Radio Frequency Circuit Design Enhance Design Flexibility for Engineered PCBs
In a modern electronic device, radio frequency circuit design signals carry data and provide the link between digital, analog, and wireless components. These signals, along with power and ground planes, need to be routed through the PCB in order to deliver required functionality. In addition, electromagnetic interaction at these high frequencies leads to parasitic effects such as signal reflections, crosstalk and electromagnetic interference (EMI). These interactions must be taken into account early on in the design process to ensure that the RF circuit design meets performance requirements.
RF circuits are designed using a combination of integrated and discrete semiconductor devices, along with printed RF elements such as antennas and dipoles. Using the latest RF integrated circuit (RFIC) technology allows designers to converge multiple functions into a single SoC, significantly increasing system efficiency and performance. However, this convergence also increases the complexity of RF circuits, and traditional SPICE simulation tools may not be sufficient to qualify a RF PCB design.
High-speed circuits must be designed to withstand the vibration and vibration-induced degradation of the electromagnetic environment, known as shot noise. This degradation affects the sensitivity and accuracy of RF receivers, which in turn impacts SNR and dynamic range. To minimize shot noise, RF designers can increase current levels and use low-noise active devices such as GaAs FETs and GaN HEMTs.
A critical feature of RF circuits is the transmission line, which provides a controlled characteristic impedance for high-frequency signals. This allows for efficient signal propagation over long distances with minimal reflections and losses. To maintain proper characteristic impedance, designers need to select a PCB laminate and bondply material with the desired dielectric constant, and implement a matching network.
How Do Radio Frequency Circuit Design Enhance Design Flexibility for Engineered PCBs?
RF amplifiers are used to boost the signal levels of a transmission line in order to deliver adequate power to the RF antenna and other RF components. They can be based on a number of active devices such as Si LDMOS, GaAs FETs, GaN HEMTs and InP HBTs, depending on the exact tradeoffs required.
Oscillators generate a desired frequency, and are usually implemented as LC oscillators, crystal oscillators or ring oscillators. They are crucial for generating stable frequencies that can be transmitted over long distances.
All time-varying electrical signals produce electromagnetic radiation (EMR), and this can interfere with other devices in the vicinity. Often, this EMR is unwanted and is referred to as EMI. It is important to identify and eliminate sources of EMI in the RF circuit design, such as unused or mismatched transmission lines, improper impedance matching and signal traces, packaging parasitics, uncontrolled loading of amplifier output stages and more.
This can be accomplished by performing a thorough RF circuit and PCB layout. Then, the circuit design can be refined to reduce EMI using component selection, component positioning and more. To complete the process, RF circuits must be tested to verify that they meet their desired specifications. This can be performed using techniques like TDR, which can spot impedance mismatches and signal traces that degrade performance.