A Guide to PCB Signal Integrity
An uninterrupted signal is critical to the success of circuit manufacturing work. However, the signal transmission can be impacted by external and internal circuitry elements. Therefore, the design of the circuit takes on an extra level of importance to mitigate signal interruptions and ensure each component within the system performs to its peak capacity.
Understanding the rules of signal integrity in circuit design can help you meet your capacity objectives in all future projects.
Our Toronto-based prototype manufacturing team members are the local design experts. Let’s explore the steps required to maintain signal integrity.
What does signal integrity mean?
Before we outline the rules for ensuring signal integrity within your circuits, we should go over what we mean by signal integrity. When a signal has lost integrity, its shape distorts from its initial profile. A signal that has lost its integrity can also adversely affect other circuitry on the PCB (printed circuit board).
The goal is to avoid electromagnetic interference and ensure the entire PCB performs as the manufacturer intended after production.
How to Ensure PCB Signal Integrity
Below are the steps your team can take to ensure the signal integrity across your PCB is maintained:
Uniformly Controlled Impedances
The signal quality within a PCB is dependent on the signal having a uniform trace and return path.
With high-speed systems, however, this level of precision can be challenging to achieve, and any change in the uniformity of the transmission line can cause signal distortion. That’s why design teams should ensure that high-speed lines are laid out with uniformly controlled impedance by routing lines on layers adjacent to the reference plane. This design results in a clear path of signal return.
To fully ensure uniform impedances, specific trace widths should match the board configuration.
Match Trace Lengths to Minimize Signal Degradation
Propagation delay is another element to review in PCB design processes. Signals travel in finite times as they make their way from the source to the receiver, so signal delays are directly related to line lengths and inversely matched to signal speed. If the data signals and the clock signals don’t equal the overall delays, then they arrive at different times at the receiver, thus causing detection issues and skewing the signal.
By matching trace lengths to one another, design teams can minimize problems with signal skewing and degradation over the line length.
Maintain Spacing to Avoid Crosstalk
Crosstalk within a signal is the result of placing circuit board traces too close to one another. Also referred to as unintentional electromagnetic coupling, crosstalk can cause one signal to mimic the qualities of a different signal. Again, this is a common problem within high-speed traces, even when upholding minimum spacing standards in the manufacturing process.
In most cases, your design team will have to maintain larger spacing between sensitive traces, such as clock lines. Designers should separate each PCB trace by at least three times the traditional distance. Another mistake designers make when considering spacing is routing traces on parallel lines over long distances on the PCB.
This design mistake can result in the ideal conditions for crosstalk. Therefore, designers should work to prevent this issue to the greatest extent possible in the design phase. Use alternative vertical and horizontal lines to mitigate the potential for crosstalk in the design.
Route Traces Carefully to Avoid EMI
Designers will find that traces with high-frequency signals can act as antennas and radiate electromagnetic interference (EMI) when they don’t carefully consider routing. So, PCB traces must be kept clear of splits and other nearby potential obstructions, and should be routed on a single plane. Traces should also have very few 90-degree corners, as this movement can also lead to interference.
As well, designers should avoid trace and via configurations that are stubs. This design can cause the signal to reflect and act as an antenna, thus pushing the signal across the local area on the PCB.
Mitigate Signal Bounce
Signal bounce is another top consideration for PCB design teams looking to avoid signal integrity issues. When high-speed switching occurs between components on a PCB, the voltages may “bounce” above the ground rather than returning to it via the trace. The bounce leads to the receiver misinterpreting the signal pulse and then producing false results.
Avoiding this problem requires designers to place decoupling capacitors as close as possible to their associated power supply system. By doing so, the design team can reduce the potential for current spikes during signal switching.
Each ground pin must connect to the ground individually, as this can simplify the signal routing process by reducing the number of vias. It can also increase the return current loop, ensuring limited issues with inductance.
PCB Laminate Selection
Another significant element in ensuring signal quality is the material used to produce the PCB within the manufacturing line. Ensure you speak with your Toronto-based prototype manufacturing company about the type of laminate used in the manufacturing phase.
The more cost-effective options might save you some money in the design phase, but you may find that a higher-speed laminate provides the best value for money in the long term by protecting signal integrity.
Testing is Key to Ensuring PCB Project Success
To maintain signal integrity throughout the board, designers must work with qualified testing experts who can analyze the design and review the board’s performance within a broad range of applications. For example, our prototype manufacturing experts often complete tests with a time-domain reflectometer. So, they can then track signal path impedance variation and limit radiofrequency interruptions.
We also review the modeling behaviour of drivers and receivers, and complete simulations to determine the vias and planes within the PCB. This level of comprehensive testing can help companies save thousands of dollars in the prototyping and manufacturing phases.
Book a Consultation With Circuits Central to Analyze PCB Signal Integrity
Our trusted and experienced prototype manufacturing team at Circuits Central in Toronto can help you overcome issues with signal integrity in your PCB designs. We understand the challenges that companies face in building complex components on smaller boards, and we use our component and design expertise to ensure the production readiness of your upcoming PCB designs.
Are you ready to book a consultation with a Toronto-based prototype manufacturing expert? Call our trusted specialists today.