In a nutshell, high speed PCB design is any design where integrity of your signals begins to get impacted by physical characteristics of your circuit board like your packaging, interconnection, layout etc. If you initiate designing boards and encounter issues like delays, reflections crosstalk or emissions then welcome to the world of high speed PCB design.
High speed design is distinct due to the attention paid to these issues. One may be utilized to design a simple board where primary focus is on component placement and routing. With high speed design, it is paramount to consider exactly where you are placing the traces, how close they are to signals and the nature of connected components. Making considerations of this type will take the model to a completely next level.
Signals and its integrity
We have a brief idea about high speed design in the context of signal integrity but what does it exactly mean? Here we need to understand signals in a nutshell.
Regardless of the nature of design you are working on, it will send some sort of signals down your sections of copper traces to an ultimate destination. The signal can either be analog or digital. Both of these types are prone to interference and this is where we are concerned about signal integrity. Whenever a signal is impacted by its environment, an issue arises. There are a number of things that can interfere with your signal integrity like signal reflection, signal ringing, signal noise, signal timing etc. These causes disturbances in the signal that you are trying to get from one designated point to another. This results into corrupt data being transmitted. So the job of an engineer performing on high speed PCB design project is to protect integrity of these signals.
Big problems
There are a number of issues faced while working on this project. But here are the main concerns:
- The signals on your PCB layout may not arrive on proper time in relation to other signals.
- Integrity of signals is not protected. It doesn’t reach as they should to their end destination.
- Emission of noise through PCB which results into data corruption.
These issues can be corrected in the following three ways.
- Have proper impedance between transmitter and receiver.
- Match the lengths of two integrated traces to ensure that they arrive at the same time.
- Do not place the traces closer to reduce the amount of noise.
How to tell if your project is high speed?
There are few ideologies on this issue but the fact is that there is no one specific definition of what categorizes PCB as high speed. It differs from case to case. As mentioned above, if there are some signal integrity issues then there is high tendency that you have access to high speed project.
Conclusion
Learning about high speed PCB design is learning about a different segment of engineering. What actually this article covered is an understanding of high speed design and how the integrity of signals come into play.
