CURRENT STATE AND DEVELOPMENT TRENDS OF MICROWAVE FREQUENCY SYNTHESIZERS

This article discusses the current state and development trends of microwave frequency synthesizers for test-and-measurement instruments. The discussed trends are also applicable for other synthesizer types used as modules in more complex systems. Test-and-measurement synthesizer market is estimated at $300. with an annual growth rate about 3%. A modern trend for the development of frequency synthesizers is associated with low phase noise, low spurious and fast switching speed. Important parameters also include operating frequency range, frequency resolution, modulation capabilities as well as size and cost characteristics. The main architectures based on direct analog, direct digital and indirect synthesis are evaluated. As of today, traditional indirect phase-lock-loop (PLL) architectures still dominate. On the other hand, direct analog synthesis is the most advanced approach that demonstrates extremely fast switching speed and low phase noise. Nevertheless, future developments are associated with direct digital synthesis (DDS) due to the rapid progress in solid-state technologies. DDS are currently available as special integrated circuits (IC) or can be build using field-programmable logic arrays (FPGA) and high-frequency digital-to-analog converters (DAC). Parallel (multichannel) digital structures coupled with high-frequency DACs allow generating output signals at microwave frequencies. Further improvements are possible using two or more DACs in an interleaved data mode. Wider frequency coverage through several tens of gigahertz and lower spur characteristics are expected. The article notes that modern frequency synthesizers allow generating complex signals using vector IQ-modulation. The modulation bandwidth is constantly increases through hundreds of megahertz or even several gigahertz. Further advances in microwave frequency synthesizers are associated with new reference types such as sapphire-loaded cavity oscillators with combined frequency stabilization as well as optoelectronic methods.