Quantifying Differential Phase Skew Caused by Reinforcement Fiber Bundle Periodicity
Reinforcement fiber bundle periodicity causes localized dielectric constant variation, driving phase skew that requires spread glass or rotated routing to control.
Differential Pairs
Impedance Balance
Transmission line configurations consist of two complementary conductors carrying signals of equal magnitude and opposite polarity. In high-speed digital design, differential pairs minimize the effects of external electromagnetic interference by ensuring that noise is coupled equally onto both lines. This balance preserves the signal.
The receiver subtracts the incoming voltages to recover the original data while cancelling out common-mode noise. Such routing maintains signal integrity over longer distances than single-ended traces.
Geometric Constraint
Spacing and width parameters govern the characteristic impedance of the coupled lines. Designers must route differential pairs with consistent gap distances to avoid impedance discontinuities that cause signal reflections. Tight coupling between the traces reduces the radiated emissions of the circuit.
Variations in the dielectric thickness or copper width alter the differential impedance and lead to timing errors known as skew.
Physical Routing
Serpentine traces or length-matching structures ensure that both signals arrive at the destination simultaneously. If one conductor is longer than the other, the phase shift converts some of the differential signal into a common-mode signal. This conversion increases electromagnetic radiation and degrades the eye diagram at high frequencies.
Every bend in the path must be compensated to preserve the timing relationship between the two conductors within the differential pairs.