JPH06237231A - Waveform discriminating device - Google Patents

Abstract

PURPOSE:To automate the eye pattern aperture evaluation of a digital signal containing a multilevel signal. CONSTITUTION:A sampling circuit 11 samples a specific time slot section of a digital signal S1 and generates sampling data S3. This data S3 is divided into plural levels by a level discriminating circuit 12 and becomes level discrimination data S4. This level discrimination data S4 is counted at every level and becomes counting data S5 by a counter circuit 13. When the digital signal S1 of the prescribed number of bits is inputted to this device, a CPU 2 calculates a standard deviation of the counting data S5 within a specific level range, and evaluates eye pattern aperture of the digital signal S1 from this standard deviation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waveform discriminating apparatus for evaluating eye pattern aperture of digital signals, and more particularly to a waveform discriminating apparatus suitable for evaluating eye pattern aperture of multi-valued PCM signals.

[0002]

2. Description of the Related Art Conventionally, eye pattern aperture evaluation is widely used as a waveform identifying means for determining the quality of a waveform of a digital signal. This eye pattern opening degree evaluation is generally performed by visually observing an eye pattern of a digital signal on a sampling oscilloscope using an eye mask to determine whether or not a desired eye pattern is obtained.

However, this visual identification of a digital signal waveform requires a human observation, so that it has a drawback that automatic measurement cannot be performed. Further, with respect to a signal whose eye pattern is deteriorated with a low probability, this deterioration may be overlooked.

Therefore, a test method for automating the above-described eye pattern aperture evaluation is disclosed in Japanese Patent Laid-Open Publication No. 1-15.
4660, published June 16, 1991). In this test method, the discrimination level of the digital signal to be evaluated is modulated with a sine wave, and the discrimination phase is modulated with a sine wave having a phase difference of π / 2 with the sine wave, and the discrimination point moves on a circle or an ellipse. To generate (a kind of Lissajous waveform), identify the digital signal by this identification point, and measure the error rate of the identified signal to evaluate the eye pattern aperture of the digital signal. There is.

[0005]

In the eye pattern opening degree evaluation of the digital signal described above, in the visual method, as described above, in addition to the fact that the automatic measurement cannot be performed, the signal whose eye pattern is deteriorated with a low probability is There was a drawback that it was not possible to perform a sufficient evaluation.

Further, since the above-mentioned automatic test method needs to perform an error rate measurement requiring a relatively long measurement time in eye pattern aperture evaluation, a device of a PCM communication device required to perform waveform identification in a short time. There was a drawback that it was difficult to adopt it when adjusting.

Further, this test method has a drawback that the eye pattern aperture of multi-level digital signals cannot be evaluated.

[0008]

A waveform discriminating apparatus of the present invention comprises a sampling circuit for sampling digital signals repeatedly input at a constant bit rate to generate sampling data, and dividing the sampling data into a plurality of levels. Level identification circuit that generates level identification data, a counter circuit that counts the level identification data for each level in a specific time slot section of the digital signal, and temporarily stores the count data, and a count circuit for the counting data in a specific level range. Waveform identifying means for calculating the standard deviation.

The specific time slot section may be set near the eye pattern convergence point of the digital signal, or may be set near the bit center point of the digital signal.

The waveform discriminating apparatus of the present invention comprises a sampling circuit for sampling digital signals of multi-valued amplitude level repeatedly input at a constant bit rate to generate sampling data, and dividing the sampling data into a plurality of levels. Level identification circuit that generates level identification data, a counter circuit that counts the level identification data for each level in a specific time slot section of the digital signal, and temporarily stores the count data, and a count circuit for the counting data in a specific level range. A waveform identifying means for calculating a standard deviation, the specific time slot section is set in the vicinity of the eye pattern convergence point of the digital signal, and the specific level range is 1 centered on the level of the eye pattern convergence point. It is possible to adopt a configuration having a unit amplitude level or less.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention. 2 is a signal waveform diagram for explaining one of the operations of the embodiment of FIG. 1. FIG. 2 (a) is an eye pattern diagram of the input digital signal S1, and FIG. 2 (b) is a count accumulated by the counter circuit 13. It is an amplitude histogram figure of data S5.

Referring to FIGS. 1 and 2 together, this waveform discriminating apparatus generates a waveform sampling signal S5 corresponding to the signal S1 in response to the repeatedly input digital signal S1 and the clock signal S2 of the signal S1. Measuring device 1 and count data S5 supplied from this measuring device 1.
Control circuit (hereinafter CPU) that calculates the degree of variation
2 and. The digital signal S1 is a P-channel demodulation signal from a PCM demodulation device that demodulates a 16-value QAM signal modulated by a random code sequence, and is a signal to be evaluated by the waveform identification device for eye pattern aperture. The digital signal S1 is a multilevel signal whose level randomly changes, and has five amplitude levels of -2, -1, 0, +1 and +2 when the unit amplitude level is 1, as shown in the figure. Also, this signal S1 is
Distortion and noise are added by the device and the transmission path through which the waveform has deteriorated, causing waveform deterioration.

