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

Thread Starter

Himanshoo

Joined Apr 3, 2015
265
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:

JDT

Joined Feb 12, 2009
657
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.
 
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