With the advancement of communication technology, handheld radio frequency circuitry is increasingly utilized in devices such as wireless pagers, mobile phones, and wireless PDAs. The performance of RF circuits directly impacts the overall product quality. Miniaturization is a key characteristic of these handheld products, resulting in high component density and significant mutual interference between components (including SMDs, SMCs, and bare chips). Improper handling of EMI signals can disrupt the entire circuit system. Therefore, effectively preventing and suppressing EMI while improving EMC has become crucial in RF circuit PCB design. The performance metrics of the same circuit can vary greatly depending on different PCB design structures.
1. First, determine the position of interface components on the PCB and their connection with other PCB boards or systems. Pay close attention to the coordination between these components, including their orientation. Given the compact size of handheld devices, prioritize the placement of larger components and ensure their optimal arrangement. Analyze the circuit structure carefully, processing it in blocks such as high-frequency amplification, frequency mixing, and demodulation circuits. Segregate high-current signals from low-current ones, digital circuits from analog ones, and group circuits performing similar functions to minimize signal loop areas. Ensure that filter networks for each circuit section are positioned nearby to reduce radiation and interference.
2. Once component layout is finalized, proceed with wiring. The primary principle is to maintain low-density wiring wherever possible, ensuring that signal traces are appropriately sized to facilitate impedance matching. For RF circuits, meticulous attention must be paid to the design of signal line direction, width, and spacing to prevent cross-interference. Consider the inherent noise interference in the system’s power supply when designing the RF circuit PCB. During wiring, keep all traces at least 2mm away from the PCB board edges to prevent potential damage during fabrication. Optimize power traces for minimal resistance and align their direction with data transmission paths to enhance anti-interference capabilities. Minimize signal trace lengths and via counts, and avoid parallel routing of incompatible signal lines. Use 135° angles at corners to prevent sharp turns. Ensure that traces directly connected to bonding pads are appropriately sized, and keep them clear of unconnected components to prevent short circuits. Place vias away from components to avoid production issues such as false soldering or short circuits.
3. Many interference issues on PCBs stem from power and ground lines, with ground lines typically causing the most noise interference due to their impedance. When current flows through ground lines, it induces voltage and forms ground loop currents, leading to interference. When multiple circuits share a ground line segment, they create common impedance coupling, resulting in ground loop noise. Therefore, when wiring the ground lines of RF circuit PCBs, divide them into sections. Separate digital and analog ground lines and connect them to power ground separately. Ensure each circuit section follows single-point grounding principles to minimize signal loop areas and connect to nearby filter circuits. Ideally, isolate each module with dedicated ground lines to prevent mutual signal coupling.
4. The core of RF circuit PCB design lies in minimizing radiation and enhancing anti-interference capabilities. A well-executed layout and wiring strategy are crucial for RF circuit PCB reliability. The methods discussed here aid in improving the electromagnetic interference performance and achieving electromagnetic compatibility. With the increasing prevalence of IoT technologies, integrating wireless communication functions into electronic products via RF circuit PCBs requires professional design and simulation tools.
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