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Oscillator fits high-performance comms systems

Posted: 04 Nov 2009     Print Version  Bookmark and Share

Keywords:crystal oscillator  communications  Ethernet 

DS4625 oscillator

Maxim Integrated Products has launched the DS4625 dual-output LVPECL crystal oscillator. Designed for demanding communications applications, the device produces dual-output-frequency combinations ranging from 100MHz to 625MHz, thus it can replace two oscillators with a single device. Packaged in a 5mm x 3.2mm LCC, it is 55 per cent smaller than conventional solutions that typically measure 5mm x 7mm. Jitter performance is ensured at <1psRMS (12kHz to 20MHz) for high-current (95mA to 105mA, typ), high-frequency (>100MHz), differential-output (LVPECL) applications. The DS4625 fits communications systems that require high-performance clock generation such as Fibre Channel, Ethernet, 10G Ethernet, SONET/SDH, InfiniBand, GPON, BPON, PCIe, 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°C to +70°C 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 ageing of less than ±7ppm over 10 years, and exceptional frequency stability characteristics of less than ±50ppm, including variations due to voltage, temperature, initial tolerance and ageing.

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°C to +70°C 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.

Because the DS4625 design is based on an LC-PLL IC that uses fundamental AT-cut crystals, spurious modes of operation resulting in extreme frequency deviation are not possible. Additionally, the PLL-based design easily accommodates operating frequencies up to 622.08MHz and higher if desired. Standard frequency combinations for the DS4625 include: 100/150, 125/125, 125/156.25, 150/150, and 150/200MHz. Custom frequency combinations are also available.

Prices start at Rs.473.51 ($9.70) for 1,000-units, FOB USA, and vary depending on frequency combinations. Samples are available now.





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