Using Eye Diagrams


Other Eye Diagram topics

Overview

PLTS constructs measurement-based eye diagrams (or patterns) by convolving the calculated time domain impulse response (generated from frequency domain measurement data) with a synthesized pattern of bit sequences. The following is a simplified block diagram of the eye diagram creation process.

With eye diagrams you can see signal quality with one display, you can diagnose problems, such as attenuation, noise, jitter, and dispersion that arise or characterize specific parts of the system. You can then view the measurement in the Time Domain mode to help isolate the source of the problem.

2-Level (PAM2) versus 4-Level (PAM4) Eye Diagrams

NRZ (non return to zero), also known as PAM2, is a Pulse Amplitude Modulated (PAM) signal with two amplitude levels. This signaling method transmits one bit of data for every bit, unit interval, or symbol interval.

NRZ (PAM2) Signal

 

Instead of a 0 and 1 level as in NRZ, PAM4 has four amplitude levels (0, 1, 2, and 3). This signaling method transmits 2 bits of data for every symbol. As a result, PAM4 transmits twice as much data per unit time.

PAM4 Signal

The Eye Diagram

The eye diagrams shown below identify key eye diagram definitions.

2-Level Eye Diagram (PAM2)

4-Level Eye Diagram (PAM4)

 

1

Zero Level

Zero Level is a measure of the mean value of the logical 0 of an eye diagram.

2

One Level

One Level is a measure of the mean value of the logical 1 of an eye diagram.

3

Rise Time

Rise time is a measure of the transition time of the data from the 10% level to the 90% level on the upward slope of an eye diagram.

4

Fall Time

Fall time is a measure of the transition time of the data from the 90% level to the 10% level on the downward slope of an eye diagram.

5

Eye Height

Eye height is a measure of the vertical opening of an eye diagram. An ideal eye opening would be measured from the one level to the zero level. However, noise on the eye will cause the eye to close. The eye height measurement determines eye closure due to noise.

6

Eye Width

Eye width is a measure of the horizontal opening of an eye diagram. Ideally, the eye width would be measured between the crossing points of the eye. However, jitter may appear on the waveform and influence the eye opening. A preference setting determines exactly how this measurement is made. Learn more.

7

Deterministic Jitter

Deterministic jitter is the deviation of a transition from its ideal time caused by reflections relative to other transitions.

8

Eye Amplitude

Eye amplitude is the difference between the logic 1 level and the logic 0 level histogram mean values of an eye diagram.

9

Bit Rate

Bit rate (data rate) is the inverse of bit period (1 / bit period). The bit period is a measure of the horizontal opening of an eye diagram at the crossing points of the eye.

10

Two-Level

Two-Level is a measure of the mean value of the logical 2 of a PAM4 eye diagram.

11

Three-Level

Three-Level is a measure of the mean value of the logical 3 of a PAM4 eye diagram.

Time Domain Windowing and Eye Diagrams

Changing the Time Domain Window setting has the following effect on Eye Diagrams:

To select Time Domain Window Settings

Click Tools, then Time Domain Settings

Learn more about Time Domain Windowing

Changed Data Icons

During an Eye Diagram conversion, one of the following may appear in the corner of the display. Learn more about these icons.

Icon

 Icon Name

Resampled Data - This icon indicates that only the harmonically-related data points were used to generate time domain data.

Interpolated Data - This icon indicates interpolation is performed to calculate the harmonically-related points that were not measured. Any measurements that were performed at harmonically-related points are left unchanged. The interpolated data is used, along with the measured harmonically-related data, to perform the Inverse Fast Fourier Transform (IFFT) for the calculated time domain data.

Bad Data - This icon indicates there are less than 10 harmonically-related data points in the measured data. In this case, all of the non harmonically-related data is used to perform the Inverse Fast Fourier Transform (IFFT) to calculate time domain data. This may result in inaccurate time domain data.

Viewing Data using Eye Diagrams

Learn how to open Eye Diagram plot windows.

With Eye Diagrams, only transmission paths are displayed; no reflection paths are displayed.

1. On the Parameter Format Selection pane:

2. The Choose Bit Pattern dialog box may be displayed.  The dialog box is NOT displayed if the bit pattern has already been selected for the data.

