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Tackling high-speed transceiver clocking with new high-performance oscillators

Silicon Labs has introduced a family of high-performance I2C-programmable crystal oscillators (XOs).

With jitter performance as low as 95 femtoseconds (fs), the Si544/Si549 Ultra Series programmable XOs maximise jitter margin for clocking high-speed 28 Gbps and 56 Gbps transceivers used in 100/200/400G communications and data centre applications.

The devices are capable of generating any frequency from 200 kHz to 1.5 GHz with no frequency gaps and 4 parts-per-trillion (ppt) tuning resolution, enabling a single device to be used across a broad spectrum of applications.

The Si544/Si549 XOs support up to four pre-set, pin-selectable start-up frequencies. After power-up, the device operating frequency can easily be changed via an I2C interface and this flexibility means that it is possible to replace multiple single, dual and quad-frequency XOs and multiplexer (mux) devices with a single oscillator. The device can be powered from a single 1.8, 2.5 or 3.3 V supply, eliminating the need for different XO part numbers for different supply voltages. The Si54x XO’s I2C interface supports update rates as high as 1 MHz (Fast-mode Plus), maximising compatibility with a broad range of ASSPs, ASICs, SoCs and FPGAs.

The Si544/Si549 XOs are available in 3.2 mm x 5 mm and 5 x 7 mm packages.

The Si54x XOs are purpose-built for 56 Gbps transceiver designs that rely on pulse-amplitude modulation (PAM4) signalling for serial data transmission.

PAM4 uses four-level signalling to increase the bit rate per channel while keeping the bandwidth constant but this tends to make the design inherently more susceptible to noise. Using an ultra-low-jitter reference clock such as the Si544/Si549 devices helps to maximise signal-to-noise ratio (SNR) headroom, helps prevent bit-errors and helps maintain signal integrity.

The Si544/Si549 oscillators use Silicon Labs’ advanced fourth-generation DSPLL technology to provide an ultra-low-jitter clock source at any output frequency. The devices are programmable to any frequency from 200 kHz to 1.5 GHz with 4 ppt resolution. On-chip power supply regulation provides power supply noise rejection, enabling consistent, reliable low-jitter operation in noisy environments often found in high-speed networking and data centres.

The Si544/Si549 XOs also provide flexible, reliable drop-in replacements for low-jitter surface acoustic wave (SAW)-based oscillators while offering superior frequency tolerance and temperature stability. The Si544/Si549 oscillators support all popular output formats including LVDS, LVPECL, HCSL, CML, CMOS and Dual CMOS.

Author
Neil Tyler

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