How to mitigate Crosstalk in PCB

Crosstalk is the unintended interaction between closely spaced high-speed signals in the PCB. It is the main cause of signal integrity problems. It occurs due to near-field / reactive-field electromagnetic coupling between parallel signal traces through mutual inductance and stray/mutual capacitance between two or more conducting traces. 

Due to the increased speed of signals in modern designs, issues like crosstalk arise. Crosstalk is all about electric and magnetic fields. There is always one or more signal (including the return path) that acts as the aggressor (or the noise source) and a victim on which you see the noise. 

The fundamental cause of all crosstalk is a combination of both electric and magnetic fringe fields between the aggressor and victim. If all fields are confined within a very close vicinity between the aggressor signal and its return paths, ensuring minimum field-spread, there will be little or no crosstalk. To simulate the behavior of electric and magnetic fields, circuit elements like capacitors and inductors are used. 

If you want to reduce crosstalk, you must reduce the electric and magnetic field coupling between the aggressor and victim. There are several ways to minimize this electric and magnetic field coupling: 

1. Placing traces close to the reference plane.  
2. Increase the dielectric constant to reduce fringing fields and thus, coupling.  
3. Increase spaces between the traces by using the 3W (trace width) rule to reduce crosstalk by approximately 70%. This is most important for signals on the same layer, which run in parallel for long distances.  
4. Match line terminations to reduce reflection, and in turn, crosstalk. Configure the board so that signals on adjacent layers will cross each other perpendicularly rather than run parallel to one another.  
5. Isolate high-frequency signals such as clocks from other high-frequency traces by using shielding techniques. 

Share any other design rules or best practices you follow in your designs to mitigate crosstalk.