1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Transfer function of RC circuit

  1. Dec 7, 2009 #1
    Hello all,

    I need transfer function of this circuit (it is Bandaxall tone stack). Here is the sheme:

    ubnk2iv2.png


    Any help would be greatly appreciated.
     
  2. jcsd
  3. Dec 7, 2009 #2

    berkeman

    User Avatar

    Staff: Mentor

    What is the context of your question? If it's for schoolwork, I can move the thread to the Homework Help section of the PF. In any case, you will need to show some effort on your question. How would you go about writing some equations to help you get to the transfer function? Would you use KVL or KCL?
     
  4. Dec 7, 2009 #3

    berkeman

    User Avatar

    Staff: Mentor

    Oh, and the transfer function will also depend on the Zout of the previous stage, and the Zin of the next stage. Do you have those?
     
  5. Dec 7, 2009 #4
    Thank You for response,

    I'm sorry, I probably put it in a bad section :(


    I tried to solve it with my basic knowledge of Kirchoff's laws, but I'm not mathematician, I'm an IT student... my task on this project is to simulate this circuit using a C++ library, but to obtain a block scheme I need differential equatins from transfer function.

    When I tried to solve it, I ran into 7 equations, of which 4 were current-related (6 unknown currents), and after discussion with my friend I came to conclusion, that I did either something wrong, or the set of those equations cannot be solved (from my point of view - 6 variables, 4 equations), that means I cannot figure out the currents.

    The input and output impedances... well I dont have those. (consider it as an ideal circuit?)
     
  6. Dec 7, 2009 #5

    berkeman

    User Avatar

    Staff: Mentor

    No worries, I moved the thread. I only see 5 nodes for writing the KCL equations. Could you please show us the equations you have so far?

    And you are being required to solve for the transfer function of this circuit for an IT class?
     
  7. Dec 8, 2009 #6
    First I substituded RA||C2 and RB||C3 for impedaces ZA=RA/(1+s*RA*C2) and ZB=RB/(1+s*RB*C3):

    fejjiag7.png


    Here I drew the nodes and the currents. And my equations:

    KCL:
    I1=I2+I3
    I5=I2+I4
    I3=I4+I6
    I1=I5+I6

    KVL:
    VIN=R1*I2+ZA*I2+ZB*I5+R3*I5
    0=-R1*I2-ZA*I2+(1/(s*C1))*I3+RX*I3+R2*I4
    0=-R3*I5-ZB*I5-R2*I4+R4*I6+(1/(s*C4))*I6

    And this is my dead end :(


    I had to choose a circuit for simulation, but maybe this one is too complicated for me... I simply need a "not basic analog filter".
     
    Last edited: Dec 8, 2009
  8. Dec 8, 2009 #7
    After deeper studying of that C++ toolkit, I actually dont need transfer function, but only Kirchoffs equations (not in s-domain, but with all integrals and derivations).
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook