JPS6133502B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a jitter measuring device that measures a reference signal that displays a predetermined jitter standard value, etc., and a jitter display signal that magnifies and displays a jitter component included in a video signal. It is an object of the present invention to provide a device that can very easily measure a jitter component included in a video signal without requiring any skill by displaying it on a reproduced image in a predetermined format on a receiver.

Generally, when transmitting a video signal, jitter (also referred to as a jitter component) occurs. As used herein, "jitter" refers to the lateral wobbling of an image in a receiver of defined characteristics, and its units are time units (usually μsec) calibrated by horizontal scanning time. Further, the predetermined characteristic means that the characteristic of the horizontal scanning AFC oscillator has a reference weighting curve characteristic described later.

However, since the jitter generated during the recording and reproducing process is relatively small on the reproduced image, it has been extremely difficult to measure it in the past. Further, since jitter depends on the AFC characteristics of commercially available television receivers, jitter may be relatively large or not so much of a problem depending on the television receiver. Conventionally, jitter meters and the like that display jitter on a meter have been known as devices for measuring such jitter.

However, conventional measuring instruments such as jitter meters
Since the jitter component contained in the playback video signal from a magnetic recording/playback device using multiple playback heads is measured using the horizontal synchronization signal of the playback video signal, the output switching point of the playback head, that is, the switching point The disadvantage is that the phase of the reproduced horizontal synchronizing signal changes at certain points due to tape elongation, dimensional errors in the drum diameter, tape compatibility, etc., resulting in a large amount of noise. Another drawback is that it is affected by the equalization pulse of the video signal containing jitter to be measured.

The present invention eliminates the above-mentioned drawbacks, and an embodiment thereof will be described below with reference to the drawings.

FIG. 1 shows a schematic connection diagram when using the apparatus of the present invention to measure jitter components generated during the recording and reproducing process of video signals by a VTR. In the figure, reference numeral 1 denotes a VTR, and a video signal input to its input terminal 2 is recorded on a magnetic tape (not shown) by the VTR 1. The video signal reproduced from the magnetic tape is supplied from the output terminal 3 to the input terminal 5 of the jitter measuring device 4 of the present invention. Here, a jitter component is included in the reproduced video signal during the recording and reproduction process. Note that the reproduced video signal output of the VTR 1 may be an RF signal that has been RF converted.

As will be described later, the jitter measuring device 4 has a configuration as shown in the block diagram of FIG. In addition to generating and outputting a jitter display signal, it also generates and outputs a reference signal that serves as a reference for jitter measurement, and these signals are sent from an output terminal 6 to a television receiver 7.
is supplied to input terminal 8 of. Here, the input terminal 8 is a video input terminal or an antenna input terminal of the television receiver 7, depending on the type (bandwidth) of the reproduced video signal.

The television receiver 7 has a predetermined reference weighting characteristic, which will be described later, and includes an image based on the reproduced video signal, a white line J representing jitter that is an enlarged version of the actual jitter based on the jitter display signal, and two lines based on the reference signal. White lines (hereinafter referred to as standard white lines) A and B are reproduced and displayed. Now, the jitter white line J is measured by the jitter measuring device 4 to determine the actual value of the jitter white line J.
If jitter magnified 10 times is to be displayed, the interval between two stationary reference white lines A and B is set to 10 times the jitter standard value. Therefore, in the case of Fig. 1, the jitter white line J, which varies according to the jitter, is between the standard white lines A and B, so the measurer can very easily determine that the VTR 1 satisfies the predetermined jitter standard. Can be distinguished. Furthermore, the jitter value can be measured by measuring in units of time calibrated with the horizontal scanning line length of the television receiver 7 and reducing this to 1/10.

Note that when measuring jitter, do not measure jitter when there is a particular lack of stability, such as immediately after starting playback or immediately after the screen shakes significantly due to scratches on the tape, etc.

Next, the present invention will be explained in more detail.

FIG. 2 shows a block system diagram of an embodiment of the apparatus of the present invention. In the figure, 9 is a video signal input terminal containing jitter, and the video signal input from this is supplied to a mixer 10, which will be described later, and is also sequentially passed through a synchronization signal separation circuit 11 and a horizontal synchronization signal separation circuit 12. Only the horizontal synchronizing signal is supplied to the monostable multivibrator 13. Note that the signal that enters the input terminal 9 is not limited to a VTR playback video signal, but can be any signal that contains jitter.
A signal other than the VTR playback signal may be used.

