Change cutoff frequency for lowpass analog filter
[bt,at] = lp2lp(b,a,Wo)
[At,Bt,Ct,Dt] = lp2lp(A,B,C,D,Wo)
lp2lp transforms an
analog lowpass filter prototype with a cutoff angular frequency of
1 rad/s into a lowpass filter with any specified
cutoff angular frequency. The transformation is one step in the digital
filter design process for the
lp2lp function can perform the transformation
on two different linear system representations: transfer function
form and state-space form. In both cases, the input system must be
an analog filter prototype.
[bt,at] = lp2lp(b,a,Wo) transforms an analog
lowpass filter prototype given by polynomial coefficients into a lowpass
filter with cutoff angular frequency
Wo. Row vectors
the coefficients of the numerator and denominator of the prototype
in descending powers of s.
Wo specifies the cutoff angular frequency in units of rad/s.
lp2lp returns the frequency transformed filter in row vectors
[At,Bt,Ct,Dt] = lp2lp(A,B,C,D,Wo) converts the continuous-time
state-space lowpass filter prototype in matrices
into a lowpass filter with cutoff angular frequency
the lowpass filter in matrices
lp2lp is a highly accurate state-space formulation
of the classic analog filter frequency transformation. If a lowpass
filter is to have cutoff angular frequency ω0,
the standard s-domain transformation is
The state-space version of this transformation is
At = Wo*A; Bt = Wo*B; Ct = C; Dt = D;
lp2bp for a derivation of the bandpass
version of this transformation.