dfilt.df2sos

Discrete-time, second-order section, direct-form II filter

Syntax

Hd = dfilt.df2sos(s)
Hd = dfilt.df2sos(b1,a1,b2,a2,...)
Hd = dfilt.df2sos(...,g)
Hd = dfilt.df2sos


Description

Hd = dfilt.df2sos(s) returns a discrete-time, second-order section, direct-form II filter, Hd, with coefficients given in the s matrix.

Hd = dfilt.df2sos(b1,a1,b2,a2,...) returns a discrete-time, second-order section, direct-form II object, Hd, with coefficients for the first section given in the b1 and a1 vectors, for the second section given in the b2 and a2 vectors, etc.

Hd = dfilt.df2sos(...,g) includes a gain vector g. The elements of g are the gains for each section. The maximum length of g is the number of sections plus one. If g is not specified, all gains default to one.

Hd = dfilt.df2sos returns a default, discrete-time, second-order section, direct-form II filter, Hd. This filter passes the input through to the output unchanged.

Note

The leading coefficient of the denominator a(1) cannot be 0.

The resulting filter states column vector is

$$\left(\begin{array}{cc}z1(1)& z2(1)\\ z1(2)& z2(2)\end{array}\right)$$

For filters with more than one section, each section is a separate column in the vector.

Examples

Specify a second-order sections, direct-form II discrete-time filter with coefficients from a sixth order, lowpass, elliptical filter using the following code:

[z,p,k] = ellip(6,1,60,.4);   % Obtain filter coefficients
[s,g] = zp2sos(z,p,k);        % Convert to SOS
Hd = dfilt.df2sos(s,g)

Version History

Introduced before R2006a