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Why split the transistors in currnet source??

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DZC

DZC

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In some publications I found some current sources(loads) split the transistors,as shown below.
I'd like to know what's the benefit and waht if we combine them.
In addition,any cautions on sizing and biasing such circuit.(It seems the lower transistor always work in the linear region)
 

This is the self cascode current mirror. M1 and M3 are designed with small overdrive so M2, M4 are keeped closely to saturation. Rout of such cascode is better than simple current mirror, nut is poor relative to trivial cascode.
 

DenisMark said:
This is the self cascode current mirror. M1 and M3 are designed with small overdrive so M2, M4 are keeped closely to saturation. Rout of such cascode is better than simple current mirror, nut is poor relative to trivial cascode.
Click to expand...

then you mean it's a trade-off between simple current mirror and cascode?
 

Yes. Try to compare.
 

    DZC

    DZC

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DenisMark is right. You can caculate by hand.
 

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