JP2004357050A - System and method for evaluating waveform quality - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a waveform quality evaluation system capable of evaluating waveform quality on the basis of the characteristic of the form itself represented by a waveform. <P>SOLUTION: This waveform quality evaluation system is provided with an oscilloscope 2 and a waveform quality evaluating device 3, and the waveform quality evaluating device 3 is provided with a storing means 32 and a CPU 36. The storing means 32 stores waveform evaluation value calculation reference and an adjustment parameter corresponding to an evaluation value of a waveform. The oscilloscope 2 inputs a waveform based on an adjustment parameter set by a DUT 1 and samples the waveform. Also, the CPU 36 calculates the characteristic amount of the sampled waveform, refers to the waveform evaluation value calculation reference to calculate an evaluation value based on the characteristic amount and outputs an adjustment parameter corresponding to the calculated evaluation value to the DUT 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a waveform quality evaluation system and a waveform quality evaluation method for evaluating waveform quality.
[0002]
[Prior art]
In a conventional waveform identification device, a digital signal to be identified is sampled, and a standard deviation of an amplitude level in the sampled data is calculated by dividing the standard deviation into a specific time and amplitude level, and the eye pattern aperture is calculated from the calculation result. It is evaluated (for example, see Patent Document 1).
[0003]
[Patent Document 1]
JP-A-6-237231 (page 4, FIG. 1)
[0004]
[Problems to be solved by the invention]
The conventional waveform discriminating apparatus evaluates the eye pattern aperture based on the standard deviation. This evaluation utilizes that the bit error rate of the digital signal obtained by the standard deviation corresponds to the eye pattern aperture. Was something. For this reason, when searching for the optimal adjustment parameter of the device under test, there is an inconvenience that the quality of the waveform cannot be evaluated from the characteristics of the shape itself represented by the waveform as a digital signal based on the adjustment parameter. In general, when searching for an adjustment parameter of a device under test, the output waveform from the device under test changes according to the adjustment parameter. It was desired to evaluate the waveform from the characteristics of the shape itself represented by the digital signal to be identified.
[0005]
The present invention has been made to solve the above-described problem, and an object thereof is to search for an adjustment parameter of an object to be measured, based on a characteristic of a shape itself represented by an output waveform from the object to be measured. To obtain a waveform quality evaluation system and a waveform quality evaluation method capable of evaluating waveform quality.
[0006]
[Means for Solving the Problems]
A waveform quality evaluation system according to the present invention includes a sampling unit, a storage device, and a processing unit. The sampling means inputs a waveform based on the adjustment parameters set for the device under test, and samples this waveform. Further, the storage means stores a waveform evaluation value calculation reference which is a reference for calculating an evaluation value of the waveform based on the characteristic amount of the waveform, and stores an adjustment parameter corresponding to the evaluation value. Further, the processing means calculates the waveform feature value based on the shape of the waveform after sampling, and calculates the waveform evaluation value based on the calculated feature value with reference to the waveform evaluation value calculation criterion, A search is made from storage means for storing the adjustment parameter corresponding to the calculated evaluation value, and the adjustment parameter after the search is output to the device under test.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
Embodiment 1 of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an overall configuration of a waveform quality evaluation system according to Embodiment 1 of the present invention. In the drawings, the same reference numerals indicate the same or corresponding parts.
[0008]
In FIG. 1, a DUT (device under test) 1 outputs a waveform based on predetermined adjustment parameters, and for example, an optical transmitter is used. The adjustment parameters are used to change the output waveform of the DUT 1, and include, for example, a voltage value parameter and a current value parameter. The oscilloscope (sampling means) 2 inputs a waveform (digital signal) based on the adjustment parameters set by the DUT 1, and samples this waveform. The waveform quality evaluation device 3 evaluates the quality of the waveform output from the DUT 1, and uses, for example, a personal computer. The pulse pattern generator 4 supplies a data pattern to the DUT 1 and generates a clock signal used when the oscilloscope 2 samples a waveform.
