Eye Diagram FrontPanel

The Eye Diagram FrontPanel enables easy computation of waveform and eye diagram measurements. Many of the Eye Diagram FrontPanel measurement algorithms are derived from the Agilent Technologies Digital Communication Analyzer but with simplified implementation. The Eye Diagram FrontPanel supports the NRZ data type.

For information on measurement expressions specific to the Eye Diagram FrontPanel, see Chapter 12, "FrontPanel Eye Diagram Functions," in the Measurement Expression documentation.

The Eye Diagram FrontPanel can be accessed from the Data Display window or from the Schematic window.

• To access the Eye Diagram FrontPanel from the Data Display window, choose Tools > FrontPanel > Eye.
• To access the Eye Diagram FrontPanel from the Schematic window, choose DesignGuides > Signal Integrity Applications > Eye Diagram FrontPanel.

The basic measurements steps are:

1. Select Dataset.
2. Select Trace.
3. Define Data Rate in frequency units and define a measurement expression if required. See Defining Data Rate.
4. Select Measurement buttons to display various measurements. See Making Measurements.

Defining Data Rate

When you select a trace name, the User Defined Data Rate dialog box appears.

The selected trace name appears in the Enter Trace Expression field. This field can also be used to enter an expression. For example, the expression in the following dialog box produces the time difference differential NRZ waveform from a Harmonic Balance simulation.

For waveform/eye diagram parameters, you need to define the NRZ data rate in the Data Rate field. If the data rate is unknown, click the Estimate Data Rate button to approximate the rate. For circuit envelope simulation data, you can define the expression to extract the NRZ baseband envelope using the frequency index.

Changing Measurement Settings

The Measurement Settings button displays the Plot Settings dialog box. You can define the Start Time, Stop Time, Data Rate, Eye Boundary and Threshold Settings for waveform and eye diagram measurements. You can also change the color preference for traces.

To enable trace color grading for rise, fall, and eye diagram traces, select the Color Grade check box located below the Measurement buttons.

Making Measurements

The Eye Diagram FrontPanel has two different measurement modes:

• Oscilloscope Mode

• Eye/Mask Mode

Oscilloscope Mode

In Oscilloscope mode, all measurements are performed automatically. Some measurements, such as peak-to-peak jitter, require user intervention.

The Waveform button displays the time domain waveform.

The pointer maker on the waveform indicates the segment of the waveform used for parameter measurement. To change the start and stop values, click the Measurement Settings button then edit the Plot Settings dialog box.


The Amplitude Histogram button displays the amplitude histogram waveform.

A default sampling rate of 451 samples per wavelength across the time axis and 321 samples across the amplitude axis is used to construct the amplitude histogram. This provides an idea of the level one and the zero of the waveform. To smooth out the noisy display of the amplitude histogram, increase the smoothing factor by adjusting the Smoothing factor slider on the Amplitude Histogram dialog box. To readout the number of samples and amplitude information, adjust the Marker slider.


The Rise Time Measurement button displays the overlaid rising edge plot used for rise time computation.

Rise time is a measure of the transition time of the data on the positive (rising) edge of a waveform. The edge crosses through the lower, middle, and upper threshold levels. The rising edges, which do not cross through all three threshold levels, are not displayed and are not included in rise time computation. Horizontal histograms are created across lower, middle, and high threshold levels of this display. The mean values at low and high threshold levels are computed for rise time calculation. The default setting for the threshold levels are the 20% to 80% points on the transition. To change the default threshold settings, click the Measurement Settings button then edit the Threshold Settings tab in the Plot Settings dialog box.

Pointer markers are placed at low, middle, and high threshold levels.

The Fall Time Measurement button displays the overlay falling edge plot used for fall time computation.

Fall time is a measure of the transition time of the data on the negative (falling) edge of a waveform. The edge crosses through the upper, middle, and lower threshold levels. The falling edges, which do not cross through all three threshold levels, are not displayed and are not included in fall time computation. Horizontal histograms are created across lower, middle, and high threshold levels of this display. The mean value at low and high threshold levels is computed for fall time calculation. The default setting for the threshold levels are the 20% to 80% points on the transition. To change the default threshold settings, click the Measurement Settings button then edit the Threshold Settings tab in the Plot Settings dialog box.

Jitter is a measure of the time variances of the rising or falling edges of a pulse waveform at the middle threshold. When a jitter measurement is selected, the instrument's measurement database is enabled. The waveform data that is sampled is accumulated in the measurement database.

The Rising Edge Jitter Histogram button displays the jitter histogram for the rising edge.

Jitter is a measure of the time variances of the rising or falling edges of a pulse waveform at the middle threshold. When a jitter measurement is selected, a measurement window is placed horizontally through the middle threshold. This measurement window is narrow in amplitude. A time histogram is then generated and the peak-to-peak jitter value is determined. RMS jitter is defined as one standard deviation from the histogram mean.

