JPS6144365A - Noise measuring apparatus - Google Patents

Abstract

PURPOSE:To make it possible to measure noise under a condition near to an actual use state, by sampling th rising or falling part of a signal and calculating the standard deviation of the time prior to reaching a predetermined magnitude. CONSTITUTION:The test signal recorded by a video tape recorder 1 to be measured is regenerated to be applied to a sampling circuit 11 and a sampling section setting circuit 6 outputs the horizontal synchronous signal from a monitor television 3 after a definite time from the rising of a drum FF signal (a). This signal (d) is inputted to a flip-flop (FF) circuit 8 and a counter circuit 9 and, when n-signals are inputted, the FF circuit 8 is reset. During this time, a gate oscillator 10 oscillates and n-signals (c) are sampled by the sampling circuit 11 and the above-mentioned operation is performed over the m-cycles of the signals (c). A computer 12 calculates respective standard deviations of times before the signals (c) reach A1, A2...Al to measure noise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a noise measuring device, and a device for measuring noise in a signal in a device that handles a signal having a percent periodicity.

[Prior art]

Examples of devices that handle periodic signals include video tape recorders (VTRs) and video disk players (VTRs).
Conventionally, the SIN ratio of a reproduced image in these devices has been measured by dividing the maximum amplitude of the signal by the effective value of the noise superimposed on the signal flat part. [The effective value of noise is usually measured using a video noise meter, FMS voltmeter, or oscilloscope.

As mentioned above, conventional noise measurement targets only the flat part of the reproduced signal, and when the rise or fall of the reproduced signal is at the 9 part, (1) the high frequency component is strong and the noise reduction circuit does not operate well. It is not possible to measure noise due to factors such as the propagation of the reproduced FM signal due to (co)pre-emphasis, and for this reason, it is generally not possible to evaluate the image quality of video tape recorders and video disc players. The drawback was that it couldn't be done.

It was made possible to measure the amount of noise that occurs in the 9 parts of the rising or falling edge of the reproduced signal,
Therefore, it is an object of the present invention to provide a noise measuring device that can measure noise under conditions closer to actual usage conditions than conventional ones.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. 1st
The figure shows a schematic block diagram of a noise measuring device according to an embodiment of the present invention.

In the figure, / is the video tape recorder to be measured.

A is a video output terminal, 3 is a monitor television, 9 is an F signal output terminal, a horizontal synchronizing signal terminal, A is a sampling period setting circuit, and 7 is a delay circuit. k is a flip-flop circuit, and ri is a counter circuit.

i'o is a gate oscillator, // is a sampling circuit, and /2 is a computer. The video tape recorder I to be measured is connected to video output terminals F, F, and signal output terminals Hiroshi, respectively.

The video output terminal is connected to the input side of the monitor television J and the input side of the sampling circuit //, and the output side of the monitor television J is connected to the horizontal synchronizing signal terminal 5. The F, F signal output terminals and horizontal synchronizing signal terminals are connected to the input side of the sampling period setting circuit 6, and the output side of the sampling period setting circuit B is connected to the clip-flop circuit t via the delay circuit 7. and the set input side of the counter circuit 9 (connected. The output side of the flip/70 tube circuit 5 is
It is connected to the gate oscillator ioo input sensor, and the output side of this gate oscillator 10 is a counter circuit? and the synchronous input side of the sampling circuit //. Counter circuit? The output side of is connected to the recent input side of the clip-flop circuit, and the output side of the sampling circuit /l is connected to the computer. Further, FIG. 2 shows a waveform diagram of the signal a=h of each part in the block diagram shown in FIG. 1.

The operation will be explained below using FIG. 1 and FIG. The test signal recorded on the video tape recorder under test is reproduced and applied to the video output terminal λ. Signal (c
) indicates the playback signal.

