JPS63117272A - Time interval analyzer - Google Patents

Abstract

PURPOSE:To enable accurate measurement of the amount of a jitter contained in a pulse, by performing a time-voltage conversion of a pulse to be measured to input the resulting voltage variation signal being A/D converted into a spectrum analyzer. CONSTITUTION:A time interval device is provided with a time-voltage conversion circuit 12 on the input side of a spectrum analyzer. The circuit 12 is a simple staircase wave generation circuit with which the pulse width of a pulse Pa to be measured can be converted to a voltage signal. A controller 14 detects the trailing edge of the pulse Pa to generate a pulse Pb synchronous with the trailing edge thereof to be applied to an A/D converter 13 and a buffer memory 27. When the analyzer 11 is operated as oscillograph, changeover switches 18 and 28 are turned to contacts A respectively. As a result, an output of the converter 13 is written as intact into the memory 27 and transferred to a buffer memory 21. The data taken into the memory 21 is subjected to a Fourier transform by a fast Fourier transform means 23 to be stored into a main memory 24 and a frequency spectrum is shown on a display device 25.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a time interval analyzer capable of measuring jitter of a pulse signal, frequency analysis of jitter, frequency of occurrence, etc.

"Background of the Invention" For example, in a magnetic disk device used as an external storage device for a personal computer, a digital audio device called a compact disk, or even a video device such as a laser disk, the signal played back is a coded pulse train signal. It is. If this pulse train signal includes a shifter, errors are likely to occur during decoding. Particularly in the case of a computer's external storage device, errors cannot be tolerated. Therefore, in order to determine the quality of these digital devices, it is necessary to measure whether the shifter of the reproduced pulse train signal is within a specified range.

``Prior art'' The conventional method for measuring the jitter of a pulse train signal is to project the pulse to be measured on an oscilloscope as shown in Figure 12, and measure the fluctuation width W of the bright line that depicts this pulse (width of the VI line). to measure the amount of shifter.

Another method may be to manually input the pulse to be measured to a spectrum analyzer, analyze the frequency component of the pulse to be measured by the spectrum analyzer, and measure the shifter component.

[Problem to be solved by the invention] In the method using an oscillograph, the measurer determines the amount of shifter by measuring the width W of the bright line projected on the tube surface of the oscillograph. It is difficult to quantitatively capture the amount of pulses, especially in digital audio equipment or digital video equipment, where there are many different pulse widths of the reproduced pulses, so pulse waveforms with different pulse widths overlap and appear on the screen of the oscilloscope. Served. As a result, the measurement of the bright line width W becomes increasingly difficult, and only uncertain measurement results are obtained.

On the other hand, when a method using a spectrum analyzer is adopted, if an ideal spectrum analyzer with a good S/N ratio is used, the frequency components of jitter can be quantitatively observed.

However, since the signal level of the shifter component is minute compared to the frequency component of the pulse to be measured, in order to display the jitter component as a spectrum, a spectrum analyzer with a significantly superior S/N ratio must be prepared.

In other words, if a normal spectrum analyzer were used, the spectrum representing the shifter component would be hidden in the noise component and would be impossible to observe. In addition, when there are many types of pulse widths of the pulse to be measured, there are fundamental wave spectra for each type of pulse width, and countless harmonic spectra are generated for each type of pulse width, so the spectrum of these signals alone is complicated. It becomes an image, and the spectrum representing jitter becomes increasingly difficult to discern.

Furthermore, if the jitter frequency varies over time, it is almost impossible to measure the jitter frequency variation.

SUMMARY OF THE INVENTION An object of the present invention is to provide a time interval analyzer that can accurately measure the amount of jitter contained in a pulse and can also measure fluctuations in the frequency of jitter.

