Serdes Designer, Characterization folks, I am seeing commercial ISI platforms (the latest one is on sale) that have rather mediocre return-loss (SDD11) in the 1X Nyquist region for 112G PAM4.  Our ISI-112 has almost -30dB of return-loss through 53GHz, with 10dB margin at 67GHz!  This is by far the industry’s best performance.   Return loss reflect energy, which limits Serdes reach and impacts PAM4, especially due to 9.04dB S/N penalty.

A third element is skew or mode conversion.   We used 2 plies or orthogonal glass, spread X-Y and then rotated the panel 22.5degrees.  Our skew is typically less than 100femtoseconds.   Serdes do not like SCD21 or differential to common-mode skew and this adversely impacts the reach characterization. The ISI-112 platform to platform skew is very low which improves correlation between characterization centers.

Ping me for measured S-parameters of our next revision.  We improved the impedance to 2% tolerance and expect to get even better signal integrity.  We created a process to achieve consistent 2% impedance.
Message me how I can help with advancing Serdes characterization.  We are also releasing some novel normative test platforms testing for skew and mode conversion impact on reach.