RF circuit design is a discipline that focuses on the creation of circuits that operate in radio frequencies.
RF stands for Radio Frequency, which represents the oscillation rate of electromagnetic waves. Frequency is measured in Hertz (Hz), which is equal to the number of oscillation cycles per second (1/s). RF can refer to frequencies as high as 300 GHz, or as low as 30 KHz.
RF applications include:
RF waves can have other names such as microwaves (as in “microwave oven”), or millimeter waves (mm-wave). Microwave often refers to radio waves with the wavelength (λ) ranging from 1cm to 10cm, corresponding frequencies (f) of 30GHz to 3GHz. Millimeter wave often refers to radio waves with the wavelength (λ) ranging from 1mm to 10mm, corresponding to frequencies (f) of 300GHz to 30GHz. The relation between wavelength (λ) and frequency (f ) is expressed as λ=c/f, where λ is measured in meters, c is the speed of light (3×10^8 m/s), f is measured in Hz, or 1/second).
RF circuits are “analog” in nature, with continuous time stimulus and response. While they previously were made with vacuum tubes and discrete transistors, these materials have largely been replaced by integrated circuits (ICs), except for a few high-power applications. In the applications where high power is not needed, such as cell-phone transceivers, WiFi transceivers, Bluetooth transceivers, and satellite receivers circuits often take the form of a silicon-based IC.
RF IC design typically involves a top-down design and implementation process, followed by a bottom-up verification process. There are many variations on this overall approach. Here are the basic steps:
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.
Break free from outdated analog design tools
Digital design treats circuit stimulus as a series of discrete logic “ones” and logic “zeros” over time. A logic “one” is typically represented by the presence of the supply voltage for the IC and a logic “zero” is represented by the absence of this voltage (i.e., zero volts). The devices in digital circuits must spend most of their time at either logic “one” or logic “zero.” If the circuits processing these signals are consistent in their response to these logic levels, digital design works well. Analog design is responsible for delivering these qualities. This allows the behavior of the circuit to be analyzed using combinatorial and sequential models, only considering two voltages (“one” and “zero”), which substantially simplifies the design and verification process.
To put RF circuits, analog circuits, and digital circuits together in a radio system, an analog-to-digital converter (ADC) acts as a bridge between analog circuits and digital circuits. A mixer acts as a bridge between analog circuits and RF circuits. An antenna acts as an interface between an RF circuit and air space.
The Synopsys Custom Design Platform is a unified suite of design and verification tools featuring a complete RF development flow. It facilitates design/layout collaboration that makes it easy to communicate design intent and achieve RF design closure, as shown below.
Synopsys Custom Design Platform tools include:
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