This signal (C) is connected to the monitor TV J and the sampling circuit/
given to /. Note that this signal (c) VC contains noise. Monitor TV 3 that monitors the signal (cl)
A horizontal synchronizing signal is taken out from the horizontal synchronizing signal terminal and applied to the sampling period setting circuit 6. signal(
b) shows this horizontal synchronization signal. During the test, the drum F, F signals during signal reproduction are taken out from the video tape recorder under test l to the F, F signal output terminal 4 (K) and given to the sampling section setting circuit 61C. (i! No. is shown. In the sampling section setting circuit 6 which receives the signal (at) and the signal (bl), the drum F, F
The horizontal synchronizing signal is outputted for a period of S/time by delaying the rise of the signal (a) by a fixed time 1/. Signal (a) shows a horizontal synchronizing signal output from this sampling period setting circuit 6.

The delay time 1/ determines from which position on the monitor television screen sampling starts, and the S/time sets the number of sampling times. j, / is given by the position t// (/field time) on the sampling screen, and S/time is given by / (time of the horizontal synchronizing signal). For example, if the sampling screen is at position //J from the top and the number of samplings is rn-100, then tz S!
,! RS, 8/-61,73m5.

Horizontal synchronization signal (d
) is further determined by the predetermined time in the delay circuit.
The signal is delayed by a certain amount and becomes signal (e). This signal (e) is
Cent input side of clip/70g circuit l and counter circuit? The set input side is given. Note that the pulses shown by the seven lines in the signal (d) shown in the upper part of FIG. 2 correspond to one pulse signal of the signal (d) in the lower part of the figure. Flip-flop circuit t is powered by signal (e) and generates a pulse signal (f). In response to the pulse signal (f), the gate oscillator 10 oscillates at a predetermined constant frequency f Hz and outputs a signal (j). on the other hand,
Counter circuit? Now, in response to signal (e),
Start counting.

When a predetermined number of 'FL' is reached, a signal (h) is output to reset the nine-furlong circuit t.

This causes the gate oscillator IO to stop outputting.@The time Bs during which the gate oscillator IO outputs is given by /f. Determine the delay time tJ, the frequency f of the gate oscillator IQ, and the number of pulses the counter circuit counts until it resets the seven lip-flops t so that the rising edge of the signal (signal body) is included in this time SJ. do it. - As an example, tkoniλ,j tt'R13,f
It is conceivable to set w 20 MHz, R: J s.

On the other hand, the sampling circuit /I receives the reproduced signal (C1) as described above and samples the magnitude of the signal (C) once in synchronization with the signal (tl) which is the output of the gate oscillator io. operations are performed over n periods of the signal (C1). Since one sampling in each period is performed at equal intervals, the operation of the signal (C1) at the same point on each period over R periods is performed. to be sampled.

FIG. 3A shows the signal sampled by the above operation (of the magnitude of cl, the jJE/cycle. In the figure, A// * A/J, . . .
A/R represents the magnitude of the sampled signal (C). A// is the ME/signal at the same point in the first period (C
), A/J is the signal f at the fourth same point in the first period
The magnitude of c), A and Y represent the magnitude of the signal (C) at the 9th identical point in the first period. Sampling is n
Since this is carried out over a period, a diagram like that shown in FIG. 7A will be produced. In general, f of the jth period
xk The magnitude of the sampled signal at the same point is A, 1. k (l≦j≦melon, l≦ni≦ru, j.

k is a regular c! l). Computer/-2 is Aj. k
Then, the noise is measured by performing the calculations described below.

The @JB diagram shows the time required for the signal (c) to reach a predetermined signal magnitude A=(t 4 i−≦t, L is an integer). This magnitude is larger than Q and smaller than the value of the upper flat part of signal (c). In the figure, T// is a signal of 1 period (the time until cl is reduced to the magnitude of A/, and Tj2 is a signal of 8F!/period (
The time it takes for cl to reach the size of AJ, set Tit
represents the time it takes for the first period signal (cl to reach the magnitude of At. In other words, there are m diagrams like the KJB diagram. Generally, the Jth period signal (
Tj, Q (
/4j 4m, i4;-41,j.

L is an integer). Aj. Data conversion to obtain Tj and Q from k is performed by the following operation.