The sampling circuit 11 built in the waveform sampling and measuring apparatus 1 divides the digital signal S1 into a number of sections for each bit section (for example, time T1 to T5 = Tb) and performs sampling to generate sampling data S3. The sampling data S3 is output by the level identification circuit 12 to a plurality of suitable levels, for example, amplitude levels −2 to +.
The two are divided into 256 levels, and the levels are identified. This level identification data S4 is sent to the counter circuit 13 by the counter circuit 13.
In the specific time slot section of the digital signal S1, counting is performed for each level (for each identification level number i, i is an integer of 0 to n), and the count data S5 is temporarily stored in the counter circuit 13.

The above-mentioned waveform sampling measuring device 1 forms a main function of a commercially available sampling oscilloscope, for example, manufactured by Sony Tektronix (T
The YPE CSA 404) digital oscilloscope has this capability. Then, the eye pattern D of the digital signal S1 is displayed on the display screen of the above-mentioned oscilloscope in synchronization with the repeatedly input clock signal S2 as shown in FIG. There are three openings of the eye pattern D corresponding to the number of amplitude levels (5 levels) of the digital signal S1, and the opening degree is determined by the degree of amplitude variation of the level identification data S4 shown in dots.

Here, times T1 and T5 indicate the bit center point, and time T3 indicates the convergence point of the eye pattern. The sampling data S3 corresponds to the waveform deterioration of the digital signal S1 and its level varies even when it should show the same amplitude level. This level variation is small at the eye pattern convergence point T3, and conversely, at the bit center point T1.
(Or T5) has the characteristic of being large. Figure 2
Referring to (b), this amplitude histogram diagram shows the time T2 to T4 near the eye pattern convergence point T3 as the counting time T.
m, and the frequency (dot frequency) of the count data S5 in the range of the mask A in which the range of amplitude level −2 to +2 is set as the count level range is counted. In the vicinity of the eye pattern convergence point T5, the dot frequencies are amplitude levels -2, -1, 0,
It has a minimum at +1 and +2, and conversely has a maximum at eye pattern convergence point levels (amplitude levels -1.5, -0.5, +0.5 and +1.5) intermediate these amplitude levels.

The CPU 2 of FIG. 1 reads the count data S5 from the measuring device 1 through the GP-IB bus at regular time intervals (for example, a specific number of bit inputs to the waveform sampling measuring device 1 of the digital signal S1), and counts this count. Data S
The degree of amplitude variation of 5 is statistically processed.

One of the above statistical processes is executed as follows. Now, the count data S5 at the identification level number i
The dot frequency of is Y (i). CPU1 determines the range of i which should evaluate the amplitude variation. When performing the statistical processing, the range of i is set to the level range of the amplitude levels −2 to −1 so that the peak part of the dot frequency Y (i) is collected (that is, the amplitude variation can be calculated). (Note that this amplitude level setting range may be set to another level range as long as the peak part of the dot frequency becomes a set). CPU2 is the dot frequency Y
From (0) to Y (n), the standard deviation σ representing the degree of amplitude variation of the count data S5 is calculated. Here, the variance of the count data S5 is s.

[0019]

The CPU 2 has a standard deviation σ of the count data S5.
Is calculated, a predetermined decision constant C and this standard deviation σ
When the standard deviation σ is smaller than the judgment constant C,
It is determined that the eye pattern opening degree of the digital signal S1 input to the waveform sampling measurement circuit 1 is good.

FIG. 3 is a diagram showing an example of an amplitude histogram of the count data S5 shown in FIG. 2 (b).

This counting data S5 has an identification level of 25.
Level identification data S4 divided into 6 sections (n = 255) is accumulated. Further, 40 sections (i = 0 to i = 39) are set between the amplitude levels -2 and -1. The count data S5 is obtained by accumulating the digital signal S1 for 5 bits and during the measurement time Tm. The bit interval of the digital signal S1 is 820 μS, and the sampling interval of the sampling circuit 11 is 20 nS. The standard deviation σ of this count data S5 calculated between the level identification numbers i = 0 to i = 39 is 7.3, and the digital signal S1 with the value of this standard deviation is the bit error rate 1
The result was × 10 ^-3 .

Since the bit error rate substantially corresponds to the eye pattern aperture, one of the operations of the embodiment of FIG. 1 is generated by using the sampling waveform measuring circuit 1 and the CPU 2 in response to the digital signal S1. Count data S
By calculating the standard deviation σ of 5, the digital signal S
The eye pattern opening degree of 1 can be easily evaluated in a short time.

In the embodiment of FIG. 1, the input digital signal S1 is a multi-level signal, but this signal S
If 1 is a binary signal, it is obvious that the eye pattern aperture evaluation can be performed more easily.

