# Eye Diagram Scope

Display eye diagram of time-domain signal

• Library:
• Communications Toolbox / Comm Sinks

Communications Toolbox HDL Support / Comm Sinks

Mixed-Signal Blockset / Utilities

SerDes Toolbox / Utilities

## Description

The Eye Diagram block displays multiple traces of a modulated signal to produce an eye diagram. You can use the block to reveal the modulation characteristics of the signal, such as the effects of pulse shaping or channel distortions. For more information, see .

The Eye Diagram block has one input port. This block accepts a column vector or scalar input signal. The block accepts a signal with the following data types: double, single, base integer, and fixed point. All data types are cast as double before the block displays results.

To modify the eye diagram display, select View > Configuration Properties or click the button (). Then select the Main, 2D color histogram, Axes, or Export tabs and modify the settings.

## Ports

### Input

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Input signal, specified as a scalar or column vector.

Data Types: `double`

## Parameters

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### Main Tab

Display mode of the eye diagram, specified as ```Line plot``` or `2D color histogram`. Selecting `2D color histogram` makes the histogram tab available.

Tunable: Yes

Select this check box to enable eye measurements of the input signal.

Select this radio button to display the jitter histogram. This can also be accessed by using the histogram button drop down on the toolbar.

#### Dependencies

This parameter is available when Display mode is `2D color histogram` and Enable measurements is selected.

Select this radio button to display the noise histogram. This can also be accessed by using the histogram button drop down on the toolbar.

#### Dependencies

This parameter is available when Display mode is `2D color histogram` and Enable measurements is selected.

Select this radio button to display neither the histogram noise nor the histogram jitter.

#### Dependencies

This parameter is available when Display mode is `2D color histogram` and Enable measurements is selected.

Select this check box to display the horizontal bathtub curve. This can also be accessed by using the bathtub curve button on the toolbar.

#### Dependencies

This parameter is available when Enable measurements is selected.

Select this check box to display the vertical bathtub curve. This can also be accessed by using the bathtub curve button on the toolbar.

#### Dependencies

This parameter is available when Enable measurements is selected.

Select either `Real only` or `Real and imaginary` to display one or both eye diagrams. To make eye measurements, this parameter must be `Real only`.

Tunable: Yes

Select this check box to fade the points in the display as the interval of time after they are first plotted increases.

Tunable: Yes

#### Dependencies

This parameter is available only when the Display mode is `Line plot`.

Number of samples per symbol, specified as a positive integer. Use with Symbols per trace to determine the number of samples per trace.

Tunable: Yes

Sample offset, specified as a nonnegative integer smaller than the product of Samples per symbol and Symbols per trace. The offset provides the number of samples to omit before plotting the first point.

Tunable: Yes

Number of symbols plotted per trace, specified as a positive integer.

Tunable: Yes

Number of traces plotted, specified as a positive integer.

Tunable: Yes

#### Dependencies

This parameter is available only when the Display mode is `Line plot`

### Axes Tab

Label that appears above the eye diagram plot.

Tunable: Yes

Toggle this check box to turn the grid on and off.

Tunable: Yes

Minimum value of the y-axis.

Tunable: Yes

Maximum value of the y-axis.

Tunable: Yes

Text that the scope displays along the real axis.

Tunable: Yes

Text that the scope displays along the imaginary axis.

Tunable: Yes

### 2D Histogram Tab

The 2D histogram tab is available when you click the histogram button or when the display mode is set to `2D color histogram`.

Oversampling method, specified as `None`, `Input interpolation`, or `Histogram interpolation`.

To plot eye diagrams as quickly as possible, set the Oversampling method to `None`. The drawback to not oversampling is that the plots look pixelated when the number of samples per trace is small. To create smoother, less-pixelated plots using a small number of samples per trace, set the Oversampling method to `Input interpolation` or `Histogram interpolation`. `Input interpolation` is the faster of the two interpolation methods and produces good results when the signal-to-noise ratio (SNR) is high. With a lower SNR, this oversampling method is not recommended because it introduces a bias to the centers of the histogram ranges. `Histogram interpolation` is not as fast as the other techniques, but it provides good results even when the SNR is low.

