Meaning
Propagation delay mismatch between different transmission lines or signal paths within a communication link defines the difference in arrival times of simultaneously transmitted signals. The channel skew occurs in multi-channel interfaces like parallel buses and differential pairs. This mismatch can arise from differences in trace lengths or dielectric variations.
In high-speed data transmission, minimizing this difference is necessary to prevent data corruption. Designers must account for this phenomenon during high-frequency board layout to ensure that signals that are launched simultaneously arrive at their destination within the specified receiver window.
Time Alignment
Managing the timing relationship between the clock and data signals requires that all lines have closely matched propagation times. If the difference in propagation delay exceeds the setup or hold time of the receiver, the receiver will sample incorrect data. Hardware designers often use length-matching routing techniques to equalize the physical path lengths on printed circuit boards.
Hardware Source
Physical variations in the board substrate or cable materials are the primary causes of these differential delays. For instance, the glass-weave pattern in printed circuit boards can cause the dielectric constant to vary slightly along parallel traces. These microscopic variations lead to differences in signal velocity, even when the physical traces are of identical length.
System Tolerance
Receiver circuitry often incorporates active de-skewing mechanisms to compensate for small timing mismatches automatically. These circuits use adjustable delay lines to align the incoming signals before they are sampled by the receiver clock. However, when the timing mismatch exceeds the dynamic range of the de-skew circuits, the link cannot operate at its rated speed.
