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Frequency Response

Discussion in 'Electronics Homework Help' started by vick5821, Dec 18, 2012.

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  1. vick5821

    vick5821

    700
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    Jan 22, 2012
    Dear All,

    [​IMG]

    For this question, seriously, I do not have the correct answer for it. I am not sure if the given answer is correct or not.

    This is what I have done so far :
    [​IMG]

    I am so so so confuse that how can I determine the cutoff frequency, corner frequency or center frequency ? Are all these the same things ?

    Thank you. :)
     
  2. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    See the attachment which confirms that the book answer is correct for the cutoff frequency of 25K radians. Note that cutoff and corner frequency are the same thing for a low pass or a high pass filter. However the center frequency is something quite different. I usually prefer to work directly with the node equation rather than model a voltage divider.

    The cutoff frequency is the point where the transfer function is 3dB down from where it is in the passband. In this case the passband is where Vo is -6dB from Vi so the cutoff is where the transfer function is at -9dB. But you will not want to be calculating in dB. Look for the cutoff frequency at the half-power point in reference to the passband response.

    When looking at your work I did not see the point where you convert the complex function to a scalar magnitude. In order to find the cutoff frequency one must look for the ratio of scalar magnitudes that equals the reciprocal of the square root of 2, i.e., half power.
     

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  3. vick5821

    vick5821

    700
    0
    Jan 22, 2012
    You mean I square both side ? What is the correct way of doing ? Ya, I know thee cutoff frequency equals the reciprocal of the square root of 2
     
  4. Laplace

    Laplace

    1,252
    184
    Apr 4, 2010
    You may need to review the basics of complex arithmetic, particularly the process of finding the magnitude of a complex number using multiplication with the complex conjugate of the number.
     
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