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Crystal oscillator offers dual-output-frequency

Posted: 04 Nov 2009 ?? ?Print Version ?Bookmark and Share

Keywords:crystal oscillator? communications? Ethernet?

DS4625 oscillator

From Maxim Integrated Products comes a dual-output LVPECL crystal oscillator designed for demanding communications applications.

The DS4625 produces dual-output-frequency combinations ranging from 100MHz to 625MHz. It can replace two oscillators with a single device. Packaged in a 5mm x 3.2mm LCC, the device is 55 percent smaller than conventional solutions that usually measure 5mm x 7mm. It ensures jitter performance of RMS (12kHz to 20MHz) for high-current (95mA to 105mA, typ), high-frequency (>100MHz), differential-output (LVPECL) applications. The DS4625 is suited for 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 -40C to +70C 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 less than 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 -40C to +70C 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 $9.70 (1,000-units, FOB USA) and vary depending on frequency combinations. Samples are available now.

For application notes on crystal oscillators click here.

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