RLC i dont understand

Discussion in 'General Electronics Chat' started by michael1978, Feb 6, 2018.

  1. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    Hello to everbody can you help me how come C6 to be 10p and c5 13.5 and and l1 to be 190n and L6 240n
    i start with 100Meghz, with one circuits 50/XL or 50/XC now become three different thanks
    i take it from this tutorial

    rlc.gif
     
    Last edited: Feb 6, 2018
  2. WBahn

    Moderator

    Mar 31, 2012
    23,972
    7,424
    How can we possibly tell you why particular components are particular values unless you tell us what the point of the circuit is to begin with, what the goal is, and what parameters you have control over and which ones are fixed?
     
  3. wayneh

    Expert

    Sep 9, 2010
    16,011
    6,101
    The components are those values because the person that drew the schematic chose those values. Without knowing what the designer was trying to do, it's impossible to guess the "why". I would assume the values were chosen to provide a tuned oscillator. If this was all done in simulation, it's probably useless because the components and the PCB itself will have real inductances and such that the model does not account for.
     
  4. MrAl

    AAC Fanatic!

    Jun 17, 2014
    5,897
    1,255
    Hi,

    Just for fun I'll take a guess...

    "Transform the filter into a highpass, lowpass, and bandpass".
    possibly with some other criteria also such as input/output impedances.

    This could be checked out by analyzing all three circuits and see what they have in common.
    Just a guess so this could be true or totally false :)
     
  5. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    i put the tutorial
     
  6. WBahn

    Moderator

    Mar 31, 2012
    23,972
    7,424
    Others can download and wade through a 1.2 MB tutorial. I don't have the bandwidth.
     
  7. MrAl

    AAC Fanatic!

    Jun 17, 2014
    5,897
    1,255

    Hi,

    Ok i see you added the tutorial, but perhaps you can explain what you want to know in your own words and why you want to know that.
     
  8. kubeek

    Expert

    Sep 20, 2005
    5,484
    1,053
    And did you actually read the text in that tutorial, not just the pretty picutres?
     
  9. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    -------
    this
    It is very interesting to check the effects of this modifications on the
    filter response in Fig.7
    The response show that while the filter with
    series inductor and capacitor has a symmetrical
    response (blue trace), the two inductor filters has
    steeper response at higher frequencies (red
    trace), this network is normally referred as low
    pass coupling
    . The two capacitor filter has
    steeper response at low frequencies (green
    trace), this type of coupling is referred as high
    pass coupling
    .
    Fig. 7
    Note that in the two coupling capacitor filter, the
    value of resonant capacitor C5 has been
    decreased in order to compensate the frequency
    shift caused by the two coupling capacitors, in
    the two inductor filter inductance L1 has been
    increased to compensate for the frequency shift
    caused by the two inductors.
     
  10. WBahn

    Moderator

    Mar 31, 2012
    23,972
    7,424
    That's what you consider "in your own words" or telling us what you want to know?

    Seems more to me like a direct copy/paste from the tutorial.
     
  11. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    yes that is true, i never work with electronics filter design
     
  12. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    i read but they don come those value til i read twoo circuit was good i understand, but now with three circuit i dont know where they come those new value
     
  13. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    those
    how come C6 to be 10p and c5 13.5 and and l1 to be 190n and L6 240n
     
  14. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    yes i read, first circuit was easy , second circuit was easy, third i dont know
    how come C6 to be 10p and c5 13.5 and and l1 to be 190n and L6 240n
     
  15. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    i want to know, how come C6 to be 10p and c5 13.5 and and l1 to be 190n and L6 240n
     
  16. MrAl

    AAC Fanatic!

    Jun 17, 2014
    5,897
    1,255
    Hello again,

    Well the goal of any filter is to meet the design requirements which are usually at least:
    1. Resonant peak at some particular frequency Fo or Fc (many kinds of network applications),
    2. Match input and output impedances (networks like this one).
    3. Possibly a certain circuit Q.

    That means to find out what values you need, you have to be able to analyze the circuit first, then figure out how to get the input impedance to match the required spec, the output to meet that required spec, and the resonant peak to match the required frequency spec.
    For this circuit it looks like 50 ohms, 50 ohms, and 100MHz. That's three things you have to accomplish, and the solution will provide you with the required component values. You may have some arbitrary choice too, such as the output capacitor value which you may want to match the input capacitor value. You may also want a certain minimum Q.

    It looks like what they did was design three different circuits to match the input and output impedance (did not check this yet though) and the resonant peak point frequency. They then analyzed the circuit Q indirectly to compare sharpness.
    Note higher Q's require more exact component values and less change in component values over the life of the equipment too.
    In some circuits you can change values also to get a higher Q. I dont know if you can do that with these circuits or not but you could try to determine that.

    So can you analyze this circuit? After that you try to solve simultaneously for component values that meet all the specs.
     
    Last edited: Feb 6, 2018
  17. BobaMosfet

    Distinguished Member

    Jul 1, 2009
    560
    120
    I'll download your tutorial and see if I can help.
     
    Last edited: Feb 6, 2018
  18. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    thnx
     
  19. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
     
  20. michael1978

    Thread Starter Member

    Jun 29, 2014
    303
    1
    Yes this is for higher Q
     
Loading...