Group delay present the derivative of the phase as a function of angular frequency ( df/dw ).

     Example:
     This example illustrate a group delay plots  for mathematical model of active filter .

     The specification of our filter are:

Description of a design	Specification
File Name:          FILTER   Order:                 4   Data type:            Continous   Function:              Low Pass   Approximation:    Chebyshev	Pass band cutoff frequency:                   1.0000K Hz    Stop band cutoff frequency:                   1.5000K Hz    Pass band ripple frequency:                    2.0000 dB    Stop band attenuation:                           25.0000 dB    Gain:                                                          0.0000 dB

 
    Group delay plots are presented in the figure shown below.

Assigned reading:

1.  Shoikova, Е., A Theory of Electronic Circuits, Active Filter Design. Section Three, 3.5 Bessel filter approximation, pp.3-37, 3-46.