i have a small problem with amplifier !

Discussion in 'Homework Help' started by tallo, Mar 10, 2011.

  1. tallo

    Thread Starter New Member

    Mar 4, 2011
    12
    0
    hi engineers ..

    i have a small problem with the following question

    [​IMG]


    how can i determine the input impedance for the two types of amplifiers

    thank you
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    What do you know about inverting terminal impedance vs non-inverting terminal impedance?
     
  3. tallo

    Thread Starter New Member

    Mar 4, 2011
    12
    0
    Zin(I) = Ri

    Zout(I) Almost equal to 0

    :::::::::

    Zin(NI = (1+Aol B ) Zin

    Zout(NI) = Zout/(1+Aol B)

    where B + Ri/(Ri+Rf)
     
  4. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Are the op amps ideal?
     
  5. tallo

    Thread Starter New Member

    Mar 4, 2011
    12
    0
    yes they are
     
  6. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    With ideal op amps, your equations will give you the answers. That is, if you know the values of Ri and Aol for an ideal op amp.
     
  7. tallo

    Thread Starter New Member

    Mar 4, 2011
    12
    0
    But i don't have the values of Aol, Zin & Zout
    So what can I do in this case ?
     
  8. tallo

    Thread Starter New Member

    Mar 4, 2011
    12
    0
    suppose that the op amps in practical model

    what will be the solution ?
     
  9. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    You would have to look up Ri and Aol in the datasheet.
     
  10. tallo

    Thread Starter New Member

    Mar 4, 2011
    12
    0
    I'm waiting
     
  11. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    What are you waiting for?
     
  12. tallo

    Thread Starter New Member

    Mar 4, 2011
    12
    0
    i am very confusing

    if these amps are ideal , what will be the solution

    and, if they are in practical model

    what the solution will be ?
     
  13. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Your equations are very simple.

    Many op amps don't specify input resistance, but they all specify voltage gain.
    This is homework. We don't do homework for you. Work on it until you get stuck, show us your results and how you got them, and we will try to help.
     
  14. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    You cannot calculate the gain of the inverting opamp unless you know the input impedance of the source which is in series with the input resistor.
    Can you assume it is zero ohms?
     
  15. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    OMG! He's confused enough already. You've just opened a whole new can of worms.:D
     
  16. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    An inverting opamp is a can of worms because its gain is determined by the input resistor value in series with the source impedance.

    Make a non-inverting opamp circuit with a very high input impedance instead.
     
Loading...