Using high-speed op amps for high-performance RF design, Part 1

Why use op amps for RF design? Traditional RF design techniques using discrete transistors have been practiced successfully for decades. RF designers who are comfortable with things “as-is” will scrutinize introduction of a new design technique using op amps. The cost of high-speed op amps, in particular, will raise eyebrows. Why replace a transistor that costs a few cents with a component that may cost several dollars? This is a valid question to ask for high-volume consumer goods; and, in almost every case, the answer will be to stay with traditional techniques. For high-performance RF equipment, however, high-speed op amps have some distinct advantages. Many other applications have migrated to op amps to take advantage of the superior performance they provide. It is reasonable to assume that high-speed applications such as RF will also make the move. This article will be presented in two parts. Part 1 focuses on the actual topology of RF stages formed with op amps and the scattering parameters. Part 2 will focus on some fine points of RF design and more specifications unique to RF.