op amp

Discussion in 'Homework Help' started by acw_wellsy, Oct 16, 2006.

  1. acw_wellsy

    Thread Starter New Member

    Oct 1, 2006
    a feedback amplifier has a closed loop gain of 100, and the negative feedback is 0.8% of the output signal. the opamp has an open loop gain which is considerably less than the ideal value of infinity.
    a) what is the open loop gain?
    b)what would the closed loop gain be if the opamp had an infinite open loop gain.

    what equation of formula would i need i know that A = Vout/Vin = 1/B

    any ideas...

  2. Dave

    Retired Moderator

    Nov 17, 2003
    The equation Af = 1/B for the closed-loop gain is a special case (for where AB >> 1) of the general equation:

    Af = A/(1 + AB)


    Af is the closed loop gain
    A is the open-loop gain
    B is the feedback factor

    From this equation you should be able to rearrange the equation to get A as the subject, from which you have sufficient information to answer part (a).

    Part (b) can be answered using Af = 1/B

    You should find your answers for (a) and (b) to be very similar. You can post up your attempts if you want to check your answers.

  3. stocky

    New Member

    Oct 18, 2006
    acw_wellsy, do you go to swinburne as well? im struggling with exactly the same question