"Means for Solving Problems" This invention comprises: ^. A digital spectrum analyzer equipped with an AD converter in its input circuit; B. A time-voltage converter that converts the pulse width of a pulse into a voltage signal proportional to the pulse width, and a time-voltage converter that detects the trailing edge of the pulse to be measured that is input to the time-voltage converter and converts it into an AD converter. D. A buffer memory for sequentially storing the AD conversion results of the AD converter; E. A reading means for reading out the contents of the buffer memory by a predetermined address while sequentially shifting the reading start address. , F. Fast Fourier transform means for performing Fourier transform on the data read by this reading means and converting it into frequency domain data; G. Preset frequency interval from among the frequency domain data Fourier transformed by this fast Fourier transform means. 11. A display device that displays the sum, peak value, or ratio of the frequency components stored in the memory along the time axis. This is a configuration of an interval analyzer.

"Operation" According to the configuration of the present invention, the time-voltage converter can extract fluctuations in the pulse width of the pulse to be measured and fluctuations in the time between pulses as a voltage signal. By AD converting this voltage signal in synchronization with the trailing edge of the pulse to be measured, it is possible to obtain a digital signal that changes in response to fluctuations in the pulse width of the pulse to be measured.

In other words, this array of digital signals is a signal representing the amount of jitter that changes according to fluctuations in the pulse width of the pulse to be measured. Therefore, by frequency-analyzing this digital signal using a fast Fourier transformer, it is possible to know the frequency of the shifter and the amount of jitter.

In addition, the AD-converted signal is loaded into the memory, the data loaded into the memory is divided into predetermined blocks and extracted, and the data for each block is Fourier-transformed using a fast Fourier transformer to convert it into frequency domain data. The sum of frequency components existing in a preset frequency interval from frequency domain data or the peak value or ratio existing in that frequency interval is stored, and this stored sum or peak value or ratio of frequency components is plotted on the time axis. By displaying on the display along the line, the frequency fluctuation of the shifter can be displayed and viewed.

Embodiment FIG. 1 shows an embodiment of the present invention. Reference numeral 11 in FIG. 1 shows a conventionally known digital spectrum analyzer.

In this invention, a clock pulse synchronized with the trailing edge of the pulse to be measured is given to the time-voltage converter 12 and the AD converter 13 equipped in the digital spectrum analyzer 11, and It is characterized by a configuration in which a controller 14 is attached to perform AD conversion operation.

First, a commonly used digital spectrum analyzer will be explained. The digital spectrum analyzer 11 includes an amplifier 16, an analog filter 17 provided at the subsequent stage, an AD converter 13, and a magnification change switch f18.
1 magnification conversion circuit 19° buffer memory 21. Microcomputer 22° Fast Fourier Transform 1 23. 5 memory 241 display 25 (-).

In the example shown in the figure, a case is shown in which a reciprocal converter 26 and a buffer memory 27 are provided between the AD converter 13 and the magnification change switch 18. 13 + - Therefore, the period of jitter (2) Therefore, it is a converter that performs reciprocal conversion of a changing signal and converts it into a signal in the frequency range.Switch F-28 is used to select whether or not to perform reciprocal conversion. When selecting, data that changes with the jitter period of the pulse to be measured is provided to the buffer memory 271.When contact B is selected, the signal that changes with the jitter period is reciprocally converted and a frequency domain signal (two-dimensional signal) is provided. However, the buffer memory 271 becomes deaf.

In this way, this example has a structure in which it is possible to take in either a signal that changes according to the period of the buffer memory 27C, or a signal that is converted into a frequency range of (3).

The data taken into the buffer memory 27 is read out and transferred to the second buffer memory 21 after selecting whether or not to change the magnification using the magnification change switch 18.

The magnification change switch f18 is switched to the state of no magnification change by selecting the contact A (C2), and the magnification change state Bc is prevented by selecting the contact B (2).

The magnification changing circuit 19 is a digital frequency converter 19A, 1
9B, digital filters 190° and 19D, and resampling switches 19K and 19F.