FIG. 4 is a signal waveform diagram for explaining another operation of the embodiment shown in FIG. 1. FIG. 4A is an eye pattern diagram before the waveform of the input digital signal S1 is improved, and FIG. Is an amplitude histogram diagram of the count data S5 accumulated in the counter circuit 13 in FIG. 7A, FIG. 7C is an eye pattern diagram after the waveform of the input digital signal S1 is improved, and FIG. 7D is a counter circuit diagram in FIG. It is an amplitude histogram figure of the count data S5 which 13 accumulates.

In the operation of the embodiment shown in FIG. 4, the count data S of the mask B portion shown in FIG. 2A or FIGS. 4A and 4C is obtained.
From 5, the standard deviations σ1 and σ2 of this data S5 are calculated. The mask B is a bit center point T1 of the digital signal S1.
, Between time (T1-Td) and time (T1 + Td), and near the peak point of the amplitude, amplitude levels +2 to +
It is formed in the range of 1.5. When the waveform of the digital signal S1 is deteriorated (see FIGS. A and b, when the device is not adjusted, etc.), the convergence of the peak point of the signal S1 to the time T1 is poor, so that the dot frequency of the count data S5 is The peak spreads over a wide range of amplitude levels, and thus the standard deviation σ1 of the count data S5 spreads at ya / 2 as shown in the figure. However, when the waveform of the digital signal S1 is good (see the diagrams c and d, after adjustment of the device, etc.), the peak of the signal S1 converges to the time T1 well, and the count data S1.
The peak of the dot frequency of 5 becomes narrow, and this count data S
As shown in the figure, the standard deviation σ2 of 5 becomes narrow as yb / 2. Therefore, also in the operation of this embodiment, the eye pattern opening degree of the digital signal S1 can be evaluated by calculating the standard deviation of the count data S5.

[0027]

As described above, the waveform discriminating apparatus according to the present invention samples a digital signal whose eye pattern aperture should be evaluated (waveform discriminating), and specifies the standard deviation of the amplitude level in this sampling data. It is divided into time and amplitude levels and the eye pattern aperture is evaluated from the result of this calculation.Evaluation of the eye pattern aperture of digital signals is performed automatically and even for signals with degraded eye patterns with a low probability. The effect is that sufficient evaluation can be performed.

Further, since the present invention can identify a waveform in a short time by using a simple device, it can be effectively used when adjusting a device of a PCM communication device.

Further, the present invention has an effect that the eye pattern opening degree of a multilevel digital signal can be evaluated.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

2A and 2B are signal waveform diagrams for explaining one of the operations of the embodiment of FIG. 1, in which FIG. 2A is an eye pattern diagram of an input digital signal, and FIG. 2B is count data S accumulated in a counter circuit 13.
5 is an amplitude histogram chart of FIG.

FIG. 3 is a diagram showing an example of an amplitude histogram of count data S5 of FIG. 2 (b).

4A and 4B are signal waveform diagrams for explaining another operation of the embodiment of FIG. 1, where FIG. 4A is an eye pattern diagram before waveform improvement of an input digital signal, and FIG. 4B is a counter in FIG. Amplitude histogram diagram of the count data S5 accumulated in the circuit 13, (c) is an eye pattern diagram after waveform improvement of the input digital signal, (d) is an amplitude histogram diagram of the count data S5 accumulated in the counter circuit 13 in (c) Is.

[Explanation of symbols]

 1 waveform sampling measurement circuit 2 CPU 11 sampling circuit 12 level identification circuit 13 counter circuit

Claims (5)

[Claims] 1. A sampling circuit for sampling digital signals repeatedly input at a constant bit rate to generate sampling data; a level discrimination circuit for dividing the sampling data into a plurality of levels to generate level discrimination data; A counter circuit for counting level identification data for each level in a specific time slot section of the digital signal and temporarily accumulating the counted data; and a waveform identification means for calculating a standard deviation of the counted data in a specific level range. Waveform identification device characterized by. 2. The waveform identifying apparatus according to claim 1, wherein the specific time slot section is set near an eye pattern convergence point of the digital signal. 3. The waveform identifying apparatus according to claim 1, wherein the specific time slot section is set near a bit center point of the digital signal. 4. The digital signal according to claim 1, wherein the digital signal has a multi-valued amplitude level, and the specific level range is one unit amplitude level or less centered on the level of the eye pattern convergence point. Waveform identification device. 5. A sampling circuit for generating sampling data by sampling a digital signal of multi-valued amplitude level repeatedly input at a constant bit rate, and a level for dividing the sampling data into a plurality of levels to generate level identification data. An identification circuit, a counter circuit for counting the level identification data for each level in a specific time slot section of the digital signal, and temporarily storing the counted data, and a waveform identification for calculating a standard deviation of the counted data in a specific level range. The specific time slot section is set in the vicinity of the eye pattern convergence point of the digital signal, and the specific level range is 1 unit amplitude level or less centered on the level of the eye pattern convergence point. Waveform identification device characterized by.