Tunable: Yes

Color scale of the histogram plot, specified as either `Linear` or `Logarithmic`. Set Color scale to `Logarithmic` if certain areas of the eye diagram include a disproportionate number of points.

Tunable: Yes

The toolbar contains a histogram reset button , which resets the internal histogram buffers and clears the display. This button is not available when the display mode is set to `Line plot`.

### Export Tab

Select this check box export the eye diagram measurements to the MATLAB® workspace.

Tunable: Yes

Specify the name of the variable to which the eye diagram measurements are saved. The data is saved as a structure having these fields:

• `MeasurementSettings`

• `Measurements`

• `JitterHistogram`

• `NoiseHistogram`

• `HorizontalBathtub`

• `VerticalBathtub`

• `BlockName`

Tunable: Yes

### Style Dialog Box

In the Style dialog box, you can customize the style of the active display. You can change the color of the figure containing the displays, the background and foreground colors of display axes, and properties of lines in a display. To open this dialog box, select View > Style.

Specify the background color of the scope figure.

Specify the fill and line colors for the axes.

Specify the line style, line width, and line color for the displayed signal.

#### Dependencies

This parameter is available only when the Display mode is `Line plot`.

Data point marker for the selected signal, specified as one of the choices in this table data point markers. This parameter is similar to the `Marker` property for MATLABHandle Graphics® plot objects.

SpecifierMarker Type
noneNo marker (default)
Circle
Square
Cross
Point
Plus sign
Asterisk
Diamond
Downward-pointing triangle
Upward-pointing triangle
Left-pointing triangle
Right-pointing triangle
Five-pointed star (pentagram)
Six-pointed star (hexagram)

#### Dependencies

This parameter is available only when the Display mode is `Line plot`.

Specify the colormap of the histogram plots as one of these schemes: `Parula`, `Jet`, `HSV`, `Hot`, `Cool`, `Spring`, `Summer`, `Autumn`, `Winter`, `Gray`, `Bone`, `Copper`, `Pink`, `Lines`, or `Custom`. If you select `Custom`, a dialog box pops up from which you can enter code to specify your own colormap.

#### Dependencies

This parameter is available only when the Display mode is ```2D color histogram```.

### Measurement Settings Pane

To change measurement settings, first select Enable measurements. Then, in the Eye Measurements pane, click the arrow next to Settings. You can control these measurement settings.

Time range for calculating eye levels, specified as a two-element vector. These values are expressed as a percentage of the symbol duration.

Tunable: Yes

Amplitude level threshold in V, specified as a scalar. This parameter separates the different signaling regions for horizontal (jitter) histograms. This parameter is tunable, but the jitter histograms reset when the parameter changes.

For non-return-to-zero (NRZ) signals, set Decision boundary to 0. For return-to-zero (RZ) signals, set Decision boundary to half the maximum amplitude.

Tunable: Yes

Amplitude levels of the rise and fall transitions, specified as a two-element vector. These values are expressed as a percentage of the eye amplitude. This parameter is tunable, but the crossing histograms of the rise and fall thresholds reset when the parameter changes.

Tunable: Yes

Amplitude tolerance of the horizontal crossings in V, specified as a scalar. Increase hysteresis to provide more tolerance to spurious crossings due to noise. This parameter is tunable, but the jitter and the rise and fall histograms reset when the parameter changes.

Tunable: Yes

BER used for eye measurements, specified as a nonnegative scalar from 0 to 0.5. The value is used to make measurements of random jitter, total jitter, horizontal eye openings, and vertical eye openings.

Tunable: Yes

BER values used to calculate openings of bathtub curves, specified as a vector whose elements range from 0 to 0.5. Horizontal and vertical eye openings are calculated for each of the values specified by this parameter.

Tunable: Yes

#### Dependencies

To enable this parameter, select Show horizontal bathtub curve, Show vertical bathtub curve, or both.

Duration of initial data discarded from measurements, in seconds, specified as a nonnegative scalar.

## Block Characteristics

 Data Types `Boolean` | `double` | `enumerated` | `fixed point` | `integer` | `single` Direct Feedthrough `no` Multidimensional Signals `no` Variable-Size Signals `no` Zero-Crossing Detection `no`

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