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non linear phase Butterworth- Can be an anti alias filter?

Ras Sharif50
Genius 3455 points

dear All,

i have seen in several literature that the butterworth filter used for anti aliasing filter.

usually, signals have several frequency component.

butterworth has a non linear phase response.

so the signal disturbed when passing the filter.

so how can be used as an anti aliasing filter?

regards, Rasool

  • 0
    TI__Genius 17777 points
    Rasool,

    Bessel is a very commonly used active filter type. It has linear phase response up to the cutoff frequency. It is common to set the cutoff frequency one decade above the maximum frequency of interest to minimize phase shift effects. If you are not already doing so, I recommend using filter pro or filter designer. Filter designer is free active filter software that allows you to develop different filter designs on the web. Filter pro is an older downloadable filter design program. Below is a reference that discusses different active filter types (advantages and disadvantages). Also below is a link to filter designer.

    focus.ti.com/.../sloa088.pdf

    www.ti.com/.../webench-filters.html
  • 0
    TI__Guru* 93105 points

    Hi Rasool,

    Any filter will introduce phase delay and some filter reponses are more, or less, phase non-linear with frequency than others. The Bessel and Linear Phase filters produce a more linear phase vs frequency response than the Butterworth and Chebyshev responses. However, that latter responses can provide a flatter amplitude response in the pass-band which may be more important than the phase distortion characteristics. Commonly, a Butterworth response is selected for the anti-alias filter because it offers the flatest amplitude vs frequency respnse of any of the common filter types.

    I found a good EDN article online about designing anti-alias filters for ADCs. The author discusses the phase concerns in the last paragraph under the section labeled Ideal and Practical Filters. 

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Thomas Kuehl
    Genius 3455 points

    i found that there is a trade off between flatness and phase delay.
    and it completely depends on the application to select which type is suitable as anti alias filter.
    in some applications the signal may distorted using butterworth filter.


    regards,

  • 0 in reply to Ras Sharif50
    TI__Guru* 93105 points

    Hi Ras,

    Understood, there certainly are other responses such as the Bessel and Equiripple that will provide much more linear phase characteristics than the Butterworth. Unfortunately, they do not provide the maximally flat passband response of the Butterworth. It becomes a matter of compromise and what provides the best overall performance in the application.

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0 in reply to Art Kay
    Intellectual 650 points

    Hi,

    The link to sloa088.pdf is broken. Could you please correct the link. Thanks.

  • 0 in reply to Viking
    TI__Guru* 93105 points

    Hello Viking,

    It looks like there are a number of links that aren't working this morning. From what I can gather it appears that sloa088.pfd is chapter 16, of TI's Op amps for Everyone book, which covers active filters.

    Every TI link I tried didn't get me to it; however, I did find a link at an MIT website that has the book in pdf form:

    Certainly, someone internally must be working on the link issue.

    Regards, Thomas

    Precision Amplifiers Applications Engineering