In the Rise Histogram dialog box, adjust the sliders on the Window Marker tab to define the rectangular area for jitter histograms. Adjust the sliders on the Curve Fit tab for Gaussian fitting of the jitter histogram. If the jitter histogram has a deterministic jitter component, the curve fit can be used to create a Gaussian curve in the tail region. The mean and standard deviation of this Gaussian curve is displayed.


The Falling Edge Jitter Histogram button displays the jitter histogram for the falling edge.

Jitter is a measure of the time variances of the rising or falling edges of a pulse waveform at the middle threshold. When a jitter measurement is selected, a measurement window is placed horizontally through the middle threshold. This measurement window is narrow in amplitude. A time histogram is then generated and the peak-to-peak jitter value is determined. RMS jitter is defined as one standard deviation from the histogram mean.

In the Fall Histogram dialog box, adjust the sliders on the Window Marker tab to define the rectangular area for jitter histograms. Adjust the sliders on the Curve Fit tab for Gaussian fitting of the jitter histogram. If the jitter histogram has a deterministic jitter component, the curve fit can be used to create a Gaussian curve in the tail region. The mean and standard deviation of this Gaussian curve is displayed.

The Measurement Summary button displays the measurement summary of the waveform parameters.

Eye/Mask Mode

In Eye/Mask mode, the eye diagram is displayed for the user defined data rate and most measurements are performed automatically.


The Eye Diagram measurement button displays the eye diagram.

The Eye Boundary measurement button displays the detected eye crossing points, the level one and level zero, the 3 sigma points, and the eye boundary (40% -60%), which indicates the measurement region between eye crossing points. Use this display to verify and debug eye diagram measurements.

The Eye Rise Time measurement button displays the rising edge trace on the eye diagram.

The pointer markers indicate the threshold values. The eye diagram level one and level zero (computed within eye boundary region) are used to compute the threshold levels. Rise time is a measure of the transition time of the data on the waveform's positive (rising) edge. The edge crosses through the lower, middle, and upper threshold levels. The rising edges, which do not cross through all three threshold levels, are not displayed and are not included in rise time computation. Horizontal histograms are created across lower, middle, and high threshold levels of this display. The mean value at low and high threshold levels is computed for rise time calculation. The default setting for the threshold levels are the 20% to 80% points on the transition. To change the default threshold settings, click the Measurement Settings button then edit the Threshold Settings tab in the Plot Settings dialog box.


The Eye Fall Time button displays the falling edge trace on the eye diagram.

The pointer markers indicate the threshold values. The eye diagram level one and level zero (computed within eye boundary region) are used to compute the threshold levels. Fall time is a measure of the transition time of the data on the negative (falling) edge of a waveform. The edge crosses through the lower, middle, and upper threshold levels. The falling edges, which do not cross through all the three threshold levels, are not displayed and are not included in fall time computation. Horizontal histograms are created across lower, middle, and high threshold levels of this display. The mean value at low and high threshold levels is computed for rise time calculations. The default setting for the threshold levels are the 20% to 80% points on the transition. To change the default threshold settings, click the Measurement Settings button then edit the Threshold Settings tab in the Plot Settings dialog box.


The Eye Jitter Histogram button displays the eye diagram jitter histogram.

NRZ Eye Jitter is the measure of the time variances of the rising and falling edges of an eye diagram as these edges affect the crossing point of the eye. When a jitter measurement is selected, a measurement window is placed horizontally through the middle threshold. This measurement window is narrow in amplitude. A time histogram is then generated and the peak-to-peak jitter value is determined. RMS jitter is defined as one standard deviation from the histogram mean.

In the Rise Histogram dialog box, adjust the sliders on the Window Marker tab to define the rectangular area for jitter histograms. Adjust the sliders on the Curve Fit tab for Gaussian fitting of the jitter histogram. If the jitter histogram has a deterministic jitter component, the curve fit can be used to create a Gaussian curve in the tail region. The mean and standard deviation of this Gaussian curve is displayed.


The Eye Mask button displays the Eye Mask overlaid on the eye diagram plot.

A mask is a template that defines the regions on the eye diagram plots. Mask testing enables you to verify that the displayed waveform complies with an industry standard waveform shape. To comply with the industry standard, the NRZ waveform must remain outside the mask regions. The mask tracks the waveform as the waveform's parameters are modified. The top, bottom, and center mask is automatically placed between the eye crossing points.
To modify the mask, adjust the slider bars in the Eyemask dialog box. You can alter the slope, the center mask length, height and position of top/lower mask. You can also save masks at a global, local, or project level.


The Measurement Summary button displays the measurement summary of the eye diagram parameters.

Saving the FrontPanel

The Save As FrontPanel Data Display toolbar icon saves the FrontPanel as a FrontPanel Data Display. The file is saved with a .dds file extension. To open the saved FrontPanel, choose File > Open from the Data Display window.

The Save As Regular Data Display toolbar icon saves the FrontPanel as a regular data display and does not retain the slider information. The file is saved with a .dds file extension.