How to adjust the sampling waveform of an eye diagram analyzer

To adjust the sampling waveform of an eye diagram analyzer, you need to configure the trigger source, sampling delay, scale, and offset to optimize the display and measurement of the eye pattern.

Trigger Configuration

The first step is to select an appropriate trigger source. Eye diagram analyzers can use the data signal itself, a recovered clock, or a divided clock as the trigger. Using a clock trigger provides a classical eye diagram showing all possible bit transitions, while a divided clock trigger can help if the instrument's trigger bandwidth is narrower than the data rate, though care must be taken to avoid missing parts of the pattern.

For encoded or double data rate signals, triggering on the correct clock edge (rising or falling) ensures consistent waveform alignment.

Sampling Delay and Equivalent Time

Sampling oscilloscopes use equivalent-time sampling to capture high-speed signals. The waveform is built sequentially by sampling the signal at slightly delayed intervals on successive trigger events. Adjusting the sweep time and the number of horizontal points determines the delay between samples, which affects the horizontal resolution of the eye diagram.

This allows the analyzer to reconstruct the waveform accurately even at very high data rates.

Scale and Offset Adjustment

Once the trigger and sampling are set, adjust the vertical scale and offset to clearly view the eye opening. Most analyzers default to auto-scale, but manual adjustment can improve visibility of signal details. Enter the desired Y-axis scale and offset values to center the eye diagram and optimize the amplitude representation.

This is particularly useful when analyzing overshoot, undershoot, or jitter.

Pattern and Rise Time Settings

If your analyzer supports a virtual bit pattern generator, define the bit pattern and set the rise time to match the device under test. After changing these settings, redraw the eye diagram to reflect the updated waveform. This ensures the displayed eye accurately represents the signal characteristics.

Practical Tips

Use persistence mode to layer multiple waveform captures, highlighting jitter and noise patterns. For detailed analysis, move the decision point in time or voltage to probe different parts of the eye and measure error rates. Save results for further analysis using export functions, typically in CSV format.

By carefully configuring the trigger, sampling delay, scale, offset, and pattern settings, you can optimize the eye diagram display for accurate measurement of signal integrity, jitter, and timing characteristics.