How does a current mirror behaving as active load in this circuit....

Discussion in 'General Electronics Chat' started by Himanshoo, May 17, 2015.

  1. Himanshoo

    Thread Starter Member

    Apr 3, 2015
    Ordinary resistor as load in a transistor amplifier has a certain short coming…we cant have voltage and current gain simultaneously …..means that if we need large voltage gain R load value should be very large ..and on other hand if we need high output current (Ic) R load value should be low..

    In this circuit a current mirror is actings as an active load in place of R load …I wonder how this current mirror able to give voltage as well as current gain at same time??

    bjt_amplifier_stage.png active load.png
    Last edited: May 18, 2015
  2. JDT

    Well-Known Member

    Feb 12, 2009
    The current mirror is a constant current source. Therefore it appears to have a very high output resistance. The voltage gain of Q1 is approximately RL/RE. So if RL is a very high value the voltage gain is high.
    Himanshoo likes this.