6. RF Circuits

There are two types of high-frequency circuits. One is a wideband circuit covering DC to RF or microwave frequencies. The other is a narrowband circuit operating at RF or microwave frequencies. The former is broadbanded by feedback while the latter operates in open loop, but occasionally with local feedback. The former is also for wireline baseband systems such as fiber and networking, but the latter is mostly for wireless RF transceivers. The key RF circuit elements are low-noise amplifier (LNA), mixer, power amplifier, and voltage-controlled oscillator (VCO). Most performance parameters for RF circuits can be enhanced mostly by optimizing open-loop parameters, but system-level DC parameters such as offset, image, and spurious tone can be self-trimmed. The bottleneck in RF system designs is the mixer spurious-free dynamic range (SFDR) performance. RF systems can be configured using global feedback and IF quantization concepts, which facilitate the integration of on-chip wireless systems. RF circuit and system issues are referred to the mixer SFDR performance, and various design concepts such as static and dynamic mixer linearity, impedance matching, loaded Q and fractional spur are addressed for efficient RF system implementations.