JPH0457230B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a jitter measuring device for digital signals.

(Prior art) Among digital information recording media, for example, a CD (compact disk) etc. has a reference time T (T≒231×
A digital signal consisting of nine types of fundamental pulses having widths of integer multiples from 3 times to 11 times (10 ^-9 seconds) is recorded. A reproduced digital signal obtained by reproducing such a digital signal using an optical pickup or the like usually contains jitter.

(Problems to be Solved by the Invention) Various measuring devices are known for measuring such jitter, but they also take time to measure. Therefore, it was not suitable for use in displaying changes in jitter in real time from moment to moment.

(Means for Solving the Problems) For this reason, the present invention provides an integer multiple n of the reference time T from the leading edge of a plurality of basic pulses input directly in time.
(However, n = 3, 4, 5, 7, 11) Elapsed time nT
means for obtaining the number n ₁ of trailing edges of a plurality of fundamental pulses occurring within a first time having a time width approximately equal to a reference time T centered at The number of trailing edges of the plurality of fundamental pulses occurring within a second time period having a time width within a narrow and predetermined fundamental pulse variation tolerance range n ₂
The invention is characterized in that it has a means for obtaining.

(Function) Therefore, the number of trailing edges of each basic pulse generated within the first time n ₁ The number of trailing edges of each basic pulse generated within the second time n ₂ is a value representing the magnitude of jitter. N=(n ₁ −n ₂ )/n ₁ can be displayed in real time.

(Embodiment) In FIG. 1, a reproduced digital signal pulse train from a CD player 1 is applied to a fall detector 6 and a rise detector 7 via a shaping circuit 2, a switch 4, and a differentiation circuit 5. The output of the falling detector 6 is applied to one input terminal of the AND circuits 11 and 12, and the output of the rising detector 7 is applied to the AND circuit 11 through the first and second time window generators 8 and 9. and the other input terminal of 12. The outputs of AND circuits 11 and 12 are
It is applied to the CPU 15 via counters 13 and 14. The jitter measurement result is output terminal 1 of CPU15.
Obtained from 6. Also, control output 1 from CPU15
7 is added to the counters 13 and 14, and the control output 18 is added to the switch 4.

2 and 3 are waveform diagrams of various parts of the embodiment shown in FIG. 1, and waveforms a to g in FIGS. 2 and 3 indicate waveforms appearing in parts a to g in FIG. 1. .

Now, the reproduction pulse train signal from CD player 1 is
The waveform is shaped by the shaping circuit 2 and becomes the measured waveform a. In a normal case, the pulse width of waveform a is an integer multiple of a certain time T and has a value corresponding to nine types of reference times between 3T and 11T. Now, it is assumed that among these waveforms a, it is measured whether the waveform a having a width of the reference time 3T is definitely 3T. Waveform a above
is differentiated by the differentiating circuit 5 to form a waveform b, and from this waveform b, a positive pulse _b1 corresponding to the rising part of the waveform a is detected by the rising detector 7, and the pulse is centered at the time 3T has elapsed from immediately after that. A wide pulse waveform d and a narrow pulse waveform e are generated by first and second time generators 8 and 9, respectively.
On the other hand, pulse b of waveform b indicating the falling edge of waveform a
2 is detected by the fall detector 6 to obtain a waveform C, and the waveform C and the large and small window pulses d and e are added to AND circuits 11 and 12, so that the waveform C is detected within the window pulses d and e. to detect that

Here, the width of the large window pulse d is determined to be approximately the reference time T as the maximum width at which the width of the waveform a can normally deviate, and the width of the small window pulse e is determined to be approximately within the allowable variation range of the waveform a. Therefore, if waveform c indicating the falling time of waveform a is within the large window pulse d, waveform a
It can be seen that is a pulse representing a 3T width, and if it does not fall within the large window pulse d, it can be seen that the waveform a is a pulse representing a width other than 3T. Furthermore, if waveform c indicating the falling edge of waveform a is within the small window pulse e, it can be seen that the pulse width of waveform a with the width of 3T is within the permissible range. Of the waveform c generated within the predetermined measurement time,
Number of items contained within large and small window pulses d and e
Measure n ₁ and n ₂ respectively, and use the CPU 15 to calculate N=
Calculate n ₁ − n ₂ /n ₁ . Since n ₁ -n ₂ is the number of pulses that do not fall within the small window pulse e, it can be seen that the larger N is, the larger the jitter is. In this case, N is the number of basic pulses having various widths.
This value indicates the degree of jitter for a 3T pulse.

Note that the ratio N' of n ₂ to n ₁ mentioned above is also related to jitter. That is, in this case, it can be assumed that the larger the ratio N' is, the smaller the jitter is. Furthermore, if the above-mentioned n ₁ is predetermined, n ₁ - n ₂ or n ₂ alone can represent the amount of jitter.

Also, instead of calculating n ₁ - _{n 2} as described above, a double pulse is created by subtracting the small window pulse e from the large window pulse d, and the number n of trailing edges occurring within this double pulse is calculated. ₃ may be used as a value indicating the amount of jitter.

Moreover, the pure time of the time window generators 8 and 9 is 3T, 4T, 5T,
It is assumed that the time can be arbitrarily selected from among 7T and 11T, and in conjunction with this switching, the generation positions of the large window and small window pulses d and e are also switched accordingly.

(Effects) As described above, according to the present invention, a plurality of basic pulses
3T from a pulse train containing a mixture of 3T to 11T,
The degree of jitter for basic pulses of 4T, 5T, 7T, and 11T can be easily measured.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIGS. 2 and 3 are explanatory diagrams of the operation. 1... Regenerator, 8, 9... Time window pulse generator, 16... CPU.

Claims (1)

[Claims] 1. An integer multiple n of the reference time T (where n=3,
4, 5, 7, 11) Means for obtaining the number n ₁ of trailing edges of a plurality of fundamental pulses occurring within a first time having a time width approximately equal to the reference time T centered at the elapsed time nT and the first point centered at the time nT.
and means for obtaining the number n ₂ of trailing edges of the plurality of basic pulses occurring within a second time period having a time width narrower than the time width and within a predetermined permissible range of variation of the basic pulses. jitter measurement device for digital signals. 2 Integer multiple n of reference time T from the leading edge of multiple fundamental pulses input in series in time (however, n=3,
4, 5, 7, 11) Means for obtaining the number n ₁ of trailing edges of a plurality of fundamental pulses occurring within a first time having a time width approximately equal to the reference time T centered at the elapsed time nT and the first point centered at the time nT.
and means for obtaining the number n ₃ of trailing edges of the plurality of basic pulses occurring within a time excluding a second time having a time width narrower than the time width and within a predetermined basic pulse variation tolerance range. A digital signal jitter measuring device featuring: