What LC circuit produces this response?

Discussion in 'General Electronics Chat' started by tx.x, Jun 27, 2017.

  1. tx.x

    Thread Starter New Member

    Jun 27, 2017
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    I am trying to come up with an equivalent circuit for a structure that I'm working on. The response is shown below:

    [​IMG]

    The modelling of the structure hasn't incorporated any loss, therefore the real part of the impedance is 0. I am not a circuit expert, and would like some pointers on what kind of circuits would be capable in producing a response like this.

    I was pointed to this circuit:

    [​IMG]

    However, it generates a different response as shown below:

    upload_2017-6-27_0-34-44.png

    Where the imaginary impedance first increases near resonance, then decreases.

    I tried a few simple LC circuit configurations but wasn't able to find one that matches my expectation, I was wondering if anyone could give me some pointers.

    Thanks!
     
  2. crutschow

    Expert

    Mar 14, 2008
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    How about a simple LC series circuit.
    The impedance of that reduces near resonance and then increases after resonance.
     
  3. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
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    Try replacing C2 in the crystal equivalent circuit with a 3nH inductor.
     
  4. tx.x

    Thread Starter New Member

    Jun 27, 2017
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    This is the first thing I tried and I don't think it behaves as what I observed on the graph.
     
  5. tx.x

    Thread Starter New Member

    Jun 27, 2017
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    I have and it didn't seem to work, does it also depend on other factors (frequency, value of L and C, etc.?)
     
  6. tx.x

    Thread Starter New Member

    Jun 27, 2017
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    The response I got is as below
    upload_2017-6-27_10-5-31.png
     
  7. tx.x

    Thread Starter New Member

    Jun 27, 2017
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    Response I got for a series LC circuit:

    upload_2017-6-27_10-8-57.png
     
  8. crutschow

    Expert

    Mar 14, 2008
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    Here's the LTspice simulation of an arbitrary series, ideal LC circuit.
    I drove it with a current source (1Aac) so V(in) is a measure of the circuit impedance.
    As you can see, below resonance, the impedance steadily drops until going to a very low value at resonance, and then steadily rises above resonance.

    upload_2017-6-27_9-24-41.png
     
  9. tx.x

    Thread Starter New Member

    Jun 27, 2017
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    But the *impedance* response that I am expecting is

    [​IMG]

    Y axis is impedance, not current.
     
  10. BR-549

    AAC Fanatic!

    Sep 22, 2013
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    Maybe some negative resistance will give you a range of Z at resonance.
     
  11. tx.x

    Thread Starter New Member

    Jun 27, 2017
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    T
    The Z I'm plotting is imaginary.
     
  12. AlbertHall

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    Why do you want this response?
     
  13. tx.x

    Thread Starter New Member

    Jun 27, 2017
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    I'm trying to map the antenna I designed to a circuit model so I could have a systematic way of analyzing it....
     
  14. crutschow

    Expert

    Mar 14, 2008
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    Here's the plot in of my simulation in ohms.
    The difference is that yours has the ohms scale magnitude reversed in direction from mine.

    upload_2017-6-27_10-11-8.png
     
    Last edited: Jun 27, 2017
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