Signal Distortion
High-frequency transmission impairments characterized by the frequency-dependent attenuation and velocity alteration of electromagnetic waves dictate the layout constraints of high-speed digital circuits. Insertion loss phase shift occurs when the dielectric material absorbs energy and changes the propagation velocity across different frequencies. This distortion alters the timing of digital signals, leading to jitter and closure of the eye diagram.
Designers must account for these variations in gigahertz-range applications.
Dielectric Influence
The magnitude of insertion loss phase shift depends heavily on the dissipation factor and the dielectric constant of the laminate material. Epoxy-glass substrates show significant signal dispersion, which forces high-speed designs to utilize specialized fluoropolymer or hydrocarbon resins. These premium materials provide a flat response across a wide frequency band, ensuring that signal harmonics travel at the same speed.
This coherence prevents rise-time degradation and preserves the integrity of serialized data streams, which is necessary for multi-gigabit backplanes. Engineers calculate these parameters during the initial stackup phase to avoid late-stage layout redesigns.
Testing Methodology
Vector network analyzers measure these phase changes by comparing the output signal against a reference trace of known length. This measurement ensures that the fabricated board meets the timing budgets required by modern serial interfaces.