[0009]
The oscilloscope 2 has an O / E converter (optical / electrical converter) 21, a sampling circuit 22, a filter circuit 23, and a memory 24.
[0010]
In addition, the waveform quality evaluation device 3 includes a communication port 31, a storage device (storage unit) 32, a keyboard 33, a mouse 34, a display 35, and a CPU (processing unit) 36. Then, the storage device 32 stores a waveform evaluation value calculation reference and an adjustment parameter corresponding to the waveform evaluation value. Here, the “waveform evaluation value calculation criterion” is a criterion for calculating the evaluation value of the waveform based on the characteristic amount of the waveform, and for example, a function is used. The “waveform feature amount” is a quantitative value obtained using the waveform shape itself, and corresponds to, for example, the distance between the determination mask and the waveform. The “evaluation value” is an index value for evaluating the quality of the output waveform from the DUT 1, and a numerical value such as “0” or “1” is used, for example. This evaluation value is an objective judgment material for judging the quality. Note that the storage device 32 is, for example, a ROM, a RAM, an HDD, or the like.
[0011]
Next, the operation of the waveform quality evaluation system according to the first embodiment will be described. FIG. 2 is a flowchart showing the operation of the waveform quality evaluation system according to the first embodiment.
[0012]
The DUT 1 is set with a certain adjustment parameter, and automatically outputs a waveform based on the adjustment parameter to the oscilloscope 2.
[0013]
In step 100, the sampling circuit 22 of the oscilloscope 2 inputs the waveform output from the DUT 1 via the O / E converter 21. The O / E converter 21 converts an optical signal into an electric signal. Further, the sampling circuit 22 inputs the clock signal generated by the pulse pattern generator 4.
[0014]
Next, in step 101, the sampling circuit 22 performs sampling on the electric-converted waveform based on the waveform converted into the electric signal by the O / E converter 21 and the clock signal generated by the pulse pattern generator 4. Do. This sampling is, for example, a process of periodically extracting instantaneous voltage components of a plurality of different waveforms converted into electric signals by the O / E converter 21. Then, the filter circuit 23 filters the waveform after sampling (referred to as sampling data) and stores the filtered waveform in the memory 24.
[0015]
Next, in step 102, the CPU 36 of the waveform quality evaluation device 3 sequentially inputs the waveform stored in the memory 24 from the oscilloscope 2 via the communication port 31, and the voltage axis direction (y-axis direction) of this waveform is In addition, an area distribution (a cross point and a voltage level described later) in the time axis direction (x axis direction) is calculated. An example of this calculation is shown in FIG.
[0016]
FIG. 3 is a diagram illustrating an example in which the waveform quality evaluation device illustrated in FIG. 1 calculates a region distribution in a voltage axis direction and a time axis direction for an output waveform from a DUT. In FIG. 3, a plurality of different output waveforms continuously exist in the target region 6 for a certain voltage axis and a time axis, and these have different voltage values from each other. The CPU 36 calculates points (hereinafter referred to as “cross points”) Tcrs0 and Tcrs1 where the waveforms cross in the time axis direction, and the 0 level (Vlv0) and 1 level (Vlv1) of the voltage in the voltage axis direction.
[0017]
Next, in step 103, the CPU 36 normalizes the waveform. When normalizing the waveform, the CPU 36 normalizes the waveform for each of the time axis component and the voltage axis component using, for example, the following equations (1) and (2).
[0018]
Time axis component X ′ = {(X−Tcrs0)} (Tcrs1−Tcrs0)} (1)
Voltage axis component Y ′ = {(Y−Vlv0)} (Vlv1−Vlv0)} (2)
Here, (X, Y) is sampling data, and (X ′, Y ′) is normalized data.
[0019]
Next, in step 104, the CPU 36 divides the target area 6 into predetermined areas, and creates a density histogram for the divided areas. FIG. 4 shows an example of this creation.
[0020]
FIG. 4 is a diagram showing an example of a density histogram created by the waveform quality evaluation device shown in FIG. FIG. 4A shows a divided area 311 of the target area 6 shown in FIG. 3, and FIG. 4B shows a density histogram 311a for the divided area 311.