The digital frequency converters 19A and 19B respectively output jitter signals 1; (2) 2 to fo and si! 12πfot frequency mixing and shifts the center frequency of the jitter signal to an arbitrary frequency (2).The digital filters 19c and 190 shift the center frequency to a desired frequency (2) and shift the center frequency of the jitter signal to a desired frequency (2) to remove unnecessary wave components parasitic to the signal C2. In order to remove unnecessary wave components, the signal is resampled by the signal beam length sampling switches 5'-19E and 19F and taken into the buffer memory 21. The change in magnification is determined by the sampling period (thinning rate) of IT-Resampling Suite 19E and 19F.

In other words, if the capacity of the buffer memory 21 is, for example, 1024 data, and if the data taken into the memory capable of storing 1024 data by taking 1 unit of time T every cycle is set to the magnification rlJ, then the same signal is every hour 2T
If the image is multiplied by , the magnification becomes "2".

By changing the magnification C2, the array of frequency spectra displayed on the display 2552 can be enlarged and displayed at an arbitrary magnification with respect to the frequency axis, and the resolution can be increased by that magnification. Improved resolution (2) It is now possible to display spectra that were previously invisible (-).

As an actual example, the magnifying power of 2x to 256x is used in practical use.

The decision factor for determining the frequency is the sampling frequency 'aI (thinning rate) of 1.9K and 19F, and the center frequency for expansion is the digital frequency converter 19A. The center frequency is set with 19B.

The data is taken into the buffer memory 21 and sent to the fast Fourier transformer 23, where it is Fourier transformed and stored in the main memory 24. Display 25C displays the frequency spectrum.

The configuration and operation of the digital spectrum analyzer 11 will be understood from the above C2.

In this invention, a time-voltage converter 12 is provided on the input side of such a digital spectrum analyzer.An example of the time-voltage converter 12 will be explained with reference to FIG. The example shown in FIG. C2 illustrates Gozo's time-voltage converter, which is as simple as possible, in order to simplify the explanation.

During this period, the paper pressure transducer 12 receives the measured pulse Pa shown in FIG.
d (D in Figure 3) 12A and the Glock pulse Pe (E in Figure 3) punched out by this gate 12 are given, and the clock pulse Pe is turned on (D) only during the H logic period.
- a controlled switching element 12B, a constant current circuit 12c that provides a constant current of this switch element 12Bl, and a capacitor 12D that is filled with a constant slip every time the switching element 12B is turned on. , Both ends 1 of capacitor 12D: connected and capacitor 12D [2 charges r:,
The reset switch Y-element 12F2 and 1 releases the F4 load by supplying a reset signal Po (S4 & 3C)
- Therefore, it can be configured.

This circuit is a simple staircase wave generation circuit. This staircase wave generation circuit (; Therefore, the pulse width Tp of the pulse Pa is set to a voltage of 1 g.
No. V5 (Figure 3F) can be converted into two.

The controller 14 detects the trailing edge of the pulse Pa to be measured.

A pulse Pb (FIG. 3B) synchronized with this trailing edge is generated. This pulse Pb is applied to the ADE converter 13 and the buffer memory 27, causing the AD converter 131 to perform an AD conversion operation and the buffer memory 271 to perform a data input operation.

When operating the spectrum analyzer 11 as an oscilloscope, the switching switches y-18 and 28 may be switched to contact ON (;1.rl).

In this way, the AD conversion output of the AD converter 13 is stored in the buffer memory 271:1F as it is, that is, in the state of a periodic signal, and is transferred to the buffer memory 21i and then transferred to the display 25 (2 You can make it come out.

Here, as an example, assume that the pulse width of the input pulse Pa is one type of pulse width, and that one type of pulse width is fluctuating due to a malfunction in the reproduction system. - is a voltage waveform corresponding to a change in the pulse width of the input pulse Pa, for example, as shown in FIG. 4 (-).

This voltage waveform is a pulse width, and it shows how it fluctuates with the passage of time. You can know the period and frequency.

Also, by measuring the amplitude of this waveform (#A%), the maximum value and minimum value of jitter g11 can be determined from the following.

If we invert the polarity of the input pulse Pa and input it as a negative polarity pulse, then the pulse P, the time interval between them (the corresponding time (2) is converted to voltage 1, and this is AD converted, so this The AD converted signal is displayed on display 2.
By displaying C2 in 5, it is possible to display variations in the time interval between pulses.

