Frequency Synthesizers: Concept to Product

Feb. 18, 2011
SO ESSENTIAL ARE FREQUENCY synthesizers to communications systems, it would be hard to imagine the modern "wireless revolution" without them. These stabilized sources, both fixed and tunable, can be found in every cellular telephone, in ...

SO ESSENTIAL ARE FREQUENCY synthesizers to communications systems, it would be hard to imagine the modern "wireless revolution" without them. These stabilized sources, both fixed and tunable, can be found in every cellular telephone, in every cellular base station and repeater, and in most high-performance wireless products requiring a stable frequency source for transmission and reception of RF and microwave signals.

They may not be simple, but understanding frequency synthesizer technologies is a huge step toward understanding the block diagram of most wireless systems. In Frequency Synthesizers: Concept to Product, renowned synthesizer designer Alexander Chenakin of Phase Matrix ( shares his knowledge on the different technologies collectively known as "frequency synthesizers." He also offers practical advice on how to turn these technologies into practical products, based on his extensive experience.

The 214-page text provides a short but effective lesson on frequency synthesizers. It is not meant to be an allinclusive textbook on the topic. Those seeking a more comprehensive review of frequency synthesizer technologies and design approaches might be better served by one of Ulrich Rohde's excellent texts on the subject, such as Synthesizer Design for Microwave Applications, published by John Wiley, Digital PLL Frequency SynthesizersTheory and Design, from Prentice-Hall, or Microwave and Wireless Synthesizers: Theory and Design, from Wiley-Interscience.

Frequency Synthesizers: Concept to Product, does not try to match the density of those books in terms of theoretical understanding of frequency synthesizers. Rather, it attempts to bridge the gap between a mathematical representation of a frequency synthesizer and a practical implementation of the technology. Alexander Chenakin provides information in an informal style easily accessible to any engineer with a basic understanding of microwave design. The book is divided into six chapters, stepping a reader from fundamental concepts to advanced functions.

The book is liberally illustrated with photographs of product examples from various companies, as well as clear block diagrams and performance plots. In a book of this size, some of the discussionssuch as that of phase noise in oscillatorsare very basic. But they provide enough mathematical background and information to help the reader appreciate the effects of phase noise on system performance and how it is generated within an oscillator or frequency synthesizer.

The book includes brief sections on transmission lines, building-block components, and packaging techniques. But the essence of the text can be found in Chapters 4 and 5, which include guidelines on designing a frequency synthesizer and optimizing its performance, respectively. Chapter 4 includes discussions on board layouts and schematic diagrams, offering several examples of each, as well as assembly techniques, mechanical design, and control software. Chapter 5 reviews the effects of switching from single-loop to multiple-loop synthesizer architectures, and the advantages and disadvantages of incorporating a direct-digital synthesizer (DDS) within a PLL architecture. While the DDS is known for fast switching speed and fine frequency resolution, it can also add unwanted spurious content to the outputs of a frequency synthesizer.

Each section is documented in terms of source material, with references providing information from names synonymous with phase-lock-loop (PLL) and frequency synthesizer design, including Rohde, Paul Khanna, Darko Kajfez, Steve Maas, and Inder Bahl.

Not coincidentally, the book includes a section comparing fundamental frequency sources for use in a frequency synthesizer, including the tradeoffs in using a voltage-controlled oscillator versus a slower YIG-tuned oscillator. Both are capable of generating microwave frequencies, although the VCO offers switching speed as the main tradeoff to improved phase noise in a YIG-tuned oscillator. Mr. Chenakin will be publishing a more detailed comparison of the two oscillator technologies in the upcoming April issue of Microwaves & RF.

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