Group Delay (Approximation)

Formula

Description

Group delay represents the time delay experienced by the envelope of a modulated signal passing through a filter or transmission system. For a first-order system with bandwidth BW, the group delay is approximately 1/(2π×BW). Constant group delay across the passband means all frequency components arrive at the same time, preserving signal shape. Variation in group delay (group delay distortion) causes pulse spreading and intersymbol interference in digital communications. Bessel filters are designed specifically for flat group delay.

Variables

• τg — Group delay (s)
• BW — 3 dB bandwidth of the system (Hz)

Practical Notes

This approximation applies to simple single-pole systems. Higher-order filters have more complex group delay profiles. Butterworth filters have moderate group delay variation, Chebyshev filters have significant variation near the passband edge, and Bessel filters have maximally flat group delay. In high-speed serial links (PCIe, USB3), group delay variation must be minimized to maintain eye diagram quality.