Control Interfaces for RF and Microwave Frequency Synthesizers

Frequency synthesizers come in a variety of forms ranging from tiny PLL chips and moderate-size modules to bench-top signal generators [1-5]. Single-chip synthesizers are available in a die form or as surface-mount integrated circuits. They include key elements (such as RF and reference dividers, phase detector, lock indicator, etc.) required to build a simple single-loop PLL synthesizer. More complex ICs include a built-in VCO, multiple PLLs, DDS, and other valuable components integrated on a single chip. Such ICs are installed on a printed-circuit board (PCB) with additional circuitry (e.g., loop filter components). The PCB-based modules range from small, surface-mount, “oscillator-like” designs to more complex connectorized assemblies. The level of complexity varies from simple single-loop PLLs to sophisticated multiloop and DDS-based designs. Such PCB assemblies can be packaged into a metal housing and are presented as stand-alone, complete synthesizer modules. Connectorized synthesizer modules (often called “bricks”) can be used to build larger bench-top and rack-mountable signal generators for test-and-measurement applications. They come with high-end technical characteristics, precise calibration, and extended functionality including frequency and power sweep, various modulation modes, built-in modulation sources, and many other functions. The synthesizers come with various control interfaces that are almost as diverse as the number of synthesizer designs. The most popular interfaces are reviewed next; more details can be found in [6].