Eye Diagram Margin Calculator

Work out eye diagram margin instantly with clear inputs, formula shown and shareable results.

About Eye Diagram Margin Calculator

The unit interval at 25 Gbit/s is 40 ps, so 12 ps of total jitter consumes 30% of the eye horizontally. Vertical margin is amplitude minus twice the noise, since noise closes the eye from both rails. Both margins must remain open at the target bit error rate.

Formula

Eye margin

UI = 1 / bit rate; horizontal margin = (UI - total jitter) / UI; vertical = (amplitude - 2 x noise) / amplitude

Worked example

With the default values below, Eye Diagram Margin Calculator returns Horizontal eye margin of 70.00%. Change any input above and every figure here is recalculated in your browser.

Inputs used

Bit rate: 25 Gbit/s
Total jitter: 12 ps
Vertical noise: 45 mV
Signal amplitude: 400 mV

Results

Horizontal eye margin: 70.00% %
Vertical eye margin: 77.50% %
Unit interval: 40.00 ps
Eye opening: 310.00 mV

Step by step

1Values used
2Eye margin
3Horizontal eye margin= 70.00 %
4Vertical eye margin= 77.50 %
5Unit interval= 40.00 ps
6Eye opening= 310.00 mV

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why subtract jitter from the whole UI?

Because total jitter is the peak-to-peak spread at the target BER, and it closes the eye from both edges within a single unit interval.

What margin is needed?

Standards typically require 0.3-0.5 UI of horizontal opening and tens of millivolts vertically at the receiver after equalisation.