By the way, for example, like a compact disc C; T = 23
When inputting a pulse signal that has nine types of pulse widths from 3T to 11T in units of 1.3850S and in which signals with these nine types of pulse widths are generated irregularly, C2 is the tube surface of the oscilloscope (C2 is the 5ei2 Nine bright lines LN1 as shown
~LN, is drawn. In other words, these nine bright lines LN, ~L
N, microscopic C2 dots DI + DB + each displayed by one pulse (2) as shown in Figure 6 (2)
The result of D3... (2) Since the dots are drawn as lines, and the dots move at high speed between each other, most of the bright lines are displayed between the lines LN1 to LN. It will not be done.

In this way (9 bright lines LN, ~LN, displayed as -)
shows the pulse width fluctuation of each pulse width.

In other words, the width of each bright line LN1 to LN (width in the vertical direction)
Whether the pulse width is wide or thin (-Therefore, it can be known whether the pulse width is fluctuating or not.

By the way, if all nine lines LN, ~LN, are drawn, it is possible to determine whether the width of each line is thick or thin (depending on whether the pulse width is changing or not). It is not possible to measure whether or not there is a regularity in the fluctuations, and if there is a regularity (it is not possible to measure until the period of 27 is displayed).

This allows the spectrum analyzer 11 to operate as an original spectrum analyzer. For this purpose, the changeover switches 18 and 28 can be moved to the contact position.

The changeover switch 28 is connected to the contact B (2). Therefore, the periodic signal is reciprocally converted by the reciprocal converter 26 and becomes a signal in the frequency range. It is synchronously taken into the buffer memory 27.

The signal taken into the buffer memory 27C is read out and transferred to the second buffer memory 2IC through the magnification changing circuit 19. Double S4! - The change circuit 19 presents the magnification in the frequency axis direction and determines the resolution in the five frequency axis directions.

After the magnification is changed by the magnification changing circuit 19, the data is once taken into the second buffer memory 211, and is subjected to Fourier transform in the first stage of fast Fourier transform 23 and subjected to frequency analysis.

The frequency analysis results are sequentially taken into the memory 24 (2) and displayed on the display 25 (2).

An example of the display is shown in Fig. 7 (2). The spectra sp1, sp, sp, sp4, etc. shown in Fig. 7 indicate the frequency components of jitter. SP1 indicates the fundamental wave component of jitter. This fundamental wave (-sp2.sp, .

It can be seen that signals of frequencies indicated by sp4... are superimposed. Each spectrum sp1. sp2...
The frequency of the signal represented by . . . can be read from the scale 31 on the horizontal axis on the display surface. The fundamental wave and the signal superimposed thereon can be read by the scale 32 on the vertical axis on the display screen.

By performing frequency analysis using the dual accumulative fast Fourier transformer 23 in this manner, it is possible to frequency analyze and measure the jitter contained in the pulse to be measured Pa. Further, even if there are many types of pulse widths of the pulse Pa to be measured, the frequency components of jitter can be displayed as a spectrum.

Furthermore, in order to obtain the jitter superimposed on a pulse of one pulse width, when reading data from the buffer memory 27, only the data of the corresponding frequency components are read using the window function of the microcomputer 22, and this data is subjected to fast Fourier transform. Then frequency analysis can be performed. In this way, only the jitter superimposed on a single period pulse can be displayed as a spectrum.

On the other hand, the present invention also includes a function that can measure the state of fluctuation when the frequency of the shifter fluctuates.

In other words, if the jitter frequency is changing, each spectrum 5Pl-S on the spectrum shown in Figure 7
There are phenomena in which the magnitude of Ps changes over time, or spectra other than the spectra sp and -sp appear instantaneously.

Even if the magnitude of the spectrum SPI -sp varies, it moves so fast that it is impossible to remember the observed phenomenon in the mind.Also, even if a spectrum other than spectra SP1 to SP occurs instantaneously, that spectrum is It is also not possible to measure at what frequency it occurs.