The monostable multivibrator 13 is provided to remove equalization pulses so as not to malfunction due to equalization pulses in the video signal, and applies its output pulses to the phase comparator 14 together with monostable multivibrators 19 and 20, which will be described later. . The phase comparator 14 constitutes a phase locked loop (PLL) together with the voltage controlled oscillator 15, and the output oscillation frequency of the oscillator 15 and the output pulse of the monostable multivibrator 13 (that is, the horizontal synchronization signal containing jitter) The jitter component is detected and output by comparing the phase with the The output of this phase comparator 14 is applied as a control voltage to a voltage controlled oscillator 15, and is also supplied to a frequency correction circuit 16.

The frequency correction circuit 16 is a television receiver.
Since the degree to which jitter components appear differs depending on the difference in AFC characteristics, the frequency is corrected as shown in the reference weighting curve shown in FIG. Third
In the figure, the horizontal axis represents the frequency, and the "1" on the vertical axis indicates, for example, that when the input signal has a frequency fluctuation of 1% _pp , the screen shake will be 1% _pp of the length of one horizontal scanning line. means. The larger this value is, the more likely the television receiver is to shake. In addition to the standard weighting curve, FIG. 3 also shows the AFC characteristics of commercially available television receivers from various companies for reference.

In addition, the AFC characteristic of the television receiver is 1Hz.
While all of the curves below are flat, the reason why the standard weighting curve is lowered below 1 Hz is to take into consideration the visual characteristics of jitter. The reference weighting curve of 1 Hz or more is selected as an intermediate value for various commercially available television receivers.

Therefore, jitter can be measured most accurately when using a television receiver that has the same AFC characteristics as the reference weighting curve shown in Figure 3, but by selecting the characteristic values above, Most television receivers can be used without any practical problems.

The output signal of this frequency correction circuit 16 is transmitted to the amplifier 1.
7, where it is amplified. This amplifier 1
Reference numeral 7 is provided to magnify and display the jitter amount of the jitter white line on the screen of the television receiver. The amplification factor is selected to be 10 times. Of course, this multiple can be any desired magnification.

Each of the blocks 11 to 17 is a jitter detector 18.
It detects the jitter component of the input video signal, corrects the frequency characteristics, and magnifies the jitter component for output.

The jitter component extracted from the amplifier 17 is 10
The signal magnified (at 1 Hz) (jitter detection signal indicating the amount of jitter) is applied to the monostable multivibrator 20, where the horizontal synchronization signal is delayed, and then supplied to the differentiating circuit 21, where it is It is differentiated to form a white line on the reproduced image. The monostable multivibrator 20 and the differentiating circuit 21 constitute a jitter display signal generating section 22. Although the jitter display signal is shown as a white line on the reproduced image, it may be displayed in other ways.

On the other hand, the monostable multivibrator 19 is for delaying the reproduced horizontal synchronizing signal for a certain period of time in order to determine the positions of the reference white lines A and B,
The delay time is adjusted by the volume so that the position on the reproduced image can be arbitrarily adjusted.

The output horizontal synchronizing signal of the monostable multivibrator 19 is supplied to the monostable multivibrator 23, where it is further delayed for a certain period of time, and is supplied to the differentiating circuit 24, where it is separated from the white line on the reproduced image of the television receiver. The reference white line A is formed. Further, the output signal of the monostable multivibrator 23 is supplied to a differentiating circuit 25, where it is differentiated so as to form a white line on the reproduced image, thereby forming the reference white line B. The monostable multivibrator 23 is provided to determine the interval between the reference white lines A and B, and is configured so that this interval can be adjusted arbitrarily on the reproduced image by adjusting the volume, but usually it is set according to a predetermined jitter standard. set to the value.

The differential outputs of the differentiating circuits 24 and 25 are supplied to the mixer 10 via a mixer 26 as a reference signal. In this way, the blocks 19 to 26 constitute the reference signal generating section 27.

The mixer 10 mixes the reproduced video signal, the jitter display signal from the differentiating circuit 21, and the reference signal from the mixer 26, and outputs the mixed signal from an output terminal 28 to the television receiver.

