Working out total Inductance and Capacitance

Discussion in 'General Electronics Chat' started by abc14, May 4, 2019.

  1. abc14

    Thread Starter Member

    Oct 15, 2017
    105
    0
    Just wanted to validate the vaules I worked out total Inductance and Capacitance are correct.

    upload_2019-5-4_14-30-16.png


    For total Inductance I think L1 and L2 are parallel hence it would be L1*L2/L1+L2 = 155/4.7+33 = 4.11

    And L3 and L4 are series to L1||L2 hence 4.11 + 6.8 + 6.8 = 17.71 nH

    And for Capacitance.. C2 and C3 are in series hence it will be 47*5.6/47+5.6 = 4.91 and C5 and C7 are in parrallel hence it will be 4.91 + 8.2 + 6.8 = 19.91


    Hence Ltotal= 17.71 nH
    and Ctotal = 19.91 pF
     
  2. Papabravo

    Expert

    Feb 24, 2006
    12,188
    2,680
    Because the components interact with each other, the circuit above will not behave the same as two lumped components with the values you have calculated. It looks like a multi-pole bandpass filter
     
  3. abc14

    Thread Starter Member

    Oct 15, 2017
    105
    0
    upload_2019-5-4_15-31-49.png


    Yes its acting as filter for 868Mhz rf ICs, but I cannot figure out how they setting up required frequency of 868 mhz with this circuit.
     
  4. Papabravo

    Expert

    Feb 24, 2006
    12,188
    2,680
    The methods for setting up such a filter are derived from the requirements. The methods are detailed in a college text like the following:

    https://www.amazon.com/Analog-Filte...=Analog+filter+Design,aps,247&sr=1-2-fkmrnull

    As for reverse engineering the filter, I would try simulation in LTSpice as a first step.
    https://www.analog.com/en/design-center/design-tools-and-calculators/ltspice-simulator.html
     
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