A band pass filter which doesn't alter my signal

Discussion in 'The Projects Forum' started by nyasha, Nov 2, 2011.

  1. nyasha

    Thread Starter Active Member

    Mar 23, 2009
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    Okay, so l want to design a band pass filter that doesn't attenuate my signal. Is that possible. I want it to allow frequencies between 1khz and 3khz. I have tried to make one, but it ends up with my signal getting attenuation. Any hints on how l can achieve this ?
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Do you mean an active filter design?
     
  3. justtrying

    Active Member

    Mar 9, 2011
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  4. SgtWookie

    Expert

    Jul 17, 2007
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    If you're going to make a passive filter, you'll have some loss. The better you tune the filter, the less loss you'll have.

    Here's a pretty decent one I threw together; it's a modification of a Cauer.

    See the attached for a plot of the transmission (S21) and reflection (S11).
    At 1kHz, the signal is about -0.443dB, at the center, around -0.223db, and @3kHz, -0.288dB

    [​IMG]
     
    justtrying and nyasha like this.
  5. joeyd999

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    Jun 6, 2011
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    nyasha likes this.
  6. nyasha

    Thread Starter Active Member

    Mar 23, 2009
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    I think the tank filter which shorts out signals within the frequencies l do not like is what l will try to design given the parts l have which include only one 10mH inductor. I will post my multism circuit for you guys to critique. Thanks very much for the hints.
     
  7. crutschow

    Expert

    Mar 14, 2008
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    An active filter is a good fit for this application and requires only resistors and capacitors. You can easily design one using TI's free software.
     
  8. SgtWookie

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    You missed the part about the opamp. ;)
     
  9. justtrying

    Active Member

    Mar 9, 2011
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    well then, active is the way to go, does not sound like you would need a fourth order one (although it is impressive) :)
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    You could always put an adjustable amplifier in front of or after your filter. This is called buffering and prevents one filter from loading a previous or subsequent stage. Most engineers, realizing the benefits of buffering, do it without giving the insertion loss a second thought.
     
  11. crutschow

    Expert

    Mar 14, 2008
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    True enough. I should have said the only passive components required are resistors and capacitors. Of course it's hard to have an "active" filter circuit without some sort of amplifier.:rolleyes:
     
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