amplifier feedback factor

Discussion in 'Homework Help' started by anita bosher, Nov 8, 2008.

  1. anita bosher

    Thread Starter New Member

    Nov 8, 2008
    hi guys , ive been given the question
    4) What is the effect of negative feedback when applied to an amplifier? If an amplifier has a gain of 200 and this produces oscillations, what will be the feedback factor?

    ive given the following answers to the first bit of the question but im stuck on the feedback factor bit, any help would be much apreciated.

    Negative feedback on a amplifier cause:

    A) Reduction in gain
    B) Reduction of distortion
    C) Increase in gain stability
    D) Increase in Bandwidth
    E) Increase in input resistance
  2. KL7AJ

    Senior Member

    Nov 4, 2008
    Positive feedback is a whole different animal. When an amplifier breaks into oscillation, your feedback factor is infinite. (Look for some interesting references on regenerative radio receivers, which had infinite gain!)

    You have to be careful of phase shift in ANY feedback system.....or what you intend to be negative feedback can become positive. The classic feedback formulas for inverse feedback always assume a 180 degree phase shift.

  3. anita bosher

    Thread Starter New Member

    Nov 8, 2008
    thanks for the reply eric,but im still none the wiser on what formula to use.
  4. raybo


    Oct 18, 2008
    C the more f/b the more the stability.the more open loop gain and the more -f/b more stability
  5. anakdandan

    New Member

    Nov 13, 2008
    i have the same problem can anyone help me find the answer....thank you for your help