Simple Resistor Circuit

Discussion in 'General Electronics Chat' started by mig78, Mar 30, 2006.

  1. mig78

    Thread Starter New Member

    Mar 30, 2006
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    [attachmentid=1328]The attached network is at the input of a digital channel, the output is later routed to a comparator. Can anyone explain why they need to let the signal through [attachmentid=1328]this network. Whats is the application of this circuit?

    Appreciate some feedback

    Thanks

    mig78
     
  2. paultwang

    Well-Known Member

    Mar 8, 2006
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    Looks like a slightly complicated frequency filter to me. You can derive a transfer function, make a Bode plot, and see what it does.




    Please do not upload bmp images as it is very size inefficient.
     
  3. paultwang

    Well-Known Member

    Mar 8, 2006
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    While ignoring R=30, I got this Bode plot using your circuit schematic.
     
  4. mig78

    Thread Starter New Member

    Mar 30, 2006
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    Hi Paul,

    Thanks, it looks like a high pass filter.

    I was in assumptions it was just an attenuator....
     
  5. n9352527

    AAC Fanatic!

    Oct 14, 2005
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    Shouldn't it be low-pass?
     
  6. nanobyte

    Senior Member

    May 26, 2004
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    No. It's definitely a High Pass Filter because a capacitor comes before the resistors in the circuit. High Pass Filters go capacitorsa first then resistors. Low Pass Filters are the opposite way around.
     
  7. Papabravo

    Expert

    Feb 24, 2006
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    Its a cute saying but improperly applied. Is there not a DC path from In to Out? If there is, then it cannot be a highpass circuit! Boom! Done!
     
  8. dbwgwee

    Member

    Mar 30, 2006
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    Great! Pass the lotion!
     
  9. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    It's a low pass filter.

    Here's a redrawn circuit with bode plot.
     
  10. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    The Bode plot is more meaningful if you plot it out past where the zero cuts in.
    The step response is also interesting.
     
  11. mig78

    Thread Starter New Member

    Mar 30, 2006
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    Thanks for your input it looks definitely more like a low pass filter.
    The redrawn circuit makes it look more clearer.
     
  12. mig78

    Thread Starter New Member

    Mar 30, 2006
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    hi Ron,

    I couldn't understand what you mean "plot it past where the zero cuts in"

    Can you spend some time to xplain. Appreciate them.

    By the way how can I figure out what is the bandwidth of this filter up to -3db roll off.
     
  13. Papabravo

    Expert

    Feb 24, 2006
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    Systems, like your filter, have transfer functions. A transfer function maps an input function in the frequency domain to an output function in the frequency domain. Most all the transfer functions you will ever see, besides all the ones you won't, are rational functions.

    What is a rational function you say? It is a quotient of two polynomial functions. The poynomial functions can be of different orders. You may remember that polynomial functions have roots. What happens to a polynomial at a root? It's vale is goes to zero. But wait, there's more.

    If the poynomial in the numerator is zero, the value is called a "ZERO" of the transfer function.
    If the polynomial in the denominator goes to zero, the value is called a "POLE" of the transfer functiion.

    POLES and ZEROS interact to produce the behavior captured in the Bode Plot, which has two parts, MAGNITUDE and PHASE. Don't forget the PHASE when trying to understand things.

    Does this help, or are you now even more confused?
     
  14. mig78

    Thread Starter New Member

    Mar 30, 2006
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    Hello PapaBravo,

    Man....I'm even more confused. Can you address me to a good reference link that you know of that xplains BodePlot and Poles & Zeros. Pls help.

    Thanks.

    By the way can you also let me know how to calculate the cutoff frequency for this filter?

    Appreciate your reply,

    Thanks!
     
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