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

[z(1)z(2)z(n)]

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)
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