Differential amplifiers

Discussion in 'Homework Help' started by lizherr98, Feb 29, 2004.

  1. lizherr98

    Thread Starter New Member

    Feb 29, 2004
    I need a head start for the following problem:

    An op-amp differential amplifier is built using four identical resistors, each having a tolerance of +-5%. Calculate the worst possible CMRR?

  2. Battousai

    Senior Member

    Nov 14, 2003
    I believe CMRR = Acm-dm/Adm, where Acm-dm = Vo,d/Vi,c and Adm=Vo,d/Vi,d. Since you want to calculate the worse possible CMRR, you want to produce the highest Acm-dm. To do this you should unbalance your amplifier. On one side make both the resistors have a +5% value and on the other side make them have a -5% value. Then simply calculate Acm-dm and Adm.