PAM4 Eye & TDECQ Explorer
Every 200G lane carries PAM4, and the conformance number for its transmitter is TDECQ. This page synthesizes a PAM4 waveform with adjustable impairments, passes it through the standard's Bessel-Thomson reference receiver and 5-tap equalizer, and computes TDECQ by the same histogram-and-noise procedure a sampling oscilloscope uses. The eye, the equalized histograms, and the tap weights are all live, so each impairment can be traced from cause to penalty. Four guided experiments ask for a prediction before they show the result.
The 3.4 dB tag is a representative ceiling: IEEE clauses in the 200G-per-lane generation set TDECQ limits near this value, with the exact number depending on the PMD. Consult the clause for compliance.
Four short experiments. Each sets the controls, asks for a prediction, then shows the result.
Two unit intervals of the waveform after the Bessel-Thomson reference filter, all 2048 symbols overlaid. Dashed horizontals are the measured level means; the amber verticals mark the two histogram phases, 0.047 UI either side of the chosen sampling instant.
Amplitude histograms of the equalizer output at the two phases. TDECQ asks: how much Gaussian noise can be poured onto these histograms before the symbol error ratio crosses 4.8 × 10⁻⁴? Dashed lines are the decision thresholds.
These rows run in your browser on every load. The filter and constants are checked in closed form; the TDECQ values are checked against an independent reference implementation of the same procedure, run offline, to a tolerance of 0.01 dB.
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