An RF circuit is a special type of analog circuit operating at the very high frequencies suitable for wireless transmission. One salient feature of an RF circuit is the use of inductive elements to tune the resonant circuit operation around a specific radio carrier frequency. The primary difference between RF design and low-frequency analog design is the type of analysis performed on the circuit.
In RF design, steady-state operation is of primary concern. The behavior of the circuit is often modeled in frequency domain with attention focused on the signal fidelity, noise, distortion, and interference. When modeling a modulated signal on an RF carrier, a hybrid time-frequency domain analysis is most efficient, where time domain focuses on the dynamic signal changes and frequency domain focuses on the RF carrier and its harmonics and intermodulation products. RF circuit variability, both manufacturing and design induced, must be modeled, and compensated for.
In analog design, circuit stimulus is treated as a continuously varying signal over time. In the context of wireless communications, analog design often refers to the “low frequency” or “baseband” circuit as opposed to the “RF” circuit. In the context of wireline communications, analog design often refers to the analog front end or high-speed analog transceiver circuits. The behavior of the analog circuit is modeled in the time and frequency domains with attention focused on the fidelity/precision, consistency, and performance of the resultant waveforms. Circuit variability, both manufacturing and design induced, must be modeled, and compensated for as well.