dfilt.df2

Discrete-time, direct-form II filter

Syntax

Hd = dfilt.df2(b,a)
Hd = dfilt.df2


Description

Hd = dfilt.df2(b,a) returns a discrete-time, direct-form II filter, Hd, with numerator coefficients b and denominator coefficients a.

Hd = dfilt.df2 returns a default, discrete-time, direct-form II filter, Hd, with b=1 and a=1. 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

$$\left[\begin{array}{c}z(1)\\ z(2)\\ ⋮\\ z(n)\end{array}\right]$$

Examples

Create a direct-form II discrete-time filter with coefficients from a fourth-order lowpass Butterworth design:

[b,a] = butter(4,.5);  
Hd = dfilt.df2(b,a)

Version History

Introduced before R2006a