Current mirror for mosfet

Wendy

Joined Mar 24, 2008
23,395
I'll be interested in this one, I don't think there is such a thing. As far as I know a current mirror only works with BJTs. I know some FETs (don't think this applies to all) self limit current, as shown in this experiment.
 

steveb

Joined Jul 3, 2008
2,436
Hello,
Can someone explain the current mirror concept for mosfets?
thanks
The current mirror concept is the same for both mosfets and bipolar junction transistors. The basic idea is to use two identical transistors. One is configured as a diode with the drain and gate (or collector and base for BJT) connected together. When current is driven thru the diode, the diode voltage is used to drive the source/gate terminals (or emiter/base terminals for BJT) of the other transistor. If the transistors are identical and at the same temperature, then the current in the second transistor will match the first transistor that is operating like a diode.
 

Ron H

Joined Apr 14, 2005
7,049
If you want to see some gnarly current mirrors, see "CMOS Circuit Design, Layout, and Simulation" by R. Jacob Baker, Harry W. Li, and David E. Boyce, published by IEEE Press, 1988. It has an entire chapter on MOSFET current sources.
 
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