[0021]
Next, in step 105, the CPU 36 smoothes the density histogram 311a for the divided area 311. The CPU 36 smoothes the density histogram 311a using, for example, the following equation (3).
[0022]
g (i, j) = [ {A 1 × f (i-1, j-1)} + {A 2 × f (i, j-1)} + {A 3 × f (i + 1, j-1) ｝ + ｛A ₄ × f (i-1, j)｝ + ｛A ₅ × f (i, j)｝ + ｛A ₆ × f (i + 1, j) + ｛A ₇ × f (i-1, j + 1) )｝ + ｛A ₈ × f (i, j + 1)｝ + ｛A ₉ × f (i + 1, j + 1)] ÷ ΣAi (3)
Here, f (i, j) is a value at the target point of the density histogram, and g (i, j) is a smoothed value. Ai is the weight at each point, Ai is the value from _{A 1} to _{A 9.}
[0023]
FIG. 5 shows values including the value f (i, j) used in the above equation (3). FIG. 5 is a diagram illustrating an example of values used in the smoothing process by the waveform quality evaluation device illustrated in FIG. 1. In FIG. 5, values f (i−1, j−1), f (i, j−1), f (i + 1, j−) at eight neighboring points are centered on the value f (i, j) at the point of interest. 1), f (i-1, j), f (i + 1, j), f (i-1, j + 1), f (i, j + 1), and f (i + 1, j + 1).
[0024]
FIG. 6 shows the weights Ai used in the above equation (3). FIG. 6 is a diagram illustrating an example of weights used in the smoothing process by the waveform quality evaluation device illustrated in FIG. In FIG. 6 (A), that the definitive from _{A 1} to _{A 9} is shown, FIG. 6 (B), the are shown typical examples of (C), in (D), respective weight values. For example, in the case of FIG. 6 (B), the weight of the _{A 1 A 9} are all "1".
[0025]
FIG. 7 shows an example in which the CPU 36 performs smoothing. FIG. 7 is a diagram illustrating an example of a waveform after smoothing performed by the waveform quality evaluation device illustrated in FIG. 1. FIG. 7 shows a waveform 311b obtained by smoothing the waveform 311a. The waveform 311a is density-divided into gray levels from 0 to 23, and the waveform 311b is smoothed into gray levels from 0 to 15.
[0026]
In step 105, when smoothing the density histogram 311a, the CPU 36 repeatedly executes the above-described smoothing process. The waveform after this smoothing is shown in FIG. FIG. 8A is a diagram illustrating an example of a smoothed waveform repeatedly executed by the waveform quality evaluation device illustrated in FIG. 1. FIG. 8A shows a waveform 311c smoothed to gradations from 0 to 13 (a waveform in which the smoothing process is performed four times in succession). In this way, it is possible to remove the noise component included in the waveform, it is easy to identify the shape itself represented by the waveform, and it is possible to obtain the effect of enhancing the characteristics of the waveform. Note that the determination mask 313 is used for calculating the characteristic amount of the waveform, as described later.
[0027]
Next, in step 106, the CPU 36 binarizes the smoothed waveform. This waveform is shown in FIG. FIG. 8B is a diagram illustrating an example of a waveform after binarization executed by the waveform quality evaluation device. FIG. 8B shows a binarized waveform 311d.
[0028]
Next, in step 107, the CPU 36 calculates the characteristic amount of the waveform based on the waveform represented by the binarized waveform, and refers to the waveform evaluation value calculation criterion stored in the storage device 32 to calculate the feature value. An evaluation value of the waveform is calculated based on the later feature amount. Specifically, the CPU 36 calculates the distance between the determination mask 313 and the waveform 311d when calculating the characteristic amount of the waveform. FIG. 9 shows an example of this calculation.
[0029]
FIG. 9 is a diagram illustrating an example of a feature amount calculated by the waveform quality evaluation device illustrated in FIG. 1 using the determination mask. In FIG. 9, the distances a1 to a4 between the determination mask 313 and the waveform 311d, and b and c are calculated as the feature amounts, respectively. By calculating b and c from these distances a1 to a4, it is possible to quantitatively analyze changes in the output waveform from DUT1.
[0030]
When calculating the evaluation value with reference to the waveform evaluation value calculation criterion in step 107, the CPU 36 calculates the evaluation value based on b and c, for example, from the distances a1 to a4 described above. .
[0031]
Next, at step 108, the CPU 36 determines whether or not the calculated evaluation value is an allowable value. The permissible value defines a permissible level for the quality of the waveform indicated by the evaluation value, and includes a specific value and a value in a certain range. This allowable value is stored in the storage device 32.
[0032]
Next, in step 109, if the evaluation value after the calculation is not the allowable value, the CPU 36 searches (determines) an adjustment parameter corresponding to the evaluation value after the calculation from the storage device 32, and stores the adjustment parameter in the communication port 31. Is output to the DUT 1 via the.
[0033]
The DUT 1 inputs the adjustment parameters from the waveform quality evaluation device 3 via an adjustment terminal (not shown), sets the adjustment parameters, and then automatically regenerates a waveform based on the adjusted adjustment parameters to the oscilloscope 2. Output and go to the next step 100.
[0034]
The oscilloscope 2 executes the processing of steps 100 and 101, and the waveform quality evaluation device 3 executes the processing of steps 102 to 107.
[0035]
Then, in step 108, the CPU 36 determines whether or not the evaluation value after calculation is an allowable value. If the evaluation value after calculation is not an allowable value, the processing from steps 100 to 107 is repeated. That is, the following processes (1) and (2) are sequentially repeated. (1) The oscilloscope 2 re-inputs the waveform based on the adjustment parameter output by the CPU 36 of the waveform quality evaluation device 3 from the DUT 1, and samples the waveform after the re-input. (2) The CPU 36 calculates the characteristic amount of the waveform based on the shape of the waveform after sampling, and refers to the waveform evaluation value calculation criterion in the storage device 32 and calculates the characteristic amount of the waveform based on the calculated characteristic amount. An evaluation value is calculated, an adjustment parameter corresponding to the evaluation value after the calculation is searched, and the adjustment parameter after the search is output to the DUT1.
[0036]
Then, in step 108, the CPU 36 determines whether or not the calculated evaluation value is an allowable value. If the calculated evaluation value is an allowable value, the process ends.
[0037]
Thereafter, when the user performs a predetermined operation via the input means of the keyboard 33 or the mouse 34, the CPU 36 of the waveform quality evaluation device 3 causes the associated characteristic amount, evaluation value, and output waveform of the DUT 1 to be output. The adjustment parameter is read out from the storage device 32, and the feature amount, the evaluation value, and the adjustment parameter are output to the display (display unit) 35 in association with each other. As a result, the user can grasp the quality evaluation of the output waveform from the DUT 1.
[0038]
As described above, the oscilloscope 2 inputs a waveform based on the adjustment parameters set by the DUT 1 and samples this waveform. Then, the waveform quality evaluation device 3 calculates a characteristic amount of the waveform based on the shape of the waveform after sampling, searches for an adjustment parameter corresponding to the evaluation value of the calculated waveform based on the characteristic amount, and Is output to the DUT1. For this reason, when searching for the optimal adjustment parameter to be set in the DUT 1, it is possible to automatically search for the adjustment parameter corresponding to the evaluation value that expresses the characteristic of the shape itself represented by the output waveform of the DUT 1 in an index manner. Further, in this manner, the entire shape represented by the waveform can be set as an evaluation target. This point is different from a conventional waveform discriminating apparatus that performs evaluation based on a waveform in a specific range.
[0039]
Moreover, when searching for adjustment parameters, the waveform quality evaluation device 3 determines whether or not the calculated waveform evaluation value is an allowable value. If the evaluation value is not an allowable value, the waveform quality evaluation device 3 searches for an adjustment parameter. Outputting (reading) these adjustment parameters to the DUT 1 and repeatedly calculating the evaluation value of the waveform based on the output adjustment parameters are repeatedly performed. Therefore, the optimum output waveform of the DUT 1 can be automatically searched.
