Coherent optical clocks simplify 100/400G design

25th April 2016
Nat Bowers


Providing a high-frequency, flexible clocking solution that significantly reduces system-level cost and complexity, Silicon Labs' latest jitter-attenuating clocks simplify 100/400G coherent optical line card and module design.

The Si534xH coherent optical clocks replace discrete timing solutions that rely on expensive, large-footprint VCSOs to provide low-jitter reference timing for data converters. Unlike VCSOs that support single, fixed frequencies, these devices operate over a wide frequency range, supporting frequencies up to 2.7GHz without the need to change BoM components.

The Si5344H and Si5342H clocks combine best-in-class frequency flexibility with unparallelled jitter performance of 50fs RMS. The devices simplify component sourcing, replacing multiple custom, long-lead time VCSOs with a clock IC solution available with short, two-week lead times. Featuring a jitter-attenuating PLL, high-frequency output drivers, fractional frequency synthesis and digitally controlled oscillator technology, the Si534xH family provides all the clocking functions required for coherent optical transceiver applications while enabling 40% smaller footprint and 40% lower power than competing solutions.

One of the largest growth drivers in the communications market is the industry's transition from 10 to 100G in metro area networks and data centre interconnect. Coherent optics is an enabling technology for 100 and 400G applications because it allows service providers to send more data over existing optical fibre, minimising the cost and complexity of network upgrades for bandwidth expansion. Current timing solutions for coherent optics are not optimised for cost or size, requiring a diverse mix of VCSOs, clock generators and discrete components.

Silicon Labs' Si534xH clocks are purpose-built to address the timing requirements of 100/400G coherent optics. In addition to supporting the ultra-high frequency synthesis necessary for clocking optical transceiver data converters, the Si534xH clocks combine Silicon Labs' proven DSPLL jitter attenuation technology and MultiSynth low-jitter fractional frequency synthesis technology to deliver an elegant, easy-to-use, single-chip solution. All 100/400G transmitter or receiver clocks can be generated by a single device, minimising BoM cost and complexity by eliminating the need for numerous discrete components.

James Wilson, Senior Marketing Director, Timing Products, Silicon Labs, commented: "To meet demands for increasing bandwidth, service providers require 100/400G coherent designs that enable higher line card port density and lower cost-per-bit than legacy solutions. Silicon Labs' Si534xH clocks provide the high-frequency clock synthesis, jitter attenuation and stringent phase noise required by coherent optical applications at significantly smaller footprint and lower power than traditional VCSO-based solutions."

Silicon Labs supports coherent clock development with ClockBuilder Pro, an easy-to-use software tool that simplifies clock tree design, device configuration and detailed performance evaluation. The tool can be used in standalone mode to generate device configuration files or to directly control a Si534xH device on an evaluation board. ClockBuilder Pro can also be used to create factory-customised versions of Silicon Labs' jitter attenuators and clock generators individually tailored to meet each customer's unique timing requirements.

Samples of the Si5344H and Si5342H coherent optical clocks are available now in 7x7mm 44QFN packages, with production quantities planned for May. Pricing begins at $27 each in 10,000 unit quantities. Standard and custom devices are available with short lead times (two weeks for samples and four weeks for production orders), simplifying procurement for prototyping and production quantities. The Si5344H-EVB and Si5342H-EVB evaluation boards, priced at $199 each (MSRP), are available to simplify device evaluation and system-level timing design.

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