SPICE simulation of the group delay of a second order FIR filter. A second order FIR filter is implemented with a Laplace component. Its tranfer function is H(z)= 1+ 0.75*z^-1+0.15*z^-2. When each frequency in the input signal has a different phase shift, the phase response isn’t linear, then the output signal will be distorted. The shift change with frequency can be represented with the concept of group delay, defined as the derivative of phase shift with respect to frequency. Actually it represents the slope of the phase response. The amplitudes of the three pulses are the same as the filter coefficients, 1, 0.75, 0.15, where the transfer function is multiplied by three delays to fix causal problems i.e. delayed by 3*s*T.