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LT Spice response of 6-resonator filter

  1. Sep 14, 2015 #1
    The following circuit is giving me the following response at each resonator, however it's not the correct response. There's supposed to be a time delay for each resonator response, however they're all more or less starting around 0 seconds...when I'm expecting a proper time delay between each one, so there should be a horizontal shift if that makes sense. I think it's to do with an LT Spice setting, or something in the options? Right now that's just the transient response, with a sine wave input, at 730MHz.
    1.jpg

    2.jpg
     

    Attached Files:

  2. jcsd
  3. Sep 14, 2015 #2

    Baluncore

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    Can you please attach your .asc file to a post.
    Then we can easily simulate and probe your circuit without typos.
    Since it is ascii text file you might call it filename.asc.txt
     
  4. Sep 14, 2015 #3
    Thanks. I've included the .asc file in my original post.
     
  5. Sep 14, 2015 #4

    Baluncore

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    It seems to work OK but;
    1. Your use of 2e12 resistors is questionable. 1e6 is a challenge in our environment.
    2. You have no series R in L or C. I would insert Rs = 0.1m into each L or C to reduce Q.
    3. You are driving 50 amp into 50 ohms. That is 2.5kV. I reduced it to 50 milliamp.
     
  6. Sep 14, 2015 #5

    meBigGuy

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    1. All points will start at time 0. just ramp differently.

    2. Did you include the proper source impedance in your source generator. Should your generator be in series with the 50 ohms.
     
  7. Sep 14, 2015 #6
    Thanks for the suggestions.
    meBigGuy: yes I do have a source impedance.
    Baluncore: if I make those changes, would they solve my time delay issue? I'll try them later.
     
  8. Sep 15, 2015 #7

    Baluncore

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    Source is a current into the 50 ohm so it is 50 ohm input.
    The problem then is analysis of DC operating point with inductors in series.
     
  9. Sep 15, 2015 #8

    meBigGuy

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    I see, your source is a current generator. It was chopped off in the diagram.

    I don't understand your transient response. Where is the DC level coming from? You have a DC step in your source?

    Do an AC response and look at the phase. Isn't that what really matters? Or am I completely out of whack?

    I'm seeing significant delay. The whole circuit will start responding at 0. What would stop it?
     
  10. Sep 15, 2015 #9

    Baluncore

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    The rise time of the resonators is the reciprocal of their bandwidth.
    Without series R in the LC it will have very high Q = impossible, = zero bandwidth, = infinite risetime.
    Only the external circuit is taming it.
     
  11. Sep 15, 2015 #10

    Baluncore

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    Attached is a more real version of the model. Restricted to 5 digits and with series R for all inductors.

    filter1.png
     

    Attached Files:

  12. Sep 15, 2015 #11
    Thanks for your input Baluncore. Do you have any further suggestions on how I could get the time delay I'm expecting between the different resonators? I've altered the circuit a bit here and there, including the series resistors you mentioned, but it only changes the response...no delay. I think it might be an LT Spice option but I'm not sure.
     
  13. Sep 15, 2015 #12

    Baluncore

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    I do not know your expectations.
    The resonators have different resonant frequencies and unspecified Q, so you must expect a slight phase shift between elements determined by frequency of analysis and centre frequency of resonators. But the L and C coupling across the top of the circuit will feed some signal forward and reduce phase shifts.
    The attached file.asc has the centre frequencies of the resonators if isolated.
    Where is the design from. What Qs were specified for the resonators?
     

    Attached Files:

  14. Sep 16, 2015 #13
    That's okay, I think I'll just leave it now. My friend and I made the circuit for an assignment, designing a BPF, with simulated component values...I'll see what he has come up with.
     
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