04-09-2015, 02:25 PM

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Enhancement of ECG Signal

ECG signal is usually corrupted by 50 Hz power line frequency and their first and

second harmonis. Hum noise is created by poor power supplies, transformers or electro

magnetic interference sourced by a main power supply is characterized by a frequency of

50 Hz and its harmonics. If this noise interfers with a desired audio or biomedical signal

(e.g., electrocardiography [ECG]), the desired signal is not useful for diagnosis purpose.

To eliminate these unwanted signal frequencies, it is desired suitable filtering process. In

most practical applications, elimination of the 50 Hz hum frequency with its second and

third harmonics is sufficient. This filtering process can be achieved by cascading with

digital notch filters having notch frequencies of 50 Hz and 100 Hz respectively. Further it

is needed to eliminate DC drift and muscle noise, which may occur at approximately 40

Hz or more. Hence a bandpass filter with pass band frequency 0.25-40 Hz is desired. The

following figure dipicts the functional block diagram.

Functional Block diagram of cascaded Notch filters

Objectives

(a) Load, display and manipulating of ECG signals

(b) Design notch filters both in FIR and IIR for 50 Hz and 100 Hz respectively.

© Design a band pass filter to eliminate muscle noise.

(d) Plot the spectrum of the designed filters.

(e) Display the corrupted and filtered ECG signals and their spectrum.

Task1: Load an ECG signal. add a 50 Hz, and 100 Hz frequency sinusoidal signals to

this ECG signals. Plot the original ECG signal, corrupted ECG signal and their spectrum.

Task2: Design two notch filters with the following specifications.

Dr. M. Venu Gopala Rao, Professor, Dept. of ECE, KL University, A.P., India.

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Notch Filters:

Frequencies to be suppressed : 50 Hz and 100 Hz.

3 dB bandwidth for each filter : 4 Hz.

Sampling rate : 600 Hz

Type of Notch filter : Second order IIR filter

Design methods : (a) FIR and (b) IIR using Pole zero placement.

Bandpass Filter:

Passband frequency range : 0.25 – 40 Hz.

Passband ripple : 0.5 dB

Sampling rate : 600 Hz

Filter type : Chebyshev fourth order

Design method : Bilinear transformation

Step1: Design a second order FIR notch filter.

Step2: Design a second order pole-zero notch filter.

In both cases choose the gain

0

b

so that

| | ω 1

for

ω 0 . Write the mathematical

equations for both transfer function and its difference equations in each case.

Step3: Plot the spectrums of each notch filters and cascaded filters.

Task3: Design a fourth order digital IIR band pass filter using bi-linear transformation

with Chebyshev approximations. The specifications are given above. Plot the original,

corrupted and filtered ECG signals and their spectrum