Help in the conversion of circuit to a T section Bandpass

Discussion in 'Homework Help' started by Muhammad Salleh, Oct 12, 2018.

  1. Muhammad Salleh

    Thread Starter New Member

    Oct 5, 2018
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    Hi Guys,

    I have attached here a filter i acquired from one of my professors. From first glance, I saw that the presence of the inductor and capacitor at the two ends seem to mimic the Tee section bandpass filter. Since I am trying to solve for the bandwidth to be used from the formulas available, i was wondering if what i am doing is in the right direction or if anybody can propose a solution?

    Currently this is what I have...
    upload_2018-10-12_16-2-39.png

    I am not sure if I am able to justify the parallel arrangement of the two 33n inductors with the 8.2n inductor.

    Thanks for any advice and help!!
     
  2. Muhammad Salleh

    Thread Starter New Member

    Oct 5, 2018
    7
    0
    upload_2018-10-12_16-4-14.png

    upload_2018-10-12_16-4-36.png

    Attached here is also the schematic i draw inspiration from which i assume is the basis of the filter. Thank you to whoever took the time out their friday to answer this :)
     
  3. MrAl

    AAC Fanatic!

    Jun 17, 2014
    5,189
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    Hi,

    Just curious, is the output load impedance supposed to be 50 ohms too?
     
  4. Muhammad Salleh

    Thread Starter New Member

    Oct 5, 2018
    7
    0
    Hi sir! Thanks for taking the time to reply! Actually the output goes into an RF switch and the impedance attached is actually 20kohms
     
  5. MrAl

    AAC Fanatic!

    Jun 17, 2014
    5,189
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    Hi,

    Wow, 20k that sounds high.
    Usually we see 50 in, 50 out.
     
  6. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,580
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    What is your ultimate goal here? Are you required to find the cutoff frequencies (f1 and f2) of the filter you got from your professor?

    You could proceed in a couple of ways. You could just derive the transfer function of the given filter and from that you could calculate f1 and f2 as the frequencies where the filter gain is .707 times the midband gain (or whatever else is your criterion for the cutoff frequencies). This method would not involve trying to convert the given filter into a T section filter.

    Or you could try to convert the transfer function into the equivalent series and shunt arms of a T network, and then determine f1 and f2 from the formulas given for the theoretical T section circuit.

    So what is your goal? Are you required to find the equivalent T section, or can you use whatever method you wish to achieve your goal?

    For a start, you need to find the transfer function. For the T section to behave according to the theoretical formulas, it must be driven by and loaded by Zo. You should probably initially calculate the transfer function assuming 50 ohm source impedance and 50 ohm load.

    By the way, you never did come back to the other thread: https://forum.allaboutcircuits.com/threads/help-on-node-analysis-for-filter-interpretation.152941/

    where you were having trouble setting up the nodal equations. If you are going to have trouble with that here, we can help you.
     
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