Elementary Mr. Watson: Routing Hunger Games—May the Traces Be Ever in Your Favor
Target Condition: Floor Planning Without a Floor
Happy’s Tech Talk #42: Applying Density Equations to UHDI Design
Paving the Way for 400Gb Ethernet and 5G
June 26, 2018 | Chang Fei Yee, Keysight TechnologiesEstimated reading time: 1 minute
This article briefly introduces the 4-level pulse amplitude modulation (PAM-4) and its application in 400 Gigabit Ethernet (400GbE), to support the booming data traffic volume in conjunction with the deployment of 5G mobile communications. Furthermore, this article also highlights the essential pre-layout effort from signal integrity perspective for physical (PHY) link design on a PCB, including material selection, transmission line design and channel simulation to support 56Gbps data rate that paves the way for seamless communication in 400GbE.
I. Introduction
400GbE is a new wired communication standard to accommodate the booming data traffic volume with the implementation of 5G mobile communications. In the implementation of 400GbE communication, electrical interface with 4-level pulse amplitude modulation (PAM-4) signaling over 8 lanes is adopted. The communication of eight lanes at 56Gbps (i.e., 28GBaud) per lane enables the total bandwidth of 400Gbps over the Ethernet. The electrical specifications of 400GbE with PAM-4 signaling are defined in IEEE 802.3bs.
PAM-4 has 4 digital amplitude levels, as shown in Figure 1. It has an advantage over non-return-to-zero (NRZ) signals because each level or symbol in PAM-4 contains two information bits providing twice as much data throughput for the same baud rate. For instance, 28GBaud is equivalent to 56Gbps in PAM-4 and 28Gbps in NRZ respectively.
II. Essential pre-layout effort from signal integrity perspective
According to guidelines, a PAM-4 channel with trace length up to 8 inches on a PCB shall have insertion loss less than 10dB at 14GHz (i.e., Nyquist frequency of 28GBaud) and 20dB at 28GHz (i.e., 2nd harmonic of 28GBaud) respectively to achieve seamless data communication between the transceivers.
To read this entire article, which appeared in the May 2018 issue of Design007 Magazine, click here.
Share on:
Testimonial
"Advertising in PCB007 Magazine has been a great way to showcase our bare board testers to the right audience. The I-Connect007 team makes the process smooth and professional. We’re proud to be featured in such a trusted publication."
Klaus Koziol - atgSuggested Items
Mastering PCB Floor Planning
08/28/2025 | Stephen V. Chavez, Siemens EDAPlacement of PCB components is far more than just fitting components onto a board. It’s a strategic and critical foundational step, often called “floor planning,” that profoundly impacts the board’s performance, reliability, manufacturability, and cost. Floor planning ties into the solvability perspective, with performance and manufacturability being the other two competing perspectives for addressing and achieving success in PCB design.
Elementary Mr. Watson: Routing Hunger Games—May the Traces Be Ever in Your Favor
08/26/2025 | John Watson -- Column: Elementary, Mr. WatsonI’d like to share a harsh truth, and I say this as a friend: PCB designers are often their own worst enemy. It’s rarely the complexity of the circuit, the last-minute changes from mechanical, the limited enclosure space, or the ever-expanding list of design rules that send projects to the dust heap of failed boards. More often, it's our own decisions, made too quickly and narrowly, and with too little foresight, that sabotage an otherwise good design.
Target Condition: Floor Planning Without a Floor
08/27/2025 | Kelly Dack -- Column: Target ConditionBy a show of hands, how many PCB designers have been asked to start a layout without a board outline, keep-out zones, or even height constraints? How many have had to work within a specific enclosure before the schematic was finalized? If this sounds familiar, you're not alone. Starting a PCB layout without critical constraints is like hiring an interior designer to buy furniture and carpet for a house you haven’t even purchased yet, or, even worse, trying to fit four bedrooms' worth of furniture in a one-room cabin.
I-Connect007 Editor's Choice: Five Must-Reads for the Week
08/22/2025 | Andy Shaughnessy, I-Connect007In this week’s roundup, we have a variety of articles covering design, manufacturing, sustainability, and, of course, tariff negotiations. We have a milestone anniversary to celebrate as well, with Dan Beaulieu about to publish his 1,000th column. When does Dan even sleep? Here’s to hoping that we have 1,000 more weeks of "It’s Only Common Sense."
New Episode Drop: MKS’ ESI’s Role in Optimize the Interconnect
08/26/2025 | I-Connect007In this latest episode, Casey Kruger, director of product marketing at MKS’ ESI, joins On the Line With… host Nolan Johnson to share how CO₂ laser technology delivers faster, more accurate vias in a smaller, more energy-efficient footprint.