In the apparatus of the present invention, jitter is measured by displaying a reproduced image as shown in FIG. 4A. First, the volume of the monostable multivibrator 19 is variably adjusted to align the reference white line A with the peak (or valley) of the jitter white line J. Next, the volume of the monostable multivibrator 23 is variably adjusted to change the reference white line B to the jitter white line J.
are aligned with the valleys (or peaks) of , and the display state is as shown in FIG. 4A. In this state, read the rotation position display of the volume adjustment knob of the monostable multivibrator 23. The amount of adjustment of the volume of the monostable multivibrator 23 corresponds to the width in the horizontal scanning direction of the reference white lines A and B in the reproduced image, that is, the amount of jitter. In the rotational position display of the knob for adjusting the volume of the monostable multivibrator 23, the amount of jitter corresponding to the amplification factor of the amplifier 17 is written. Therefore, jitter can be measured by reading the value of the volume adjustment knob of the monostable multivibrator 23.

In addition, Fig. 4B shows the monostable multivibrator 19.
By varying the amount of delay, the jitter white line J is set to the reference white line A.
Jitter can be measured by reading the value indicated by 30 in the reproduced image when the values are aligned. However, in this case, it goes without saying that the jitter measurement value is determined by taking into account the magnification rate of the jitter component.

Note that in the above embodiment, the jitter component detection section 18
Although PLL is used in the above, jitter components can also be detected by other methods such as a frequency discriminator.

As described above, the jitter measuring device according to the present invention includes a jitter detecting section that detects a jitter component in a video signal and amplifies the detected jitter component, and displays an output signal of the jitter detecting section on a television receiver. a jitter display signal generating section for generating a jitter display signal for displaying the video signal; and a reference signal for generating a first reference signal and a second reference signal for display as measurement standards on a reproduced image of a television receiver from the video signal. a first adjusting means for arbitrarily adjusting the display image position of the first reference signal on the television receiver; and a first adjusting means for arbitrarily adjusting the display image position of the second reference signal on the television receiver; A second adjustment means that arbitrarily adjusts the display image position of the reference signal, and an adjustment of the second adjustment means corresponding to the interval in the horizontal scanning direction between the display image positions of the first and second reference signals. The jitter measurement result is displayed on the display by simply adjusting the reference signal image display position so that it matches the peaks and/or valleys of the jitter display image on the playback screen. As a result, jitter measurement can be made extremely easily and accurately.Since jitter is detected in relation to a reference line, it is possible to quickly determine whether or not jitter tolerance has been exceeded without requiring any skill. The switching point and equalization pulse are not affected by noise because they fall within the vertical blanking period on the reproduced image, and the video signal is also reproduced at the same time. It has many features such as being able to measure jitter while measuring resolution.

[Brief explanation of the drawing]

Fig. 1 is a schematic connection diagram when measuring jitter with the device of the present invention, Fig. 2 is a block system diagram of an embodiment of the device of the present invention, and Fig. 3 is an example of the frequency characteristics of the main part of Fig. 2. FIGS. 4A and 4B are diagrams showing the AFC characteristics of commercially available television receivers, respectively, and are diagrams showing reproduced images when jitter is measured by the apparatus of the present invention. 1...VTR, 4...Jitter measuring device, 7...
. . . Television receiver, 9 . . . Image signal input terminal containing jitter components, 10, 26 . . . Mixer,
12...Horizontal synchronization signal separation circuit, 13, 19, 2
0,23...monostable multivibrator, 14...
...Phase comparator, 16...Frequency correction circuit, 17...
...Amplifier, 18...Jitter detection section, 21,2
4, 25...Differentiating circuit, 22...Jitter display signal generation section, 27...Reference signal generation section.

Claims (1)

[Claims] 1. A jitter measuring device that outputs a jitter component of a video signal containing a jitter component from a jitter source to a television receiver as a jitter display signal for displaying the jitter component on the playback screen of the television receiver. a jitter detection unit that detects a jitter component in a signal and amplifies the detected jitter component; and a jitter display signal generation unit that converts the output signal of the jitter detection unit into a jitter display signal to be displayed on the television receiver. a reference signal generating section that generates a first reference signal and a second reference signal for display as measurement standards on a reproduced image of the television receiver from the video signal; A first method for arbitrarily adjusting the display image position on the television receiver.
and a second adjusting means for arbitrarily adjusting the display image position of the second reference signal on the television receiver with respect to the display image position of the first reference signal.
and a display section that displays an adjustment amount of the second adjustment means as a jitter measurement value corresponding to an interval in the horizontal scanning direction between display image positions of the first and second reference signals. , a jitter measuring device characterized in that the video signal, the jitter display signal, and the first and second reference signals are respectively supplied to the television receiver.