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Parameters needed to design a Butterworth filter?

Discussion in 'Electronics Homework Help' started by Shivani tiwari, Sep 8, 2015.

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  1. Shivani tiwari

    Shivani tiwari

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    Sep 8, 2015
    I wanted to design a butterworth bandpass filter for photoplysthemograph signals.I have bandpass and stopband frequency values..I know I need to know the passband and stopband ripple values too...but how can I calculate them when I am not sure about the order of the filter? Can the order of filter be chosen randomly?I am sorry I am new with the filter desgning process :(
     
  2. duke37

    duke37

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    Jan 9, 2011
    This is a difficult one. You must decide what filtering you want and this will decide the type and complexity of the filter.
    If I remember rightly, there should be no ripple with a Butterworth filter.
    I have a book 'Electronic Filter Design' by Arthur B. Williams. I could look up a design depending on your specifications.
    If the bandwidth is large, then a high pass and low pass filter should be used.
    You could simulate a filter with a program such as LTspice.

    P.S. What is a photoplysthermograph?
     
  3. Shivani tiwari

    Shivani tiwari

    11
    0
    Sep 8, 2015
    If I use Butterworth low pas filter for a particular signal..I'll be needing passband freq, stopband freq as well as passband ripples and stopband attenuation in order to calculate the order of the filter.can uu please tell me how to determine the value of passband ripples and stopband attenuation if I have the values of passband and stopbamd frequencies.
     
  4. LvW

    LvW

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    146
    Apr 12, 2014
    Both parameters (passband ripple and stop attenuation) must be specified by YOU!
    These parameters are determined by the specific application - sometimes passband ripple is allowed and sometimes not.
    Some applications specify the stopband with 20 dB attenuation (minimum) and some others require 60 dB.
    Do you know what I mean?
     
    Shivani tiwari likes this.
  5. duke37

    duke37

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    Jan 9, 2011
    There will be no ripple with a Butterworth filter.
    Filters with sharper cut off such as a Chebyshev will have a ripple, the sharper the cut off, the bigger the ripple.

    Please tell us what is required and what the gubbins is.
     
  6. Shivani tiwari

    Shivani tiwari

    11
    0
    Sep 8, 2015
    If I try designing a Butterworth low pas filter (digital) using matlab...to determine the order of filter I'll be needing cutoff frequencies...passband ripple and stopband attenuation..so..I wanted to ask what will be the passband ripple and stopband attenuation value for a signal similar to that shown in image attached.
     

    Attached Files:

  7. duke37

    duke37

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    Jan 9, 2011
    The image tells us nothing as the axes are not labled.

    For the third time, what is the signal from?
    What is the amplitude of the signal?
    Why do you need to filter it?
    What will be done with it after filtering?
     
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