Notch Filter design aptitude

8/13/2019 Notch Filter design aptitude

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OUTLINE Introduction

Justification of topic

Area of work

Present applications

Literature survey of topic

Problem formulations

Schedule plan of the project

Reference


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INTRODUCTION

In signal processing , a band-stop filteror band-rejection filteris a filter that

passes most frequencies unaltered, but attenuates those in a specific range to very

low levels. It is the opposite of a band-pass filter.

A notch filteris a band-stop filter with a narrow stopband (high Q factor)i.e. it often wants to filter out the undesired signal in the specific

frequency (e.g. noise , interferences of frequencies)

It attenuates highly a particular frequency component in the input signal while

leaving nearby frequencies relatively unattenuated.

In many signal-processing applications, it is desired to remove narrowband or

single-frequency sinusoidal interference while leaving the broadband signal

unchanged.


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GRAPH OF NOTCH FLTER


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AREA OF WORKDesigning of notch filters according to applications and frequencies it

rejects.

Various works has been illustrated in literature survey and problem

formulation.

(1) Fixed notch filters : only diminishes a prescribed frequency. At times, more

than one interfering frequency exists, so the multiple notch filter is required to getrid of more than one prescribed frequency.

(2) Tunable notch filters : are similar to fixed notch filters that have a range of

frequencies that they can be set to and then fixed at that frequency.

(3) Adaptive notch filters (ANFs) : signals which are variable frequency an

depend on events over time, i.e. we dontknow the notch frequencies in advance,then adaptive notch filters (ANFs) are utilized in this kind of situation. They can

automatically adjust their frequency response depending upon circumstances


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LITERATURE SURVEYThe first notch filters came out in amateur radios in the late-1970s and notched

the IF with a fixed notch width.

Survey in the context of designing of notch filters

1) Infinite Impulse Response (IIR) design :. In situations where linearity of phase

is not important, IIR filters are preferred since these require much lower order than

the FIR ones for the same set of magnitude response specifications.

2) Finite Impulse Response (FIR) design :The digital FIR notch filter is always

stable and it provides linear phase response.

Three main classes of designing of linear phase FIR :1.Frequency sampling 2. Windowing method 3.Optimal design


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FIR DESIGN SURVEY1) Frequency sampling : Most straightforward approach to the

linear phase FIR notch filter design. A small number of

transition samples ensures efficient realization and a low order

optimization problem.

2) Windowing method is easy to use and close form expressionsare available for windows coefficients . Several windows are

reported in literature such as hamming, hanning, blackman ,

barlett , kaizer etc.

These windows offer various tradeoffs between 3db transitionbandwidth and stopband attenuations.


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Contd...3) Optimal design : Vidyanathan and Ngueyen in 1987 introduced

filters which are optimal in the least square sense . Objective

functions are defined only as a sum of passband and stopband

errors except approximation error in transition band .

Advantage : design to incorporate wide variety of time domainconstraints in stopband .


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Contd...

Parks-McClellan Iterative design(1972): It yieldsthe best results with some inherent limitations. Equiripple

designs only consider the specified passband and

stopband but transition band consider as dont careregion in the design procedure.

Disadvantage: Numerical solution may fail in transition

region


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Contd...

Tian-Hu yu proposed methods:

1) A notch filter is derived from Lowpass filter by

using the relation

H(w)=2HLP(w)-1


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Contd...provides a change of 180 deg phase change at the notch

frequency Wd.

alternative method is based on complimenting a narrow

passband filter B(w).

H(w)= 1- B(w)

Another method for designing a notch filter was proposed by

M.H Er in 1991 where the symmetry constraint for the

coefficients was relaxed and the design yields non linear phase FIR

filters.


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Contd...Bernstein polynomial has been used to design maximally flat FIR

notch filter. This design procedure gives us an explicit formula for

the weights of frequency response. However, the designed

magnitude response is not exactly zero valued at notch

frequency.(improved FIR notch design by C.C tseng in 2001).


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PROBLEM FORMULATION IN PRESENT APPLICATION

Filtering of power line interference is very meaningful in themeasurement of biomedical events recording, particularly in the

case of recording signals as weak as the ECG. The available filters for

power line interference either need a reference channel or regard

the frequency as fixed 50Hz. Methods of noise reduction havedecisive influence on performance of all electro-cardio-graphic

(ECG) signal processing systems.

problems of power line interference reduction

deals with design and development of digital FIR equiripple filter.The basic ECG has the frequency range from .5Hz to 100Hz.


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Contd...

Linear-phase equiripple filters are desirable because they have the

smallest maximum deviation from the ideal filter when compared to

all other linear-phase FIR filters of the same order

An Equiripple or Remez Exchange (Parks-McClellan) design

technique provides an alternative to windowing by allowing thedesigner to achieve the desired frequency response with the fewest

number of coefficients so its a problem design for

electrocardiogram power interference problem.


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TIME FRAME OF THE PROJECT

SEMESTER VII:

P1- Application study and literature Survey on design of FIR notch filters.

P2- Mathematical Formulation of the filter design selected and outlay of the designin block diagrams on present application.

SEMESTER VIII :

P1- Design module completion of the notch filter and working on the simulation ofthe design in matlab and theoritical comparison with other compatible designs.

P2-Final simulation of the filter design . Comparison of the results and outcomeswith other formulated designs .


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REFRENCES

SUHASH CHANDRA DUTTA ROY, BALBIR KUMAR and SHAIL BALA

JAIN:FIR Notch Filter Design. Electronics and Energetics vol. 14, No. 3, 295-

327 December 2001.

P.P. VAIDYANATHAN and T.Q. NGUYEN: Eigen Filters: a new approach to

leastmsquares FIR filter design & applications including Nyquist filters. IEEE

Trans. Circuits Sys., Vol. CAS-34, pp. 11-23, January 1987

T.W PARKS and J.H. McCLELLAN:A program for the design of linear

phase finite impulse response digital filters. IEEE Trans. Audio Electroacoust.,

Vol. AU-20, pp. 195-199, August 1972.

Digital Signal Processing by Sanjit K. Mitra.


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Notch Filter design aptitude