[0040]
Further, when calculating the characteristic amount of the waveform, the waveform quality evaluation device 3 converts the sampled waveform into a density histogram, and performs a smoothing process using the density histogram. As a result, a signal from which the noise component included in the waveform has been removed can be extracted, so that the characteristics of the waveform can be evaluated in an optimal state. Further, when calculating the characteristic amount of the waveform, the waveform quality evaluation device 3 binarizes the sampled waveform. This makes it easy to compare the waveforms and to easily evaluate the degree of change of the waveform due to the difference in the adjustment parameter.
[0041]
In the first embodiment, the waveform quality evaluation device 3 calculates the distance between the determination mask 313 and the waveform 311d when calculating the characteristic amount of the waveform. However, the present invention is not limited to this. For example, the waveform quality evaluation device 3 may calculate a difference between a plurality of different waveforms as a waveform feature amount. An example of this calculation is shown in FIGS. FIG. 10 is a diagram showing an example of a plurality of waveforms used when the waveform quality evaluation device shown in FIG. 1 calculates the characteristic amount of the waveform, and FIG. 11 is a diagram showing the waveform quality evaluation device shown in FIG. 11 is a diagram showing an example of a feature amount calculated using the waveform shown in FIG. 10A, 10B, and 10C show waveforms 3111, 3112, and 3113 after binarization, respectively, and in FIG. 11, a difference between the waveform 3112 and the waveform 3113 is obtained. As a result, it is possible to determine the amount of change in each waveform, and it is possible to capture a transitional change in the waveform when conditions such as the adjustment parameter and the temperature of the DUT 1 change.
[0042]
In addition, the waveform quality evaluation device 3 uses the number of predetermined sampling data (waveform after sampling) and the number of decompositions of the density histogram 311a when calculating the characteristic amount of the waveform, but is not limited thereto. When the number of sampling data and the number of decompositions of the density histogram 311a change, the accuracy of the characteristic amount of the waveform also changes, so that the accuracy of the evaluation value can be changed. This relationship is shown in FIG. FIG. 12 is a diagram showing the relationship between the number of sampling data and the number of decompositions of the density histogram and the accuracy of the evaluation value. According to FIG. 12, for example, when the number of sampling data and the number of decompositions of the density histogram are changed (in the direction of “small” or “large” in FIG. 12), the search for the adjustment parameter according to the coarse adjustment or the fine adjustment is performed. It is possible to do.
[0043]
Furthermore, although the oscilloscope 2 and the waveform quality evaluation device 3 have been described as being independent from each other, an integrated device having these functions may be used. For example, the integrated oscilloscope 2 having the function of the waveform quality evaluation device 3 may be used.
[0044]
【The invention's effect】
As described above, the waveform quality evaluation system according to the present invention, when searching for an adjustment parameter set in a device under test, evaluates an evaluation value that expresses the characteristic of the shape itself represented by the waveform based on the adjustment parameter as an index. The quality of the waveform can be evaluated based on this.
[Brief description of the drawings]
FIG. 1 is a diagram showing an overall configuration of a waveform quality evaluation system according to Embodiment 1 of the present invention.
FIG. 2 is a flowchart showing an operation of the waveform quality evaluation system according to the first embodiment of the present invention.
FIG. 3 is a diagram illustrating an example of a waveform input by the oscilloscope illustrated in FIG. 1;
FIG. 4 is a diagram showing an example of a density histogram created by the waveform quality evaluation device shown in FIG.
FIG. 5 is a diagram illustrating an example of a value at a point of interest used in the smoothing process by the waveform quality evaluation device illustrated in FIG. 1;
FIG. 6 is a diagram illustrating an example of weights used for a smoothing process by the waveform quality evaluation device illustrated in FIG. 1;
FIG. 7 is a diagram showing an example of a smoothed waveform processed by the waveform quality evaluation device shown in FIG. 1;
8 is a diagram showing an example of a waveform obtained by smoothing and binarizing the waveform shown in FIG. 7 by the waveform quality evaluation device shown in FIG.
