JPS62299Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a video power detection circuit used for detecting power in an output power meter or AGC unit in a television broadcasting device.

Power detection in a television broadcasting apparatus that directly amplifies a television signal in which a video signal and an audio signal are multiplexed has been conventionally performed as shown in FIG. That is, the signal taken out from the output line 1 via the coupler 2 is supplied to the audio component removal filter 3 to remove the audio component, and then supplied to the tripeak value detection circuit 4.

The output power of a television broadcasting device is usually defined by the video synchronous peak power because the video level changes depending on the screen, and therefore the peak value detection circuit 4 detects the video synchronous peak power.

Now, depending on the channel handled by the television broadcasting equipment, the audio component removal filter 3 passes only the carrier wave carrying the video signal component of that channel and removes the carrier wave carrying the audio signal. sexuality is required. Therefore, the filter 3 has a large shape and is expensive. Another drawback was that it could not be manufactured unless the output channel of the television broadcasting device was determined.

Therefore, an object of the present invention is to provide a video power detection circuit that can be used regardless of the type of channel used and does not use the conventional expensive audio component removal filter.

According to the present invention, there are provided a coupler that is coupled to an output line and takes out a part of the output, an envelope detector that inputs the output from the switch that interrupts the output from the coupler at a timing different from the position of the synchronization signal, and an envelope detector that takes out a part of the output. Video power detection comprising a filter with an attenuation range of 4.5 MHz for removing audio components from the output of the detector, a peak clamp circuit installed behind the filter, and a peak value detector installed after the peak clamp circuit. A circuit is obtained.

Next, the present invention will be described in detail with reference to the drawings showing an embodiment of the present invention. FIG. 2 is a diagram showing an embodiment of the present invention, and FIG. 3 is a waveform diagram of each part in FIG. In the figure, part of the output taken from line 1 by coupler 2 is sent to switch 5 and interrupted at a different position from the synchronizing signal. 3a shows the output taken from the combiner 2, and b shows the output interrupted by the switch 5. FIG. a, b
, the audio component is superimposed on the video signal and synchronization signal component _S1 . The output from the switch 5 is supplied to an envelope detector 6 and a video/synchronization signal is extracted. The waveform at this time is shown as shown in FIG. 3c, in which the audio signal _S3 of 4.5 MHz, which is the difference between the audio carrier frequency and the video carrier frequency, is superimposed on the video/synchronization signal.

The output of the envelope detector 6 is sent to a filter 7, where the 4.5MHz FM audio signal _S3 is removed. Regardless of the type of channel, this filter 7 can be configured with a low-pass filter having an attenuation range of 4.5MHz, which is often used in equipment that handles the television standard system in Japan, and is extremely rational. The output of the filter 7 {Fig. 3 d} is the clamp circuit 8
, and the bottom p of the waveform is clamped to a constant voltage. The output of the clamp circuit 8 is as shown in FIG. 3e. The output of the clamp circuit 8 is sent to the peak value detection circuit 9, and a detection output corresponding to the peak value, as shown in FIG. 3f, is obtained.

To time the interruption in switch 5 in FIG. 2, the signal from line 1 is sent to a sync signal separator 10, where the sync signal is extracted.
The phase is adjusted and sent to switch 5. Note that when the clamping in the clamping circuit 8 is a pulse clamping method, the output from the synchronizing signal separation circuit 10 is also supplied to the clamping circuit 8.

In the embodiment described above, the peak value was detected by clamping the lowest point p in FIG. 3 d, but the peak value was detected by clamping the synchronous peak q in FIG. Of course, the level may be detected by a peak value detection circuit.

As explained above, according to the present invention, the same circuit can be used even if the channel frequency changes, so the effect is great.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional video power detection circuit, Figure 2 is a diagram showing an embodiment of the present invention, and Figure 3 is a diagram showing a second embodiment of the present invention.
Waveform diagram of each part of the figure.

Claims (1)

[Scope of utility model claims] coupled to the output line of the television broadcaster,
A coupler that takes out a part of the output, a switch that interrupts the output from the coupler at a timing different from the position of the synchronization signal, an envelope detector that inputs the output from the switch, and an audio component from the output of the envelope detector. A video power detection circuit comprising: a filter having an attenuation range at 4.5 MHz for removing 4.5 MHz; a peak clamp circuit provided behind the filter; and a peak value detector provided after the peak clamp circuit.