Eye Diagram from S-Parameters
Upload a Touchstone (.s2p) file and generate a PRBS-15 eye diagram. Extracts insertion loss, group delay, and impedance profile, then renders the eye with jitter and ISI.
How It Works
An eye diagram superimposes many unit intervals (UI) of a digital waveform to visualise signal integrity. The "eye opening" shows how much voltage and timing margin exist for a receiver to correctly sample the data.
This tool constructs the eye from S-parameter data: it reads the channel's insertion loss (S21) from a Touchstone file, converts it to a time-domain impulse response via windowed IFFT, then convolves a PRBS bit sequence through the channel. The resulting waveform is sliced into UI-length segments and overlaid.
Key metrics extracted: eye height (vertical opening at the sampling instant), eye width (horizontal opening at the decision threshold), jitter (timing variation at the crossing points), and rise/fall time. A larger eye means better signal integrity and lower bit error rate.
PRBS-7 is suitable for quick checks; PRBS-15 covers most realistic ISI patterns; PRBS-31 (Pro) stresses the channel with longer run lengths and is required by standards like IEEE 802.3.
Related Calculators
FAQ
What Touchstone file format do I need?+
Upload a 2-port .s2p file where S21 represents the channel insertion loss. The file should cover frequencies from DC (or near-DC) up to at least 1.5x the Nyquist frequency of your data rate. 4-port .s4p files are also supported for differential channels.
Why is my eye completely closed?+
A closed eye typically means the channel loss is too high at the Nyquist frequency for the specified data rate. Check that your S21 insertion loss is reasonable (e.g. < 20 dB at Nyquist). Also verify the frequency range covers the full bandwidth needed.
What is the difference between PRBS-7 and PRBS-15?+
PRBS-7 generates a 127-bit sequence; PRBS-15 generates 32,767 bits. Longer sequences contain more bit patterns, producing more realistic inter-symbol interference (ISI). PRBS-15 is the standard choice for most signal integrity analysis.
How does the tool handle differential channels?+
For .s4p files, the tool extracts the differential insertion loss (SDD21) using mixed-mode conversion. Make sure your port numbering follows the convention: ports 1-2 on the near end, ports 3-4 on the far end.