How to decide between PMOS and NMOS current mirrors for better results?

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when i study current mirrors i always get one question that how we decide either we have to use NMOS current mirror or PMOS current mirror...

Please reply as soon as possible..if possible give comparison...
 

It depends on the stage which is generating the current.....which is Vdd== through a resistor === nmos diode. The idea is the drop on the diode is small so the current can be VDD/R= Iconstant assuming you have a less noisy VDD and relatively stable "R". Then the current can be mirrored to NMOS followed by PMOS.... The idea is figure out the constant current generation. The rest of design of current mirror will depend on the voltage headroom that you need for the other portions of the circuit that you are using the current source for.
 

In fact, the main difference in current mirrors designed in complementary way is their matching, which is usually better for pMOS version. Second difference is a voltage drop on biasing diode-connected fet due to a slightly lower threshold voltage of nfets.
 

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