The selected Eye Diagrams are plotted.

3. To view a single plot, double-click on the plot. Double-click again to view all plots.

Note:  Beginning with PLTS 4.5, the vertical axis of Eye Diagrams can be scaled using the scaling toolbar. Reset the vertical scale by right-clicking the Eye diagram, then click Reset.

4. When a Multi-channel Eye Diagram is active, the buttons (red circle in above image) are displayed.

Eye Diagram Markers

To add markers to an Eye Diagram, right-click on the plot, then click Insert.

Each eye diagram marker has two components:

  1. The X-axis component is displayed as a line that extends from the top to the bottom of the eye diagram.

  2. The Y-axis component is displayed as a line that extends from the left side to the right side of the eye diagram.

These markers can be moved ONLY from Marker Bar slider control.

Automated Eye Diagram Measurement Results

To see Eye Diagram measurement results, statistics, and the following Eye Diagram options:

On the Parameter toolbar click the Parameter Meas Tab

1. Hide Histogram and re-measure Eye Parameters - Click to refresh the results.

2. Draw Eye Color Grades - Click to show the densest patterns as red, then yellow, then light green, then dark blue (as least dense).

3 through 8  (not available for PAM4 signal) Show histograms and dimensions of how the measurements are made:

9. Launch the Configure Eye Measurements dialog.

 

2-Level Signal (PAM2)

Eye Amplitude plotted on selected eye diagram.

Name

Definition

Eye Level Zero (mV)

Mean value of logical zeros

Eye Level One (mV)

Mean value of logical ones

Eye Level Mean (mV)

Mean value of logical ones and zeros

Eye Amplitude (mV)

Difference between logical 1 and logical 0 histogram mean values.

Eye Height (mV)

Vertical opening of the eye diagram

Eye Height (dB)

Vertical opening of the eye diagram

Eye Width

Horizontal opening of the eye diagram

Eye Opening Factor

Ratio of eye height to eye amplitude

Eye Signal to Noise

Ratio of the signal difference in logical 1 to logical 0 relative to the noise present at both levels.

Eye Duty Cycle Distortion

Time separation between the rising edge and falling edge at the 50% (middle) threshold of the eye diagram.

Eye Duty Cycle Distortion (in %)

Percent of duty cycle distortion

Eye Rise Time (20-80)

Mean transition time of the data on the upward slope (rising edge).

Eye Fall Time (80-20)

Mean transition time of the data on the downward slope (falling edge).

Eye Jitter (PP)

Time variances between the rising and falling edges. These edges affect the crossing point of the eye. PP= full width of the histogram at the eye diagram crossing point.

Eye Jitter (RMS)

Time variances between the rising and falling edges. These edges affect the crossing point of the eye. RMS= standard deviation of the histogram at the eye diagram crossing point.

4-Level Signal (PAM4)

Click on a parameter to view the result on the plot

Name

Definition

Levels

 

Level 0

Mean value of logical zeros

Level 1

Mean value of logical ones

Level 2

Mean value of logical twos

Level 3

Mean value of logical threes

Levels RMS

 

Level 0 RMS

Jitter amplitude in RMS of level zeros

Level 1 RMS

Jitter amplitude in RMS of level ones

Level 2 RMS

Jitter amplitude in RMS of level twos

Level 3 RMS

Jitter amplitude in RMS of level threes

Levels Peak-Peak

 

Level 0 Peak-Peak

Peak-peak jitter amplitude of level zeros

Level 1 Peak-Peak

Peak-peak jitter amplitude of level ones

Level 2 Peak-Peak

Peak-peak jitter amplitude of level twos

Level 3 Peak-Peak

Peak-peak jitter amplitude of level threes

Levels Skew

 

Level 0 Skew

Skew time of level zeros

Level 1 Skew

Skew time of level ones

Level 2 Skew

Skew time of level twos

Level 3 Skew

Skew time of level threes

Eye Levels

 

Eye 0/1 Level

Skew time between level zeros and level ones

Eye 1/2 Level

Skew time between level ones and level twos

Eye 2/3 Level

Skew time between level twos and level threes

Eye Skews

 

