Impedance mismatches occur when the characteristic impedance of a transmission line does not match the impedance of the source or load. This mismatch causes a portion of the signal energy to be reflected back towards the source, creating signal distortions. Reflections can manifest as ringing, overshoot, or undershoot, all of which can be misinterpreted by receiving components.
Crosstalk is the unwanted coupling of signals between adjacent conductors. In high-speed designs, closely spaced traces can act as antennas, picking up or radiating electromagnetic energy. This can lead to interference, where a signal on one trace corrupts the signal on another. Careful layout, shielding, and proper termination techniques are employed to mitigate crosstalk.
Electromagnetic interference (EMI) is a broader category of unwanted electromagnetic energy that can disrupt electronic circuits. This can originate from external sources like radio transmitters or internal sources like switching power supplies. Proper grounding, shielding, and filtering are essential for minimizing EMI's impact on signal integrity.
Signal attenuation refers to the loss of signal amplitude as it propagates. This can be caused by the resistance of the transmission medium, dielectric losses, and radiation. For long traces or high-frequency signals, attenuation can significantly reduce the signal strength, making it difficult for the receiver to accurately interpret the data.
Maintaining good signal integrity requires a combination of careful circuit design, appropriate component selection, and meticulous PCB layout practices. This includes controlled impedance routing, proper termination strategies, effective grounding, and minimizing signal path lengths. The goal is to ensure that the signal arrives at its destination with sufficient amplitude and minimal distortion to be correctly interpreted by the receiving circuitry.