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
    239
    6
    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
    658
    85
    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.
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