detecting means 65 is configured as a circuit as shown in FIG. The output video signal 4b is input to an input terminal 48, and a power supply voltage is supplied through a resistor 49. The value of the resistor 49 is set to a value sufficiently larger than the characteristic impedance of the transmission cable to be connected.

When the transmission cable is not connected to the video output terminal 7, the potential of the input terminal 48 is equal to the power supply voltage, the transistor 51 is turned off by the resistors 52 and 50, and the output terminal 53 is opened.

When a load resistance is connected to the video output terminal, the DC potential of the input terminal 48 is GN due to the effect of the load resistance.
The potential becomes the D potential, the transistor 51 is turned on by the resistors 52 and 50, and the output terminal generates the Hi level and is output as the detection signal 11.

Here, the operation of this video output device will be specifically described. The input video signal 2 is input to the video signal output unit 3 via the video input terminal 1, and the video signal output unit 3 converts the input video signal 2 to low impedance and outputs an output signal 4a.

The output signal 4a is input to the output impedance setting means 5 and converted into a required impedance, that is, a characteristic impedance value of a transmission cable to be connected to the video output terminal 7, and then converted to a video output terminal. 7
Then, an output video signal 4b is output.

The output video signal 4b is also input to the video output detection means 65. The video output detection means 65 detects a DC voltage component superimposed on the video signal of the output video signal 4b, and outputs the detection signal 11b. Is output to the control means 8.

In the control means 8, the input detection signal 11
The control signal 9 is output to the video signal output means 3 based on With this configuration, it is possible to detect whether or not the transmission cable is connected to the video signal output terminal 7 with a normal load impedance, and to supply the output video signal 4b to the video output terminal 7 not connected to the transmission cable. The drive current of the signal output means 3 can be reduced, and the power consumption of the video output device can be reduced.

In the fourth embodiment, when the display means 6 of the second embodiment is provided instead of the control means 8, the transmission cable is displayed by the display of the display means 6 as in the second embodiment. It is possible to visually check whether or not the connection is established, and it is possible to instantly grasp troubles such as poor contact or disconnection of the transmission cable.

In the fourth embodiment, when the processing means of the third embodiment is provided in place of the control means 8, the power supply of the processing means is supplied / stopped as in the third embodiment. Can be.

[0060]

As described above, according to the video output apparatus of the present invention, a video signal output means for converting an input video signal into impedance and outputting the output signal, and a transmission cable for externally connecting the output impedance of the video signal output means. Output impedance setting means for externally outputting an output signal from the video signal output means as an output video signal in accordance with the characteristic impedance of the output signal, and an output signal of the video signal output means and an output video signal of the output impedance setting means. By providing the video output detecting means for detecting whether or not the output video signal is transmitted from the output impedance setting means to the outside based on the amplitude level difference, it is possible to detect the connection of the transmission cable. .

The video output detecting means detects whether or not the output video signal is transmitted from the output impedance setting means to the outside based on a change in the DC voltage component superimposed on the output video signal of the output impedance setting means. In this case, the presence or absence of the connection of the transmission cable can be detected.

In the case where control means for controlling the drive current of the video signal output means based on the detection signal from the video output detection means is provided, the video output when the transmission cable is not connected and there is no load in AC. The drive current of the video signal output means for supplying the output video signal to the terminal can be reduced,
Power consumption can be suppressed, and a video output device that saves power can be obtained.

In the case where the output impedance setting means is provided with a display means for displaying whether or not a transmission cable in an appropriate use state is connected based on a detection signal from the video output detection means, contact failure of the transmission cable may be caused. Troubles such as disconnection and disconnection can be grasped instantaneously, and transmission troubles of video signals can be prevented.

When the video output detecting means is provided with a processing means for performing a predetermined operation when it detects that the transmission cable is connected to the output impedance setting means, the transmission cable is not connected and the predetermined operation is required. The drive current of the processing means when not performed can be reduced.

Specifically, when this processing means is an on-screen generator for superimposing character information on a video signal, the drive current of the on-screen generator when the transmission cable is not connected can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a video output device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a video signal output unit according to the first embodiment;

FIG. 3 is a circuit diagram of an output impedance setting unit according to the first embodiment;

FIG. 4 is a circuit diagram of a video output detection unit according to the first embodiment;

FIG. 5 is a waveform chart of the video output detection means when the transmission cable is not connected according to the first embodiment.

FIG. 6 is a waveform chart of a video output detection unit when the transmission cable is connected according to the first embodiment.

FIG. 7 is a block diagram showing a video output device according to a second embodiment of the present invention.

FIG. 8 is a circuit diagram of a display unit according to the second embodiment.

FIG. 9 is a block diagram showing a video output device according to a third embodiment of the present invention.

FIG. 10 is a block diagram showing a video output device according to a fourth embodiment of the present invention.

FIG. 11 is a circuit diagram of a video output detection unit according to the fourth embodiment.

FIG. 12 is a block diagram showing a conventional video output device.

FIG. 13 is a circuit diagram of a conventional video signal output unit.

[Explanation of symbols]

 Reference Signs List 1 video input terminal 2 input video signal 3 video signal output means 4a output signal 4b output signal 6 display means 7 video output terminal 8 control means 9 control signal 10 video output detection means 11 detection signal 47 on-screen generator means 65 video output detection means

Claims (6)

[Claims] A video signal output means for converting an input video signal into an impedance and outputting the converted video signal; and adjusting an output impedance of the video signal output means to a characteristic impedance of an externally connected transmission cable. Output impedance setting means for externally outputting an output signal as an output video signal; and, based on a difference in amplitude level between an output signal of the video signal output means and an output video signal of the output impedance setting means, an output from the output impedance setting means. And a video output detecting means for detecting whether or not an output video signal is transmitted to the video output device. 2. A video signal output means for converting an input video signal into an impedance and outputting the converted output video signal, and an output impedance of the video signal output means adapted to a characteristic impedance of an externally connected transmission cable. Output impedance setting means for externally outputting an output signal as an output video signal; and, based on a change in a DC voltage component superimposed on the output video signal of the output impedance setting means, an output video signal is output from the output impedance setting means to the outside. A video output device provided with video output detection means for detecting whether or not transmission is being performed. 3. The video output device according to claim 1, further comprising control means for controlling a drive current of the video signal output means based on a detection signal from the video output detection means. 4. An output impedance setting means for displaying whether or not a transmission cable in an appropriate use state is connected based on a detection signal from the video output detection means. 3. The video output device according to 1. 5. The video output apparatus according to claim 1, further comprising processing means for performing a predetermined operation when the video output detection means detects that the transmission cable is connected to the output impedance setting means. 6. The video output device according to claim 5, wherein the processing means is an on-screen generator for superimposing character information on the video signal.