Mid-Board to Front Panel 112 Gbps PAM4 Interconnect Solutions
A live demonstration at DesignCon 2021 shows how Samtec Flyover® Twinax Cable assemblies allow designers to extend signal reach and density, enabling 112 Gbps PAM4 performance.
In this video, Jean-Remy Bonnefoy, Systems Engineer at Samtec, walks us through the signal path, then discusses the system performance. This demo shows Mid-Board and Front Panel Samtec Flyover Cable solutions.
The Signal Path
It all begins with Alphawave’s AlphaCORE Multi-Standard SerDes, which generates 31 bit PRBS data at 112 Gbps PAM4.
These signals travel from the silicon through about 1” of differential traces in Isola I-Tera MT40 material, to a Samtec Bulls Eye high-performance test connector system located opposite the chip on the back of the board. This Bulls Eye connector, the BE70A, is rated at 70 GHz.
The signals travel from the Bulls Eye system connector, through 20” of low-loss microwave cable, which terminate to Samtec precision 1.85 connectors. These 1.85 mm precision RF connectors are mounted on a Samtec SI Evaluation board.
The signals travel through another 2” of PCB trace to the solder ball termination of an NVAM-C connector, which is a Samtec NovaRay® high-density board-level connector. A NovaRay cable assembly, an NVACP series, mates with the board level connector, and carries the signal through 6” of 34 AWG Eye Speed® ultra-low skew twinax cable to the panel mount interface.
The fully shielded NovaRay I/O cable assembly, the NVACE series, plugs into the panel and moves the signal through two meters of 28 AWG Eye Speed ultra-low skew twinax cable.
The signal goes back through a second panel, to another NVAC cable with 6” more of ultra-low skew twinax cable, and back to a second SI Evaluation board. The data travels through about 2” of pcb trace to another 1.85 mm precision RF connector, through another 20” of low-loss microwave cable, to the Bulls Eye BE70A, and back to the SERDES receiver where the data is collected and checked for errors.
This demonstration has eight different interconnect transitions and runs 3.5 meters. But, the total loss for the entire signal path, including all cable assemblies and PCBs, is approximately 35.7 dB at 28 GHz.
Using Alphawave’s user interface and analysis tools, we see the eye diagram captured at the receiver after equalization. The margins are wide. The vertical bathtub is showing the calculated bit error rate (BER) for all three levels of the PAM4 signaling is approximately 1e-7 for this long-reach channel. The performance is well within specifications, by several order of magnitudes, providing the designer with plenty of margin.
The histogram and scatter plots show the probability density estimate of the PAM4 signaling. This shows really good separation and signal to noise ratio.
Speaking Of 112 Gbps PAM4 Samtec Flyover Cable Systems …
As the data rate requirements increase, system designers struggle with propagating these signals through PCBs. Samtec Flyover solutions allow them to extend the signal reach and density by routing signals via ultra-low skew twinax cable instead of lossy PCBs.
If you have questions about this demo, email us at SIG@samtec.com