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active filter design

Discussion in 'General Electronics Discussion' started by sarjan88, Apr 22, 2011.

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  1. sarjan88


    Apr 22, 2011
    Design a circuit using op-amp that will reject the 60kHz power line noise and also reject high signal frequency above 800Khz. The stop-band width around the 60kHz centre frequency is 10kHz. Use a cascade of 1st order high pass and 1st order low pass filter to implement this circuit. The voltage gain at passband frequencies is 10.

    As mentioned in the title, can sum1 tell me this should be a band reject or band pass filter?
    i try to construct a band reject filter but the result seem like not correct.

    here is my circuit using multisim
    here is the result using AC analysis in decibel

    can sum1 help me out of this?
    Last edited: Apr 22, 2011
  2. davenn

    davenn Moderator

    Sep 5, 2009
    welcome to the forums

    60kHz ? power line noise (freq) is 60Hz or 50Hz is some countries

    your images didnt get attached, so cant see your cct

  3. sarjan88


    Apr 22, 2011
    sorry..the image link is edited..based on the question provided to me it mention is 60khz.
    the circuit i design based on formula i found in notes...i need to make a ac analysis and bode plot diagram...
  4. duke37


    Jan 9, 2011
    I do not understand the question, however, It does say use the filters in cascode, I assume that this means in series. Your circuit has the two filters in parallel so that even if one filter rejects some signal, it will be supplied by the other filter. Try your 2 filters in series, adjusting the gain to suit. The final summing amplifier is then not needeed.
  5. sarjan88


    Apr 22, 2011
    if i make it in series isnt it become a band pass filter??i thought this should be a band reject question, one of my friend told me that he think the question is want me to construct a avtive filter which reject 60khz frequency, then the center frequency is 60khz with bandwidth the filter should accept frequency from 0-55khz and 65khz to 800khz..and reject frequency from 55khz to 65khz
    lecturer provide hint is "combine a lowpass and a highbass filter" and the question mention Use a cascade of 1st order high pass and 1st order low pass filter to implement this circuit
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