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Low phase noise frequency synthesisers

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article image Blue Tops ULN 5MHz oscillator.

WENZEL Associates, represented by ASD Technology , has announced extremely low jitter phase noise sources, featuring Blue Tops technology, for operating and testing new components and systems.

Such applications include radar local oscillators, communications systems, phase noise measurement systems and low jitter clocks for testing data converters and other high performance semiconductors.

These systems often require a source that provides several frequencies at a time with virtually no spurious content and significantly better phase noise than provided by the best commercial synthesizers.

Building such a source can be a daunting challenge.

Low noise crystal oscillators are readily available but little or no phase noise data is provided for most RF functional modules and the processes of multiplying, dividing, mixing and amplifying can produce unwanted and unexpected spurious and harmonic content along with white and flicker phase noise.

Block diagrams can grow unwieldy as additional power splitters, filters, and attenuators are included to control the undesired signals.

Contracting the job out can be prohibitively expensive since virtually the whole system must be a custom design.

An alternative semi-custom approach is now available in the form of Wenzel Associates' Blue Tops modules and systems.

The Blue Tops product line includes dozens of modules including amplifiers, oscillators, multipliers, dividers, mixers, detectors, filters and other RF functions.

The modules typically contain amplifiers, attenuators, filters, voltage regulators, level detectors, and other ancillary functions in addition to the primary function in order to achieve function density while preserving the flexibility of connectorized components.

Phase noise performance is the Blue Tops' primary emphasis and all of the modules are tested on a phase noise measurement system.

A multi-chassis standardised multiple-frequency source made almost exclusively with Blue Tops provides up to 35 low noise frequencies from 10MHz to over 1GHz and a custom chassis built with RF modules makes quick work of synthesising additional frequencies.

The source includes the Blue Top ULN 5MHz oscillator which features superb phase noise, a ULN 100MHz oscillator and a ULN 80MHz oscillator for excellent noise floor performance at the higher frequencies.

An additional VHF oscillator at 110MHz, 125MHz or another frequency may be included, depending upon the customer's requirements.

The 5MHz internal oscillator may be locked to an external 5 or 10MHz reference with low loop bandwidth without the use of frequency dividers to preserve phase coherency.

The 5MHz signal drives an active power splitter which generates 8 high level outputs.

Ten megahertz is derived by frequency doubling the 5MHz with a special version of a circuit developed at NIST resulting in noise degradation near the theoretical 6dB at all offset frequencies.

Additional frequency multipliers generate low noise signals for phase-locking the VHF oscillators to the 5MHz reference.

The low frequency chassis has room for additional frequencies and a few standard versions are envisioned.

For example, 20 and 40MHz are easily added and can be handy for generating other frequencies.

An additional set of outputs is located on the rear panel for instrument interconnections.

Front panel indicators display the status of the PLLs, the oscillators' oven status and rear output levels.

The VHF chassis uses frequency multipliers to provide 100, 200, 300, 400, 500, 600, 700, 800, 900 and 1000 MHz from the lower frequencies with resulting phase noise.

No frequency dividers are used in these basic units and all of the VHF frequencies pass through narrow-band tubular filters for superb spectral purity and the lower frequencies employ lumped-element filters.

The two units are connected with coaxial jumpers on the rear.

A similar design supplies 80, 160, 240, 320, 400, 480, 560, 640, 720 and 800 MHz, and other models similarly provide 10 frequencies based on a chosen VHF frequency (110MHz, 125MHz, etc.).

The power supply in these models consists of two high performance components.

An electrostatic shielded toroid transformer, rectifiers, filter capacitors and power entry module are combined in a self-contained mumetal enclosure which installs from the rear of the instrument.

This "raw" supply has been designed to provide superb common-mode line isolation and magnetic field shielding.

Individual voltage regulators are separately packaged and typically mount on the inside rear panel with a heatsink on the outside.

These regulators exhibit very low noise voltage and, when combined with the highly shielded raw supply, provide the ideal power source for noise sensitive electronics. An optional external DC input is provided.

The chassis is designed to be compatible with the Agilent System II rack system and it features removable mounting ears for bench-top use.

The rugged aluminum case and machined aluminum front panel provide additional RF shielding and heatsinking.

The internal layout of both units is "bathtub" style with the components lining the walls and floor with easy access to all mounting hardware for easy modifications and servicing.

For customers that require non-standard output frequencies, a matching custom chassis is used.

The empty chassis features the same high performance power supply and has plenty of room for the direct or indirect synthesis of several additional frequencies.

The additional frequencies are typically generated with Blue Tops modules and other connectorized RF components, as needed.

The designs and layout are typically done by Wenzel Associates but customer designs are easily accommodated.

A complex system might have as many as five stacked chassis providing up to 45 different frequencies simultaneously.

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