dfilt.df2 (Signal Processing Toolbox)

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

Examples

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

[b,a] = butter(4,.5);  
Hd = dfilt.df2(b,a)
Hd = 
     FilterStructure: 'Direct-Form II'
           Numerator: [0.0940 0.3759 0.5639 0.3759 0.0940]
         Denominator: [1 -3.6082e-016 0.4860 3.6545e-017 0.0177]
    PersistentMemory: false

dfilt.df1tsos dfilt.df2sos