Aj, k≦AL≦4＾Qj, K+
, H when Tj, shi=(k-1)・t, +{(AL-
Aj,k)/(Aj,l(+z-Aj,k)l・t・
...(1) However, t is the sampling interval time order K U = (Σ 'pj j ) / 111 ・
...(,2) Perform the operation of J-/, and the signal (c) that crosses the 0m period is AL.
Find U↓, which is the average time taken to reach the size of . FIG. 3C shows the average value UL of mHJ estimation of the time until the signal (c) reaches AQ.

lastly.

Find the standard deviation σ↓ of each time until jt.

σ represents the variation in the time axis direction in the rising portion of the signal (TC), which represents the magnitude of noise in the rising portion of the signal (C). Because of IXJD.

σb are shown in series. From this figure, it can be seen that as the signal level increases, the variation increases, which means that the part where the transition from white to black becomes blurred.

In the above embodiment, only the rising portion of the signal &C was explained, but the same can be applied to the falling portion &C. In this case, Tj,
Data conversion to obtain Q is Aj. k≧AL≧Aj. When k+l.

Tj, = = (k-z)-1+{(Aj.k-A=)/
(Aj , k −Aj .k+t )) meeting t
......(da), return to equation (2) below and continue the above operation.0Furthermore, this noise measuring device is applicable not only to video tape recorders and video disk players, but also to the one-cycle incoming signal. It can also be used with other equipment to achieve the same effect.

〔Effect of the invention〕

As described above, according to the present invention, when measuring the noise contained in a signal, instead of measuring only the flat part of the signal as in the conventional method, it is possible to By making it possible to measure noise in the falling portion, it is possible to measure noise under conditions closer to the actual usage conditions, and as a result, image quality can be adequately evaluated.Further.

Since all data collection and calculations are performed mechanically and digitally, there is no error in reading the measured values as in the past, for example with an oscilloscope, and accurate measurements can be achieved.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram of a noise measuring device according to an embodiment of the present invention, FIG. 1 is a waveform diagram of each part of the noise measuring device shown in FIG. 1, and FIG. Diagram showing the rising part of the signal, 3rd
Figure B is a signal obtained by converting the rising part of the signal in Figure jA into data by a computer, Figure 3C is a diagram showing the average of the data-converted signal over the door period, and Figure 3D is the data conversion. FIG. 3 is a diagram showing the standard deviation of the obtained signal. l...Video tape recorder to be measured, J@'' video output terminal, 3. Monitor TV, V...F, F signal output terminal, 5. Horizontal synchronization signal terminal, 6. Sampling section setting circuit, 7 ...Delay circuit, ...Flip-flop circuit, 9..Counter circuit, 10..Gate oscillator, /
/...Sampling time i, /co...computer. In each figure, the same reference numerals indicate the same or corresponding parts. Punishment number 1! ? )2 tsuri flood 3A diagram

Claims (1)

[Claims] (1) A device for measuring noise contained in a periodic signal, comprising a predetermined period of m (m is an integer of 2 or more) of the signal.
n (n is 1) predetermined for each period of
The magnitude of the signal A at the same point on the period of (integer greater than or equal to)
j. k (Aj.k is the magnitude of the signal at the kth same point in the jth period, Aj.k: 1≦j≦m, /≦k≦n
); and an output Aj. of the sampling means. k is a predetermined signal magnitude Ai (Ai is a real number greater than 0 and smaller than the value of the upper flat part of the signal, and 1≦i≦l)
Time taken to reach Tj. a data conversion means for converting the data into Tj. 1. Tj. 2...
...Tj. 1. A noise measuring device, comprising: means for determining the standard deviation of each signal, and sampling the magnitude of a signal at a rising portion or a falling portion of the signal. (j) When the sampling means samples the rising edge of the signal, the data conversion means samples Aj. k≦Ai
≦Aj. When k+1, Tj. i=(k-1)・t+{(
Ai-Aj. k)/(Aj.k+1-Aj.k)}・t
The noise measuring device according to claim 1, wherein t is a sampling interval time for data conversion. (3) When the sampling means samples the falling portion of the signal, the data conversion means samples Aj. k≧Ai
≧Aj. When k+1, Tj. i=(k-1)・t+{(Aj.k-Ai)/(
Aj. k-Aj. k+1)}·t, where t is a sampling interval time for data conversion.