9 is a diagram illustrating an example of a feature amount calculated by the waveform quality evaluation device illustrated in FIG. 1 using a determination mask.
FIG. 10 is a diagram illustrating an example of a plurality of waveforms used when the waveform quality evaluation device illustrated in FIG. 1 calculates an evaluation value.
11 is a diagram illustrating an example of a feature amount calculated by the waveform quality evaluation device illustrated in FIG. 1 using the waveform illustrated in FIG. 10;
FIG. 12 is a diagram showing the relationship between the number of sampling data and the number of density histogram decompositions.
[Explanation of symbols]
1 DUT (DUT), 2 oscilloscope, 3 waveform quality evaluation device, 4 pulse generator, 21 O / E converter, 22 sampling circuit, 23 filter circuit, 24 memory, 31 communication port, 32 storage device, 36 CPU.

Claims (8)

A storage unit that stores a waveform evaluation value calculation criterion that is a criterion for calculating the evaluation value of the waveform based on the characteristic amount of the waveform, and stores an adjustment parameter corresponding to the evaluation value.
Sampling means for inputting a waveform based on the adjustment parameter set in the device under test and sampling the waveform,
Calculating a characteristic value of the waveform based on the shape of the waveform after sampling; calculating an evaluation value of the waveform based on the characteristic value after calculation with reference to the waveform evaluation value calculation criterion; Processing means for searching for an adjustment parameter corresponding to the evaluation value after the calculation with reference to, and outputting the adjustment parameter after the search to the device under test. The processing means includes:
When searching for the adjustment parameter, determine whether the evaluation value after the calculation is an allowable value, if the evaluation value after the calculation is not the allowable value,
A process of searching for an adjustment parameter corresponding to the evaluation value after the calculation,
A process of outputting the adjustment parameter after the search to the device under test,
The sampling means re-inputs a waveform based on the adjustment parameter output by the processing means from the device under test, and samples the waveform after the re-input,
The processing means recalculates the characteristic value of the waveform based on the shape of the waveform after the sampling, and re-calculates the evaluation value based on the characteristic value after the calculation with reference to the waveform evaluation value calculation criterion. 2. The waveform quality evaluation system according to claim 1, wherein the calculating process is repeatedly executed. The method according to claim 1, wherein, when calculating the characteristic amount of the waveform, the processing unit converts the waveform after the sampling into a density histogram, and performs a smoothing process using the density histogram. Waveform quality evaluation system. 3. The waveform quality evaluation system according to claim 1, wherein the processing unit performs a binarization process on the waveform after the sampling when calculating the characteristic amount of the waveform. 4. A sampling step of inputting a waveform based on the adjustment parameter set in the device under test and sampling the waveform;
A feature value calculating step of calculating a feature value of the waveform based on a shape represented by the sampled waveform;
An evaluation value calculation step of calculating the evaluation value based on the calculated feature value, with reference to a waveform evaluation value calculation criterion that is a criterion for calculating the evaluation value of the waveform based on the feature value of the waveform; ,
A search step of searching an adjustment parameter corresponding to the calculated evaluation value from storage means,
Outputting a searched adjustment parameter to the device under test. The method further includes a determination step of determining whether the evaluation value calculated in the evaluation value calculation step is an allowable value,
When it is determined in the determining step that the evaluation value is not the allowable value, the search step, the adjustment parameter output step, the sampling step, the feature amount calculation step, and the evaluation value calculation step are repeatedly executed. 6. The waveform quality evaluation method according to claim 5, wherein: 7. The waveform quality according to claim 5, wherein the feature amount calculating step includes a step of converting the waveform sampled in the sampling step into a density histogram, and performing a smoothing process using the density histogram. Evaluation method. 7. The waveform quality evaluation method according to claim 5, wherein the feature amount calculating step includes a step of performing a binarization process on the waveform sampled in the sampling step.

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