[SOLVED] Current Mirror Inaccuracy

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chandlerbing65nm

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Hi all!

I'm using current mirror to copy the current of my circuit from Voltage to Current converter, but when I simulated it the current(Io) at the mirrored side seems not an exact copy of the Iref(attached image). Why this happens? I need a constant current Io.

Thanks for reading.
 

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I guess the difference is coming from VDS voltages of 2 upper PMOS transistors due to NMOS .
While the current is increased the difference becomes more evident.
 
You find the answer in any CMOS circuit design text book that discusses the behavior of real MOSFET transistors. You should particularly look for channel length modulation parameter λ. It causes a Vds dependent Id slope in saturation.
 

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