Signal Distortion
The reduction in the transition speed of a digital signal occurs as the pulse propagates through a transmission line or circuit component. This loss of transition speed, termed slew rate degradation, increases the rise and fall times of the signal and rounds off the sharp edges of square waves. The effect can cause timing errors and increased jitter in high-speed digital systems.
Circuit boards must be designed to minimize this distortion to ensure reliable data transmission.
Transmission Impedance
High-frequency losses and parasitic capacitance in the printed circuit board substrate and copper traces attenuate the higher frequency components of the signal. This low-pass filtering action directly causes slew rate degradation as the signal travels along long board traces. Dielectric absorption and skin effect losses are the primary physical mechanisms that reduce the signal’s high-frequency energy.
Board trace geometry and material selection determine the severity of this signal loss. Using lower loss dielectrics and wider trace geometries can mitigate the attenuation of the high-frequency harmonics.
Mitigation Strategy
Active driver configuration and buffer insertion restore the transition speeds of degraded signal waveforms. To counteract slew rate degradation, designers use redrivers or increase the drive strength of the transmitting integrated circuit. These devices refresh the signal transitions before the receiver sampling window opens.
