The applet below shows the impulse response of a 2nd order Butterworth filter in red and the impulse response of a sampled version of the filter in magenta obtained by using the Step invariant approximation. The 2 responses are "identical" for small sampling times but some differences develop as the sampling time is increased.

Applet below shows the step response of the filter. In both applets the horizontal scale is from 0 to 10s and the vertical is from -1 to +1 when gains are 1. The analog and sampled step response are "identical" for all sampling times.

COPYRIGHT © 1999 Cuthbert A. Nyack.