Transfer function help

Discussion in 'Homework Help' started by jstrike21, Jan 21, 2010.

  1. jstrike21

    Thread Starter Member

    Sep 24, 2009
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    I'm struggling with problems 3 and 6 in the attached pdf.
    I haven't attemted 6 but on 3 i have come up with the transfer function
    (jw)/(5*(jw-.0002))

    I think this is wrong, could someone help?
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    It looks wrong. Why not show your working in detail - rather than just giving an answer. It's easier then to pin point where the mistake has arisen.
     
  3. jstrike21

    Thread Starter Member

    Sep 24, 2009
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    I just wrote the equation

    (Vout-Vin)/1000 + Vout/(-1/(s*.0000001))+Vout/250 = 0

    and solved for Vout/Vin
     
  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Your approach is correct so the error is in your re-arranging to solve for Vout/Vin.

    The correct answer in a simpler form could be

    Vout/Vin=1/(5(1+0.0002jω))

    or perhaps

    Vout/Vin=0.2/(1+0.0002jω)

    Your solution does not reduce to either of these.

    It comes close - where you would have for instance

    Vout/Vin=1/(5(1+j0.0002/ω)) - the ω being misplaced as a denominator term in the overall denominator - if you get my drift.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
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    Your starting equation looks reasonable for the s-domain transfer function with one exception. The term Vout/(-1/(s*.0000001)) needs a revisit. There are two errors that jump out at me. One is the sign of 1 should not be negative. I will leave the second error for you to discover.

    HINT: Double check the decimal number you have written.

    hgmjr
     
  6. jstrike21

    Thread Starter Member

    Sep 24, 2009
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    0
    Thanks for the help from both of you! On 7b i need a little help. My book doesn't go over fourier series so I'm not really sure how to find the coefficients from what I read on the internet i think you have to put the equation into an integral of some sort but im not sure what the formula is.
     
  7. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Both functions are the simple addition of two sinusoids of different frequency. The two are almost identical, save for the phase shift of 45° in the second term of the second function V2(t).

    While the two will be different when viewed as time based waveforms, their individual component magnitudes at the two frequencies will be the same when plotted in the frequency domain.
     
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