For this reason, in the present invention, jitter signals that are sequentially taken into the memory as time passes are divided into blocks and taken out in accordance with the order of passage of time, and the data taken out in blocks is subjected to Fourier transform to perform frequency analysis. Data existing in a predefined frequency interval is extracted from the frequency-analyzed data, and the sum of the data is displayed on a display along the time axis. The displayed data represents fluctuations in components within the frequency range included in the measurement data acquired from the start to the end of the measurement.

Therefore, according to the present invention, for example, when the rotation of a rotating body changes over time, it is possible to display how the jitter frequency changes on the display. This display allows you to know that the jitter frequency is changing.

The configuration for this purpose includes a reading unit that blocks data from the backup memory 21 or 27 and sequentially reads it out, a fast Fourier transformer 23 that performs Fourier transform on the data read by the reading unit, and converts it into a frequency domain signal. The fast Fourier transformer 23 includes a storage device that stores the sum or peak value or ratio of spectra existing in a preset frequency interval from the frequency domain signal, and a storage device that stores the sum or peak value or ratio of the frequency components stored in this storage device. It can be configured with a display 25 that displays values or ratios along the time axis.

As the buffer memory referred to here, either 27 or 21 can be used. Here, for example, the backup memory 21
A case will be described in which data that has been AD converted sequentially over time is fetched via the buffer memory 27, and this data is sequentially read out and subjected to fast Fourier transform.

Assume that the backup memory 21 stores a jitter signal whose level changes as shown in FIG. 9, for example.

The microcomputer 22 reads out the block indicated by 8+ for this jitter signal as the first block, and sends, for example, 1024 digital shifter signals included in this first block B+ to the fast Fourier transform means 23, which converts the jitter signals to the fast Fourier transform means 23. Frequency analysis is performed on the jitter signal of 1 block B. Assume that the frequency analysis result is shown in FIG. 10A.

Next, the read address of the backup memory 21 is shifted by a numerator n corresponding to Δt in terms of time, and the second block B2
Read out. The jitter signal of this second bronch B2 is subjected to frequency analysis by the fast Fourier transform means 23. The results of this frequency analysis are shown in Figure 1B.

Furthermore, the read address of the buffer memory 21 is shifted by +n,
The third block B is read. The jitter signal of this third block B is subjected to frequency analysis by a fast Fourier transformer 23.

The results of this frequency analysis are shown in FIG. 10C.

In this way, the jitter signal stored in the buffer memory 21 is read out while sequentially shifting the read address by +n,
The jitter signal of each block is subjected to frequency analysis, and the frequency analysis results are stored in the main memory 24, for example.

Using the frequency-analyzed data stored in the main memory 24, the sum of frequency components included in a preset frequency interval f1 to f2 is determined. This calculation is performed by the microcomputer 22
The calculated data ΣA, ΣB, ΣC, . . . are stored in the main memory 24 again.

Therefore, the microcomputer 22 constitutes a reading means for reading out the contents of the backup memory 21 by predetermined addresses while sequentially shifting the reading start address, which is a component of the present invention.

Further, the storage device for storing the sum, peak value, or ratio of signal components existing in a preset frequency interval from the Fourier-transformed frequency domain data can be configured by the main memory.

The microcomputer 22 further takes out the calculated data stored in the main memory 24 and transfers it to the display 25. The display 25 shows calculated data ΣA and ΣB.

ΣC... are arranged according to the level along the time axis as shown in FIG. The curve drawn as a result of the arrangement is included in the frequency interval f1 to ft among the frequency components included in the shifter within the time from the time when the jitter signal is started to be captured into the buffer memory 21 to the time when the capture is finished. It shows how the signal components change over time.

Therefore, for example, by extracting and displaying only the component of frequency f, it is possible to display fluctuations in the component of frequency f.

Also, in this example, the frequency section f in the jitter signal.

