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Design >> Analog Design >> Current Mirror
https://designers-guide.org/forum/YaBB.pl?num=1479875798

Message started by asorab on Nov 22^nd, 2016, 8:36pm

Title: Current Mirror
Post by asorab on Nov 22^nd, 2016, 8:36pm

Good day guys! What is the difference between PMOS current mirror and NMOS current mirror? What are their advantages towards each other? Thank you for your response... :)

Title: Re: Current Mirror
Post by subtr on Dec 29^th, 2016, 10:57pm

There is no different between PMOS and NMOS current mirrors in the way they operate. PMOS sources current from supply, while the NMOS sinks current to the ground.
In order to understand more, I suggest you to learn the basic MOSFET functionalities. What I would blindly ask you to do is to watch a few lectures from IIT Madras by Professor Shanthi Pavan :

http://www.ee.iitm.ac.in/videolectures/doku.php?id=ec201_2010:start

Title: Re: Current Mirror
Post by ocmob on Jan 31^st, 2017, 7:51am

I think for the same device length there will be difference in resistance seen from drain for PMOS and NMOS. This means your Vds variations between mirror transistors will introduce current mismatch. What you would want to do is just take one PMOS and one NMOS and make a sim of Id vs Vds. The one which has more flat characteristic in the saturation area (and for the same Vgs) will make a better current mirror.

EDIT: That and PMOS will require more overdrive to provide the same current - lower hole mobility.