Electronic Design

Oscillator Boasts Low Phase Noise And Aging Up To 1.5 GHz

The VFT-5 crystal oscillator em-ploys unique methods for frequency multiplication and for vacuum sealing the quartz crystal to meet the high-frequency clocking requirements of Sonet and other optical networking applications.

Available as either a clock oscillator or as a voltage-controlled crystal oscillator (VCXO), the device is available in frequencies ranging from 0.6 to 1.5 GHz. Its performance is significantly better than competing frequency sources, such as surface acoustic wave (SAW) resonators and phase-locked loop (PLL) multipliers.

Phase noise for the VFT-5 ranges from ­65 dBc/Hz at a 10-Hz offset down to a noise floor of ­140 dBc/Hz at a 10-KHz offset. In contrast, SAW resonators exhibit phase noise that is 20 to 30 dBc/Hz worse, while also reaching the noise floor at a wider offset of 1 MHz. For PLL multipliers, phase noise is greater still, with values that are 30 to 40 dBc/Hz noisier than the VFT-5.

The oscillator's temperature stability, which is determined by the AT-cut crystal, is ±10 to ±15 ppm over the ­40°C to 85°C range. Although PLL multipliers may offer the same stability, the stability of SAW resonators is about ±150 ppm.

The VFT-5's long-term stability (aging) is better than1 ppm per year. As with temperature stability, the PLL multipliers may achieve similar aging. For SAW devices, this parameter is 10 ppm per year. To achieve its low aging, the quartz crystal is sealed using a high-vacuum technique that affords high volume and low cost.

The company plans to extend the frequency range of the VFT-5 up to 2.5 GHz by developing a new oscillator-buffering technique. There are also plans to introduce the oscillator with a low-voltage differential signaling output in addition to the ECL output now offered. Units are available with volume pricing ranging from $40 to $60 each, depending on performance specifications.

Valpey Fisher, www.valpeyfisher.com; Douglass Gay, (508) 435-6831.

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