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Implementing IIR/FIR Filters

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Network Diagram<br />

Transfer Function<br />

Gain<br />

Phase<br />

x(n)<br />

Coefficients<br />

z -1<br />

z -1<br />

G( θ)<br />

Hz ( )<br />

α 1– 2z<br />

1 –<br />

z 2 –<br />

( + )<br />

1/2 γz 1 –<br />

– βz 2 –<br />

= --------------------------------------------<br />

+<br />

( 1 – cosθ)<br />

( 1 + cosθc)<br />

( dsinθsinθc) 2 4( cosθ<br />

– cosθc)<br />

2<br />

[ +<br />

] 1/2<br />

= --------------------------------------------------------------------------------------------------<br />

φθ ( )<br />

α<br />

−2α<br />

α<br />

Σ<br />

– 1<br />

π+ tan<br />

2 θ θ ( cos – cos c)<br />

--------------------------------------dsinθsinθc<br />

tan 1 – 2 θ θ ⎧<br />

⎪<br />

⎪<br />

= ⎨<br />

⎪ ( cos – cos c)<br />

⎪ ----------------------------------------<br />

⎩<br />

dsinθsinθc 1<br />

β ⎛--⎞ 1 d 2<br />

⎝2⎠ ⁄ θ – sin c<br />

= ---------------------------------<br />

1+ d ⁄ 2sinθc<br />

γ = ( 1/2 + β)<br />

cosθc<br />

α = ( 1/2 + β+ γ)<br />

⁄ 4<br />

for θ≤θ c<br />

for θ>θ c<br />

Figure 2-13 Direct-Form Implementation of Second Order Highpass <strong>IIR</strong> Filter and<br />

Analytical Formulas Relating Desired Response to Filter Coefficients<br />

2-16 MOTOROLA<br />

2<br />

γ<br />

−β<br />

z -1<br />

z -1<br />

y(n)

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