“Designing & Implementation of Digital Filter for removal

of Power Supply Noise”

A SEMINAR REPORT

Submitted by

NAIVEDYA MISHRA(2011H140033H)

M ASHWIN(2011H140038H)

PEEYUSH PASHINE(2011H140033H)

PRAVESH TAMRAKAR(2011H140036H)

M.E. (EMBEDDED SYSTEMS)

BIRLA INSTITUTE OF TECHNOLOGY AND SCINCE PILANI-

HYDERABAD

Abstract :- An ECG is a test which records the rhythm and electrical activity of

the heart of patient.ECG detects problem with the heart rhythm. The machine

which operates for ECG is standardized for power line frequency i.e. 50Hz, but

ideally the exact frequency of operation is not achieved. It is either above or below

the ideal value, in small scale. Whereas interference of noise in useful components

of ECG signal also creates ambiguity.

Digital Filter design problem involves the determination of a set of

filter coefficients to meet a set of design specifications, i.e. type of filter ,and its

parameters. Here we are focusing on power line noise interference to ideal ECG

signal, and designing filter specification to recover back the original useful

components of signal.

TABLE OF CONTENTS Page No.

1) Introduction 1.1 Types of Noise

1.2 How to get a pure ECG signal? 1.3 Tools used

2) Filter Design 2.1 Idea behind the filter design

2.2 How to choose right filter?

2.3 Filter specifications

3) Matlab Simulations 3.1 Ideal ECG signal

3.2 Ideal ECG signal Filtering

3.3 MIT-BIH ECG signal

3.4 Filtering of MIT-BIH ECG signal

3.5 FFT of filtered signal

3.6 comparison of FFTs

3.6 Inferences

4) Verilog Simulations

4.1

Introduction :-

ECG signals are simple tool,with big advantages.It is widely used in

Medical science.The disease related to heart are indicated primarily by ECG

signals. Interpretation of the electrical activity of the heart over a period of time, as

detected by electrodes attached to the outer surface of the skin and recorded by a

device external to the body.The ECG are performed for diagnostics and research

purpose on human hearts.

In actual ECG signal differs from the standard database of ECG signal.This

causes disturbance (interference of noise) in applied signal,further response of the

ECG signal might get obstractions,which are highly undesirable.There are noises

which can affect the proper operation, the source of noise can be different.

Thus to remove interfered noise from the ECG signal,gives the standard

ECG signal,with useful components after taking the response from heart.

1.1 Types of Noises:-

Generally, the recorded ECG signal is often contaminated by noise and

artifacts that can be within the frequency band of interest and manifest with

similar characteristics as the ECG signal itself. In order to extract useful

information from the noisy ECG signals.

There are several types of noise which maninly effect the ECG

operation.

a) Power line noise:- The standard alternating frequency is about 50Hz,in US

standard power line frequency is 60Hz,so we concentrate upon 60Hz,the

signal and devices are designed for standard powerline frequency for optimum

performance, but random noise with frequency about 1-5 hz are overlapped

with the main line, in turn pure frequency of operation is not achieved.

b) Baseline wandor noise:- Baseline wander is a low-frequency component

present in the ECG system. This is due to offset voltages in the electrodes,

respiration, and body movement. This can cause problems in the analysis of

the ECG waveform. The offset also limits the maximum value of gain which

can be obtained from the instrumentation amplifier. At higher gains, the signal

can saturate.

c) Muscular noise :- Muscular noise arises due to movement in muscle of

patient. When skeletal muscles undergo tremors, the ECG is bombarded with

seemingly random activity. This noise can be controlled via precautions.

1.2How to get a pure ECG signal?

Main focus is always to remove power line noise ,as it is the measure

source of noisy effect on ECG signals.The main interest lies in the band

frequency of signal, which is interfered with noise.Generally the power line

frequency is either added or substracted with low frequency noise

components ranging from “+ -1-+-5” Hz.

The designing of filter thus depends upon this factor. The cofficents of

importance are

a)what is the passband frequency?

b)what is the ripple present in frequency?

c)what is the type of filter?

d)functioning of filter?

e)transiton sharpness,ripple in stopband?

This all parameters are decided when signal properties of interest are

deeply observed.

1.2 Tools used :-

Designing of filter can be done by deciding the parameters,writing the

code, and checking the simulation in popular digital signal processing tool

MATLAB.

Furthur hardware implementation is done on FPGA ,using the tool iSIM

of MATLAB, conversion to VERILOG has been performed.The generated

VERILOG code is verified through test bench which is written on XILINX

13.1. and considered FPGA architecture is SPARTAN 3E.

2 Filter design

2.1 Idea behind the filter design:-

It can be understood by the flow chart.

2.2 How to choose right filter ?

Based upon the above flow chart, a proper filter can be decided,here several

features are more added on filters,which helped to get desired response,after

going through several filters.

a)IIR VS FIR :- IIR filters are suited for high speeded design, as they have

less no of cofficeients, which gives more flexibility towards implementing on

hardware,since it has less no. of multiply to cover.where as in FIR it requires

more no. of cofficents to perform the same filtering operation compared to

IIR,which leads larger memory requirement, and also a bigger order of filter

compared to IIR filter.when phase condition can be comprmised,it is better to

use IIR filters.also IIR filters can be designed to have a frequency response

that is discrete version of the frequency response of an analog filter.

b) Chebyshev over others :- although chebyshev filter has ripple in

passband(chebyshev 1) and ripple in stopband (inverse chebyshev/chebyshev

2) they have a sharper attenuation after transition band, compared to

butterworth filter and others.butterworth has an advantage of maximally flat

response in passband .If equiripple response of chebyshev can be

compromised then, it is always better to use chbyshev filters over

others.However elliptic filters give better response than chebyshev,but they

require more no of components.hence we go in tred off.

c)chebyshev 1 over chebyshev 2:- The only difference between chebyshev 1

and chebyshev 2 is ,formar has ripples in passband and later has in

stopband.we have seen the chebyshev 1,combined with IIR filter feature

having better performance than the later one.It has sharpe transition and

attenuation.

2.3 Filter Specifications The following image is created by the fdatool,in MATLAB,this GUI shows

filter response of IIR CHEBYSHEV 1 filter.