Although we have explained the case where the sum of the signal components included in ~ft is calculated and its fluctuation is displayed, it is also possible to extract the maximum value contained in the interval from frequency f1 to ft and display the fluctuation of that maximum value. . It is also possible to display fluctuations in the ratio of the level of a certain specific frequency to other frequency components.

FIG. 8 shows another embodiment of the present invention. In this example, a time measuring means 33 for measuring the pulse width of the pulse to be measured is provided, and a time between an upper limit value and a lower limit value set in the time measuring means 33 is provided. A case is shown in which the configuration is such that data can be taken into the buffer memory 27 only when a pulse is input.

By providing the time measuring means 33 in this manner, even when the pulses to be measured with a plurality of pulse widths are manually applied, a pulse with one pulse width is extracted from among the pulses with a plurality of types of pulse widths and the buffer memory 27 can be written to. As a result, when measuring a shifter superimposed on a pulse with a single pulse width, the buffer memory 27 stores only the data indicating the fluctuation of that pulse width, and does not store data of other pulse widths. can make maximum use of its capacity.

"Operations and Effects of the Invention" As explained above, according to the present invention, the pulse to be measured is time-voltage converted to convert the pulse width fluctuation or pulse interval fluctuation of the pulse to be measured into voltage fluctuation, and this voltage fluctuation signal is Since the signal is AD-converted and input to the spectrum analyzer, it is possible to input to the spectrum analyzer a signal that does not contain the frequency component of the pulse to be measured, that is, has only the jitter component. As a result, when operated as a spectrum analyzer, only the spectrum showing the frequency components of jitter can be displayed on the display, and other signals with large levels are not displayed. Therefore, the displayed spectrum is displayed sufficiently large compared to the noise component, and the level, frequency, etc. can be reliably measured without being overwhelmed by the noise component.

However, if you operate the spectrum analyzer as an oscilloscope, you can see the jitter waveform. Therefore, the maximum and minimum values of jitter can be measured from the amplitude of this waveform.

Further, according to the present invention, since it is possible to display the temporal fluctuations of the jitter frequency on the display 25, it is possible to increase the probability of pointing out a defective part of, for example, a compact disk or magnetic disk drive device. can.

As described above, according to the present invention, various measurements related to pulse train signals can be carried out, and the effect is extremely large when it is used for evaluating digital regenerators and determining whether or not they are good or bad.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing an embodiment of this invention, Fig. 2 is a connection diagram for explaining an example of a time-voltage converter used in this invention, and Fig. 3 is a time-voltage converter and an AD converter. 4 and 5 are front views showing examples of the analysis results of the time interval analyzer according to the present invention, and FIG. 6 shows the analysis results shown in FIG. 5. FIG. 7 is a front view to explain additional analysis results obtained by the apparatus of the present invention, and FIG. 8 is a block diagram to explain another embodiment of the present invention. 9 to 11 are graphs for explaining the main analysis method of the apparatus of the present invention and the analysis results, and FIG. 12 is a diagram for explaining the conventional shifter measurement method. 11 spectrum analyzer, 12: time-voltage converter, 13: AD converter, 14: controller, 21.27: buffer memory, 22: microcomputer, 23: fast Fourier transform means, 24: main memory, 25: display.

Claims (1)

[Claims] (1) A. A digital spectrum analyzer equipped with an AD converter in its input circuit, and B. A time period for converting the pulse width of the pulse to be measured into a voltage proportional to the pulse width, which is provided before the AD converter. a voltage converter; C. a controller that detects the trailing edge of the pulse to be measured input to the time-voltage converter and causes the AD converter to perform an AD conversion operation; D. an AD of the AD converter; A buffer memory that sequentially stores conversion results; E. Reading means that reads out the contents of this buffer memory by predetermined addresses while sequentially shifting the reading start address; F. Fourier transforms the data read by this reading means and converts it into a frequency domain. G, storing the sum or peak value or ratio of signal components existing in a preset frequency interval from the frequency domain data Fourier transformed by the fast Fourier transformer; A time interval analysis device comprising: a storage device; and a display device that displays the sum, peak value, or ratio of frequency components stored in the storage device along a time axis.