Determining LowPass, BandPass, and HighPass filters

Discussion in 'Analog & Mixed-Signal Design' started by iONic, Dec 4, 2018.

  1. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    OK, let me guess, the middle filter is a BandPass.
    Now, which is the HighPass and LowPass filters?

    HPBPLP.PNG
     
  2. MrChips

    Moderator

    Oct 2, 2009
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  3. LvW

    Well-Known Member

    Jun 13, 2013
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    Your "guess" is correct - however, it is not necessary to "guess" because you can see (via optical inspection) why it is a bandpass:
    * Because of the capacitors C1 (C4, C6) no DC component can enter the amplifier; very low frequencies can produce a negligible output only:
    * The series connection of both capacitors (each filter) causes full negative feedback for very high frequencies (resulting in zero gain for inverting configurations);

    Hence, only frequencies in the "middle" range (between the mentioned extremas) will cause an output with a maximum that can be computed or measured.
     
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  4. iONic

    Thread Starter AAC Fanatic!

    Nov 16, 2007
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    OK, all three are band-Pass filters. Let me rephrase my question. Which one is "passing" high freq, & which one is "passing" low freq. audio....given the input is the audio spectrum.
     
  5. danadak

    Well-Known Member

    Mar 10, 2018
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    Since all 3 share same R values, good guess is that higher cap values =
    lower frequency.

    Regards, Dana.
     
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