Dual-Output Crystal Oscillator Provides High-Frequency Differential Outputs and Robust Jitter Performance for Demanding Communications Applications

28th October 2009
Posted By : ES Admin
Dual-Output Crystal Oscillator Provides High-Frequency Differential Outputs and Robust Jitter Performance for Demanding Communications Applications
Maxim has introduced the DS4625, a dual-output LVPECL crystal oscillator designed for demanding communications applications. This device produces dual-output-frequency combinations ranging from 100MHz to 625MHz, allowing designers to replace two oscillators with a single device. Packaged in a 5mm x 3.2mm LCC, the DS4625 is 55% smaller than conventional solutions (5mm x 7mm). This device ensures leading-edge jitter performance [< 1.0 psRMS (12kHz to 20MHz)] for high-current (95mA to 105mA, typ), high-frequency (> 100MHz), differential-output (LVPECL) applications. The DS4625 is thus ideal for communications systems that require high-performance clock generation such as Fibre Channel, Ethernet, 10G Ethernet, SONET/SDH, InfiniBand(R), GPON, BPON, PCI Express(R), and SAS/SATA.
The DS4625 solves the heat dissipation problems typically encountered by small ceramic packages in high-frequency, high-current designs. An integrated thermal pad provides thermal relief for the crystal element, thus ensuring reliable operation over the entire -40 degrees Celsius to +70 degrees Celsius temperature range. The DS4625 is manufactured using fundamental AT-cut crystal technology--with no overtones--and a low-noise PLL-based oscillator designed in Maxim's SiGe foundry. The overall design provides extremely low aging of < ±7ppm over 10 years, and exceptional frequency stability characteristics of less than ±50ppm, including variations due to voltage, temperature, initial tolerance, and aging. Compared to competitive devices such as SAW-based oscillator designs, the DS4625 offers a smaller footprint, comparable jitter performance, and better stability (±50ppm versus ±100ppm or greater) across a wider -40 degrees Celsius to +70 degrees Celsius temperature range.

Third-overtone oscillator designs provide for robust phase-jitter performance and good stability versus temperature, but can suffer from undesired spurious modes of operation as package size and crystal resonator size decrease. Spurious modes are generally excited based on temperature, which results in significant frequency deviations from the desired nominal frequency. In addition, third-overtone designs provide limited frequency operation with maximum frequencies of approximately 200MHz.

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