Partitioning for RF Designs in Communication Systems

Key Takeaways

• When there are issues in a circuit board due to poor PCB materials, layering, or routing choices, it usually leads to the mixing of signals of different types.

• Isolating RF circuits from other types of subsystems is the primary aim of partitioning for RF design. 

• Partitioning in RF designs conserves signal integrity and prevents the degradation of signals due to noise, leakage, or interference.

Today’s communication systems are a blend of analog, embedded, and RF technologies. Each circuit type in a system, whether digital, analog, or RF, should perform excellently and not interfere with the operation of other circuits. If there is any interference or disturbance caused by RF, digital, or analog circuits, then the system design needs to be altered to mitigate this. 

With the emergence of 5G and IoT applications, it has become a design requirement to partition the RF, analog, and digital circuits in a communication system. In this article, we will focus on the importance of partitioning for RF designs and why this is so crucial to achieving reliable system performance and efficiency. 

The Importance of Partitioning for RF Designs

When there are issues in the circuit board due to poor PCB materials, layering, or routing choices, it can lead to the mixing of signals of different types. If signals are mixed up, the whole purpose of a circuit board falters. It is critical to prevent such incidents in communication systems handling RF, analog, and digital signals simultaneously. 

Isolating RF circuits from other types of subsystems is the primary aim of partitioning for RF designs. This partitioning conserves signal integrity and prevents the degradation of signals due to noise, leakage, or interference. 

Why is Partitioning So Critical?

The present-day electronics market favors compact designs. However, this compact size has become a major concern when designing high-performance communication systems, because as a system is downsized, the different types of signals must co-exist in a smaller footprint area. 

In compact circuit designs, DC power signals from a power converter, external source, or battery energize the entire circuit board. The voltage level of the power rails connecting different sections of a single board differs. The embedded systems, logic controls, and control systems in the communication system typically prefer digital pulses. These digital pulses moving in a transmission line might be surrounded by lines carrying analog signals. There can be ADCs or DACs converting analog signals to digital signals and digital signals to analog signals, respectively. 

Along with these signals, communication signals of high frequency are also present. They undergo frequency changes or get modulated or demodulated, depending on the system’s purpose. The proliferation of integrated circuits into communication circuits has worsened the scenario of placing lines carrying different signal types in close proximity. 

RF Layout Tips for Partitioning

There are many rules for partitioning for RF designs, and the specific rules that need to be applied depend on the application platform. The performance index of RF circuits in applications such as medical devices, missile systems, or mobile phones is entirely different. In some systems, signal integrity is more important than reliability or efficiency. Depending on where you are going to implement partitioning, slight changes might be necessary to protect the system’s purpose and performance.

Here are some general rules to follow in RF layout design:

1. Most communication systems and gadgets are an integration of RF signals, analog signals, and digital signals. When mounting RF components in a circuit, keep them together, but away from analog and digital signals. This can reduce the signal coupling, noise, and EMI problems that persist in mixed-signal RF circuits. Within the RF subsystem, two circuits with a chance of interference can be placed at opposite ends. Or, a time-shared operation can be scheduled for these kinds of circuits, so that when one is working, the other goes off. 

2. Electrical isolation can be brought into RF circuit design by utilizing microvias and high-density interconnectors. These techniques can conserve space in the circuit layout and are suitable for compact RF designs. The physical separation of inputs and outputs is a key recommendation for isolation in RF designs—if the floor area supports it. 

3. EMI and small-signal disturbances are often seen in RF circuits, especially in high speed or high-frequency applications. In such circuits, RF transmission lines are isolated from other signal traces by placing them on ground separated layers. Designers should provide one solid ground plane without partitioning or splits in RF designs. Avoid sharp bends, making the RF transmission lines short in length, or directly connecting the lines to antennas as well.

For better signal integrity, reliability, and circuit performance, partitioning for RF designs is critical. There are several guidelines to follow when partitioning, and we hope our short guide has provided some guidance on these recommendations.

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