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design very low active low pass filter

Discussion in 'General Electronics Discussion' started by john.agcos, Dec 12, 2013.

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  1. john.agcos

    john.agcos

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    Dec 12, 2013
    i am suffering to design very low frequency like 0.0001hz to 50KHz filter for very low signal.
    i want to design this preamplifier circuit. i have design but it can not amplify lower frequency signal.
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi John
    welcome to the forums :)

    0.0001 is extremely low!!
    the ones I use for seismic recording go down to ~ 0.005
    Im mainly interested in seismic waves of ~ 10 to 100 seconds

    what are you recording/measuring that has a period down to ~ 10,000 seconds ??

    Dave
     
    Last edited: Dec 12, 2013
  3. john.agcos

    john.agcos

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    Dec 12, 2013
    thanks a lot davenn
    i am designing this preamplifier circuit.
    and i am fine if i design for 0.001Hz to 50KHz.

    can u give me that circuit which is you use for 0.005
     
    Last edited: Dec 13, 2013
  4. davenn

    davenn Moderator

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    Sep 5, 2009
    I will see if the guy will release a copy of the circuit
    He likes to keep the info reasonably secure ;)

    Just curious, cuz of my geophysics background.....
    when you say, geophysical sensor, what sort of sensor ?

    I know in years gone bye that both Australian and Greek geophysics guys have done research into large earth currents

    a geophone or other seismometer ? or an EM emission from the earth ?

    for your interest here's a link to my online seismograms

    cheers
    Dave
     
    Last edited: Dec 13, 2013
  5. davenn

    davenn Moderator

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    1,785
    Sep 5, 2009
    here's a freq response for his preamp
    it may be a bit narrow for your needs ?

    [​IMG]


    all you really need is a preamp ( LOW NOISE) that has a 50kHz LPF cutoff
    doing some google searching on 50kHz LPF may well give you some options
    as the above plot is showing that the preamp front end is being band passed rather than just low passed

    cheers
    Dave
     

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    Last edited: Dec 13, 2013
  6. john.agcos

    john.agcos

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    Dec 12, 2013
    thanks davenn

    is that sallenkey active amplifier works at very low frequency?
     
  7. john.agcos

    john.agcos

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    0
    Dec 12, 2013
    hi daven
    can you tell me which kind of amplifier is use for that preamplifier0.005 to 50KHz.

    and can you tell me how to reduce flicker noise?
     
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