Important Signal Integrity Considerations for PCB Designers

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All printed circuit boards in general must be sensitive in their design to facilitate the various signals which will be running on them. Certain devices such as smartphones are more demanding in their needs of course, but all devices with a PCB inside rely on signal integrity invariably. Depending on how many high-power components are on a board and the complexity of their functions, maintaining signal integrity could become much harder in complex layouts.

Frequencies and Signal Integrity: How They Are Related

Low frequency signal integrity is not a concern for the most part, but it’s almost always the higher frequency signals that get distorted on account of reflection, ground bounce, ringing, and crosstalk.

Higher frequencies are a direct result of the high-speed nature of these signals, which means that the disturbances can affect the integrity of the original signal on both an analog, as well as on a digital level.

Distance/Length and SignalIntegrity: A Directly Proportional Relationship

The transmission medium can be air for wireless signals, or it can be a physical cable. Whichever it might be, there is a direct and proportional relationship in between the issuing point and the reception point of a signal.

In case of wireless tech, both integrity and quantity are lost in direct proportion with the distance. When the two points are connected via cables/wiring though, the amount of signal lost is directly proportional to the length of the transmission medium and the materials used to construct it.

In both wired and wireless transmission mediums, the signal strength is a common factor for determining the integrity. The stronger (not the same as faster) the signal is, the longer it will be able to stay undistorted while travelling via their respective transmission mediums; which is what we call β€œrange.”

Analysis: Signal Integrity, Speed and Strength

There are multiple methods that are used effectively to reduce the impact of interference on high speed signals. The very first step involves a proper signal and power analysis in order to detect the problems if and where they exist on the PCB design.

Not only should your 3D PCB designer tool come well equipped with signal strength, speed and integrity analysis tools, but it should also allow you to make the necessary corrections with suggestive guidance via 3D simulations.

A Few Intelligent Steps to Preserve High-Speed Signal Integrity

As mentioned above, your PCB software should have the features necessary to simulate, analyze and detect issues, if and where they exist. That being said, there are a few general guidelines which are largely effective in most PCB designs that are meant to handle high-frequency loads.

  • Avoid 90-degrees angles to reduce chances of inconsistent trace widths and inadequate etching
  • Restrict the use of vias as best as possible to reduce the inductance and capacitance from them
  • Use differential pair routing methods
  • Plan components and trace paths to keep high and low frequencies apart from each other
  • Practice the same separation of digital and analog signals as well
  • Rogers RO4350 is an ideal laminate for high-speed signals; FR4 may not cut it

These brief points should be sufficient to provide an introduction on how to handle high-speed signals on a PCB effectively.

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