Square wave Response of Ideal Filter.
The frequency characteristic of an ideal band pass filter
is shown in the plot below. The gain changes from 0 to 1 at the
lower frequency F1 and from 1 to 0 at the higher frequency F2. The
characteristic can also have a phase delay which changes
linearly from +A to -A over the bandwidth of the filter.
Ideal filters are not acheivable in practice but are used as
a reference to gauge the performance of real filters.
The applet below shows the output from an ideal band pass filter
when the input is a square wave shown in orange.
The Ideal Filter characteristic is shown in magenta
and the input signal spectrum
The spectrum components which pass unattenuated through the
filter and the output in the time domain is shown in red.
Phase changes from +Phase to -Phase where Phase is shown on applet.
Lower and upper frequency are given in units of the fundamental
Some eg parameters are:-
(0.5, 20.5, 0.0p, 1.0) this shows the
output containing spectral components from 1 to 20 and approximating the square wave.
(2.5, 25.5, 0.0p, 1.0) this shows the
output containing spectral components from 3 to 25 and approximating the square wave minus the fundamental.
(16.5, 17.5, 0.0p, 12.0) this shows the
output containing a single spectral component n = 17(17 periods fit in 1 period of the fundamental).
(16.5, 19.5, 0.0p, 6.0) this shows the
output containing 2 spectral components n = 17 and n = 19 and the result is a beating between the 2 frequencies.
(16.5, 21.5, 0.0p, 6.0) this shows the
output containing 3 spectral components n = 17 n = 19 and n = 21 and the result is a beating between the 3 frequencies.
When activated the following gif image show how the applet should appear.
Return to main page
Return to page index
COPYRIGHT © 1996 Cuthbert Nyack.