Building a Microwave Frequency Synthesizer—Part 1: Getting Started

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  • Author: Alexander Chenakin
The frequency syn thesizer is a key building block of virtually any microwave test and measurement, communication or monitoring system. Synthesizers come in a variety of forms ranging from a tiny PLL chip to a bench-top signal generator. Traditionally we imagine them as a connectorized metal box or “brick” which can be put into a more complex instrument or subsystem. This series of articles presents an overview of microwave frequency synthesizer technologies and design techniques with a specific focus on the synthesizer “brick” modules. It starts with general requirements and specifcations followed by a review of the main synthesizer architectures. Direct analog, direct digital, and indirect techniques are compared in terms of performance, circuit complexity, and cost impact. A simple, single-loop PLL example is used to demonstrate the most important aspects of the design process from a general block diagram and component selection to schematic, board layout, assembling, and testing. The design trade-offs are further analyzed and complemented with a detailed review of the most advanced synthesizer solutions including DDS-based and multiloop schemes.