Controlled Impedance Routing vs Length Matching Routing
Designing a printed circuit board is no easy feat. There are multiple aspects to consider, and one of the most crucial ones is ensuring signal integrity. Signals need to travel through the PCB with little to no degradation or interference. This is where controlled impedance routing and length matching routing come into play.
What is Controlled Impedance Routing?
Controlled impedance routing is a technique that helps maintain a consistent impedance level throughout the PCB by varying the trace width, gap between traces, and the thickness of the dielectric material between the traces. This technique is typically used in high-speed designs such as those involving microprocessors, memory ICs, and FPGAs.
What is Length Matching Routing?
Length matching routing is the practice of ensuring that critical traces that carry signals of the same frequency or wave are equal in length. This helps to minimize time delays, prevent signal skew, and cross-talk in the PCB. This routing technique is used for high-speed designs, such as DDR memory.
Controlled Impedance Routing vs Length Matching Routing
Now that we know what controlled impedance routing and length matching routing are, let's compare them based on a few factors:
Complexity
Controlled impedance routing is more complicated than length matching routing. This technique requires careful considerations such as layer stack-up, trace widths, and dielectric properties. On the other hand, length matching routing involves merely ensuring that traces of the same frequency have equal lengths.
Accuracy
Controlled impedance routing needs to achieve a specific target impedance for signal integrity, and this can be a bit challenging. Any deviation from the target impedance can disrupt the signal, leading to signal integrity problems. In contrast, length matching routing can have some tolerances without adversely affecting signal quality.
Cost
Controlled impedance routing can be more expensive as it requires specialized PCB manufacturing processes such as impedance-controlled layer stack-up and etching. Length matching routing, on the other hand, has no added cost since it just involves length matching of traces.
Final Thoughts
Both controlled impedance routing and length matching routing are essential techniques for designing high-speed PCBs. Each has its advantages and disadvantages, and designers must choose the right technique depending on the design specifications and requirements. In summary, the more stringent the signal requirements, the more critical it is to use controlled impedance routing.
References
- F. Lau, T. Xie, X. Wang, W. Xue, and Y. Liu, "Controlled-impedance routing for high-speed printed circuit boards and packages," Proc. 9th IEEE Int. Conf. ASIC. Proc. Conf., 2017.
- S. Aditya and K. S. Raut, "A comparative study of routing techniques for high-speed memory interfaces," Proc. Int. Conf. Circuit, Power, and Computing Technologies, pp. 26-31, 2016.