Eye 0/1 Skew

Eye skew time between level zeros and level ones

Eye 1/2 Skew

Eye skew time between level ones and level twos

Eye 2/3 Skew

Eye skew time between level twos and level threes

Eye Heights

 

Eye 0/1 Height

Vertical opening of level zeros and level ones

Eye 1/2 Height

Vertical opening of level ones and level twos

Eye 2/3 Height

Vertical opening of level twos and level threes

Eye Widths

 

Eye 0/1 Width

Horizontal opening of level zeros and level ones

Eye 1/2 Width

Horizontal opening of level ones and level twos

Eye 2/3 Width

Horizontal opening of level twos and level threes

Linearity

 

Linearity

Linearity RLM (Ratio Level Mismatch) between all four amplitude levels (0, 1, 2, 3) of a PAM4 eye diagram. Linearity is a measure of the variance in amplitude separation (distribution) between the different PAM4 levels.

Configure Eye Measurements

Click on the Parameter Measurement Results tab.

Configure EYE Measurements  dialog box help

2-Level Signal (PAM2)

In the Sample Window Boundaries, you can increase or decrease the size of three measurement areas. This will change the results of the corresponding measurements.

Sample Window Boundaries

  1. Click one of the Measurements Affected selections.

  2. Increase or decrease the sample window value. Click Default Value to reset the value to its default setting.

  3. Click OK to recalculate the results on the display and in the Results table.

Eye Diagram User Preferences tab

This tab contains shortcuts to set the following Eye Diagram User Preferences. These preferences also appear in the main User Preferences dialog.

Disable the use of the 3 sigma buffers for eye measurement calculations.

Check to use the following equation:

eye width = (tmin of right crosst max of left cross)

Clear (uncheck) to use the following equation:

Do not update plot when calculating eye data  

When checked, do NOT show progress dialog and do NOT draw eye until all data calculated. When plotting long bit pattern eye diagrams, this setting can save a LOT of time.

Clear to show progress and draw eye diagram as data is being calculated.

Eye Mask - Use measured amplitude values for eye mask scaling.  

This preference applies ONLY for eye masks defined in ratios.

  • When cleared (default setting), use the amplitude of selected bit pattern dialog to scale mask when importing.

  • When checked, use measured amplitude as was done in previous PLTS revisions.

4-Level Signal (PAM4)

Receiver Sample Timing - This setting configures the timing for sampling the data. Use this setting to match the timing method used by a receiver. For signals with skewed eyes, measurements results will vary depending on this setting.

Base On Center Eye - Sampling timing is based on the location of the center eye (eye 1/2). This is the default setting.

Independent Per Eye - Sampling timing is independently based on the location of each of the three eyes.

Eye Center Location - This setting selects the basis for determining the location of an eye's center on the waveform.

Maximum Eye Width - The eye's center is located at the eye's maximum width midway between the eye's inside left and right edges. This is the default setting.

Maximum Eye Height - The eye's center is located at the eye's maximum height midway between the eye's inside top and bottom edges.

Eye Level Width - This setting defines the timespan over which an eye's amplitude level is measured. The timespan is specified as a percentage (from 1% to 25%) of the symbol period. The default setting is 10%.

Time of Level - This setting specifies the method used to locate the time at which to measure an eye's level.

Eye Center - The time of a level is the average of the centers of the adjacent eyes. This is the default setting.

Minimum RMS - The time is located within the eye's level width at the minimum level thickness (RMS values).

Time Units - This setting specifies the time units.

Second - Width and skew measurements are reported in seconds. This is the default setting.

Unit Interval - Width and skew measurements are reported in unit intervals.

Amplitude Units - This setting specifies amplitude units.

Amplitude - Level and height measurements are reported in the current amplitude units: volts or Watts. This is the default setting.

Percent - Level and height measurements are reported in percent.

 


Last Modified:

8-Dec-2016

Added PAM4 information

13-Nov-2012

New features for 2013

21-Oct-2011

Broke out topics.

Added results buttons

5-Oct-2009

Added Eye Mask create (5.2)

16-Dec-2008

Added Import Bit Pattern (5.0)

3-Apr-2008

Added scaling note

26-Feb-2008

Added Eye Mask Test