help please on deriving transfer functon

Discussion in 'Homework Help' started by BuMalak, Oct 19, 2012.

  1. BuMalak

    Thread Starter New Member

    Oct 12, 2012
    17
    0
    hi everyone,:D

    can someone please help me in deriving the transfer function of the following active filter circuit

    [​IMG]

    Note: the capacitors are not the same

    Thank you :)
     
  2. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,281
    326
    Did you read the sticky at the top of the forum?

    http://forum.allaboutcircuits.com/showthread.php?t=3002

    You need to show some effort to solve the problem before anyone will help you.

    If the two capacitors are not the same, then you should label them differently, perhaps C1 and C2.
     
    BuMalak likes this.
  3. BuMalak

    Thread Starter New Member

    Oct 12, 2012
    17
    0
    Ok I will.

    Thank you
     
  4. BuMalak

    Thread Starter New Member

    Oct 12, 2012
    17
    0
    This is what I found:

    (0.01s^2 + 10s ) / 10^-9*s^3 + 0.02s^2 + 20s +1

    Could any one verify please?
     
  5. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,281
    326
    It is not possible to verify if you don't tell us the value of the resistors and capacitors.

    Suppose your result is incorrect; wouldn't you like to know where your mistake is? If you only give a final result but don't show your work, nobody can help you.
     
  6. BuMalak

    Thread Starter New Member

    Oct 12, 2012
    17
    0
    R1=R2=R3=10kohm
    C1=C2=0.1uF
     
  7. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,281
    326
    This is not correct. Your denominator is a 3rd order polynomial, but your circuit only has two capacitors (I assmume the opamp is ideal).

    Have a look here:

    http://sim.okawa-denshi.jp/en/OPtazyuBakeisan.htm

    If you'll show your work, we can see where you went wrong.
     
  8. BuMalak

    Thread Starter New Member

    Oct 12, 2012
    17
    0
    It is difficult for me to write down all my steps here ><
    but, you actually helped me and I figured out my mistake.

    Thank you very much :)
     
  9. blah2222

    Well-Known Member

    May 3, 2010
    554
    33
    Also for next time, a clear way to present your math is to use LaTeX formatting.

    Instead of having everything look like this:

    H(s) = (2s^2 + 3s + 1)/(4s + 2)

    Use LaTeX to get this:

    <br />
H(s) = \frac{2s^{2} + 3s + 1}{4s + 2}<br />

    Here's the link to other functions for LaTeX. Quote this message to see how it works:

    http://www.access2science.com/latex/Functions.html
     
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