In today’s electronic engineering landscape, the demand for high-speed design has never been higher. With interfaces like USB-C, WIFI, DDR, MIPI, and others becoming cornerstones of tomorrow’s products, designers need to have an understanding of what high-speed signals are and the challenges they pose.
In this series we will delve into some of the important considerations required to make these designs successful.
What is “High Speed”?
The “speed” of a signal is defined by two main factors.
The first and most obvious factor is the frequency of the electrical signal. Although there is no strict definition, anything greater than 50MHz is generally considered high speed.
The second and sometimes overlooked factor is the rise time or edge rate. A simple explanation of edge rate is how quickly a signal shifts from one state to another. Typically this is measured as the time required for the signal to transition from 10% to 90%. Any edge rate faster than 5ns would be considered high speed.
Either one of these two factors is enough to warrant special consideration. While general rules of thumb are helpful in determining when to consider high-speed design principles, the best way to determine if a signal is high speed is based on the physical wavelength. The physical wavelength can be calculated using the simple equation below.
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If the physical size of the structures you are working with are greater than 5% of the wavelength it’s important to leverage high speed design principles to ensure a robust design.
What are some of the challenges in high speed design?
When it comes to routing these signals, there are two main challenges that may require mitigation in the design: signal integrity and EMI (Electromagnetic Interference).
Signal Integrity
Signal integrity is the ability of a signal to maintain its intended shape, amplitude, and timing without being distorted by various factors in the PCB layout and design. Optimizing for signal integrity is important because any distortion on the signal will add error to the receiving end.
Electromagnetic Interference
Electromagnetic interference (EMI) refers to the unwanted disruption of electrical circuits due to electromagnetic radiation or conduction from external sources. This interference can cause malfunctions, data loss, or degraded performance in electronic devices. EMI can be generated by various sources, including other electronic devices, power lines, and even natural phenomena like lightning.
Controlling EMI is crucial to ensure that circuits operate without signal degradation and in compliance with FCC regulations.
Examples of Porticos projects utilizing PCB layouts.
Final Thoughts
When designing high speed PCBs it’s important to prepare the design correctly. This includes identifying any high speed signals and requirements, and planning for their optimum implementation.
Stay tuned for part 2 of our series, Preparing For High Speed PCB Layout, to take a deep dive on preparing your design for layout.
Ready to start your high speed design? Porticos has a team of engineers to help you with your design and implementation. Get in touch to learn more.
