Enabling Multi-mode Interconnectivity in Next-gen Data Center

Article By : Maurizio Di Paolo Emilio

The growing demand for low latency web connections and the spread of the internet of things (IoT) are set to drastically change the way the…

The growing demand for low latency web connections and the spread of the internet of things(IoT) are set to drastically change the way the data center industry will operate over the next decade. The data center industry needs to ensure increasing data management capacity and faster processing speeds to meet real market demands. The highest costs in a data center construction revolve around the inclusion of optics. The need to reduce these modules’ costs and power is very much in demand, primarily as the industry seeks to move from NRZ interconnections to PAM4. Semtech Corporation announced some time ago the availability in production of the GN2558 and GN2559, the Tri-Edge CDR SR Tri-Edge CDR solutions to enable multi-mode interconnectivity in next-generation data centers. GN2558 is a quad PAM4 CDR with an integrated VCSEL driver, and GN2559 is a quad PAM4 CDR with an integrated linear trans-impedance amplifier (TIA). “Building on the success of Sem tech’s ClearEdge NRZ-based CDR platform technology, Tri-Edge is a CDR platform optimized for PAM 4 optical interconnect in next-generation 200G and 400G data center and AOC applications,” said Timothy Vang, vice president, Marketing and Applications, Signal Integrity Product Group at Semtech. He continued, “Semtech’s Tri-Edge PAM 4 CDRs offer the lowest power, lowest cost solution for optical modules by enabling use of 25G bps optics.” GN2558 and GN2559 integrated circuits provide the low-power, low-latency analog solution to meet the needs of high-performance computing (HPC), artificial intelligence (AI), and cloud data center networks. These chipsets are also fully compliant with the 200G-SR4 Open Eye MSA specification. The GN2558 CDR includes proprietary VCSEL compensation to enable a wide range of VCSEL options with fully adaptive input equalization and a quick start to streamline system tuning. The GN2559 includes configurable output equalization allowing robust electrical interfaces.

PAM4 technology

Hyper-scale data centers sought transceiver solutions with higher port densities and lower cost per bit, which drove the development of PAM4 (Four-Level Pulse Amplitude Modulation) technology. Compared to the expensive, consistent multi-state modulation scheme, simple PAM4 can offer the right combination of speed, low cost, and low power consumption in data centers. PAM4 is a technology that uses four different signal levels for signal transmission, and each symbol period represents 2 bits of logical information (0, 1, 2, 3). By transmitting two bits in a symbol slot, PAM4 halves the signal bandwidth. With half the bandwidth, PAM4 can achieve a data rate transmission of 50 Gb/s in an electrical tolerance environment of 25 Gb/s. In addition, PAM4 can minimize signal degradation and double the data rate. PAM4 allows us to input more data on existing fiber. While PAM4 offers important speed improvements on Nrz, the downside is that the data must be encoded before transmission and then decoded once received.

Tri-Edge overview

Semtech opens the way to enable analog PAM4-based solutions in the data center market and helps to create a complete analog PAM4 ecosystem with the Open Eye MSA. Both the Tri-Edge SR and LR product lines are compliant to the Open Eye MSA specifications for SR and LR links. Seeking to minimize the need for signal processing in optical modules, significantly reduce latency, power consumption, and cost, Semtech joined MACOM and over 20 other companies to form the Open Eye MSA, a consortium dedicated to developing an industry-standard optical interconnection. Open Eye MSA aims to improve IEEE standards and work to develop a range of low-cost, energy-efficient, interoperable solutions for the growth of PAM4. Low latency is a key requirement for HPC and AI data centers. Tri-Edge solutions incur less than 1 ns of latency at the chip, while DSP solutions can incur over 100ns of latency. “Tri-Edge is based on SiGe technology that offers low development costs and low mask costs versus advanced CMOS nodes,” said Vang. “Tri-Edge enables the use of existing, high volume, low cost 25Gbps optics.” The data centers of the future will be increasingly agile, distributed and automated infrastructures. They will guarantee the required services with higher performance and efficiency than traditional structures. The technological paradigm shift stems, on the one hand, from new business applications that require a substantial change in infrastructure management, and on the other hand, from the need to continue to support the legacy world.

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