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Thursday, January 25, 2018

Industry's first 400Gbit/s DSP with integrated laser drivers targets cloud data centres

By Nick Flaherty

MaxLinear has launched the industry's first 400Gbit/s pulse-amplitude-modulation (PAM4) digital signal processing (DSP) systems-on-chip (SoC) that include integrated electro-absorption modulated laser (EA-EML) drivers to drive a new generation of high speed optical interconnects

The MxL935XX Telluride family is a key component for system designers to develop a 400Gbit/s optical interconnect module in a compact form factor for intra-datacentre applications with a transmission distance up to 2km.

The 16nm CMOS chip consumes an extremely low power of 6.7W, which includes the integrated EA-EML driver power dissipation. This meets the stringent power constraints of 400Gbits optical module form-factors such as QSFP-DD, OSFP and COBO devices.

MaxLinear is currently sampling the device to optical module vendors who are actively developing 400Gbit/s modules that are expected to enter mass production in the latter half of 2018.

The chip supports of one, two or four lanes of 100Gbit/s optical connectivity combined with a flexible 25G NRZ and 50G PAM4 electrical interface supporting multiple generations of switch ASICs. This means it can be used in a wide-range of optical interconnects supporting 100Gbit/s, 200Gbit/s and 400Gbit/s optical fibre data speeds in cloud mega-scale and enterprise data centres.

The integrated laser drivers directly interface with the external optical lasers and eliminate the need for expensive external high-frequency components required for laser driver and modulator bias.

"The exploding data traffic, and the demand for high-speed data have placed an enormous burden on the cloud and enterprise data network infrastructure. This is, in turn, not only compressing the network upgrade cycle, but is also accelerating the need to deploy 400Gbit/s optical networks inside mega-scale cloud and enterprise data centers," said Dr. Kishore Seendripu, CEO of MaxLinear. "With the recent announcement of the availability of next-generation switch ASICs that support 50Gbit/s PAM4 I/Os, we believe the growth trajectory for PAM4 DSP-based 400Gbit/s optical fibre interconnect solutions is at an inflection point. The cost pressure and thermal constraints of 400Gbit/s networks necessitate the use of new optical interconnects based on single-lane 100Gbit/s optical wavelength technology.

"Our Telluride MxL935XX 16nm CMOS SoC family, with integrated EA-EML laser drivers, reduced external components, and superior link-margin performance, is perfectly positioned to enable this leapfrogging industry transition. We believe that, currently, the total addressable market for 100Gbit/s and 400Gbit/s optical interconnect modules greatly exceeds 10 million units annually, not including the anticipated future rapid growth driven by the exploding internet traffic," he said. 

The first SoCs to be available from the Telluride family are the MxL93542 and MxL93543, which feature several operating modes that can connect to multiple generation of switch ASICs (128x25G NRZ, 256x25G NRZ or 256x50G PAM4) enabling 3.2Tbit/s, 6.4Tbit/s or 12.8Tbit/s front panel capacity per data centre rack unit. These different operating modes span a variety of optical module form factors such as QSFP28, SFP-DD, QSFP-DD, OSFP and COBO.

For modes where the MxL93542 and MxL93543 interface with a legacy 25G NRZ switch ASIC, the corresponding forward error correction (FEC) functionality required for PAM4 optics is integrated into the device. Two separate instantiations of the FEC engine are available on-chip to support two distinct lanes of 100Gbit/s optics.

The integrated laser driver in the MXL93542 delivers greater than 1.8V of single-ended driver output swing necessary for EA-EML lasers. This output swing easily meets the optical modulation amplitude (OMA) specification requirements across the wide operating temperature and bias ranges of all EA-EML lasers. The chip package also includes all the high frequency components required for driver & modulator biasing.

The second version of the SoC, the MxL93543, delivers 800mV of peak-to-peak differential driver output swing and can be easily paired with an external laser driver implemented in alternate optical technologies such as silicon photonics.

The devices feature a comprehensive digital pre-distortion (DPD) engine in the transmit direction to compensate for laser non-linearity, and to cancel packaging limitations that cause reflections and bandwidth degradation at these extremely high signal frequencies. On the receive path, the DSP includes an auto-adaptive signal enhancement engine, which integrates a continuous time linear equalizer (CTLE), automatic gain control (AGC), a feed forward equalizer (FFE), and a decision feedback equalizer (DFE).

The MxL93542 and MxL93543 are sampling now to optical module manufacturers. 

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