high pass active filter

Discussion in 'Homework Help' started by skaterboy, Apr 12, 2010.

  1. skaterboy

    Thread Starter New Member

    Apr 12, 2010
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  2. Audioguru

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    Dec 20, 2007
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    The gain is 1 like a piece of wire at high frequencies because the opamp is a follower.
    Its Rin doesn't matter because it must be fed from a very low impedance like the output of an opamp.
     
  3. skaterboy

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    Apr 12, 2010
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    Thanks alot.
    But do you know how to find V- and V+ ?

    And what is the formula for the Gain? I need to show formulas.
     
  4. Audioguru

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    Dec 20, 2007
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    if it is the dual polarity power supply then select the voltages to match your opamp and to match your desired max output level.

    Don't you know the calculation of gain in a non-inverting opamp circuit?
    It is 1 + (Rf/Rg). This simple circuit has the opamp as a follower without Rf and without Rg so its gain is 1 at high frequencies.
     
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  5. skaterboy

    Thread Starter New Member

    Apr 12, 2010
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    Isn´t R1 = Rg ?

    Am I supposed to take the C1 and C2 out and just short circuit it instead?

    Is there no current flow in R2?
     
    Last edited: Apr 12, 2010
  6. The Electrician

    AAC Fanatic!

    Oct 9, 2007
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    Are you supposed to be able to derive the formula, or just find it?
     
  7. Audioguru

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    The output of the opamp is directly connected to the (-) input so the opamp has a gain of 1 like a piece of wire but its input impedance is very high and its output impedance is very low.
    R1 applies a little positive feedback at the cutoff frequency of the filter so that the response is sharp and is not droopy.
    C2 and R2 make the second RC of the second-order Butterworth filter.
     
  8. skaterboy

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    Apr 12, 2010
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    Sorry i don´t understand those complicated explanations. I need only to know simply how to find the gain...
     
  9. Ron H

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  10. Audioguru

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    The "geek talk" is not complicated. It is the basics.
    I explained why the gain is only 1.
     
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