Meeting the Demands of PAM4 Systems at 56Gbps and Beyond

July 2019

Alfred P. Neves, CTO, Wild River Technology
Matthew Burns, Product Marketing Manager–High Speed, Samtec

Mike Gianfagna, VP, Marketing, eSilicon

Tim Horel, Director of Field Applications, eSilicon

Our discussion will focus on PAM4 (pulse amplitude modulation) systems operating at 56 Gigabits per second and beyond. PAM4 is a modulation technique whereby four distinct pulse amplitudes are used to convey the information. PAM4 enables twice the transmission capacity when compared to binary modulation. Because the additional voltage levels in PAM4 reduce the level spacing by a factor of three, PAM4 is more susceptible to noise than a binary digital signal, thus requiring a higher signal- to-noise (SNR) ratio. Consequently, PAM4 is normally used for short-reach applications where a higher SNR can be obtained.

We will explore how this shortcoming can be overcome, resulting in very long-reach signaling with PAM4 encoding over a copper cable to enable next-generation 25.6 and 51.2Tb/s switches, routers and 800G systems. Delivering this capability has two challenges — working silicon that can deliver the required performance and a SerDes test fixture that allows system designers to verify performance in their target application. We will discuss both challenges. Download white paper.

A Practical Method to Model Effective Permittivity and Phase Delay Due to Conductor Surface Roughness

DesignCon 2017

Lambert (Bert) Simonovich, Lamsim Enterprises Inc.

In the GB/s regime, accurate modeling of conductor loss and phase delay is a precursor to successful high-speed serial link designs. In this paper, a practical method to model effective permittivity and phase delay, due to conductor surface roughness, is presented. By obtaining the dielectric and roughness parameters, solely from manufacturers’ data sheets, phase delay and effective permittivity can now be easily predicted. Detailed case studies and several examples test the model`s accuracy. Download white paper.

BER- and COM-Way of Channel-Compliance Evaluation: What are the Sources of Differences?

DesignCon 2016

Vladimir Dmitriev-Zdorov, Mentor Graphics

Cristian Filip, Mentor Graphics

Chuck Ferry, Mentor Graphics
Alfred P. Neves, Wild River Technology

We analyze the computational procedure specified for Channel Operation Margin (COM) and compare it to traditional statistical eye/BER analysis. There are a number of differences between the two approaches, ranging from how they perform channel characterization, to how they consider Tx and Rx noise and apply termination, to the differences between numerical procedures employed to convert given jitter and crosstalk responses into the vertical distribution characterizing eye diagrams and BER. We show that depending on the channel COM may potentially overestimate the effect of crosstalk and, depending on a number of factors, over- or underestimate the effect of transmit jitter, especially when the channel operates at the rate limits. We propose a modification to the COM procedure that eliminates these problems without considerable work increase. Download white paper.