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Simplify Crosstalk Measurements and Mitigation Using Crosstalk Analysis

Author Cadence PCB Solutions

Key Takeaways

  • Crosstalk is the phenomenon in which the signal transmitted through one path creates undesired effects on its neighboring path.

  • Crosstalk effects typically result in functional failures, where they either change the signal amplitude (crosstalk glitch) or timing (crosstalk delay).

  • Crosstalk analysis can determine the relative error or noises introduced by each aggressor on the victim.

High-speed communication

Crosstalk is a serious issue concerning signal integrity in high-speed communication

To achieve high data communication speeds along with high circuit density, data transfer rates must increase on the traces, interconnects, wires, or cables that are placed adjacent to each other. The space congestion higher bit rate introduces crosstalk distortion in communication signals.

Crosstalk is a serious issue concerning signal integrity. For error-free, high signal-to-noise ratio communication, signal transmission, or reception, crosstalk needs to be diagnosed, measured, and mitigated. Crosstalk analysis is one of the methods developed to characterize and measure crosstalk effects in electronic circuits. We will discuss crosstalk and crosstalk analysis in this article. 

Crosstalk 

Crosstalk is the phenomenon in which the signal transmitted through one path creates undesired effects on its neighboring path. Depending on the system, the path can be traces, interconnects, wires, or cables. The path carrying the signal (which creates crosstalk) is called the aggressor and the adjacent path (which suffers from crosstalk) is called the victim. The effects of crosstalk are significant in high-speed printed circuit boards, integrated circuits, and communication systems and can even lead to system failures. 

How Does Crosstalk Occur?

As signals transmit over traces, wires, or cables, they radiate electromagnetic energy. The energy interferes with the signals in the neighboring pairs in the same bundle of wires or cables. If the signal transmission or reception over a cable bundle is in the same frequency, the original signal gets mixed up with crosstalk-induced signals. As the distance between the neighboring wire or cable pairs decreases, it increases the crosstalk value on the original data signal. For the smallest distance between the cables, crosstalk reaches the maximum value.

As the data traffic increases, crosstalk interference and its effects on the signal increase.  High-frequency signal transmission is more vulnerable to a higher amount of self radiation, and thereby more crosstalk. Crosstalk changes the shape of data signals and decreases the SNR of the original signal. Crosstalk reduces the data transmission rate and thus slows down the network. It can even lead to sudden shutdowns of the network in an instant, which may require a restart. 

Crosstalk Effects

The signal flowing through a wire or cable produces a magnetic field around it. When several wires are placed close to each other, the magnetic fields of each wire or cable interact with each other. This causes cross-coupling of electromagnetic energy between the signals and produces crosstalk.

The coupling mechanisms that generate crosstalk can be either mutual inductance or mutual capacitance. Crosstalk is unintentional and undesired in electronic systems expecting high signal integrity. Crosstalk effects typically result in functional failures, where they either change the signal amplitude or timing.

The two types of crosstalk effects can be summarized as:

  • Crosstalk glitch: A crosstalk glitch introduces noises into the steady victim signal. The reason for the crosstalk glitch is coupling due to switching activities in the adjacent aggressors. 

  • Crosstalk delay: Switching activities cause coupling between aggressors and victims and lead to the time delay in particular victim signals.

Crosstalk Analysis

It is important to diagnose, measure, and mitigate crosstalk to maintain signal integrity in electronic systems. Conventionally, electronic and communication circuits under test are operated under special modes for measuring crosstalk in victim signals. The special modes are established by selectively disabling certain channels and enabling some other channels. The accuracy of the diagnosis and quantification depends on the optimal modes constructed for crosstalk measurements.

The characterization and troubleshooting of crosstalk by conventional methods is challenging. Crosstalk analysis is one computational method of diagnosis and quantification that helps in identifying the crosstalk present on victims from aggressors. Crosstalk analysis is best suited for giving predictions of crosstalk in complicated, high-density electronic circuits and high-speed communication systems.

Crosstalk analysis can handle several aggressors and victims in a system at a time. Crosstalk analysis can determine the relative error or noises introduced by each aggressor on the victim. Crosstalk analysis features the provision of comparing the crosstalk-affected signal and original signal side-by-side. An engineer can directly quantify the volume of improvement that the crosstalk mitigation methods would bring into the communication system by performing crosstalk analysis.

Performing crosstalk analysis provides several design insights, which help the engineer to modify the board for better signal integrity. Cadence offers software tools for crosstalk analysis that can assist in the design of high-speed or high-density electronic circuits. Subscribe to our newsletter for the latest updates. If you’re looking to learn more about how Cadence has the solution for you, talk to our team of experts.