dfilt.df1

Discrete-time, direct-form I filter

Syntax

Hd = dfilt.df1(b,a)
Hd = dfilt.df1


Description

Hd = dfilt.df1(b,a) returns a discrete-time, direct-form I filter, Hd, with numerator coefficients b and denominator coefficients a. The filter states for this object are stored in a filtstates object.

Hd = dfilt.df1 returns a default, discrete-time, direct-form I 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.

Image of direct form one filter diagram

To display the filter states, use this code to access the filtstates object.

Hs = Hd.states       % Where Hd is the dfilt.df1 object and
double (Hs)          % Hs is the filtstates object

The vector is

$$\left[\begin{array}{c}zb(1)\\ zb(2)\\ \cdots \\ zb(n)\\ za(1)\\ za(2)\\ \cdots \\ za(n)\end{array}\right]$$

Examples

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

[b,a] = butter(4,.5);  
Hd = dfilt.df1(b,a)

Version History

Introduced before R2006a