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| 38 (i.e., RF bandwidth) below 20GHz, with commercially available products typically below 15GHz of RF bandwidth. Many systems sacrifice resolution (i.e., bit count) for conversion rate to achieve higher RF bandwidth. Reduced resolution results in poorer signal quality, which is a hard constraint in many high-performance RF systems. In many cases, it is more efficient and lower cost to leverage RF hardware for frequency translation and signal conditioning to and from the digital domain beyond several gigahertz of RF bandwidth. Digitizing much of the RF signal chain can benefit complex antenna systems and systems with extremely high numbers of RF channels. With complex antenna structures that use beamforming, beamsteering, multi-input multi-output (MIMO), or other spatial-multiplexing technologies, digitizing much of the RF signal chain may reduce the overall RF element count, size, interconnect, and power distribution. Implementing digital RF also comes with challenges and constraints, but companies that build digital RF chips often address these challenges. These companies often provide extensive support tools and resources to aid in the development of digital RF systems using their products. Many RF development boards come with software support, including open-source firmware, MATLAB® integration, and graphical user interfaces (GUIs) that allow users to evaluate custom waveforms and test system functionality (Figure 2). These tools may support standalone and loopback modes for ADCs and DACs and may be compatible with widely used design suites and embedded Linux platforms. Digital RF Theory and Concepts Engineers use digital RF technology to provide some performance, cost, or size benefit using DSP and conversion or synthesis. DSP technology, including field-programmable gate arrays (FPGAs) and dedicated digital hardware, enables precise RF signal generation, RF-to-digital conversion, digital frequency translation, and digital filtering. It also supports advanced controls like amplitude and phase adjustment and time- based signal correlation for spatial multiplexing. Some newer products can incorporate all these functions on a single chip, but many RF applications still use discrete chips for some functions, such as DDS and DDC, that are separate from the DSP. This section provides a primer on these digital RF concepts and briefly discusses how they are implemented. Digital Sampling Theory For an RF ADC to successfully sample an RF signal to a maximum desired frequency and resolution, the ADC must be able to sample fast enough to digitally recreate Figure 2: Overview of the relationship between the AMD RF Data Converter Evaluation Tool and the AMD ZCU208 RF evaluation board. (Source: Mouser Electronics)

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