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VCXOs Quiet Phase Noise to -162 dBc/Hz

April 29, 2016
These LVPECL logic-output crystal oscillators are available with outstanding short- and long-term stability, plus low-voltage operation, for output frequencies from 40 to 125 MHz.
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Phase noise is one of the limiting factors in receiver and transmitter performance in communications systems. Whether for analog or digital transmissions, excessive phase noise can cause side effects such as interference for closely spaced carriers and degradation of digital bit error rate (BER) performance.

To limit the phase noise at the starting point in a high-frequency signal conversion chain—the clock oscillator—Crystek recently introduced its CVPD-922 family of voltage-controlled crystal oscillators (VCXOs) with differential, low-voltage positive-emitter-coupled-logic (LVPECL) output signals. Available in a frequency range from 40 to 125 MHz, these “quiet” sources feature close-in single-sideband (SSB) phase noise of -85 dBc/Hz offset 10 Hz from the carrier, dropping to a noise floor of -162 dBc/Hz.

The CVPD-922 family of LVPECL crystal oscillators can be supplied with output frequencies from 40 to 125 MHz.

The CVPD-922 family of oscillators (see figure) provides a new degree of freedom for designers working on high-speed ECL-based circuits. Since ECL logic circuitry is extremely sensitive to noise, these oscillators provide a noise-floor limit that enables transmission of signals with higher signal integrity and improved BERs. The oscillators provide differential LVPECL outputs with worst-case 20-to-80% rise/fall time of 1 ns and ±10% linearity in support of logic signals with sharp pulse edges.

These are VCXOs with excellent time-domain performance and low noise to help achieve high levels of signal integrity in many different high-speed logic circuits. In the time domain, the typical phase jitter is just 85 fs at 100 MHz. In the frequency domain, the SSB phase noise drops steady from close to the carrier to offsets of 1 MHz and greater from the carrier (see table).  

The CVPD-922 oscillators support power-efficient designs with low current consumption and fast switching between enabled/disabled logic modes (controlled by package pin number 2). They feature a maximum startup time of 2 ms, with typical startup time of only 1 ms. The oscillators’ output disable time is only 200 ns. They offer typical tuning sensitivity of +25 ppm/V for a tuning range of 1.65 ±1.65 V dc. The VCXOs provide a typical 3-dB modulation bandwidth of greater than 10 kHz.

The crystal oscillators are available with a standard operating-temperature range of 0 to +70°C and with an operating-temperature range of -40 to +85°C as an option. They operate on a supply voltage of +3.3 ± 0.3 V dc with maximum current consumption of 88 mA. They are extremely stable with time, with an aging rate of less than 3 ppm during the first year of operation, and then less than 1 ppm per year after that. The oscillators conform to the applicable mechanical and environmental conditions of MIL-STD-883.

The CVPD-922 oscillators are supplied in surface-mount-device (SMD) housings measuring 0.560 × 0.360 × 0.210 in. (14.12 × 9.14 × 5.3 mm). They are available in tape-and-reel packaging for automated electronic manufacturing lines.

Crystek Crystals, a division of Crystek Corp., 12730 Commonwealth Dr., Fort Myers, FL 33913; (239) 561-3311, (800) 237-3061

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Download this article in .PDF format
This file type includes high resolution graphics and schematics when applicable.