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Are you talking about BJT or MOS current mirror? The input impedance of a "simple" (two transistor) BJT current mirror is the diode impedance Vt/id, you can't change it. The MOS input impedance depends on Vth and Idss and can be adjusted by varying the transistor geometry.
In general simple current mirror has always input impedance equal to 1/gm at dc. If you want to decrease it by some serious factor you will need to apply negative feedback loop to cover input node. However, it would not be a simple current mirror anymore ;-)
However, the simplest solution is to provide a current buffer (CG configuration) on the input. Check how high swing cascode CM and/or flipped source follower looks like.
The high swing cascode biasing is the same as flipped voltage follower which is nothing more than applying negative feedback loop with current buffer - as in attached scheme:
In the linked article are almost all known current mirror configurations and in one section the configuration with decreased input impedance are discussed.
Thank you Dominik, very helpful. The thing is that I don't have access to that paper through Elsevier website. I have tried to find it on ieeexplore and they don't have it.
Any idea how to get it?
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