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Active Electrical Cable Technology—A Growing Necessity in the Era of Generative AI

Cable manufacturers who need to quickly develop 800G active electrical cable solutions for up to 112G PAM4 signals can benefit from Microchip’s META-DX2C retimer-based complete reference design.

Generative Artificial Intelligence (AI), with its potential to transform several industries, has been making waves since the release of ChatGPT in late 2022. As a consequence, the immense need for data, its inference and transformation has put new demands on data center infrastructure. AI clusters today demand larger neural networks, which means more hardware and more power consumption. This requires solutions that not only provide better networking through lower latency but also cost versus power optimization and easier hardware management.

Data center servers and networking equipment rely on copper cables for making connections within a rack and between racks. These cables, called Direct Attach Copper (DAC) cables, have traditionally been passive in nature and were able to meet data center needs. However, with the advent of Generative AI, hyperscalers are pushing for signal speeds at 112Gbps with PAM4 signal modulation and beyond to meet the high-bandwith requirements between AI servers. At such high data transfer rates, passive DACs fail to meet the Signal Intregity (SI) requirements. Moreover, a significant increase in the volume of DACs within a rack makes cable management a cumbersome task from a bend radii and heat dissipation perspective. Hence, data centers are transitioning from passive DACs to active cable solutions.

This blog post will describe the various active cable solutions, the trade-off amongst these solutions, why Active Electrical Cables (AECs) stand out and how can cable vendors benefit from Microchip’s META-DX2C retimer-based comprehensive AEC solution.

There are primarily three types of active cable technologies that we observe in the market. Active Optical Cables (AOCs) contain Digital Signal Processors (DSPs) at both ends of the cable and convert the electrical signal to light signal. The optical fiber used is flexible and significantly lighter in comparison to a passive copper cable. AOCs are best suited for long reach applications; however, they are costly and power hungry. Active Copper Cables (ACCs) are copper cables with redrivers at both ends as the active component. The redriver helps in signal amplification and equalization. ACCs, although less flexible than AOCs, are a more cost-effective and lower-power alternative. To achieve a balance between performance and cost/power, Active Electrical Cables (AECs), comprising of retimers at the ends of cables, stand out.

While redrivers are typically linear amplifiers that amplify the high-frequency portion of a signal, which gets attenuated by copper cable, retimers are mixed-signal analog/digital devices capable of retransmitting the data using a clean clock so that the overall signal quality is improved. This underscores the prowess of a retimer utilized in creating efficient AECs for routing 112G PAM4 signals inter-rack and intra-rack faithfully. These additional capabilities of a retimer over a redriver allow the user to make a tradeoff between performance versus cost and power consumption when choosing between AECs and ACCs.

As data center infrastructure continuously evolves, the option of interoperability of newer hardware with existing hardware is highly beneficial to hyperscalers to future-proof their existing investments. This translates to plug-and-play ability in active cables. With their signal integrity features, AECs and AOCs provide superior plug-and-play compatibility. Long-term reliability of cables is another important aspect. Unequivocally, passive DACs provide the highest reliability due to absence of an active component which degrades with use over time. However, optical cables are well known to be fast degrading and requiring replacements, making AOCs the least reliable yet cost intensive active cable option.

A comparison of various data center cable technologies is provided in the table below. Overall, AECs demonstrate to be advantageous over other cabling solutions.

Cable vendors today need to quickly deploy AEC solutions that meet the demands of their end customers. This becomes challenging when the in-house design of AECs and the sourcing of appropriate electronic components for their development pose significant risks and/or undertaking. To alleviate this, we have released META-DX2C, a compact retimer for AEC applications supporting up to 800G data capacity at 112Gbps PAM4 data transfer rates. It comes with a complete hardware reference design and Common Management Interface Specification (CMIS) software package that helps cable vendors to reduce the engineering efforts needed for AEC development, minimize supply chain issues by sourcing key components directly from Microchip and speed up the time to market.

For additional information please visit the META-DX family web page or contact a Microchip sales representative.

Raghav Gupta and Stephen Docking, May 14, 2024

Tags/Keywords: Communications, Computing and Data Center, AI-ML

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