JP2807052B2 - Video signal extraction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial application field" The present invention relates to an SN of a device such as a television camera and a VTR.
The present invention relates to a video signal extracting device that can be used when measuring a ratio.

[Background Art] In a device such as a television camera or a VTR, the smaller the level of noise generated by the device, the better, and can output a video signal with good image quality.

For this reason, a television camera has conventionally taken out a video signal in a state where, for example, a white screen is captured, and measured a noise level superimposed thereon. In a VTR, the noise level of a video signal is measured while a white image tape is being reproduced, and the quality is determined based on the level of the noise level.

FIG. 3 shows an example. In the figure, 1 is a TV camera, VT
A video signal source 2 such as R indicates a video signal extraction device.
The video signal extracting device 2 includes a sample and hold circuit 3 and a timing generating circuit 4.

The timing generation circuit 4 separates and takes out the synchronization signal from the video signal, and outputs a rectangular wave PB shown in FIG. 4B based on the synchronization signal. This rectangular wave PB is given to the sample hold circuit 3. When the square wave PB is at H logic, the switch 3A is turned on and the video signal _VY is directly output to the output terminal 5 through the buffer amplifier 3B. When the square wave PB is at L logic, the sample and hold circuit 3 3
Switch 3A is controlled to be off, then the hold voltage V _C which is charged in the hold capacitor 3C is outputted to the output terminal 5.

Such signal video signal V _Y and the sample hold voltage V _C and a continuous so-called DC level does not vary as shown in FIG. 4 C is taken out to the output terminal 5 in the AC component and amplifies the signal By extracting only the noise level, the noise level can be measured.

[Problem to be Solved by the Invention] In the device shown in FIG. 3, the sample-and-hold circuit 3 is inserted on the transmission path of the video signal, and therefore needs a wide band characteristic capable of sufficiently passing the video signal. .

For this reason, it is necessary to use an expensive amplifying element for the buffer amplifier 3B.

Further, the video signal extracted to the output terminal 5 is affected by the S / N ratio and distortion characteristics of the buffer amplifier 3B itself, so that there is a disadvantage that an error occurs in the measurement of the noise level.

Further, in this conventional device, since the sample and hold timing of the sample and hold circuit 3 is the end point of the video signal section, for example, as shown in FIG.
When Shudengu downhill in V _Y occurs, signal extracted at the output terminal 5 step occurs for each start of the video signal V _Y as shown in FIG. 5 B, which is for example a high-pass filter for As shown in FIG. 5C, a spike noise KC is generated at the stepped portion, which makes it impossible to measure the noise at the beginning of the video signal section. That is, there is a disadvantage that the section where noise can be measured becomes narrow.

SUMMARY OF THE INVENTION It is an object of the present invention to measure the noise in the entire video signal section without being affected by the shading of the video signal, and to measure the frequency characteristics and distortion of the buffer amplifier constituting the sample and hold circuit. It is an object of the present invention to provide a video signal extraction device which is not affected by characteristics.

[Means for Solving the Problems] In the present invention, a sample and hold circuit that samples and holds the level of a video signal at a start point of a video signal section, a video signal is selected in a video signal section, and a sample and hold circuit is selected in a synchronization signal section And a switching circuit for selecting and outputting a hold voltage, thereby forming a video signal extracting device.

According to the configuration of the present invention, since the sample and hold circuit samples and holds the level of the start point of the video signal section, even if shading occurs in the video signal section, there is no step at the start point of the video signal section.

That is, the step occurs at the end point of the video signal section. Even if spike noise occurs at the end point of the video signal section due to this step, the measurement of the noise in the video signal section is not affected at all since the rear of the spike noise is the synchronization signal section.

Therefore, according to the present invention, noise can be measured over the entire area of the video signal section.

FIG. 1 shows an embodiment of the present invention.

In the present invention, a sample and hold circuit 3 that samples and holds the level of a video signal at the start point of the video signal section, a video signal is selected during the video signal section, and a hold voltage of the sample and hold circuit 3 is selected during the synchronization signal section. The switching circuit 6 constitutes a video signal extraction device.

That is, the switching circuit 6 can be constituted by, for example, an analog switch. The video signal source 1 is connected to the contact A, and the output terminal of the sample and hold circuit 3 is connected to the contact B.

The switching circuit 6 is supplied with the rectangular wave PB shown in FIG. 2C from the timing generation circuit 4, and the switching control is performed by the rectangular wave PB. That is, this example shows a case where the switching circuit 6 is switched to the contact A when the rectangular wave PB is at the H logic, and is switched to the contact B when the rectangular wave PB is at the L logic.

The clock PC shown in FIG. 2B is given from the timing generation circuit 4 to the sample hold circuit 3, and the video signal V _Y
Sample and hold the DC level of the video signal at the start point of Figure 2 D shows the sample hold output voltage V _C.

With this configuration, the signal extracted from the switching circuit 6 to the output terminal 5 is such that the video signal _VY is extracted during the video signal period as shown in FIG. hold voltage V _C is extracted for.

Therefore if there is Shedengu the video signal V _Y video signal V _Y extracted to the output terminal 5 step occurs in the end point of the video signal section.

Even if a spike noise KC (FIG. 2F) occurs in a subsequent high-pass filter (not particularly shown) due to this step, it is a synchronization signal section after the spike noise KC, so it waits until the spike noise KC is sufficiently attenuated. However, there is no influence on the measurement of noise included in the video signal.

As described above, according to the present invention, the video signal _VY is extracted at the start point of the video signal without generating a step at which the DC level suddenly changes, and the step since but occurs, it is possible to perform measurement of noise from the start point to the end point of the video signal V _Y.

Therefore, the SN of a video signal source such as a TV camera or VTR
The ratio can be measured accurately.

Further, since the video signal _VY is extracted without passing through the sample and hold circuit 3, it is not affected by the frequency characteristics and distortion characteristics of the sample and hold circuit. Further, the influence of noise generated by the sample and hold circuit 3 can be removed.
Therefore, also in this respect, the measurement accuracy of the noise can be improved.

The buffer amplifier 3B constituting the sample-and-hold circuit from the video signal V _Y does not pass through the sample hold circuit 3 can use an inexpensive device. Therefore, cost reduction can be expected.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an embodiment of the present invention, FIG. 2 is a waveform diagram for explaining this operation, FIG. 3 is a connection diagram for explaining a conventional technique, and FIG. FIG. 5 is a waveform diagram for explaining the operation of the technology, and FIG. 5 is a waveform diagram for explaining the disadvantages of the conventional technology. 1: video signal source, 2: video signal extraction device, 3: sample and hold circuit, 4: timing generation circuit, 6: switching circuit.

Claims (1)

(57) [Claims] 1. A sample and hold circuit which samples and holds a DC level of a video signal at a start point of a video signal section; and B. a video signal is selected in a video signal section and the sample and hold circuit is held in a synchronization signal section. A video signal extraction device comprising: a switching circuit that selects and outputs a voltage.