WINDOWING TECHNIQUES OF FIR FILTER DESIGN

Presented by,Soumil Agarwal (J001), Aayush Maheshwari (J015), Rohan Nagpal (J019), Vibhuti

Maheshwari (J036)

WHAT IS A WINDOWING?

A window is a finite length sequence.

Windowing is a process of forming a finite length sequence from an infinite length sequence by multiplying an infinite length sequence with a window.

GENERAL PROCEDURE FOR WINDOWING1. Choose the desired frequency response of the filter Hd (ω)

2. Take inverse fourier transform of Hd (ω) to obtain the desired impulse response hd (n)

3. Choose a window sequence W(n) and multiply hd (n) by Hd (n) to convert IIR to FIR h(n)=W(n) x hd (n)

4. Taking ZT of h(n) we obtain a transfer function H(z)

5. Realize the filter using suitable filter method

TYPES OF WINDOWS

WINDOWS

Rectangular Hanning Hamming Blackman Bartlett

Depending on the stop band attenuation we will select a window. Stop band attenuation (As) are the lower limits of attenuation.For example, if As is 40 dB, we will choose Hanning Window

WINDOW EQUATIONS

EXAMPLE

STEP 1- CHOOSE THE DESIRED FREQUENCY

STEP 2 – TO FIND Hd (n)

STEP 3 – CONVERSION OF FINITE TO INFINITE SERIES

STEP 4– TO FIND H(z)

STEP 5 - LINEAR PHASE REALISATION

ADVANTAGES AND DISADVANTAGES Simple – involves minimum computation Maximum ripple amplitude in filter response is fixed regardless of

how large the filter order is

Lack of flexibility When the expression for the desired filter response Hd(e^jw) is

complicated or cannot be put into a closed form mathematical expression, evaluation of Hd(n) becomes difficult.

THANK YOU